Synthesis, structural and magnetic characterisation of tris(1-methyl-4,5-diphenylimidazol-2-yl)methanol (L) and [{CuL(NO₃)}₂][NO₃]₂

Abstract

Tris(1-methyl-4,5-diphenylimidazol-2-yl)methanol (L) has been synthesized and characterised. It crystallises as L·0.5 1,2-Cl₂C₂H₄ from 1,2-Cl₂C₂H₄–light petroleum and its crystal structure has been determined. This compound reacts with Cu(NO₃)₂·3H₂O to yield [{CuL(NO₃)}₂][NO₃]₂ which has also been crystallographically characterised. Each [{CuL(NO₃)}₂]²⁺ is located on a crystallographic inversion centre; the N₂O₃ co-ordination sphere has a geometry intermediate between square pyramidal and trigonal bipyramidal, with a slight bias towards the former. The Cu(1)–O(1)–Cu(1*) bridging angle is small at 95.1(2)° and the Cu  · · ·  Cu separation of 3.011(1) Å is typical of a coplanar-type di-µ-oxo-copper(II) dimer. Magnetic susceptibility (300–4 K) measurements indicated that the dimeric complex has a spin-triplet ground state, i.e. the two copper(II) ions are ferromagnetically coupled. Variable-temperature (300–4 K) EPR spectroscopy confirmed an S = 1 ground state described by the spin-Hamiltonian parameters g_xx = 2.09, g_yy = 2.08, g_zz = 2.24, |D| = 0.35 cm^-1 and |E| = 0.049 cm^-1 at room temperature. The magnitude of the zero-field splitting parameter |D| and the value of 2J decrease with decreasing temperature.

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