Synthesis and crystal structure of bis(1H-benzo[d][1,2,3]triazole-κN 2){2,2′-[N-(phenylphosphorylmethyl-κO)azanediyl]diacetato-κ3 O,N,O′}cobalt(II)–1H-benzo[d][1,2,3]triazole (1/1)

In the molecule, the CoII cation is N,O,O′,O′′-chelated by a 2,2′-[N-(phenylphosphorylmethyl)azanediyl]diacetate dianion and coordinated by two 1H-benzo[d][1,2,3]triazole molecules in a slight distorted octahedral coordination.


Chemical context
Over the past few decades, many researchers have focused their attention on the preparation of organophosphorus materials because of their biological activities (Miller et al., 2008;Leonova et al., 2010;Sharma & Clearfield, 2000). In particular, aminophosphinic acid ligands as phosphorus analogues of natural amino acids have attracted significant attention because of their strong coordination ability with metals. It has been shown that aminophosphinic acid derivatives can be used as potent and selective inhibitors of many proteolytic enzymes, especially metalloproteases (Latajka et al., 2008;Cates & Li, 1985;Katoh et al., 1996). For the design and preparation of extraordinary enzyme inhibitors with considerable pharmacological activity and low toxicity, it is necessary to understand the metal-binding properties in order to obtain a profound insight into the mechanism of their biological activity.
In addition to their biological activities, aminophosphinic acids are also attracting interest in many areas such as the construction industry, aerospace and electronics for their excellent flame retardancy to polymeric materials (Lin, 2004;Lin et al., 2010;Lu & Hamerton, 2002). Aminophosphinic acid reactive flame retardants also have the advantage of low evolution of toxic gases and smoke in the event of fire, but cannot be used to make polyesters flame retardant because their decomposed temperatures do not match those of the polymers. In the early 80s, many metal salts of dialkylphosphinates were used by Pennwalt to increase the fire safety of polyesters (Sandler, 1979(Sandler, , 1980. Later, researchers from the Clariant company researched in detail the variety of dialkylphosphinates aluminum salts in glass-filled nylons (Kleiner et al., 1998(Kleiner et al., , 1999Weferling et al., 2001). They found ISSN 2056-9890 that the aluminum diethylphosphinate can give a V-0 rating at 15 wt% in plain PBT and commercialized it as Exolit OP 930 (DEPAL), which is also used in thermoset resins (Horold et al., 2002;Campbell et al., 2005). Unfortunately, aluminum diethylphosphinate was prepared at high temperature and pressure. The coordination complexes of aminophosphinic acids and metals that are easily obtained at normal temperature have the elements phosphorus, nitrogen and the metal coexisting in the molecular structure, which may give a significant improvement of flame-retardant efficiency for polyesters. We therefore decided to explore new coordination complexes of aminophosphinic acids and metals as halogenfree flame retardants and as excellent candidates to replace the aluminum diethylphosphinate flame retardant. To the best of our knowledge, neither the title ligand 2,2 0 -({[(phenyl)phosphoryl]methyl}azanediyl)diacetic acid (synthesized by a typical Mannich reaction) nor any complexes based on this ligand have been reported anywhere. We therefore report herein the synthesis and crystal structure of a cobalt(II) complex of this ligand, [Co(C 11 H 12 NO 6 P)(C 6 H 5 N 3 ) 2 ]ÁC 6 H 5 N 3 . Research of its potential applications (especially for use as a flame retardant) of this and analogous complexes is currently being undertaken.

Structural commentary
The molecular structure of the title complex is shown in Fig. 1

Database survey
Aminophosphonates acting as ligands have been widely used in coordination chemistry. Over the past two decades, many studies have been reported that use alkylamino-N,N-bis methylenephosphonates to coordinate with main group metals such as Ca, Ba (Vivani et al., 2006), transition metals such as Cd, Mn, Zn, and Pb (Taddei et al., 2011) and lanthanide metals (Mao et al., 2002) to obtain large numbers of zero-, one-twoand three-dimensional structures. However, the use of 2,2 0 -({[(phenyl)phosphoryl]methyl}azanediyl)diacetic acid as a ligand has not been reported elsewhere. The ligand has three functional groups, carboxyl, imino and organophosphate, and all of them are affected by pH values in solution. One of the Figure 1 The molecular structure of the title compound.  Hydrogen-bond geometry (Å , ). key factors for the ligand used is to adjust the acidity of the reaction solution. Exploiting more analogous ligands and their complexes and developing their potential applications remains a big challenge.

Synthesis and crystallization
Phenylphosphinic acid (1.42 g, 0.01 mol) and iminodiacetic acid (41.33 g, 0.01 mol) were dissolved in hydrochloric acid (6 M, 50 ml) and refluxed for 1 h under a nitrogen atmosphere. 50 ml of formaldehyde in hydrochloric acid (37%) was added dropwise under vigorous stirring, and the temperature was maintained at 378-383 K for 4 h. This solution was then concentrated under reduced pressure and allowed to cool to room temperature. 100 ml of acetone was added, and the white precipitate of 2,2 0 -({[(phenyl)phosphoryl]methyl}azanediyl)diacetic acid was collected by filtration. Colourless crystals of the title compound were obtained as follows: 2.38 g CoCl 2 Á6H 2 O (0.01 mol) and 3.57 g 1H-benzo[d][1,2,3]triazole (0.03 mol) were added to a stirred hydrochloric acid solution (4 M, 40 ml), then 3.24 g of 2,2 0 -({[(phenyl)phosphoryl]meth-yl}azanediyl)diacetic acid (0.01 mol) were added in one portion. The mixture was stirred for 1 h, then filtered and left undisturbed. Single crystals were obtained by slow evaporation of the reaction mixture after several days.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Water H atoms were located in difference-Fourier maps and O-H distances were restrained to 0.82 Å . Other H atoms (CH and CH 2 groups) were positioned geometrically and refined using a riding model with U iso (H) = 1.2U eq (C). The carboxyl H atom was refined as rotating group with U iso (H) = 1.5U eq (O). View in the bc plane of the crystal packing showing hydrogen bonds as green dotted lines.    where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.42 e Å −3 Δρ min = −0.26 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq