Mn^II and Co^II Coordination Polymers Showing Field-Dependent Magnetism and Slow Magnetic Relaxation Behavior

Four new Mn^II- and Co^II-containing magnetic coordination polymers, [{Mn(Br-isa)(bpe)·¹/₂H₂O}_n (1), {Co(Br-isa)(bpe)_1.5·¹/₂H₂O}_n (2), [{Mn(Br-isa)(4-bpmh)}₄·6H₂O]_n (3), and [{Co(Br-isa)(4-bpmh)}₂·2¹/₂H₂O]_n (4)] [isa = isophthalic acid, bpe = 1,2-bis-(4-pyridyl)ethylene and 4-bpmh = N,N′-bispyridine-4-yl-methylene-hydrazine], have been synthesized at room temperature, using 5-bromo isophthalic acid (Br-H₂isa) and two different N-donating ancillary ligands. The complexes have been characterized by single-crystal X-ray diffraction and other physicochemical techniques. Structure determination reveals two-dimensional (2D) coordination network architectures for all the complexes. In 1, 3, and 4, Mn^II and Co^II dinuclear units are connected via Br-H₂isa ligands to form infinite 1D chains. The ancillary N,N′-donor spacer ligands interconnect the 1D chains into 2D coordination layers. Complex 2, on the other hand, can be viewed as being composed of cationic [{Co(bpe)}₄]⁸⁺ square units that are joined by anionic Br-isa^2- bridges into a 2D gridlike framework. Topology analysis shows an SQL/Shubnikov tetragonal plane net topology for complexes 1, 3, and 4, and an SP 2-periodic net (4, 4) Ia topology for complex 2. Complexes 1 and 3 show a field-dependent change in magnetic behavior which is confirmed from the susceptibility measurements at varying fields, field-dependent magnetization measurements, as well as from hysteresis data. Complex 2 exhibits a slow magnetization relaxation phenomenon manifested by the AC susceptibility measurements at different temperatures and frequencies. Finally, complex 4 exhibits a magnetic feature that can be interpreted as antiferromagnetic exchange interactions between two syn-syn carboxylate-bridged Co^II atoms.