Preliminary investigation of an 8-quinolinol complex of uranium(v1)

Transcription

1 Preliminary investigation of an 8-quinolinol complex of uranium(v1) J. E. FLEMING AND H. LYNTON Depnrt~lzent of Clzeflzzstry, Cniversity of Victoria, Victoria, British Columbia Received September 14, 1966 The present work suggests that the chelate UOa(C9HsNO)n.CgHsNOH can be crystallized from chloroform as orange-red crystals which are monoclinic, space gt;oup PZ1 with a = 14.98a4 (a = 0.03A), b = 20.38A (c = 0.05A),c = 14.75A (a = 0.03A), andp = " (a = 0.20'). It is believed that six molecules are in the unit cell: three sets of molecules in the general positions (2a). The uranium positions have been established and show the higher symmetry P21/m with four atoms in general positions and two atoms in the pseudo mirror planes. The molecular arrangement of 8-quinolinol molecules around the more general uranium atoms has been obtained from three-dimensional Fourier syntheses. This arrangement of 8-quinolinol molecules is essentially the same as found by Hall, Rae, and it'aters in the adduct U02(CgH6- NO)~.C~HGNOH.CHC~~. The molecular arrangement around the two remaining uranium atoms has not been established because of false detail introduced by the pseudo-symmetry. This is enhanced by pronounced termination of series errors in the b-axis direction. Canadian Journal of Chemistry. Volume 45, 1637 (1967) INTRODUCTION A number of papers have reported on the 8-quinolinol chelates of uranium(v1) (1-4). Three compounds have been discussed : (A) UOz(CgH~NO)~.CgHo~OH (I), (B) UOz- (C9HsN0) 2 (I), and (C) [U02(CgH6NO) CgH6NOH (2, 3). The structure of the red compound A has been determined in the form of its adduct with chloroform, (D) U02(C9HsNO)2.C9H6NOH.CHC13 (4). The green compound B, prepared by heating A for about 48 h at 210 to 215" (5), is well established but no structure has been reported. Little is known of the structure of the orange compound C, which may be obtained as an alternative to A by a change in ph of the precipitating solution (2), although it has been suggested that it is structurally similar to compound A (3). It was the intention of the authors to prepare and investigate the structure of the green chelate B. With this in view, compound A, in the form of a red-brown powder, was prepared by the method of Rloeller and Wilkins (5). This compound, when recrystallized from chloroform, formed lath-like crystals orange in color when viewed through the thin section but red when seen through the thicker edge. X-ray examination confirmed these to be the adduct D examined by Hall, Rae, and Waters (4). Compound A, when heated, gave a greenbrown powder, at first thought to be the green chelate. This green-brown material seemed sparingly soluble in chloroform. Evaporation of this solvent from some saturated solutions gave as the main product a few crystal clusters (compound E), color orange to red. These clusters were accompanied by some lath-like crystals also colored orange to red, which were identified as the adduct D. Preliminary X-ray examination of the crystals E established thein as monoclinic, space group P21, or <21/rn, with unit cell dimensions a = 15.1 A, b = 20.6 A, c = 14.9 A, and = 115.3". Since the crystals were orange-red they could not be the green chelate B. If the green-brown pox% der obtained on heating were mostly unchanged or modified compound A, these new crystals could be either A itself or a new adduct. Any green chelate present probably did not dissolve in the chloroform. The authors believed that the structure of the new crystals would be sufficiently interesting to warrant a more complete X-ray investigation. CRYSTALLOGRAPHIC AND INTESSITY DATA A more accurate set of cell dimensions for compound E was later obtained using a Buerger single-crystal equi-inclination diffractometer manufactured by the Charles Supper Company. Nickel-filtered Cu Ka radiation was used with a Philips xenonfilled proportional counter as detector.

