Unprecedented coordination of dithiocarbimate in multinuclear and heteroleptic complexes

Abstract

An uncommon coordination protocol induced by the p-tolylsulfonyl dithiocarbimate ligand (L) [L = p-CH₃C₆H₄SO₂NCS₂²⁻] in conjunction with PPh₃ allowed the formation of novel homodimetallic, Cu₂(PPh₃)₄L (1), trinuclear heterometallic Cu₂Ni(L)₂(PPh₃)₄ (2) and heteroleptic complexes of general formula cis-[M(PPh₃)₂L] [M = Pd(II) (3), Pt(II) (4)]. The complexes have been characterized by microanalysis, mass spectrometry, IR, ¹H, ¹³C and ³¹P NMR and electronic absorption spectra and single-crystal X-ray crystallography. 2 uniquely consists of square planar, trigonal planar and tetrahedral coordination spheres within the same molecule. In both heteroleptic complexes 3 and 4 the orientation of aromatic protons of PPh₃ ligand towards the Pd(II) and Pt(II) center reveals C–H⋯Pd and C–H⋯Pt rare intramolecular anagostic or preagostic interactions. These complexes exhibit photoluminescent properties in solution at room temperature arising mainly from intraligand charge transfer (ILCT) transitions. The assignment of electronic absorption bands has been corroborated by time dependent density functional theory (TD-DFT) calculations. Complexes 1 and 2 with σ_rt values ∼ 10⁻⁶ S cm⁻¹ show semi-conductor properties in the temperature range 313–403 K whereas 3 and 4 exhibit insulating behaviour.