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Cite this: Dalton Trans., 2014, 43, 2733 Received 29th October 2013, Accepted 1st December 2013 DOI: 10.1039/c3dt53048e
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(enH2)4.5[In(AsVS4)3][As2III(μ-S2)S3]Cl and (enH2)MnAsIIIAsVS6: two thioarsenates(III, V) with mixed-valent optical properties† Ke-Zhao Du,a Mei-Ling Feng,a Xing-Hui Qi,a,b Zu-Ju Ma,a Long-Hua Li,a Jian-Rong Li,a Cheng-Feng Du,a,c Guo-Dong Zoua,c and Xiao-Ying Huang*a
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Two mixed-valent thioarsenates, namely (enH2)4.5[In(AsVS4)3][As2III(μ-S2)S3]Cl (1) and (enH2)MnAsIIIAsVS6 (2) (en = ethylenediamine), have been solvothermally synthesized and characterized. Thermal stability, magnetic and mixed-valent optical properties, as well as theoretical band structures and DOSs, of 1 and 2 have also been studied.
Chalcogenidoarsenate materials have attracted much attention for their potential applications such as optical nonlinearity,1–3 glass forming abilities,4–7 and magnetism.8–10 The structures and properties of these compounds could be further enriched by forming multinary chalcogenidometalates through the selfassembly reactions of chalcogenidoarsenate building blocks (e.g. [AsS3]3− and [AsS4]3−) with metal ions (e.g. Mn2+, In3+, Ag+) under solvothermal conditions.11–18 Meanwhile, mixed-valent compounds are of great interest because of their unique properties, exemplified by those of the iron–sulfur proteins and Y–Ba–Cu–O superconductive system.19–27 Among the numerous chalcogenidoarsenates, there are only three mixed-valent chalcogenidoarsenates(III, V) isolated, namely, 1D-{[Mn( phen)]3(AsVS4)(AsIIIS3)}n·nH2O,8 0D-{[Mn( phen)2]2(AsSe4)}2[As2Se6]·H2O ( phen = 1,10-phenanthroline),28 and 0D-[Mn(en)3]2[Mn(en)2AsS4][As3S6].14 Referring to the Robin–Day model, there are three classes of mixed-valent compounds.29,30 In class I, the mixed-valent ions are in ligand fields of very different symmetry and the valences are very firmly trapped; thus they always are insulators. In class II, the
a State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, People’s Republic of China. E-mail: [email protected]; Fax: +86 591 83793727 b College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou, Fujian 350002, P.R. China c Graduate University of the Chinese Academy of Sciences, Beijing 100049, People’s Republic of China † Electronic supplementary information (ESI) available: Syntheses, diagrams for calculated band structures, more structural details, elemental analysis, EDS, TGA, IR spectrum and PXRD. CCDC 958717 for 1 and 958716 for 2. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt53048e
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mixed-valent ions are in ligand fields of nearly identical symmetry and the valences are slightly delocalized. The compounds of class II always are semiconductors. In class III, the mixed-valent ion sites are crystallographically indistinguishable. The most striking feature of many mixed-valent compounds is the intense absorption in the visible region, which is due to the charge transfer between the mixed oxidation state ions.30–34 Hence the colors of K4FeII(CN)6 and Fe2III(SO4)3 are pale yellow whereas that of KFeIIIFeII(CN)6 is deep blue.29 Here we report on the syntheses, crystal structures, and characterizations of two new mixed-valent thioarsenates (enH2)4.5[In(AsVS4)3][As2III(μ-S2)S3]Cl (1) and (enH2)MnAsIIIAsVS6 (2).