Electron paramagnetic resonance and density-functional theory studies of Cu(II)-bis(oxamato) complexes

In this work we present the investigation of the influence of electronic and structural variations induced by varying the N,N'-bridge on the magnetic properties of Cu(II)-bis(oxamato) complexes. For this study the complexes [Cu(opba)](2-) (1, opba = o-phenylene-bis(oxamato)), [Cu(nabo)](2-) (2, nabo = 2,3-naphthalene-bis(oxamato)), [Cu(acbo)](2-) (3, acbo = 2,3-anthrachinone-bis(oxamato)), [Cu(pba)](2-) (4, pba = propylene-bis(oxamato)), [Cu(obbo)](2-) (5, obbo = o-benzyl-bis(oxamato)), and [Cu(npbo)]2- (6, npbo = 1,8-naphthalene-bis(oxamato)), and the respective structurally isomorphic Ni(II) complexes (8-13) have been prepared as ((n)Bu(4)N)(+) salts. The new complex ((n)Bu(4)N)(2)[Cu(R-bnbo)] center dot 2H(2)O (7, R-bnbo = (R)-1,1'-binaphthalene-2,2'-bis(oxamato)) was synthesized and is the first chiral complex in the series of Cu(II)-bis(oxamato) complexes. The molecular structure of 7 has been determined by single crystal X-ray analysis. The Cu(II) ions of the complexes 1-7 are eta(4)(kappa(2)N, kappa(2)O) coordinated with a more or less distorted square planar geometry for 1-6 and a distorted tetrahedral geometry for 7. Using pulsed Electron Nuclear Double Resonance on complex 6, detailed information about the relative orientation of the hyperfine (A) and nuclear quadrupole tensors (Q) of the coordinating nitrogens with respect to the g tensor were obtained. Electron Paramagnetic Resonance studies in the X, Q, and W-band at variable temperatures were carried out to extract 9 and A values of N ligands and Cu ion for 1-7. The hyperfine values were interpreted in terms of spin population on the corresponding atoms. The obtained trends of the spin population for the monomeric building blocks were shown to correlate to the trends obtained in the dependence of the exchange interaction of the corresponding trinuclear complexes on their geometry.