Study On Coordination Polymers Of Biphenyl Tetracarboxylic Acid Based On Nitro Functionalization And Its Properties

In recent years, the construction of Coordination Polymers (CPs) has become a hot research spot in the domain of chemistry not only owing to their beautiful architectures but also due to their potenical applications in magnetism, absorption, fluorescence and drug delivery etc. As far as we know, polycarboxylic ligands are the good ligand candidates because of their adjustable length and multiple coordination sites, as well as the abundant bridging modes of the carboxylate groups. In contrast to biphenylcarboxylates ligands, there are only limited examples of CPs with carboxylate ligands containing NO2-groups. More importantly, nitro groups have a profound effect on the assembling process, structures and physical properties of the complexes due to its electronegative and steric effects.6,6’-dinitro-2,2’,4,4-biphenyl tetracarboxylic acid (H4nbtc) with unique structural characteristic inspire our research interests. In this paper, we study its coordination modes and explore the effect of nitro groups on the structure and properties of resultant products.Eleven CPs were synthesized with/without N-donor auxiliary ligands under hydro/solvothermal conditions:Zn2(nbtc)(bpa) (1), Zn2(nbtc)(bpe) (2), Zn(nbtc)(2-bpy) (3), Zn (H2nbtc)(phen)2 (4), Cd3(nbtc)2(H2O)3·4H2O (5), [Mn2(nbtc)(H2O)2(G)]·G·0.5H2O (G= DMF (6), DMA (7), NMP (8), DEF (9)), Mn2(nbtc)(bpe) (10), [Cu4(nbtc)1.5(μ3-OH)2(H2O)4]·8H2O (11). Single crystal X-ray diffraction analyses reveal that: 1 and 2 are isostructural 3D "pillar-layer"; 3 is the "brick-walled" shaped 3D architecture based on Zn2(COO)3 SBUs; While 4 is the 0D mononuclear complex; 5 also shows a 3D architecture, of which the 6-,7-,8-coordinated Cd2+ions coexist; 6-9 are isostructural 3D open framework based on 1D rod-shaped Mn-COO SBUs, in which the channels are occupied by the carbonyl molecules; 10 also displays 3D "pillar-layer" structure, which is constructed by 1D Mn-COO chains; Whereas 11 represents the first example of MCCP (Metal-Cluster-based Coordination Polymer) simultaneously containing boat- and chair-configured tetranuclear copper clusters [Cu4(μ3-OH)2]6+. In addition, these compounds are further characterized by powder X-ray diffraction (PXRD), elemental analyses (EA), Infrared spectra (IR), and thermogravimetric analyses (TGA). On the basis of their individual characteristic, the fluorescence, magnetism and adsorption properties have been investigated.