‡ The deep colors and narrow band gaps suggest that they are class II style. Their optical and magnetic properties, as well as theoretical band structures and DOSs, have also been studied. Compound 1 could be obtained from the solvothermal reactions of a mixture of In, As2S3, S, NH4Cl, ethylenediamine (en) and CH3OH, which was sealed in a stainless steel reactor with a 20 mL Teflon liner and kept at 150 °C for 6 days. Similarly, 2 was obtained from a mixture of LaCl3·7H2O, As2S2, S, Mn and NH4Cl, en and H2O, which was sealed in a stainless steel reactor with a 28 mL Teflon liner and kept at 130 °C for 3.5 days. More details of the syntheses could be found in the ESI.† Single crystal X-ray crystallography reveals that 1 belongs to ˉ. It is composed of the isolated anionic the space group P1 V groups of [In(As S4)3]6−, [As2III(μ-S2)S3]2−, Cl−, and the doubly protonated ethylenediamine. In the asymmetric unit of 1, there are one In3+, two AsIII, three AsV, seventeen S2− ions, 4.5 protonated (enH2)2+ and one Cl− ion. The AsIII(4, 5) are coordinated to three sulfur atoms to form a ψ-AsS3 trigonal pyramidal geometry with the As–S distances ranging from 2.1566(12) to 2.3124(12) Å, whereas all the AsV(1–3) ions are four-coordinated, with As–S distances ranging from 2.1348(11) to 2.1984(10) Å. The As(1–3)S4 tetrahedra acting as bidentate ligands are chelated to In3+ to form the highly negatively charged [In(AsVS4)3]6− cluster (Fig. 1a), with the In–S distances ranging from 2.5777(11) to 2.6630(10) Å. The In–S lengths of 1 are similar to those of [InAsS4(2,2-bpy)]2,35 M(tren)InAsS4
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Fig. 1 (a) The isolated [In(AsVS4)3]6− and [As2III(μ-S2)S3]2− clusters in 1; (b) the [MnAs2S6]n2n− layer in 2 with the [Mn2As2S12]10− cluster and [Mn2As2S10]n6n− ribbon highlighted; symmetric codes: a: 1 − x, 1 − y, −z; b: −x, 1 − y, −z; c: −x, 2 − y, −z.
(M = Mn, Co, Zn)13 and (Ph4P)2[InAs3S7].18 The AsIII(4) and AsIII(5) are interconnected by sharing S(15) and S2(13, 14) groups to form a five-membered ring-like [As2III(μ-S2)S3]2− cluster (Fig. 1a). The remaining Cl− and [enH2]2+ as charge balancing agents reside in the inter-spaces of the anion clusters. Finally, a three-dimensional (3D) supramolecular network is formed by intensive N–H⋯Cl and N–H⋯S hydrogen bonds (Fig. S1a†). Compound 2 crystallized in the monoclinic space group P21/n. Its structure features a 2D anionic layer of [MnAsIIIAsVS6]n2n−, Fig. 1b. Its asymmetric unit contains one formula unit. The AsV(1) ion adopts a [AsS4] tetrahedral geometry with the As–S distances ranging from 2.165(2) to 2.175(2) Å, whereas the AsIII(2) ion is coordinated to three sulfur atoms to form a ψ-AsS3 trigonal pyramidal coordination geometry with the As–S distances ranging from 2.218(2) to 2.308(2) Å. Then two [AsS3] units share one edge (S(6) and S(6c)) to form a trans-[AsIII2S4] dimer. The Mn2+ ion is octahedrally surrounded by six S2− ions with the Mn–S bond lengths ranging from 2.584(2) to 2.795(2) Å. One [AsVS4] tetrahedron and two distorted [MnS6] octahedra form an incompletecubane-like cluster. Then, the two centrosymmetrically related clusters share the Mn(1)–S(2)–Mn(1a)–S(2a) face to form an incomplete double-cubane-like [Mn2As2S12]10− cluster as a second building unit (SBU). In the cluster, S(2) acts as a μ3 metal-linker connecting one AsV ion and two Mn2+ ions, while S(1) and S(4) are the μ2 metal-linkers connecting one AsV ion and one Mn2+ ion, respectively. Such a SBU could also be found in compounds such as [Mn3( phen)3(AsVS4)2]n·nH2O,9 [Mn3(2,2-bpy)3(AsVS4)2]n·nH2O,10 and A8[Mn2(AsS4)4] (A = K,
