Pyrophosphate-Bridged Cu(II) Chain Magnet {[a3Cu(P2O/)(NO3)].3H2O}

SARTORIS ROSANA P.; SANTANA RICARDO C.; BAGGIO RICARDO; PENA OCTAVIO; PEREC MIREILLE; CALVO RAFAEL

INORGANIC CHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington DC 20036; Año: 2010 vol. 49 p. 5650 - 5657

0020-1669

A CuII…CuII pyrophosphate-bridged compound of formula {[Na3Cu(P2O7)(NO3)].3H2O}n 1 has been characterized. X-ray diffraction measurements show that it crystallizes in the monoclinic space group P21/m, with unit cell dimensions a = 7.2492(5) Å, b = 8.2446(6) Å, c = 9.9050(7) Å, β = 107.123(1)°,  Z = 2. The structure consists of chains of CuII cations at inversion symmetry sites bound to four equatorial oxygen atoms provided by two pyrophosphate anions halved by a symmetry plane, and two axial oxygen atoms of nitrate anions. The molar magnetic  susceptibility c0 of a powdered sample was measured in the temperature range 2 < T < 273 K, and a isothermal magnetization curve, M(B0,T), was obtained at T = 30 K, with the magnetic field B0 between 0 and 5 T. Fitting a spin chain model to the susceptibility data, we evaluate an antiferromagnetic exchange coupling 2J = –24.3(1) cm-1 (defined as Hex = –2JSi.Sj) between CuII neighbors. For any orientation of B0, single crystal EPR spectra obtained at 9.8 and 33.9 GHz at 300 K display a single signal having a g-matrix with orthorhombic symmetry, arising from the  merger produced by the exchange interaction of the resonances corresponding to the two rotated CuII sites. The g-matrices of the individual molecules calculated assuming axial symmetry yielded principal values g// = 2.367(1), g^ = 2.074(1) at both frequencies, indicating a d(x2-y2) ground state orbital for the CuII ions. The angular variation of the EPR line width suggests exchange narrowing in a system with one dimensional spin dynamics, as expected from the structure and the susceptibility data. The results, discussed in terms of the crystal and electronic structure, and of the spin dynamics of the compound, are compared with those obtained in other materials.