The crystal structure, spectroscopy and EPR of tetragonal bis(2-(aminomethyl)pyridine)Cu(II) compounds. Rare cases of the absence of Cu(II) plasticity

Abstract

Two new Cu(II) coordination compounds, [Cu(amp) 2(CF 3SO 3) 2] and [Cu(amp) 2](BF 4) 2 (in which amp=2-(aminomethyl)pyridine) have been synthesized and investigated by X-ray analysis, ligand field and EPR spectroscopy. The first compound crystallizes in the monoclinic space group P2(1)/ c with a=10.911(3), b=11.876(3), c=8.039(3) Å, β=75.70(3)° and refined to an R value of 0.0293. The second compound crystallizes in the triclinic space group P 1 ̄ with a=7.490(4), b=7.841(4), c=7.869(4) Å, α=106.51(4), β=108.95(5), γ=95.98(4)° and refined to an R value of 0.0428. Both mononuclear compounds have a tetragonally elongated octahedral structure in which the Cu(II) ion is equatorially surrounded by four nitrogens of the two amp ligands. The axial positions are occupied by the O atom of the triflate anion and the F of the tetrafluoroborate anion, respectively. EPR spectra, recorded as a solid and as a frozen solution, and ligand field spectra, as a solid by diffuse reflectance, were measured and compared with earlier reported Cu-amp compounds of stoichiometry [Cu(amp) 2(X′) 2] (where X=NO 3, ClO 4, CF 3SO 3, BF 4 and H 2O). EPR spectra in frozen solutions (DMF) at 77 K revealed g ⊥ at about 2.05, g ‖ of 2.22 with a splitting A ‖ of 19.0 mT for both compounds. The LF maxima occur at 17.5–18.0×10 3 cm −1. The group of compounds with stoichiometry [Cu(amp) 2(X 2)], appears to be a rare case where Cu(II) plasticity in trans-Cu(LL) 2(X) 2 (where LL=chelating organic ligand) is not observed, despite significant changes in ligand field strength of the (X) anions.