Synthetic , Spectral and Thermal Studies of Tin ( IV ) Complexes of 1 , 5-Benzodiazepines

Tin(IV) complexes of 7-substituted 6,7-benzo-1,5-dizepines have been synthesized in absolute alcoholic medium. Elemental analysis indicates that the complexes have 1:2 stoichiometry of the type L2SnCl4, TGA data support this conclusion. Molar conductance values in DMF at 10 M suggest that, these complexes are non-electrolytes. Infrared spectral data shows the involvement of C=N and NH groups in coordination with the metal ion. X-ray diffraction pattern of few representative complexes indicate that, these are having simple cubic crystal structure. The energy of activation and order of reaction are calculated using TGA data of the complexes. All these information support that Sn(IV) in these complexes exhibits coordination number eight.


Introduction
Tin is a toxic metal 1 .The effective antidotes tried to remove toxic metals from human body involves chelating agents 1,2 .Benzodiazepines are well known for their complexing capabalities [3][4][5][6][7] .A few transition metal complexes of 1,4-benzodiazepines have been reported [1][2][3][4] hitherto.We have reported a few transition metal complexes of 1,5benzodiazepines 8,9 (DMBDA).There is no report on the synthesis and characterization of tin IV complexes of benzodiazepines.In this paper we report the synthesis, characterization and thermal studies of Tin(IV) complexes with the following benzodiazepines.

Materials and methods
The chemicals used to prepare the ligands were of reagent grade.Substituted DMBDA were prepared using Thiele and Stimmig method 9 .Tin(IV) chloride from E-Merck was used without further purification.

Preparation of the complexes
To a solution of 0.01 M of the ligand in 25 mL dry ethyl alcohol was added with 0.005 M Tin(IV) chloride with constant stirring.The reaction mixture was stirred for half an hour and the complex separated was filtered, washed with ethyl alcohol and ether and dried over fused calcium chloride.The dried complex was powdered and purified by extracting in Soxhlet thimble using dry ethyl alcohol.

Elemental analysis
Tin(IV) and chloride in the complexes were estimated gravimetrically 10 .The nitrogen was determined by Dumas method 10 .

Physical measurements
The molar conductance measurements at the complexes were made on Elico CL-24 Conductivity Bridge with cell of cell constant 0.1.The infrared spectra of the ligands and their complexes were recorded on a Hitachi 290 spectrophotometer in the region 4000-250 cm -1 .The electronic spectra were taken with a Shimadzu UV-160A spectrophotometer and X-ray diffraction on PW1820 diffractometer with Cu LEF 40KV, 30mA X-ray tube in the'd' value range o 1.5406 -14.7184.

Results and Discussion
The elemental analysis (Table 1) conforms to the formation of 1:2 complexes of the type Cl 4 Sn(DMBDA) 2 .The molar conductance values of the complexes (Table 2) in DMF at 10 -3 M concentration are too low to account for any dissociation.Hence, these complexes are regarded as non-electrolytes in DMF.

IR spectra
Important infrared frequencies of the ligands, complexes and their assignments are set out in Table 3 & 4. In the IR spectra of ligands, a broad band of medium intensity around 3350 cm -1 has been assigned to ν(NH) vibrations in view of the previous reports 11 .A high intensity band at 1580 cm -1 and bands in the 1225-960 and 750-650 cm -1 regions have been assigned to ν(C=N), aromatic inplane and outplane vibrations respectively on analogy with previous assignments [11][12][13][14][15] .In the infrared spectra of complexes the following changes are observed.The band due to ν(NH) shifts and appears in the region 3320-3100 cm -1 as a medium intensity split band.Coordination of -NH group to the metal increases the multiplicity associated with nitrogen and thus results in splitting and shifting of the band 13 .In the present context the NH vibration show a low frequency shift compared with the ligands.The ν(C=N) band appears in the region 1570-1600 cm -1 as high intensity band indicating that, the C=N group is involved in coordination with tin IV through nitrogen.Coordination of these groups to the metal ion leaves the nitrogen atom partially positively charged, resulting in mobolising π electron density associated with C=C consequently affecting the bond order.As a result of this ν(C=C) appears around 1640 cm -1 as a band of varying intensity.
In addition to these changes, we observe medium intensity bands in the region 570-425 cm -1 attributable to ν(Sn-N) vibrations coupled with ν(ligand) vibration.The bands appearing in the region 470-425 cm -1 are regarded as due to ν(Sn-N) vibrations.The medium intensity bands in the region 285-300 cm -1 are assigned to ν(Sn-Cl) vibrations.The assignments made in these regions are purely tentative and based on the previous reports [5][6][7]15 .

Electronic spectra
The electronic spectra were taken in DMF at 10 -3 M concentration.The spectra are characterized by two bands in the region 20,000-33,333 cm -1 and are attributed to π-π transitions 16 .In the spectra of complexes, the ligand bands are replaced by high intensity broad bands.In addition to the usual bands of the ligands, the high intensity band is observed around 29,411 cm -1 and attributed to metal-ligand charge transfer band 16 .Appearance of this band confirms the formation of complexes.

X-ray (powder) diffraction
The powder diffraction of selected complexes have been indexed for simple cubic systems and the observed sin 2 θ, d-values together with h, k, l and 'a' values are set out in Table 5.The values obtained for unit cell parameters a, b and c remain almost constant indicating viz., a = b = c.This is the condition for simple cubic system.

Thermal studies
Thermograms obtained for a few complexes have been recorded and the data are summarized in Table 6.The thermogram for complex Ig shows four breaks.A gradual loss in the weight is observed from 255-325 o C and the loss is about 8.59%.This computes to the loss of two of the four chlorides.The second weight loss is observed from 325-350 o C and the per cent of weight loss is 8.59 which corresponds to the elimination of remaining two chlorides.Further, a steep decrease in the weight of 35.17% in the temperature range of 350-430 o C is attributed to the oxidation of the ligand moiety.After this temperature there is no weight loss, as the formed species is thermally stable.The weight calculations agree well with the formation of SnO 2 .Where, W = weight loss up to time t, Wr = (Wc-W) difference of weight loss between completing of reaction up to time t, E = energy of activation, X = order of reaction and T = absolute temperature.
The dw and Wr for the purpose of plot can be directly determined from thermograms.Intercepts directly gives order of reaction, and using R gas constant, slope can be calculated.The values of order of reaction and energy of activation are shown in Table 5.The high values of energy of activation obtained for these complexes are suggestive of their stability.
On the basis of elemental analysis, spectral and thermal studies the following structure may be assigned to the Cl 4 Sn(DMBDA) 2 :

Table 1 .
Analytical data of complexes

Table 2 .
Molar extinction coefficient data of complexes

Table 3 .
Important infrared frequencies of ligands and their assignments

Table 6 .
Thermo gravimetric data of complexesThe complex Ia lost the weight between 100 o and 235 o C. The weight loss is gradual.In 235 o -350 o C range the complex shows the steep decrease in the weight.This is due to the elimination of two chlorides.The other two chlorides are eliminated between 350-400 o C and the oxidation of the ligand in 400-560 o C with the formation of SnO 2 .The percentage loss of weight is in accordance with the suggested empirical formula of the complexes.The Freeman and Corroll 17 equation has been deployed to evaluate order of reaction and energy of activation from thermograms.