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Syntheses, crystal structures and magnetic properties of a series of μ-phenoxo-μ1,1carboxylato-μ1,3-carboxylato trinickel(II) compounds† Sagarika Bhattacharya,a Sujit Sasmal,a Luca Carrella,b Eva Rentschler*b and Sasankasekhar Mohanta*a The work in this report describes the syntheses, characterization, crystal structures and magnetic properties of eight linear trinickel(II) compounds of the composition [NiII3(Lsal–pyr)2( propionate)4] (1), [NiII3(Lsal–pyr)2(benzoate)4]·CH3CN (2), [NiII3(Lsal–pip)2(acetate)4]·2CH3CN (3), [NiII3(Lsal–pip)2( propionate)4] (4), [NiII3(Lsal–pip)2(benzoate)4]·CH2Cl2 (5), [NiII3(Lsal–mor)2( propionate)4] (6), [NiII3(Lsal–mor)2(benzoate)4]·3CH2Cl2 II

(7) and [Ni 3(Lsal–mor)2(o-Cl-benzoate)4]·2CH3CN·2H2O (8), where HLsal–pyr, HLsal–pip and HLsal–mor are the 1 : 1 condensation products of salicylaldehyde and 1-(2-aminoethyl)-pyrrolidine, 1-(2-aminoethyl)-piperidine and 4-(2-aminoethyl)-morpholine, respectively. One-half of the trinuclear core in each complex is symmetry related to the second part due to the presence of an inversion centre on the central metal ion and so the terminal nickel⋯central nickel⋯terminal nickel angle is 180°. The terminal and central nickel(II) ions are triply bridged by a phenoxo, a µ1,1-carboxylato and a µ1,3-carboxylato moiety. The µ1,1-carboxylato also acts as a chelating ligand for the terminal metal ion. Both the variable-temperature (2–300 K) susceptibilities at a fixed field strength of 0.1 T and variable-field (up to 7 T) magnetization at different fixed temperatures (2–10 K) were recorded. The magnetic data indicate the ferromagnetic interaction in Received 22nd March 2014, Accepted 17th June 2014 DOI: 10.1039/c4dt00862f www.rsc.org/dalton

all the cases with J (Ĥ = −2Jij∑SiSj ) values ranging between 2.37 and 3.89 cm−1 and the single-ion zerofield parameter (D) ranging between 7.21 and 8.94 cm−1. Satisfactorily simulation of both the χMT vs. T and M vs. H data has been obtained. Comparison of the structures and magnetic properties of compounds 1–8 with those of the previously published related systems reveals some interesting aspects.

Introduction Molecular magnetism has been a frontier research area.1–15 Studies on varieties of systems have been made over the decades to understand the intimate relationship of spin coupling. Eventually, a number of magneto-structural correlations (both theoretical and experimental) have been determined and the derived ideas have been utilized to obtain molecule-based magnetic materials including single-molecule-magnets. It is well known that complementarity/countercomplementarity effects of the second bridging ligand (X) play a crucial

a Department of Chemistry, University of Calcutta, 92 A. P. C Road, Kolkata 700 009, India. E-mail: [email protected] b Institut für Anorganische Chemie und Analytische Chemie, Johannes-Gutenberg Universität Mainz, Duesbergweg 10-14, D-55128 Mainz, Germany. E-mail: [email protected] † Electronic supplementary information (ESI) available: Fig. S1–S14, Table S1. CCDC 986865–986872 for 1–8 respectively. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt00862f

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role in governing the magnetic properties of heterobridged μ-hydroxo/alkoxo/phenoxo-μ-X dicopper(II) compounds (X = azide, thiocyanate, cyanate, pyrazolate, carboxylato, 7-azaindolate, etc.).1,16 However, magnetic properties of the heterobridged compounds of other 3d metal ion complexes in terms of the effects of two or more different bridging ligands have been much less explored.17,18 While copper(II) has one magnetic orbital, other 3d metal ions (e.g. NiII, MnII and CoII) have two or more magnetic orbitals and so it is challenging to explore complementarity/countercomplementarity effects in such complicated systems having a number of combinations of magnetic orbitals. It is worth mentioning also that determination of experimental and even theoretical magneto-structural correlations in heterobridged systems is also complicated because it is not possible to vary one parameter keeping others constant. Regarding correlations in heterobridged systems, a recent report on μ-phenoxo-μ-azide dinickel(II) compounds in defining new parameters, which are functions of two other parameters, represents the rare example.7b The complementarity/countercomplementarity effects in other metal ion systems

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were recorded in the region 400–4000 cm−1 on a Bruker-Optics Alpha-T spectrophotometer with samples as KBr disks. Magnetic measurements were carried out with a Quantum Design MPMS XL-7 SQUID magnetometer.

Syntheses of 1–8

Scheme 1

Chemical structures of HLsal–pyr, HLsal–pip and HLsal–mor.

(having more than one magnetic orbitals), being not as smooth as in copper(II) systems, have been demonstrated theoretically in FeIIINiII compounds very recently.19 All in all, exploration of magnetic properties of heterobridged discrete systems of metal ions, other than copper(II), deserves importance. Recently, we have reported structures and magnetic properties of nickel(II)–pseudohalide compounds derived from acyclic Schiff base ligands, obtained on condensation of salicylaldehyde or substituted salicylaldehyde with 4-(2-aminoethyl)morpholine, 1-(2-aminoethyl)-piperidine or ethanolamine.7b,c,17 One aim of the present investigation is to explore the composition/structure of nickel(II) compounds derived from this class of acyclic ligands in the presence of different carboxylatos. As the derived systems in this investigation have been trinuclear discrete NiII3 compounds having simultaneous phenoxo and carboxylato bridges, having similar structures and having closely similar phenoxo bridge angles, we have considered these as good examples to explore the complementarity/countercomplementarity effects. With these aims, we are reporting herein syntheses, crystal structures and magnetic properties of a series of eight trinickel(II) compounds with the composition [NiII3(Lsal–pyr)2( propionate)4] (1), [NiII3(Lsal–pyr)2(benzoate)4]·CH3CN (2), [NiII3(Lsal–pip)2(acetate)4]·2CH3CN (3), [NiII3(Lsal–pip)2( propionate)4] (4), [NiII3(Lsal–pip)2(benzoate)4]· CH2Cl2 (5), [NiII3(Lsal–mor)2( propionate)4] (6), [NiII3(Lsal–mor)2(benzoate)4]·3CH2Cl2 (7) and [NiII3(Lsal–mor)2(o-Clbenzoate)4]·2CH3CN·2H2O (8), where HLsal–pyr, HLsal–pip and HLsal–mor are the 1 : 1 condensation products of salicylaldehyde and 1-(2-aminoethyl)-pyrrolidine, 1-(2-aminoethyl)-piperidine and 4-(2-aminoethyl)-morpholine (Scheme 1), respectively.

