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ISSN 2229-5518

Synthesis and Reactivity of Chromium

and Manganese Dibromoacetates and Their Complexes with Organic Bases Jugal Kishore Puri and Rajni Chhoker

AbstractComplexes of composition CrCl(Br2 CHCOO)2 , Cr 3 O(Br2 CHCOO) 6 Cl, [Cr3 O(Br 2 CHCOO)6 (Br 2 CHCOOH)3 Cl], Cr(Br 2 CHCOO)3 , Cr(Br2 CHCOO)3 .Py, Cr(Br 2 CHCOO) 3 .Q, Cr(Br2 CHCOO) 3 (C2 H 5 )3 N, [Cr 3 O(Br 2 CHCOO) 6 (NH 3 ) 3 ]Cl.5NH 3 , Mn(Br2 CHCOO)2 , Mn(Br2 CHCOO)2 .2Py, Mn(Br2 CHCOO)2 .2Q, Mn(Br2 CHCOO)2 .2(C 2 H 5 ) 3 N and (Me4 N)2 Mn(Br 2 CHCOO)4 have been synthesized. All these compounds have been characterized by ele- mental analysis, molar conductance, infra-red, reflectance and thermo-gravimetric studies. These studies indicate the hexa co-ordination of chromium and manganese in these compounds having octahedral geometry and suggest the formation of polymeric structures. Further attempts are in progress to isolate the single crystal of these complexes in order to throw more light on the structure of these complexes from single crystal x-ray studies.

Index TermsChromium and manganese dibromoacetates and their adducts, spectroscopic techniques, TGA studies.

1 INTRODUCTION

—————————— ——————————
N the recent past, we have published few papers on the synthesis of metal bromoacetates and their complexes with bases [1-9]. Now in the present investigation we report the formation of some new Chromium (III) and Manganese (II) dibromoacetates and their complexation with various bases. These resulting dibromoacetates have been characterized by using physico-chemical methods. These new compounds may be having good insecticides properties due to
the presence of bromine.
Compound of composition [Cr 3 (OH)(OOCCH3) 8 ] has been reported [10]. Chromium (III) acetate has been synthesized by react- ing chromium (III) nitrate with acetic anhydride [11] but later studies showed the formation of a trinuclear basic acetate [Cr3(OH) 2(OOCCH3 ).6H2O]+ [12]. Further the trimeric structure for this compound has been proposed on the basis of magnetic and X- ray diffraction studies [13-15]. Adducts of these compounds with ammonia, dimethylsulphoxide and pyridine have been reported [16]. Dubicki and Martin [17] have interpreted the visible spectra of the trinuclear chromium (III) acetate [(Cr3 O)(OOCCH3) 6]Cl in terms of the ligand field theory. Krauss [18] has isolated a compound by re- acting chromium oxide and acetic anhydride and has formulated it as
(loc.cit).

2 MATERIALS AND METHOD

2.1 Preparation of Dibromoacetates of Chromium and Manga- nese
The dibromoacetates Cr(Br2 CHCOO)3 and Mn(Br2CHCOO)2 were prepared from CrCl3 (anhydrous) (4.5 g, 28.40 mmole) and MnCl2 (anhydrous) (1g, 7.94 mmole) and dibromoacetic acid (18.58 g, 85.23 mmole) ; (3.46 g, 15.88 mmole) respectively which were taken in separate round bottomed flask containing 30 ml of carbon tetrachloride and fitted with the condenser and a guard tube. The respective reaction mixtures were then refluxed in an oil bath for 30-
35 hrs. The green coloured product in case of chromium and the buff coloured product obtained in case of manganese were then filtered through sintered glass filtration unit in a dry nitrogen atmosphere under vacuum. The products were washed with anhydrous hot ben- zene to remove any excess of dibromoacetic acid. Finally the prod- ucts were washed with anhydrous dichloromethane and dried under vacuum and analysed (Table I).
The compound corresponds to the composition
Cr2O(OOCCH3) 2.
Compounds of manganese (II) acetate of type
CrCl(Br2CHCOO)2
was prepared by anhydrous chromium(III) chlo-
Mn(OCOH)2.2H2 O, Mn(OOCCH3) 2.4H2O, Mn(OOClF3) 2 and Mn(OOCCl3) 2 have also been reported in literature [19-21]. It has been suggested that complex Mn(OCOCH3) 2.(C 6 H5NHNH2) 2 may have a similar structure.
The adducts Mn(OCOCX3) 2.L4 where X = Cl, L = Pyridine or γ-picoline, Mn(OCOCX3)2L2 and Mn(OCOCX3)2L where L = pyridine-N-oxide or γ-picoline-N-oxide have also been prepared and characterized by infra red, electronic and magnetic studies. All these compounds have been shown to possess octahedral manganese (II)

