Rare intermolecular M⋯H–C anagostic interactions in homoleptic Ni(ii)–Pd(ii) dithiocarbamate complexes

Abstract

New functionalized homoleptic dithiocarbamates of the form [M(L)₂] (M = Ni(II), L = L1, N-(3-methoxybenzyl)-N-(methylbenzyl)dithiocarbamate (1), L3, N-(3,4,5-trimethoxybenzyl)-N-(3-methylpyridyl)dithiocarbamate (3), L4, N-(4-methoxybenzyl)-N-benzyldithiocarbamate (4); Pd(II), L2, N-(N′-methyl-2-pyrrole)-N-benzyldithiocarbamate (2)) have been synthesized and characterized by microanalysis and their structures have been investigated using X-ray crystallography. All the four structures are centrosymmetric with the metal located in a square plane with minor distortions, Pd(II) greater than Ni(II). The crystal structures of 1 and 2 revealed the existence of unique intermolecular C–H⋯M (Ni, Pd) anagostic interactions between the methylene hydrogen atom on the ligand substituents and the metal centres and these enable the formation of 1-D polymeric chains. Particularly, geometric parameters (Pd⋯H–C = 2.61 Å; ∠Pd⋯H–C = 173°) for the C–H⋯Pd interactions in 2 are at the border of anagostic and hydrogen bonding. By contrast, 4 shows interactions between the methylene hydrogen atom and the CS₂Ni ring rather than the metal alone, while the interaction in 3 is intermediate between the two aforementioned types. These interactions are not shown in solution as revealed by their ¹H NMR studies. DFT calculations have been performed to analyse these rare interactions. 1, 3 and 4 are weakly conducting, σ_rt = 10⁻¹⁰–10⁻¹² S cm⁻¹, and show semiconductor behaviour in the 313–373 K range.