Indian Journal of Chemistry Vol. 41A, June 2002, pp. 1157-1162

Heterobimetallic chemistry: Heterobimetallic complexes derived from monometallic copper(II) complex of bis(2-hydroxy-l-naphth­

aldehyde )malonoy ldihydrazone

R A Lal*, J Chakraborty & S Bhaumik, Department of Chemistry, Tripura University, Suryamaninagar 799130, Tripura, India

and

A Kumar Department of Chemistry, Indian Institute of Technology, Powai 400 076, Mumbai, India.

Received 24 April 2001 ; revised 13 February 2002

Monometallic copper(II) complex [Cu(LHz)(HzO)21 ( 1) and heterobimetallic complexes [MCu(L)(H20hl (where M = UOz(2) and Zn(4)) and [MCu(L)(H20)41 (where M = Mo02(3), Ni(5), Co(6) and Mn(7)) and homobimetallic copper(II) complex [Cuz(L)(H20)41.2HzO(8) have been isolated and characterized by analytical, molecular weight, magnetic moment, electrical conductance, electronic IR and ESR spectral data. IR spectral evidences indicate that dihydrazone coordinates to the metal centres in enol forms. The monometallic copper(IJ) complex (1) and the heterobimetallic complexes U02Cu (2) and Mo02Cu (3) and Zn-Cu (4) are normal paramagnetic indicating absence of any metal-metal interaction in the structural unit of the complexes while the remaining heterobimetallic complexes Ni-Cu(5), Co-Cu (6) and Mn-Cu (7) have much less Ileff va lues than those required for 3, 4 and 6 unpaired electrons indicating considerable metal - metal interactions. Copper has distorted octahedral geometry in monometallic and heterobimetallic complexes. Uranium has pentagonal bipyramidal stereochemistry while zinc has square pyramidal stereochemistry. However, copper(II) has square pyramidal stereochemistry in homobimetallic complex (8).

Cooperative interaction between different metal ions in hetero-polynuclear complexes I constitutes an active area of research of cooperative interaction between metal ions in polynuclear complexes2

• They might prove helpful in investigating the mutual influence of the two metal centres on the electronic, magnetic and redox properties of such systems) . Multidentate ligands possessing more than one coordination environment serve as an important means of synthesizing hetero-metal compounds. They can selectively bind one metal ion to one site and different metal ions to another. The dihydrazone derived from condensation of o-hydroxy-aromatic aldehydes and ketones with acyl, aroyl and pyridoyl-dihydrazines are potentially polyfunctional ligands capable of forming polynuclear metal complexes? The malonoyl-dihydrazones constitute a special class of polyfunctional hydrazones, which ossess acti ve methylene group flanked by keto groups in addition to phenol and azomethine functions 8

.

The literature survey revealed that although hetero­bimetallic complexes from a variety of metal ions and

ligand systems have been investigated, those derived from dihydrazones are quite meagre 9.10. In view of the above importance of hetero-bimetallic complexes of dihydrazones, the present paper describes the synthesis and characterization of hetero-bimetallic complexes of copper(II) with first row transition metal ions and oxometal species like M002

2+ and

UO/+ derived from bis (2-hydroxy-l­naphthaldehyde) malonoyldihydrazone (LH4).

Materials and Methods Ammonium heptamolybdate, metal(lI) salts and

uranyl acetate dihydrate, diethylmalonate, hydrazine

Bis(2 -hydroxy-1-naphthaldehyde )malonoyldihydrazone

1158 INDIAN J CHEM, SEC A, JUNE 2002

hydrate, acetylacetone and 2-hydroxy-I­naphthaldehyde were of E.Merck or equivalent grade. Mo02(acach was prepared by the literature method II. Malonoyldihydrazine was prepared by reacting diethylmalonate (1 mol) with hydrazine hydrate (2 mol) . The bis(2-hydroxy-I-naphthaldehyde) malono­yldihydrazone (LH4) was prepared by reacting a warm ethanol solution of malonoyldihydrazine (l mol) with 2-hydroxy-I-naphthaldehyde (2 mol) and was suction filtered , washed with ethanol and dried in vacuo (m.p. 265°C). [Found: C, 68.45; H, 4.62; N, 13.00; Reqd. for C2s H2oN40 4, C, 68.18; H, 4.55; N, 12.73 %].