————————————————

Prof. Jugal Kishore Puri, (Corresponding Author) Centre of Advanced

Studies and Department of Chemistry, Panjab University, Chandigarh

160014, India, Email : prof_ jkpuri@yahoo.com

Rajni Chhoker, Chemistry Department, Mewar University, Chittorgarh,

ride (1.5g, 8.90 mmole) on refluxing with dibromoacetic acid (3.88g,
17.81 mmole) for 8-10 hrs in carbon tetrachloride. The final green coloured product was obtained after washing with carbon tetrachlo- ride and on drying under vacuum.
Solution of excess of dibromoacetic acid in carbon tetrachloride was when added dropwise to chromyl chloride diluted in the same solvent, colour changed from red to green which further on refluxing for nearly 20 hrs. gave the product which was after washing with petroleum ether (40-60o ) and dried under vacuum and analysed was found to correspond to composition [Cr3O(OOCHBr 2COO)6(CHBr 2 COOH)3]Cl (Table I).

2.2 Preparation of adducts of dibromoacetates of Chromium & Manganese with bases

Rajasthan, India, Email : rajni68123@gmail.com

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The addition compounds Cr(Br2 CHCOO)3.Py , Cr(Br2 CHCOO)3.Q , Cr(Br 2CHCOO)3 .(C2 H5 ) 3N , Mn(O2CCHBr2 ) 2.2C5 H5 N , Mn(O2CCHBr 2) 2 .2C9 H7N , Mn(O2CCHBr2 ) 2.2(C2 H5 ) 3 N were prepared by taking Cr(Br2 CHCOO)3 (1.2 g, 1.70 mmole) and Pyridine (0.134 g, 1.70 mmole) ; Cr(Br 2 CHCOO)3 (1.45 g, 2.06 mmole) and Quinoline (0.162 g, 2.06 mmole) ; Cr(Br2CHCOO)3 (1.45 g, 2.06 mmole) and Triethylamine (0.208 g, 2.06 mmole) ; Mn(Br2CHCOO)2 (2g, 4.09 mmole) and Pyridine (0.65 g, 8.18 mmole); Mn(Br2 CHCOO)2 (2g,
4.09 mmole) and quinoline (1.06g, 8.18mmole); Mn(Br2 CHCOO)2
(2g, 4.09 mmole) and Triethylamine (0.208 g, 2.06 mmole) respec-
tively in round bottomed flask separately equipped with calcium
chloride guard tube in each case. The contents were mixed together and stirred for about 10-12 hrs. The corresponding products were washed with anhydrous dichloromethane and dried under nitrogen atmosphere. Their analyses are shown in Table I. The products were slightly hygroscopic and are insoluble in all the conventional organic solvents except are sparingly soluble in dimethyl formamide and acetonitrile.

2.3 Preparation of [Cr3 O(CHBr2 COO)6 ]Cl & adduct

[Cr3 O(CHBr2 COO)6 (NH3 )3 ]Cl.5NH3

When excess of dibromoacetic acid in CCl4 was added to anhy-
drous chromium(III) chloride diluted in the same solvent and kept
under 36 hrs refluxing, a green coloured product was formed. The analytical result corresponds to [Cr 3O(CHBr 2COO)6 ]Cl. Excess of ammonia (10-12 folds) diluted with 20 ml CCl4 was added to a suspension containing known weight (~10mmol) of the anhy- drous trinuclear [Cr3 O(CHBr 2 COO)6]Cl in 25ml CCl4. The content was stirred at room temperature for 4 hrs. Solid formed was filtered under dry nitrogen atmosphere, washed with CCL4 & finally dried in vacuum. Analytical result corresponds to [Cr3O(CHBr2 COO)6(NH3 ) 3 ]Cl.5NH3 (Table I).

