Studies in eight-co-ordination. Part 5. Crystal and molecular structure and electron spin resonance spectra of tetrakis(diethyldithio-carbamato)molybdenum(V) hexamolybdate and chloride

Abstract

The crystal structures of [Mo(S₂CNEt₂)₄]₂[Mo₆O₁₉](1) and [Mo(S₂CNEt₂)₄]Cl (2) have been determined from diffractometer data by direct methods and refined by full-matrix least-squares calculations to R 0.050 and 0.083 over 2 893(1) and 3 079(2) statistically significant reflections. Both are monoclinic: (1), space group C2/c, a= 23.54(1), b= 12.72(1), c= 26.94(1)Å, β= 102.60(5)°, Z= 4; (2), space group P2₁/c, a= 10.67(1), b= 27.96(1), c= 11.13(1)Å, β= 93.06(5)°, Z= 4. The dimensions and configurations of the [Mo(S₂CNEt₂)₄]⁺ ions are very similar in both crystals, with highly significant differences occurring only in the methyl-group orientations. The sulphur atoms from four bidentate ligands span the m edges of a D_2d dodecahedron with mean Mo–S_A 2.536(15) and Mo–S_B 2.491(8)Å in (1), and corresponding values of 2.531 (9) and 2.505(12)Å in (2). Dimensions of the [Mo₆O₁₉]^2– ion accord well with those determined in an earlier study: Mo–O(terminal) 1.673(13)–1.698(10), M–O(bridging), 1.881(10)–1.948(11), and Mo–O(central) 2.303(1)–2.323(1)Å. The single-crystal e.s.r. spectra of (1) and (2) are reported, and the molecular g values discussed in terms of the molecular structures and the electronic-absorption spectra of these complexes.