Supramolecular assemblies of dimanganese subunits and water clusters organized by strong hydrogen bonding interactions: Single crystal to single crystal transformation by thermal De-/rehydration processes.

Abstract

New three-dimensional (3D) supramolecular assemblies held together by strong hydrogen bonding interactions between two-dimensional (2D) layers of the [Mn2(adc)2(bpta)2(H2O)2] subunit (where adc = acetylene dicarboxylate and bpta = N,N-bis-(2- pyridylmethyl)-tert-butylamine) containing a pore (8.225 Å × 4.048 Å) and a cluster of water molecules (five at 296 K and six at 120 K) are reported. The water cluster arrangement in the channel is found to be different at these two temperatures. In the two-dimensional layers, there exists strong intermolecular hydrogen bonding interactions (O⋯H-O) between the uncoordinated oxygen atoms of the adc and hydrogen atoms of the bound water molecules. [Mn2(adc)2(bpta)2(H2O)2]·5H2O (1·5H2O) is prepared by mixing equimolar amounts of bpta and Mn(ClO4) 2·6H 2O in methanol at room temperature followed by the addition of 1 equiv of disodium acetylene dicarboxylate in 55% yield. Direct layering of the starting materials results in the formation of a similar 3D supramolecular assembly, 1·4H2O·CH3OH. When a single crystal of 1·5H2O is slowly heated to 350 K, it undergoes a solid-state structural transformation to the 2D framework 1, where the cluster of five water molecules in the channel of the former is completely removed, showing remarkable stability. Upon rehydration of 1 under ambient conditions over a few weeks, the 3D supramolecular assembly 1·4H2O, where strong hydrogen bonding as well as C-H⋯O interactions exist, was obtained. The solid-state structural transformation between 3D, 2D, and 3D during the dehydration and rehydration processes in 1·5H2O, 1, and 1·4H 2O, respectively, was verified by single crystal and powder XRD measurements. These compounds were also characterized by elemental analysis, IR, and Raman spectroscopy and thermogravimetric and differential scanning calorimetry analyses.