Supramolecular association in Cu(II) and Co(II) coordination complexes of 3,5-dimethylpyrazole: Experimental and theoretical studies

Two coordination complexes of Cu(II) and Co(II) involving 3,5-dimethylpyrazole viz. { [Cu(mu-O,O'-SO4) (Hdmpz)(2)(H2O)]center dot 2H(2)O}(n) (1) and [Co(Hdmpz)(4)(H2O)(2)Cl-2 (2) (where Hdmpz = 3,5-dimethylpyrazole) have been synthesized in purely aqueous medium at room temperature. Crystal structure of complex 1 consists of a polymeric chain of distorted square pyramidal Cu(II) centers bridged by bidentate sulfato ligands. The polymeric chain in 1 has been stabilized by N-H center dot center dot center dot O and C-H center dot center dot center dot pi interactions. Particularly relevant is the polymeric chain in 1, since in addition to the afore mentioned non-covalent contacts, unprecedented chalcogen bonding interactions involving the sigma-hole at the tetrahedral sulfur atom are observed and characterized using theoretical calculations. To our knowledge, sigma-hole chalcogen bonding interactions involving tetrahedral sulfur atom have not been previously reported in the literature. The lattice water molecules self assembles the polymeric chains of 1 into a 3D supramolecular architecture via C-H center dot center dot center dot O hydrogen bonding interactions. The cationic units in the crystal structure of 2 self assembles via O-H center dot center dot center dot Cl, N-H center dot center dot center dot Cl and C-H center dot center dot center dot Cl weak hydrogen bonding interactions into a 2D supramolecular architecture induced by chloride anions in the lattice. PXRD patterns of 1 and 2 demonstrate good phase purity of the complexes. In addition, the thermal behaviour of the complexes has also been investigated.