Experimental section Caution! Perchlorate complexes of metal ions in the presence of organic moieties are potentially explosive. Only a small amount of material should be prepared and it should be handled with care. Materials and physical measurements All the reagents and solvents were purchased from commercial sources and used as received. Elemental (C, H and N) analyses were performed on a Perkin-Elmer 2400 II analyzer. IR spectra

12066 | Dalton Trans., 2014, 43, 12065–12076

All these eight compounds were prepared following a general procedure using the appropriate amine and carboxylato as follows: 1-(2-aminoethyl)-pyrrolidine for 1 and 2; 1-(2-aminoethyl)-piperidine for 3–5; 4-(2-aminoethyl)-morpholine for 6–8; sodium acetate for 3; sodium propionate for 1, 4 and 6; sodium benzoate for 2, 5 and 7; and o-chlorobenzoic acid plus triethylamine for 8. The general procedure is described below for the synthesis of compound 1. A solution of 1-(2-aminoethyl)-pyrrolidine (0.114 g, 1 mmol) and salicylaldehyde (0.123 g, 1 mmol) in 15 ml methanol was refluxed for 2 h. To the red-coloured solution, a methanol solution (5 ml) of nickel(II) perchlorate hexahydrate (0.366 g, 1 mmol) was dropwise added, resulting in an immediate colour change from red to green. To the green solution, a methanol solution (2 ml) of triethylamine (0.101 g, 1 mmol) and sodium propionate (0.384 g, 4 mmol) in 5 ml methanol solution was successively added with stirring. After 1 hour, a green solid was precipitated out which was collected by filtration and washed with cold methanol. Recrystallization from the dichloromethane–acetonitrile (1 : 1) mixture produced a green crystalline compound containing diffraction quality single crystals. Data for 1. Yield: (0.232 g; 77%). Anal. calcd for C38H54N4O10Ni3: C, 50.55; H, 6.03; N, 6.21%. Found: C, 50.60; H, 6.25; N, 6.22%. IR (KBr pellet, cm−1): ν(CvN), 1647s; νas(CO2−), 1579vs; νs(CO2−), 1452m. Data for 2. Yield: (0.295 g; 78%). Anal. calcd for C56H57N5O10Ni3: C, 59.20; H, 5.06; N, 6.16%. Found: C, 59.35; H, 5.15; N, 6.22%. IR (KBr pellet, cm−1): ν(CvN), 1644s; νas(CO2−), 1600vs; νs(CO2−), 1449m. Data for 3. Yield: (0.210 g; 66%). Anal. calcd for C40H56N6O10Ni3: C, 50.20; H, 5.89; N, 8.78%. Found: C, 50.32; H, 5.75; N, 8.67%. IR (KBr pellet, cm−1): ν(CvN), 1644s; νas(CO2−), 1598 m; νs(CO2−), 1451s. Data for 4. Yield: (0.221 g; 71%). Anal. calcd for C40H58N4O10Ni3: C, 51.61; H, 6.28; N, 6.02%. Found: C, 51.52; H, 6.15; N, 6.16%. IR (KBr pellet, cm−1): ν(CvN), 1647s; νas(CO2−), 1579vs; νs(CO2−), 1451m. Data for 5. Yield: (0.282 g; 70%). Anal. calcd for C57H60N4O10Ni3Cl2: C, 56.67; H, 5.01; N, 4.64%. Found: C, 56.52; H, 5.15; N, 4.52%. IR (KBr pellet, cm−1): ν(CvN), 1649s; νas(CO2−), 1602vs; νs(CO2−), 1450s. Data for 6. Yield: (0.240 g; 77%). Anal. calcd for C38H54N4O12Ni3: C, 48.82; H, 5.82; N, 5.99%. Found: C, 48.72; H, 5.75; N, 5.82%. IR (KBr pellet, cm−1): ν(CvN), 1647s; νas(CO2−), 1601m; νs(CO2−), 1451m. Data for 7. Yield: (0.346 g; 75%). Anal. calcd for C57H60N4O12Ni3Cl6: C, 49.54; H, 4.38; N, 4.05%. Found: C, 49.71; H, 4.30; N, 4.19%. IR (KBr pellet, cm−1): ν(CvN), 1649s; νas(CO2−), 1600vs; νs(CO2−), 1451s.

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Data for 8. Yield: (0.351 g; 76%). Anal. calcd for C58H60N6O14Ni3Cl4: C, 50.37; H, 4.37; N, 6.08%. Found: C, 50.27; H, 4.57; N, 6.21%. IR (KBr pellet, cm−1): ν(H2O): 3443m; ν(CvN), 1648vs; νas(CO2−), 1597vs; νs(CO2−), 1452s. X-ray crystallography The crystallographic data for 1–8 are summarized in Table 1. X-ray diffraction data were collected on a Bruker-APEX II SMART CCD diffractometer at 296 K using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). For data processing and absorption correction, the packages SAINT20a and SADABS20b were used. The structures were solved by direct and Fourier methods and refined by full-matrix least-squares based on F2 using SHELXTL20c and SHELXL-9720d packages for 1–4, 6 and 8 and the Olex-220e software for 5 and 7. During the development of the structures, it became apparent that some atoms in 5, 7 and 8 are disordered. The DCM molecule in 5 does not possess crystallographic twofold symmetry, but is disordered equally between two positions related by this axis. The morpholine group in 7 was refined as disordered between two alternative orientations with equal occupancies (A and B). One DCM molecule in 7 is severely disordered, which was modeled as four alternative orientations: (i) Cl3, its inversion equivalent and C29 (with attached hydrogens), (ii) Cl3 and the inversion equivalents of Cl3 and C29, (iii) Cl4C30Cl5 and (iv) its inversion equivalent with contributions of 35%, 35%, 15% and 15%, respectively. Independent atoms for this DCM molecule in 7 are thus the following: Cl3 (70%), C29 (35%), Cl4, Cl5 and C30 (15% occupancies). The solvated water oxygen (O7) atom in 8 was modeled as disordered over two sites with occupancies 60% and 40%. The instruction EADP was used to restrain isotropic thermal parameters of some carbon atoms (C1, C2, C10, C35–C38 and C40) in 2. It was not possible to locate/insert two hydrogen atoms of the solvent water molecule in 8. All other hydrogen atoms in the compounds 1–8 were inserted on geometrical calculated positions with isotropic thermal parameters and refined. C29 in 5 and C29 and C30 in 7 had to be refined isotropically. All other non-hydrogen atoms in 1–8 were refined anisotropically. The final refinement converged to the R1 values [I > 2σ(I)] of 0.0299, 0.0849, 0.0387, 0.0300, 0.0427, 0.0333, 0.0509 and 0.0482 for 1–8, respectively.

