Bis(μ2-4-amino-3-nitrobenzoato)bis(4-amino-3-nitrobenzoato)octabutyldi-μ3-oxido-tetratin(IV)

The tetranuclear molecules of the title compound, [Sn4(C4H9)8(C7H5N2O4)4O2], reside on a crystallographic inversion center. Both the two independent Sn atoms are five-coordinate, with distorted trigonal–bipyramidal geometries. One Sn atom is coordinated by two O atoms of the carboxylate anions, one bridging O atom and two butyl groups and the other Sn atom is coordinated by an O atom of the carboxylate anion, two bridging O atoms and two butyl groups. All the butyl groups are equatorial with respect to the SnO3 trigonal plane. The molecular structure is stabilized by intramolecular N—H⋯O hydrogen bonds. In the crystal, pairs of intermolecular bifurcated acceptor N—H⋯O and C—H⋯O hydrogen bonds link the molecules into chains along [10]. Weak intermolecular C—H⋯π and π–π interactions [centroid–centroid distance = 3.713 (2) Å] are also observed.

The tetranuclear molecules of the title compound, [Sn 4 (C 4 H 9 ) 8 (C 7 H 5 N 2 O 4 ) 4 O 2 ], reside on a crystallographic inversion center. Both the two independent Sn atoms are five-coordinate, with distorted trigonal-bipyramidal geometries. One Sn atom is coordinated by two O atoms of the carboxylate anions, one bridging O atom and two butyl groups and the other Sn atom is coordinated by an O atom of the carboxylate anion, two bridging O atoms and two butyl groups. All the butyl groups are equatorial with respect to the SnO 3 trigonal plane. The molecular structure is stabilized by intramolecular N-HÁ Á ÁO hydrogen bonds. In the crystal, pairs of intermolecular bifurcated acceptor N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds link the molecules into chains along [101]. Weak intermolecular C-HÁ Á Á andinteractions [centroid-centroid distance = 3.713 (2) Å ] are also observed.

Comment
In general, there are many well-documented structures on complexes isolated from 1:1 molar ratio reaction between diorganotin(IV) with the respective organic acids (Khoo & Hazell, 1999;Parvez et al., 2004;Li et al., 2006;Win et al., 2008a,b). This dimeric structure is known as organodistannoxane dimer with the core geometry consisting of a centrosymmetric planar Sn 2 O 2 group (Win et al., 2008a,b). The centrosymmetric planar Sn 2 O 2 group is bonded to the exo-and endocyclic tin(IV) atom moiety via the bridging oxygen atoms so that the oxygen atoms are tri-coordinated (Khoo & Hazell, 1999;Parvez et al., 2004;Li et al., 2006). In this study, the crystal structure of the title complex is similar to bis(2,3dibromopropionato)tetrabutyldistannoxane(IV) dimer and consists of a centrosymmetric planar Sn 2 O 2 group (Win et al., 2008b). The only exception is 4-amino-3-nitrobenzoic acid is utilized in the reaction to obtain the title complex.
The asymmetric unit of the title complex ( Fig. 1) lies on a crystallographic inversion center and comprises of one-half molecule, with the other half of the molecule is generated by symmetry code -x, -y+1, -z. The Sn1 atom is five-coordinated by two butyl groups in equatorial position, an O atom of the monodentate carboxylate anion, an O atom of the bridging carboxylate atom and one bridging O atom in a distorted trigonal bipiramidal geometry. The Sn2 atom also has a distorted trigonal bipiramidal geometry, being coordinated by two butyl groups in equatorial position, one bridging carboxylate O atom and two bridging O atoms. Intramolecular N1-H2N1···O1 and N3-H2N3···O5 hydrogen bonds (Table 1) form two different six-membered rings, generating S(6) ring motifs (Bernstein et al., 1995) which help to stabilize the molecular structure. All geometric parameters are consistent to those observed in closely related structures (Khoo & Hazell, 1999;Parvez et al., 2004;Li et al., 2006;Win et al., 2008b).

Experimental
The title complex was obtained by heating under reflux in a 1:1 molar mixture of dibutyltin(IV) oxide (0.50 g, 2 mmol) and 4-amino-3-nitrobenzoic acid (0.36 g, 2 mmol) in methanol (50 ml The amino group H atoms were located from the difference Fourier map and constrained to ride with the parent atom with U iso = 1.2 U eq (N). All other H atoms were placed in their calculated positions, with C-H = 0.93 -0.97 Å, and refined using a riding model with U iso = 1.2 or 1.5 U eq (C). The rotating group model was used for the methyl groups. The highest residual electron density peak and the deepest hole were located at 0.72 Å from atom Sn1.  Bis(µ 2 -4-amino-3-nitrobenzoato)bis(4-amino-3-nitrobenzoato)octabutyldi-µ 3 -oxido-tetratin(IV) Crystal data [Sn 4 (C 4

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1)K.
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.
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 > 2sigma(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