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Rb, Cs).36 Further, the clusters of [Mn2As2S12]10− are interconnected by sharing S(5) and S(5b) to form a [Mn2As2S10]n6n− ribbon extended along the a axis. Finally, interconnections of the 1D ribbons by the bridging [AsIII2S4] dimers along the b axis lead to a [MnAs2S6]n2n− layer parallel to the ab plane. The [enH2]2+ as cations fill in the interlayer spaces and form extensive N−H⋯S and C−H⋯S hydrogen bonds giving rise to a 3D supramolecular network (Fig. S1b†). Noticeably, the previously known mixed-valent chalcogenidoarsenates(III, V) incorporating a second metal ion are all (TM)-S–As(III, V) (TM = transition metal) compounds.8,14,28 Compound 1 is the first example of mixed-valent chalcogenidoarsenate(III, V) incorporating main group metal ions. On the other hand, 2 is the first mixed-valent Mn–As(III, V)–Q (Q = S, Se, Te) compound featuring a two-dimensional anionic structure. As depicted in Fig. 2, the optical absorption spectra indicate a sharp absorption edge at about 1.41 eV for 1 and 1.87 eV for 2, respectively. These are consistent with the dark green color of 1 and dark red color of 2, respectively. There is a noticeable red shift of the absorption edges of 1 and 2 compared to those of (Ph4P)2[InAs3S7] (3.1 eV) and [NH4][MnAs3S6] (2.08 eV).18,37 The red shift could mainly be ascribed to the mixed valent color phenomenon, which is due to the inter-valence transfer (IT) band of mixed-valent ions in the visible region.25,30,38 But why is the color of {[Mn( phen)]3(AsVS4)(AsIIIS3)}n·nH2O red with the band gap of 2.55 eV?8 The organic ligand of phen, which is an optically active species, could be the key.39–44 We have proved the different contributions of phen and dien (dien = diethylenetriamine) to the band gap both theoretically and experimentally in our previous work.45 To further investigate the electronic structures of 1 and 2, the DOS calculations as well as band structures have been studied. The methodology used for the DOS and band structure calculations is described in the ESI.† Compound 1 has a band gap of 2.28 eV, which is significantly larger than the experimental value (1.41 eV). This is because the many-body interactions,45 e.g. electron–hole (e–h) effects, are not included in the present DFT calculations. In fact, we found a value of
Fig. 2 Solid state optical absorption spectra of 1 and 2; the insets show photographs of the crystals of 1 and 2, respectively.
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Fig. 3 The total density of states and partial density of states for 1 and 2. The Fermi level is set at 0 eV. The black DOS curves are the sum states of s, p, d, f.
1.35 eV for 1 after including e–h effects in the optical calculation. In contrast, compound 2 has a band gap of 1.24 eV, which is smaller than the experimental value (1.87 eV). In the DOS curve of 1 (Fig. 3a), the conduction band minimum above the Fermi level (the Fermi level is set at 0.0 eV) is mainly contributed by In3+, AsV, AsIII and S2−, while the valence band maxima are derived from AsIII and S2−. Similarly, the conduction band minimum of 2 is dominated by AsV, AsIII and S2−, while the valence band maxima are derived from Mn2+, AsIII and S2− (Fig. 3b). C, H and N contribute little to the band gaps of 1 and 2. The AsIII of the two title compounds contribute more to the top of the valence band than AsV, while their contributions to the bottom of the conduction band are almost equal. The distinctive bonding energy of AsIII–S and AsV–S may cause the different partial density of states of AsIII and AsV. This suggests that there may be a charge-transfer transition between AsIII and AsV, which may cause the intense absorption of 1 and 2 in the visible region. To investigate the magnetic behavior of 2, the direct current (dc) temperature-dependence magnetic susceptibility was measured on the pure crystalline sample of 2 in an applied field of 1000 Oe from 300 to 2 K. The corresponding plot of χmT and χm−1 for 2 is shown in Fig. 4. The χmT product of 3.57 emu K mol−1 at 300 K is smaller than the spin-only value
Fig. 4
Plot of temperature dependence of χmT and χm−1 for 2.
