Second ligand-directed assembly of photoluminescent Zn(II) coordination frameworks

Three new coordination polymers, {[Zn(H(2)Bpz)(Tph)]center dot 1/2(H(2)Bpz)}(n) (1), [Zn-2(H(2)Bpz)(Bpz)(Iph)](n) (2), and {[Zn-2(H(2)Bpz)(HBtc)(2)(H2O)(2)]center dot 7/6(H2O)}(n) (3) (H(2)Bpz = 3,3',5,5'-tetramethyl-4,4'-bipyrazole; H(2)Tph = terephthalic acid; H(2)Iph = isophthalic acid; H(3)Btc = benzene-1,3,5-tricarboxylic acid), have been isolated from parallel hydrothermal reactions of ZnSO4 and H(2)Bpz with H(2)Tph, H(2)Iph, and H(3)Btc, respectively. These crystalline solids have been structurally defined, of which 1 was revealed to construct in a 3D architecture with porosity. Interestingly, because of its large porosity, 1 allows the concurrent 2-fold interpenetration and inclusion of free H(2)Bpz as guest molecule. In contrast to 1, polymer 2 structures in a 2D framework of note for containing both neutral and deprotonated H(2)Bpz as mu(2)-and mu(4)-bridging linkers, respectively. This case demonstrates a rare usage of H(2)Bpz as ligand in the construction of MOFs. The partial deprotonation of H(2)Bpz may be a consequence of less acidity of H(2)Iph than H(2)Tph, by which the influence of a second ligand on the reactivity of the main ligand is reified. Likewise, 3 is also assembled in a 2D framework, containing H(2)Bpz and monoacid HBtc(2-) as ligands, which indicates the stronger acidity of H(3)Btc. Moreover, to probe the effect of substitution of second ligands, we have investigated the luminescence of 1-3 in the solid state at room temperature, revealing that the polymers are photoluminescent and their emissions are varied with the alteration of second ligands.