2.4 Preparation of (Me4 N)2 [Mn(O2 CCHBr2 )4

In a typical preparation, manganese chloride, MnCl2.4H2O (1.98g,
10.00 mmol) and tetramethyl ammonium chloride (2.19g, 20.00
mmol) in 1:2 molar ratio were separately dissolved in absolute etha- nol. On mixing the two solutions, a light green solid of composition (Me4N) 2 [MnCl4] was precipitated which was filtered and dried un- der vacuum. The analysis and yield confirmed the formation of Bis(tetramethylammonium) tetrachloromanganese(II) i.e; (Me4N) 2 [MnCl4] (Yield- 78% ; Manganese- Observed 15.72%, Calculated 15.94% ; Chlorine- Observed 40.90%, Calculated
41.16%).
Bis(tetramethylammonium)trtrabromoacetatomanganese(II) was prepared by mixing Bis(tetramethylammonium) tetrachloromanga- nese(II) (1.03g, 2.98mmol) with silver dibromoacetate (3.88g,
11.94mmol) in nitromethane in stochiometric amounts. Silver chlo-
ride formed after stirring for 5 hrs was filtered under dry nitrogen atmosphere. Filterate was evaporated to dryness which gave a light green product with yield of 85%.

3 RESULTS AND DISCUSSION

In the present studies we have explored the possibility of the synthetic reactions and the formation of some new dibromoace- tates of Chromium and Manganese from the reaction of anhydrous metal chlorides in dibromoacetic acid.

3.1.1 Chemistry of Chromium with dibromacetic acid

Chromium(III) chloride undergoes substitution reaction

when reacts with excess of dibromoacetic acid in carbon tetrachlo- ride as solvent at room temperature with the steady evolution of HCl gas. On refluxing at a moderate temperature solvolysed products of composition [Cr 3O(CHBr 2 COO)6]Cl is obtained (Table-I). Our ana- lytical data clearly indicates that chlorine in CrCl3 is not completely solvolysed at moderate temperature, even on further refluxing this resulting compound with fresh dibromoacetic acid. The product still contain chlorine and agrees with the composition of starting dibro- moacetate. Such type of analogous compound containing trinuclear chromium(III) acetates are already known in literature (loc.cit). As suggested previously dibromoacetic acid undergoes self dissociation as [1, 4];
It is further assumed that water generated in the above equilibrium is taken up by the chromium(III) chloride and CHBr2 CO+ ions are re- moved as CHBr2COCl. Bromoacetyl chloride and water occur to- gether are known to combine with each other to form dibromoacetic acid and HCl according to the equation;
CHBr 2COCl + H2 O ↔ CHBr2COOH + HCl ↑
The mode of solvolytic reaction may thus be represented as ;
3CrCl3 + 7CHBr2 COOH → [Cr3O(CHBr 2COO)6 ]Cl + CHBr 2COCl + 7HCl
The compound formed is green solid, slightly hygroscopic and is
insoluble in common organic solvents such as benzene, nitroben- zene, nitromethane and acetonitrile except this is fairly soluble in methanol. Molar conductance value of its milimolar solution indicate it to be a monomer.
This compound is paramagnetic having magnetic moment in the range 2.45 to 2.8 BM at room temperature. This value is sig- nificantly lower from the spin only value of 3.88 BM which is exper- imentally observed for Cr(III) complexes [22] and fall in the same range as is observed for similar basic trinuclear chromium(III) car- boxylates. The low value suggests the presence of some antiferro- magnetic exchange interaction between chromium atoms and also point to the polymeric nature of the compound in solid state.
Infra red spectral studies of this compound was carried out to understand the nature of the compound. The bands assign- ments have been made by comparison with the spectra of sodium dibromoacetates [23, 24]. The difference (∆Ѵ) between Ѵ asymCOO- stretching and Ѵ symCOO- frequencies has been extensively used in the
structure elucidation of metal carboxylates since COO- stretching
frequencies have been observed to be sensitive to co-ordination to a metal. The compound show bands at 1660 cm-1and 1415 cm-1 which have been assigned to Ѵ asymCOO- and Ѵ symCOO- stretching vibration, respectively.