2 1638 CANADIAK JOURSAL OF CHEhIISTRY. VOL. 45, 1967 Accurate T, p, and u values were measured for several Ok0 and h01 reflections, with the b crystallographic axis parallel to the 4 axis of the diffractometer (10). In no case was the Kal, Kaz doublet resolved. The crystal data is gixren in Table I. Using the multiple film pack technique, equi-inclination Weissenberg photographs were taken of layers hol-h61, hk0, and Okl. Common reflections in the layers hko and Okl were used to ~ uall t data on the same arbitrary scale. Two different crystals mere used in the data collection, both irregular in shape with average thicknesses of 0.08 mnl and 0.11 mm. No absorption corrections were applied. The intensities of all reflections were estimated bv visual comparison with a calibration strip prepared using a suitable reflection from one of the crystals. TABLE I Crystal data System hlionoclinic Space group P21 orop2l/m - a 14.98A (u=0,03a) a (u=0.05.&) c 14.75A (,=0.03 A) " (a=0.20 ) A3 Dm (by flotation) 1 75 g ctn-" D, (assuming 6 molecules of UOa(CsHsSO)2.C~HsNOH in the un~t cell) 1.72 g ~ rn-~ Systematic absences OkO: k=2n+l There are approximately independent lattice points within the range of Cu Ka radiation, but an examination of the photographs showed a rapid decrease of intensitv with increase in sin 8 such that very few reflections were observed for p(2 sin 8) > If the decrease in intensity is assumed to be the same in all directions. this limits the total number of observable independent reflections to approximately The total number of independent reflections photographed was 2 323, of which had measurable intensities. The data was more limited in the b-axis direction than in either a or c, since the highest layer collected was h61 for which LX 0.45 ; this does not compare favorably with an intensity limit at p N 1.50 in the other directions. The initial stage of the structure analysis mas carried out n-ith h01 data only. A Patterson synthesis1 showed two pronounced peaks, P1 and Pz, which were interpreted as two independent uranium atoms in the follon ing positions: U(1) x = 0.102, z = 0.043; U(2) x = 0.742, z = An examination of the electron content of the Patterson peaks, however, showed that P, had approximately twice the content of PI. This suggested a solution in P21/rn, n-ith four atoms (U(2)) in general positions (4f) and two atoms (U(1)) in special positions (2e), that is a total of six uranium atoms in the unit cell. A set of structure factors \\as calculated for these uranium positions and gave a discrepancy index of R = 0.242, which confirmed the interpretation. The structure factors were calculated using an isotropic temperature factor of B = 4.63 obtained from a Wilson plot, and uranium scattering curves (given by f = [Cf, + Af')2 + (Af")2]1i2) from ref. 7. Attempts to find a possible arrangement of 8-quinolinol rings by an h01 Fourier synthesis were unsuccessful, as considerable overlap of the molecules was obviously present. From a consideration-of the OkO reflections, where 060 has the largest IF,I and 0,12,0 is very large for its sin 0 value, and a study of molecular packing, the y coordinates of the uranium atoms U(2) in the general positions were assessed at approximately 1/12, 5/12, 7/12, and 11/12. The uranium atoms U(1) lie in the mirror planes at y = 1/4 and 3/4. A three-dimensional set of structure factors based on these coordinates and using the same temperature factor and scattering curves as before gave a discrepancy index of R = Some refinement of the uranium positions resulted in the final coordinates listed in Table 11. A set of structure factors (s.f. 1) based on these final coordinates gave a discrepancy index R = laa1l cornputatio~ls were done on an I.B.M computer, using the programs of Xhmed, Gabe, NIair, and Pippy (6).

3 FLEMING AND LYNTOK: PRELIMIXARY IKVESTIG4TIOS 1639 TABLE I1 Fractiollal atolllic coordi~lates for the uranium atoms in space group P21/112 Atom X Y z FIG. -1. Molecular arrangernetlt of 8-quinolinol molecules around uranium U(2). These structure factors (sf. 1) were used to compute several sections of a threedimensional Fourier synthesis, perpendicular to the b axis, near the position of the uranium atom U(2j. These Fourier sections indicated the nearly planar molecular arrangement of 8-quinolinol groups shown in Fig. 1. There are three 8-quinolinol molecules surrounding the uranium atom, two bidentate with bonds from both phenolic oxygen and ring nitrogen, and one monodentate molecule bonded from the phenolic oxygen. This monodentate 8- quinolinol molecule is probably also bonded to a neighboring nlolecule by a link from its nitrogen to a phenolic oxygen. This arrangement is essentially the same as that found by I-Iall, Rae, and Waters in the adduct D (4). If, as packing considerations suggest, the molecular arrangement around U(1) is similar to that found around U(2), then its three 8-quinolinol molecules must be exactly in the mirror plane, giving an arrangement that is completely coplanar with the uranium atom. It was difficult to understand why both a planar and a nonplanar arrangement should be present in the same structure, and indeed a planar arrangement would require a very tight fit of 8-quinolinol molecules about the uranium atom. This consideration, coupled with a lack of success in establishing from a Fourier section in the mirror plane any molecular arrangement at all, suggested that this mirror plane did not in fact exist. This implies that the correct space group is P21 with three sets of molecules in the general positions (2a). A refinement in P21 was tried, but attempts always led to pseudo mirror planes at y = 1/4 and 3/4 and did very little to resolve the molecular arrangement at these positions. FJG. 2. (a) F, Fourier line synthesis through uranium atom U(1). (b) F, Fourier line synthesis through uranium atom U(2). Since there is a distinct lack of data in the b direction (the highest layer photographed was h61 and it ~vould be possible to obtain equi-inclination photographs up to k = 16), it mas thought that the termination of series effects resulting from this might be acting in conjunction with the pseudosymmetry effect to mask the molecular arrangement around U(1). The existence of pronounced diffraction ripples in the b direction is shown in F, line syntheses through both uranium atoms (Fig. 2(a-b)). Difference syntheses were also computed along these lines and indicated the presence of uranyl-oxygen ato?s at bond distances of the order of A.