Metals in the complexes were determined by standard literature method 12 . Carbon, hydrogen and nitrogen were determined microanalytically. Water molecules were determined by heating the samples in an oven at 110°C, and passing the vapours through a trap containing anhydrous copper sulphate, which turned blue and the weight loss estimated. The molecular weights of the complexes were determined in DMSO solution by freezing point depression method. The molar conductance of the complexes at 1O-3M dilution in DMSO was measured on a direct reading conductivity meter with a dip-type conductivity cell.

IR spectra were recorded on a Paragon 500 Spectrophotometer in the range 4000-350 cm-' in KBr discs . The electronic spectra of the ligand and complexes in DMSO solution were recorded on a Milton Roy spectronic 21 spectrophotometer. The ESR spectra of the compounds in powdered form at room temperature and liquid nitrogen temperature were recorded at X-band frequency on a varian E- L 12 E-line Century series ESR spectrometer using TCNE (g = 2.00277) as an internal field marker.

Preparation of the complex [Cu(LH2) (H20hl (1) In order to prepare the complex [Cu(LH2)(H20 h ]'

the ligand, LH4 (0.88 g, 2.0 mmol) in ethanol (20 ml) was allowed to react with CuCh.2H20 (1.023 g, 6.0 mmol) in ethanol (20 ml) under refl ux for 6 h. The dark-brown precipitate thus obtained was filtered, washed with hot water, ethanol and dried over anhydrous CaCho Yield : 0.8 1g (75 %).

Preparation of the complexes [MCu(L)(H20).d (where, M = UOl 2) and 2n(4)) and [MCu(L)(H20)41 (where, M = MoO/+(3), Ni (5), Co (6) and Mn (7))

The suspension of the precursor complex [Cu(LH2)(H20)2] (0.538 g,I.O mmol) in methanol (30 mL) was added to a solution of U02(OAch2H20 (0.466

g, 1.1 mmol) in methanol (50 mL) containing a trace of acetic acid over a period 10-15 min with constant stirring. The reaction mixture so obtained was further stirred for another 30 min. at 70°C followed by refiuxing for 3 h, which precipitated dark-brown compound of composition [U02Cu(L)(H20)3] (2). The complexes were crystallized out from acetonitrile. The compound was dried over anhydrous CaCho Yield: 0.54 g (65 %).

The complexes (3) to (8) were also synthesized by essentially following the above procedure using either metal acetates (M = Zn(4), Ni(5) , Co(6), Mn (7) and Cu(II» or Mo02(acach instead of uranyl acetate, respectively. The complexes were crystallized from acetonitrile. Yield: (70-65 %).

Results and Discussion The monometallic complex [Cu(LH2)(H20 h ] (I)

has been obtained from direct reaction of copper (II) chloride with preformed dihydrazone in 3: 1 molar ratio in methanol. When his complex was treated with Mo02(acach or uranyl acetate or second metal acetates in methanol, the heterobimetallic complexes [MCu(L)H20)] (M=U02(2),Zn(4» and [MCu(L)(H20)] (M=Mo02(3), Ni(S) , Co (6) and Mn (7» were obtained.

The complexes are dark-green and dark-brown in colour. The complexes are insoluble in water and common organic solvents but freshly prepared complexes are slightly soluble in acetonitrile and completely soluble in highly coordinating solvents like DMF and DMSO. The complexes decompose above 300°C except the 1 which melts with decomposition at 280°C. The high decomposition temperature of the complexes also indicate their good thermal stability. The molar conductance of the complexes lies in the range 1.8-2.5 ohm-' cm2 mor' of 10-3 M DMSO solution indicating their non­electrolytic nature 13

.

None of the complexes shows weight loss at 110°C ruling out the possibility of lattice water. On the other hand, the monometallic copper(II) complex (1) shows weight loss corresponding to two water molecules whi le the complexes (2) and (4) show weight loss corresponding to three water molecules at 180°C and the remall1l11g complexes show weight loss corresponding to four water molecules at this temperature suggesting that they are present in the first coordination sphere around the metal centre.

The complexes (1) and (3) are found to have molecular weights equal to (660±30) and (900±40), respectively. These values are very close to the

LAL ef al.: STUDIES OF HETEROBIMETALLIC COMPLEXES 1159

theoretical values for monomer formulation, respectively. On the other hand, for the remaining complexes, the experimental values were found to be close to the theoretical values calculated for dimeric formulation. However, the experimental values are much higher than the values calculated either for the monomeric formulation (for 1 and 3) or for the dimeric formulation (for 2, 4-8). Such a higher experimental value of molecular weight strongly suggests that the coordinated water molecules appear to be substituted by DMSO molecules.

