1. INTRODUCTION:

In sharp contrast to well documented hydrocarbon and polyhalogenated derivatives of antimony (III) and antimony (V) very few studies have been devoted to corresponding polyhalogenated nitrogen (e.g. tetrachloro and tetrafluoropyridyl) containing hetrocyclic based analogs.

However, the synthesis and reaction of organo-mercury, sulphur, phosphorous, titanium and silicon derivatives containing tetrachloropyridyl and tetrafluoropyridyl are known in the literature^1-5. A few tertiary stibines containing tetrachloropyridyl groups tris (2,3,5,6-tetra chloro-4-pyridyl) stibines, bis (2,3,5,6-tetrachloro-4-pyridyl) stibine and tolyl bis (2,3,5,6 tetrachloropyridyl) stibine and their corresponding dibromide have been synthesized^6,7. In continuation to our work on the synthetic, reactivity and biological aspects of organoantimony derivatives⁸. It may be noted that polyhalopyridyl derivatives of metals and metalloids have assumed importance due to their application in pharmaceuticals and organochemicals⁹. These organometallic derivatives are particularly interesting because of the extreme electronegativity of the organic group¹⁰. In the present communication we wish to report:

(i) Oxidative addition reactions of (C₅Cl₄N)₃Sb with interhalogens, pseudohalogens and halopseudohalogens and elemental sulphur

(ii) Metathetic reactions of (C₅Cl₄N)₃SbCl₂ and (C₅Cl₄N)₃SbIX(X=Cl,Br) with metallic salts to give disubstituted pseudohalide, oximate, amide and carboxylate and halo, pseudohalo derivatives respectively

(iii) Reductive cleavage of (C₅Cl₄N)₃SbS and (C₅Cl₄N)₃SbX₂(X= NCO,Cl) with hexaphenyl di-lead compounds and (iv) action of to (C₅Cl₄N)₃SbCl₂ on (Ph₃Sn)₂S derivatives, respectively.

2. EXPERIMENTAL:

Tris(tetrachloropyridyl) stibine was prepared from tetrachloropyridyl magnesium bromide, (C₅Cl₄N)₃Br and SbCl₃ and was converted to the corresponding dichloride in the reported manner. Hexa phenyldileads and bis (triorganotin)sulphides were synthesized by reported methods. Iodine monochloride was distilled before use Iodine monobromide was prepared and purified by the published method¹¹. Fresh iodine isocyanate¹², iodineazide¹³ and thiocyanogen¹⁴ in approximately known concentration were generated in an approximate solvent by slandered methods. Freshly prepared metallic salt except NaN₃, were dried in vacuo before use. All solvent were purified and dried by slandered procedures and reactions were carried out under anhydrous conditions. All the reactions and subsequent manipulations were carried out in an atmosphere of nitrogen. IR spectra were recorded in the rang 4000-200cm^-1by using KBr pellets on a Perkin-Elmer 557 Spectrophotometer .The molar conductance of 10^-3M solutions was determined at 25°C with a Phillips Conductivity assemblyPR-9500. Molecular weight was determined cryoscopically in benzene using Beckmann thermometer of accuracy of ±0.01°C. Typical experimental details of the reaction are described below. Relevant IR assignments, analytical data and molar conductance value are listed in Tables 1-2.

2.1. OXIDATIVE ADDITION REACTIONS:

2.1.1 Reactions of (C₅Cl₄N)₃Sb with interhalogens, ICl and IBr (I, II):

A solution of Iodine monochloride (0.326g, 2mmol) in acetonitrile (40cm³) was dropwise added to a stirring solution of tris(tetrachloropyridyl) antimony (1.53 g, 2 mmol) in the same solvent (50cm³) at –5^oC during 1 h. The reactants were allowed to attain room temperature and stirred further for 30 minutes to ensure complete reaction. Concentration of this solution followed by the addition of petroleum-ether (60-80^oC) afforded a off-white solid tris(tetrachloropyridyl) antimony(V) iodide, chloride, m. p: 172^oC.

