Unexpected Coordination Behaviour of 3,5-Di(2-pyridyl)-1,2,4-oxadiazole

The coordination behaviour of 3,5-di(2-pyridyl)-1,2,4-oxadiazole (L′) has been studied and compared with that of the 2,5-di(2-pyridyl)-1,3,4-chalcadiazoles LO, LS and LSe [LO = 2,5-di(2-pyridyl)-1,3,4-oxadiazole, LS = 2,5-di(2-pyridyl)-1,3,4-thiadiazole, LSe = 2,5-di(2-pyridyl)-1,3,4-selenadiazole]. Ligand L′ and the new complexes [CuII(L′)3](ClO4)2·1.5MeOH·H2O (1·1.5MeOH·H2O), 1·MeCN, [CoII(L′)2(MeOH)2](ClO4)2 (2), [CoII(LO)2(MeOH)2](ClO4)2 (3), [CuII(L′)2Cl2] (4), [CuII(L′)2Br2] (5) and [CuII(LSe)2Cl2]·MeOH (6·MeOH) have been structurally characterised by single-crystal X-ray diffraction analyses. With the help of DFT calculations and the analyses of metal–ligand bond lengths of similar complexes of L′, LO, LS and LSe the binding capacities have been determined as L′ << LO < LS < LSe.