Organotin(IV) Derivatives of N-Tolyl-m-methoxybenzohydroxamic Acid: Synthesis and Structural Elucidation

A series of organotin (IV) complexes of the type R2SnL2, where R = phenyl, butyl and methyl and HL = NTolyl-m-methoxybenzohydroxamic acid were synthesized and characterized by physico-chemical (elemental analysis,and electrolytic conductance) and spectral Infrared and (1H , 13C and 119Sn NMR) techniques. Monomer structures forthe complexes, bidentate and octahedral geometry was proposed for the complexes prepared.


Introduction
In the past decades the chemistry of tin compounds has gained considerable importance, both in basic research and in industrial applications. There are many interesting aspects of inorganic and organic tin chemistry discussed in various reviews. Tin (IV) and organotin (IV) compounds, a deceptively simple area of inorganic and metal-organic chemistry, have been receiving more attention due to the important industrial (Tammy and Georges, 2005) and environmental applications. Nitrogen, oxygen, and sulfur donor ligands have been used to enhance the biological activity of organotin derivatives (Mohammad et al., 2004;Jason et al., 2000). Also organotin compounds with such ligands have widely been tested for their possible use in cancer chemotherapy (Shang et al. 2008;Zhou et al. 2005). The coordination chemistry of tin is extensive with various geometries and coordination numbers known for both inorganic and organometallic complexes (Katsoulakou et al. 2008;Baul et al. 2007;Farina et al. 2008). Hydroxamic acids constitute a very important class of chelating agents with versatile biological activity ( Farkas et al. 2002;Wang et al. 2003) In view of the diverse fields of applications of organotin complexes, we have synthesized new ligand N-methylm-nitrobenzohydroxamate (HL) and

Synthesis of N-Tolyl-m-methoxybenzohydroxamic acid
An ether solution of m-metoxybenzoyl chloride (0.01 mole) was added dropwise to a stirred cold ethereal solution of N-Tolylhydroxylamine (0.01 mole) containing sodium hydrogen carbonate (0.01 mole). The precipitate was filtered and washed with cold ethanol. Good quality crystals suitable for X-ray analysis were obtained by recrysallization from ethyl acetate. <Scheme 1>

Preparation of Complexes
Complexes were synthesized by dissolving the free ligand N-Tolyl-m-methoxybenzohydroxamic acid (5 mmol) in hot toluene and adding the organotin (2.5 mmol) to the solution. The solution was refluxed for 6 hours with magnetic stirrer and then cooled and filtered. The filtrate was reduced under vacuum to a small volume and solid was precipitated by the added of petroleum ether (60-80 ºC).

Instrumentation
The percentage compositions of the elements (CHN) for the compounds were determined using an elemental analyzer CHNS Model Fison EA 1108. Molar conductance measurements were made in anhydrous DMF at 25 o C using Inolop-Cond Level 1 WTW, The infrared spectra were recorded as potassium bromide discs using a Perkin-Elmer spectrophotometer GX. The 1 H and 13 C nuclear magnetic resonance spectra were recorded using the JEOL JNM-ECP 400 spectrometer. Electronic UV-Vis spectra were recorded with 1650 PC SHIMADZU Spectrophotometer in the range 200-400 nm. And for ultraviolet using Shimadsu-UV-Vis spectrophotometer UV -2450, DMSO used as solvent. Crystals structures determination were carried out on a Bruker Smart APEX CCD area detector diffractometer equipped with graphite monchromatised Mo-K a ( =0.71073A° radiation in each case. All data collection was carried out at room temperature. The program SMART (Siemens 1996) was used for collecting frames of data, indexing reflections and determination of lattice parameters, SAINT (Siemens 1996) for absorption correction, and SHELXTL (Sheldrick 1997 )

Results and Discussion
The ligand was prepared by the reaction of m-methoxybenzoyl chloride with one mole N-Tolyl -m-hydroxylamine in presence of sodium hydrogen carbonate as a catalyst. The purity of the ligand and its complexes were checked by TLC using silica gel-G as adsorbent. The conductance of these complexes has been recorded in DMF at room temperature in the range 10-19 ohm -1 cm 2 mol -1 , suggesting their non-electrolytic nature. Their physical properties and analytical data are recorded in Table (1). The calculated values were in a good agreement with the experimental values.

