Synthesis, structure, and magnetic properties of a family of copper(II) complexes and salts of isoquinoline: (Isoquinoline)nCu(X)2 [X = Cl, Br] and (isoquinolinium)2CuX4(H2O)n [X = Cl, Br; n = 0,1

Abstract

The compounds (iQuin)2CuX2 (X = Br (1), Cl (2)), (iQuinH)2CuBr4·H2O (3) and two polymorphs of (iQuinH)2CuCl4 (4, 5) (iQuin = isoquinoline) have been prepared and studied via X-ray crystallography and variable temperature magnetic susceptibility measurements. Compound 1 crystallizes in the monoclinic space group P21/n while 3, 4 and 5 all crystallize in the triclinic space group P1¯). Magnetic susceptibility measurements for 1 are best fit by an antiferromagnetic alternating chain model (J/kB = −56.6(2) K, J′/kB = 5.1(8) K) although the crystal structure suggests a uniform chain. Compound 2 is well described as an isolated uniform antiferromagnetic chain (J/kB = −25.6(1) K), while 3 agrees well with the antiferromagnetic rectangular model (J/kB = −5. 03(2) K, J′/kB = −1.0(1) K). The two polymorphs, 4 and 5, exhibit distinctly different behavior as 4 is well described by the 2D-square antiferromagnetic layer model (J/kB = −4.24(2) K), but 5 crystallizes as well isolated magnetic dimers (J/kB = −15.8(1) K). Magnetic superexchange is proposed to occur via either the bihalide or two-halide pathways. Finally, compound 6, isoquinolinium tribromide, was isolated as a biproduct of the synthesis of 3 and was characterized via X-ray diffraction. The formation of the tribromide ion in situ provides support for the mechanism of electrophilic aromatic bromination reactions which have been previously observed in syntheses similar to that of 3.