Mono- and bis-phenanthroline cobaltous oxalates

2316

Notes

product. After filtration, the filtrate was distilled under reduced pressure. The product was analysed and it corresponded to the composition CsH~A1C12.3C2HsOH. The compound on crystallisation from petroleum ether (60--80°) gave dark brown crystals and was found to he identical to the product obtained by the reaction of CsI-L and AIC13.3ROH. The cyclopentadienyl derivatives of methanolate and higher alcoholates were prepared by a similar procedure at suitable temperatures. Their characteristics and analytical data are given in Table 1. Some of the higher alcoholate derivatives were also prepared by alcohol interchange method [5].

and alkalies. They are non-volatile and do not sublime in vacuo. They change the chromic acid solution (12% H2SO4 1N K2CF2OT) to green colouration. The i.r. spectra, elemental analysis and some physical properties of these compounds are compatible with the formulae C~HsMC12.3ROH where R is methyl to isoamyl. The infrared spectrum also suggests that the linkage between the cyclopentadienyl ring and the metal atom retains the character of delocalized ~r bonds while the alcoholate groups are probably attached to the metal atom by ~r bonds.

RESULTS AND DISCUSSION The i.r. spectra of the above compounds were recorded using KBr pellets, Nujol mull or in thin layer on a Perkin Elmer Infracord Model-137 Spectrophotometer at 4000-670cm -1. The cyclopentadienyl group exhibited characteristic v-H stretching at -3010cm -t, C-C stretching band at 1480-1450cm -~. C-H in plane bending at about 1030 cm-1 and C-H out of plane bending at -840cm -1. The vibrational band at llg0cm -1 attributable to methoxy, at 1170 cm-1 to ethoxy at 1110, 1160 cm-~ to isopropoxy groups while the bands at 1100, 1150-1170 cm-1 are characteristic of butoxy groups and those at 1I00, 1050 cm-~ of the isopentyloxy groups[6,7]. The bands at 1600-1660cm -1 are probably associated with the C-O linkage of the alkoxy group. The compounds are generally dark brown in colour, quite sensitive to moisture but stable in dry inert atmosphere. They are soluble in THF, dioxane and halogenated solvents but are insoluble in aromatic hydrocarbons. They are insoluble in water and being easily hydrolysed on heating or treatment with dil. acids

Department of Chemistry University of Delhi Delhi- l lO007 India

SHUSHMA MEHRA R.K. MULTANI

REFERENCES I. G. Wilkinson, Org. Syn. 36, 31 (1956). 2. C.A. Adams and L R. Nicholls, Analyst (Lond.), 2, 54 (1929). 3. D. C. Bradley, F. M. Abdel Halim and W. Wardlaw, J. Chem. Soc. 3450 (1950). 4. D. C. Bradley, R. K. Multani and W. Wardlaw, J. Chem. Soc. 4153 (1958). 5. D. C. Bradley, R. K. Multani and W. Wardlaw, J. Chem. Soc. 4651 (1958). 6. H. A. Ory, Anal. Chem. 32, 509 (1960). 7. J. V. Bell, J. Heisler, H. Tannenbaum and J. Goldenson, Anal. Chem. 25, 1720 (1953).

1. inorg,nucl.Chem.,1975,Vol.37, pp. 2316-2317. PergamonPress. Printedin GreatBritain

