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

Graphical abstract Crystal structures of two coordination complexes of Cu(II) and Co(II) involving 3,5-dimethyl pyrazole has been reported. An unusual σ-hole chalcogen bonding interaction at the tetrahedral sulfur atom was observed in the solid state of the polymeric Cu(II) complex. The polymeric chains are further self assemled into a 3D supramolecular architecture via hydrogen bonding interactions. The cationic units of the monomeric Co(II) complex self assembles into a 2D supramolecular architecture via chloride induced hydrogen bonding interactions. Highlights • Cu(II) and Co(II) complexes involving 3,5-dimethylpyrazole are structurally characterized. • Unprecedented chalcogen bonding interactions are confirmed in the polymeric Cu(II) complex. • 2D architecture of Co(II) Complex is induced by chloride anions in the lattice. Abstract Two coordination complexes of Cu(II) and Co(II) involving 3,5-dimethylpyrazole viz. {[Cu(μ-O,O′-SO 4)(Hdmpz) 2 (H 2 O)]·2H 2 O} n (1) and [Co(Hdmpz) 4 (H 2 O) 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⋯O and C–H⋯π 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 σ-hole at the tetrahedral sulfur atom are observed and characterized using theoretical calculations. To our knowledge, σ-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⋯O hydrogen bonding interactions. The cationic units in the crystal structure of 2 self assembles via O–H⋯Cl, N–H⋯Cl and C–H⋯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. [ABSTRACT FROM AUTHOR]