A 3D Hybrid Praseodymium-Antimony-Oxochloride Compound: Single-Crystal-to-Single-Crystal Transformation and Photocatalytic Properties

A 3D organic-inorganic hybrid compound, (2-MepyH)(3) [{Fe(1,10-phen)(3)}(3)][{Pr4Sb12O18(OH) Cl-11.5}(TDC)(4.5)({Pr4Sb12O18(OH)Cl-9.5} Cl)]3(2-Mepy)28H(2)O (1; 2-Mepy=2-methylpyridine, 1,10-phen=1,10-phenanthroline, H2TDC=thiophene-2,5-dicarboxylic acid), was hydrothermally synthesized and structurally characterized. Unusually, two kinds of high-nuclearity clusters, namely [(Pr4Sb12O18 (OH)Cl-11)(COO)(5)](5-) and [(Pr4Sb12O18 (OH)Cl-9)Cl(COO)(5)](4-), coexist in the structure of compound 1; two of the latter clusters are doubly bridged by two (2)-Cl- moieties to form a new centrosymmetric dimeric cluster. An unprecedented spontaneous and reversible single-crystal-to-single-crystal transformation was observed, which simultaneously involved a notable organic-ligand movement between the metal ions and an alteration of the bridging ion in the dimeric cluster, induced by guest-release/re-adsorption, thereby giving rise to the interconversion between compound 1 and the compound (2-MepyH)(3)[{Fe(1,10-phen)(3)}(3)][{Pr4Sb12O18(OH)Cl-11.5}(TDC)(4)({Pr4Sb12O18Cl10.5(TDC)(0.5)(H2O)(1.5)}O-0.5)] 25H(2)O (1). The mechanism of this transformation has also been discussed in great detail. Photocatalytic H-2-evolution activity was observed for compound 1 under UV light with Pt as a co-catalyst and MeOH as a sacrificial electron donor.