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TABLE - I
PHYSICAL AND ANALYTICAL DATA OF DIBTOMOACETATES OF Cr(III) & Mn(II) AND THEIR COORDINATION COMPLEXES WITH VARIOUS BASES

TABLE - II
INFRARED VIBRATIONAL FREQUENCIES (cm-1) Of
CHROMIUM COMPLEXES
The presence of more than one band which has been assigned to Ѵ asymCOO- stretching mode may suggest that the car- boxylato groups may be unsymetrically coordinated in the solid state. The ∆Ѵ values of 160-210 and 120 cm-1 may be attributed to the presence of bridging bidentate carboxylato groups and this is quite likely in view of the tendency of chromium(III) to acquire six co-ordination bonds are shown in Table-II. The appearance of a weak to medium intensity band between 510 to 545 cm-1 have been assigned to (Cr3O) stretching mode by analogy to a similar assignment in a trinuclear iron(III) acetate [25]. Bands below 500 cm-1 have been tentatively assigned to Cr3O and modes of Cr-O arising due to the bonding of dibromoactato groups to chromium atom.


TG-DTG curve of this compound indicate that their de- composition takes place in a single step.
FIGURE : I THERMOGRAVIMETRIC CURVE OF [Cr3O(OOCCHBr2 ]Cl

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This begins to loose weight on heating above 60 oC. The weight loss is quite slow at the beginning but becomes rapid above 260 oC. The formation of the final residue, Cr2O 3 is com- plete near 580 oC. The total weight loss is in agreement with the value calculated on the basis of their proposed formulae. TG curve for the compound is given in Figure-I. The observed weight
loss, near 70% agrees well with the theoretically required weight loss value 72%.
This compound further form complex with ammonia and the resulting complex correspond to the composition [Cr3O(OOCCHBr2 ) 6(NH3 ) 3 ]Cl.5NH3. This compound has been made in analogy to some known adducts of trinuclear basic chro- mium(III) acetate [16]. Its infra red spectra indicate all the charac- teristic bands which had been observed in the parent compound and this is in agreement with its proposed structure in which the basic frame work is not disturbed. Some new bands obtained at
3250 cm-1 and 3130 cm-1 are observed which may be attributed to
(NH) stretching mode of co-ordinated NH3. These bands are sig- nificantly lowered as compared to the NH stretching frequencies in free ammonia [26] which are observed at 3414 and 3336 cm-1 have shown that bands owing to symmetrical bending vibration (δs) and rocking vibrations (δѴ ) of ammonia are of diagnostic importance in compound where it forms stable coordinate bonds. In the spectra of this compound, the NH3 band could not be clear- ly identified due to the overlap of other vibrations such as Ѵsym (COO-) in the same region. The band due to NH3 Ѵ ) vibrations has been observed at 780 cm-1 in this compound.
Chromium(III) chloride when reacts with dibromo- acetic acid in the 1:2 stochiometric ratio and refluxed in carbon tetrachloride, it forms CrCl(OOCCHBr2 ) 2 as shown in Table-I. This compound is green solid, soluble in most of the organic sol- vents like nitrobenzene, nitromethane, acetonitrile etc. The molar conductance values (Table-I) of its milimolar solution suggest that it behaves as non-electrolyte. Molecular weight determinations of this compound corresponds to its monomeric nature. Compound is paramagnetic in nature and have effective magnetic moment value which is below the spin only value of 3.88 BM [22] (Table- IV) thereby suggesting antiferromagnetic coupling between chromium atoms. The spectra of Cr(III) complexes are well un- derstood [loc.cit]. The UV-visible spectra of the compound is given in Table-III. If we consider an energy level diagram for a d3 ion in an octahedral field, it is seen that three spin allowed transi- tions;
one type of carboxylate groups. The ∆Ѵ (COO-) value of 185 cm-

1 may be attributed to ionic or bridging carboxylate groups. How- ever molar conductance measurements rule out the presence of

ionic carboxylate ligands. Other important bands due to carbox- ylate groups are also recorded in Table-II. This compound show a strong band around 300 cm-1 which by analogy with literature [27] and by comparison with the spectra of Cr(OOCCHBr2 )3 compound may be attributed to Cr-Cl mode. A strong band be- tween 425-450 cm-1 is assigned to Cr-O modes. Their observed physical properties, UV-Visible spectra and infra red data favour bidentate bridging carboxylate groups over bidentate chelating arrangement, resulting in polymeric structures.
TABLE - IV
ELECTRONIC SPECTRAL AND MAGNETIC MOMENT DATA OF COMPLEXES OF Cr(III) DIBROMOACETATES

