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Two 5-bromo-2-aminopyridinium quantum Heisenberg antiferromagnetic (QHAF) complexes of copper(II) have been synthesized and studied structurally and magnetically. The structures of (5-BAPH) 2 [CuCl 4 ] ( 1 ) and (5-BAPH)(3,5-diBAPH)[CuBr 4 ] ( 2 ) are reported [5-BAPH = 2-amino-5-bromopyridinium; 3,5-diBAPH = 2-amino-3,5-dibromopyridinium]. Single-crystal X-ray diffraction measurements show that  1  crystallizes in the triclinic space group Pī and  2  crystallizes in the monoclinic space group P2 1 /c. Both products crystallize with a four-coordinate Cu(II) ion and are stabilized with extensive hydrogen bonding between the halide ions and pyridinium and amino substituents on each cation. The tetrahalidocuprate ions in  1  and  2  exist in distorted geometries between square planar and tetrahedral with mean  trans  angles of 139.48° and 131.85°, respectively. Halogen bonding is also observed. Magnetic susceptibility data were collected on  1  and  2 . Magnetic susceptibility data of  1  exhibit moderate antiferromagnetic interactions which are best fit using an alternating chain model [CC = 0.4262(3) cm 3  K mol −1 , J/k B  = −22.75(2) K,  α  = 0.134(3)]. Magnetic susceptibility data of  2  exhibit weak antiferromagnetic interactions, best fit using a uniform chain model [CC = 0.410(6), J/k B  = −6.1(4) K].

Copper(II) halide salts of 5-bromo-2-aminopyridine and 3,5-dibromo-2-aminopyridine: syntheses, structures and magnetic behavior