Similarly, 1:1 molar reaction of tris(tetrachloropyridyl) antimony (1.61g, 2mmol) and iodine monobromide (0.41g, 2mmol), yielded tris (tetrachloro-pyridyl)antimony(V) iodide bromide, m. p: 145^oC.

2.1.2 Reaction of (C₅Cl₄N)₃Sb with IN₃ and INCO (III, IV):

A freshly generated solution of iodine azide (0.338g, 2 mmol) in acetonitrile (50cm³) at –10^oC was added to a precooled (–10^oC) vigorously stirring solution of tris(tetrachloropyridyl)antimony (1.53g, 2mmol) in the same solvent (50 cm³) during 15 minutes under nitrogen atmosphere. The reactants were stirred for 1 h at initial temperature and then at room temperature. The solution was evaporated under reduced pressure and cooled overnight, after adding petroleum-ether (40-60^oC) (10 cm³). A brownish yellow solid of tris(tetrachloropyridyl)antimony azide iodide was obtained, (III)m.p.:280^oC.

Similarly, (C₅Cl₄N)₃SbINCO(IV) was obtained as a white solid by the method described above by employing on equimolar ratio of the corresponding reactants, m. p: 148^oC.

2.1.3 Reaction of (C₅Cl₄N)₃Sb with Sulphur:

A solution of tris(tetrachloropyridyl)antimony (1.53 g, 2 mmol) in acetonitrile (50cm³) was refluxed with elemental sulphur (0.064g, 2mmol) for one hour under nitrogen atmosphere. The solution was concentrated and cooled overnight to afford off white crystalline solid. It was characterized as tris(tetrachloropyridyl) antimony sulphide, (C₅Cl₄N)₃SbS, m. p: 196^oC

2.1.4 Reaction of (C₅Cl₄N)₃Sb with (SCN)₂:

Tris(tetrachloropyridyl)antimony (1.53g, 2mmol) was taken in CCl₄ (30 cm³) and kept stirring. To this was then added a freshly prepared solution of thiocyanogen (0.24g, 2mmol) in CCl₄ (50 cm³) at –5^oC during 15 minutes. The reaction mixture was subsequently stirred for 1 h and warmed to room temperature. The removal of the solvent under reduced pressure afforded a brownish-yellow solid. After recrystallization from ethanol it was characterized as tris(tetrachloropyridyl)antimony diisothiocyanate, (C₅Cl₄N)₃Sb(NCS)₂,m.p: 235^oC.

2.2. METATHETICAL REACTIONS:

2.2.1Reaction of (C₅Cl₄N)₃SbICl with KNCO and KSCN:

A suspension of potassium cyanate (1g, 1.24mmol) in acetonitrile was added to a solution of tris(tetrachloropyridyl) antimony chloride iodide (0.931 g, 1mmol) in the same solvent (60 cm³) and refluxed for 3-4 h. The mixture was then filtered to remove potassium chloride and unreacted potassium cyanate. The filtrate was concentrated under vacuum to afford white solid, which was recrystallized from petroleum-ether (40-60^oC) and characterized as tris(tetrachloropyridyl) antimony(V) iodine isocyanate, m. p: 148^oC.

The similar procedure as described above was adopted to obtain tris(tetrachloropyridyl)antimony(V) iodide isothiocyanate and tris(tetra-chloropyridyl)antimony bromide isothiocyanate by the reaction of tris(tetrachloropyridyl)antimony iodide bromide with the corresponding potassium thiocyanate, m .p: 165^oC

2.2.2 Reaction of (C₅Cl₄N)₃SbCl₂ with AgSCN and KNCO:

Tris(tetrachloropyridyl)antimony dichloride (1.680 g, 2 mmol) and silver thiocyanate (0.664 g, 4 mmol) were stirred together in benzene (100 cm³) at room temperature for 3 h and then refluxed for 1 h to ensure completion of the reaction. Silver chloride was filtered off and on concentration of the solution under reduced pressure followed by the addition of pet-ether (40-60^oC) yielded off white solid tris(tetrachloropyridyl) antimony(V) dithiocyanate, m. p: 235^oC (d).