Mono- and bis-phenanthroline cobaltous oxalates (First received 13 November 1974; in revised form 19 March 1975) PREPARATIONof several compounds containing cobalt (II/III) and o-phenanthroline (phen) with different anions has been reported[l-5].. Co(II).phen.ox.H20 is the only compound reported[5] in which divalent cobalt and oxalate anion are involved. In the course of similar investigations in our laboratory, mono- and bis-phen cobaltous oxalates were obtained under different experimental conditions. This paper describes their preparation, thermal decomposition and IR spectra. EXPERIMENTAL All chemicals used were of analytical grade. TG and DTA curves were obtained with heating rates of 4 and 5°C/min in static air on Stanton and Houston Omnigraphic Corporation equipments respectively. A Perldn Elmer Model 21 IR spectrophotometer with filter-grating interchange facility was used to record the IR spectra in Nujol mulls. To mixtures of cobalt(II) and phen in the molar ratio of 1 : 1 and 1:3, excess oxalic acid (10 times the metal) was added and the pH adjusted to 2.0 and 4.0 respectively. The pink and yellow compounds that separated were filtered, washed with warm water and dried in vacuum over magnesium perchlorate. The metal contents of the compounds were determined by fusing a known weight with KHSO4, dissolving in water and titrating the cobalt with standard EDTA using xylenol orange as indicator[6]. Nitrogen and H20 were estimated by the usual Kjeldahl and Karl Fischer titration methods [6] respectively. To evaluate the oxalate content, a solution of the compound in 0.1 N sulphuric acid was passed through a column of Dowex-50x 8 (H +) (10 x 0.75 cm), followed by 150 ml of 0.1 N acid. The effluent and washings were titrated with standard permanganate. The important bands in the i.r. spectra of the two complexes are given in Table I.

DISCUSSION Analysis of the pink and yellow compounds obtained at pH 2.0 and 4.0 gave mole ratios of Co: phen: ox as 1: 1.0 -+0.05:1.0 -+0.01 and 1.0: 2.0 -+0.02:1.0 -+0.01 respectively. The second compound gave 2 moles of H20 per mole of Co. Hence the compounds were assigned the molecular formulae Co(phan)ox and Co(phen)2ox.2H20 respectively. These compositions were further confirmed by precipitating the compounds from synthetic mixtures and analysing the supernatant liquid. The same mono-phen complex forms in the pH range 2.0-4.0, when phen and cobalt are taken in 1: 1 (molar) ratio. With increase in relative amount of phen (3 times the metal or more), bis-phenanthroline complex forms at pH values 3.0 and 4.0, while a mixture of the two results at lower pH values. It appears, therefore, that the complex formed depends on the relative concentration of phen as well as pH, contrary to the conclusion of Singh et al.[5]. The TG curve of the mono phen oxalate shows a weight loss of 75% between 200 and 350°C in a single step, which is ascribed to simultaneous release and oxidation of phen and ox, resulting in Co304. Between 800 and 850°C, there is a further weight loss of 1-8%, which corresponds to conversion of Co30, to CoO. The TG curve of bis-phen oxalate shows weight losses of 9.5 and 26% between the temperature ranges of 50-130°C and 130-280°C respectively. At higher temperatures its thermal behaviour is similar to that of the mono-phen compound. This compound, on heating at 160°C for several hours showed loss of H~O and a major part of one phen but not oxalate. Hence the initial weight loss in the TG curve is attributed to the loss of H20 and the second to a major part of the first phen. The DTA curves indicated endothermic peaks for the loss of moisture and exothermic peaks for the release and oxidation of organic moieties. It may be

Notes

2317

Table I. I.R. spectra of cobaltous phen oxalates Co(phen)ox

Co(phen)~ox.2H20

Assignments

1680 (vs) cm ~ 1620 (vs) 1530 (m)

1650 (vs) cm '

C=O stretching in the oxalate

1520 (m)

C=C stretching vibration (characteristic

1440 (s}

1430 (m)

frequency of aromatic compounds) C=C, and C-N stretching vibration in aromatic amines

1325 (s)

1290 (m)

1160 (s)

1150 (m)

l120(m) 880 (m) 860 (s}

ll00(m) 875 (s) 855 (m)

810 (s)

790 (m)

735 (s)

735 (s)

