The ubiquitous paddle-wheel building block in two-dimensional coordination polymers with square grid structure

This work describes design of a series of new paddle-wheel binuclear clusters containing 2-D coordination polymers based on ditopic carboxylate linkers, 1,4-benzenedicarboxylate (BDC) or 2-amino,1,4-benzenedicarboxylate (Am-BDC). The strategic use of strongly coordinating base/solvent as blocking ligand to restrict the structure in 2-D space is explored, and the role of organic base on the overall structure formation is further elaborated. The isostructural [Zn(BDC)(Py)](n) (1) and [Co(BDC(Py)](n) (2) were formed by the use of strong base pyridine (Py) as a blocking ligand whereas reaction using N-methylimidazole (Mim) in place of pyridine gives [Co(BDC)(Mim)](n) (3) with similar topology and coordination environment. The use of weak/non-coordinating base such as 2-chloropyrimidine, pyrazine, and tetramethylammoniumhexafluorophosphate [(CH3)(4)N(PF6)] gives the DMF-coordinated 2-D frameworks, [Cu(BDC)(DMF)](n) (4), [Zn(BDC)(DMF)](n) (5), and [Zn(AmBDC)(DMF)](n) (6). All the structures crystallize in monoclinic crystal system yielding 2-D nets with square grid 4(4) topology and solid state 3-D structure via extensive non-covalent supramolecular interactions. Surface area analysis via N-2 adsorption of three representative 2-D coordination polymers, 1, 4, and 6, indicate that 4 has a surface area of 450m(2)g(-1) which is a signature of microporosity, while 1 and 6 have moderate (161.6m(2)g(-1)) and negligible (33m(2)g(-1)) surface areas, respectively. [GRAPHICS]