title: Electron paramagnetic resonance and density-functional theory studies of Cu(II)-bis(oxamato) complexes.
abstract: 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 4N) (+) salts. The new complex ( (n)Bu 4N) 2[Cu(R-bnbo)].2H 2O ( 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 g 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.
authors.affiliation: Department of Chemistry, Chemnitz University of Technology, 09107 Chemnitz, Germany. bbj@hrz.tu-chemnitz.de
authors.forename: Björn
authors.initials: B
authors.lastname: Bräuer
authors.forename: Florian
authors.initials: F
authors.lastname: Weigend
authors.forename: Maria
authors.initials: M
authors.lastname: Fittipaldi
authors.forename: Dante
authors.initials: D
authors.lastname: Gatteschi
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Reijerse
authors.forename: Annalisa
authors.initials: A
authors.lastname: Guerri
authors.forename: Samuele
authors.initials: S
authors.lastname: Ciattini
authors.forename: Georgeta
authors.initials: G
authors.lastname: Salvan
authors.forename: Tobias
authors.initials: T
authors.lastname: Rüffer
mesh_terms: D000042:Absorption; D002942:Circular Dichroism; D003300:Copper / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D009942:Organometallic Compounds / Q000737:chemistry*; D010072:Oxamic Acid / Q000737:chemistry*; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
chemical_list: D009942:Organometallic Compounds; D003300:Copper; D010072:Oxamic Acid