Lanthanide complexes in hybrid halometallate materials: interconversion between a novel 2D microporous framework and a 1D zigzag chain structure of iodoargentates templated by octakis-solvated terbium(III) cation

Abstract

Octakis solvated terbium iodide complexes [Tb(DMSO)₈]I₃ (1) and [Tb(DMF)₈]I₃ (2) (DMSO = dimethylsulfoxide; DMF = dimethylformamide) were used as synthons to construct novel iodoargentate fabrics. Reaction of 1 with 6 equivalents of AgI in the presence of NH₄I produced a novel framework compound [Tb(DMSO)₈]₂[Ag₂(μ-I)₃I₂][Ag₅(μ₃-I)₄(μ-I)₄]_2∞ (3) involving alternate layers of discrete [Tb(DMSO)₈]³⁺ cation, [Ag₂I₅]³⁻ anion and a 2D microporous sheet of the composition [Ag₅I₈]³⁻, whereas similar reaction of 2 yielded [Tb(DMF)₈][Ag₆(μ₄-I)₂(μ₃-I)₂(μ-I)₅]_1∞ (4) with a 1D zigzag structure. The two structural forms are completely inter-convertible on mutual exchange of DMSO and DMF ligands, the partial substitution of the former ligand in 3 yielding a mixed-ligand complex [Tb(DMF)_6.7(DMSO)_1.3][Ag₆(μ₄-I)₂(μ₃-I)₂(μ-I)₅]_1∞ (5). Single crystal X-ray structures are reported for all the complexes. Thermo-gravimetric analyses of these complexes show that thermal stability decreases in the order 4 > 2 > 3 > 1, whereas the diffuse reflectance spectra of 3 and 4 exhibit an optical band gap of about 3.7 eV, thus revealing the insulator nature of these hybrid iodoargentates. Compared to solvated terbium iodide complexes 1 and 2, the high energy transitions in the excitation spectra of the iodoargentate complexes 3 and 4 are quenched by a process which can best be attributed to the auto-ionization of the carriers in the above materials.