Pyrophosphate-Bridged Cu^II Chain Magnet: {[Na₃Cu(P₂O₇)(NO₃)]·3H₂O}_n

Abstract

A Cu II 3 3 3 Cu II pyrophosphate-bridged compound of formula {[Na 3 Cu(P 2 O 7 )(NO 3 )] 3 3H 2 O} n (1) has been characterized. X-ray diffraction measurements show that it crystallizes in the monoclinic space group P2 1 /m, with unit cell dimensions a = 7.2492(5) Å , b = 8.2446(6) Å , c = 9.9050(7) Å , β = 107.123(1)°, and Z = 2. The structure consists of chains of Cu II 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 χ 0 of a powdered sample was measured in the temperature range 2 K < T < 273 K, and an isothermal magnetization curve, M(B 0 ,T), was obtained at T = 30 K, with the magnetic field B 0 between 0 and 5 T. Fitting a spinchain model to the susceptibility data, we evaluate an antiferromagnetic exchange coupling 2J = -24.3(1) cm -1 (defined as H ex = -2JS i S j ) between Cu II neighbors. For any orientation of B 0 , single-crystal electron paramagnetic resonance (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 Cu II sites. The g matrices of the individual molecules calculated assuming axial symmetry yielded principal values g ) = 2.367(1) and g^= 2.074(1) at both frequencies, indicating a d x 2 -y 2 ground-state orbital for the Cu II ions. The angular variation of the EPR line width suggests exchange narrowing in a system with onedimensional spin dynamics, as expected from the structure and susceptibility data. The results, discussed in terms of the crystal and electronic structures and of the spin dynamics of the compound, are compared with those obtained in other materials.

Exchange Interactions Through π–π Stacking in the Lamellar Compound [{Cu(bipy)(en)}{Cu(bipy)(H2O)}{VO3}4]n

“…With the same assumptions, and considering now the susceptibility data in the low-temperature range (1.8–50 K), a regular spin chain model was used to estimate the mean J -value. The polynomial approximation of Hatfield, obtained from the predictions of the model of Bonner and Fisher for finite chains of 11 spins 1 / 2 , as reformulated by Kahn, was used to fit the susceptibility data. , Following this procedure, we obtained J = −1.7 cm –1 and an average g -factor equal to 2.19 from the low-temperature susceptibility data; these values are similar to the results from the molecular field approximation. The experimental values of χ 0 T ( T ) at T < 50 K and those calculated with the chain model with J = −1.7 cm –1 and g = 2.19 are shown in Figure .…”

Structure and magnetism of catena-poly[copper(II)-μ-dichloro-l-lysine]hemihydrate: Copper chains with monochloride bridges

“…Eigenvalues and thermodynamic properties for chains of up to 20 spins ½ have been reported [33,50,51]. For simplicity we chose the approximate results given by Hall et al [52] (calculated with chains of up to 11 spins) and by Sartoris et al [53] (calculated with chains of up to 16 spins):…”

“…In the ab and bc ⁄ planes it displays a second maximum at 90°of the chain axis. This symmetry allows attributing the widths to magnetic dipolar interactions between copper ions, narrowed by the exchange couplings [2,53,63]. The behavior of the peak-to-peak line width in the three orthogonal planes results from the one-dimensional magnetic behavior.…”