Chromyl chloride reacts with dibromoacetic acid exo- thermally to form green solid (Table-I). This compound contain chromium in +3 oxidation state. This is suggested by its green colour and also by the inability of this compound to oxidize KI to free iodine. The compound is better represented as [Cr3O(OOCCHBr2 ) 6(CHBr 2COOH) 3]Cl. This green coloured compound is fairly soluble in nitrobenzene, methanol and acetoni- trile. The molar conductance value of its milimolar concentration in actonitrile suggest the non-ionic nature of the compound. This compound is paramagnetic in nature and its magnetic moment value fall in the range of 3.1-3.5 BM at room temperature. The value is significantly below the spin only value of 3.88 BM (loc.cit) and suggest that this compound is magnetically concen- trated.
Infra red spectra of this compound (Table-II) do not show any band between the region 3300-3100 cm-1 which are characteristic of (OH) band. Bands between the regions 1600-
1680 and 1400-1440 cm-1 are assigned to Ѵ asym (COO-) and
Ѵ sym (COO-) stretching frequencies, respectively of the bridging

4T2g (F) ← 4A2g ; 4T1g (F) ← 4A 2g ; 4T1g (P) ← 4A2g

carboxylate group (loc.cit). The large Ѵ

COO

values of the order of
are expected (loc.cit) and these has been observed.
TABLE - III
ULTRAVIOLET SPECTRAL DATA AND MAGNETIC

MOMENT OF CrCl(OOCCHBr2) 2
Some important infrared bands and their assignments for this compound are reported in Table-II. This compound show more than one band which may be assigned to Ѵ asym (COO-) stretching vibrations, thus suggesting the presence of more than
approximately 215 cm-1 are comparable to those observed for bridging carboxylate groups. Other bands due to carboxylate
group are assigned at their usual position. The appearance of a weak to medium band at 540 cm-1 is assigned to Cr3O group [25]. These observations combined with physical properties like lack of volatility, insoluble nature, intercluster hydrogen bonding con- cludes trinuclear formulation resulting in polymeric structure.
Compound of type Cr(OOCCHBr2) 3 has also been prepared by refluxing anhydrous Cr(III) chloride with anhydrous dibromoacetic acid in carbon tetrachloride. The green compound formed which is slightly hygroscopic. The compound is insoluble in common organic solvents such as carbon tetrachloride, ben- zene, nitrobenzene, nitromethane and except it is slightly soluble in acetontrile and methanol. At this moment owing to its low sol- ubility in acetonitrile, it is very difficult to predict its nature.
The magnetic moment of a Cr(III) complex lies be-

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tween 3.88 BM and 5.2 BM. Since 4A2g (F) is the ground term, there is no orbital contribution to the magnetic moment (loc.cit), therefore the magnetic moment value should be close to spin only value of 3.88 BM. The experimental value has been found to be in range as expected for a d3 system (loc.cit).
This compound has been further supported by its infra red spectral studies. The difference between Ѵ asym (COO) and Ѵ sym (COO) frequencies has been extensively used in the structure elucidation of the metal carboxylates since COO-
stretching frequencies have been observed to be sensitive to co- ordination to a metal. This compound show bands at 1600-1660,
1550, 1555 cm-1 and 1410, 1415 cm-1 which have been assigned
to Ѵ asym (COO-) and Ѵ sym (COO-) stratching vibrations respective- ly. The presence of more than one band has been assigned to Ѵ a- sym (COO-) stretching mode and suggest that the carboxylate group may be unsymmetrically co-ordinated in this solid state. The ∆Ѵ (COO-) value 140 cm-1 may be attributed to the presence
of bridging bidentate carboxylate groups and this is quite likely in view of the tendency of Cr(III) to acquire six co-ordination. The appearance of a weak to medium intensity band between 520 to
540 cm-1 in this compound has been assigned to Ѵ Cr-O stretching mode by analogy to similar assignment in trinuclear iron(III) ace-
tate.

