Well-isolated pyrazine-bridged copper(II) chains: synthesis and magneto-structural analysis

A pair of well-isolated 1-D-QHAF compounds with the molecular formula [Cu(pz)(L)(2)(H2O)(2)](ClO4)(2)with L = 3-Cl-4-hydroxypyridine (1) and 3-Br-4-hydroxypyridine (2) (catena-(diaqua-bis(3-chloro/bromo-4-pyridono-kappa O)(mu-pyrazine)copper(II) diperchlorate) were synthesized via slow-evaporation crystallization and characterized structurally and magnetically to develop magneto-structural correlations. Single-crystal X-ray diffraction at 120 K provided the structures of1and2which comprise six-coordinate Cu(II) pyrazine-bridged chains propagating parallel to the crystallographica-axis in the triclinic space-groupP-1. Chains are offset from each other in thec-direction by the bulk of L and along the d(z2)axis occupied by a semi-coordinate water molecule engaged in hydrogen bonding with the perchlorate gegenion. Magnetic susceptibility experiments showed that1and2behave as quasi-Heisenberg 1-D-AFMs withJ approximate to 8 K and no sign of 3 D ordering down to 1.8 K. Aspects of crystal engineering are addressed to understand the potential to design systems with desired magnetic properties in light of comparisons with a variety of pyrazine-bridged chains already in the literature. The effect of L and the general structural scaffold are investigated to this end. Powder X-Band EPR experiments were performed to determine the electronic environment of the Cu(II) ion and average g-factor. The pyrazine-bridged chains in1with the AFM electronic spins represented as glowing arrows.