Theoretical investigation of magnetic properties of a dinuclear copper complex [Cu2(μ-OAc)4(MeNHpy)2]

Abstract We have investigated the magnetic properties of a recently synthesized dinuclear complex, [Cu 2 (μ-OAc) 4 (MeNHpy) 2 ], by broken-symmetry (BS) density functional (DFT) methodology. The complex has several pairs of magnetic orbitals. Therefore, we have explicitly calculated the overlap integral S ab between the two natural magnetic orbitals , and found a value of 0.8589. Deviating from the common practice of approximating S ab by 1 for the strongly delocalized systems, the computed value has been used in calculating the magnetic exchange coupling constant ( J ) from the two electron-two orbital BS model. The calculated J is −290 cm −1 , in excellent agreement with the observed value of −285 cm −1 . The contribution of the overlap between the orbitals of the two copper atoms to S ab is negligibly small. Also, the calculated J value is a weakly varying function of the Cu–Cu distance. The last two observations confirm that the through-ligand superexchange phenomenon is responsible for the high magnetic exchange interaction in the Cu 2 (μ-OAc) 4 complex(es). Furthermore, we have shown that the onset of intramolecular hydrogen bonding reduces the spin density on the bridging atoms and consequently the magnitude of J . This explains why the complex under investigation has a J value smaller than that of [Cu 2 (μ-OAc) 4 (H 2 O) 2 ] (−299 cm −1 ). While establishing this trend, we predict that the complex [Cu 2 (μ-OAc) 4 (py) 2 ] would have a higher J value, about −300 cm −1 .

[1]  Roald Hoffmann,et al.  Orbital interactions in metal dimer complexes , 1975 .

[2]  K. Houk,et al.  Extended Hartree-Fock (EHF) theory of chemical reactions , 1988 .

[3]  Coen de Graaf,et al.  Multiconfigurational Perturbation Theory: An Efficient Tool to Predict Magnetic Coupling Parameters in Biradicals, Molecular Complexes, and Ionic Insulators , 2001 .

[4]  B. Delley,et al.  Evidence for Transmission of Ferromagnetic Interactions through Hydrogen Bonds in Alkyne-Substituted Nitroxide Radicals: Magnetostructural Correlations and Polarized Neutron Diffraction Studies , 2000 .

[5]  Frank Jensen,et al.  A spin correction procedure for unrestricted Hartree-Fock and Møller-Plesset wavefunctions for singlet diradicals and polyradicals , 1988 .

[6]  P. Anderson.  Theory of Magnetic Exchange Interactions:Exchange in Insulators and Semiconductors , 1963 .

[7]  Sambhu N Datta,et al.  Broken-symmetry density functional theory investigation on bis-nitronyl nitroxide diradicals: influence of length and aromaticity of couplers. , 2006, The journal of physical chemistry. A.

[8]  J. Seco,et al.  Synthesis, crystal structure, magnetic properties and EPR spectra of copper(II) acetate derivatives: tetra-(μ-acetato)bis(2-methylaminopyridine)copper(II) and catena-poly(aquadiacetato-μ-3-aminomethylpyridine)copper(II). Sheets formed by chains connected through hydrogen-bonds , 2004 .

[9]  D. Gatteschi,et al.  X.alpha.-SW calculations of the electronic structure and magnetic properties of weakly coupled transition-metal clusters. The [Cu2Cl6]2- dimers. , 1986, Journal of the American Chemical Society.

[10]  K. Fink,et al.  A quantum chemical ab initio study of the superexchange coupling in binuclear oxygen-bridged Ni(II) complexes , 1995 .

[11]  John B. Goodenough,et al.  Magnetism and the chemical bond , 1963 .

[12]  S. Alvarez,et al.  Tailor-made strong exchange magnetic coupling through very long bridging ligands: theoretical predictions. , 2003, Inorganic chemistry.

[13]  T. Tokii,et al.  Magnetic Properties of Dimeric Copper(II) Trichloroacetate Adducts with 3-Substituted Pyridines , 1987 .

[14]  J. Malrieu,et al.  Analysis of the magnetic coupling in binuclear complexes. I. Physics of the coupling , 2002 .

[15]  D. Case,et al.  Orbital interactions, electron delocalization and spin coupling in iron-sulfur clusters , 1995 .

[16]  R. Doedens.  Structure and Metal‐Metal Interactions in Copper(II) Carboxylate Complexes , 2007 .

[17]  K. Bowers,et al.  Anomalous paramagnetism of copper acetate , 1952, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[18]  Louis Noodleman,et al.  Valence bond description of antiferromagnetic coupling in transition metal dimers , 1981 .

[19]  S. Cotton.  Elements of Magnetochemistry , 1994 .

[20]  S. Fletcher,et al.  Refined crystal structure of tetra-µ-acetato-bisaquodicopper(II) , 1973 .

[21]  Evert Jan Baerends,et al.  Electronic structure, magnetic properties, ESR, and optical spectra for 2-iron ferredoxin models by LCAO-X.alpha. valence bond theory , 1984 .

[22]  F. Howell,et al.  CHARACTERIZATION AND CRYSTAL STRUCTURE OF COPPER(II) COMPLEX WITH BETAINE HAVING A WATER-WHEEL-LIKE STRUCTURE , 1999 .

[23]  G. Schaftenaar,et al.  Molden: a pre- and post-processing program for molecular and electronic structures* , 2000, J. Comput. Aided Mol. Des..