Results and discussion Description of the structures of 1–8 All structures reveal the same core structure, built up by three nickel(II) ions in a linear fashion; the terminal nickel(II) ⋯central nickel(II)⋯terminal nickel(II) angle is 180° due to the inversion centre at the central nickel(II) ion. The central motifs were completed by two deprotonated Schiff base ligands and four carboxylatos. Additionally, five compounds contain solvent(s) of crystallization: 2, one acetonitrile; 3, two acetonitrile; 5, one dichloromethane; 7, three dichloromethane; and 8, two acetonitrile and two water. There are two independent

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units in compound 2: Unit-I and Unit-II. Regarding the Schiff base ligand in these eight compounds, two contain [Lsal–pyr]− (1 and 2), three contain [Lsal–pip]− (3–5) and three contain [Lsal–mor]− (6–8). Regarding carboxylato in these eight compounds, one contains acetate (3), three contain propionate (1, 4 and 6), three contain benzoate (2, 5 and 7) and one contains o-chlorobenzoate (8). The crystal structures of [NiII3(Lsal–pyr)2(benzoate)4]·CH3CN (2), [NiII3(Lsal–pip)2(acetate)4]·2CH3CN (3), [NiII3(Lsal–mor)2( propionate)4] (6) and [NiII3(Lsal–mor)2(o-Clbenzoate)4]·2CH3CN·2H2O (8) are shown, respectively, in Fig. 1–4, while the crystal structures of the other four compounds [NiII3(Lsal–pyr)2(propionate)4] (1), [NiII3(Lsal–pip)2(propionate)4] (4), [NiII3(Lsal–pip)2(benzoate)4]·CH2Cl2 (5) and [NiII3-(Lsal–mor)2(benzoate)4]·3CH2Cl2 (7) are displayed in Fig. S1–S4, respectively, in ESI.† The terminal (Ni1) and central (Ni2) metal ions are bridged by one phenoxo oxygen atom afforded by the Schiff base ligand and two carboxylatos, which bridge in two different ways: µ1,3- through O4 and O5 in 1, 6 and 8, through O4 and O5A in Unit-I of 2, 3–5 and 7 and through O9 and O10 in UnitII of 2; µ1,1- through O2 in 1, Unit-I of 2, 3, 5, 7 and 8, through O2A in 4 and 6 and through O7 in Unit-II of 2. Moreover, µ1,1carboxylato also acts as a chelating ligand to the terminal metal ion. Thus, four coordination positions of the terminal metal ion are occupied by one bridging phenoxo oxygen atom, one oxygen atom from µ1,3-carboxylato and two oxygen atoms of chelating/µ1,1-carboxylato moieties. The remaining two coordination positions of the hexacoordinated terminal metal ion are satisfied by the imine (N1) and tertiary (N2) nitrogen atoms, afforded by the corresponding Schiff base ligand. Obviously, the central metal ion is also hexacoordinated by two bridging phenoxo oxygen atoms, two oxygen atoms of two µ1,3-carboxylato moieties and two bridging oxygen atoms of the two chelating/µ1,1-carboxylato moieties. The bond lengths and bond angles in the coordination environment of both the terminal and central metal ions in 1, Unit-I in 2 and 3–8 are listed/compared in Table 2, while those of both the units in 2 are listed/compared in Table S1 in ESI.† The range of bond distances in all the compounds is much wide: 1.983–2.253 Å in 1, 1.992–2.183 Å in Unit-I in 2, 1.983–2.184 Å in Unit-II in 2, 1.969–2.237 Å in 3, 1.980–2.238 Å in 4, 1.957–2.206 Å in 5, 1.983–2.246 Å in 6, 1.968–2.185 Å in 7 and 1.977–2.210 Å in 8. However, in all complexes, three bond distances involving phenoxo (O1) and µ1,3-carboxylato (O4) oxygen atoms and the imine (N1) nitrogen atom are significantly smaller than the other three bond distances; considering all the eight complexes, the overall ranges of the former three and latter three bond distances are 1.957–2.034 Å and 2.078–2.253 Å. The longer three bond distances that involve a µ1,1-carboxylato oxygen atom (O2/O2A), tertiary nitrogen atom (N2) and nonbridging/chelating carboxylato oxygen atom (O3) do not follow a general order in all the complexes. For example, for the propionate compounds 1, 4 and 6, which are derived from three different Schiff base ligands, Ni1–O2/O2A (2.078–2.082 Å) < Ni1–N2 (2.174–2.216 Å) < Ni1– O3 (2.238–2.253 Å) but this order is not valid for the three

Dalton Trans., 2014, 43, 12065–12076 | 12067

12068 | Dalton Trans., 2014, 43, 12065–12076 C56H57N5O10Ni3 1136.20 Green Triclinic ˉ P1 13.709(3) 14.024(3) 16.630(4) 111.754(3) 95.086(4) 111.703(3) 2663.2(11) 2 296(2) 2.74–51.12 1.112 1.417 1184 Multi-scan −16 ≤ h ≤ 16 −17 ≤ k ≤ 17 −20 ≤ l ≤ 20 19449 9770 (0.0826) 0.0849, 0.1932 0.1943, 0.2378

C38H54N4O10Ni3 902.98 Green Monoclinic P21/c 9.450(3) 18.825(6) 12.001(4) 90.00 106.273(8) 90.00 2049.3(11) 2 296(2) 4.14–54.78 1.423 1.463 948 Multi-scan −12 ≤ h ≤ 12 −24 ≤ k ≤ 24 −15 ≤ l ≤ 15 26684 4581 (0.0236) 0.0299, 0.1011 0.0368, 0.1081

Empirical formula Formula weight Crystal colour Crystal system Space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z T (K) 2θ (°) μ (mm−1) ρcalcd (g cm−3) F(000) Abs. cor. Index ranges

a

R1 = [∑kFo| − |Fck/∑|Fo|]. b wR2 = [∑w(Fo2 − Fc2)2/∑wFo4]1/2.

