Synthesis, structure, transformation studies and catalytic properties of open-framework cadmium thiosulfate compounds

Abstract

Five new thiosulfate based inorganic–organic hybrid open-framework compounds have been synthesized employing mild reaction conditions. Of the five compounds, [Na₂(H₂O)₈][Cd(C₁₀H₈N₂)(S₂O₃)₂]·2H₂O, I and [Cd₂(C₁₀H₈N₂)₂(HS₂O₃)₂(S₂O₃)₂][(C₁₀H₉N₂)₂(C₁₀H₈N₂)₂]·8H₂O, II have one-dimensional (1D) structures and [Cd(C₁₀H₈N₂)(H₂O)₂(S₂O₃)]·2H₂O, III, [Cd₂(C₁₀H₈N₂)₃(S₂O₃)₂], IV and [Cd₂(C₁₀H₈N₂)_2.5(S₂O₃)₂], V have three-dimensional (3D) structures. The 1D structures are somewhat related, formed by the bonding between tetrahedral Cd centers (CdN₂S₂) and 4,4′-bipyridine (bpy) units. The inter-chain spaces are occupied by the hanging thiosulfate units in both the cases along with Na(H₂O)₆ chains in I and free bpy units in II. The three 3D structures have one-dimensional cadmium thiosulfate chains linked by bpy units. Interpenetration has been observed in all the 3D structures. The 3D structures appear to be related and can be derived from fgs net. Transformation studies on the 1D compound, [Na₂(H₂O)₈][Cd(C₁₀H₈N₂)(S₂O₃)₂]·2H₂O, I, indicated a facile formation of [Cd(C₁₀H₈N₂)(H₂O)₂(S₂O₃)]·2H₂O, III. Prolonged heating of I gave rise to a 3D cadmium sulfate phase, [Cd₂(C₁₀H₈N₂)₂(H₂O)₃(SO₄)₂]·2H₂O, VI. Compound VI has one-dimensional cadmium sulfate chains formed by six-membered rings connected by bpy units to form a 3D structure, which appears to resemble the topological arrangement of III. Transformation studies of III indicates the formation of IV and V, and at a higher temperature a new 3D cadmium sulfate, [Cd(C₁₀H₈N₂)(SO₄)], VII. Compound VII has a 4 × 4 grid cadmium sulfate layers pillared by bpy units. All the compounds were characterized by PXRD, TGA, IR and UV-visible studies. Preliminary studies on the possible use of the 3D compounds (III–VII) in heterogeneous cyanosilylation of imines appear to be promising.