3.1.2 Adducts of Dibromoacetates of Chromium with Pyri- dine, Quinoline and Thriethylamine

We have prepared the adducts of the type Cr(CHBr2 COO)3.Py, Cr(CHBr 2COO)3.(C 2 H5) 3 N and Cr(CHBr2 COO)3.Q in a manner analogous to some known ad- ducts of trinuclear basic chromium(III) acetate (16). Their infra red spectra show all the characteristic bands which had been ob- served in their proposed structures in which the basic frame work
is not disturbed. Some new bands observed may be attributed to Ѵ N-H stretching modes of co-ordinated base. These bands are sig- nificantly lower in comparison to the Ѵ N-H stretching frequencies in the free base (Table-V).
TABLE - V
INFRARED VIBRATIONAL FREQUENCIES (cm-1) OF
are expected and these have been observed in the region 13.0-
39.0 KK. The Ѵ 3 transitions which is observed above 30.0 KK is obscured if ligand absorb in the ultra violet region.
The electronic spectra of Cr(CHBr 2 COO)3 , Cr(CHBr2 COO)3.Py and Cr(CHBr 2COO)3 .Q have been studied and recorded in Table-IV. The spectra of all these compounds have all the features requisite of a octahedral geometry.

Tris(dibromoacetato)chromium(III) i.e. Cr(CHBr2 COO)3 (d3 system) compound absorbs at 16-22 KK respectively are due to 4T1g (F) ← 4A2g transitions (Ѵ 2) which is characteristics of a Cr3+ compound in an octahedral ligand field. Unfortunately, 4T1g (P) ← 4A2g could not be observed unambigu- ously since it appears as a weak shoulder on the main charge transfer for chromium(III), and Ѵ 1 is a direct measure of 10 Dq. Also β’ value has been calculated from energy ratio diagrams. From these observations a structure may be assigned to these compound as ;
Similarly the 10 Dq values for Cr(CHBr 2 COO)3 , Cr(CHBr2 COO)3.Py and Cr(CHBr2 COO)3.Q are obtained at
16.22, 15.99 and 16.68 KK, respectively. From the 10 Dq values a β’ values of 0.709, 0.72 and 0.595 cm-1 are obtained for these compounds.
The infra red spectra of pyridine complex Cr(CHBr2 COO)3.Py is complicated as was observed in case of analogous vanadium(III) compounds. The important infra red absorption bands for these compounds have been tabulated in Table-V.
In the adduct Cr(CHBr2 COO)3.Py, the Ѵ 8a modes of pyridine could not be distuinguished clearly due to its overlapping with the Ѵ COO stretching mode of the carboxylate group which occurs in the same region. The bands at 1010 cm-1 and 1015 cm-1

-1

corresponds to the 991 cm
1 mode) band of pyridine. Other
ADDUCTS OF CHROMIUM(III) DIBROMOACETATES
WITH PYRIDINE, QUINOLINE AND TRIETHYLAMINE

The ultraviolet and visible spectra of these compounds are given in Table-III. If we consider an energy level diagram for a d3 ion in an octahedral field, it is observed that these spin al- lowed transitions ;

4T2g (F) ← 4A2g , 4T1g (F) ← 4A2g , 4T1g (P) ← 4A2g

significant changes involve shift to higher frequencies in amine ring vibrations of free pyridine at 601, 605 and 403, 406 to 640,
420 cm-1 in these complexes. These changes show that pyridine is co-ordnated to Cr-atoms.

3.2.1 Chemistry of Manganese with dibromoacetic acid

A few acetates of manganese(II) and their addition complexes have already been prepared and characterized by infra-
red, electronic spectral and magnetic susceptibility studies and appear to contain octahedral manganese(II) [28-29]. In the pre- sent studies the compound Mn(OOCCHBr2 ) 2 has been prepared by the solvolysis of anhydrous Mn (II) chloride with fused dibro- moacetic acid under reflux. The stoichiometry of this compound is further confirmed by its analysis (Table-I).
The infra-red spectral studies of the compound Mn(OOCCHBr2 ) 2 have been recorded in the range 4000-200cm-1. The bands at 1690, 1590, 1290 are marked to asymmetric and symmetric Ѵ (COO-) absorption bands which further indicate that the co-ordination of metal atom is through the carboxyl atom.
Electronic spectra has been recorded in support of the formation of the compound Mn(OOCCHBr2 ) in Table- VI. It shows weak absorption bands in the region 5.0-15.0 KK. No