Reflections collected Independent reflections (Rint) R1 a, wR2 b [I > 2σ(I)] R1 a, wR2 b (for all data)

2

1

Crystallographic data for 1–8

Compound

Table 1

C40H56N6O10Ni3 957.04 Green Triclinic ˉ P1 9.2422(16) 11.427(2) 11.940(2) 71.389(7) 86.472(7) 68.480(6) 1109.5(3) 1 296(2) 3.60–53.0 1.320 1.432 502 Multi-scan −11 ≤ h ≤ 11 −14 ≤ k ≤ 12 −14 ≤ l ≤ 14 12958 4552 (0.0748) 0.0387, 0.1098 0.0795, 0.1337

3 C40H58N4O10Ni3 931.03 Green Monoclinic P21/c 9.721(2) 18.581(4) 12.238(3) 90.00 104.402(8) 90.00 2141.1(9) 2 296(2) 4.08–54.00 1.365 1.444 980 Multi-scan −12 ≤ h ≤ 12 −23 ≤ k ≤ 23 −15 ≤ l ≤ 14 26726 4635 (0.0288) 0.0300, 0.1045 0.0399, 0.1186

4 C57H60N4O10Ni3Cl2 1208.12 Green Monoclinic C2/c 21.737(17) 10.824(8) 23.427(18) 90.00 103.020(9) 90.00 5370(7) 4 296(2) 3.57–52.30 1.204 1.494 2512 Multi-scan −21 ≤ h ≤ 26 −13 ≤ k ≤ 13 −28 ≤ l ≤ 28 19507 5239 (0.0411) 0.0427, 0.1096 0.0568, 0.1178

5 C38H54N4O12Ni3 934.98 Green Monoclinic P21/c 9.5838(3) 18.8156(7) 11.9457(4) 90.00 106.1170(10) 90.00 2069.44(12) 2 296(2) 4.16–61.80 1.416 1.500 980 Multi-scan −13 ≤ h ≤ 12 −27 ≤ k ≤ 27 −17 ≤ l ≤ 15 29489 6458 (0.0343) 0.0333, 0.1029 0.0501, 0.1185

6

C57H60N4O12Ni3Cl6 1381.92 Green Monoclinic P21/n 10.9987(16) 19.977(3) 15.049(2) 90.00 109.934(4) 90.00 3108.5(8) 2 296(2) 3.52–51.68 1.219 1.476 1424 Multi-scan −13 ≤ h ≤ 13 −24 ≤ k ≤ 22 −18 ≤ l ≤ 18 37221 5991 (0.0808) 0.0509, 0.1353 0.0869, 0.1567

7

C58H60N6O14Ni3Cl4 1383.05 Green Triclinic ˉ P1 11.2050(18) 12.005(2) 13.346(2) 107.023(5) 103.618(6) 104.109(5) 1571.0(4) 1 296(2) 3.38–50.6 1.127 1.462 714 Multi-scan −13 ≤ h ≤ 13 −14 ≤ k ≤ 14 −15 ≤ l ≤ 16 18341 5675 (0.0284) 0.0482, 0.1503 0.0592, 0.1619

8

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Fig. 1 Crystal structure of [NiII3(Lsal–pyr)2(benzoate)4]·CH3CN (2). All the hydrogen atoms and one acetonitrile molecule (solvent of crystallization) are omitted for clarity. Symmetry codes: A, 1 − x, 1 − y, −z; B, −x, 1 − y, 1 − z.

Fig. 2 Crystal structure of [NiII3(Lsal–pip)2(acetate)4]·2CH3CN (3). All the hydrogen atoms and two acetonitrile molecules (solvent of crystallization) are omitted for clarity. Symmetry codes: A, 1 − x, 1 − y, 2 − z.

benzoate compounds 2, 5 and 7, each of which follow three different orders. In contrast to those in the Ni1 environment, the bond distances of the central metal ion, Ni2, are less wide and follow a general order. The range of bond distances of Ni2/Ni4 (Ni4 is in Unit II of 2) is 2.033–2.127 Å in 1, 1.997–2.125 Å in Unit-I in 2, 1.983–2.136 Å in Unit-II in 2, 2.037–2.115 Å in 3, 2.028–2.112 Å in 4, 1.995–2.110 Å in 5, 2.026–2.119 Å in 6, 2.021–2.133 Å in 7 and 1.994–2.136 Å in 8. The general order here is Ni2/Ni4–O5/O10 (1.983–2.037 Å) < Ni2/Ni4–O1/O6 (2.047–2.114 Å) < Ni2/Ni4–O2/O7 (2.110–2.136 Å). Both Ni1 and Ni2 have a distorted octahedral coordination environment, where the terminal Ni1 ions show a greater deviation from the ideal octahedral coordination than Ni2, which can be easily seen by comparing the bond distances and bond angles. For example: (i) while all the three transoid angles for

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Fig. 3 Crystal structure of [NiII3(Lsal–mor)2( propionate)4] (6). All the hydrogen atoms are omitted for clarity. Symmetry codes: A, 1 − x, 2 − y, −z.

Ni2/Ni4 are 180°, the range of these angles for the Ni1/Ni3 centre (Ni3 is in Unit II of 2) is 155.91–175.64°; (ii) in comparison with the cisoid angles of the ideal octahedral geometry, cisoid angles for Ni1/Ni3 (60.05–106.50°) vary much more than for Ni2/Ni4 (79.05–100.95°). Comparison of the structures of 1–8 with those of related systems Only a few (I–IV in Table 3) linear trinuclear nickel(II) compounds similar to 1–8 have been reported previously.21 There are also only a few linear trinickel(II) compounds (A–D in Table 3)21d,22 which are closely similar to 1–8/I–IV; the difference between 1–8/I–IV and A–D is that while the µ1,1-carboxylato is also chelating in the former, it is not a chelating ligand in the latter. The ligand providing the phenoxo bridge, the carboxylato moiety and some structural parameters of 1–8, I–IV

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Fig. 4 Crystal structure of [NiII3(Lsal–mor)2(o-Cl-benzoate)4]·2CH3CN· 2H2O (8). Two acetonitrile and two water molecules (both solvent of crystallization) and all the hydrogen atoms are omitted for clarity. Symmetry codes: A, 2 − x, 2 − y, 1 − z.

