Copper(II) halide salts and complexes of 4-amino-2-fluoropyridine: synthesis, structure and magnetic properties

Abstract

Reaction of 4-amino-2-fluoropyridine (2-F-4-AP) with copper halides produced the neutral coordination complexes: (2-F-4-AP)₂CuX₂ (X = Cl(1), Br(2)). 1 crystallizes in the orthorhombic space group Pccn in a distorted square planar geometry. Magnetic susceptibility data were fit to the uniform chain Heisenberg model resulting in C = 0.439(6)emu-K/mole-Oe and J = −28(1) K. 2 crystallizes in the monoclinic space group C2/m and is closer to distorted tetrahedral. Intermolecular Br⋯Cu contacts generate a square layer. Magnetic data show very weak ferromagnetic interactions [C = 0.42(1)emu-K/mol-Oe, J = 0.71(2) K]. Similarly, reaction of 2-F-4-AP with copper halides and aqueous HX in alcohol solvents produced the salts (2-F-4-APH)₂CuX₄ (X = Cl(3), Br(4)). 3 crystallizes in the triclinic space group P-1. Crystal packing reveals short Cl⋯Cl contacts which generate a structural ladder. However, analysis of the magnetic data suggests that only the rails of the ladder produce a viable magnetic superexchange pathway; the uniform Heisenberg chain model provides C = 0.449(1)emu-K/mol-Oe and J = -6.9(1) K. 4 is isostructural and is also best fit by a chain model [J = −2.7(4) K]. The brominated complex (2-F-3-Br-4-APH)₂CuBr₄·2H₂O, 5, (2-F-3-Br-4-APH = 4-amino-3-bromo-2-fluoropyridinium) was serendipitously produced as a byproduct of the synthesis of 4 and was characterized by single-crystal X-ray diffraction.

Keywords:

• Copper(II)
• magnetism
• X-ray
• aminopyridines
• halogen bonds

Acknowledgements

Financial contributions from The National Science Foundation (IMR-0314773) towards the purchase of the MPMS-XL SQUID magnetometer, PCI Synthesis, Inc. towards the purchase of the Bruker D8-Advance powder X-ray diffractometer and The Kresge Foundation toward the purchase of both instruments are gratefully acknowledged. The assistance of Prof. Ray Butcher (Howard University) in the X-ray data collection for 1 is also appreciated.