Structural changes in MII dithione/dithiolato complexes (M = Ni, Pd, Pt) on varying the dithione functionalization

The Ni triad [M(R2pipdt)(dmit)] based on donor/acceptor S,S′ ligands, where R2pipdt = 1,4-diisopropyl-piperazine-2,3-dithione (acceptor) and dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato (donor), was completed by preparing and characterizing the Pd(2) and Pt(3) compounds in addition to the already known Ni(1) complex. The rationale behind the work was to compare the properties and structures inside the triad with those of the corresponding Ni(4), Pd(5) and Pt(6) complexes where R = Bz. Minor changes in the properties as redox active nonlinear second-order (NLO) chromophores were observed in solution for the two triads. Instead, different structural features, reflected by changes in the diffuse reflectance spectra, were observed in their crystals on changing R from Bz to Pri in the piperazine ring and also, more surprisingly, inside the triads. 2 (isostructural with 1) and 3 crystallized in monoclinic P21/n and orthorhombic Pbca space groups, respectively. The crystal packings of 2 and 3 are also markedly different. In particular 1 and 2 form head-to-tail dimers whereas 3 forms supramolecular layers characterized by a partial stack between the molecular planes. Large differences in the crystal structures, induced by the diverse number and types of interactions exchanged by the peripheral fragments of the ligands, were found in the Bz-triad. Indeed, the molecules are stacked in a head-to-head and in a head-to-tail fashion in 4 and in 5/6, respectively. Moreover, significantly different packings were observed. The Hirshfeld surface analysis was used to provide a detailed description of the main types of interactions involved in the crystal packing of the six complexes.