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Reactivity of Copper(I) Complexes with Tripodal Ligands towards O2: Structures of a Precursor [L3CuI(NCCH3)](BF4), L3 = Tris(3-isopropyl-4,5-trimethylenepyrazolyl)methane and of its Oxidation Product [L3CuII(-OH)2CuIIL3](BF4)2 with Strong Antiferromagnetic Spin-Spin Coupling
W. Kaim, C. Titze, T. Schurr, M. Sieger, L.M. Lawson Daku, J. Jordanov, D. Rojas, A.M. García and J. Manzur
Zeitschrift für anorganische und allgemeine Chemie, 631 (13-14) (2005), p2568-2574
DOI:10.1002/zaac.200500053 | unige:3316 | Abstract | Article PDF
The molecular structure of the highly oxygen-sensitive complex [L3CuI(NCCH3)](BF4) (1) reveals approximately symmetrical coordination by the fac-tridentate (tripodal) ligand L3 = tris(3-isopropyl-4,5-trimethylenepyrazolyl)methane and a rather short CuI-N(acetonitrile) distance of 1.865(5) Å. In CH2Cl2 at -78 °C the colourless compound reacts with O2 to yield a labile purple intermediate (λmax 517 nm) - presumably a peroxodicopper(II) complex - which decomposes at -30 °C. No such intermediate was observed on reaction of the CuI complex of bis(2-pyridylmethyl)benzylamine with O2 at -80 °C. However, an EPR spectrum with g|| = 2.17 and g_|_ = 2.03 without 63,65Cu hyperfine splitting was observed at low temperatures. Exposure of the precursor 1 to air under ambient conditions yields dinuclear [L3Cu||(μ-OH)2CuIIL3](BF4)2 (2) which exhibits an EPR detectable dissociation into monomers in CH2Cl2 solution. The structure of the hexakis(dichloromethane) solvate of 2 with Cu-Cu and Cu-O distances of 3.055 and 1.94Å, respectively, is typical for dihydroxo-bridged dicopper compounds with square-pyramidal Cu|| configuration (τ = 0.03), adopting an anti arrangement. In agreement with the relatively wide Cu-O-Cu angles of 103.5° an analysis of the temperature dependence of the magnetic susceptibility revealed a rather strong (J = -633 cm-1) antiparallel spin-spin coupling. The effect is ascribed to the steric bulk of the ligand L3.