Polar protic solvent-trapping polymorphism of the HgII-hydrazone coordination polymer: experimental and theoretical findings

A novel series of Hg-II coordination polymers with a general formula [HgL(N)(3)](n)center dot n(solv) (HL = 2-pyridinecarbaldehyde isonicotinoylhydrazone; n(solv) = 0.5H(2)O (1), 2MeOH (2), EtOH (3), PrOH (4) and 0.5BuOH (5)) was prepared and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction. The crystal structure of HL, elucidated by X-ray diffraction, comprises two independent molecules in the asymmetric unit cell, each of which is stabilized by an intramolecular hydrogen bond formed between the carbohydrazide hydrogen atom and the 2-pyridyl nitrogen atom. Crystal structures of 1-5 each reveal a similar 1D zigzag metal-organic chain [HgL(N)(3)] n, where the organic ligands bridge metal centers. These chains are extended into distinct 2D supramolecular nets by strong hydrogen bonds with the solvent molecules and/or short Hg center dot center dot center dot N supramolecular contacts. These networks were topologically classified as the hcb in 1 and fes in 2-5 underlying nets. On comparing the H-bonding patterns, it can be concluded that the lattice water molecules in 1 and methanol molecules in 2 form H-bonding interactions with the O and amide N atoms of L in the former structure and the O atom of L in the latter structure. In the remaining coordination compounds, the lattice solvent prefers the azide N atom for H-bonding. Furthermore, the existence of Hg center dot center dot center dot N interactions in 2-5 and their absence in 1 clearly highlights the importance of the size and polarity of the solvents on the self-assembly generation of Hg-II coordination polymers. A broad network of intermolecular pi center dot center dot center dot pi stacking interactions, formed between the pyridyl fragments, provide further reinforcement of crystal packing patterns in the structures of HL and 2-5. DFT based charge and energy decomposition scheme (ETS-NOCV) was applied to characterize the obtained polymers.