4 1640 CASADIAN JOURNAL OF CHEMISTRY. VOL. 45, 1967 T.4BLE I11 Approximate coordinates for the three 8-quinolinol molecules around U(2) in space group P21/nz Atom x Y z It was considered that further work in ' the space group P21 would be unprofitable, so using the approximate coordinates for the three 8-quinolinol molecules around U(2) (Table 111) and the coordinates for the six uranium atoms (Table 11), a set of structure factors (s.f. 2) was computed in the space group P21/m. An isotropic temperature factor of B = 4.63 was used for all atoms, and the scattering curves were those given in refs. 7 and 8. These structure factors gave a discrepancy index of R = as compared with the value R = obtained from s.f. 1. This drop in the R factor supports the partial interpretation of the Fourier synthesis, and further support is provided by a comparison of the agreement summary analyses (9) for the two sets of structure factors (Table IV). Although 172 reflections in all changed categories, s.f. 2 shows a net gain of 16 reflections in TABLE IV Agreement summary s.f. 1 R = observed reflections (13 < F,i < 955) 1 Fthl = threshold amplitude = 35 Category Limits Yumber - / 1 F. 0 F or IAFI/IFoI <2R 1.0 lfthl <jafl<2.0 Fthl, or 140 2R<lAFI/I F,j <3R IFtt, <iafi<3.0 Fthi, or 23 3R <lafi/l F,j <4R IFthl< IAFI, or 9 4R<IAFI/IFoI s.f. 2 R = observed reflections (14 < jf,i < 984) 1 Fthl = threshold amplitude = 35 Category Limits Number category 1 and a corresponding loss in categories 2, 3, and 4. C0SCLUS10N By the method of preparation, compound E would appear to be an 8-quinolinol complex of uranium(v1). The four molecules resolved in the structure analysis show the presence of three 8-quinolinol molecules surrounding each uranium atom in an arrangement essentially the same as found by Hall, Rae, and Waters in the adduct D. There is no reason to suppose that the molecular arrangement around the two remaining uranium atoms is significantly different. There is no evidence of any other molecule, such as chloroform from the solvent, in the structure and, indeed, there is little room to accommodate such a molecule. This suggests that compound E is probably the chelate UO~(C~H~NO)~.C~HGNOH. The observed density was obtained by flotation using only one crystal and could be in error by 1-2%. This may account for the small discrepancy between the observed and calculated densities.

5 FLEMING AND LYNTON: PRE :LIMINXRY INVESTIGATION 1641 Compound E has been prepared on more than one occasion but in minute quantities only. In total, less than 30 mg was available for examination. After wastage in the X-ray investigation, there was insufficient left for a reliable chemical analysis. Attempts at establishing the molecular arrangement around two of the uranium atoms have proved unsuccessful in each of the possible space groups P21 and P21/m. This is thought to be due to the pseudo mirror symmetry introduced into the more probable space group P21 by the highly symmetrical arrangement of uranium atoms. This effect is enhanced by pronounced termination of series effects in the b-axis direction. The authors are at present unable to collect more data and do not intend extending the analysis in the near future. The structure factors2 s.f. 1 and s.f. 2 have been placed in the Depository of Unpublished Data, National Science Library, National Research Council of Canada, Ottawa. Canada. 2Photocopies may be obtained, upon request, from: Depository of Unpublished Data, National Science Library, National Research Council of Canada, Ottawa, Canada. - ACKSOWLEDGMEST We acknowledge the financial support of the National Research Council of Canada for this work and we thank Dr. W. W. Wendlandt, Texas Technological College, Lubbock, Texas, for his interest at the start of this work. REFERESCES 1. G. R. HORTOS and W. W. I~ENDLANDT. J. Inorg. Nucl. Chem. 25, 241, 247 (1963) (bibliography). 2. J. BORDXER, E. D. SALESIN, and L. GORDOK. Talanta, 8, 579 (1961). 3. R. J. MAGEE and L. GORDOK. Talanta, 12, ). 4. b. HALL, A. D. RAE, and T. K. IVATERS. Proc. Chem. Soc. 21 (1964). 5. T. MOELLER and D. H. ITILKINS. Inorg. Syn. 4, 101 (1953). 6. F. R. HHMED, E. 1. GABE, G. A. MAIR, and M. E. PIPPP. A unified set of crystallographic programs for the I.B.M computer. Divisions of Pure Physics and Pure Chemistry, Kational Research Council of Canada, Ottawa, Canada. Sept INTERKATIOXAL TABLES FOR X-RAY CRYSTAL- LOGRAPHY. Vol The Kyrloch Press, Birmingham, England Tables 3.3.1B. and 3.3.2B. 8. IP\TERNATION.~L TABLES FOR X-RAY CRYSTAL- LOGRAPHY. ltol The Kynoch Press, Birmingham, England Table F. R. XHMED and 117. H. BARNES. Acta Cryst. 16, 1249 (1963). 10. M. J. BUERGER. X-ray crystallography. John IViley and Sons, New York