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bands have been observed in the region 15.0-30.0 KK which rules out the possibility of tetrahedral derivative. A distinction between the tetrahedral and octahedral complexes could best be made from the measurements of extinction coefficients. The octahedral com- plexes have a low extinction coefficient in order of 10-2 - 10-1
Lcm-1mole-1 whereas for the tetrahedral complexes it ranges be-
tween 1-10 Lcm-1mole-1. The extinction coefficient of Mn(II)
compound could not be evaluated owing to their very low solubil-
ity in all conventional solvents. However, very weak absorption bands obtained for the compound (Table-VI) are suggestive of an octahedral environment around manganese(II). A band is ob- served at 33.35 KK in all these compounds may be assigned to the charge transfer spectra.
The magnetic moment values for a high spin octa- hedral derivative exist in the range 5.68 - 6.10 B.M. whereas the value for a low spin octahedral derivatives ranges from 1.8 -
2.1B.M. The spin only value for Mn(II) is expected to be 5.92
B.M. Compound posses magnetic moment values calculated for the Mn(II) compounds (Table-VI) indicate these systems to be consisting of five unpaired electrons. It also rules out the possibil- ity of a low spin configuration.

3.2.2 Adducts of Manganese dibromoacetates with Pyridine,


In the higher frequency region all the complexes give strong absorption bands in the range 1400-1500 and 1500-1700 cm-1 marked to the symmetric and asymmetric stretching bands respectively of the carboxylate group (Table-VII). The frequency difference between these bands has been previously used to pro- vide evidence for the bonding of the carboxylate group [30] but the results are conflicting and are also sensitive to the nature of the substituent [23]. From these complexes it is clear that group of complexes with similar stoichiometry and most probably similar structure show very similar values of ∆Ѵ. The band which occurs

-1

Quinoline and Thriethylamine

near 865 cm
has been described as a pseudo symmetric Ѵ C-C
Adducts of Mn(OOCHBr2 ) 2 have been prepared with pyridine, triethylamine and quioline. Their stoichiometric compo- sitions have been confirmed by their elemental analyses, given in Table-I. Their infra red spectra have also been recorded in the range 4000-200 cm-1. The various bands and their assignments are shown in Table-VII. The infra red spectra of the amine complexes does not give great deal of information on the details of its struc- ture. Octahedral pyridine metal halides give information on the
details of the structure.
TABLE – VI
ELECTRONIC SPECTRAL AND MAGNETIC MOMENT
DATA OF Mn(II) DIBROMOACETATES AND ITS COMPLEXES WITH BASES

TABLE - VII
INFRARED VIBRATIONAL FREQUENCIES (cm-1) OF ADDITION COMPLEXES OF Mn (II) DIBROMOACETATES
WITH PYRIDINE, QUINOLINE AND TRIETHYLAMINE
stretching mode also seems to be metal sensitive. Similar results
to those previously reported for copper pyridine complexes [23]
were found for other amine complexes.
The evidence in favour of the formation of above complexes has been given by the electronic spectral studies. They show weak bands in the region 5.0-15.0 KK. No bands have been observed in the region 15.00-30.00 KK, which rules out the possibility of a tetrahedral derivative and suggest an octahedral arrangement in these complexes. A band obtained at 33.33 KK in these complexes may be assigned to charge transfer spectra. [31-
32]
The magnetic susceptibility measurements gave the value of Mn(OOCCHBr 2) 2 . , Mn(OOCCHBr 2) 2 .2Q, Mn(OOCCHBr2 ) 2. 2Py and Mn(OOCCHBr2 ) 2 .2(C2 H5) 3 N com- plexes at 5.42-5.82, 5.70 and 5.74 B.M. respectively (Table-VI) which further support the octahedral arrangement around the met- al atom in these complexes.
Metathetical reactions of [Me4 N] 2[MnCl4] with sil- ver dibromoacetates in nitromethane has further been carried out which yields corresponding dibromoacetate in nitrometane. This solution on evaporation to dryness gives the dibromoacetate com- plex. The analytical data of compound is presented in Table-I. This compound is solid, hygroscopic in nature and soluble in polar organic solvents like acetonitrile and nitromethane but in- soluble in non polar organic solvents. The reaction of [Me4 N]2 [MnCl4] with dibromoacetic acid do not give completely substi- tuted product and the mathematical reaction in absolute ethanol are not promising. The molar conductance value of its millimolar solution in acetonitrile (i.e. 230 ohm-1 mole-1 cm2) is well in the range expected for ionic formulations.
The infra red spectra of this compound has been recorded in the range 2000-200 cm-1 (Table -VIII). The character- stic features of the spectra are appearance of Ѵ asymCOO- between
the region 1680-1650 cm-1. The bands between the region 1435-
1415 cm-1 have been assigned to Ѵ symCOO- . The ∆Ѵ COO- values of the range 250 cm-1 comparable well with that of 270 cm-1 as re-
ported earlier which suggest that the compound contain uniden-