Out of plane motion of the hydrogen atoms in the central aromatic ring C-H out of plane deformation of the heterocyclic hydrogen atoms

vs, very strong; s, strong; m, medium. mentioned that, in Ni(phen)2ox also, one mole of phen is released at a lower temperature than oxalate (unpublished work in our laboratory). These observations show that the oxalate is more strongly bound to the metal in these complexes than the phen. IR absorption characteristics of cobaltous phen oxalate compounds and assignments of some bands to specific group vibrations are given in Table 1. The shift of the band at 755 cm -t in phen.H20 to 730-740 cm -1 in the compounds is ascribed to the coordination of phen with Co, on the basis of the studies of Schilt and Taylor [7]. The mono- and bis-phen.oxalates have strong bands at 1680 and 1650cm-' respectively. These are assigned to asymmetric C=O stretching in oxalate. Comparing these with that observed in cobalt-oxalate (1630cm ') it may be inferred that the oxalate is more covalently bound to the metal in the phen compounds than in cobalt oxalate.

Acknowledgements--The authors thank Shri S. Ganapathy Iyer, Drs. V. B. Kartha, A. K. Sundaram and M. Sankar Das, Head, Analytical Chemistry Division for their keen interest and helpful discussions.

Analytical Chemistry Division Bhabha Atomic Research Centre Modular Labs., Trombay Bombay-400 085 India

H. PARASURAMA IYER P. S. RAMANATHAN Ch. VENKATESWARLU

REFERENCES 1. A. A. Schilt and K. Fritsch, J. lnorg. Nucl. Chem. 28, 2677 (1966). 2. Th. I. Pirtea and Marg. Dumitru: Analele. Univ. C. L Parhon, Ser. Stiint Nat 10, 211 (1961); cf, Chem. Abstr. 58, 7357b (1963). 3. A. V. Ablov and D. M. Palade, Zh. Neorgan Khim. 7, 2514 (1962). 4. P. Pfeiffer and Br. Werdelmann, Z. Anorg. Allg. Chem. 263, 31 (1950). 5. G. P. Singh, P. R. Shukla and L. N. Srivastava, J. Inorg. NucL Chem. 34, 3251 (1972). 6. A. I. Vogel, Quantitative Inorganic Analysis, 3rd Edn, pp. 443, 256, 944. Longmans Green, London (1962). 7. A. A. Schilt and R. C. Taylor, J. Inorg. Nucl. Chem. 9, 211 (1959).

J. inorg,nacl.Chem..1975,VoL37, pp. 2317-2319. PergamonPress. Printedin GreatBritain

Complex formation of aluminium with arsenazo I I I (Received 1 March 1975) IN our previous work[l] arsenazo III was proposed as a suitable reagent for the photometric determination of aluminium. In this connection it seemed of interest to make a more detailed examination of the complex formation between arsenazo III and AI3÷. In the present paper the equilibrium constants of this reaction are determined and the structure of the complex is discussed.

azo III ionic forms, using the data of Bud~/nsk~[3]. Since in the pH range 3--4 H~L 3- and H4L 4- forms of arsenazo III are predominating (Fig. 2), the following reactions for the 1:I complex[l] should take place: M3+ + H~L 3 ~ MH5 .L 3 ~3+.)+ n H ~

(1)

EXPERIMENTAL

M~÷+ H4L 4- ~ MH, ,L 3-'''"~ +nH t.

(2)

All the experiments are performed as described in [2]. RESULTS AND DISCUSSION The complex formation proceeding in the equimolar solutions was studied by the spectrophotometric method based on the relationship A =f(pH). As the straight line portion of the Sshaped curve lies over the pH range 3-4 (Fig. l), it is important to know the existence forms of the reagent at these conditions. For this purpose we have calculated the distribution curves of arsen-

JINC VOL.37 NO. ]I-..G

The values of the equilibrium constants of these reactions were calculated, using the expression: Ke. -

[MR][H] ° [MI[R]

(3)

where [MR] and [R] are the equilibrium concentrations of the complexes and of the reagent. The concentrations of the forms