Indian Journal of Chemistry Vol. 16A, May 1978, pp, 431-433

Complexes of Uranyl Acetate, Uranyl Chloride & Uranyl Nitrate with N-Methylpiperazine, z-Methylpiperazine, N·Phenylpiperazine & N ,N '-Dimethyl piperazine

BALDEV SINGH MANHAS & ARUN KUMAR TRIKHA Department of Chemistry, Punjabi University, Patiala 147002 and MANGAL SINGH Department of Chemistry, Guru Nanak Dev University, Amritsar 143005

Received 30 April 1977; revised 28 November 1977; accepted 25 January 1978

Stable uranyl complexes have been synthesized with the title ligands starting from uranyl acetate, uranyl chloride dihydrate and uranyl nitrate hexahydrate. The complexes have been characterized on the basis of analytical data and IR spectral studies. IR evidence indicates that the ligands probably exist in the chair conformation in the case of complexes derived from uranyl nitrate and uranyl acetate, and in both chair and boat conformations in the case of complexes derived from uranyl chloride.

OMPLEXES of uranyl ecetate with various br se in THF gave the same stoichiometry for the nitrogen and oxygen donors h; ve been products even ,1 fter refluxing for 4 hr. C recently reviewedv", Adducts of urr nyl Uranium wrs estimated 2S UaOs' Chloride W3S chloride with oxygen and nitrogen donors=" and estims ted by Volhard's method. Elemental analyses uranyl nitrate complexes of the type U02(N03)2·L for C, H end N were performed at CSIRO, Melbourne, and U02(N03)2.2L (where L = an oxygen or nitrogen Austra lia. The <' nalyticr I da ta a re recorded in donor ligand)5-7 have a lso been reviewed extensively. Tsodium hydroxide and be essigned to the c symmetric stretch of the uranyl distilled. The colourless liquids were stored over groups. The band corresponding to the symmetric sodium hydroxide. 2-Methylpiperazine (Fluka) W2S stretch of OUO, expected" around 850 crrr+, is not kept in vacuo over cone, H2S04 for three days observed. This implies tha t even in the complexes before use. Tetrahydrofuran and petroleum ether this stretch is IR-in2 ctrve 2 nd tha t the linea rity (40-60°) were dried by usual methods and were of OUO group is mrintained. The band due to stored over sodium. OUO bending mode, expected'' to appear Hound Preparation of the complexes - Uranyl chloride 210 crrr+, is not clearly observed as this region is dihydrate and uranyl nitrate hexahydrate were very close to the end of the spectrophotometer range. dissolved in THF. However, uranyl acetate, having A sharp band around 255 crrr? in U0 Cl complexes 2 2 very low solubility in THF, had to be taken as a is probably due to the \lU-CPo. Strong bonds at susper.sion. The br se dissolved in THF was r dded 1550, 1470 and 675 crrr ! are observed in the spectra in excess (metal:base = I:3) to the uranyl salt of uranyl acetate complexes. The positions of these solution or suspersion drop by drop with constant bands, which may be assigned to \lo.OCO, \I.COO stirring. Bright yellow-co loured complexes preci- and 3COO respectively, are characteristic of chelatir g pita ted which were sepa re ted completely by the bidentate acetate groupll,12. The presence of addition of petroleum ether. These complexes were chelating bidentate acetate in these complexes is filtered, washed with THF and petroleum ether not surprising since there is no steric hindrr nce and dried in vacuo. In case of uranyl acetate com- ~owards the coordination of the bases to the urt nyl plexes, a mixture of the salt suspension and the ion,

431 INDIAN J. CHEM., VOL. 16A, MAY 1978

methylpiperazine and N,N'-dimethylpiperazine, both TABLE 1- ANALYTICALDATA OF URANYL COMPLEXES the amine nitrogens are involved in coordination to the uranyl ion. This may be expected in the Complex Found (Calc.) (%) complexes of N -phenylpipera zine too. U C H N CI The N liga tion of the bases is confirmed by the occurrence of a strong and broad (often split) band, UO.(OAc) a- (N- 48'80 21'38 3·68 5·76 which may be assigned to v0 U-N, in the region mepip) (48·77) 2 (22'13) (H8) (5'73) 450-540 crrr? in all the complexes. This assign- UO.(OAc) a- (2- 48'56 21'35 3'51 5'40 mepip) (48 '77) (22,13) (H8) (5'73) ment is reasonable in view of the reported U-N UO.(OAc) s-O· 5 53·00 19·36 3·00 3·25 stretching frequency a round 600 cm-l in the C2 se (Di-mepip) (5H8) (18'87) (2'92) (3'14) of UCl5-Schiff br se complexest? and at 405 cm-I in UO.(OAc) •.O· 5 50·26 23·27 2·99 3·10 (N-phpip) (50'74) (23,02) (2·77) (2-98) UCI4-(piperidine)4 (ref. 18). This broad band most probably overlaps the band due to 02U-0 stretchw UO.(N03).·2·5 36·80 22·81 4'58 14'97 (N-mepip) (36'95) (23'28) (4-65) (15'21) in the U02(N03)2 and U02(CHaCOO)2 complexes. UO.(N03).·2· 5 36'94 23'31 4'80 15·00 This value is much higher than the only other (2-mepip) (36'95) (23'28) (4-65) (15·21) recorded value of ",270 crrr+ for O2U -N stretch UO.(N03).·2(N- 33·00 33·78 4·10 11'28 phpip) (33'14) (3H2) (3'90) (11-69) in bipyridine complexes of uranyl salts20• This

