Chakravorty, A.

Raghavendra, B. S.

English

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Indian Journal of ChemistryVol. 14A, March 1976, pp, 166-169Structure of Complexes of 2-Phenylazopyridine with Perchlorate Halidesof Ni(lI) & with Ferrous IodideB. S. RAGHAVENDRA & A. CHAKRA VORTY*Department of Chemistry, Indian Institute of Technology, Kanpur 208016Received 9 October 1975; accepted 19 November 19752-Phenylazopyridine (L) acts as an unsymmetrical bidentate chelatlng ligand. The trisspecies Niq+ and FeL~+are isolated in the form of perchlorate and iodide respectively. Thecomplex cations are pseudooctahedral presumably with a meridional trans structure. Fromthe ligand field spectrum of paramagnetic NiL:+, Dq of L is calculated to be 1080cm", a valuewhich is close to that for ethylenediamine in Nienj+ but is considerably less than that of chelat-ing diimines, such as pyridinalimine. The isoelectronic relationship between the diimine andazoamine fragments is noted, FeL~+ shows an intense band in the visible region which isassigned to electron transfer from metal tZI1 (idealized On) to ligand 1t* orbital. That thecharge transfer state has contribution to the ground state also is evident from IR data. The N= Nstretch is considerable lowered in Feq+ in comparison to those in the ligand and in Ni(II)complexes. The paramagnetic complexes NiL2X2,0·5 CH2Cl2(X = CI, Br) and diamagneticNiL2I2 are reported. On the basis of magnetic, electrical conductivity and electronic spectraldata, it is suggested that NiL2X2,0·5 CH2Cl2has pseudooctahedrat Ni(II) (X in cis positions)with dichloromethane held in the crystal lattice but not influencing the Ni(II) environment inany major manner. In NiL,I2 the two Ilgands are believed to be held in a trans planar manner.Iodide ions may be providing weak axial coordination. Major bands in the IR spectra of thevarious complexes are assigned.AN azo group suitably linked to an aromaticring carrying additional donor sites is wellsuited for closure of a chelate ring. Goodexamples of such a situation are provided by themetal complexes of arylazophenols whose chelatingactivity has been known for many years':", Aphenyl azo group attached to the 2-position of apyridine ring as in 2-phenylazopyridine (1) maybe expected to give stable metal chelates. Thisproblem is explored for the first time in the presentpaper. Some related studies recently reported inliterature are those on more complicated systemssuch as 2,2'-, 3,3'- and 4,4'-azopyridines4-6.qN N\ 0g'~"5N=N c6"Hs .Jb NIC6HS-1 2- .aMaterials and Methods2-Phenylazopyridine was prepared in relativelypoor yield by condensing 2-aminopyridine withnitrosobenzene according to the literature? procedure.NiLa(CI04)2- A solution of Ni(Cl04)2.6HzO (0·001mole) in methanol was added to a solution of theligand (0·003 mole) in the same solvent. Thecolour of the reaction mixture was dark green.