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expected for one isolated Mn2+ ion (4.38 emu K mol−1), considering g = 2.00 and S = 5/2. Upon cooling, the χmT product continuously decreases to 0.16 emu K mol−1 at 2 K, suggesting an antiferromagnetic behavior. The inverse magnetic susceptibility data in the range of 50–300 K can be fitted well to the Curie–Weiss law 1/χm = (T − θ)/C with the Curie constant C = 4.35 emu K mol−1 and a Weiss constant θ = −64.29 K, confirming the antiferromagnetic property of 2. In summary, we have presented the solvothermal synthesis, crystal structure, thermal stability, optical and magnetic behavior as well as theoretical calculations of two class II mixedvalent compounds (enH2)4.5[In(AsVS4)3][As2III(μ-S2)S3]Cl and (enH2)MnAsIIIAsVS6. The respective effects of As3+ and As5+ on the band gap have been studied. Likely the mixed-valence of As results in the intense absorption in the visible region of the spectra. This work would promote further research on mixedvalent chalcogenidometalates.
Acknowledgements This work was supported by grants from the NNSF of China (no. 21221001 and 21171164) and the 973 program (no. 2012CB821702).
Notes and references ‡ Crystal and structure refinement parameters for 1: C9H45As5ClInN9S17, ˉ, a = 12.2025(3), b = 12.2240(3), c = 14.8497(3) Å, M = 1349.43, triclinic, P1 α = 92.360(2), β = 91.777(2), γ = 95.691(2)°, V = 2200.87(9) Å3, Z = 2, Dcalc = 2.036 g cm−3, F(000) = 1330, μ = 5.158 mm−1, T = 293(2) K, 17 559 reflections measured, 8330 unique reflections (Rint = 0.0339), 6986 observed reflections [I > 2σ(I)] with R1(wR2) = 0.0326 (0.0638), R1(wR2) = 0.0434 (0.0708) (all data), GOF = 1.002. For 2: C2H10As2MnN2S6, M = 459.26, monoclinic, P21/n, a = 7.9460(6), b = 9.1633(4), c = 17.5871(8) Å, β = 92.494(6)°, V = 1279.33(13) Å3, Z = 4, Dcalc = 2.384 g cm−3, F(000) = 892, μ = 7.104 mm−1, T = 293(2) K, 5798 reflections measured, 2696 unique reflections (Rint = 0.0478), 1945 observed reflections [I > 2σ(I)] with R1(wR2) = 0.0518 (0.1143), R1(wR2) = 0.0823 (0.1319) (all data), GOF = 1.008.
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Cite this: Dalton Trans., 2014, 43, 2733 Received 29th October 2013, Accepted 1st December 2013 DOI: 10.1039/c3dt53048e
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(enH2)4.5[In(AsVS4)3][As2III(μ-S2)S3]Cl and (enH2)MnAsIIIAsVS6: two thioarsenates(III, V) with mixed-valent optical properties† Ke-Zhao Du,a Mei-Ling Feng,a Xing-Hui Qi,a,b Zu-Ju Ma,a Long-Hua Li,a Jian-Rong Li,a Cheng-Feng Du,a,c Guo-Dong Zoua,c and Xiao-Ying Huang*a
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Two mixed-valent thioarsenates, namely (enH2)4.5[In(AsVS4)3][As2III(μ-S2)S3]Cl (1) and (enH2)MnAsIIIAsVS6 (2) (en = ethylenediamine), have been solvothermally synthesized and characterized. Thermal stability, magnetic and mixed-valent optical properties, as well as theoretical band structures and DOSs, of 1 and 2 have also been studied.
