Structures of two five-coordinated metal chelates of 2-methyl-8

Synthesis and characterization of 8-quinolinolato vanadium(IV) complexes. Kentaro Takano , Yukinari Sunatsuki , Masaaki Kojima , Isamu Kinoshita , Tak...
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Structures of Two Five-Coordinated Metal Chelates of 2-Methyl-8-quinolinol Motoo Shiro and Quintus Fernando Department of Chemistry, University of Arizona, Tucson, Ariz. The crystal and molecular structures of the compounds VO(CloH8N0)2, bis(2-methyl-8-quinolinolato)oxovanadium(lV), and GaCI(CloH8N0)2,bis(2-methyl-8-quinolinolato)c hlorogalli um( II I), have been determined by three dimensional single crystal X-ray techniques. Both compounds crystallize in the monoclinic space group C2/c, with four molecules of the oxovanadium complex in the unit cell (a = 17.045 i 0.006, b = 7.843 i 0.004, c = 13.400 i 0.006 A, p = 105O 14’ f 1‘), and eight molecules of the gallium complex in the unit cell (a = 28.884 =t0.010, b = 9.594 =t0.004, c = 15.199 =t0.006 A, p = 118O 43’ i 1’). The intensity data were collected on a four-circle automatic diffractometer with MoK, radiation and the structures were solved by Patterson and Fourier methods. Refinement by full-matrix least squares gave conventional R values of 6.2% for 873 reflections for the VO(C,oH8N0)2compound and 7.4% for 1591 reflections for the GaCI(CloH8NO)z compound. The crystallographically imposed symmetry requires that the oxovanadium group lies on a twofold axis. The vanadium atom is in a five coordinate distorted trigonal bipyramidal environment in which three oxygen atoms and the vanadium atom define the equatorial plane and the two nitrogen atoms of the bidentate ligand occupy the apical positions. The coordination polyhedron around the gallium atom is also a distorted trigonal bipyramid with a chlorine atom and two oxygen atoms of the bidentate ligand in the equatorial plane and the two nitrogen atoms in the apical positions.

THE LIGAND, 2-methyl-8-quinolinol precipitates almost all the transition and nontransition metal ions from aqueous solution but does not precipitate aluminum(II1). This property of 2-methyl-8-quinolinol has made it a very useful analytical reagent for the determination and separation of many metal ions in the presence of aluminum(II1) (I). Of particular interest is its reaction with gallium(III), indium(III), and thallium(II1) to form tris-chelates and with beryllium(I1) to form a bis-chelate. The explanation for the anomalous behavior of aluminum(II1) that has been widely accepted is that the packing of three molecules of 2-methyl-8-quinolinol around the small A13+ ion would be sterically hindered, whereas the larger ions (Ga3+, In3+,and TI3+)are able to accommodate the three ligand molecules. The Be2+ion, which is smaller than the AI3+ion, is able to form a bis-chelate since the two ligand molecules are in a tetrahedral configuration, thereby avoiding any steric effects that might arise from the 2-methyl substituents (2). The failure to isolate either 1 :1 or 1:2 complexes of A13f and 2-methyl-8-quinolinol from aqueous solutions has been attributed to the steric interaction of the 2-methyl group with the hydration sphere of the A13+ ion. An added effect is the difficulty that is experienced by 2-methyl-8-quinolinol in displacing the water molecules that are quite strongly bound to the A13+ ion. In nonaqueous media, however, it has been established that 2-methyl-8(1) L. Merritt, Jr., and J. K. Walker. IND.ENG.CHEM., ANAL.ED., 16, 387 (1944). (2) H . Irving, E. J. Butler, and M. F. Ring, J. Cliem. SOC.,1949, 1489. 1222

