Synthesis, molecular and crystalline architectures, and properties of mononuclear cobalt(II)thiocyanates containing a symmetrical tailored diimine/an unsymmetrical bidentate Schiff base

Abstract

Two hexacoordinated mononuclear cobalt(II)thiocyanate complexes of general formula [Co(LL) 2(NCS) 2]. nH 2O [LL = 2,2′-dipyridylamine (dpa), n = 1, 1; LL = N-((pyridin-2-yl)benzylidene)benzylamine (pbba), n = 0, 2] have been prepared and characterized using microanalytical, spectroscopic and other physicochemical results. The compounds are non-electrolytes and behave as three-electron paramagnets. Structures of 1 and 2 are solved by X-ray diffraction measurements. Structural analyses show that each metal center in 1 and 2 adopts a distorted octahedral geometry with a CoN 6 chromophore ligated through four N atoms of two bidentate LL units; the hexacoordination is completed by two N atoms of terminal thiocyanates in mutual cis orientation. The mononuclear units in 1 are engaged in weak intermolecular N–H…S and C–H…S hydrogen bonds to give a 2D sheet structure, which is further stabilized by π…π interactions among the pyridine rings of dpa units. In the long-range form, two mononuclear units of 2 are locked by weak doubly C–H…S hydrogen bonds producing a dimeric unit, which packs through C–H…π interaction leading to a 2D continuum. In MeCN solutions, the compounds show a nearly reversible one-electron oxidative response corresponding to cobalt(III)–cobalt(II) couple. The complexes display intraligand 1(π–π∗) fluorescence at room temperature and intraligand 3(π–π∗) phosphorescence in glassy solutions (DMF at 77 K).