A similar reaction of tris(tetrachloropyridyl)antimony dichloride (1.680 g, 2 mmol) and potassium cyanate (0.324 g, 4 mmol) resulted in the formation of tris(tetrachloropyridyl)antimony(V) diisocyanate, m. p: 230^oC (d)

2.2.3 Reaction of (C₅Cl₄N)₃SbCl₂ with NaN₃:

An aqueous solution of sodium azide (0.260 g, 4 mmol) was added to an etheral solution of tris(tetrachloropyridyl)antimony dichloride (1.680 g, 2 mmol) and the mixture was stirred for 3 h at room temperature. The ethereal layer was separated and dried over sodium sulphate. It was then evaporated and cooled to yield off white crystalline solid which was characterized as oxybis [tris(tetrachloropyridyl) antimony] diazide, m.p: 260^oC.

2.3 Preparation of tris(tetrachloropyridyl)antimony disubstituted amide, -oximate and carboxylate derivatives:

In a typical experiment tris(tetrachloropyridyl)antimony dichloride (1.680 g, 1 mmol)and sodium succinimide (0.238g, 2mmol) in benzene (60 cm³), was stirred at room temperature for 3 hr. Sodium chloride was filtered off and the filtrate was concentrated under vacuum followed by the addition of n-hexane(10ml) and on scratching yielded a white solid. It was it was recrystallised from petroleum-ether(40-60^oC) and characterized as tris(tetrachloropyridyl)antimony di succinimide, m.p.225^oC. Compounds oximate and carboxylate were synthesized from tris(tetrachloropyridyl)antimony dichloride and the corresponding sodium salt of oximate or carboxylate in 1:2 molar ratio, respectively under similar condition to those described for the disuccinimide.

2.4 INTERACTIONS OF (C₅CL₄N)₃SBCL₂WITH BIS(TRIORGANOTIN) SULPHIDES:

2.4.1 Reaction of (C₅Cl₄N)₃SbCl₂ with (Bu₃Sn)₂S:

To a stirred ice cold solution of tris(tetrachloropyridyl) antimony dichloride (0.840 g, 1 mmol) in chloroform (50cm³), bis(tributyltin) sulphide (0.610g, 1mmol) in the same solvent (40ml) was added dropwise during half an hour. The reactants were further stirred for 3 h and simultaneously allowed to attain room temperature. The solution was concentrated upto dryness and residue was dissolved in hot petroleum-ether (60-80^oC). The solution was subsequently cooled and filtered. The solid was identified as tris(tetrachloropyridyl)antimony sulphide, m.p: 196^oC. The filtrate was concentrated at reduced pressure to yield tributyl tinchloride, characterized as tributyl tin fluoride (m p: 242^oC while reported (30) 244^oC).

Under similar condition tris(tetrachloropyridyl)antimony dichloride (0.840g, 1mmol) and bis(triphenyltin) sulphide(0.73g,1mmol) afforded tris(tetrachloropyridyl) antimony sulphide and triphenyl tinchloride (m.p 106°C while reported as (30), m.p. 105-107^oC).

2.5 REDUCTIVE CLEAVAGE REACTION:

2.5.1 Reaction of (C₅Cl₄N)₃SbS with Ar₆Pb_2.(1:1)

To acetonitrile solution (50cm^-3) of tris(tetrachloropyridyl)antimony sulphide (0.652g 1mmol) hexaphenyldilead (0.876g,1mmol) in the same solvent (30 cm^-3) was added and stirred for 3 hr at room temperature. The solution was concentrated and petroleum ether (60-80^oC) was added to precipitate a white crystalline solid characterized as bis(triphenyllead) sulphide, m.p.-140-143^oC,(lit, m.p.139-143^oC). After filtering the precipitate, the filtrate was concentrated and cooled to yield off-white crystals of tris(tetrachloropyridyl)antimony m.p.74^oC.