quinolinol does react with aluminum(II1) (3-3, and the results of an X-ray structure determination of one of the compounds that was isolated have been reported recently (5). There is insufficient experimental data t o substantiate the above explanation for the anomalous behavior of aluminum (111) with 2-methyl-8-quinolino1. For example, it is not possible to compare the aluminum-oxygen and aluminumnitrogen distances with the corresponding gallium, indium, or thallium distances, even in the parent 8-quinolinol chelates since structural data on these compounds are unavailable. As a first step toward the understanding of the anomalous behavior of aluminum(1II) with 2-methyl-8-quinolino1, we have initiated structural studies on a series of metal chelates of this ligand. The structure of a gallium(II1) chelate, that has a formal resemblance to the five coordinate aluminum(II1) chelate of 2-methy1-8-quinolinol (5), is reported below. One of the objectives in this study was to determine the galliumoxygen and gallium-nitrogen distances for purposes of comparison with the aluminum-oxygen and aluminum-nitrogen distances that have already been determined (5) in the same type of chelate ring. Another aspect of the chemistry of 8-quinolinol complexes that has been controversial is the structure and composition of chelates with transition metal ions in their higher oxidation states. For example, there have been several conflicting reports on the composition of the complexes of 8-quinolinols with oxovanadium(V) (6). The 8-quinolinol chelate of oxovanadium(1V) has been isolated and is probably the bischelate since it has a normal magnetic moment of 1.75 BM (7). However, it has been observed that oxovanadium(1V) in the presence of 8-quinolinol, is readily oxidized even by atmospheric oxygen (6). As a result of the continuing interest in the spectral and magnetic properties of oxovanadium(1V) complexes, the structures of a large number of their complexes have been determined (8). Almost all the complexes that have been selected for structural studies are chelates of bidentate ligands with oxygen donors, and have high symmetry to facilitate the interpretation of their optical absorption spectra. The recent interest in the ligand field transitions found in oxovanadium(1V) complexes of low symmetry was an added incentive for the synthesis of an oxovanadium(1V) chelate of 2-methyl-8-quinolino1, and for the determination of its structure which is reported below. EXPERIMENTAL

Bis(2-methyl-8-quinolinolato)chlorogallium(III), GaC1(CloH8NO)r,was prepared by the addition of a solution 03 2-methyl-8-quinolinol in ethanol to an aqueous solution of (3) W. E. Ohnesorge and A. L. Burlingame, ANAL.CHEM.,34, 1080 (1962). (4) P. R . Scherer and Q. Fernando, ibid., 40, 1938 (1968). (5) Y . Kushi and Q. Fernando, J. Amer. Clzem. SOC.,92,91 (1970). (6) J. Selbin, Chem. Rec., 65, 153 (1965). (7) E. Bayer, H. J. Bielig, and K. H. Hausser, A m . Clzem., 584, 116 (1953). (8) J. Selbin, Coord. Chem. Rec., 1,293 (1966).

ANALYTICAL CHEMISTRY, VOL. 43, NO. 10, AUGUST 1971

gallium trichloride until a pale yellow color was obtained. The resulting solution contained slightly less than a 1 : 3 molar ratio of gallium(II1) :ligand. Slow evaporation of this solution gave yellow crystals that were suitable for X-ray analysis. Dark yellowish brown crystals of bis(2-methyl-8-quinolinolato)oxovanadium(IV) were prepared in a similar manner by the reaction of a slight excess of 2-methyl-8-quinolinol with vanadyl sulfate in an ethanol solution. Crystals that were suitable for an X-ray structure determination were grown from a toluene solution. Preliminary oscillation and Weissenberg photographs taken with CuK, radiation indicated that both compounds had crystallized in the monoclinic space group C2/c or Cc. The crystal data for the two compounds are summarized in Table I. A Picker FACS-1 automated four circle diffractometer was used for all the data collection which was carried out at room temperature (23 "C). The orientation angles for 12 reflections and the cell parameters for each crystal (Table I) were determined by a least squares refinement. Crystals of the two compounds, cut into cubes of side approximately 0.15 mm and mounted along their crystallographic b-axes, were usedoin the data collection using MoK, radiation (A = 0.71069 A) obtained with a graphite crystal monochromator. The take off angle was 1.5" and the Bragg angle of the graphite monochromator was 11.89'. The intensities of the reflections were measured with a scintillation detector in conjunction with a pulse height analyzer. Metal foil attenuators were placed in the diffracted beam whenever the number of counts exceeded about 10,000 counts/sec. The mosaic spread of the crystals was determined by the w-scan technique and in both crystals the peak half-width at half-height was about 0.15" with no observable peak splitting. The 6-20 scan technique was employed with a scan range from -0.75" to +0.75" of the 26 value of the reflection, at a scan rate of 2"imin with 10-second background counts collected at both ends of the 26 scan range. During the data collection, the intensity of a standard reflection was monitored for every 50 reflections that were measured. The maximum deviation of the intensity of the standard reflection from its mean value was 3.5% for the oxovanadium compound and 4.0% for the gallium compound. Intensity data were collected for values of 26 between 4" and 45', and corrected for Lorentz and polarization factors, but not for absorption or secondary extinction effects. The intensity data were reduced to F 2 and u(F2)by a program which made use of the following expressions : I

