Synthesis and crystal structure of two new heterometallic thioantimonates(III) [Ni(pda)₂]Cu^I₄Sb^III₂S₆ and [Ni(dien)₂]Cu^ISb^III₃S₆,

Abstract

Two different dimensional inorganic–organic hybrid heterometallic sulfide, [Ni(pda)₂]Cu₄Sb₂S₆ (1) and [Ni(dien)₂]CuSb₃S₆ (2) were obtained by using 1,2-propanediamine (pda) and diethylenetriamine (dien) as the ligand, respectively.

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Chalcogenidometalate chemistry is an attractive subject due to compounds' integrating properties of classical electronics, optics and semiconductor materials associated with unique topological structures,¹ and the potential application as catalysts² or as superconductors.³ The design and synthesis of chalcogenidometalates have received considerable attention⁴ during the last decades. To design and synthesize more compounds with various configurations, it is very important to understand which factors affect the structures of chalcogenidometalates. We have to some extent studied how the structures of the sulfur-containing transition metal polymers are influenced by the size or charge of cations.⁴ By using different cations such as [Nd(DMF)₈]³⁺ and [La(DMF)₈]³⁺, we have successfully synthesized and characterized a large number of complexes with different structures.⁵ Now we further extend our interest to the study of main-group sulfides, thioantimonates.⁶

During the last few years a large number of thioantimonates have been synthesized under solvothermal conditions with organic amines as structure-directing agents.^6–27 In some of these compounds another transition metal ion (TMⁿ⁺) is incorporated into the SbS_x network forming a ternary TM–Sb–S anionic framework.^7–17 The protonated amine normally acts as a cation in most of these templated TM-thioantimonates, whereas in a few compounds such as [M(NH₃)₆]Cu₈Sb₃S₁₃ (M = Mn, Fe, Ni), [Fe(NH₃)₆]AgSbS₄ and [Co(en)₃]CoSb₄S₈ a transition metal complex serves as counterion directing to the anionic structures.^18,19

Herein we present two amine-templated nickel-copper-thioantimonates(III), [Ni(pda)₂]Cu₄Sb₂S₆ (1) and [Ni(dien)₂]CuSb₃S₆ (2). Compound 1, to the best of our knowledge, is the first inorganic–organic hybrid example of a 3D hetero-trimetallic sulfide, in which both Ni^II and Cu^I are incorporated into the SbS_x framework. Compound 2 consists of large 18-membered Cu₂Sb₇S₉ and small 6-membered CuSb₂S₃ hetero-rings.

Both compounds [Ni(pda)₂]Cu₄Sb₂S₆ (1) and [Ni(dien)₂]CuSb₃S₆ (2) were synthesized in Teflon-lined steel autoclaves under solvothermal conditions. In the synthesis progress, a mixture of Sb (1 mmol), S (4 mmol), CuCl₂·2H₂O (1 mmol), NiCl₂·6H₂O (1 mmol) and pda (5 ml) for 1, and a mixture of Sb (1 mmol), S (3 mmol), Cu (1 mmol), NiCl₂·6H₂O (1 mmol) and water solution of dien (60%, 5 ml) for 2 were, respectively, heated to 140 °C for 6 d, followed by cooling to room temperature in 3 h. The reacted mixtures were filtered, washed with ethanol and water, successively dried in air, yielding 1 and 2. The majority of the red crystal 1 was contaminated, all attempts to purify the crystals and increase the yield unfortunately failed, and we could only physically pick out several clear crystals of 1.

Single crystal X-ray analysis revealed that compound 1 is an amine-templated 3D hetero-trimetallic sulfide, the structure is shown in Fig. 1–3. As shown in Fig. 1, the Ni²⁺ ion located on an inversion centre is coordinated by four N atoms of two pda ligands, the Ni²⁺ ion and four N atoms being in the same plane. The Ni–N bond distances are in the range of 2.077(11)–2.079(11) Å and comparable to those in the other thioantimonates(III).^20,21 Furthermore, the Ni²⁺ ion is surrounded by the other two S atoms from the 2D (Cu₄Sb₂S₆²⁻)_n sheets (Fig. 2), resulting in the 3D configuration of compound 1 (Fig. 3). The Ni²⁺ ion is in an ideal octahedral coordination and the Ni–S bond lengths are 2.633(4) Å, which are comparable to those in complex [Ni(tren)]Sb₂S₄⁹. The crystallographically unique Sb(1) atom is coordinated by three S atoms to form a SbS₃ trigonal pyramid. The Sb–S distances range from 2.435(4) to 2.438(4) Å and S–Sb–S angles from 99.48(13) to 99.68(13)°, which are common for SbS₃ trigonal pyramids in thioantimonates.^22,23 Both the Cu(1) and Cu(2) atoms are surrounded by three S atoms yielding two nearly trigonal planar CuS₃ moieties (the Cu(1) and Cu(2) atoms are 0.1760 and 0.0740Å above the S₃ planes, respectively). The Cu–S bond lengths scatter from 2.255(4) to 2.278(4) Å and the S–Cu–S angles from 113.00(15) to 127.36(16)°. These values are in agreement with those found in many templated copper-thioantimaonates.^10,14 The S(2) and S(3) atoms present a trigonal pyramid coordination by one Sb and two Cu atoms, while S(1) atoms are tetrahedrally coordinated by one Sb, one Ni and two Cu atoms. The tetrahedral coordination of the S atom has been seldom observed in amine-templated copper-thioantimaonates. The 2D (Cu₄Sb₂S₆²⁻)_n sheet of compound 1 consists of 6-membered Cu₂SbS₃ rings (Fig. 2) and the inter-sheet separations are about 4.6201Å, which is shorter than that of other amine-templated copper-thioantimonates.^12,16