3.1 RESULT AND DISCUSSION:

3.1.1 Oxidative Addition Reactions:

Interhalogens ICl and IBr on treatment with tris (2,3,5,6 tetra chloropyridyl)antimony at –5^oC in acetonitrile yielded oxidative addition products in the sense of equation shown below:

Similarly, freshly generated solution of IN₃ and INCO in carbon tetrachloride at a temperature of –5^oC add oxidatively to (C₅Cl₄N)₃Sb to give (C₅Cl₄N)₃SbIN₃ and (C₅Cl₄N)₃SbINCO.

Reaction of freshly generated solution of (SCN)₂ in carbon tetrachloride proceeded in the same fashion as that of IN₃ and INCO.

Reaction of IN₃, INCO, (SCN)₂ were carried in dark to retard its polymerization. All the three electrophiles IN₃.INCO and (SCN)₂ are prone to polymerization at room temperature¹⁵.

Elemental sulphur is added to (C₅Cl₄N)₃Sb to give monomeric compound (C₅Cl₄N)₃SbS in refluxing benzene in a dry nitrogen atmosphere.

Similar observation has earlier been made for triaryl-antimony(III) compounds. (C₅Cl₄N)₃SbS could also be obtained by passing H₂S gas to an ammonical solution of (C₅Cl₄N)₃SbCl₂ in alcohol¹⁶.

Both the sulphide derivatives were identified by elemental analysis and superimposible IR spectra and mixed melting point. No lowering of melting point was observed and thus supporting the fact that sulphides derivatives obtained by two different methods are same. The molecular weight of sulphide derivatives determined cryoscopically in benzene indicates that it exists as a monomer.

3.1.2 Metathetical Reactions:

(C₅Cl₄N)₃SbCl₂ forms an important source for obtaining various disubstituted tris(tetrachloropyridyl)antimony(V) derivatives. Thus the treatment with the corresponding sodium or silver salts in benzene under moderate conditions leads to the replacement of both the chloride atoms. The metallic chlorides separate immediately in each case after mixing the reactants.

(C₅Cl₄N)₃SbCl₂ + 2 MY (C₅Cl₄N)₃SbY₂ + 2 MCl …(8)

M = Ag; Y = NCO, NCS

M = Na; Y = OCOMe₂, ONCMe₂, ONCMePh, NCO(CH₂)CO,

3.1.3 Formation of oxo-bridge compound:

Reaction of aqueous NaN₃ with (C₅Cl₄N)₃SbCl₂ in ether solution, however,yielded binuclear oxo-bridge compound insted of (C₅Cl₄N)₃Sb(N₃)_2.

(C₅Cl₄N)₃SbCl₂ + 2NaN₃ → [(C₅Cl₄N)₃Sb-O- Sb(C₅Cl₄N)₃](N₃)₂ + 2NaCl

Formation of such a binuclear derivative is not surprising since Goel et al¹⁷. Have reported that R₃Sb(N₃)(R=Me,Ph) could only be preprad and isolated in the presence of hydrizoic acid in benzene. One of the most usually employed method for the preparation of organometallic azides involving water/ether system as described above results in the formation of oxo-bridge compound [R₃Sb-O-SbR₃](N₃)₂.

3.1.4 Selective Replacement Reactions:

Equimolar reactions involving mixed halogen compounds (C₅Cl₄N)₃SbIX (X=Cl,Br) and metallic salts in benzene produced mixed iodo-pseudohalo derivatives, through selective replacement of chloride or bromide group by a pseudohalo group. The iodide invariably remains bonded to the antimony irrespective of the nature of the metallic salt used.

(C₅Cl₄N)₃SbICl + NaN₃ (C₅Cl₄N)₃SbI(N₃) + NaCl ... (9)

(C₅Cl₄N)₃SbIBr + KNCO (C₅Cl₄N)₃SbI(NCO) + KBr .(10)

The products (C₅Cl₄N)₃SbIN₃ and (C₅Cl₄N)₃SbINCO obtained through exclusive replacement of halo groups are similar to those obtained by the oxidative addition method mentioned above and had similar melting point and super imposable IR spectra.

