화학공학소재연구정보센터
Inorganic Chemistry, Vol.46, No.6, 2224-2236, 2007
Functional tetrametallic linker modules for coordination polymers and metal-organic frameworks
The new biphenol-based tetranucleating ligand, 2,2',6,6'-tetrakis(N,N-bis(2-pyridylmethyl)aminomethyl)-4,4'-biphenolate , dbpbp(,)(2-) comprises two linearly disposed phenolato-hinged dinucleating heptadentate units, each of which offer one O and three N donors to a total of four metal ions. The ligand has been isolated as the zinc chloride complex [Zn-4(dbpbp)Cl-4](2+), and the Zn-II ions have been completely or partially substituted by Cu-II, Fe-III, Co-II, and Co-III in metathesis reactions. Similarly, the chloride ligands of [Zn-4(dbpbp)Cl-4](2+) have been exchanged for solvent molecules (acetonitrile and/or water) and bridging carboxylate ligands. The resulting complexes have been characterized by single-crystal X-ray diffraction, ESI mass spectrometry (ESI-MS), cyclic voltammetry (CV), and EPR spectroscopy. The structures containing [M-4(dbpbp)Cl-4](2+) with M = Zn-II or Cu-II exhibit 2-D polymeric honeycomb sheets in which intermolecular M center dot center dot center dot Cl interactions bridge between adjacent [M-4(dbpbp)Cl-4](2+) cations. Two mixed-metal tetrabenzoate complexes [M-4(dbpbp)(O2CC6H5)(4)](2+/3+) have also been prepared, namely a stoichiometric (Cu2Zn2II)-Zn-II complex and a nonstoichiometric Fe-III/Zn-II system. In the latter case, ESI-MS identifies FeZn3, Fe2Zn2, and Zn-4 species, and X-ray crystallography suggests an average composition of Fe0.8Zn3.2. Preparation of a Co-4(II) complex by metathesis was considerably more difficult than preparation of [Cu-4(dbpbp)Cl-4](2+), requiring both a large excess of the cobalt source and the presence of auxiliary benzoate. In the presence of 2 equiv of benzoate per starting [Zn-4(dbpbp)Cl-4](2+) unit and excess Co-II, dioxygen binds as peroxide at each end of the molecule to give the Co-4(III) complex [Co-4(dbpbp)(O-2)(2)(O2CC6H5)(2)](4+). This latter complex, together with new tetra- and hexametallic benzenedicarboxylato- and benzenetricarboxylato-bridged complexes of dinuclear [Co-2(O-2)(bpbp)](3+) units (bpbp(-) = 2,6-bis(N,N-bis-(2-pyridylmethyl)aminomethyl)-4-tert-butyl-phenolate), is a module for potential construction of 1-D and 2-D coordination polymers/metal-organic frameworks (MOFs) capable of reversible O-2 binding.