Tetrakis(dimethylammonium) trans-dichloridobis[5,5′-(pyrazine-2,3-diyl)bis(1H-tetrazol-1-ido-κN 1)]copper(II)

The title compound, (C2H8N)4[Cu(C6H2N10)2Cl2], consists of an anionic complex which is composed of a CuII ion surrounded by four N atoms from two pyrazine-2,3-diylbis(1H-tetrazol-1-ide) ligands, and two Cl− atoms in a trans-Cl2N4 coordination geometry; the CuII atom lies on a site of symmetry 2/m. The Cu—Cl distance of 2.8719 (5) Å is long due to the Jahn–Teller distortion of the d 9 electron configuration of CuII ion. The tetrazole and pyrazine rings make an N—C—C—N torsion angle of 38.25 (17)°. The charge of the anionic complex is balanced by four dimethylammonium cations, which interact with the anionic complexes via N—H⋯N and N—H⋯Cl hydrogen bonds.


Ju-Hsiou Liao and Pei-Shan Shi Comment
Multifunctional tetrazolate ligands have recently been of great interest for the formation of metal-organic frameworks (MOFs). Thus far, the di-topic tetrazolate-based ligand, 2,3-di-1H-tetrazol-5-ylpyrazine (H 2 dtp) has only been found in a chiral, porous and thermally robust MOF, Zn(dtp) (Li, 2008). In our laboratory, the reaction of H 2 dtp and CuCl 2 in dimethylformamide (DMF) under acidic conditions afforded the title compound (I).
In the title complex anion, the Cu II ion is six-coordinated in a distorted octahedral environment, surrounded by two Clanions and four N-atoms from two chelating (dtp) 2anionic ligands, forming a trans-Cl 2 N 4 coordination geometry ( Fig.   1). The bonding mode is quite different from that observed in Zn(dtp). The asymmetric unit of the [CuCl 2 (dtp) 2 ] 4anion contains one quarter of the complex, with the Cu II ion located at a site of 2/m symmetry, and the two Clanions lie in a mirror plane. The Cu-Cl bond length, 2.8719 (5) Å, is unusually long due to Jahn-Teller distortion of the d 9 electron configuration of Cu II ion, while the Cu-N distance is normal at 2.0029 (10) Å. The tetrazolyl and pyrazinyl rings are not coplanar, with a torsion angle of 38.25 (17)°, in accord with the single-bond character of C1-C2 bond, 1.4678 (17) Å. In the aromatic CN 4tetrazolate ring, the N2-N3 bond, 1.3071 (16) Å, has slightly more double bond character than those of N1-N2 and N3-N4 bonds, 1.3455 (15) Å and 1.3450 (17) Å.
Four equivalents of [(CH 3 ) 2 NH 2 ] + cations are present to balance the charge, as shown in the packing diagram (Fig. 2).
Slabs parallel to the bc-plane are formed by hydrogen bonding networks, which are constructed by the N-H bonds of [NH 2 (CH 3 ) 2 ] + cations interacting with the Clatoms and tetrazolate-N atoms of anionic complexes. Such slabs are stacked along the a-axis through van der Waals interactions among the methyl groups of the dimethylammonium cations. respectively. The solutions were mixed in a reaction vial, adding 50-ml 3M HCl to adjust the pH value to ~1.5. The mixture was ultrasonicated to form a homogeneous yellowish green solution, and was kept at 120°C for three days. The product was washed with a small amount of DMF and acetone, and then dried in air. 18.2 mg of blue plate-like crystals were collected in 97.7% yield, based on Cu.

Figure 1
The structure of the title compound, with displacement ellipsoids drawn at the 50% probability level for non-H atoms.

Tetrakis(dimethylammonium) trans-dichloridobis[5,5′-(pyrazine-2,3-diyl)bis(1H-tetrazol-1-ido-κN 1 )]copper(II)
Crystal data (C 2  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.