4. REDUCTIVE CLEAVAGE REACTIONS:

4.1 Reaction of (C₅Cl₄N)₃SbX₂ (X=Cl, NCO) with Ar₆Pb₂

Exploratory work reveals that hgher valent metallic halides, viz. Cu(II), Hg(II), and Fe(III) cleve the Pb-Pb bond in hexaorganodilead compounds while themselves getting reduced to the lower oxidation state. It was therefore, considered worthwhile to study the reactions of tris(tetrachloropyridyl)antimony dichloride and diisocyanate against Pb-Pb bond. The former are readily reduced to (C₅Cl₄N)₃Sb in the sense of equation shown below

Ar₆Pb₂+ (C₅Cl₄N)₃SbX₂→ Ar₄Pb+Ar₂PbX₂+ (C₅Cl₄N)₃Sb

Ar = Phenyl, p-tolyl X= Cl, NCO

It is well established that higher valent metallic halides, viz. Cu(II), Hg(II) and Fe(III) cleave the Pb-Pb bond in hexaorganodi-lead compounds while themselves getting reduced to the lower oxidation state. It was therefore, considered worthwhile to study the reactions of (C₅Cl₄N)₃SbCl₂ and (C₅Cl₄N)₃Sb(NCS)₂ against Pb-Pb bond. (C₅Cl₄N)₃SbX₂ (X = Cl, NCS) are readily reduced to (C₅Cl₄N)₃Sb.

Ph₆Pb₂ + (C₅Cl₄N)₃Sb → Ph₄Pb + Ph₂PbX₂ + (C₅Cl₄N)₃Sb (11)

The reaction appears to involve the cleavage of Pb-Pb bond and Pb-C bond in hexaaryldilead yielding stable Ph₄Pb and unstable Ph₂Pb which further reduces the (C₅Cl₄N)₃SbCl₂ to (C₅Cl₄N)₃Sb.

Ph₆Pb₂ Ph₄Pb + Ph₂Pb … (12)

Ph₂Pb + (C₅Cl₄N)₃SbX₂ (C₅Cl₄N)₃Sb + Ph₂PbX₂ … (13)

4.2 Reaction of (C₅Cl₄N)₃SbS with Ph₆Pb₂:

It has been reported by Okawara et al.^18,19 that the Sb-S bond in triorganoantimony sulphides is semipolar in nature, which facilitates the resonance hybride of sulphides in the ground state due to which triorganoantimony(V) sulphides are more reactive.

R₃Sb⁺ ------ S^– → R₃Sb=S (14)

It is, therefore, not surprising that on reaction of (C₅Cl₄N)₃SbS with hexaaryldileads insertion of sulphur into Pb-Pb bond take place.

(C₅Cl₄N)₃SbS + Ph₆Pb₂ (C₅Cl₄N)₃Sb + (Ph₃Pb)₂S (15)

The reaction seems to proceed through initial rupture of Pb-Pb bond followed by the insertion of sulphur which may be attributed to the enhanced semipolar nature of Sb-S bond in (C₅Cl₄N)₃SbS, which facilitates the hemolytic fission of Pb-Pb bond²⁰. In the process (C₅Cl₄N)₃SbS is reduced to (C₅Cl₄N)₃Sb(III) similar results have been observed for the reaction of triorganoantimony with hexaarylditins.

It can thus be concluded that the reactions of hexaaryldileads with (C₅Cl₄N)₃SbX₂ or (C₅Cl₄N)₃SbS proceeds via two different pathways depending upon the nature of the anion attached to antimony atom. In the case of sulphide derivative cleavage of the Pb-Pb bond is favoured while in the other cases (X= NCS, Cl) dissociation of hexaaryldileads to Ph₄Pb and Ph₂Pb occurred. Both these reactions thus lend support to an earlier held view that the reaction hexaorganodileads with different reagents differed mechanistically.