Infra-Red Spectroscopy
Solid state infrared spectra of the N-Tolyl-m-methoxybenzohydroxamic acid are recorded in the range 4000-370 cm -1 and the most important bands are presented in the below table studied here. In agreement for diagnostic purpose, the principal infrared absorption bands are those due to -OH, C=O, C-N and N-O stretching vibrations of the hydroxamate group free hydroxamic acids have been shown to exist principally in the keto form. In compound (C=O) group is positioned at 1617cm -1 significantly, below the typical ketonic (C=O) of 1600 cm -1 . The (O-H) band is located at 3251 cm -1 as broad band. The presence of the carbonyl band at lower frequency where together with the broad OH band. In general, the (C-N) and (N-O) bands occur as a sharp peak in the ranges 1429, 953 cm -1 respectively (Shahid et al.2002).
On complexation, there are clear differences between the infrared spectra of the free ligand and the diorganotin(IV) complexes. In all cases, the most important features of the infrared spectra are the absence of the (OH) bands due to the complexation of the metal to the ligand through oxygen of the carbonyl group. This suggests the deprotonation of the hydroxamate group on complex formation, and (C=O) group are shifted to lower frequencies in the range 1624-1691 cm -1 in there respective diorganotin (IV) complexes. The bands for (Sn-C) and (Sn-O) are assigned in the range of (573-445) and (454-443) cm -1 respectively (Saad et al. 2003). The IR data of the complexes are shown in Table (2). The Table lists the stretching frequency ( ) for some of the characteristics groups exhibited by the ligand and complexes. Major bands in the electronic spectra of the ligand and their tin(IV) complexes also are given in Table (2), Figure (1 to  4).

Nuclear Magnetic Spectroscopy
The 1H NMR spectra for all compounds were recorded in [ 2 H 6 ] DMSO using tetramethysilane as the internal standard. The data are compiled in Table (3). The conclusion drawn from 1 HNMR studies of a few compounds lend further support to suggested formation of N-Tolyl-m-methoxybenzohydroxamic acid. Ligand (HL) give a singlet -OH resonance near 10.64 ppm due to hydroxy group. The hydroxy resonances is absent in the spectra of the complexes indicting deprotonation and coordination of Tin to the oxygen. There is a small upfield shift of the aromatic protons resonances of the ligand upon chelation with the diorganotin(IV) moiety. The complexes Ph 2 SnL 2 , Bu 2 SnL 2 and Me 2 SnL 2 Show additional signals. The methyltin (Sn-CH 3 ) accurse at 1.36, 1.34 and 1.32 ppm as on the sharp singlet at integrates for the protons accompanied by satellites due to the 1 H-119 Sn coupling that corresponds to the hydrogen atom of the methyl protons of the Me-Sn for the Me 2 SnL 2 (Najeeb et al. 2009). In dibutyltin(IV) complex the butyl protons appears as a multiple and a triplet in the range1.53-0.70 ppm due -CH 2 CH 2 CH 2 CH 3 group. The aromatic protons in Ph-Sn appears in the 7. 16-8.18 ppm (Shahid et al.2002), Figure (5 to 8).
The 13C NMR of the ligand and its complexes are presented in Table ( ppm. It is most likely that shift is due to the decrease of electron density at carbon atoms when oxygen is bonded to metal ion (Saad et al. 2003), (Figure 9 to 12).
On the basis of the observed spectral evidence, the following structure suggested for the prepared complexes <Scheme 2>

X-ray structural studies of N-tolyl m-methoxybenzohydroxamic acid
The structure contain an C 15 H 15 N O 3 ligand, which is a molecule of 3-methoxybenzoyl chloride bonded with N-Tolyl hydroxylamine. The bond angles which will connect Sn atom with the ligand are: C(7)-N(1)-O2 = 117.43 (16) , O(1)-C(7)-N(1)=120.14(15), respectively, giving the conformation of an octahedral with the oxygen atoms later at the bottom and the tin atom at the top. This coordination sphere is completed by the both oxygen atoms of the ligands and will be cis positions covering the oxygen atoms. The methoxybenzoyl chloride and tolyl hydroxylamine are chelated by carboxyl groups as shown bellow. And other data in table below. <Scheme 3>

Conclusion
The ligand N-Tolyl-m-methoxybenzohydroxamic acid was successfully synthesized. The ligand was treated to different diorganotin(IV) oxide metal to afford the corresponding complexes. It may conclude that the ligand coordinated through oxygen to the Tin atom leading to the formation of five member ring chelate. Octahedral geometry was proposed for the prepared complexes.