d0 =

[CT

=

CT

+9 +

+ Bz) + B? + 18) + (pZ)'l"2

= '/z(fc/fb)(Bi

'/4(fc/fb)'(Bi

where: CT B1 Bz t, fb

p

= = = = = = = =

total integrated count = 10 x (output of FACS) background count for time t b on low 20 side of peak 10 X (output of FACS) background count for time f b on high 26 side of peak 10 X (output of FACS) time elapsed during scan counting time for background 0.04

From a calculation of the statistical distribution of E values (normalized structure factors), it was assumed initially that both compounds were in the centric space group C2/c. This assumption was verified later after both structures were refined in this space group. The molecule VO(CloHsON)2 is required crystallographically t o have C2 symmetry. The y-coordinate of the vanadium atom at ( I / ? , y , 3 / 4 ) was obtained from a three-dimensional Patterson synthesis and the positions of the rest of the atoms, except the hydrogen atoms, in the molecule were located by successive Fourier and difference Fourier syntheses. The structure was refined by a full matrix least squares technique. The refinement was

Table I. Summary of Single Crystal X-Ray Data VO(CloH8N0)2 GaCI(CloH8N0)2 Crystal data = 17.045(6)-A N = 28.844(10)-A b = 7.843(4) A, h = 9.594(4) AD c = 13.440(6)A c = 15.199(6)A @ = 105"14' (1') = 118"43'(1') 2 = 4 Z=8 U = 1734A3 U = 3689A3 D = I .46 g/cm3 D = 1.51 g/cm3 Linear absorption Linear absorption coefficient = 6 . 2 coefficient = cm-l for M o K a 16.8 cm-1 for MoKa

Systematic absences: Systematic absences k = hkl, h k = hkl, / I 2r7 + 1 2/1 I hO[, / I = 2/f 1 k01, if = 212 + 1 I = 2/1 + 1 I = 212 1 Space Group: C2/c Space Group: C2/c (or Cc) (or Cc) 1200 1733

+

+ + +

+

Number of reflections measured Number of reflections 873 F' 2u(F') 3-D Patterson Solution of phase problem Final R = B(/F,1 - IFc])/8 . 1 ZIF,/with isotropic temperature factors With anisotropic tem6.2x perature factors Largest parameter shift 0.0001 A for y-coordinate of

1591

>

3-D Patterson

x

11.0% 7.4x 0.008 A for

y-coordinate of C (26)

c (8)

(Figure 1)

(Figure 2)

Table 11. Positional and Isotropic Thermal Parameters with Their Standard Deviations for VO(CloH8NO)? X

V

013 Nl

c2 c3 C4 c5 C6

c7 C8 c9

C10 C11 012

0.5000 0.5000

0.5246(3) 0.4818(4) 0,5142(4) 0.5921(5) 0.7199(4) 0.7585(4) 0.7219(4) 0.6435(4) 0.6387(4) 0.6021(4) 0.3966(4) 0.6042(2)

Y

2

B

0,2273(2) 0.0233(9) 0.2723(7) 0.2379(9) 0.2700(10) 0.3325(9) 0.4367(10) 0.4715(11) 0.4400(10) 0.3727(9) 0.3697(9) 0.3383(9) 0.1613(10) 0.3363(6)

0.7500 0.7500 0.6044(4) 0.5078(5) 0.4220(5) 0.4372(6) 0.5630(7) 0,6649(7) 0.7468(6) 0.7241(5) 0.5389(5) 0.6192(5) 0.4911(6) 0.7963(3)