The present ligand shows strong broad bands centred at 3450, 3200 and 3047 cm·' which are assigned to stretching vibrations of naphtholic -OH and secondary -NH- group. Upon complexation, the bands at 3200 and 3047 cm·' disappear and a single strong broad band is observed in the 3550-3000 cm-' region. The disappearance of the bands at 3200 and 3047 cm-' and appearance of a single strong broad band in the 3550 -3000 cm-' region in all of the complexes suggests enolization of the ligand and presence of water molecules. As the water molecules are lost at 180°C upon heating the complexes, this band is assigned to arise due to asymmetric and symmetric vibration of coordinated water molecules.

The vC=O band at 1697 and 1661 cm-' in free dihydrazone is absent in all of the complexes. This suggests coordination of the dihydrazone to the metal centre in the enol form. The free dihydrazone shows a strong band at 1532 cm-'. This band is assigned to have composite character due to mixed contribution of the amide(II) and v(C-O) (naphtholic) bands. The band in the 1538-1548 cm-' region in the complexes is very strong and shows a shift of about 6-16 cm-' . Such a feature associated with thi s band is attributed to the fact that they have contribution from the vNCO- band arising from enolization'4. The vC=N band appears in the 1600-1618 cm-' region as a couple of bands in the heterobimetallic complexes . The complexes (2) and (4) to (7) show medium to weak intensity band in the region 875-869 cm-'. This

o / " M M band IS characteristic of tetraatomic "0/

species resulted from involvement of naphthol ate oxygen atom in bridge formation 15. On the other hand, the complex (3) does not show such a band in this region, which rules out the possibility of

/0, M M species in the structural unit of the

'\.. / o

complex '6. Further, the heterobimetallic complex (2) shows a new strong band at 919 cm-' which is assigned to trans V3(U02

2+). The Mo-Cu heterobimetallic complex (3) shows bands at 939s, and 912s cm-' characteristic of cis-MoO/+ group'7.

The non-ligand bands appearing in the 525-590 cm-' region have been assigned to v(M-O) (naphtholic) vibrations '8. The new bands appearing in the 420-460 cm-' region are attributed to arise due to v(M-O) band resulting from coordination of carbonyl oxygen atom'9.

The magnetic moment value for the complexes are presented in Table 1. The monometallic copper complex (1) and heterobimetallic complexes U02- Cu (2) , MoOrCu (3) and Zn-Cu (4) have magnetic moment value in the 1.95-l.71 8.M region . These values are very close to the spin only value for one unpaired electron (1.73 8M) which suggest either there is no interaction or very weak interaction in the structural unit of the complexes.

On the other hand, /J.B values for the heterobimetallic copper(II) complexes (5), (6) and (7) containing nickel(II), cobalt(II) and manganese(II), are 2.60, 3.50 and 5.40 8M, respectively. These /J.B values are less than the spin-only value for 3, 4 and 6 unpaired electrons resulting from bivalent hetero­metal combinations Ni-Cu, Co-Cu and Mn-Cu , respectively, indicating that there is an appreciable metal-metal interaction between hetero-metal atoms in the structural unit of the complexes2o. This observation is also supported from the fact that homobimetallic copper (II) complex [Cu2(L)(H20h].2H20 (8) has /J.B value equal to 1.34 8.M, which is much less than the spin-only value required for two unpaired electrons.

In addition to the ligand band, the electronic spectra of monometallic copper(II) complex (1) shows a band at 710 nm (cma" 35 dm3 cm-' mor') in the visible region assigned to 2T2g-'i2Eg transition . Due to Jahn-Teller distortion, this band is considerably blue shifted, as has been reported in some olive green square planar copper (II) chelates22. The band position together with molar extinction coefficient in the complex suggests that it has tetragonally distorted octahedral stereochemistry. On the other hand, homo-

