Noncovalent-bonded 3D Cd(II) and Zn(II) supramolecular metal-organic frameworks from 3,3′,5,5′-tetramethyl-4,4′-bipyrazole and carboxylates

Abstract

The present study pertains to the syntheses and characterizations of four mixed-ligand complexes of Cd(H2Bpz)(L1)2(H2O) (1) (L1 = 2-methyl-2-phenoxypropanoic acid), Zn(H2Bpz)(L2)2 (2) (L2 = m-nitrobenzoate), Cd(H2Bpz)2(L3)2 (3) (L3 = 3,4-(methylenedioxy)benzoate) and [Cd2(H2Bpz)3(L4)2]2·2(THF)0.5·4MeOH·4H2O (4) (L4 = o-phthalate). The resulting complexes were formulated via EA, IR and SCXRD, and the TGA. X-ray studies revealed that these complexes have mononuclear to dinuclear structures with distorted octahedral geometry at Cd2+ and square pyramidal geometry for Zn2+, and metal ions show N2O3, N2O4, N3O3 and N4O2 bonding cores. H2Bpz in all compounds is coordinated only in bismonodentate fashion with its neutral N. The CO2 - in 1 and 4 exhibited bisunidentate and monodentate coordination units, the CO2 - in 2 has both chelating bidentate and monodentate coordination mode, and the CO2 - in 3 is only monodentate. The CH3 of H2Bpz in all compounds except 1 participated in noncovalent bonds. Complexes 1-4 have many intra- and intermolecular weak interactions (including classical H-bonds, O···O, C-H···O, CH2···O, CH3···O, C-H···π, CH2···π, CH3-π, OH-π and π-π interactions) in their crystals, which lead to the total 3D supramolecular structures. The thermal stabilities for 1-4 show that the complexes are good candidates for hybrid inorganic-organic materials with good thermal stability.