and A–D are compared in Table 3. The ligands providing the phenoxo bridge in I–IV are aldehyde–amine systems having O( phenoxo)N(imine)N(amine) donor centres, which are closely similar to those in 1–8. The aldehyde part is salicylaldehyde in all, while the amine part is 1-(2-aminoethyl)-pyrrolidine/ 1-(2-aminoethyl)-piperidine/4-(2-aminoethyl)-morpholine in 1–8 but N-methyl-1,3-diaminopropane/N,N-dimethyl-1,3-diaminopropane in I–IV and A. Compound D has also been derived from a Schiff base ligand and the ligand in this case is a O( phenoxo)N(imine)O( phenoxo) system, produced from the condensation of salicylaldehyde and o-hydroxybenzylamine. On the other hand, the ligand providing the phenoxo bridge in B is an O( phenoxo)N(amine)O(hydroxy) system and in C an O( phenoxo)N(imine)N( pyridine) system. The carboxylato moieties in the previously reported compounds I–IV and A–D are acetate, benzoate and cinnamate, while those in 1–8 are acetate, propionate, benzoate and o-chlorobenzoate. It may be relevant to discuss in brief the similarities and differences in some structural parameters in spite of or as a result of variation of ligands in the compounds 1–8/I–IV/A–D. In all these cases, the terminal metal–phenoxo bond distance is less than the central metal–phenoxo bond distance, where, in general, the ranges of both the two types of bond distances and the range of asymmetry in these two bond distances in 1–8, I–IV and A–D are not very different. In contrast to the metal–phenoxo bond distances, the metal–µ1,1-carboxylato bond distances do not follow a general order; the terminal metal–µ1,1-carboxylato bond is longer in some compounds but shorter in some others than the central metal–µ1,1-carboxylato bond and even the latter are very close or exactly equal in some compounds, revealing the role of the variation of the primary and secondary ligands in providing variation in structural

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parameters. The metal–µ1,1-carboxylato–metal bridge angle in compounds 1–8/I–IV (90.35–93.33°) is clearly smaller than those in compounds A–D (94.05–96.49°) because of the additional chelating nature of the µ1,1-carboxylato in the formers. Regarding the metal–µ1,1-carboxylato–metal bridge angle in the present series of compounds, an interesting correlation can be noted: for the aliphatic carboxylato (acetate or propionate in compounds 1, 3, 4 and 6), the bridge angles (92.98–93.33°) are greater than the bridge angles (90.47–91.40°) in compounds involving aromatic carboxylatos (benzoate or o-chlorobenzoate in compounds 2, 5, 7 and 8). Such a correlation is not observed in the compounds I–IV which have similar bridging/chelating environment to that in 1–8. The metal–phenoxo–metal bridge angles in compounds A–D (98.83–101.76°) are greater than those in compounds 1–8 (96.39–96.79°) or compounds I–IV (94.61–97.63°), which can be again rationalized on the basis of additional chelation of the µ1,1-carboxylato and accompanied strain in the bridging core in 1–8/I–IV. Regarding the phenoxo bridge angle, a surprising aspect can be noted in 1–8: it is almost the same (range is 96.39–96.79°) irrespective of variation of the primary Schiff base ligand and the bridging/chelating carboxylatos, while one can see that the phenoxo bridge angles in similar compounds I–IV vary between 94.61° and 97.63°. At least the steric effect (benzoate/o-chlorobenzoate versus acetate/propionate) should have influenced the phenoxo bridge angle and therefore an almost constant phenoxo bridge angle in 1–8 is surprising. As already mentioned, some structural parameters of A–D are different from those of 1–8/I–IV because of the difference in the structures of the two sets: µ1,1-carboxylato is also chelating in 1–8/I–IV but not in A–D. On the other hand, the difference in some structural parameters in 1–8 in comparison with those in I–IV seems to be unusual. It is relevant therefore to mention the possible reason of such anomaly. All the three Schiff base ligands in compounds 1–8 form 5-membered or 6-membered chelate rings, while Schiff base ligands in I–IV form two 6-membered chelate rings. This may be a possible reason for the above mentioned differences in the values of some structural parameters in the two sets of compounds. Magnetic properties of 1–8 Variable-temperature (2–300 K) magnetic properties of complexes 1, 7 and 8 are shown in Fig. 5–7 in χMT versus T plots, while the similar profiles of complexes 2–6 are shown in Fig. S5–S9,† respectively. The observed χMT values of 3.73, 3.89, 4.07, 3.84, 3.82, 3.92, 3.87 and 4.22 cm3 K mol−1 for 1–8 at 300 K are higher than the expected value of 3.00 cm3 K mol−1 for three uncoupled with S1 = S2 = S3 = 1. On lowering of the temperature, χMT values of all these complexes follow a similar trend: χMT increases slowly in the temperature range of 300 K to 50 K and increases rapidly in the temperature range of 50 K to ca. 8 K, followed by a sharp drop on further cooling to 2 K. However, maximum values of 5.23, 5.85, 6.46, 5.62, 5.61, 5.72, 6.19 and 6.12 cm3 K mol−1 are observed at 8, 8, 6, 6, 8, 8, 8 and 8 K for 1–8, while at 2 K the following values are

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Table 2 Selected bond lengths (Å) and bond angles (°) in the coordination environments of the metal centres in 1–8. Symmetry code (A): 1 − x, −y, −z (1); 1 − x, 1 − y, −z (Unit I, 2); 1 − x, 1 − y, 2 − z (3); 1 − x, 2 − y, 2 − z (4); 0.5 − x, 0.5 − y, 1 − z (5); 1 − x, 2 − y, −z (6); 1 − x, 2 − y, 1 − z (7); 2 − x, 2 − y, 1 − z (8)

Compound no.

1

2 (Unit-I)

3

4

5

6

7

8

Ni1–O1 Ni1–O2/O2Aa Ni1–N1 Ni1–N2/N2A_ab Ni1–O3 Ni1–O4 Ni2–O1 Ni2–O2 Ni2–O5 Ni1⋯Ni2 N1–Ni1–O2/O2Aa N2/N2A_ab–Ni1–O1 O3–Ni1–O4 N1–Ni1–N2/N2A_ab N1–Ni1–O1 N1–Ni1–O3 N1–Ni1–O4 N2/ N2A_ab–Ni1–O2/O2Aa N2/ N2A_ab–Ni1–O3 N2/ N2A_ab–Ni1–O4 O1–Ni1–O2/O2Aa O1–Ni1–O3 O1–Ni1–O4 O2/O2Aa–Ni1–O3 O2/O2Aa–Ni1–O4 O1–Ni2–O1A O2–Ni2–O2A O5–Ni2–O5A O1–Ni2–O2 O1–Ni2–O2A O1–Ni2–O5 O1–Ni2–O5A O2–Ni2–O5 O2–Ni2–O5A Ni1–O1–Ni2 Ni1–O2/O2Aa–Ni2 Ni1⋯Ni2⋯Ni1A

2.015(1) 2.082(1) 1.983(2) 2.174(2) 2.253(2) 2.015(1) 2.074(1) 2.127(1) 2.033(1) 3.053 159.85(6) 174.16(6) 157.81(6) 83.49(8) 90.86(7) 101.66(7) 100.37(7) 102.89(7) 87.85(7) 92.08(7) 81.96(5) 91.86(6) 90.40(6) 60.05(5) 98.49(6) 180.0 180.0 180.0 79.54(5) 100.46(5) 90.79(5) 89.21(5) 89.57(6) 90.43(6) 96.58(6) 93.00(6) 180.00

