New dicyanide-salen based chromium(III) complexes: Synthesis, crystal structures, electrochemical and thermal investigations

Two compounds with formulas [K(H2O)(CH3OH)CrIII(valen)(CN)2]2 (1) and PPh4[CrIII(valen)(CN)2]·8.5H2O (2) were synthesized and structurally characterized (H2valen is the Schiff base resulted from the condensation of o-vanillin with ethylenediamine). For compound 1, a solid-state transformation (130 °C), consisting in the elimination of CH3OH and H2O ligands, was observed. The exposure of the resulting crystal to the humidity from air led to [K(H2O)2CrIII(valen)(CN)2]2 (3). The single-crystal X-ray diffraction analysis of 1 and 3 revealed that they are isostructural, their structure consisting of a tetranuclear centrosymmetric complex, {Cr2K2}, with the CrIII ions located into the (N2O2) coordination sites and the potassium ions located into the open (O2O’2) compartments of the two organic ligands. For compound 2, the crystal structure consists of discrete anionic mononuclear species, [CrIII(valen)(CN)2]−, and tetraphenylphosphonium counter cations. Thermal (TG-DTG-DSC) and electrochemical investigations of the newly synthesized complexes were performed.