Magnetostructural correlations and catecholase-like activities of μ-alkoxo-μ-carboxylato double bridged dinuclear and tetranuclear copper(II) complexes

Abstract

Two μ-alkoxo-μ-carboxylato bridged dinuclear copper(II) complexes, [Cu 2(L 1)(μ-HCO 2)] ( 1) ((H 3L 1 = 1,3-bis(5-bromosalicylideneamino)-2-propanol)), [Cu 2(L 2)(μ-HCO 2)] · dmf ( 2) (H 3L 2 = 1,3-bis(3,5-chlorosalicylideneamino-2-propanol)), and two μ-alkoxo-μ-dicarboxylato doubly bridged tetranuclear copper(II) complexes, [{Cu 2(L 3)} 2(μ-O 2C–C(CH 3) 2–CO 2)] · 5H 2O · 3CH 3OH ( 3) ((H 3L 3 = 1,3-bis(salicylid-deneamino)-2-propanol)) and [{Cu 2(L 3)} 2(μ- O 2CCH 2–C 6H 4–CH 2CO 2)] · 2H 2O ( 4) have been prepared and characterized. The single crystal X-ray analysis shows that the structures of complexes 1 and 2 are dimeric with two adjacent copper(II) atoms bridged by μ-alkoxo-μ-carboxylato ligands with the Cu⋯Cu distances and Cu–O(alkoxo)–Cu angles are 3.511 Å and 132.85° for 1, 3.517 Å and 131.7° for 2, respectively. Complexes 3 and 4 consist of μ-alkoxo-μ-dicarboxylato doubly bridged tetranuclear Cu(II) complexes with mean Cu–Cu distances and Cu–O–Cu angles of 3.158 Å and 108.05° for 3 and 3.081 Å and 104.76° for 4, respectively. Magnetic measurements reveal that 1 and 2 are strong antiferromagnetically coupled with 2 J = −156 and −152 cm −1, respectively, while 3 and 4 exhibit ferromagnetic coupling with 2 J = 86 and 155.2 cm −1, respectively. The 2 J values of 1– 4 are linearly correlated to the Cu–O–Cu angles. Dependence of the pH at 25 °C on the reaction rate of oxidation of 3,4-di- tert-butylcatechol (3,5-dtbc) to the corresponding quinone catalyzed by 1– 4 was studied. Complexes 1– 4 exhibit high catecholase-like activity at pH 9.0 and 25 °C for oxidation of 3,5-di- tert-butylcatechol.