2.007(6) 2.148(6) 1.992(8) 2.157(9) 2.183(6) 2.020(6) 2.114(6) 2.125(6) 1.997(6) 3.051 164.3(3) 171.6(3) 157.0(2) 82.8(4) 88.9(3) 105.7(3) 97.0(3) 104.8(3) 91.1(3) 88.3(3) 83.4(2) 91.4(2) 92.5(2) 61.0(2) 97.0(2) 179.999(1) 179.998(1) 179.998(1) 81.5(2) 98.5(2) 90.1(2) 89.9(2) 89.9(2) 90.1(2) 95.5(3) 91.1(2) 180.00

2.034(2) 2.115(2) 1.969(3) 2.237(3) 2.201(2) 2.003(2) 2.080(2) 2.115(2) 2.037(2) 3.077 155.91(11) 173.04(11) 161.27(10) 83.82(12) 90.98(11) 97.82(12) 100.85(12) 106.50(10) 93.60(10) 86.90(10) 80.07(9) 91.68(9) 89.55(9) 60.50(9) 101.39(9) 179.999(1) 180.00(12) 179.999(1) 79.05(9) 100.95(9) 88.61(9) 91.39(9) 90.72(8) 89.28(8) 96.79(9) 93.33(9) 180.00

2.022(1) 2.078(1) 1.980(2) 2.214(2) 2.238(2) 2.013(1) 2.060(1) 2.112(1) 2.028(1) 3.044 162.54(7) 174.39(6) 159.93(6) 84.02(8) 90.79(7) 104.50(7) 95.50(7) 103.14(7) 87.51(7) 93.05(7) 81.26(6) 91.73(6) 89.57(6) 60.55(5) 99.94(6) 179.999(1) 180.00(6) 179.999(1) 100.43(5) 79.57(5) 88.77(6) 91.23(6) 90.24(6) 89.76(6) 96.39(6) 93.15(6) 180.00

1.991(2) 2.113(2) 1.957(3) 2.191(3) 2.206(3) 2.011(2) 2.056(2) 2.110(2) 1.995(2) 3.022 160.69(10) 175.64(10) 163.09(9) 84.29(12) 91.46(11) 101.81(11) 95.07(11) 103.01(11) 91.14(11) 91.49(11) 80.72(9) 88.75(10) 89.87(10) 60.66(9) 102.49(10) 180.00 180.00(10) 180.0 79.33(9) 100.67(9) 86.94(9) 93.06(9) 90.32(8) 89.68(8) 96.61(10) 91.40(9) 180.00

2.016(1) 2.080(1) 1.983(1) 2.216(1) 2.246(1) 2.017(1) 2.067(1) 2.119(1) 2.026(1) 3.046 161.99(6) 174.20(5) 159.11(5) 83.35(6) 91.36(6) 103.39(6) 97.33(6) 102.65(6) 87.18(6) 92.73(6) 81.70(5) 91.74(5) 90.31(5) 60.52(5) 99.29(5) 180.0 180.0 180.00(8) 100.39(5) 79.61(5) 90.96(5) 89.04(5) 89.93(5) 90.07(5) 96.45(5) 92.98(5) 180.00

2.017(3) 2.146(3) 1.968(4) 2.185(2) 2.134(3) 1.997(3) 2.051(3) 2.133(2) 2.021(2) 3.038 161.00(13) 171.4(3) 162.44(12) 82.4(3) 91.11(13) 101.16(13) 96.33(13) 102.8(3) 84.5(3) 96.3(3) 81.70(10) 91.35(11) 89.90(11) 61.72(10) 101.19(11) 180.0 180.0 180.0 81.25(10) 98.75(10) 90.13(10) 89.87(10) 88.24(10) 91.76(10) 96.65(11) 90.47(10) 180.00

2.014(2) 2.112(2) 1.977(3) 2.210(3) 2.173(3) 2.023(3) 2.047(2) 2.136(2) 1.994(2) 3.031 161.86(13) 173.62(11) 162.19(12) 83.83(13) 90.06(12) 102.16(14) 95.61(14) 103.64(11) 89.31(12) 91.47(12) 81.70(10) 90.19(11) 90.95(11) 61.98(11) 100.63(10) 180.00(14) 179.998(1) 180.0 80.38(9) 99.62(9) 90.66(10) 89.34(10) 91.13(10) 88.87(10) 96.56(10) 91.06(9) 180.00

a

O2 for compounds 1, 2(Unit-I), 3, 5, 7 and 8. O2A for compounds 4 and 6. b N2A_a for compound 7.

observed: 3.83, 4.53, 4.20, 4.58, 4.03, 4.48, 5.03 and 4.87 cm3 K mol−1 for 1–8, respectively. The above mentioned profiles indicate the ferromagnetic interaction between the metal centres in all the complexes 1–8, while the most probable reason for the sharp decrease of χMT below ca. 8 K is the single-ion anisotropy of nickel(II) ions. The χMT versus T data for all these complexes can be simulated with H ¼ 2JðS1  S2 þ S2  S3 Þ þ gβS1  B þ gβS2  B þ gβS3  B 1 1 þ D½S 2 Z;1 þ S 2 Z;1 þ S 2 Z;1  S1 ðS1 þ 1Þ  S2 ðS2 þ 1Þ 3 3 1 ð1Þ  S3 ðS3 þ 1Þ 3 where the same coupling constant between Ni1 and Ni2 and Ni2 and Ni1A was taken into account because of the presence of the inversion centre located at Ni2. To avoid over parameterization, one D value for two types of nickel(II) ions in each compound was assumed. The parameters for the best simulation obtained via full matrix diagonalization of the Hamiltonian23

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are J = 2.65 cm−1, g = 2.20, D = 8.94 cm−1 for 1; J = 2.97 cm−1, g = 2.25, D = 7.94 cm−1 for 2; J = 3.01 cm−1, g = 2.29, D = 7.95 cm−1 for 3; J = 2.87 cm−1, g = 2.22, D = 7.90 cm−1 for 4; J = 2.58 cm−1, g = 2.23, D = 7.74 cm−1 for 5; J = 2.74 cm−1, g = 2.25, D = 7.88 cm−1 for 6; J = 3.89 cm−1, g = 2.22, D = 7.30 cm−1 for 7; and J = 2.37 cm−1, g = 2.34, D = 7.21 cm−1 for 8. All data can be simulated satisfactorily as shown by the solid lines in Fig. 5–7 and Fig. S5–S9.† We have also collected M vs. H data at different constant temperatures ranging between 2 and 10 K. The observed data are shown in Fig. 8–10 for 1, 7 and 8 and in Fig. S10–S14† for 2–6. Calculated data, with the same parameters as obtained in the simulation of χMT versus T data, are nicely matched with the experimental data for all the temperatures. The terminal and central metal ions in compounds 1–8 are triply bridged by a phenoxo, a μ1,1-carboxylato and a μ1,3-carboxylato moiety. As these are heterobridged systems, the complementarity or countercomplementarity effect of a second bridge on the first bridge should be taken into consideration. It has been established that a μ1,3-carboxylato moiety in hetero-