Chalcogenidoarsenate materials have attracted much attention for their potential applications such as optical nonlinearity,1–3 glass forming abilities,4–7 and magnetism.8–10 The structures and properties of these compounds could be further enriched by forming multinary chalcogenidometalates through the selfassembly reactions of chalcogenidoarsenate building blocks (e.g. [AsS3]3− and [AsS4]3−) with metal ions (e.g. Mn2+, In3+, Ag+) under solvothermal conditions.11–18 Meanwhile, mixed-valent compounds are of great interest because of their unique properties, exemplified by those of the iron–sulfur proteins and Y–Ba–Cu–O superconductive system.19–27 Among the numerous chalcogenidoarsenates, there are only three mixed-valent chalcogenidoarsenates(III, V) isolated, namely, 1D-{[Mn( phen)]3(AsVS4)(AsIIIS3)}n·nH2O,8 0D-{[Mn( phen)2]2(AsSe4)}2[As2Se6]·H2O ( phen = 1,10-phenanthroline),28 and 0D-[Mn(en)3]2[Mn(en)2AsS4][As3S6].14 Referring to the Robin–Day model, there are three classes of mixed-valent compounds.29,30 In class I, the mixed-valent ions are in ligand fields of very different symmetry and the valences are very firmly trapped; thus they always are insulators. In class II, the
a State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, People’s Republic of China. E-mail: [email protected]; Fax: +86 591 83793727 b College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou, Fujian 350002, P.R. China c Graduate University of the Chinese Academy of Sciences, Beijing 100049, People’s Republic of China † Electronic supplementary information (ESI) available: Syntheses, diagrams for calculated band structures, more structural details, elemental analysis, EDS, TGA, IR spectrum and PXRD. CCDC 958717 for 1 and 958716 for 2. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt53048e
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mixed-valent ions are in ligand fields of nearly identical symmetry and the valences are slightly delocalized. The compounds of class II always are semiconductors. In class III, the mixed-valent ion sites are crystallographically indistinguishable. The most striking feature of many mixed-valent compounds is the intense absorption in the visible region, which is due to the charge transfer between the mixed oxidation state ions.30–34 Hence the colors of K4FeII(CN)6 and Fe2III(SO4)3 are pale yellow whereas that of KFeIIIFeII(CN)6 is deep blue.29 Here we report on the syntheses, crystal structures, and characterizations of two new mixed-valent thioarsenates (enH2)4.5[In(AsVS4)3][As2III(μ-S2)S3]Cl (1) and (enH2)MnAsIIIAsVS6 (2).‡ The deep colors and narrow band gaps suggest that they are class II style. Their optical and magnetic properties, as well as theoretical band structures and DOSs, have also been studied. Compound 1 could be obtained from the solvothermal reactions of a mixture of In, As2S3, S, NH4Cl, ethylenediamine (en) and CH3OH, which was sealed in a stainless steel reactor with a 20 mL Teflon liner and kept at 150 °C for 6 days. Similarly, 2 was obtained from a mixture of LaCl3·7H2O, As2S2, S, Mn and NH4Cl, en and H2O, which was sealed in a stainless steel reactor with a 28 mL Teflon liner and kept at 130 °C for 3.5 days. More details of the syntheses could be found in the ESI.† Single crystal X-ray crystallography reveals that 1 belongs to ˉ. It is composed of the isolated anionic the space group P1 V groups of [In(As S4)3]6−, [As2III(μ-S2)S3]2−, Cl−, and the doubly protonated ethylenediamine. In the asymmetric unit of 1, there are one In3+, two AsIII, three AsV, seventeen S2− ions, 4.5 protonated (enH2)2+ and one Cl− ion. The AsIII(4, 5) are coordinated to three sulfur atoms to form a ψ-AsS3 trigonal pyramidal geometry with the As–S distances ranging from 2.1566(12) to 2.3124(12) Å, whereas all the AsV(1–3) ions are four-coordinated, with As–S distances ranging from 2.1348(11) to 2.1984(10) Å. The As(1–3)S4 tetrahedra acting as bidentate ligands are chelated to In3+ to form the highly negatively charged [In(AsVS4)3]6− cluster (Fig. 1a), with the In–S distances ranging from 2.5777(11) to 2.6630(10) Å. The In–S lengths of 1 are similar to those of [InAsS4(2,2-bpy)]2,35 M(tren)InAsS4
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Fig. 1 (a) The isolated [In(AsVS4)3]6− and [As2III(μ-S2)S3]2− clusters in 1; (b) the [MnAs2S6]n2n− layer in 2 with the [Mn2As2S12]10− cluster and [Mn2As2S10]n6n− ribbon highlighted; symmetric codes: a: 1 − x, 1 − y, −z; b: −x, 1 − y, −z; c: −x, 2 − y, −z.
