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

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.