Copper(II) complexes with monocarboxylate ligands bearing different substituent groups: Synthesis and spectroscopic studies

Abstract

In our continuing efforts to explore the effects of substituent groups of ligands in the formation of supramolecular coordination structures, seven new CuII complexes formulated as [Cu2(L1)4(DMF)2] (1), {[Cu2(L1)4(Hmta)](H2O)0.75}∞ (2), [Cu2(L2)4(2,2′-bipy)2] (3), [Cu2(L3)4(H2O)2] (4), [Cu2(L3)4(Hmta)]∞ (5), [Cu2(L3)4(Dabco)]∞ (6) and [Cu2(L3)4(Pz)]∞ (7) with three monocarboxylate ligands bearing different substituent groups HL1–HL3 (HL1 = phenanthrene-9-carboxylic acid, HL2 = 2-phenylquinoline-4-carboxylic acid, HL3 = adamantane-1-carboxylic acid, Hmta = hexamethylenetetramine, 2,2′-bipy = 2,2′-bipyridine, Dabco = 1,4-diazabicyclo[2.2.2] octane and Pz = pyrazine), have been prepared and characterized by X-ray diffraction. In 1, 2 and 4–7, each CuII ion is octahedrally coordinated, and carboxylate acid acts as a syn–syn bridging bidentate ligand. While each CuII ion in 3 is penta-coordinated in a distorted square-pyramidal geometry. 1 and 4 both show a dinuclear paddle-wheel block, while 2, 5, 6 and 7 all exhibit an alternated 1D chain structure between dinuclear paddle-wheel units of the tetracarboxylate type Cu2-(RCO2)4 and the bridging auxiliary ligands Hmta, Dabco and Pz. Furthermore, 3 has a carboxylic unidentate and μ1,1-oxo bridging dinuclear structure with the chelating auxiliary ligand 2,2′-bipy. Moreover, complexes 1–6 were characterized by electron paramagnetic resonance (EPR) spectroscopy.