Influence of ligand coordination, solvent, and non-covalent interaction on the structural outcomes in coordination polymers with direct Cd(II)-alkanesulfonate bonds: A combined experimental and computational study

摘要

One-pot three-component Arbuzov-type reaction, involving anhydrous cadmium acetate, dimethyl sulfite, and tetraethylammonium iodide, has produced the cadmate salt, [Et4N](2)[Cd(OMs)(4)] (1) revealing weakly-coordinating methanesulfonate (OMs) ligands inside the metal-coordination sphere. The 'ate' salt 1 was found useful as a precursor in the preparation of coordination polymers with compositions, [Cd(OMs)(2) (MeOH)](n) (2) and [Cd(OMs)(2)(H2O)(2)](n) (3), when subjected to crystallization in a methanol/chloroform mixture, in dry and ambient conditions, respectively. Compounds 1-3 were characterized by spectroscopic [H-1, C-13 NMR, FT-IR] techniques, and elemental and thermogravimetric analysis, while the structural attributes of 2 and 3 were investigated using single-crystal X-ray diffraction. The composition of 1 was further scrutinized by electrospray-ionization massspectrometry (ESI-MS). The crystal structure of 2 exhibits formation of a two-dimensional (2-D) layer facilitated by the bidentate (mu(2)) and tridentate (mu(3)) modes of coordination of sulfonate ligands around the metal center. The structure of 3 demonstrates the formation of 1-D linear chains, comprising of eight-membered cyclic [-Cd-O-S-O-] rings, owing to the bridging bidentate (mu(2)) mode of coordination of the sulfonate ligands. The involvement of hydrogen-bond interactions in 2 and 3 further perpetuates the assemblies into 2-D and 3-D supramolecular coordination polymers, respectively. This paper reports noticeable features such as, (a) cadmate dianion was afforded by the in situ generation of methanesulfonate ligands and subsequent complexation to the Cd(II) atom; (b) ability of alkanesulfonate ligand to display flexible coordinating behaviour [(mu(2) and uncommon (mu(3))] and prolific H-bond acceptor; (c) competitive ligation between strong coordinating solvents (MeOH and H2O) and weakly-coordinating methanesulfonate ligands; (d) effect of types and number of solvent molecules around the metal center with their participation in non-covalent interactions in bringing variation in the structural outcome; (e) the values of distances of Cd-O bonds in 1 and 2 fall in the range of 2.24 angstrom to 2.29 angstrom, suggesting the presence of direct metal-sulfonate interactions. The dispersion-corrected density functional theory (DFT-D) and Bader's quantum theory of atoms in molecule (QTAIM) (primary and secondary) studies explored the structures, electronics, and non-covalent interactions of compounds 2 and 3. Additionally, among different involved non-covalent interactions, Hirshfeld surface analysis emphasized the presence of O center dot center dot center dot H/H center dot center dot center dot O contacts as the dominant intermolecular non-covalent interactions as the consolidating factor in crystal packing, in both compounds.