A new series of Co, Ni, Zn, and Cd metal-organic architectures driven by an unsymmetrical biphenyl-tricarboxylic acid: hydrothermal assembly, structural features and properties

This study reports the hydrothermal synthesis of a novel series of twelve coordination compounds, namely, {[Cd(mu-Hnbtc)(H2O)(4)]center dot H2O}(n) (1), [Zn-2(mu-Hnbtc)(2)(phen)2]center dot 2H(2)O (2), [Zn(Hnbtc)(phen)(2)(H2O)]center dot 4.5H(2)O (3), [Ni(Hnbtc)(phen)(2)(H2O)]center dot 6H(2)O (4), [Zn-2(mu-Hnbtc)(2)(2,2'-bipy)(2)]center dot 2H(2)O (5), [Cd-3(mu(5)-nbtc)(mu(6)-nbtc)(2,2'-bipy)(2)(H2O)]n (6), {[Zn-3(mu(3)-nbtc)(2)(phen)(3)(H2O)(2)]center dot 4H(2)O} (7), [Co(H2O)(6)][Co-2(nbtc)(2)(mu-4,4'-bipy)(4,4'-bipy)(2)(H2O)(6)]center dot 8H(2)O (8), {[N(i)3(mu(4)-nbtc)(2)(mu-4,4'-bipy)(2.5)(mu-H2O)(H2O)(3)]center dot 4H(2)O}(n) (9), {[Cd-2(mu(4)-nbtc)(mu-OH)(2,2'-bipy)(2)]center dot H2O}n (10), [Cd-2(mu(4)-nbtc)(mu-OH)(phen)(2)(H2O)](n) (11), and {[Zn-2(mu(5)-nbtc)(mu(3)-OH)(mu-4,4'-bipy)]center dot 4,4'-bipy center dot H2O}(n) (12), which are derived from 3'-nitro-biphenyl-2,4,4'-tricarboxylic acid (H3nbtc) as a virtually unexplored building block. These compounds were generated in aqueous medium from the corresponding metal(II) chlorides as a metal source, H3nbtc as a principal building block, NaOH as a base, and simple N,N-donor aromatic ligands as crystallization mediators (i.e., 1,10-phenanthroline, phen; 2,2'-bipyridine, 2,2'-bipy; or 4,4'-bipyridine, 4,4'-bipy). All products 1-12 were completely characterized in the solid state by IR spectroscopy, elemental and thermogravimetric (TGA) analyses, powder (PXRD) and single-crystal X-ray diffraction. Structures of 1-12 range from discrete 0D dimers (2 and 5) or monomers (3, 4, and 8) to 1D coordination polymers (CPs, 1, 6, 7, 10, and 11) and 3D metal-organic frameworks (MOFs, 9 and 12). A broad structural diversity of 1-12 is guided by the type of the metal(II) node, the molar ratio between H3nbtc and sodium hydroxide, and the kind of crystallization mediator. Topological analysis and classification of metal-organic underlying nets was made, disclosing the following topological types: 2C1 (in 1 and 7), 1M2-1 (in 2 and 5), SP1-periodic net (in 10 and 11), tfz-d (in 12), and some topologically unique nets (in 6 and 9). Luminescence behavior of 1-3, 5-7, and 10-12 was studied in the solid state. Magnetic properties of a Ni(II) MOF 9 were also investigated and modeled. All obtained products 1-12 represent the first structurally characterized examples of coordination compounds derived from H3nbtc, thus opening up its application in coordination chemistry as a novel tricarboxylate building block.