*To whom all correspondence should be addressed.166The mixture was kept overnight at room tempera-ture. The dark green crystals formed were filtered,washed with little methanol and dried (5 mm, 80°).FeLaI2- An aq. ethanolic solution containingFeS04· 7H20 (0·001 mole) and ligand (0·003 mole) waswarmed and to this concentrated potassium iodidesolution was added. On cooling to 5°, violet crystalswere deposited. These were recrystallized fromwater containing dissolved potassium iodide.NiL2Cl2.O·5CH2Cl2- A methanolic solution ofNiCl2·6H20 (0·001 mole) was added to a methanolicsolution of the ligand (0·002 mole). The solventwas removed by heating on a steam-bath resultingin a gum which was then extracted with dichloro-methane. The extract was concentrated and cooledto room temperature. A dark coloured crystallinesolid (green when powdered) deposited which wasfurther recrystallized from dichloromethane. Thecrystals analysed as NiL2Cl2·O.5CH2C12. The bromocompound was similarly prepared starting fromNiBr2·NiL212- A methanolic solution containingNi(CHaCOO)2.4H20 (0·001 mole) and ligand (0·002mole) was gently warmed. Potassium iodide solu-tion was then added to this mixture. The darksolid thus obtained yields dark crystals (brownwhen powdered) on recrystallization from chloroform-hexane mixture.Physical measurements - Infrared spectra wererecorded on a Perkin-Elmer 521 recording spectro-photometer. Electronic spectra were studied ona Cary-Lt recording spectrophotometer. Magneticmoments were measured using a sensitive GuoyRAGHAVENDRA & CHAKRAVORTY: COMPLEXES OF 2-PHENYLAZOPYRIDINETABLE 1 - CAHRACTERIZATIONDATACompound C (%) N (%) Metal (%)Calc. Found Calc. Found Calc. FoundFeL312 46·10 46·35 14·66 14·79 6·50 6·45NiL3\ClO4)2 49·00 49·28 15·60 15·80 7·27 7·10NiL2·O·5CH2CI2(a) 48·70 48·43 15·49 15·24 10·82 10·60NiL2Br2·O·5CH2CI2(b) 42·47 42·26 13·04 13·15 9·11 9·23NiL.I. 38·88 38·43 12·37 12·43 8·65 8·84(a) The percentage of chloride directly bound to nickel (Calc. 13·07; found 12·72%).(b) The percentage of bromide directly bound to nickel (Calc. 24·80; found 24·90%).TABLE 2 - ELECTRICALCONDUCTIVn:y(a) AND MAGNETICSUSCEPTIBILITYDATACompound Temp. AM Temp. fleff(0C) (ohm"! crn'' (OC) (B.M.)mole:")NiL3(Cl04)2 25 175 28 3·12FeL.I2 19 141 26 DiamagneticNiL2CI2·O·5CH2CI2 19 9 22 3·05NiL2Br2·O·5CH2CI2 19 16 22 3·10NiL,I. 20 45 22 Diamagnetic(a) In 10-3M nitromethane solution.balance described elsewhere". Electrical conducti-vity measurements were done in nitro methanesolution using a Systronics conductivity bridge.Results and DiscussionThe ligand (1, abbrev. as L) readily reacts withNi(II) salts yielding complexes of the typeNiL~ (Cl04) 2,NiL2X2.O·5CH2Cl2(X=Cl, Br) and NiL2I2·In the crystalline state NiL3(Cl04)2 is green while theother species are very dark coloured. In dichloro-methane or chloroform solution the respectivecolours are: NiL3(Cl04)2' green; NiL2X2,0·5 CH2Cl2,brownish green and NiL2I2' brown. The darkcoloured crystals of FeL3I2 obtained by directreaction between ferrous sulphate heptahydrateand the ligand (followed by the addition of potassiumiodide) readily dissolve in water to yield deep bluesolutions which are not very stable. Analyticaldata for all complexes are set out in Table 1.Electrical conductivity (in nitromethane solution)and magnetic data are displayed in Table 2. Somecharacteristic infrared frequencies are shown inTable 3, while electronic spectral data are presentedin Table 4.Structure of tris complexes - Electrical conducti-vity data (Table 2) for both NiL3(CI04)2 and FeL3I2falls within the range'' expected for 1: 2 electrolytes.Clearly the complex cation Mq+ is present inthese species.NiL3(Cl04)2 is fully paramagnetic (Table 2). Inthe electronic