1160 INDIAN J CHEM, SEC A, JUNE 2002

bimetallic copper (II) complex (8) shows a shoulder at 540 nm to the charge transfer band which can be attributed to d-d transition . The position of the band together with its molar extinction coefficient indicates its square pyramidal stereochemistry22. The electronic spectra of hetero-bimetallic complexes (2) to (4) and (7) show a weak broad band in the 600-750 nm region with maximum absorption in the 675-690 nm region . The band in the 675-690 nm region in the complexes is assigned to d-d transition due to copper (IJ)23 because second metal ion i.e. U02

2+, M0022+, Zn2+

and Mn2+ are not expected to show such a weak band in this region . This shows that the stereochemistry of copper centre in these complexes remains essentially the same as that in the precursor copper complex i.e. distorted octahedral geometry. Further, the hetero­bimetallic nickel-copper complex (5) shows only one band at 720 nm. The position of this band again indicates that both copper and nickel have distorted octahedral stereochemistry. A comparison of the position of this band with the corresponding band in

the spectra23 of [Ni(H20)6]2+ at 740 nm and [Ni(NH3)6]2+ at 570 nm suggests that it bears similarity with those of oxygen donor ligands. This indicates that nickel atom in this hetero-bimetallic . complex is surrounded, most probably, by oxygen atoms i.e. nickel is coordinated to carbonyl oxygen atoms. On the other hand, the hetero-bimetallic cobalt-copper complex (6) shows two bands at 630 and 540 nm assigned to Cu(II) and Co(II), respectively. The position and molar extinction coefficients together indicate that both copper and cobalt atoms have distorted octahedral stereochemistrl4

•

The monometallic copper(IJ) complex (1) shows an isotropic spectrum in the polycrystalline state with gav value equal to 2.089 (Table 2), while it shows an anisotropic spectrum at liquid nitrogen temperature (77 K). The parallel and perpendicular 63CU features are resolved in the complex. The essential features of the spectrum indicates that complex has octahedral stereochemistry.

Table.l--Characterization data for complexes of bis(2-hydroxy-l-naphthaldehyde) malonoyldihydrazone

SI. No. Complex / Colour Mol. wt. Found (Caled.), % Magnetic Electronic spectral moment bands

D.P (0C), Yield (%) Exptl. (Ther) Cu M C H N /lB B.M Amax(nm)(Emax)a

I. [Cu(LH2)(H20)2] 660±30 11.25 59.35 4.13 10.00 1.95 350(9750)

Dark-green (537.54) (11.81) (58.81 ) (4.09) (10.98) 440(8940) >280, 75% 710(35)

2. [U02Cu(L)(H20)3] I 980±90 11 .67 30.10 36.96 2.63 6.35 1.75 420(12750)

Dark-brown (1647.08) (11.81) (29.55) (58.8 1 ) (2.55) (6.80) 500(5670)

>300,65% 675(50)

3. [Mo02Cu(L)(H20)4] 900±40 9.58 13.52 43.08 3.47 8.55 1.73 430(14500)

Dark-brown (699.55) (9.08) (13.72) (42.89) (3.43) (8.01) 680(45) >300,70%

4. [ZnCu(L)(H20)3] I 540±60 10.58 10.98 48.98 3.52 9.55 1.71 425(12570)

Dark-brown ( 1237.86) (10.27) (10.56) (48.47) (3.56) (9.05) 690(40)

>300,65%

5. [NiCu(L)(H20)4] I 650±55 11.10 9.81 47.85 3.78 9.10 2.60 420(10950)

Dark-brown (1260.50) (10.08) (9.31) (47.60) (3.8 1 ) (8.90) 720(48) >300,65%

6. [CoCu(L)(H20)4] I 680±60 10.85 9.55 48.61 3.76 8.85 3.50 430(15750)

Greenish-brown (1260.96) ( 10.08) (9.35) (47.58) (3.81) (8 .90) 540(48) >300, 70% 680 (38)

7. [MnCu(L)(H20)4] 1700±65 10.66 8.55 48.10 3.79 8.54 5.40 425(13780)

Dark-brown >300, 65% (1253 .10) (10.14) (8.78) (47.88) (3.83) (8.94) 690(55)

8. [Cu2(L)(H20)2].2H20 I 390±35 20.43 47.01 3.85 8.63 1.34 350(12800)

Brownish - green ( 1270.20) (20.01) (47.24) (3.78) (8.82) 380(12908)

420 (10290) 540 (250)

", L cm·1 mo)"1

LAL et at.: STUDIES OF HETEROBIMETALLIC COMPLEXES 11 6 1

The magnetic parameters indicate gll>g.1> free-spin (2.0023), which shows that the unpaired electron is in the d./ -/ orbital of the copper(II) centre. The gil and g.1 values depart considerably from the free ion value. The presence of strong broad band centred at -710 nm in the visible region of the electronic spectra of the compound suggests distorted octahedral stereo­chemistry.