[24]  Joel S. Miller,et al.  Copper(II) carboxylate dimers and chains , 2001 .

[25]  A. P. Ginsberg.  Magnetic exchange in transition metal complexes. 12. Calculation of cluster exchange coupling constants with the X.alpha.-scattered wave method , 1980 .

[26]  J. Seco,et al.  2-Anilinopyridinate of Cu(I) and adducts of 2-anilinopyridine and metal acetates.: Crystal structure of Cu2(μ-OAc)4(PhNHpy)2 , 2002 .

[27]  M. Melnik.  Mono-, bi-, tetra- and polynuclear copper(II) halogenocarboxylates , 1981 .

[28]  S. Alvarez,et al.  Structural Modeling and Magneto-Structural Correlations for Hydroxo-Bridged Copper(II) Binuclear Complexes. , 1997, Inorganic chemistry.

[29]  R. Nesbet.  Antiferromagnetic Superexchange Effect , 1960 .

[30]  Edward I. Solomon,et al.  An electronic structural comparison of copper-peroxide complexes of relevance to hemocyanin and tyrosinase active sites , 1991 .

[31]  I. Ciofini,et al.  DFT calculations of molecular magnetic properties of coordination compounds , 2003 .

[32]  E. Davidson,et al.  Ligand spin polarization and antiferromagnetic coupling in transition metal dimers , 1986 .

[33]  D. N. Sathyanarayana,et al.  X-Ray crystal structures of some adducts of dimeric copper(II) acetate. Nature of the copper–copper interaction , 1983 .

[34]  Daniel Maynau,et al.  Direct determination of effective Hamiltonians by wave-operator methods. II. Application to effective-spin interactions inπ-electron systems , 1983 .

[35]  S. Alvarez,et al.  MAGNETIC COUPLING IN END-ON AZIDO-BRIDGED TRANSITION METAL COMPLEXES : A DENSITY FUNCTIONAL STUDY , 1998 .

[36]  F. Illas,et al.  Antiferromagnetic Exchange Interactions from Hybrid Density Functional Theory , 1997 .

[37]  V. Barone,et al.  Magnetic coupling in biradicals, binuclear complexes and wide-gap insulators: a survey of ab initio wave function and density functional theory approaches , 2000 .

[38]  R. Caballol,et al.  Structural dependence of the singlet-triplet gap in doubly bridged copper dimers: a variational CI calculation , 1994 .

[39]  E. Ruiz,et al.  Toward the Prediction of Magnetic Coupling in Molecular Systems: Hydroxo- and Alkoxo-Bridged Cu(II) Binuclear Complexes , 1997 .

[40]  S. Alvarez,et al.  Exchange coupling in carboxylato-bridged dinuclear copper(II) compounds: a density functional study. , 2001, Chemistry.

[41]  S. Alvarez,et al.  Exchange coupling of transition-metal ions through hydrogen bonding: a theoretical investigation. , 2002, Journal of the American Chemical Society.

[42]  Joan Cano,et al.  About the calculation of exchange coupling constants in polynuclear transition metal complexes , 2003, J. Comput. Chem..

[43]  R. Nesbet.  The Heisenberg exchange operator for ferromagnetic and antiferromagnetic systems , 1958 .

[44]  Jean-Paul Malrieu,et al.  Analysis of the magnetic coupling in binuclear complexes. II. Derivation of valence effective Hamiltonians from ab initio CI and DFT calculations , 2002 .

[45]  I. H. Öğüş,et al.  NATO ASI Series , 1997 .

[46]  F. Illas,et al.  Extent and limitations of density-functional theory in describing magnetic systems , 2004 .

[47]  J. Richardson,et al.  Strong supramolecular-based magnetic exchange in pi-stacked radicals. Structure and magnetism of a hydrogen-bonded verdazyl radical:hydroquinone molecular solid. , 2001, Journal of the American Chemical Society.

[48]  Dante Gatteschi,et al.  Magnetism of lanthanides in molecular materials with transition-metal ions and organic radicals. , 2002, Chemical reviews.

[49]  J. Nelson,et al.  4-substituted quinoline N-oxide complexes of copper(II) acetate , 1976 .

[50]  V. Barone,et al.  Through-bond and through-space effects in the magnetic properties of nitroxide biradicals by an integrated QM/MM approach including solvent effects , 1999 .

[51]  Joel S. Miller,et al.  Molecular magnetism : from molecular assemblies to the devices , 1996 .

[52]  Kizashi Yamaguchi,et al.  Ab Initio MO Calculations of Effective Exchange Integrals between Transition-Metal Ions via Oxygen Dianions: Nature of the Copper-Oxygen Bonds and Superconductivity , 1987 .

[53]  M. Whangbo,et al.  Spin exchange interactions of a spin dimer: Analysis of broken-symmetry spin states in terms of the eigenstates of Heisenberg and Ising spin Hamiltonians , 2003 .

[54]  J. Malrieu,et al.  Remarks on the Proper Use of the Broken Symmetry Approach to Magnetic Coupling , 1997 .

[55]  S. Alvarez,et al.  Exchange coupling in halo-bridged dinuclear Cu(II) compounds: a density functional study. , 2002, Inorganic chemistry.

[56]  F. Schoening,et al.  A new type of copper complex as found in the crystal structure of cupric acetate, Cu2(CH3COO)4.2H2O , 1953 .

[57]  Joan Cano,et al.  Broken symmetry approach to calculation of exchange coupling constants for homobinuclear and heterobinuclear transition metal complexes , 1999 .