3.05(4) 5.1(2) 3.3(1) 3.7(2) 4,5(2) 4.6(2) 5.1(2) 4.9(2) 4.4(2) 3.6(2) 3.8(2) 3.3(2) 4.6(2) 4,0(1)

based on F, and the quantity minimized was Z w ( ' F , ~ F , Iwhere ) (w)l/' = 1 for F 2 2 2u(F2) and ( w ) ' ' ~ = 0 for F2 < 2u(F2). Three cycles of refinement with individual atom isotropic temperature factors gave R = Z( 1 F, - IF, )/ ZIF,l = 8.1%. An additional three refinement cycles in which all the nonhydrogen atoms were assumed to undergo anisotropic thermal motion, gave R = 6 . 2 z . Table I1 gives the final values of the positional parameters and the isotropic temperature factors for all the atoms. Table I11 shows the final values of the anisotropic temperature factors. The molecule GaC1(CloHsN0)2does not have any symmetry properties imposed on it crystallographically. The position of the gallium atom was located from a three-dimensional Patterson synthesis and a Fourier, calculated on the basis that all the phases were determined by the gallium atom, revealed the positions of the chlorine, oxygen, and nitrogen atoms. Successive Fourier and difference Fourier syntheses

ANALYTICAL CHEMISTRY, VOL. 43, NO. 10,AUGUST 1971

e

1223

Table 111. Anisotropic Thermal Parametersa for VO(CloHsNO)~ PZP

Pi1

V 013

a

0.0027(1) 0.0065(4) N1 0.0028(2) c2 0 .oO38(3) c3 0.0049(3) c4 0.0054(4) c5 0.0042(3) C6 0 ,W36( 3) c7 O,OO26(3) C8 0.0028(2) c9 0 ,W41( 3) c10 0.00291( 2) c11 0.0033(3) 012 0 . W29( 2) The anisotropic temperature factors ~~

~~~

PI?

P33

P?3

PI3

0.001l(1) 0.0134(4) 0.0047(1) ... 0,0142(16) 0.0074(5) ... 0,0020(4) 0.01167( 11) 0.0057(4) - 0 , OOOl(4) 0.0013(3) 0.0112( 13) 0.0060(5) 0.0020(5) O.OOO8(3) 0.0151(15) O,OO63(5) 0.0019(6) 0.0021(3) 0.0127(16) 0.0068(6) 0.0008(6) 0 ,oO21(4) 0.017317) 0.0102(7) -0.0018(6) 0.0031(4) 0.0214(19) 0.0094(7) - 0.0009(6) 0.0030(4) 0.0096(6) - O,OOO9(5) 0.W18(3) 0.0 193( 17) 0.015q14) 0.0061( 5) 0.0005(5) 0,0013(3) 0.0115(13) 0.0066(5) O.OOO9(5) 0.0027(3) 0.0106(13) 0.006l(5) 0.0010(4) 0.0012(3) 0.0208(18) 0.0072(6) - 0 . oO19(6) 0,0004( 3) 0.0234(12) 0,0053( 3) -O.OOO8(3) 0.0014(2) listed are defined as exp[-(pl1hZ PZ2k2 P3J2 2/312hk 2&hl 2823kl)I.

+

~

~~

+

+

~

~~~

- 0 . oooS(5) - O,OOO6(7) 0 . OOOS(8)

0,0009(7) -0,0009(9) - 0.0012(9) - 0 .oO19(8)

-0.0007(7) 0.001q7) - 0 .OOO l(6) - 0,0020( 8) - 0,001 8(5)

+

+

~

Table IV. Positional and Isotropic Thermal Parameters with Their Standard Deviations for GaC1(CioHsNO)z Y

X

Ga

0.3744(1) 0.2947(3) 0.2499(4) 0.2001(4) 0.1993(4) 0.2508(5) 0.2996(5) 0.3468(4) 0.3447(4) 0.2472(4) 0.2944(4) 0.2509(5) 0.3872(2)

N1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 012

0.2890(1) 0.2304(9) 0.2678(12) 0.2070(13) 0.1018(13) -0.0573(13) -0.0901(13) -0.0163(13) 0.0899(11) 0.0539(11) 0.1252(10) 0.3832(14) 0.1644(8)

z

B

0.7643(1) 0.6740(6) 0.6724(8) 0.6030(8) 0.5422(8) 0.4857(9) 0.4956(9) 0.5608(9) 0.6201(8) 0.5439(8) 0.6119(7) 0.7435(10) 0.6829(5)

