Bis(acetato-κ2 O,O′)bis(3,5-dimethyl-1H-pyrazole-κN 2)copper(II)

In the title compound, [Cu(C2H3O2)2(C5H8N2)2], the CuII atom has a distorted tetragonal–bipyramidal geometry, with the equatorial plane formed by two N atoms belonging to two 3,5-dimethyl-1H-pyrazole ligands and two O atoms from two acetate anions. The second O atoms of the acetate groups provide elongated Cu—O axial contacts, so that the acetates appear to be coordinated in a pseudo-chelate fashion. The pyrazole ligands are situated in cis positions with respect to each other. In the crystal structure, molecules are linked through intermolecular N—H⋯O hydrogen bonds, forming a one-dimensional chain.

In the title compound, [Cu(C 2 H 3 O 2 ) 2 (C 5 H 8 N 2 ) 2 ], the Cu II atom has a distorted tetragonal-bipyramidal geometry, with the equatorial plane formed by two N atoms belonging to two 3,5-dimethyl-1H-pyrazole ligands and two O atoms from two acetate anions. The second O atoms of the acetate groups provide elongated Cu-O axial contacts, so that the acetates appear to be coordinated in a pseudo-chelate fashion. The pyrazole ligands are situated in cis positions with respect to each other. In the crystal structure, molecules are linked through intermolecular N-HÁ Á ÁO hydrogen bonds, forming a one-dimensional chain.
Bis(acetato-2 O,O')bis (3,5-dimethyl-1H-pyrazole-N 2   1H-Pyrazole and its 3,5-substituted derivatives have been widely used as bridging ligands in molecular magnetism and supramolecular chemistry because of their marked tendency to form high nuclearity species exhibiting specific magnetic properties (Krämer et al., 2002;Seredyuk et al., 2007). Copper complexes containing pyrazole-based ligands are of particular interest in bioinorganic chemistry, as they can be used as models for the active sites in copper proteins like hemocyanine and tyrosinase (Krämer, 1999;Raptis et al., 1999). In addition, copper carboxylates are important in biology and also in basic inorganic chemistry (Halcrow, 2001;Jain et al., 2004). The carboxylates show a large variety of coordination modes, which can lead to the formation of different assemblies, including supramolecular coordination polymers or metal-organic frameworks (Fritsky et al., 1993(Fritsky et al., , 1994aSkopenko et al., 1990). A large number of copper(II) carboxylates with flexible connection are reported (Barooah et al., 2006;Pradeep et al., 2006). Total use of 1H-pyrazole derivatives and carboxylates can lead to the formation of mononuclear complexes with vacant donor atoms, which can be use as building blocks for the preparation of polynuclear complexes or coordination polymers.
The title compound is a mononuclear complex ( Fig. 1), which consists of a Cu II ion as the central atom possessing  (Table 1). Each sort of ligands (3,5-dimethyl-1H-pyrazole and carboxylate) in the coordination sphere of central Cu II is cis-oriented with respect to each other.
According to the carboxylate coordination criteria (Poray-Coshits, 1980), the acetate anions of the title compound coordinate in a pseudo-chelate mode, forming a four-membered chelate ring. The specific chelation of the above mentioned acetate anions, when one of the two bonds always resides in the equatorial position and second bond occupies the axial position of tetragonal-bipyramidal environment, was found in many Cu II compounds (Deka et al., 2006;Karmakar et al., 2007). The Cu-O equatorial distances varying in the range of 1.970 and 1.974 Å are somewhat shorter than those in the title compound.
The axial Cu-O bond lengths in the title compound are less than 2.685 Å (Karmakar et al., 2007) In the crystal packing (Fig. 2), the complex molecules are connected through intermolecular N-H···O hydrogen bonds into a one-dimensional linear chain. The hydrogen bonds in the structure are of two types, with distances N2···O4 = 2.726 (3) and N4···O2 = 2.732 (2)Å (Table 2). Each couple of hydrogen bonds of one type takes part in forming the different tenmembered cycles. Due to this crystal packing, the shortest intra-chain Cu···Cu separations are 6.018 and 6.123 Å.

supplementary materials sup-2 Experimental
The title complex was synthesized by a direct method at free access of air oxygen. The mixture of 3,5-dimethyl-1H-pyrazole (0.96 g, 0.01 mol), ammonium acetate (0.77 g, 0.01 mol) in dimethylsulfoxide solution (15 ml) was stirred with copper powder (0.64 g, 0.01 mol) at ambient temperature until dissolved. The resulting dark-green solution was filtered and the filtrate was left to stand at room temperature for crystallization in air. Slow evaporation yielded green crystals of the title complex suitable for X-ray analysis in 5 d.

Refinement
H atoms bound to C atoms were positioned geometrically and refined as riding atoms, with C-H = 0.93 (CH) and 0.96 (CH 3 ) Å and with U iso (H) = 0.08 Å 2 . H atoms bound to N atoms were located on a difference Fourier map and refined isotropically. Fig. 1. The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. The dashed grey lines represent the elongated axial Cu-O bonds.