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

Abstract

Four new Mn II - and Co II -containing magnetic coordination polymers, [{Mn(Br-isa)(bpe)· 1 / 2 H 2 O} n ( 1 ), {Co(Br-isa)(bpe) 1.5 · 1 / 2 H 2 O} n ( 2 ), [{Mn(Br-isa)(4-bpmh)} 4 ·6H 2 O] n ( 3 ), and [{Co(Br-isa)(4-bpmh)} 2 ·2 1 / 2 H 2 O] 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-H 2 isa) 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-H 2 isa 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.