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

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)2·6H2O 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 1·4H2O, 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.