4.19(5) 4.3(2) 4.6(3) 5.0(3) 5.0(3) 5.6(3) 5.5(3) 5.7(3) 3.9(3) 4.4(3) 3.1(3) 6.4(3) 5.0(2)

Y

X

C1

N21 C22 C23 C24 C25 C26 C27 C28 C29 C30

C31 032

0.3821(1) 0.4524(3) 0.5007(5) 0.5464(5) 0.5427(5) 0.4846(5) 0.4328(6) 0.3883(5) 0.3963(5) 0.4927(4) 0.4485(4) 0.4965(5) 0.3553(2)

B

z

0.1939(4) 0.3666(9) 0.3079(14) 0.3899(16) 0.5333(16) 0.7488(13) 0.8015(14) 0.7111(14) 0.5639(12) 0.5994(14) 0.5089(13) 0.1489(13) 0.4749(8)

0.9021(2) 0.8297(6) 0.8772(8) 0.9173(10) 0.9097(10) 0.8537(10) 0.8044(10) 0.7618(9) 0.7730(8) 0.8631(9) 0.8238(8) 0.6176(10) 0.7358(6)

6.9(1) 3,9(2) 5.0(3) 5.7(3) 6.6(4) 6.6(4) 7.0(4) 6.0(4) 4.8(3) 5,5(4) 3.7(3) 6.3(4) 5.7(2)

Table V. Anisotropic Thermal Parameters5 for GaC1(ClaHsNO)z P11

Ga Cl

N1 c2

c3 c4 cs

C6 c7 C8 c9 c10

c11 012 N21 c22 C23 C24 C25 C26 C27 C28 C29 C30 C31 032 a

0.001 50) 0.0026(1) 0.0016(1) 0.0015(2) 0.0020(2) 0.0014(2) 0.0021(2) 0 .oO18(2) 0.0022(2) 0.0017(2) 0 .0018(2) 0 .W16(2) 0.0021(2) 0.0016(1) O.O019(2) 0 .W18(2) 0.0018(2) 0,0019(3) 0.0027(3) 0.0028(3) 0,0024(2) 0.0021(2) 0.0016(2) 0.0016(2) 0.0023(2) 0.0015(1)

PPZ

0.0109(1) 0.0276(7) 0.0121(13) 0.0121(17) 0.0145(19) 0.0154(19) 0.0124(18) 0.0146( 19) 0.0141(19) 0.0096(16) 0.0098(16) 0.0082(14) 0.0196(22) 0.0142(11) 0.0089(14) 0.0171(22) 0.0184(25) 0.0173(24) 0.0109(20) 0.0 144(20) 0.0136(20) 0.011 l(18) 0.0160(22) 0.0139(21) 0.0107(18) 0.0117(11)

P33

The anisotropic temperature factors listed are denfied as exp[-(p,,hz

were used to locate all the nonhydrogen atoms in the molecule. Six refinement cycles carried out as described above with isotropic temperature factors gave R = 11.0%. Three refinement cycles with anisotropic temperature factors gave R = 7.4%. Table IV shows the final values of the positional parameters and the isotropic temperature factors and Table V the anisotropic temperature factors for all the nonhydrogen 1224

PI2

0.0056(1) 0.0067(2) 0.0062(6) 0.0068(8) 0.0065(8) 0.0064(9) 0.0070(9) 0,008l(9) O.O083(9) 0.0068(8) 0.0057(8) 0.0035(6) 0.0102(10) 0.0073(5) 0.0057(6) 0.006l(8) 0.0093(10) 0.0104(11) 0.0104(11) 0.0101(11) 0.0082(9) 0.0065(8) 0.0077(9) 0.0050(7) 0.0109(11) 0.0094(6)

-0.0011(1) - 0 .W26(2) - 0.0006(4) - 0,0005(5) -0.0000(5)

O.OOO3(5) - 0.0006(5)

-0.0012(6) - 0.0002(6) O.OOOo(5) - 0.0007(5) -0.0001(4) -0.0016(6) - 0.0017(3) -0.0011(4) 0.0000(6) -0.0023(6) -0.0021(6) -0.0017(6) - O,OO16(7) - 0.0007(6) -0.0024(6) -0.0018(6) - O.OOO6(5) -0.0006(5) -0.OOO3(3)