The covalency parameter a2 Cu for the complex is

calculated from gil , g.1 and All by the following equation25

.

a 2cu = - (AW'P) + (gU-2) + 3/7(gr2) + 0.04

where, P is equal to 0.036 cm-'(ref.26) . Its value has been found to be 0.63 for the complex. The a 2cu value for the complex suggests considerable covalent character (37 %) in bonding involving metal ion and ligand.

The homo-bimetallic copper(II) complexeS) shows anisotropic ESR spectrum with three signals. The intensity of the signals in the solid state at room temperature and LNT (77K) rules out the possibility of either square planar or distorted octahedral stereochemistry for the complex and suggests to have five-coordinate structure. The two basic configuration TBP and SP for five- coordinate complexes are characterized by the ground state dz' and dx'-l., respectively. Analysis of the anisotropic spectra

according to Kneubuhl's method27 gave three g-values g,=2 .140; g2=2.218 and g3= 2.383. The R- parameter (g2-g,/g3-g2) for the complex is less than 1. This indicates that dx'-l , is the ground state in this complex. Thus, the complex may be suggested to be five-coordinate square pyramidal. The relatively high values of g-parameters are, most probably, indicative of binuclear nature of the complex. The powder spectra of the complex shows a weak signal at g == 4.450, typical of Cu-Cu interaction with an absorption corresponding to a ~ms= 2 transition.

The hetero-bimetallic complexes (2) to (4) derived from monometallic copper(II) complex (1) have almost similar ESR spectral feature . They exhibit isotropic spectra similar to that of the precursor monometallic complex in the solid state at RT with gay value in the region 2.090-2.051. Further, the complexes (2) and (4) show isotropic spectra at LNT also in solid state with g ay value equal to 2.086 and 2.080, respectively, while, the heterobimetallic Mo02

-Cu complex (3) shows an anisotropic spectrum in the solid state at LNT (77K) with gil and & values equal to 2.265 and 2.070 and metal hyperfine coupling constant equal to 180G. The magnetic parameters indicate that gll>g.1> free electron spin (2.0023), which shows that unpaired electron is in the dX2 - y2

orbital of the copper (II) centre.

The hetero-bimetallic Mn-Cu complex (7) also

Table 2- Magnetic parameters for monometallic, homobimetallic and some heterobimetallic copper complexes

Complex Temperature gay gil gl Aav All Ai (G) (G) (G)

[Cu(LH2) (H2O)2] RT (solid) 2.08g

(1) LNT (CH3CN - DMSO) 2.106 2.189 2.064 62 136 25

[U0 2Cu(L) (H2O)3] LNT (Solid) 2.086

(2) LNT (CH3CN-DMSO) 2.212 2.235 2.064 160

[Mo02Cu(L) (H2O)4] LNT (Solid) 2.135 2.265 2.070 180

(3) LNT (CH3CN-DMSO) 2.110 2.223 2.054 160

[ZnCu(L) (H2O)3] LNT (Solid) 2.080

(4) LNT (CH3CN-DMSO) 2.147 2.254 2.090 150

[MnCu(L) (H2O)4] LNT (Solid) 2.077

(7) LNT (CH3CN-DMSO) 2.146 2.258 2.090

2.035a 94b

[Cu2(L)(H20)2].2H20 RT(solid) 2.247 2.383 (g3) 2.218(g2) 2.140 g,)

(8) LNT 4.42 2.189 2.319(g3) 2.149 (g2) 2.100 (g,) 4.480

~ II II a , gay or Mn . b ,Aav for Mn

1162 INDIAN J CHEM, SEC A, JUNE 2002

[Cu(LH2)(H20)z] (1) (I) I

shows an isotropic spectrum in the solid state at RT as well at LNT with gav value equal to 2.077. However, in the CH3CN-DMSO glass at LNT, the complex shows isotropic splitting into six hyperfine line. This hyperfine structure is attributed to sSMn (l = 5/2). In the low field region, a weak signal is observed with g­value equal to 2.258. The appearance of weak signals indicates the binuclear nature of Mn(II) complex. This signal may also arise due to parallel components of copper hyperfine structure.

