Ligand-Based Modification of the Structures and Optical Properties of New Silver(I)-Rhenate(VII) Oxide/Organic Hybrid Solids

A new series of silver(I)-rhenate(VII) hybrids was systematically prepared under hydrothermal conditions from eight different N-donor organic ligands (isonicotinate = inca, pyrazine-2-carboxylate = pzc, 1,2,4-triazole = tro, pyridazine = pda, 4,4′-bipyridine = bpy, 1,2-bis(4-pyridyl)-ethane = dpa, 2,3-bis(2-pyridyl)pyrazine = bpp, and tetra-2-pyridinylpyrazine = tpp), and their resulting structures and optical properties were investigated. The reactions targeted a 1:1 molar ratio of Ag/Re, and new hybrid solids were prepared with the compositions Ag(bpp)ReO4 (1), Ag(tpp)ReO4·H2O (2), Ag(Hinca)2ReO4·H2O (3), Ag(tro)ReO4 (4), Ag(pda)ReO4·1/2H2O (5), Ag(Hpzc)ReO4 (6), Ag2(Hpzc)(pzc)(H2O)ReO4 (7), Ag(bpy)ReO4 (8), and Ag(dpa)2ReO4 (9). Hybrid solids 1, 2, and 3 each exhibit low-dimensional structures, consisting of [Ag2(bpp)4]2+ and [Ag2(Hinca)4]2+ dimers in 1 and 3, respectively, and [Ag(tpp)]nn+ chains in 2. Hybrid solids 4 and 5 contain a [Ag(tro)]+ chain and a [Ag3(pda)3]3+ cyclic trimer, respectively, that are both ReO4-bridged into layered structures. Both 6 and 8 consist of ligand-pillared "AgReO4" layers, while 7 is a Re-deficient analogue of 6 that contains ligand-pillared [Ag2(H2O)ReO4]+ layers where H2O replaces the missing ReO4− anion. The hybrid networks of 8 and 9 are interpenetrating, owing to the length of the bpy and dpa ligands, and consist of bpy-pillared "AgReO4" layers and ReO4-filled [Ag(dpa)2]+ diamond-type networks that are 2-fold and 6-fold interpenetrating, respectively. Their optical properties and thermal stabilities were investigated using UV−vis transmittance, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The measured properties were analyzed with respect to the varying structural modifications. The Ag−ReO4 network dimensionalities, Ag coordination environments, and the ligand lengths and geometries are found to play important roles in the absorption coefficients, bandgap sizes, and whether the structure collapses softly to give condensed AgReO4, respectively.