Pyridine-2-selenolate and -2-tellurolate as ligands: a multinuclear (77Se, 119Sn, 125Te) magnetic resonance study of some tin(IV) complexes, and X-ray structural analyses of Sn(SPh)2(2-Se-C5H4N-N,Se)2 and Sn(SPh)1.85(2-Se-C5H4N)2.15

Abstract

Reactions between Sn(E′Ph)n (E′ = S or Se; n = 2 or 4) and the bis(pyridine) dichalcogenides 2,2′-(C5H4NE)2 (E = Se or Te), abbreviated py2E2, have been studied using multinuclear (77Se, 119Sn, 125Te) magnetic resonance. In this way the occurrence of the pyridine-2-chalcogenate complexes Sn(E′Ph)4−x(Epy)x (E′ = S or Se; E = Se, x = 1–4; E = Te, x = 1 or 2) has been demonstrated. The pattern of 119Sn NMR chemical shifts for Sn(E′Ph)4−x(Sepy)x (E′ = S or Se, x = 0–4) is consistent with bidentate bonding for the pySe− ligand when x = 1 and 2. The pyTe− ligand is probably bidentate also in all four complexes containing this ligand. As part of the NMR analysis, 77Se and (or) 125Te NMR data were obtained for py2Te2 and for the new mixed dichalcogenides PhE′ER (E′ = S, Se, or Te; E ≠ E′ = Se or Te; R = 2-py or Ph), which were produced in the systems Ph2E′2:R2E2. The complex Sn(SPh)2(Sepy)2 (1) was isolated pure and its structure determined by the single crystal X-diffraction technique. The compound crystallizes in the monoclinic space group P21/n, with unit cell dimensions a = 9.7929(9) Å, b = 22.340(2) Å, c = 11.368(1) Å, β = 108.803(7) °, V = 2354.3(4) Å3, dcalc = 1.837 g cm−3 and Z = 4. Refinement by full-matrix least squares on F2 gave agreement factors R1 = 0.0425 and wR2 = 0.0882 for 2823 independent reflections with F0 ≥ 4σ(F0) and 258 variables. The structure confirms that the PySe− ligand behaves in a chelating manner. The molecule Sn(SPh)2(2-Se-C5H4N-N,Se)2 has a distorted octahedral structure with the PhS− ligands in cis positions and the two Se donor atoms in trans positions. The Sn—Se, Sn—S, and Sn—N distances are 2.6291(8) and 2.6358(8) Å, 2.475(2) and 2.464(2) Å, and 2.325(5) and 2.333(5) Å. The bite angles N-Sn-Se of the chelating ligands are 65.9(1)° and 65.8(1)°. En route to 1, the yellow crystalline compound Sn(SPh)1 85(2-Se-C5H4N)2 15 (2) was isolated. This was shown by 119Sn NMR spectroscopy to contain both Sn(2-Se-C5H4N)2(SPh)2 and Sn(2-Se-C5H4N)3(SPh). The crystal and molecular structure of 2 was determined by single crystal X-ray diffraction techniques. Crystal data: monoclinic, space group P21/n, a = 9.795(2) Å, b = 22.355(4) Å, c = 11.362(2) Å, β = 108.87(3)°, V = 2354.2(8) Å3, dcalc = 1.837 g cm−3, dobs = 1.87(5) g cm−3Z = 4, R1 = 0.0306, wR2 = 0.0651 for 2756 data (F0 ≥ 4σ(F0)) and 258 parameters. Crystallographic evidence for the presence of co-crystallized Sn(2-Se-C5H4N)3(SPh) occurs only in a minor lengthening of one of the two Sn—S bonds, Sn—S(1) (compared with expectation for 1), and an excess of electron density at S(1) when the data are modelled as Sn(2-Se-C5H4N)2(SPh)2. These effects are attributed to a crystallographic disorder of SPh and η1-{2-Se-C5H4N} at the S(1)Ph site, involving isostructural Sn(η2-{2-Se-C5H4N})2({η1-{2-Se-C5H4N})(SPh) and Sn(η2-{2-Se-C5H4N})2(SPh)2. Key words: pyridine-2-selenolate, pyridine-2-tellurolate, tin complexes.