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2.029

2.045 1.996 2.019 2.037

1.988 1.998 1.987

I

II III IV A

B C D

2.025 2.048 2.076

2.062 2.085 2.048 2.065

2.056

2.074 2.092 2.080 2.060 2.056 2.067 2.051 2.047

0.037 0.05 0.089

0.017 0.089 0.029 0.028

0.027

0.059 0.086 0.046 0.038 0.065 0.051 0.034 0.033

2.066 2.147 2.064

2.141 2.215 2.137 2.125

2.181

2.082 2.147 2.115 2.078 2.113 2.080 2.146 2.112

2.127 2.117 2.115

2.115 2.094 2.123 2.085

2.134

2.127 2.130 2.115 2.112 2.110 2.119 2.133 2.136

96.58 96.55 96.79 96.39 96.61 96.45 96.65 96.56 97.61 94.61 97.15 97.63 99.89 99.79 101.76 98.83

0.045 0.017 0.000 0.034 0.003 0.039 0.013 0.024 0.047 0.026 0.121 0.014 0.04 0.061 0.03 0.051

94.05 94.80 95.19

90.35 90.42 91.87 96.49

90.86

93.00 91.27 93.33 93.15 91.40 92.98 90.47 91.06

Acetate Acetate Acetate

Benzoate Cinnamate Acetate Acetate

Propionate Benzoate Acetate Propionate Benzoate Propionate Benzoate o-Chloro benzoate Cinnamate 2.01

4.4 [Lsal–N,NdiMepn − ] sal–N-Mepn − ] 3.07 [L [Lsal–N-Mepn]− 1.8 [Lsal–N-Mepn]− [Lsal–N– −3.05 Mepn − ] − 0.47 [N-HBPA] [MHAP]− 0.55 sal–o–HBA − [L ] 4.31

2.2 3.49 2.02

2.149

2.028 2.26

2.20 2.25 2.29 2.22 2.23 2.25 2.22 2.34

J/cm−1 g 2.65 2.97 3.01 2.87 2.58 2.74 3.89 2.37

[Lsal–pyr]− [Lsal–pyr]− [Lsal–pip]− [Lsal–pip]− [Lsal–pip]− [Lsal–mor]− [Lsal–mor]− [Lsal–mor]−

Ligand providing the phenoxo bridgea

2.18 1.22

2.34

8.94 7.94 7.95 7.90 7.74 7.88 7.30 7.21

0.1

−0.06 4.9%

22a 22b 22c

21b 21c 21d 21d

21a

This work

D/cm−1 zJ′/cm−1 Impurity Ref.

a N,N-diMepn, N-Mepn and o-HBA indicate N,N-dimethyl-1,3-diaminopropane, N-methyl-1,3-diaminopropane and o-hydroxybenzylamine, respectively; [N-HBPA]− is deprotonated N-(2-hydroxybenzyl)propanolamine; [MHPA]− is deprotonated N-methyl-N-(2-hydroxybenzyl)-2-amino-2-pyridine); other ligands here are Schiff bases.

μ1,1Carboxylato is not chelating

2.015 2.006 2.034 2.022 1.991 2.016 2.017 2.014

1 2 3 4 5 6 7 8

μ1,1Terminal– Central– Phenoxo carboxylato μ1,1μ1,1bridge bridge Terminal– Central– angle Carboxylato phenoxo phenoxo Asymmetry carboxylato carboxylato Asymmetry angle

Selected bond lengths (Å), bond angles (°) and some relevant structural parameters of 1–8 and previously published related trinickel(II) compounds

μ1,1Carboxylato is chelating also

Table 3

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Fig. 5 Fittings of the χMT vs. T of [NiII3(Lsal–pyr)2( propionate)4] (1) between 2.0 and 300.0 K. The experimental data are shown as black circles and the red line corresponds to the theoretical values.

Fig. 6 Fittings of the χMT vs. T of [NiII3(Lsal–mor)2(benzoate)4]·3CH2Cl2 (7) between 2.0 and 300.0 K. The experimental data are shown as black circles and the red line corresponds to the theoretical values.

bridged μ-oxo-μ1,3-carboxylato dicopper(II) systems (oxo = hydroxo, phenoxo, alkoxo) exhibits a countercomplementarity effect and thus reduces the antiferromagnetic interaction and the interaction in such systems becomes weakly antiferromagnetic and even ferromagnetic.1 For the present series of systems, it is logical that phenoxo and μ1,1-carboxylato are the first bridges and the μ1,3-carboxylato is the second bridge which may induce the countercomplementarity effect. Now, let us first consider what would be the magnetic exchange interaction in 1–8 in the absence of the μ1,3-carboxylato bridge. In that case, the terminal and central metal ions are bridged by two monoatomic oxo bridges, phenoxo and μ1,1-carboxylato. Unfortunately, there is no correlation in magnetic properties of single phenoxo/alkoxo/hydroxo/μ1,1-carboxylato systems but a number of correlations in dioxo-bridged systems have been reported. Moreover, no correlation in even bis(μ1,1-carboxylato) systems is known. Therefore, it is usual practice to extend the

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Fig. 7 Fittings of the χMT vs. T of [NiII3(Lsal–mor)2(o-Cl-benzoate)4]· 2CH3CN·2H2O (8) between 2.0 and 300.0 K. The experimental data are shown as black circles and the red line corresponds to the theoretical values.

Fig. 9 The low-temperature magnetization of [NiII3(Lsal–mor)2(benzoate)4]· 3CH2Cl2 (7) obtained at the indicated applied dc fields. The symbols are experimental data, while the solid lines represent the calculated curves listed in the inset.

Fig. 8 The low-temperature magnetization of [NiII3(Lsal–pyr)2(propionate)4] (1) obtained at the indicated applied dc fields. The symbols are experimental data, while the solid lines represent the calculated curves listed in the inset.