(M = Mn, Co, Zn)13 and (Ph4P)2[InAs3S7].18 The AsIII(4) and AsIII(5) are interconnected by sharing S(15) and S2(13, 14) groups to form a five-membered ring-like [As2III(μ-S2)S3]2− cluster (Fig. 1a). The remaining Cl− and [enH2]2+ as charge balancing agents reside in the inter-spaces of the anion clusters. Finally, a three-dimensional (3D) supramolecular network is formed by intensive N–H⋯Cl and N–H⋯S hydrogen bonds (Fig. S1a†). Compound 2 crystallized in the monoclinic space group P21/n. Its structure features a 2D anionic layer of [MnAsIIIAsVS6]n2n−, Fig. 1b. Its asymmetric unit contains one formula unit. The AsV(1) ion adopts a [AsS4] tetrahedral geometry with the As–S distances ranging from 2.165(2) to 2.175(2) Å, whereas the AsIII(2) ion is coordinated to three sulfur atoms to form a ψ-AsS3 trigonal pyramidal coordination geometry with the As–S distances ranging from 2.218(2) to 2.308(2) Å. Then two [AsS3] units share one edge (S(6) and S(6c)) to form a trans-[AsIII2S4] dimer. The Mn2+ ion is octahedrally surrounded by six S2− ions with the Mn–S bond lengths ranging from 2.584(2) to 2.795(2) Å. One [AsVS4] tetrahedron and two distorted [MnS6] octahedra form an incompletecubane-like cluster. Then, the two centrosymmetrically related clusters share the Mn(1)–S(2)–Mn(1a)–S(2a) face to form an incomplete double-cubane-like [Mn2As2S12]10− cluster as a second building unit (SBU). In the cluster, S(2) acts as a μ3 metal-linker connecting one AsV ion and two Mn2+ ions, while S(1) and S(4) are the μ2 metal-linkers connecting one AsV ion and one Mn2+ ion, respectively. Such a SBU could also be found in compounds such as [Mn3( phen)3(AsVS4)2]n·nH2O,9 [Mn3(2,2-bpy)3(AsVS4)2]n·nH2O,10 and A8[Mn2(AsS4)4] (A = K,
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Rb, Cs).36 Further, the clusters of [Mn2As2S12]10− are interconnected by sharing S(5) and S(5b) to form a [Mn2As2S10]n6n− ribbon extended along the a axis. Finally, interconnections of the 1D ribbons by the bridging [AsIII2S4] dimers along the b axis lead to a [MnAs2S6]n2n− layer parallel to the ab plane. The [enH2]2+ as cations fill in the interlayer spaces and form extensive N−H⋯S and C−H⋯S hydrogen bonds giving rise to a 3D supramolecular network (Fig. S1b†). Noticeably, the previously known mixed-valent chalcogenidoarsenates(III, V) incorporating a second metal ion are all (TM)-S–As(III, V) (TM = transition metal) compounds.8,14,28 Compound 1 is the first example of mixed-valent chalcogenidoarsenate(III, V) incorporating main group metal ions. On the other hand, 2 is the first mixed-valent Mn–As(III, V)–Q (Q = S, Se, Te) compound featuring a two-dimensional anionic structure. As depicted in Fig. 2, the optical absorption spectra indicate a sharp absorption edge at about 1.41 eV for 1 and 1.87 eV for 2, respectively. These are consistent with the dark green color of 1 and dark red color of 2, respectively. There is a noticeable red shift of the absorption edges of 1 and 2 compared to those of (Ph4P)2[InAs3S7] (3.1 eV) and [NH4][MnAs3S6] (2.08 eV).18,37 The red shift could mainly be ascribed to the mixed valent color phenomenon, which is due to the inter-valence transfer (IT) band of mixed-valent ions in the visible region.25,30,38 But why is the color of {[Mn( phen)]3(AsVS4)(AsIIIS3)}n·nH2O red with the band gap of 2.55 eV?8 The organic ligand of phen, which is an optically active species, could be the key.39–44 We have proved the different contributions of phen and dien (dien = diethylenetriamine) to the band gap both theoretically and experimentally in our previous work.45 To further investigate the electronic structures of 1 and 2, the DOS calculations as well as band structures have been studied. The methodology used for the DOS and band structure calculations is described in the ESI.† Compound 1 has a band gap of 2.28 eV, which is significantly larger than the experimental value (1.41 eV). This is because the many-body interactions,45 e.g. electron–hole (e–h) effects, are not included in the present DFT calculations. In fact, we found a value of
Fig. 2 Solid state optical absorption spectra of 1 and 2; the insets show photographs of the crystals of 1 and 2, respectively.
