Structural systematics of tellurium(II) bis( O -alkyldithiocarbonate) and tellurium(II) bis( N , N -dialkyldithiocarbamate) compounds

Structural diversity in the mercury(II) bis(N,N-dialkyldithiocarbamate) compounds: an example of the importance of considering crystal structure when rationalising molecular structure

The crystal and molecular structures of four compounds of the general formula Hg(S2CNR2)2 are reported. The pale-yellow crystals of [Hg(S2CNiBu2)2] are monoclinic, space group C2/c with unit cell dimensions a = 26.27(2) Å, b = 13.654(8) Å, c = 13.863(5) Å, β = 96.64(4)°, Z = 8 and D x = 1.639 Mg m−3. The yellow crystals of [Hg(S2CN(iPr)Cy)2] are triclinic, space group P[unk] with unit cell dimensions a = 12.291(9) Å, b = 11.534(6) Å, c = 9.559(4) Å, α = 69.82(4)°, β = 88.94(4)°, γ = 72.00(5)°, Z = 2 and D x = 1.747 Mg m−3. Crystals of yellow [Hg(S2CN(Et)Cy)2] are monoclinic, space group P21/c with unit cell dimensions a = 8.459(6) Å, b = 19.506(9) Å, c = 13.955(6) Å, β = 92.89(4)°, Z = 4 and D x = 1.748 Mg m−3. The yellow crystals of [Hg(S2CNnBu2)2] are monoclinic, space group C2/c with unit cell dimensions a = 23.210(6) Å, b = 16.48(1) Å, c = 16.285(6) Å, β = 126.81(2)°, Z = 8 and D x = 1.623 Mg m−3. The structures were solved by direct methods and each refined by a full-matrix least-squares procedure to final R = 0.037 using 2994 reflections for [Hg(S2CNiBu2)2], to R = 0.043 using 3861 reflections for [Hg(S2CN(iPr)Cy)2]; to R = 0.041 for 2895 reflections for [Hg(S2CN(Et)Cy)2]; and to R = 0.065 for 2640 reflections for [Hg(S2CNnBu2)2]. A monomeric motif, featuring distorted tetrahedral geometries, is found for the structures of [Hg(S2CNiBu2)2] and [Hg(S2CN(iPr)Cy)2]. By contrast, dimeric structures, arising from the presence of bridging dithiocarbamate ligands, are found in the structures of [Hg(S2CN(Et)Cy)2] and [Hg(S2CNnBu2)2]. A critical examination of crystal structure for these and related systems enables a qualitative explanation for the structural diversity observed in the Hg(S2CNR2)2 compounds. The primary coordination about the mercury centers in Hg(S2CNR2)2 is linear and other associations, be they intra- or intermolecular, give rise to distortions from linearity and result in varied coordination geometries. The nature of the additional interactions is dictated by the need to maximise intermolecular associations.

Thus, when there are no steric restrictions precluding association in the lattice, Hg–S interactions are present that give rise to dimeric structures or 2-dimensional layer structures in the case when R = H.

Crystal structures of 2,2′-bipyridine adducts of two cadmium O-alkyl dithiocarbonates: rationalisation of disparate coordination geometries based on different crystal packing environments

Two distinct coordination geometries are found in the structures of Cd(S2COR)2(2,2′-bipyridine). For R = CH2CH2OCH3 (1) a N2S2 donor set defines a distorted tetrahedral geometry for cadmium as the xanthate ligands adopt a monodentate coordination mode. By contrast, a N2S3 donor set is found in the structure where R is butyl (2) as one of the xanthate ligands is chelating. An analysis of the crystal structures shows that both lattices feature extensive C–H...π interactions and that in (1) there are C–H...O interactions that are not present in (2). In (2) there are π...π interactions that are absent in (1). A qualitative argument based on crystal packing considerations is proposed to explain the differences in molecular structures.

Crystal structure of anhydrous potassium O-n-propyldithiocarbonate. Theoretical calculations of O-alkyl dithiocarbonates

The xanthate anion in the structure of K[S2COnPr] displays the expected features, i.e. planar S2CO chromophore and variation in C—S and C—O distances. The K cation exists in a distorted cubic geometry defined by an O2S6 donor set. Cubes are face-shared so as to form a layer structure with cohesion between layers afforded by hydrophobic interactions. A series of theoretical gas-phase structures have been calculated for isolated S2COR anions. These show that there is a remarkable consistency in geometric parameters across the series. This observation indicates that the nature of the R substituent does not influence greatly the electronic structure of the central S2CO chromophore.