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

Abstract

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[CuCl₄] (1) and (5-BAPH)(3,5-diBAPH)[CuBr₄] (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 P2₁/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) cm³ 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].

KEYWORDS:

• Copper(II)
• halopyridines
• magnetism
• X-ray

Acknowledgements

The authors are grateful to the National Science Foundation for grants to purchase the SQUID magnetometer (IMR-0314773) and toward the purchase and construction of a helium recycling system (NSF DMR-1905950). Contributions from SEQENS toward the purchase of the powder X-ray diffractometer are also greatly appreciated. CB is grateful for a Summer Undergraduate Research Fellowship from SEQENS. The work of Mr. John Giantsidis in the initial identification of the compounds is greatly appreciated.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by National Science Foundation [DMR-1905950].