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Fig. 3 The total density of states and partial density of states for 1 and 2. The Fermi level is set at 0 eV. The black DOS curves are the sum states of s, p, d, f.
1.35 eV for 1 after including e–h effects in the optical calculation. In contrast, compound 2 has a band gap of 1.24 eV, which is smaller than the experimental value (1.87 eV). In the DOS curve of 1 (Fig. 3a), the conduction band minimum above the Fermi level (the Fermi level is set at 0.0 eV) is mainly contributed by In3+, AsV, AsIII and S2−, while the valence band maxima are derived from AsIII and S2−. Similarly, the conduction band minimum of 2 is dominated by AsV, AsIII and S2−, while the valence band maxima are derived from Mn2+, AsIII and S2− (Fig. 3b). C, H and N contribute little to the band gaps of 1 and 2. The AsIII of the two title compounds contribute more to the top of the valence band than AsV, while their contributions to the bottom of the conduction band are almost equal. The distinctive bonding energy of AsIII–S and AsV–S may cause the different partial density of states of AsIII and AsV. This suggests that there may be a charge-transfer transition between AsIII and AsV, which may cause the intense absorption of 1 and 2 in the visible region. To investigate the magnetic behavior of 2, the direct current (dc) temperature-dependence magnetic susceptibility was measured on the pure crystalline sample of 2 in an applied field of 1000 Oe from 300 to 2 K. The corresponding plot of χmT and χm−1 for 2 is shown in Fig. 4. The χmT product of 3.57 emu K mol−1 at 300 K is smaller than the spin-only value
Fig. 4
Plot of temperature dependence of χmT and χm−1 for 2.
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expected for one isolated Mn2+ ion (4.38 emu K mol−1), considering g = 2.00 and S = 5/2. Upon cooling, the χmT product continuously decreases to 0.16 emu K mol−1 at 2 K, suggesting an antiferromagnetic behavior. The inverse magnetic susceptibility data in the range of 50–300 K can be fitted well to the Curie–Weiss law 1/χm = (T − θ)/C with the Curie constant C = 4.35 emu K mol−1 and a Weiss constant θ = −64.29 K, confirming the antiferromagnetic property of 2. In summary, we have presented the solvothermal synthesis, crystal structure, thermal stability, optical and magnetic behavior as well as theoretical calculations of two class II mixedvalent compounds (enH2)4.5[In(AsVS4)3][As2III(μ-S2)S3]Cl and (enH2)MnAsIIIAsVS6. The respective effects of As3+ and As5+ on the band gap have been studied. Likely the mixed-valence of As results in the intense absorption in the visible region of the spectra. This work would promote further research on mixedvalent chalcogenidometalates.
Acknowledgements This work was supported by grants from the NNSF of China (no. 21221001 and 21171164) and the 973 program (no. 2012CB821702).
Notes and references ‡ Crystal and structure refinement parameters for 1: C9H45As5ClInN9S17, ˉ, a = 12.2025(3), b = 12.2240(3), c = 14.8497(3) Å, M = 1349.43, triclinic, P1 α = 92.360(2), β = 91.777(2), γ = 95.691(2)°, V = 2200.87(9) Å3, Z = 2, Dcalc = 2.036 g cm−3, F(000) = 1330, μ = 5.158 mm−1, T = 293(2) K, 17 559 reflections measured, 8330 unique reflections (Rint = 0.0339), 6986 observed reflections [I > 2σ(I)] with R1(wR2) = 0.0326 (0.0638), R1(wR2) = 0.0434 (0.0708) (all data), GOF = 1.002. For 2: C2H10As2MnN2S6, M = 459.26, monoclinic, P21/n, a = 7.9460(6), b = 9.1633(4), c = 17.5871(8) Å, β = 92.494(6)°, V = 1279.33(13) Å3, Z = 4, Dcalc = 2.384 g cm−3, F(000) = 892, μ = 7.104 mm−1, T = 293(2) K, 5798 reflections measured, 2696 unique reflections (Rint = 0.0478), 1945 observed reflections [I > 2σ(I)] with R1(wR2) = 0.0518 (0.1143), R1(wR2) = 0.0823 (0.1319) (all data), GOF = 1.008.
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 (M=Nb(V) or V(V)) polyoxometalates.](/assets/img/hold.png)
