catena-Poly[{μ3-3,3′-[(1,7-dioxa-4,10-diazacyclododecane-4,10-diyl)bis(methylene)]dibenzoato}cobalt(II)]

The title compound, [Co(C24H28N2O6)]n, crystallizes as infinite chains related to one another by inversion centers, giving a centrosymmetric coordination polymer. The CoII ion, situated on a twofold rotation axis, forms a complex with the crown-4 moiety of the 3,3′-[(1,7-dioxa-4,10-diazacyclododecane-4,10-diyl)bis(methylene)]dibenzoate anion. The distorted octahedral coordination sphere of the CoII ion is completed by two carboxylate O atoms from two bridging intra-chain ligands. Metallomacrocyclic rings of 16 atoms are present, with each ring containing two CoII ions and 14 atoms from the bridging ligands. These units repeat as infinite zigzag chains along [101].

The title compound, [Co(C 24 H 28 N 2 O 6 )] n , crystallizes as infinite chains related to one another by inversion centers, giving a centrosymmetric coordination polymer. The Co II ion, situated on a twofold rotation axis, forms a complex with the crown-4 moiety of the 3,3 0 -[(1,7-dioxa-4,10-diazacyclododecane-4,10-diyl)bis(methylene)]dibenzoate anion. The distorted octahedral coordination sphere of the Co II ion is completed by two carboxylate O atoms from two bridging intra-chain ligands. Metallomacrocyclic rings of 16 atoms are present, with each ring containing two Co II ions and 14 atoms from the bridging ligands. These units repeat as infinite zigzag chains along [101].
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: GG2131).

Comment
The title compound is the one of a series of coordination polymers prepared from the anionic ligand LH2, 3,3′-((1,7dioxa-4,10-diazacyclododecane-4,10-diyl)bis(methylene))dibenzoate. This ligand shows unusual adaptability in that it displays two complexation modes on binding to metals. The ligand attaches to the metal via two oxygen and two nitrogen atoms (forming a crown complex). The crown forms four bonds to the metal, while an ideal coordination number for a Co II ion is 6. Thus vacant coordination sites suitable for coordination by the carboxylate groups exist. The carboxylate ions behave as monodentate bridging ligands and the entire ligand is hexadentate. The Co II atom is moved out of the best plane of the crown since this arrangement is better for forming optimal bonds to the ligand. This new compound is novel in that, although the ligands bridge the metal atoms forming one-dimensional chains, the metal atoms are positioned in the center of the organic linker. Topologically, the Co II atoms and the ligands forms nodes in the network rather than the metal atoms only.
The title compound is synthesized from the ligand LH2, 3,3′-((1,7-dioxa-4,10-diazacyclododecane-4,10-diyl)bis-(methylene)) dibenzoic acid. The metal atoms are positioned in the center of the organic linker. The asymmetric unit of the compound contains a Co II ion and a deprotonated ligand L with formula C 24 H 28 N 2 O 6 Co. The Co II ion is 6-coordinate in a distorted octahedral geometry being bound to two N atoms and two O atoms of the crown (1,7-diaza-12-crown-4) and two carboxylic O atoms, one from each of two additional intra-chain ligands ( Figure 1s). The Co1-O1, Co1-O3 and Co1-N1 bond lengths are 1.9886 (16), 2.2399 (16) and 2.2213 (17) Å, respectively. The O1-Co1-O1 angle is 104.15 (9)°. The shortest distance between two neighboring Co II ions along a chain is 9.046 (1) Å. The Co II ion of the Co(crown-4)2+ unit is located on a 2-fold rotation axis. The symmetry independent atoms consist of one half of the ligand with the rotation axis generating the second half of the ligand at the Co atom. Bond circuits consisting of sixteenmembered metallomacrocycle rings can be identified in the structure. Each ring contains two Co II ions and fourteen non-H atoms of the ligand. Each Co II ion is a node for three ligands and two connected macrocycle rings. The pair of benzene moieties within a metallomacrocycle ring are remarkably co-planar (the two rings are in the same plane within experimental error). The dihedral angle between this plane and the plane of the next two nearest phenyl rings along the 1-D chain is 68.79 (5)°. Repetition of these units creates a 1-D polymer network with an infinite number of these rings.

Refinement
Refinement Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2sigma (F2) is used only for calculating R-factors(gt), etc and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F and R-factors based on ALL data will be even larger. Computing details Data collection: APEX2 (Bruker, 2011); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009);program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Figure 1
A view of a portion of one of the chains of (I). Non-H atoms are represented by ellipsoids at the 50% probability level.
Sixteen membered metallomacrocycle rings can be identified from this figure.