Synthesis, characterisation and crystal structure of 2-aminopyridinium (2-amino-5-bromopyridine)tribromocuprate(II) and bis(2-aminopyridinium) tetrabromocuprate(II)

Abstract

2-Aminopyridinium (2-amino-5-bromopyridine)tribromocuprate(II) 1 and bis(2-aminopyridinium) tetrabromocuprate(II) 2 have been prepared from acetonitrile solutions containing CuBr ₂ , HBr and 2-aminopyridine in 1∶2∶2 and 1∶2∶1 molar ratio, respectively. The mother-liquor of 1 was photoirradiated with a superhigh-pressure mercury lamp and the organic base underwent partial electrophilic para bromination of the substituted pyridine ring. The compounds have been characterised by elemental analysis, IR, UV/VIS and ESR spectroscopies, thermal analysis, variable-temperature magnetic susceptibility measurements and single-crystal X-ray diffraction. The crystal structure of 1 consists of infinite zigzag chains of [C ₅ H ₇ N ₂ ] ⁺ cations and distorted [CuBr ₃ (C ₅ H ₅ BrN ₂ )] ^- tetrahedral anions running along the b axis and held together by means of N–H · · · Br hydrogen contacts and non-covalent interactions between the π systems of the pyridine rings. In 2 organic cations and flattened [CuBr ₄ ] ^2- anions form two-dimensional N–H · · · Br hydrogen-bonded sheets which are connected by electrostatic interactions, van der Waals forces and face-to-face stacking interactions between the π systems of the aromatic cations. Magnetic susceptibility measurements of powdered samples showed that both compounds exhibit weak antiferromagnetic exchange interactions [J = -1.20 (1), -2.43 cm ^-1 (2)]. Thermal decomposition of both compounds yielded copper(II) oxide and metallic Cu as stable final residues in synthetic air and dinitrogen atmospheres, respectively.