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

Abstract

Abstract 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.