4.3 Action of (C₅Cl₄N)₃SbCl₂ on bis(triorganotin) sulphides:

(Ph₃Sn)₂S were found to react with (C₅Cl₄N)₃SbCl₂ in 1:1 molar ratio resulting in the complete exchange of anionic groups.

(Ph₃Sn)₂S + (C₅Cl₄N)₃SbCl₂ 2Ph₃SnCl + (C₅Cl₄N)₃SbS (16)

The separation of the products does not pose much difficulty due to the difference of solubility in organic solvent. The reactions seem to proceed via a four centered cyclic transition state involving sulphur atom as shown below:

An analogous mechanism has been proposed for the reaction of (Ph₃Sn)₂O and HgCl₂²¹. The molar conductance value of 10^-3M solution in acetonitrile of the newly synthesized tris(tetrachloropyridyl)antimony (V) compounds range between 13-35 mol^-1cm² which indicates there non-conducting nature. The value of compound (I-IV) contains a hailed atom is almost of the same order and highest than the rest of compounds but do not suggests conducting behavior. The observed molecular weight data of the compounds in freezing benzene were found comparable with those of theoretical value which suggest that these compounds exist as monomer. The newly synthesized compounds are stable at room temperature and soluble in organic solvents viz. acetonitrile, chloroform and benzene etc.

5 IR SPECTROSCOPY:

The n_asym NCS mode appears as a broad band of strong intensity at 2075+35 cm^-1 which is closer to the iso form that to the normal thiocyanate. It has been reported that the intensity of n_asym NCS mode is 50 to 100 times stronger than that of n_asym SCN and the shape is broad for the former and sharp in the latter case. The position, intensity and the shape of nNCS thus suggest an iso-structure to these compounds.

The n_sym NCS mode which is virtually nC-S mode according to the established views lies at distinctly higher frequency in the isothiocyanates. 760-880 cm^-1 and is a deciding factor about the nature of pseudohalide in these compounds. Thus, the appearance of a medium intensity band at 840+10 cm^-1 in all derivatives suggest an iso-structure. Further, the appearance of a band at 465+5 cm^-1 is suggestive of the presence of Sb-N bonding.

5.1 Amide, Oxime and Carboxylate Derivatives:

Tris(tetrachloropyridyl) antimony disuccinimide exhibit a strong band at 1700 cm^-1 assignable to "ester like" CO group, the symmetric stretching mode appears at 1232 cm^-1. Pattern and position of the bonds are comparable with those of reported triarylantimony diamides²². The separation (375 cm^-1) between the asymmetric and symmetric (OCO) stretching frequencies for tris(tetrachlorophenyl)antimony di(p-nitrobenzoate) which occur at 1680 cm^-1 and 1305 cm^-1, respectively, in the solid state suggest the presence of a monodentate "ester like" carboxylate group with a penta-coordinate structure about the antimony atom. In polar solvent like chloroform the 1680 cm^-1 band is shifted to 1675 cm^-1 but the symmetric (O=C=O) stretching frequency remains unchanged and thus carboxylate group retains its undentate character in solution as well. The non-conducting and monomeric nature and the absence of carboxylate ion in the IR spectra further rules out the possibility of an ionic structure.

The infrared spectra of o-tris(tetrachloropyridyl) antimony dioximate do not exhibit any band in the region 3000-3380 cm^-1, assignable to the intramolecularly hydrogen bonded OH in free oximes²³. The C=N vibrations ca 1636+5 cm^-1 appear as medium band and is lowered by about ca 40 cm^-1 as compared to free oximes (~1668 cm^-1). The lowering of the n C=N vibration may be attributed to the stabilization of the C=N bond by resonance with the non-bonding electron pair on oxygen atom of the imino group. However, this type of lowering may be related to mass effect as has been observed earlier in case of group 14 elements ²⁴.

The appearance of a medium band in the region 912-927 cm^-1 can be attributed to a N–O stretching vibration ²⁵ while the Sb–O stretching frequencies in the corresponding organoantimony oximate derivatives^26-28.