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tate dibromoacetate groups. Strong bands between the regions
1470-1485 cm-1 and 940-950 cm-1 are assigned to tetramethyl ammonium group.
TABLE – VIII
INFRARED VIBRATIONAL FREQUENCIES (cm-1) OF [(Me4 N)2 ] [Mn(O2CCHBr 2 ) 4]

The electronic spectra of this complex has also been studied. Octahedral field energy level diagram for Mn ( II ) ( d5 configuration ) is the same as tetrahedral field energy level se- quence. It follows that same energy level diagram may be used for octahedral, tetrahedral or cubic fields. In octahedral field, this configuration gives spin forbidden as well as partly forbidden transitions and thus extremely pale yellow colour of the com- pounds [4]. In tetrahedral environment, the transitions are still spin forbidden, but no longer partly forbidden, thus the compound has yellowish green colour. The light green colour and very weak bands at 315, 400, 540 and 680 cm-1 in diffused reflectance spec- trum of manganese complex favour a tetrahedral environment around manganese atom. These bands are similar to other tetrahe- dral manganese(II) complexes [33]. The band at 250 cm-1 is as-
signed to charge transfer band.
High spin manganese(II) compounds are expected
to indicate magnetic moment very close to spin only value of 5.92
B.M. and are independent of temperature, irrespective of whether
the ligand arrangement is octahedral, tetrahedral or is of lower symmetry. Magnetic moment of [(Me4 N) 2][Mn(O2 CCHBr 2) 4 ] is
6.14 B.M. which is very close to spin only value as reported in literature for other Mn(II) tetrahedral complexes [34-35].
Thus on the basis of infra red, electronic spectra and magnetic moments of [(Me4 N)2 ][Mn(O2CCHBr 2 ) 4 ], it may be
concluded that unlike tetranitrato metal(II) complexes, this has tetrahedral environment around central metal atom.
TG-DTG curves of [(Me4N) 2][Mn(O2CCHBr 2) 4 ] show that it decompose in two stages. However, these steps overlap (indicated
by DTG curves). They began to loose weight on heating above
45oC. The weight loss is slow at the beginning but becomes rapid around 1400C. The formation of the final residue, metal oxide, is complete above 400oC. Total loss in weight is in agreement with
the value calculated on the basis of their proposed formula. Curve for [(Me4 N)2 ][Mn(O2CCHBr 2 ) 4] is shown in Figure-II. In the first step there is a loss of two molecules of dibromacetic anhy- dride part as combustible material (Weight loss 88.68%, Calculat- ed 88.34%).
Overall thermal decomposition mode of this complex

may be shown as given below.
The presence of dibromoacetic anhydride was character- ized from the infra-red spectrum of the trapped volatile material in separate experiment.

FIGURE : II Thermogravimetric Curve of

[(ME4 N)2 ][Mn(OOCCHBr2 )4 ]

7.2 Acknowledgments

Thanks to the UGC for the award of Emeritus Professor Fellow- ship to Prof.J.K.Puri (2011-2013), Dept of Chemistry, Panjab University, Chandigarh.

7.3 References

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[5] Puri J. K, J., Vats V. K., Sharma V “Oxidation-Reduction Reaction and Analysis of Thiourea, Hydrazine and Ascorbic Acid in Monobromoacetic Acid”. Indian J. Chem. 25, (1986), 565-570

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