On the basis of various physico-chemical data presented above and spectroscopic studies, the structures for some of the complexes are suggested (Structures I and II).

Acknowledgement We would like to thank the UGC and DST, New

Delhi for financial assistance. Further, we would like to thank the Head, RSIC, CDRI, Lucknow, for carbon, hydrogen and nitrogen analyses, and to the Head RSIC, lIT, Mumbai for ESR spectral studies.

References I Fraser C, Johnston L, Rheingold A L, Haggery B S,

Wellioms G K, Whelan] & Bosnich B,Inorg Chem., 31 (1992)1835; Vincent J B, Huffman J C, Christoud G, Li Q, Nanny M A, Hendrickson D N, Fong R H & Fish R A, JAm chern Soc, 110 (1989) 6898.

2 Cador Q, Mathoniere C & Kahn 0, In org Chem, 36 (1997) 1923; Stampt H 0, Pei Y, Kahn 0, Stetten J & Renard] P, J Am chern Soc, 115 (1994) 3866.

3 Carlson J B, Davies G & Vorous P, Inorg Chem, 33 (1994) 2334.

4 Breeze S R & Wang S, Inorg Chem, 33 (1994) 5113; Wang S, Pang Z, Smith K D L & Wag nor M J, J chem Soc, Dalton Trans, (1994) 955.

5 Ramada I, Kahn 0, Jeannin Y & Robert Fjnorg Chem, 36 (1997) 930.

6 Fraser C & Bosnich B, Inorg Chern, 33 (1994) 338; Papadopoulos A N, Hatzidimitriou A G, Gourdon A & Kessissoglou D P, Inorg Chern, 33 (1994)2073; Barnard K R, Bruch M, Susan H, Enemark, J H, Grable R W & Wedd A G, Inorg Chem, 36 (1997), 637.

7 Dutta R L & Hossain M, J cient ind Res, 44 (1985) 635. 8 Lal R A & Kumar A, Indian J Chern, 37 A (1998) 921; Lal R

A, Kumar A & Chakraborty J, Indian J Chem, 38A (2001) 422.

9 Lal R A, Kumar A & Pal M L, J Indian chern Soc, 76 (1999) 70; Lal R A & Kumar A, Indian J Chern, 38A (1999) 839.

10 Husain M, Bhattacharjee S S, Singh K B & Lal R A, Polyhedron, 10 (1991) 779; Lal R A, Adhikari S, Kumar A & Pal M L, J Indian chern Soc, 75 (1998) 345.

11 Rajan 0 A & Chakraborty A,lnorg Chern, 20 (1981) 660. 12 Vogel A I, A text book of quantitative inorganic analysis, 4th

Edn (ELBS, Longmans, London), 1978, p 472. 13 Geary W J, Coord chern Rev, 7 (1971) 81. 14 Narang K K & Singh M K, Trans met Chern, 12 (1987) 385. 15 Schugar H, Walling G, Jones P B & Gray H B, J Am chern

Soc, 49 (1967) 3712. 16 Jones L H & Penneman R A, J chem Phys, 21 (1963) 542. 17 Topic J & Bachert J 0, Inorg Chem, 31 (1992) 511 . 18 Percy G C & Thornton D P, J inorg nucl Chem, 34 (1972)

3369. 19 Percy G C, J inorg nucl Chem, 37 (1975) 2071. 20 Ciampolini M & Nardi N, lnorg Chem, 6 (1967) 445. 21 Sacconi L & Ciampolini M, J chem Soc A, (1964) 273. 22 Todokoro M, Sakiyama H, Matsumoto N, Kodeva M, Okawa

H & Kida S, J chem Soc, Dalton Trans , ( 1992) 3 13. 23 Boslrup 0 & Jorgensen C K, Acta chem Scand, II (1957)

1223. 24 Goodgame D M L, Goodgame d M & Raynor Can han G W,

Inorg chim Acta, 3 (1969) 399. 25 Ki velson D & Neiman R, J chem Phys, 35 (1961) 149. 26 Abraham A & Pryce M H L, Proc Roy Soc London, A, 230,

206 (1951 ). 27 Kneubuhl F K, J chem Phys, 33 ( 1960) 1074.