Fig. 1 Local coordination of the framework atoms of 1 showing the atom-labeling scheme and thermal ellipsoids at 25% probability. Symmetry code: a: 1 − x, 1 − y, 1 − z; b: 1 + x, y, z; c: −1 + x, y, z; d: −1/2 + x, 3/2 – y, −1/2 + z; e: 1/2 + x, 3/2 – y, −1/2 + z.

Fig. 2 Structure of the 2D (Cu₄Sb₂S₆²⁻)_n sheet in compound 1.

Fig. 3 3D structure of compound 1.

Compound 2 consists of isolated transition-metal-amine [Ni(dien)₂]²⁺ cations and 2D (CuSb₃S₆²⁻)_n anionic layers, the structure are shown in Fig. 4–6. In 2, as shown in Fig. 4, there are two independent Ni atoms each one lying on an inversion centre. The Ni²⁺ ion is coordinated by six N atoms of two dien ligands, forming a standard octahedron. The Ni–N bond lengths scatter from 2.087(3) to 2.155(4) Å with N–Ni–N_tran angles of 180°. The values are comparable to other thioantimonates.^20,21 The (CuSb₃S₆²⁻)_n anionic layers contain crystallographically distinct one Cu, three Sb and six S atoms. All the Sb(1), Sb(2) and Sb(3) atoms are coordinated by three S atoms to form SbS₃ trigonal pyramids. The Sb–S bond distances vary from 2.3522(11) to 2.4767(13) Å and the S–Sb–S angles from 86.57(4) to 101.61(5)°. The Cu(1) atom is surrounded by three S atoms to form a nearly trigonal planar CuS₃ moiety, the Cu(1) atom being 0.0865 Å above the S₃ plane. The Cu–S distances range from 2.2531(13) to 2.3137(13)Å and the S–Cu–S angles from 117.12(5) to 122.12(5)°. All the above distances (Sb–S, Cu–S) and angles (S–Sb–S, S–Cu–S) are similar to those found in other thioantimonates.^12,16 Vertex-sharing of the SbS₃ trigonal pyramids and the CuS₃ moieties yield the 2D (CuSb₃S₆²⁻)_n anionic layers which lie parallel to the (100) plane. The interlayer distance is about 13.5 Å, which is longer than that of other amine-templated copper-thioantimonates.^12,16 In the (CuSb₃S₆²⁻)_n anionic network, as shown in Fig. 5, all S atoms are doubly coordinated. The 2D structure is composed of 6-membered CuSb₂S₃ rings (different from the Cu₂SbS₃ rings in compound 1) and 18-membered Cu₂Sb₇S₉ rings. The large 18-membered Cu₂Sb₇S₉ ring is about 8.1290(13) × 6.1292(10) Å (from coordinate to coordinate), this is the largest pore in the amine-templated metal-thioantimonates so far.¹⁸ The anionic layers stack onto each other along the [100] direction, and the [Ni(dien)₂]²⁺ cations lie between the anionic layers (Fig. 6).

Fig. 4 Local coordination of the framework atoms and two independent cations of 2 showing the atom-labeling scheme and thermal ellipsoids at 25% probability. Symmetry code: a: x, −1 + y, z; b: x, 1/2 − y, −1/2 + z; c: x, 1 + y, z; d: −x, 1 – y, 1 – z.

Fig. 5 Structure of the (CuSb₃S₆²⁻)_n anionic layer with 18-membered Cu₂Sb₇S₉ hetero-ring in compound 2.

Fig. 6 Structure of compound 2.

