Synthesis, NMR spectral and single crystal X-ray structural studies on Ni(II) dithiocarbamates with NiS 2PN, NiS 2PC, NiS 2P 2 chromophores: Crystal structures of (4-methylpiperazinecarbodithioato)(thiocyanato- N) (triphenylphosphine)nickel(II) and bis(triphenylphosphine) (4-methylpiperazinecarbodithioato)nickel(II) perchlorate monohydrate

Abstract

Four Ni(II) dithiocarbamates with NiS 2PX (X = NCS or CN or P) chromophores have been synthesized [[Ni(4-mpzdtc)(PPh 3)(NCS)] ( 1), [Ni(4-mpzdtc)(PPh 3)(CN)] ( 2), [Ni(4-mpzdtc)(PPh 3) 2]ClO 4 · H 2O ( 3) and [Ni(4-mpzdtc)(dppe)]ClO 4 ( 4) (where 4-mpzdtc = 4-methylpiperazinecarbodithioato anion, PPh 3 = triphenylphosphine and dppe = 1,2-bis((diphenylphosphino)ethane))] from [Ni(4-mpzdtc) 2]. Electronic spectra of the complexes show bands corresponding to d z 2 / d xy → d x 2 - y 2 transitions. IR spectra of all the compounds showed characteristic bands due to the dithiocarbamate ligand around 1500 cm −1 and 990 cm −1. CV studies showed a higher reduction potential for the parent complex indicating the reluctance to add more electron density to the already electron rich metal centre. 1H NMR spectra of the complexes showed the deshielding of α-CH 2 protons on complexation. The 13C signals show interesting variations for the S 2– 13C N carbon signals between the neutral [ 1 and 2] and ionic complexes [ 3 and 4]. The S 2– 13C N chemical shifts of the three complexes with PPh 3 follow the order: 3 < 1 < 2 indicating the influence of PPh 3, NCS, CN respectively on the mesomeric drift of electron density towards nickel. The PPh 3 complexes show the following order of increasing 31P chemical shifts: 3 (30.9 ppm) > 2 (22.1 ppm) > 1 (20.5 ppm). The observed order clearly establishes the ease with which the back bonding interaction takes place. The back bonding is best observed in the case of the NiS 2P 2 chromophore. Single crystal X-ray structures of [Ni(4-mpzdtc)(PPh 3)(NCS)] and [Ni(4-mpzdtc)(PPh 3) 2]ClO 4 indicate that the central metal atom is in a planar environment for both complexes. The planarity of the molecules is supported by the observed diamagnetism of the complexes. The short S 2–C N bonds indicate the partial double bond character in both cases.