Comparative bifunctionality of acetylacetonato versus bipyridyl CoII/CoIII/PtII complexes. Structural study, non-linear optics and biomimetic activity

Four mononuclear metal-complexes [Co-II(acac)(2)(H2O)(2)] (Co-1), [Co-III(acac)(3)] (Co-2), [Co-III(Me(2)bpy)(2)(CO3)](Cr2O7)(0.5).4H(2)O (Co-3) and [Pt(acac)(2)] (Pt-1), (where acac = acetylacetonate anion and Me(2)bpy = 5,5'-dimethyl-2,2'-bipyridine) have been synthesized and structurally characterized. The structures of Co-1, Co-2 and Co-3 have been confirmed by X-ray single crystal analysis. Of [Co-III(acac)(3)], beside the structure recurrently reported (Co-2a), we describe a polymorph form of this complex with four molecules in the asymmetric unit still crystallizing in space group P2(1)/c (Co-2b). Electrochemical studies of the complexes provide insights on their redox properties in DMF. The most predominant electronic transitions have been assigned by TD-DFT calculations using Gaussian09 rev. E.01. Hirshfeld surface fingerprints revealed distinct patterns of intermolecular interactions across the studied compounds as a function of ligand and metal-ion property and reflect the subtle changes in crystal packing arrangements upon complex formation. XRPD and Rietveld refinement confirm their bulk phase purity. Measurement of nonlinear absorption and nonlinear optical transmission by open aperture Z-scan technique using Q-switched Nd:YAG 532 nm laser demonstrate that Pt-1 exhibits strong nonlinear response with 3PA coefficient (gamma) = 8x10(-24) m(3)/W-2 although Me(2)bpy ligand shows better nonlinear optical profile than Hacac molecule. The complexes behave as biomimetic functional models of the copper-containing oxidase phenoxazinone synthase (PHS) with k(cat) values in the order Co-1>Co-3>Co-2>Pt-1. Our results highlight the key features of structure-property relationship in the bifunctional behaviour of acac and bpy complexes with detailed comparisons from recent literature.