Structural Diversity of a Series of Mn(II), Cd(II), and Co(II) Complexes with Pyridine Donor Diimide Ligands

A series of Mn(II), Cd(II), and Co(II) metal–organic frameworks, namely, {[Mn(L1)(NCS)2(CH3OH)2]·2(CH3OH)}n (1), {[Mn(L2)2(NCS)2(CH3OH)2]}n (2), {[Mn(L3)2(NCS)2]·0.5(CH3OH)·4.5H2O}n (3), {[Cd(L1)(I)2]·3(H2O)}n (4), {[Cd(L2)(I)2]}n (5), {[Cd(L3)(NCS)2]·2.5(H2O)}n (6), {[Co(L1)2(NCS)2]·4(H2O)}n (7), {[Co(L2)2(NCS)2]·(HCCl3) }n (8), and {[Co(L3)2(NCS)2]·3(H2O)}n (9) (where L1 = N,N′-bis(4-pyridylmethyl)-pyromellitic diimide, L2 = N,N′-bis(3-pyridylmethyl)-pyromellitic diimide, L3 = N,N′-bis(4-pyridylmethyl)-naphthalene diimide), were synthesized and structurally characterized by elemental analyses, thermogravimetric (TG) analyses, powder X-ray diffraction, IR spectroscopy, and single-crystal X-ray diffraction. In Mn(II) complexes 1–3, L1 connects the adjacent metal centers to form an infinite one-dimensional (1D) zigzag coordination polymeric chain, L2 acts as a monodentate ligand to give mononuclear coordination motifs, while L3 bridges two metal ions to generate two-dimensional (2D) networks of the (4, 4) net topology containing rhombic grids. In Cd(II) complexes 4–6, L1, L2, and L3 act as bidentate ligands and coordinate with two metal ions to form three different coordination polymers that display diversified structures, that is, infinite 1D zigzag chain in 4, single-stranded double helical chain in 5, and 2D networks of the (4, 4) net in 6. For three Co(II) complexes, 7 is a three-dimensional (3D) framework with 3-fold interpenetrating dia topology, while 8 and 9 have similar two-dimensional (2D) networks of the (4, 4) net topology. The results show that the conformation and coordination mode of organic ligands and the coordination geometry of metal centers play important roles in determining the structure and topology of the complexes. Furthermore, the gas sorption properties were measured, and complex 7 shows a highly selective sorption behavior toward CO2, which can be a promising candidate as adsorbents for CO2/N2 separation. In addition, the luminescence properties of 5–6 were studied in the solid state at room temperature.