μ-Cyanido-κ2 C:N-dicyanido-κ2 C-bis(N-ethylethylenediamine-κ2 N,N′)copper(II)copper(I)

In the title complex, [CuICuII(CN)3(C4H12N2)2], the CuI and CuII ions and a bridging cyanide group lie on a twofold rotation axis. The CuII ion is in a slightly-distorted square-pyramidal coordination environment, with the N atoms of the two symmetry-related N-ethylethylenediamine ligands occupying the basal positions and an N-bonded cyanide group in the apical position. The CuI ion is in a trigonal-planar coordination environment, bonded to the C atom of the bridging cyanide group and to two terminal cyanide groups. In the crystal, N—H⋯N hydrogen bonds involving two of the symmetry-unique N—H groups of the N-ethylethylenediamine ligands and the N atoms of the terminal cyanide ligands link the molecules into strands along [010].


Related literature
The title compound was synthesized as part of our continuing study of structural motifs in mixed-valence copper cyanide complexes containing amine ligands. For descriptions of similar discrete molecular copper cyanide complexes, see: ; Pretsch et al. (2005); Pickardt et al. (1999); Yuge et al. (1998). For mixed-valence copper cyanide complexes crystallizing as self-assembled polymeric networks, from preparations similar to those used in the present work, see: Williams et al. (1972); Colacio et al. (2002); Kim et al. (2005), and also Corfield & Yang (2012), although this last one involves only Cu II ions.

Experimental
Crystal data

Results and discussion
The structure determination of the title compound was undertaken as part of a continuing study of mixed-valence copper cyanide complexes containing amine ligands, with the goal of learning how to direct synthesis of specific polymeric structures. In these compounds, the divalent copper atoms are stabilized by the coordinated amines against reduction by the cyanide groups. In the present work, the synthesis involved the bidentate base N-ethylethylenediamine (eten), under conditions expected to produce a polymeric structure, as in Williams et al. (1972) or Colacio et al. (2002). The crystal structure is made up of discrete molecules, as shown in Fig. 1, with terminal cyanide groups that are not involved in covalent polymeric linkages, and is similar to structures previously reported by us  or by others (Yuge et al., 1998;Pickardt et al., 1999;Pretsch et al., 2005). The packing of the molecules is shown in Fig. 2. Intermolecular contacts appear normal.
The binuclear molecules lie on the two-fold axes of space group C2/c, with the asymmetric unit at 1/2,y,1/4. The divalent copper atom, Cu2, shows square-pyramidal coordination, with the four N atoms of the two symmetry-related eten ligands occupying the basal positions, and the N atom of the cyanide group on the two-fold axis in the apical position. The bond length to the apical N atom shows a slight Jahn-Teller extension of 0.10 Å relative to the basal positions ( Table 1). The four eten N atoms are roughly co-planar, and the Cu2 atom lies 0.360 (1)Å out of their best plane, in the direction of the apical N atom. The N-C-C-N torsion angle is -54.6 (2)° for each symmetry related chelate ring, giving the ring the λ conformation.
The bridging and terminal C-N bond lengths are not significantly different. The bridging C-N group is linearly bonded to the two copper atoms, with the angles Cu1-C-N and C-N-Cu2 both required to be 180° by symmetry.
This geometry differs from that found in the one-dimensional polymer [Cu(dien)CN] + , (Corfield & Yang, 2012) where both copper atoms are divalent, and the C-N-Cu angle is non-linear at 146.5 (2)°. The Jahn-Teller lengthening of the axial Cu-N distance is greater in the polymer, with Cu-N = 2.340 (3) Å versus 2.127 (4) Å in the present structure.
Two symmetry-unique hydrogen bonds link N-H groups from the eten ligand and nitrogen atoms of terminal cyanide groups from molecules related by translation along the b axis. They are shown in Fig. 3

Synthesis and crystallization
The compound was prepared by dissolution of 56 mmol of copper(I) cyanide, CuCN, in 30 mL of a solution containing 90 mmol of sodium cyanide, NaCN. To this were added 10 mL of a solution containing 71 mmol of N-ethylethylenediamine. Slow evaporation of the deep blue mixture resulted after two days in a yield of 1.87 g of Cu 2 (eten) 2 (CN) 3 in the form of deep blue thin plates that were often several mm long. The yield for this first batch was 18%, based upon copper.

Refinement
In the final refinement cycle, the two NH atoms involved in hydrogen bonding were allowed to refine freely. However, atom H3A on N3, which is not involved in hydrogen bonding, was constrained to an ideal position by using a dummy H3B with zero occupancy factor. This dummy atom has been removed from the final coordinates and geometry tables. N -H distances for the refined H atoms were 0.79 (2) and 0.81 (2)Å, shorter than the 0.90Å constrained N-H distance.  The molecular structure of the title molecule, with ellipsoids at the 50% level. Atoms with the same labels are related by the two-fold axis at 1/2, y, 1/4.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.