Influence of the R-substituents on the properties of [Ni(R2pipdt)(dmit)] complexes and crystal structure where R = CH2C6H5The HTML version of this article has been enhanced with colour images.CCDC reference numbers 656892. For crystallographic data in CIF or other electronic format see DOI: 10.1039/b712243hElectronic supplementary information (ESI) available: UV/Vis and EPR spectra of compounds 1a−, 1b−, 2a− and 2b−; Fig. S1–S6 and Table S1. See DOI: 10.1039/b712243h

Abstract

[Ni(R₂pipdt)(dmit)], (R₂pipdt = 1,4-disubstituted-piperazine-3,2-dithione, R = CH₂C₆H₅; dmit = 1,3-dithiole-2-thione-4,5-dithiolate) (1b) has been prepared and characterised and the properties compared with those of the known complex 2b belonging to the same class where R = Prⁱ. Cyclic voltammetry of 1b and 2b was carried out and compared with that of the respective R₂pipdt ligand precursors (1a and 2a). The nature of the R-groups of the pipdt ligand exerts an effect on the redox potentials and confirmed the position of the LUMO as mainly on the R₂pipdt part of the complex. Accordingly the low frequency absorption, assigned to the HOMO–LUMO transition which has inter-ligand charge-transfer character, is found for 1b at lower frequency when compared to the corresponding transition of 2b. In situ EPR was carried out on electroreduced radical species of the R₂pipdt ligand precursors (1a, 2a) and corresponding complexes (1b, 2b). This revealed considerable delocalisation of the unpaired electron on the R₂pipdt ligand in 1b and 2b with coupling constants to N and H comparable with those of 1a and 2a. Complex 1b crystallised in the space group Pnma and shows an essentially planar complex (with out-of-plane R groups) π stacked at a distance of 3.65(1) Å. Such a one-dimensional structure is not achieved in the case of 2b, where the complex units are almost parallel and head-to-tail with each other forming dimers and this difference in solid-state packing is apparent in the diffuse reflectance spectrum of each. Plane-wave DFT calculations for 1b revealed a highly one-dimensional band structure with considerable band dispersion along the direction of greatest molecular interaction via π-stacking.