catena-Poly[[bis[4-(dimethylamino)pyridine-κN 1]cobalt(II)]-di-μ-azido-κ4 N 1:N 3]

The title layered polymer, [Co(N3)2(C7H10N2)2]n, contains CoII, azide and 4-(dimethylamino)pyridine (4-DMAP) species with site symmetries m2m, 2 and m, respectively. The Co2+ ion adopts an octahedral coordination geometry in which four N atoms from azide ligands lie in the equatorial plane and two 4-DMAP N atoms occupy the axial positions. The CoII atoms are connected by two bridging azide ligands, resulting in a chain parallel to the c axis.

The title layered polymer, [Co(N 3 ) 2 (C 7 H 10 N 2 ) 2 ] n , contains Co II , azide and 4-(dimethylamino)pyridine (4-DMAP) species with site symmetries m2m, 2 and m, respectively. The Co 2+ ion adopts an octahedral coordination geometry in which four N atoms from azide ligands lie in the equatorial plane and two 4-DMAP N atoms occupy the axial positions. The Co II atoms are connected by two bridging azide ligands, resulting in a chain parallel to the c axis.
Pseudohalide anions are excellent ligands for obtaining discrete, one-dimensional, two-dimensional or threedimensional systems. Among these, the azido ligand is the most versatile in linking divalent metal ions. When the azide group acts as bridging ligand there are two typical coordination modes: end-to-end (EE or µ-1,3) in which the resulting complexes usually shows ferromagnetic behavior, and end-on (EO or µ-1,1) which results in antiferromagnetic behavior.
In the course of our investigation of functional coordination complexes and polymers, a new azide-bridged coordination polymer with 4-dimethylaminopyridine has been prepared and structurally characterized.
Part of the structure of (I) with the atom numbering scheme is shown in Figure 1. The structure consists of layers of cobalt atoms linked by double end-to-end (EE) azido bridges, placed along the [001] direction at b = 0 and b = 1/2, forming a one-dimensional polymeric chain with each cobalt(II) ion in an octahedral environment (Fig. 2). In the crystal, parallel one-dimensional polymers form a three-dimensional network. The minimum interdinuclear Co···Co distance bridged by the EE-azido ligands is 5.097 (2) Å. In this structure, the ligand L displays monodentate binding to Co II .
The octahedral coordination around the cobalt(II) atoms ( Fig. 3, Table 1)  This structure can be compared with that observed for [Cu(L)2(N3)2]n (L: 4-dimethylaminopyridine (Dalai et al., 2002), which shows also double end-to-end (EE) azido bridges. Here each copper is bonded to two nitrogen atoms of the pyridine ligands (1.999 (7) Å, 2.014 (7) Å) and two nitrogen atoms of the azide (2.029 (5) Å). There are also two weak attachments to two nitrogen atoms of the azide (2.611 (6) Å) in axial positions to create a doubl EE-bridged onedimensional polymer with each copper(II) ion in a pseudo-octahedral environment. The distance between two neighboring copper ions is 5.20 (1) Å.

Experimental
A mixture of NaN 3 and CoCl 2 .6H 2 O in methanol was stirred for half an hour, then 4-dimethylaminopyridine was added to the solution and the reaction continued to stir for one hour. After filtration, the pink filtrate was allowed to stand at room temperature. Pink crystals were obtained by slow evaporation.

Refinement
The aromatic H atoms were placed at calculated positions with C-H = 0.93 and 0.96 Å, for aromatic and methyl H atoms, respectively, with U iso (H) = 1.2U eq (C).

catena-Poly[[bis[4-(dimethylamino)pyridine-κN 1 ]cobalt(II)]-di-µ-azido-κ 4 N 1 ,N 3 ]
Crystal data [Co(N 3 ) 2 (C 7 H 10 N 2 ) 2 ] M r = 387.33 Orthorhombic, Cmcm Hall symbol: -C 2c 2 a = 9.622 (5)  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.43 e Å −3 Δρ min = −0.37 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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.