Thus on the basis of IR spectroscopic evidences coupled with their monomeric and non-conducting nature and in accordance with the structures of other organoantimony(V) compounds the newly synthesized disubstituted derivatives can reasonably be assigned a trigonal bipyramidal (TBP) structure with the anionic groups at the axial positions and (C₅Cl₆N) groups occupying the equatorial positions.

5.2 Azido Derivatives:

The IR spectra of azido derivatives exhibit three fundamental bands in the region. The band around 2165-2200 cm^-1, assignable to n_asym N=N⁺=N^– mode, is the strongest and the only one in the triple bond region above 1270+10 cm^-1. A second band of weak intensity is located at 710 cm^-1and is assigned to n_symN=N⁺=N^–. The N=N⁺=N^– bending mode (d) has been identified at 2165-2200 cm^-1. The spectral data thus suggest the presence of a covalently bonded linear N=N=N in the azido derivatives.

5.3¹H NMR Spectra:

The ¹H NMR spectrum of compound 6 and 7 was recorded in CDCl₃ at room temperature using TMJ as internal reference. The appearance of a singlet at d 2.68 ppm is due to the CH₂–CH₂ group. Similarly, the compound (C₅Cl₄N)₃SbN (CCH₃)NCH.CH showed a singlet at d 2.4 ppm due to Me proton and a singlet at d 2.22 ppm due to a CH proton.

5.4¹³C NMR Spectra:

On the basis of reported ¹³C spectra of pentachloropyridine by Iddon et al.²⁹ three chemical shifts are observed for (C₅Cl₄N)₃Sb, (C₅Cl₄N)₃SbCl₂ and (C₅Cl₄N)₃Sb(N₃)₂ atoms of the chloropyridine ring. In pentachloro pyridine the ¹³C chemical shifts are observed at 146.2 (C₂ and C₆), 144.7 (C₄) and 129.7 (C₃ and C₅). In (C₅Cl₄N)₃Sb the most affected carbon atom of tetrachloropyridyl is C₄ which is directly attached to antimony and the other carbon atoms will be very slightly affected. Thus, the signal 146.8 in (C₅Cl₄N)₃Sb may be assigned to C₄, the signal at 145.9 may be assigned to C₂ and C₆ and the signal at 131.4 may be assigned to C₃ and C₅.

6. UV SPECTRA:

The UV visible spectra of (C₅Cl₄N)₃Sb and (C₅Cl₄N)₃SbCl₂ on (C₅Cl₄N)₃Sb(N₃)₂ show absorption maximum in the range 285-298 nm. These bands can be assigned to p-p* transition and are red shifted compared with Ph₃Sb. Similar observations have been reported in case of phosphorus derivatives (p-p*; 260 nm) is red shifted to 317 nm in (C₅Cl₄N)₃P. The N-heterocyclic molecules contain non-bonded electron pairs in addition to p-electrons giving rise to n-p* transition. However, no other transition was observed in these compounds.

