Syntheses and characterizations of six Co(ii) and Mn(ii) coordination polymers based on amino-substituted 5-aminoisophthalate and flexible bis(imidazolyl) ligands

Abstract

Six Co(II) and Mn(II) coordination polymers, [Co(BIMB)(AIP)]_n (1), [Co(BIMB)_0.5(H₂O)(AIP)]_n (2), [Co(BMIB)_0.5(AIP)]_n·(H₂O)_n (3), [Mn₂(BIMB)₂(AIP)₂]_n (4), [Mn(BMIB)(H₂O)₂(AIP)]_n·(DMF)_n (5) and [Mn(BIMB)_0.5(PAIP)]_n·(H₂O)_n (6) (AIP = 5-aminoisophthalate, PAIP = 5-(2-pyridylmethyl)aminoisophthalate, BIMB = 1,4-bis(imidazol-1-yl-methyl)benzene and BMIB = 1,4-bis(2-methylimidazol-1-yl-methyl)benzene), were synthesized and characterized. AIP in 1–5 originates from the in situ deprotection of 5-(4-oxopentan-2-ylideneamino)isophthalic acid in the synthetic process. Complex 1 is a 2D → 3D interdigitating network, and hydrogen bonds between the uncoordinated amino and carboxylate oxygen atoms of the adjacent layers further stabilize the 3-D framework. Different from AIP in 1, the amino of AIP in 2 and 3 participates in coordination, μ₃-bridged AIP connects Co(II) to a 1-D double chain and 2-D layer, respectively, and the subsequent bridge by BIMB and BMIB results in the formation of a 2-D layer and 2-D pillared-bilayer network, respectively. Notably, the coordinated water in complex 2 may be reversibly removed with a concomitant color change and maintenance of the original structural framework. The amino of AIP in 4 and 5 is not involved in coordination, but AIP and BIMB, which has an anti-conformation, in 4 link Mn(II) to a 2-D layer consisting of dinuclear Mn(II)-carboxylate units, while AIP and BMIB, which has an gauche conformation, in 5 links Mn(II) ions to a 1-D chain. Complex 6 is a 3-D pillared-layer structure. It should be mentioned that extensive hydrogen bonds are formed in complexes 1–6. The magnetic study of complex 4 shows that there is a dominant antiferromagnetic coupling above 40 K, while a weak ferromagnetic order is caused by spin-canting at lower temperatures.