UO.(N03).·(Di- 46·00 14·73 3·01 10·80 is understanda ble in view of the genera lly observed mepip) (46'85) (14'17) (2'76) (11'02) low values of vM-N in 2,2'-bipyridine complexess-. UO.CI a- 2(N- 44'56 IHO A medium intensity band in the region 330-390 mepip) (43-99) (13-12) I UO.CI a- 2(2- 43-34 13-08 cm- may be tentatively assigned to 8NUNI8. mepip) (43-99) (13-12) The nitrogen bases employed in the present study UO.CI •.2(Di- 41'69 12-44 can form complexes either in the boat or chair mepip) (41·82) (12-48) conformation. In r.on-chelated complexes, the chair U02CI a- l·5(N- 41·00 12-43 phpip) (40'75) (12'15) form seems to be more probe ble while in the chelated complexes, the b02 t form must exist. OAc = acetate; N-mepip = N-methylpiperazine; 2-mepip The two conformr tions C3 n be distinguished on the = 2-methylpiperazine; N-phpip = N-phenylpiperazine; and basis of their IR spectra 2S has been reported in Di-mepip = N,N'-dimethylpiperazine. the case of PdCI2(N,N'-dimethylpiperr zine) 14.22. In this complex, the ligand hrs been shown to exist in the boat form by the X-ray diffraction studies-". To decide between the monodentate and bidentate The IR spectrum of the complex exhibits a number nature of nitrate group, the magnitude of the of additional bands of weak or medium intensity splitting of a band around 1400 cm! in the spectrum in addition to changes in the IR bands charr cteristic of N03 has been used often but it is not a good of the free ligandl4.22. These changes rre, therefore, criterion". The criterion due to Curtis, nd Curtisl", considered to be indicative of a char-ge in the depending on the differences between various com- ligand geometry on complexation, from the chair to bination bands of the nitrate group, could also boat form and are consistent with the consequent not be applied in the present case since these lowering of symmetry. bands could not be observed. However, the pre- The spectra of the present uranyl ccetate or sence of a weak band at 220 cm! and a sherp one uranyl nitrate complexes resemble those of the bases at about 255 crrr+, instead of just one band expected very closely with the presence of 2dditionalb,nds around 225 crrr+, is indicative of the bidentate due to the U02, acetate and nitrate groups. In nature" of the nitrate in the present complexes. these complexes, therefore, the piperazine mole- The vN-H band recorded in the region 3300-3200 cules probably coordinr te to the uranyl group in cnr? in the I.R spectra of N-methylpiperazine, the chair conformation giving bridged polynuclear N -phenylpiperazine, and 2-methylpiperazine shifts complexes. In U02(OAc)2.L (L=N-methylpiper2zine to ",3150 crrr? in the complexes of uranyl acetate and 2-methylpiper8zine) six coordination in the with N-phenylpiperazine and 2-methylpiperazine. equatorial plane of U02 is expected. The complexes In the rest of the complexes this band shifts U02(OAc)2·0.5L(L=N-phenyl piperazine and N,N'- to much lower frequencies and mixes with the dimethylpiper2zine) seem to have bridged dinuclerr C-H bands. These changes indicate that N atom structures with five coordination around the U02 of the N-H group coordinates to the uranium moiety in the equatorial plane. The complexes atom of the uranyl ion in all these complexes-v-". U02(N03)2(N-phenylpiper8zine)2 and U02(N03)2' Prominent bands due to vC-H modes of the (N,N'-dimethylpiper2zine) must contain the eight N-CHa groups are observed at 2750 and 2810 and six coordinated uranyl ions respectively. The cm! in the IR spectra of N-methylpiperazine and stoichiometry in U02(NOa)2.2.5L(L=N-methylpipe- N,N'-dimethylpiperazine. These bands are missing razine and 2-methylpipernine) indicates thet nine in the IR spectra of the complexes and presumably coordinated uranyl group may be present in these overlap with the other C-H bands by shifting to cases. higher frequencies around 2900 crrr". This shift On complexation with U02Cl2 the followirg new clearly shows that N atoms of N-CH3 group~ no IR bands of week 2nd medium intersity appear: more have lone pairs of electrons and 2c9-Ulr~ a U02CI2(N-phenylpipeuzine)I'5-762, 835, 992, 1020, partial positive chargel6 as a result of coordination 1142, 1173, 1248, 1300, 1490 crrr+: U02CI2(N- of N-CH3 groups. It may, therefore, J:le co~cluded methylpiperazine)2-950, 1163, 1186, 1210, 1242, that in the complexes of Nvmethylpiperazine, 2- 1580 crrr+; U02Cl2(N,N'-dimethylpiper2zine)2-965,

