Three two-folded interpenetrating 3D metal-organic frameworks consisting of dinuclear metal units: Syntheses, structures, and magnetic properties

Three two-folded interpenetrating 3D coordination polymers, [M(ip-OH)(Bimb)_0.5]_n [where M = Ni(II) (1), Co(II) (2), or Cu(II) (3); H₂ip-OH = 5-hydroxylisophthalic acid; and Bimb =1,4-bis(imidazol-1′-yl)butane], were synthesized by hydrothermal reactions of H₂ip-OH, Bimb, and MCl₂ in the presence of base. Single-crystal X-ray diffraction studies reveal that 1-3 consist of dinuclear metal units, which are bridged by ip-OH to form [M(ip-OH)]_n layers and are further pillared by Bimb to generate 3D α-Po networks. Bimb adopts a gauche-antigauche conformation. Both the large void in the 3D network and the hydrogen bonds between hydroxyl of ip-OH and one carboxylate oxygen atom from the other network result in the formation of two-folded interpenetrating architectures. The secondary building units in 1-3 are well separated by ip-OH and Bimb. The magnetic data of 1-3 were fitted to the dimeric modes; fitting results indicate antiferromagnetic exchange between metal centers in the dinuclear metal units.