A unique example of structural diversity tuned by apparently innocento-,m-, and p-nitro substituents of benzoate in their complexes of Mn (II) with 4,4′-bipyridine: 1D ladder, 2D sheet, and 3D framework

Abstract

Four new Mn(II) coordination polymers [Mn(4,4′-bpy)(C₆H₅COO)₂]_n (1), [Mn(4,4′-bpy)(o-(NO)₂)C)₆H4COO) )₂]_n (2), [Mn(4,4′-bpy)(m-(NO)₂)C)₆H)₄COO) )₂]_n (3) and [Mn(4,4′-bpy)(p-(NO)₂)C)₆H)₄COO) )₂]_n (4) (where 4,4′-bpy = 4,4′-bipyridine) have been synthesized by self-assembly of the primary ligands, benzoate and the o-, m- and p-isomers of nitrobenzoates, respectively, together with 4,4′-bpy as the secondary spacer. All four complexes were characterized by elemental analyses, IR spectroscopy, single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. The structural analyses reveal that complexes 1 and 3 are constructed by linear fused chains through double syn-syn (for 1) or syn-anti (for 3) carboxylate-bridged Mn (II), which are further linked to one another by trans coordinated 4,4′-bpy bridges, giving rise to a rectangular grid-like two-dimensional (2D) net. Complex 2 features one-dimensional (1D) molecular ladder formed by both syn-syn and syn-anti carboxylate-bridged dimeric Mn (II) units which are joined alternately by 4,4′-bpy. Complex 4 is formed by fused zigzag chains of double syn-syn carboxylate-bridged Mn (II) that are connected by cis oriented 4,4′-bpy to generate an unprecedented three-dimensional (3D) framework. The dimensionality of the complexes thus varies from 1D to 2D to 3D on changing the position of the nitro group from o- to m- to p- in the benzoate, showing explicitly the tuning ability of this apparently innocent substituent on the topology of the coordination polymer. Variable-temperature (1.8–300 K) magnetic susceptibility measurements showed the presence of antiferromagnetic coupling in all four complexes that have been fitted with an infinite classical-spin chain model derived by Fisher for 1, 3, and 4 (J = −0.779(2), −0.855(2) and −0.536(2) cm^–1, respectively) and van Vleck equation for 2 (J = −0.354(2) cm^–1).