Metal-organic frameworks as precursor for metal oxide nanostructures Part I: MOF-derived copper oxide embedded in carbon matrix

Abstract

Three isostructural metal-organic framework materials (MOFs) formulated as M[(HBTC)(H2O)]ˑH2O(M = Cu for 1, Zn for 2 and Ca for 3) constructed with 1, 3, 5-benzenetricarboxylate (BTC) were synthesised under hydro/solvothermal conditions. The three compounds were characterised on the basis of infrared and UV-Vis spectroscopy and the structure of 3 elucidated with the help of single-crystal x-ray crystallography. The UV-Vis spectrum of 1 exhibited a unique band at 511 nm. In the region 520 – 534 nm, the band splits into two moderately intense peaks at 527 and 531 nm. These absorption peaks along with other bands at 629 and 638 nm were assigned to d-d transitions of the copper (II) ion with distorted square planar geometry. The infrared spectra of the three compounds revealed that the ligand, BTC anion coordinated in a chelating and / or bridging mode to the metal center. The presence of absorption bands at 1699 cm-1 in 1 and 2, (1681 cm-1 in 3) can be attributed to protonated HBTC for 1-3. Single-crystal X-ray crystallographic studies of compound 3 revealed well-ordered structure with BTC ligand linking the individual chains to form a network structure. On heating Cu(HBTC)(H2O)ˑH2O up to 400oC, a copper-oxide embedded in carbon matrix was obtained with uniform particles of 10 -100 nm size.