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

In our continuing efforts to explore the effects of substituent groups of ligands in the formation of supramolecular coordination structures, seven new Cu-II complexes formulated as [Cu-2(L-1)(4)(DMF)(2)] (1), {[Cu-2(L-1)(4)(Hmta)](H2O)(0.75)}(infinity) (2), [Cu-2(L-2)(4)(2,2'-bipy)(2)] (3), [Cu-2(L-3)(4)(H2O)(2)] (4), [Cu-2(L-3)(4)(Hmta)](infinity) (5), [Cu-2(L-3)(4)(Dabco)](infinity) (6) and [Cu-2(L-3)(4)(Pz)](infinity) (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 Cu-II ion is octahedrally coordinated, and carboxylate acid acts as a syn-syn bridging bidentate ligand. While each Cu-II 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 Cu-2-(RCO2)(4) and the bridging auxiliary ligands Hmta, Dabco and Pz. Furthermore, 3 has a carboxylic unidentate and mu(1,1)-oxo bridging dinuclear structure with the chelating auxiliary ligand 2,2'-bipy. Moreover, complexes 1-6 were characterized by electron paramagnetic resonance (EPR) spectroscopy. (C) 2010 Elsevier B.V. All rights reserved.