Fig. 10 The low-temperature magnetization of [[NiII3(Lsal–mor)2(o-Clbenzoate)4]·2CH3CN·2H2O (8) obtained at the indicated applied dc fields. The symbols are experimental data, while the solid lines represent the calculated curves listed in the inset.

idea obtained in dioxo-bridged systems to single oxo-bridged systems. According to correlations in di-oxo systems, the most important parameter to govern the exchange interaction is the metal–oxo–metal bridge angle; the interaction is ferromagnetic below a cross-over angle and antiferromagnetic above a crossover angle.1,6 Regarding diphenoxo-bridged dinickel(II) compounds, there are two correlations, both experimental; the cross-over angle is 93.5° according to one6a and 97.5° according to the other.6b Hence, both the phenoxo bridge angles (96.39–96.79°) and μ1,1-carboxylato bridge angles (90.47–93.33°) in 1–8 can be considered to lie in the ferromagnetic region to result in the ferromagnetic interaction. Additionally, the countercomplementarity effect of the μ1,3carboxylato should also participate in the ferromagnetic interaction.

The magnetic parameters of 1–8 and the previously published only a few related compounds are listed in Table 3. As already discussed, compounds I–IV in Table 3 are similar to 1–8 (in both cases, μ1,1-carboxylato is chelating also),21 while compounds A–D are closely similar (μ1,1-carboxylato is not chelating here).21d,22 As IV is one part of a cocrystal, its J value is not possible to obtain, while compounds I–III exhibit the ferromagnetic interaction with J values 4.4, 3.07 and 1.8 cm−1. The phenoxo (94.61–97.61°) and μ1,1-carboxylato (90.35–90.86°) bridge angles in I–III are either close to or smaller than the cross-over angles, which along with possible countercomplementarity effects of μ1,1-carboxylatos are responsible for the ferromagnetic interaction in these three compounds. On the other hand, in A–C, both the phenoxo (99.89, 99.79 and 101.76°) and μ1,1-carboxylato (96.49, 94.05 and 94.80°) bridge

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angles are greater, resulting in very weak ferromagnetic ( J = 0.47 cm−1 in B and 0.55 cm−1 in C) or antiferromagenetic ( J = −3.05 cm−1 in A) interactions in these three compounds. For compound D, the interaction is ferromagnetic with J = 4.31 cm−1 in spite of phenoxo and μ1,1-carboxylato bridge angles of 98.83 and 95.19°, which is little bit surprising and indicative that the rationalization of the relative J values in terms of bond angles is not in line in some cases, which may also be evidenced from the data of I and III. These latter two compounds have the same carboxylato (cinnamate) and both the phenoxo (97.61 and 97.15°) and μ1,1-carboxylato (90.86 and 90.42°) bridge angles are closely similar, yet J values are 4.4 cm−1 in one and 1.8 cm−1 in another. As we have attempted the contemporaneous simulation of both the χMT vs. T data and M vs. H data of 1–8 and have obtained quality fitting, we were able to estimate the parameters with high certainty. While, as usual, χMT vs. T data have been collected and simulated for all the compounds I–III/ A–D, M vs. H data at only one temperature (2 K) have been reported only for I–III.21a–c Of these three compounds, M vs. H data have been simulated only in one case (III)21c and that simulation is based on assuming the full population of the ground state to find out D of the ground state. Of I–III and A–D, six compounds (I–III and B–D) are ferromagnetically coupled and all alike 1–8 exhibit a decrease in χMT on lowering of temperatures below the temperature of the maximum, which have been rationalized in terms of single ion anisotropy in only C22b and in terms of the intermolecular interaction in I21a and III21c but it was not possible to rationalize in others and hence the χMT vs. T data at low temperatures could not be fitted. In one case (II),21b impurity as high as 4.9% had to be taken to get a reasonable fit even avoiding the lower temperature region. Clearly, simulation of even the χMT vs. T data of most of the reported systems which are similar or closely similar to 1–8, has been complicated.

Conclusions The title compounds, 1–8, are among only a few examples of trinickel(II) compounds with the µ-phenoxo-µ1,1-carboxylatoµ1,3-carboxylato type triple bridging moiety. An interesting structural aspect in 1–8 is that the nickel(II)–phenoxo–nickel(II) bridge angle is almost identical (96.39–96.79°) in spite of changing the ligand having the phenoxo moiety and/or the ligand having the carboxylato moiety. Another structural aspect is that the nickel(II)–µ1,1-carboxylato–nickel(II) bridge angle is greater (92.98–93.33°) for aliphatic carboxylatos (acetate/ propionate) but smaller (90.47–91.40°) for aromatic carboxylatos (benzoate/o-chlorobenzoate). Both these aspects could not be observed in the previously reported related systems. All the compounds exhibit weak ferromagnetic interaction ( J range: from 2.37 to 3.89 cm−1), which can be rationalized in terms of smaller metal–phenoxo–metal (96.39–96.79°) and metal–μ1,1carboxylato–metal (90.47–93.33°) bridge angles and also the possible countercomplementarity effect of μ1,3-carboxylatos.

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Considering 1–8 and the previous compounds (Table 3), the interaction is antiferromagnetic in only one case with J = −3.05 cm−1, while the interaction in all other cases is ferromagnetic with the J value ranging between 0.47 and 4.4 cm−1. In general, all these compounds can be divided into two sets: (i) where µ1,1-carboxylato is also chelating, both the phenoxo (94.61–97.63°) and µ1,1-carboxylato (90.35–93.33°) bridge angles are smaller and the interaction is ferromagnetic with J values 1.8–4.4 cm−1; (ii) where µ1,1-carboxylato is not chelating, both the phenoxo (99.79–101.76°) and µ1,1-carboxylato (94.05–96.49°) bridge angles are greater and the interaction is less ferromagnetic or even antiferromagnetic with J values ranging between −3.05 and 4.31 cm−1. It is also worth mentioning that while the χMT vs. T data of most of the previously published compounds, related to 1–8, could not be well simulated throughout the whole temperature range, it has been possible to get good quality χMT vs. T simulation for 1–8, not only that the parameters obtained from χMT vs. T simulation here correspond well with the M vs. H data; it may be noted that such consistency was seldom reported previously.24

Acknowledgements Financial support for this work was received from the Department of Science and Technology, the Government of India ( project Number SR/S1/IC-42/2011 to S. M.). S. Bhattacharya acknowledges the Council for Scientific and Industrial Research for providing a fellowship. S. Sasmal acknowledges the DST-PURSE Program of the University of Calcutta for providing a postdoctoral fellowship. Crystallography was performed at the DST-FIST, India-funded Single Crystal Diffractometer Facility at the Department of Chemistry, University of Calcutta. S. M. is grateful to one referee for assisting in proper refinement of some structures.

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