For most copper-thioantimonates, protonated amines are used as structure-directing agents to modify the structure of the anionic framework,^10–12,16 and the anionic structure usually show a layered structure. In our work, metal complex cations are utilized to stabilize a chalcogen-containing anionic framework. For compound 1, pda serves as the chelating amine. Possibly due to steric hindrance, the Ni²⁺ ion is only planar coordinated by four N atoms of two pda ligands, and the remaining two coordination sites are further occupied by two S atoms from the 2D (Cu₄Sb₂S₆²⁻)_n sheets composed of only 6-membered Cu₂SbS₃ rings. Hence, both Ni^II and Cu^I are incorporated into the SbS_x framework to form the amine-templated 3D hetero-trimetallic sulfide, and the Ni : Cu : Sb : S ratio is 1 : 4 : 2 : 6. It should be noted that in amine-templated thioantimonates the Cu atoms tend to be coordinated by the S atoms forming the Cu–S–Sb framework,^10–12,16 whereas the Ni²⁺ ions prefer to connect with amine ligands,^{9,20,21,24–26} this can also be seen in compound 2. In 2 the Ni²⁺ ion is completely coordinated by six N atoms of three dien ligands generating a [Ni(dien)₂]²⁺ cation, further connection between Ni²⁺ ion and S atoms is prohibited. Thereby, the structure of compound 2 is similar to those of the copper-thioantimonates reported in the literature,^10–12,16 showing a 2D layered structure. The layered structure of 2 is composed of large 18-membered Cu₂Sb₇S₉ and small 6-membered CuSb₂S₃ hetero-rings. The large 18-membered Cu₂Sb₇S₉ hetero-rings in this compound may be attributed to the large steric volume of cations and the strong electrostatic interaction between ions. It should be noted that in compound 1 there exist two types of bridging sulfur conformation, µ₃–S and µ₄–S, while in compound 2 there exists only µ₂–S.

When secondary Sb–S bonds (the sum of the van der Waals radii of Sb and S is 3.8 Å ²⁸) are considered, in compound 2 the Sb(1) and Sb(3) atoms have two (3.4970, 3.6514 Å) and one more S neighbors (3.7530 Å), respectively. No secondary Sb–S bonds are found in compound 1. In both title compounds, some nitrogen atoms are directed at anionic layers. N(1) and N(2) atoms in compound 1 both have two sulfur neighbours, while N(1), N(2) and N(5) atoms in compound 2 all have one S neighbour. The N⋯S distances (Table S2†) are in the range of 3.428(1)–3.586(1) Å, implying a possible presence of hydrogen bonding between the amines and the anionic framework.

In conclusion, compound 1 is the first example of a 3D inorganic–organic hybrid hetero-trimetallic sulfide. Compound 2 offers (CuSb₃S₆²⁻)_n anionic layers in which there exist large 18-membered Cu₂Sb₇S₉ hetero-rings of about 8.1290(13) × 6.1292(10) Å, this is the largest pore in the amine-templated metal-thioantimonates reported so far. Owing to the different spatial structures and coordinating capability of the two organic amines, the as-synthesized two compounds show very varied structures. So it is reasonable to synthesize more compounds with novel structures through carefully choosing various organic amines.

Acknowledgements

This work was supported by grants from the 973 Program (2007CB815301 and 2006CB932904), the National Science Foundation of China (20333070, 20673118, 20871114), the Science Foundation of CAS (KJCX2-YW-M05) and of Fujian Province (2006J0014 and 2006F3132).

Notes and references

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Footnotes

† Electronic supplementary information (ESI) available: Selected distances and angles for 1 and 2 (Table S1); proposed hydrogen bonding geometry for 1 and 2 (Table S2). CCDC reference numbers 665818 for 1 and 665819 for 2. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/b906640c

‡ Crystal data, for 1: M_w = 896.99. monoclinic, space group P2(1)/n with a = 6.487(6)Å, b = 15.345(15)Å, c = 10.354(9)Å, β = 90.617(10)°, V = 1030.6(17) ų. T = 293(2) K, Z = 2, D_calcd = 2.891g cm⁻³, µ = 8.128 mm⁻¹. 7832 reflections collected in the range 2.3736 < θ < 27.4835, 2336 unique reflections. R1 = 0.0917 and wR2 = 0.1318 for 1521 observed reflections. For 2: M_w = 886.21. Monoclinic, space group P2(1)/c with a = 17.107(4)Å, b = 9.850(2)Å, c = 14.530(3) Å, β = 103.559(4)°, V = 2380.2(9) ų. T = 293(2) K, Z = 4, D_calcd = 2.473g cm⁻³, µ = 5.551 mm⁻¹. 17361 reflections collected in the range 2.40 < θ < 27.48, 5325 unique reflections. R1 = 0.0246 and wR2 = 0.0632 for 4836 observed reflections. Data for both compounds were corrected for Lorentz, polarization and absorption effects. The structures were solved and refined by full-matrix least-squares techniques on F² using SHELXL-97 (Sheldrick, G. M. Universität Göttingen), all non-hydrogen atoms were refined anisotropically. Hydrogen atoms were generated geometrically and allowed to ride on their parent atoms with fixed isotropic displacement parameters. Both the metal ratios (Ni : Cu : Sb = 1 : 4.19 : 2.14 for 1, Ni : Cu : Sb = 1 : 1.07 : 3.42 for 2) detected by energy dispersive spectroscopy are consistent with the theoretical stoichiometry (Ni : Cu : Sb = 1 : 4 : 2 for 1, Ni : Cu : Sb = 1 : 1 : 3 for 2).

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