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. T<Jble 1. We report here the preparation and characterization of adducts of uranyl acetate, uranyl chloride and Results and Discussion uranyl nitrate with N-methylpiperozine, 2-methyl- All the present complexes <J re sta ble a t room piperazine, Nvphenylpipere zine and N,N'-dimethyl- tempera ture in stoppered via Is. The complexes do pipera zine. not melt but decompose above 350° and are converted Materials and Methods to U30S around 700° rs indicated by TGA studies. They are insoluble in common organic solvents. U02(OAc)2.2H20 (May & Baker) WeS dehydrated The IR spectra of the ligands and complexes were by refluxing with acetic anhydride. U02C12.2H20 recorded in mull (in KBr for acetate complexes) (BDH) and U02(N03)2.6H20 (BDH) were used on Perkin-Elmer 621 and Specord 71-IR as such. N-Methylpiperazine. (Fluka}, Nephenyl- irstruments. A very strong band occurring piperazine (Aldrich) and N,N'-dimethylpiper2zine between 895 and 930 crrr+ for all the complexes may (Fluka ) were refluxed over sodium 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.