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

Abstract

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-κO)(μ-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 of 1 and 2 which comprise six-coordinate Cu(II) pyrazine-bridged chains propagating parallel to the crystallographic a-axis in the triclinic space-group P-1. Chains are offset from each other in the c-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 that 1 and 2 behave as quasi-Heisenberg 1-D-AFMs with J ≈ 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 in 1 with the AFM electronic spins represented as glowing arrows.

Graphical Abstract

Keywords:

• Antiferromagnetism
• 1-D-QHAF
• magnetic susceptibility
• crystal structure

Disclosure statement

There are no conflicts of interest as reported by the authors.

Additional information

Funding

We are grateful for funds from PCI Synthesis, Inc. (now SEQENS) for the D8 Focus Diffractometer, from the National Science Foundation (IMR-0314773) for the MPMS SQUID magnetometer, and the Kresge Foundation for both instruments.