Chemistry

Halide-bridged Cu(pyrazine)2 perchlorate layers: Structure and magnetism

Jeffrey C. Monroe, Clark University
Christopher P. Landee, Clark University
Mark M. Turnbull, Clark University
Matthew Polson, University of Canterbury
Jan L. Wikaira, University of Canterbury

Abstract

In this report a pair of halide-bridged Cu(pyrazine)2 layered complexes with the formula [Cu(pz)2X]ClO4, where pz = pyrazine and X = Cl (1), Br (2) are structurally and magnetically evaluated and compared to the complexes [Cu(pz)2X]BF4 X = Cl (3), Br (4) described previously by Kubus et al. 2018. 1 and 2 are isostructural in the space group P4/n, a slight reduction in symmetry compared to 3 and 4 (P4/nbm), which is considered in terms of magneto-structural comparisons. The magnetic susceptibility of 1 and 2 were analyzed in terms of the 2D-QHAF model and the Cu-pz-Cu superexchange strength J was quantified (11.20(2) K (1) and 11.14(2) K (2) at 1 kOe applied field; J = 11.095(7) K (1) J = 11.29(1) (2) at 150 Oe applied field) which are typical of pyrazine bridged Cu(II) complexes. The value of TN is estimated as the temperature at which a kink in the susceptibility occurs (4.2(1) K (1), 4.5(1) K (2)) which was investigated as a field induced spin-flop phase transition via magnetization experiments as a function of field and temperature. The presence of exchange anisotropy is thus considered, and assuming its absence, the interlayer exchange strength J′ was calculated. Powder EPR spectra of 1 and 2 revealed axial g-tensors with Lorentzian line shape as expected of exchange coupled systems with a small amount of single-ion anisotropy and fourfold symmetry.