spectrum three bands in the visibleregion (Fig. la) establish a gross octahedral geo-metry for the cation Nil.]". In idealized 0"symmetry the bands are readily assigned as 3A2g-+3T2g(F) , 10800 crrr+ : -+ IE(D), 11900 crrr"and -+3Tg(F) , 16400 cm-I. The 3A2 -+3Tg(P)transition is hidden under intense absorption inthe UV. The Dq value of L is thus 1080 cnr",which is considerably lower than that of is0electronic2-pyridinalimine species iDq-« 1250 em -1) but isclose to that of en in Nienj" (en = ethylene-diarninej-". Since L is an unsymmetrical bidentateligand, Niq+ can exist'! in two isomeric forms,cis and trans. In the cis form the three phenylgroups are crowded on one face of the octahedronwhile in the trans form these are meridionally dis-posed. In such a situation the trans form is usuallyof much .greater stability-t. We propose thatNiq+ has the trans structure @.FeLaI2 is diamagnetic at room temperature.The metal atom thus has a low-spin d6 configuration.It is logical to assume that Feq+ also has thetrans structure @. The most characteristic fea-ture of the electronic spectrum of FeL3I2 (Fig. Ib)is an intense band in the visible region near 16900crrr+; there is a shoulder at slightly higher energy(18200 cm+). It is well known that tris-diiminecomplexes of Fe(II) show an allowed charge transfertransition from metal t2g orbital (idealized Oft) tothe lowest empty diimine 7t* orbital'<?". Thistransition is seen in the form of a band at I""ooJ 18000cm! associated with a shoulder at slightly lowerenergies. The shoulder is believed to be the firstmember in a vibrational progression (couplingwith C:-:-:-C+C:-:-N vibrations). The azoimine group-N =N -C=N - is isoelectronic with the diiminefunction -N =C-C=N - as we have noted earlier-".Consequently low energy metal-to-ligand chargetransfer transition may be expected in Feq+ also.Indeed the 17000 crrr ! band in the latter complex isundoubtedly due to such a transition. We note thatthe metal-to-ligand transition in FeL~+ is at consi-derably lower energy than that in Fe (diimine)i+.Feq+ also shows a band at 26500 crrr ", Theorigin of this band is not certain; the ligand itselfhas absorption in this region (Table 4).The -N =N - stretching frequencies in theligand and Ni(II) complex occur in the narrowrange 1418-1431 crrr? (Table 3) as expectedv-".On the other hand, there is a dramatic decreaseof this frequency to 1353 cnr ' in FeLt. This isevidently due to some contribution of the metal-to-ligand charge transfer state to the ground levelas in the case of Fe(diiminen+ speciesl2-I5 (C:-:-:-Nstretch is lowered).Structure of NiL2X2·O·5CH2Cl2(X =Cl, Br)- Thesetwo compounds are fully paramagnetic in the solid167INDIAN J. CHEM., VOL. 14A, MARCH 1976TABLE 3(a)- SELECTEDINFRAREDFREQUENCIES(cm-1)Assignment L FeL:JIs NiL3(CIO.)2(b) NiL2CI2· NiL2Br2· NiL2I20'5CH2CI2(c) 0'5CH2CI2(c)Aromatic 1616 (5) 1599 (5) 1605 (5) 1605 (5) 1604 (5) 1600 (5)C = C and C = N 1587 (m) 1579 (m) 1586 (m) 1587 (m) 1587 (m) 1582 (m)1477 (m) 1458 (m) 1474 (m) 1472 (m) 1468 (m) 1468 (m)1456 (5) 1446 (5) 144·6 (m) 1452 (5) 1446 (5) 1447 (5)N=N 1425 (5) 1353 (5) 1428 (5) 1431 (5) 1426 (s) 1418 (5)C-H out-of-plane bending in 687 (5) 692 (5) 691 (5) 698 (5) 692 (5) 692 (5)phenyl ring784 (5) 772 (s) 770 (s) 773 (5) 765 (5) 770 (s)C-H out-of-plane