Synthesis, magnetism, 1H NMR and redox activity of dicopper(II) complexes having a discrete {Cu2(µ-phenoxide)2}2+ unit supported by a non-macrocyclic ligand environment. Crystal structure of [Cu2(L)2(OClO3)2] [HL = 4-methyl-2,6-bis(pyrazol-1-ylmethyl)phenol]†

Abstract

Reaction between 4-methyl-2,6-bis(pyrazol-1-ylmethyl)phenol (HL) or its 3,5-dimethylpyrazole derivative (HL′) and Cu(ClO₄)₂·6H₂O afforded [Cu^II₂(L/L′)₂(OClO₃)₂] 1 and 2. Complex 1 has been structurally characterized showing that each copper(II) centre is square pyramidal with two bridging phenoxide oxygens and two terminal pyrazole nitrogens in the equatorial plane and a perchlorate oxygen atom axially co-ordinated. Variable-temperature magnetic susceptibility measurements revealed that the dicopper(II) centres are strongly antiferromagnetically coupled [singlet–triplet energy separation, 2J (in cm^–1): –1204 for 1 and –798 for 2]. The complexes exhibit ¹H NMR spectra within δ 0–10 due to their S = 0 ground state. In MeCN solution they exhibit ligand field transitions in the range 14 300–16 600 cm^–1 and phenolate-to-copper(II) charge-transfer transition at ≈22 700 cm^–1. In MeCN solution each complex displays three consecutive irreversible responses (scan rate of 50 mV s^–1) with E_pc values (V vs. SCE) at –0.02, –0.54 and –0.86 (1) and 0.00, –0.42 and –0.80 (2). The first two responses are due to Cu^II–Cu^I and the most cathodic response to Cu^I–Cu⁰ redox processes, respectively.