Crystal structure of diaqua(μ2-triethylenetetraminehexaacetato)dizinc tetrahydrate

The reaction of ZnO and triethylenetetraminehexaacetic acid (H6TTHA) in aqueous solution after refluxing yields the binuclear title compound, [Zn2(C18H26N4O12)(H2O)2]·4H2O. There is a centre of symmetry in the [Zn2(H2TTHA)(H2O)2] molecule in the crystalline state. Both ZnII ions are octahedrally surrounded and bound by an N2O3 donor set from the H2TTHA4− anion and a water molecule; the N atoms are cis and the water molecule is trans to an N atom. The Zn⋯Zn separation is 7.562 (1) Å. An intramolecular C—H⋯O interaction is observed and both carboxylate H atoms are disordered over two adjacent sites. In the crystal, the components are linked by O—H⋯O and C—H⋯O hydrogen bonds generating a three-dimensonal network.


S1. Introduction
Triethylenetetraminehexaacetic acid(H 6 TTHA), a multidentate ligand having ten potential coordinating sites (six oxygen atoms and four nitrogen atoms), can play an important role in the self-assembly of chelating metals. It can be employed as a structure-directing agent to form main group metal complexes (Wullens et al., 1996, Thompson et al., 1998, transition-metal complexes (Song et al., 2003, Long et al., 2003, Qian et al., 2013, Carlson et al., 2010, Sethi et al., 2012, lanthanide complexes , Mondry & Starynowicz, 1998) and 3d-4f coordination polymers (Ouyang et al., 2007, Shi et al., 2006. To our knowledge, Zn(II) ions strongly inhibits many protein tyrosine phosphatases (Lu & Zhu, 2014). As part of the ongoing study of metal complexes inhibiting protein tyrosine phosphatases, the aim of us is to synthesize new zinc complexes employing polyamino polycarboxylic acids to form stable and soluble complexes. In this contribution, crystal structure of a binuclear zinc(II) complex of H 2 TTHA is reported.

S2.1. Synthesis and crystallization
All chemicals were of reagent grade, commercially available and used without further purification. A mixture of H 6 TTHA (0.050 g, 0.10 mmol) and ZnO (0.016 g, 0.20 mmol) in 50 mL of deionized water in a flask was refluxed for 6 h. The clear solution was cooled to room temperature and filtered. The colorless filtrate was set aside at room temperature for three weeks.

S2.2. Refinement
Crystal data, data collection and structure refinement details are summarized in bond lengths were idealized to 0.82 Å and they were refined using a riding model, with Uiso(H) = 1.5Ueq(O).

S3. Results and discussion
The molecular structure and the crystal packing are depicted in Figures 1 and 2 et al., 2013).

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.

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