Synthesis, Characterization, and Crystal Structure of a Diorganotin(IV) Complex with 2-Oxo-2-Phenylacetic Acid 4-Hydroxybenzohydrazone

The complex dibutyltin 2-oxo-2-phenylacetic acid 4-hydroxybenzohydrazone has been synthesized and characterized by elemental analysis, IR, 1H and 13C NMR, and X-ray single-crystal diffraction studies. The crystal structure belongs to triclinic, space group P-1 with a = 9.3220 (10) Å, b = 9.8779 (11) Å, c = 15.9401 (17) Å, β = 97.0930 (10)°, Z = 2, V = 1427.6(3) Å3, Dc = 1.413 mg/cm3, μ = 0.936 mm−1, F(000) = 628, R = 0.1158, and wR = 0.2522. X-ray analysis indicates that O(2), N(2), O(4), and O(4)#1 from the ligand and O(5) from ethanol molecule are in the equatorial positions; the axial positions are occupied by two n-butyl groups. It shows a distorted pentagonal bipyramid configuration with seven-coordination for central tin atom. Fascinatingly, the supramolecular infrastructures are observed, which exist as two-dimensional sheets assembled from the organometallic subunits through intermolecular and intramolecular O–H⋯X or C–H⋯X (X = O or N) hydrogen bonds.


Introduction
Organotin complexes have attracted more and more attention in recent years, partly owing to their determinately or potentially pharmic value, which have been reported many times before [1], and also for the versatile molecular structure and supramolecular architecture exhibited by these complexes [2][3][4]. Among these, Schiff base organotin complexes have received much attention, as such ligands and their metal complexes are reported to exhibit bactericidal and antitumor activities [5,6]. The coordination chemistry of tin is extensive with various geometries and coordination numbers known for both inorganic and organometallic complexes [7]. Especially, organotin complexes react with the ligands with nitrogen atoms, yielding products characterized by Sn-N bonds [8]. Studies of Schiff base organotin complexes containing carboxylate ligands with additional donor atoms (e.g., N, O or S), which are available for coordinating to tin atom, have revealed that new structural types may lead to different activities [9]. In our previous work, we have reported several novel molecular structures of organotin complexes with Schiff bases containing carboxylate [10][11][12][13][14].
As an extension of studies of organotin complexes with Schiff base, we synthesized a new diorganotin complex of 2-oxo-2phenylacetic acid 4-hydroxybenzohydrazone by the reaction of di-n-butyltin dichloride and ligand in 1 : 1 stoichiometry. The synthesis, structure, and spectra characterizations of the complex are reported herein. X-ray diffraction shows that the central tin atom is seven-coordinate by the two n-butyl carbon atoms, the imino nitrogen atom, and four oxygen atoms from ethanol and the ligand. The supramolecular infrastructures are observed, which exist as two-dimensional sheets assembled from the organometallic subunits through intermolecular and intramolecular O-H· · · X or C-H· · · X (X = O or N) hydrogen bonds.

Materials and Physical
Measurements. Di-n-butyltin chloride, 4-hydroxybenzohydrazide, and 2-oxo-2-phenylacetic acid were commercially available and used without further purification. All the solvents used in the reaction were of AR grade and dried using standard literature procedures. The melting points were obtained with Kofler micromelting point  [15,16]. All of the nonhydrogen atoms were located with successive difference Fourier syntheses. The structure was refined by full-matrix least-squares techniques on F 2 using anisotropic thermal parameters for all nonhydrogen atoms. The hydrogen atoms were added according to theoretical models. The final full-matrix least-squares refinement converged at R = 0.1158 and ωR = 0.
03, (Δρ) max = 1.45, (Δρ) min = −1.92e/Å 3 , and (Δ/σ) max = 0.007. The molecular structure and two-dimensional sheets of the title complex are shown in Figures 1 and 2, respectively. The crystal data and structure refinement are listed in Table 1. The selected bond lengths and bond angles are listed in Table 2. The hydrogen bond lengths and bond angles are listed in Table 3.  absorption values also support this. The absence of the N-H and C=O stretching vibration bands is consistent with the deprotonation of the CO-NH groups and coordination to the organotin(IV) ions in the enol form. And the characteristic absorption at 1608 cm −1 indicates the presence of C=N-N=C group [17], thus indicating the ligand coordinate to the tin centre in an enolic form, which is in accordance with the X-ray structure analysis and their corresponding reaction mechanism. The 1 H NMR spectrum of the complex shows that those signals of -OH and -CONH protons in the spectrum of the ligand are absent, thus indicating the removal of those protons and the formation of Sn-O bonds. The 13 C NMR spectrum of the complex shows that the chemical shift of the carboxylate carbon shifts to a lower field region in almost all the organotin(IV) derivatives indicating participation of the carboxyl (COO) group in coordination to tin atom [18]. On the basis, we can conclude that the tin atom of complex in solution is seven-coodinated, and this can be confirmed by the X-ray crystal structures.

Description of the Crystal Structure.
The crystal and unit cell structures are given in Figures 1 and 2, respectively.  (1)   As illustrated in Figure 1, the environment of Sn(1) is in a distorted pentagon bipyramid with a nitrogen atom, four oxygen atoms, and two n-butyl groups (C(20)-Sn(1)-C(16) = 161.8(7) • , which is deviated from linear angle 180 • ). It is a centrosymmetric arrangement leading to a Sn 2 O 2 core connected by the Sn-O bond, and the Sn(1)-O(4)#1 bond distance is 2.805(11)Å, is greater than the sum of the covalent radii of Sn and O (2.56Å), but is considerably less than the sum of the Van der Waals radii Sn-O (3.68Å), indicating the weak bonding interaction between Sn(1) and O(1)#1. The Sn(1)-N(2) distance is 2.258(12)Å, which is greater and longer than the sum of the covalent radii of Sn and N (2.15Å) but is considerably less than the sum of the Van der Waals radii (3.75Å) and should be considered as bonding interactions [19]. It is noteworthy that the solvent molecule-ethanol involved in the coordination. Fascinatingly, the supramolecular infrastructures were observed in the complex, which exist as two-dimensional sheets assembled from the organometallic subunits through intermolecular and intramolecular O-H· · · X or C-H· · · X (X = O or N) hydrogen bonds.