A copper(I) compound [(L2)Cu(MeCN)2][ClO4] (1) containing a new bidentate N-donor ligand L2, 1-benzyl-[3-(2′-pyridyl)]pyrazole, derived from the condensation of HL1 [HL1 = 3-(2-pyridyl)pyrazole] and benzyl chloride, has been synthesized. Structural analysis reveals that in 1 the copper(I) centre is coordinated by a pyridine and a pyrazole nitrogen from L2 and two MeCN molecules, providing a distorted tetrahedral geometry. Reaction of 1 with dioxygen in N,N′-dimethylformamide (dmf) at 25 °C and subsequent workup with MeCO2Et afforded an acetato-/pyrazolato-bridged polymeric copper(II) compound [(µ-L1)Cu(µ-O2CMe)]n (2). Notably, the deprotonated form of HL1 and MeCO2− have originated from debenzylation of L2 and hydrolysis of MeCO2Et, respectively. The structural analysis of 2 reveals a near-planar {Cu2(µ-L1)2}2+ core unit in which two adjacent Cu(II) ions are bridged by the deprotonated N,N-bidentate pyridylpyrazole units of two L1 and each such {Cu2(µ-L1)2}2+ unit is bridged by MeCO2− in a monodentate bridging mode [Cu⋯Cu separations (Å): 3.9232(4) pyrazolate bridge; 3.3418(4) acetate bridge], providing a polymeric network. Careful oxygenation of 1 in MeCN led to the isolation of a dihydroxo-bridged dicopper(II) compound [{(L2)Cu(µ-OH)(OClO3)}2] (3). Interestingly, complex 3 brings about hydrolysis of MeCO2Et under mild conditions (dmf, ca. 60 °C), generating a bis-µ-1,3-acetato-bridged dicopper(II) complex, [{(L2)Cu(dmf)(µ-O2CMe)}2][ClO4]2·dmf·0.5MeCO2H (4). Compounds 3 and 4 have {Cu2(µ-OH)2}2+ [Cu⋯Cu separation of 2.8474(9) Å] and {Cu2(µ-O2CMe)2}2+ cores [Cu⋯Cu separation: 3.0988(26) and 3.0792(29) Å (two independent molecules in the asymmetric unit)] in which each Cu(II) centre is terminally coordinated by L2. A rationale has been provided for the observed debenzylation of L2 and hydrolysis of MeCO2Et. The intramolecular magnetic coupling between the CuII (S = 1/2) ions was found to be ferromagnetic (2J = 82 cm−1) in the case of 3, but antiferromagnetic for 2 (2J = −158 cm−1) and 4 (2J = −96 cm−1). Absorption and EPR spectroscopic properties of the copper(II) compounds have also been investigated.
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