bending inpyridine ring(a) An unassigned band of medium intensity appears in the range 740-750 cm-! in all compounds studies. (b) Vaof ClOt is observed as a broad band of high intensity centred at 1100 cm=t, (c) C-Cl stretch of CH2Cl2 is at726 ern"! (m).TABLE4 - FREQUENCIES(V, crrr+) ANDEXTINCTIONCOEFFICIENTS(E, litre mole-I) OF SOMEELECTRONICBANDSCompound* MediumFeLaI2 Solution(water)NiL3(ClO,)2 Solution(dichloro-methane)NiL,CI a-0·5CH.Cl. Solution(chloroform)SolidNiL,Br2·O·5CH2Cl2 Solution(chloroform)SolidV (E)16900 (5150); 18200 (3850)sh ; 26320 (16900) sh ;31250 (37800)10900 (12); 11700 (15) sh;16400 (355) ; 30770(38130)8630 (13); 16500 (122) sh:22470 (510); 31250(2390)9450; 16400 sh; 232008700 (16); 17000 (202) sh;22730 (1240) sh; 29160(2825)9350; 16250 sh; 24400 sh"Ligand (L) shows bands at 22370 and 29410 crrr+,state (Table 2). The molar electrical conductivitiesof 1: 1 electrolytes in nitromethane lie" in the range75-95 ohm+em! mole". The observed conducti-vities of the present complexes show that they areonly slightly dissociated in solution (Table 2). Thedichloromethane of crystallization is strongly heldin the lattice and is not removed even at low pres-sure (5 mm) and elevated temperature (80°). Quitea few transition metal complexes which containdichloromethane of crystallization are now known".We wish to stress that the present compounds canalso be prepared as amorphous powders withoutthe dichloromethane of crystallization. On theother hand, well-formed crystals which are easyto purify are obtained when dichloromethane ispresent. The solid state IR spectra of NiL2Br2and NiL2.Br2·O·5CH2CI2were found to be essentiallysuperimposable except that the latter compoundshows bands characteristic of dichloromethane also.The dichloromethane of crystallization does notappear to affect the ligand disposition in any majorway.Considerable interest has been shown in recentyears about the stereochemistry of complexes ofthe type NiB2X2 where B is a bidentate ligand.There is evidencet? that when X is widely separated168.54lcfe32s ·9 10 1110-3 II (cm-1)(0)I12Fig. 1 -:- Electronic spectra of the complexes [(a): (1) NiL,(CIO,). lJl CH2CI2; (2) and (4) NiL2CI2.O·5CH2CI2 in nujol mullanc:t CHCla respectively; (3) and (5) NiL.Br2.O·SCH.Cl. innujol mull and CHCla respectively; in the case of nujol mullthe absorption coefficient axis is in arbitrary units. (b)FeLaI. in water]from B in the spectrochemical series the cis con-figuration is preferred over the tr~ns structure.G~od examples are Ni(phen)2X2 (ref. 19), Ni(en)2X2(dimer] (ref. 20). and Ni(po)X2 (ref. 21) where phen= o-phenanthroline, en = ethylenediamine, po = 2-pyridinaloxime and X = Cl, Br, I. In going fromNiN6 to trans-NiN4X2, the octahedral 3A2!,-+3T2g(VI) band shows observable splitting due to decrease?f symme~ry from o, to D4• A good exampleIS trans-Nl(PY)4Br~ (ref. 21, 22). The cis-NiN4X2sphere has lower symmetry (Czv) than trans-NiN4XaRAGHAVENDRA & CHAKRAVORTY: COMPLEXES OF 2-PHENYLAZOPYRIDINEbut the magnitude of orbital splitting is expectedto be less23• In practice such splitting is oftennot observedl9,2l. The complexes of 2-phenylazo-pyridine under discussion shows an unsplit Vl bandat 9400 crrr+ (solid) or at 8600 crrr? (solution) (Fig. 1).Previously we have noted that 2-phenylazopyridineand