The azide-bridged mixed-valent cobalt(II,III) compound [(CH3)3NH]2[CoIICo2 III(N3)10]

The crystal structure of the title compound, poly[bis(trimethylammonium) hexa-μ1,1-azido-tetraazidotricobaltate(II,III)], [(CH3)3NH]2[CoIICoIII 2(N3)10], consists of anionic chains [CoIICoIII 2(N3)10]2− extending parallel to the c axis and [(CH3)3NH]+ counter-cations situated between the chains. In the anionic chain, one tetrahedrally coordinated CoII atom (site symmetry 2) and two octahedrally coordinated CoIII atoms are arranged alternately and are linked by μ1,1-azide bridges. The anionic chains and cations are connected via N—H⋯N hydrogen bonding into a three-dimensional structure.


Related literature
For background to transition-metal azido-complexes templated by counter-cations of various sizes, see: Liu et al. (2006Liu et al. ( , 2008. For related cobalt complexes, see: Zhang et al. (2010).

Table 2
Hydrogen-bond geometry (Å , ).  and being an efficient magnetic coupler, the azide anion is a versatile ligand in bridging different transition metals, generating rich and fascinating architectures ranging from discrete polynuclears to extended three-dimensional networks with interesting magnetic properties (antiferromagnetic, ferromagnetic, ferrimagnetic, canted and alternating systems). In fact, remarkable structural variations of azido-bridged complexes have been reported by using various ancillary ligands, with different number of coordination sites and steric hindrance, to control over the dimensions of complexes and bridging modes of the azide anions, thus leading to the control over their magnetic properties. However, only a few metal-azido systems devoid of ancillary ligands have been obtained by varying the size of the coutercations (Liu et al., 2006(Liu et al., , 2008. A small coutercation such as (CH 3  The structure of (I) consists of anionic chains [Co II Co III 2 (N 3 ) 10 ] 2extending parallel to the c-axis. The [(CH 3 ) 3 NH] + countercations are situated between the chains (Fig. 1) (Zhang et al., 2010). The anionic chain and the cations are connected via N-H···N hydrogen bonding between the donating N-H function of the cation and non-bridging azido groups of the anion (Fig 2). 6H 2 O was layered carefully with 3 ml methanol and then with 10 ml methanol solution of 0.20M HCl, 0.20M NaN 3 , and 0.10M trimethylamine. The tube was sealed and kept undisturbed.
Tiny red columnar crystals appeared overnight. Crystallization time of one week produced crystals in a yield of 25% based on the metal salt.

Refinement
Hydrogen atoms were added geometrically and were refined using a riding model, with C-H = 0.98 Å (CH 3 ) and N-H = 0.89 Å.
Figures Fig. 1. The asymmetric unit of the title structure. All non-H atoms are labelled and are shown with displacement ellipsoids at the 30% probability level. H atoms have been omitted.

Special details
Geometry. All e.s. 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 Rfactors(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.