Table 1: Analytical Data of Tris(tetrachloropyridyl) antimony(V) derivatives

S. No.	Compound	Empirical Formula	M.P.(^oC) (Colour)	Yield (%)	Analysis Found (Calcd.)
S. No.	Compound	Empirical Formula	M.P.(^oC) (Colour)	Yield (%)	C%	H%	N%
I		C₁₅Cl₁₃N₃ISb	172 (Off white)	62	19.34 (19.36)	–	4.51(4.55)
II		C₁₅BrCl₁₂IN₃Sb	145 (Brownish yellow)	65	18.46 (18.50)	–	4.30(4.35)
III		C₁₅Cl₁₂IN₆Sb	280 (d) (Brownish yellow)	58	19.20(19.26)	–	8.96(9.00)
IV		C₁₆Cl₁₂IN₄OSb	148(White)	68	20.40(20.50)	–	5.97(6.00)
V		C₁₆Cl₁₂IN₄SSb	190(off white)	65	20.14(20.18)	–	5.87(5.89)
VI	(C₅Cl₄N)₃Sb(NCS)₂	C₁₇Cl₁₂N₅S₂Sb	235 (d) (Brownish yellow)	74	23.06(23.07)	–	7.91(7.95)
VII	(C₅Cl₄N)₃Sb(NCO)₂	C₁₇H₁₂N₅O₂Sb	230 (d)(White)	60	23.93(23.94)	–	8.21(8.23)
VIII	[(C₅Cl₄N)₃Sb-O- Sb(C₅Cl₄N)₃](N₃)₂	C₃₀Cl₂₄N₁₂O.Sb₂	260 (d)(White)	70	21.99(22.01)	–	10.26(10.29)
IX		C₂₃H₈Cl₁₂N₅O₄Sb	225(white)	60	28.61(28.64)	0.84(0.86)	7.25(7.26)
X		C₂₁H₁₂Cl₁₂N₅O₂Sb	180(White)	65	27.61(27.63)	1.32(1.33)	7.67(7.68)
XI		C₃₁H₁₆Cl₁₂N₅O₂Sb	198 (Yellow)	53	35.88(35.89)	1.55(1.57)	6.75(6.77)
XII	(C₅Cl₄N)₃Sb(OOCC₆H₄NO₂-m)₂	C₂₉H₈Cl₁₂N₅O₈.Sb	190(Off white)	80	31.62(31.69)	0.73(0.76)	6.36(6.39)
XIII	(C₅Cl₄N)₃Sb(OOCC₆H₄Cl-o)₂	C₂₉H₈Cl₁₄N₃O₄.Sb	119(White)	72	32.24(32.30)	0.75(0.78)	3.89(3.90)
XIV	(C₅Cl₄N)₃Sb(OOCC₆H₄NH₂-p)₂	C₂₉H₁₂Cl₁₂N₅O₄Sb	148 (White)	78	33.44(33.46)	1.16(1.18)	6.72(6.75)
XV	(C₅Cl₄N)₃SbS	C₁₅Cl₁₂N₃S.Sb	196(Off white)	54	22.48(22.50)	–	5.24(5.30)

Table2: Characteristic Infrared absorption frequencies of tris(tetrachloropyridyl)antimony(V) derivatives

Compound Number									Assignments
III	IV	V	VII	VIII	IX	X	XII	XII	Assignments
–	2160 mbr	2055 mbr	2055 mbr	2160 mbr	–	–	–	–	n_asy (NCX)
1275 m	–	–	–	c	–	–	–	–	n_sym (C–X)
665 w	608 m	–	475 m	625 w	–	–	–	–	d (N₃/NCX)
–	–	–	–	–	1700 s	–	–	1680 m 1675 m^b	n_asym (CO/OCO)
–	–	–	–	–	1232 m	–	–	1305 m^b 1302 m	n_sym (CO/OCO)
–	–	–	–	–	–	1632 m^b	1636 m^a	–	n (C=N)
–	–	–	–	–	–	912 m	925 m	–	n (N–O)
–	–	–	–	–	–	480 w	480 w	–	n (Sb–O)
–	372 sh 368 m^a	–	–	–	415 w	–	–	–	n (Sb–N)
–	–	–	–	–	–	2920 m	2925 m	–	n (C–H)

a = overlapped by (C₅Cl₄N) absorption; b = In CHCl₃ solution; c = absent; w = weak; m = medium; br = broad; s = strong; sh = shoulder; vw = very weak

7. CONFLICT OF INTEREST:

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8. ACKNOWLEDGMENTS:

The author are thankful to the Head Department of Chemistry, University of Lucknow, Lucknow for providing the necessary Laboratory facilities, the Director Central Drugs Research Institute, Lucknow for obtaining IR, NMR, spectra .

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Received on 31.03.2021 Modified on 06.07.2022

Asian J. Research Chem. 2023; 16(2):109-117.

DOI: 10.52711/0974-4150.2023.00018