Tetrahalocuprate salts of substituted 4-aminopyridines: Synthesis, structure and magnetic properties

Abstract

The reaction of CuX2 (X=Br or Cl) with 4-amino-2-chloropyridine or 4-amino-2-methylpyridine in aqueous acids (HX; X=Br or Cl) yields bis(4-amino-2-chloropyridinium) tetrachlorocuprate(II) 3, bis(4-amino-2-chloropyridinium) tetrabromocuprate(II) 4, bis(4-amino-2-methylpyridinium) tetrachlorocuprate(II) monohydrate 5, and bis(4-amino-2-methylpyridinium) tetrabromocuprate(II) monohydrate 6. These compounds have been characterized by IR, powder X-ray diffraction, single crystal X-ray diffraction, combustion analysis, and temperature dependent magnetic susceptibility. Compounds 3 and 4 both crystallize in the monoclinic space group C2/c, compounds 5 crystallizes in the monoclinic space group P21/c and compound 3 crystallizes in the triclinic space group P-1. Magnetic data were collected for the four synthesized compounds and their previously reported parent compounds of 4-aminopyridinium tetrachlorocuprate 1, or tetrabromocuprate 2. All compounds exhibit antiferromagnetic exchange via the two-halide exchange, with strongest exchange observed for compound 6. A number of potential magnetic exchange pathways are seen in these compounds, but fitting of the data to available analytical models suggests that the magnetic exchange constants are 2J/kB∼−0.14(2)K in 1, ∼−0.812(5)K in 2, ∼−0.173(6)K in 3, ∼−0.82(1)K in 4, ∼−2.123(6)K in 5, and ∼−30.9(1)K in 6.