Anion-Tunable Configuration Isomerism and Magnetic Coupling in a Tetranuclear Discrete, One-Dimensional (1D) Chiral Chain and 1D-Decker Copper(II) Complexes of a Carbohydrazine Derivative

The reactions of ligand N′-[(pyridin-2-yl)­methylene]­pyrazine-2-carbohydrazide (ppcd)
with different copper salts (1, acetate; 2, perchlorate; 3, sulfate) in MeOH could afford one
acetate-bridge tetranuclear discrete [Cu2(ppcd)­(ac)2(H2O)­(OH)]2·H2O (1), one-dimensional (1D) chiral chain [Cu­(ppcd)]­ClO4 (2), and a 1D-decker complex of a trinuclear copper­(II)
subunit, Cu3(ppcd)2(H2O)4(SO4)2 (3). Single-crystal X-ray
analysis revealed that conformation isomerism of the ppcd ligand was
associated with the configuration of −N–N– (trans
or cis) and could induce the versatile coordination mode in the presence
of different anions. The 1D chiral chain was interestingly obtained
from the achiral rigid ligand in complex 2. Magnetic
studies indicated that the magnitude of the antiferromagnetic coupling
can be tuned because of the configuration isomerism [compound 1 is practically diamagnetic at room temperature (J ≈ −1000 cm–1), with a
strong antiferromagnetic one (J = −255.4 cm–1) for 2 in the 1D uniform chain and an
antiferromagnetic one (J = −123.6 cm–1) for 3 within the trinuclear copper subunit].