Magneto-structural correlation in (μ-alkoxo/hydroxo)(μ-carboxylato)dicopper(II) systems: synthesis, X-ray structure and magnetic properties of aquo(μ-hydroxo)(μ-arylcarboxylato) bis(N,N,N',N'-tetramethylethane-1,2-diamine)dicopper(II) diperchlorate

Abstract

Asymmetrically dibridged dicopper(II) complexes, [Cu2(OH)(O₂CC₆H₄-_p-Me)(tmen)₂(H₂O)](ClO₄)₂ (1) and [Cu₂(OH)(O₂CC₆H₄-p-OMe)(tmen)₂(H₂O)](ClO₄)₂ (2) (tmen = N,N,N',N'-tetramethylethane-1,2-diamine), were prepared and structurally characterized. Complex 1 crystallizes in the monoclinic space group P2¹/a with a = 17.718(2), b = 9.869(1), c = 19.677(2)Å, β = 115.16(1)°, V=3114.3(6)ų and Z = 4. The structure was refined to R(wR2) = 0.067(0.178). Complex 2 crystallizes in the monoclinic space group P2¹/a with a = 17.695(3), b = 9.574(4), c = 20.104(2)Å, β = 114.18(1)degrees, V = 3107(1) ų and Z = 4. The final residuals are R(wR2) = 0.067(0.182). The complexes have a [Cu₂(μ-OH)(μ-O₂CAr)]²⁺ core with tmen Ligands occupying the terminal sites of the core. In addition, one copper is axially bound to a water molecule. The Cu … Cu distances and the Cu-OH Cu angles in the core are 3.394(1) Å, 124.4(2)° for 1 and 3.374(1) Å, 123.3(3)° for 2. The complexes show axial X-band EPR spectral features in methanol glass at 77 K giving g_⊥= 2.02, g_||=2.3 (A_||=165×10⁻⁴ cm⁻¹ and a visible band near similar to 630 nm in methanol. The complexes are weakly antiferromagnetic. A theoretical fit of the magnetic susceptibility data in the temperature range 40-295 K gives J=10 cm⁻¹, g = 2.05 for 1 and -J = 10 cm⁻¹, g = 2.0 for 2. Plots of -2J versus the Cu-OH-Cu angle (Φ) in this class of asymmetrically dibridged dicopper(II) complexes having d_x²y²d_x²-y² magnetic orbitals show a linear magneto-structural correlation: -2J(cm^-1) = 11.48 Φ(deg) 1373.