432 MANHAS et al.: URANYL COMPLEXES WITH PIPERAZINES

1119, 1198, 1337, 1530 crrr+, V.o2CI2(2-methyl- 2. TROTMAN-DICKENSON. A. F.. Comprehensive inorganic chemistry. Vol. 5 (Pergamon Press. Oxford). 1973. piperazine)2-980, 1075, 1204, 1585 crrr '. Heredl 462. or a p2 rt of the be se molecules me y be considered 3. BAGNALL. K W .• in Halogen chemistry. Vol. 3. edited to have adopted the boat conformation. In the by V. Gutmann (Academic Press. London), 1967. last three complexes six coordination in the equa- 363. torial plane of U'O, results with one or both of the 4. BROWN. D .• Halides of lanthanides and actinides (John Wiley. London). 1968. 121. base molecules acting as chelating ligands giving 5. COMYNS. A. E .. Chern. Rev .• 60 (1960). 115. rise to a bridged dinuclear complex or a frlly 6. BAGNALL. K W .• Chemistry of actinide elements (Elsevier chelated mononuclear species. The stoichiometry Publishing Co .. Amsterdam). 1972. 154. of Va CI (N-phenylpiperazineh'5' however, requires 7. TROTMAN-DICKENSON, A. F.. Comprehensive inorganic 2 2 chemistry, Vol. 5 (Pergamon Press. Oxford). 1973. a bridged structure with at least one base molecule 301. acting as a chelating bidentate ligand to account 8. BULLOCK. J. 1.. J. inorg. nucl. cu«; 29 (1967). for the changes in the IR spectrum, the other base 2257. molecule proba bly existing in the chair form bridging 9. TOPPING. G .• Spectrochim. Acta. 21 (1965). 1743. 10. DAY. J. P. & VENANZI. L. M., J. chem. Soc.• (1966), the two va2 groups. In this complex the coor- 1363. dination number is expected to be five with the 11. JONES. L. R .• J. chem. Phys .. 23 (1955), 2105. ligands arranged in the equatorial plane Hound 12. SAVANT. V. V. & PATEL. C. C.• J. inorg. nucl. cu«, 31 the uranyl group. (1969). 2319. 13. CURTIS. N. F. & CURTIS. Y. M., Inorg, Chem-, 4 (6) (1965), Of the two conformations, the boat conformrtion 804. is sterically bulkier. The existence of only the 14. HENDRA, P. J. & POWELL, D. B., J. chem. ss«, (1960), chr ir form of these bases in the Vaz(Na3)z and vaz 5105. (aAc)z complexes and that of the bor.t conformation 15. GREENWOOD, N. N. & WADE, K, J. chem. Soc., (1960), 1130. for at least one base molecule in Va2Clz complexes 16. BRAUN HOLTZ, J. T., EBSWORTH, E. A. V., MANN, F. G. & is, therefore, understandable in view of the greeter SHEPPARD, N., J. chem. soe., (1958), 2780. steric crowding already existing in the former 17. VIJAY, R. G. & TANDON. J. P., Indian J. cie«, 15A compared to that in the latter around the vaz unit. (1977). 466. 18. SELBIN. J .• ORTEGO. J. D. & SCHOBBER. M .• J. inorg, Acknowledgement nucl. Chern.• 28 (1966). 1383. 19. NAKAMOTO, K.• MORIMOTO, Y. & MARTELL. A. E., J. Financial help in the form of a junior reserrch Am. chem. Soc.• 83 (1961). 4533. fellowship (to A.K.T.) and contingent grant under 20. AHUJA. 1. S. & SINGH. R.. Inorg, nucl. Chern. Left .• 9 a research scheme of CSIR, New Delhi, is gratefully . (1973), 283. 21. NAKAMOTO. K. Infrared spectra of inorganic and coordi- acknowledged, nation compounds (Wiley-Interscience, New York). 1970. 229. References 22. MANN. F. G. & WATSON. R. R.. J. chem. Soc., (1958), 2772. 1. BAGNALL. K. W .• Chemistry of actinide elements (Elsevier 23. HASSEL. O. & PEDERSEN. B. F.. Proc. chem. Soc., Publishing Co .• Amsterdam). 1972. 188. (1959). 394.

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