ethylenediamine have similar ligand fieldstrengths. In this context it is significant thatvl of solid Nien2Cl2(dimer) is at 10200 cm! (ref. 21),a value which is very close to that of the presentlysynthesized NiL2Cl2• However, NiL2Cl2 unlike theethylenediamine complex cannot be dimeric, i.e.L2NiCl2NiL2Cl2,in view of the electrical conductivitydata (vide supra). On the basis of above discussionwe propose that NiL2X2 has the structure @).NiL2I2- This is diamagnetic and shows no ligandfield bands below 16000 crrr '. In this complexthe NiL2 sphere is evidently grossly planar pre-sumably with a trans (steric overcrowding of phenylgroup in cis geometry) disposition of ligand mole-cules. The iodide ions remain partially bound insolution, since the observed electrical condutivityis much lower than that expected for a 1: 2 electro-lyte. In view of the proposed difference in stereo-chemistry of the NiL2 fragment in the chloro (bromo),and iodo complexes, it may be significant that theN =N stretch in former (no centre of symmetry)is considerably more intense than that of the latter(centre of symmetry).AcknowledgementThe financial support provided by the CSIR,New Delhi, and the Department of Atomic Energy,Government of India, are gratefully acknow-ledged.References1. ELKINS, M. & HUNTER, L., J. chem, Soc., (1935), 1598.2. PFEIFFER, P., HESSE, TH., PFlTZINGER, H., SCHOLL. W& THIELERT, H., Z. prakt. Chem., 109 (1937), 217.3. CHAKRAVORTY, A. & KALlA, K. C., Inorg. Chim, Acta, 2(1968), 154.4. BALDWIN, D. A., LEVER, A. B. P. & PARISH, R. V., Lnorg .Chem.,8 (1969), 107.5. BEADLE, P. J., GOODGAME, D. 1\11.L., GOLDSTEIN, M. &GRAZESKOWIAK, R., Inorg. cie«; 8 (1969), 1490.6. BEADLE, P. J. & GRAZESKOWIAK, R., J. chem, Soc., (A)(1970), 305.7. CAMPBELL, N., HENDERSON, A. W. & TAYLOR, D., J. Lchem, Soc., (1953), 1281.8. KANNAN, T. S. & CHAKRAVORTY, A., Inorg. Chem., 9 '(1970), 1153.9. GEARY, W. J., Coord. Chem, Rev., 7 (1971), 81.10. RABINSON, M. A., CURRY, J. D. & BUSCH, D. H., Tnorg,Chem.,2 (1963), 1178.11. CHAKRAVORTY, A. & KALlA, K. C., Inorg. cie«; 7(1968), 2016.12. KRUMHOLZ, P., Structure and bonding, 9 (1971), 139.13. SANDERS, N., J. chem, Soc. (A) (1971), 1563.14. ITo, T, TANAKA, N., HANAZAKI, I. & NAGAKURA, Bull.chem, Soc. Japan, 41 (1968), 365.15. KRUMHOLZ, P., Lnorg . Chem., 4 (1965), 612.16. GUPTA, S. & CHAKRAVORTY, A., Lnorg . Nucl. Chem. Lett.,9 (1973), 109.17. BASSIGNANA, P. & COGROSSI, C., Tetrahedron, 20 (1964), '2361.18. ADDISION, A. W. & GILLARD, R. D., J. chem. Soc. (A),(1973), 2002.19. McKENZIE, E. D., Coord. Chem. Rev., 6 (1971), 187.20. PORAI-KoSHlTS, M. A., SHRELASHVILl, A. E., ANTSYSH-KINA, A. S. & MINACHEVA, L. KH., Russ. J. Inorg.Chem., 13 (1968), 651.21. LEES, G., HOLMES, F., UNDERHILL, A. E. & POWELL,D. B., J. chem, Soc. (A) (1971), 337.22. SACCONI, L., Transition metal Chem., 4 (1968), 199.23. YAMATERA, H., Bull. chem, Soc. Japan, 31 (1958), 95;MCCLURE, D. S., Advances in the chemistry of coordi-nation compounds (McMillian, New York), 1961. 498.169

Structure of Complexes of 2-Phenylazopyridine with Perchlorate Halides of Ni(II) & with Ferrous Iodide

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Structure of Complexes of 2-Phenylazopyridine with Perchlorate Halides of Ni(II) & with Ferrous Iodide

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