+ &k2 +

P3312

PI 3

0, 0012 ( 1) 0.0017(1) 0 .oO16(2) 0.0015( 3) 0.0016(4) 0.001 1( 3) 0.0014(4) 0.0010(4) 0.0020(4) 0.0016(4) 0.0010(3) 0.0011(3) 0,0026(4) 0.0015(2) 0.0016(3) 0.0014(4) 0 . oO17(4) 0.0017(4) 0.0019(5) 0.oO21(5) 0.0016(4) 0.0013(4) 0.016(4) 0 .0016(3) 0 . W16(4) 0.0008(2)

623

- 0 , 0015(1)

0,0013(3) - O.OOOl(8) -0 0.0004(10) .ooO4(11)

0.0030(11) - O.O014(10)

-0,0023(11) - 0.0025(12)

0,001l(20) O.OOO6(9) 0.0002(8) - 0.0070(13) - O.O030(6) - 0.0015(7) -0.0008(11) -0.0033(13) - 0 .W29( 13) -O,OO17(11) -0.0007(13) 0.OOOS(l1) - O,OO27(10) -0.0023(11) -O.O008(9) 0 .0001(11) - 0.0000(7)

+ 2hhk + 2P13hl + 2P23kl)l.

atoms. The atomic scattering factors used for carbon, oxygen, and nitrogen atoms were from “International Tables” ( 9 ) . All the refinement cycles for the two structures were (9) “International Tables for X-Ray Crystallography,” Vol. 111, The Kynoch Press, Birmingham, England, 1962,pp 202-205.

ANALYTICAL CHEMISTRY, VOL. 43, NO. 10, AUGUST 1971

T

Table VI. Bond Angles and Their Standard Deviations (deg) for VO(CIOHSNO)Z 012-V-0 13 N 1-V-013 N 1-V-012’ N 1-V-012 V-N1-ClO V-N1-C2 C2-N 1-C10 N 1-C2-C 3 C3-C2-C11 NI-C2-C11 c2-c3-c4 c3-c4-c9 C6-C5-C9 C5-C6-C7 C6-C7-C8 C7-C8-C10 CIO-C8-012 C7-C8-012 c4-c9-c5 C4-C9-C10 c 5 - c 9 - c 10 N l-ClO-C8 N 1-C10-C9 C8-Cl 0-C9 V-O12-C8

116.4(.7) 99.3.5) 91 .O( .4) 80.6(. 4) 109.9(,5) 131 .8(. 8) 118.1(1. O ) 121 .3(1 .3) 120.3(1,1) 118.3(1.1) 120.4(1,2) 119.3(1.1) 118.4U.3) 122.8(1.5) 119.1(1 .4) 119.0(1.1) 117,5(.9) 123.5U.l) 123.7(1.3) 117.1(1.2) 119.2(1.1) 114.8(1.0) 123.8(,9) 121.5(1.3) 116,9(.7)

i

c1 ^.

1,.

CII

1

Figure 1. Perspective view of the molecule VO(C,OHSNO)Z Values in parentheses (deviations in the last digit) are the estimated standard deviations of the bond distances. The esd’s for all the bond distances between the light atoms are 0.01 A

Table VII. Bond Angles and Their Standard Derivations (de& for GaCI(CloHsNO)z CI-Ga-N 1 CI-Ga-N2 CI-Ga-012 CI-Ga-032 Nl-Ga-N21 012-Ga-032 N1-Ga-032 N21-Ga-012 N1-Ga-012 N21-Ga-032 Ga-Nl-C2 Ga-Nl-ClO C2-N1-C10 N1 -C2-C3 Nl-C2-Cll c3-c2-c11 c2-c3-c4 c3-c4-c9 C6-C5-C9 C5-C6-C7 C6-C7-C8 C7-C8-C10 C7TC8-012 ClO-C8-012 c4-c9-c5 C4-C9-C10 C5-C9-C10

95.1(.4) 95.7(.6) 113.7(.7) 120.3(,7) 169.1(1.O) 126.0(.9) 89.8(.5) 91.9(.6) 84.2(.6) 84.3(.5) 133,2(1 , 7 ) 106.7(.8) 119,9(2.0) 121.6(1.6) 119.4(2.1) 1 19.0(2.2) 119.1(2.1) 121.3(2.1) 118.6(2.1) 123.1(1.8) 119.5(2.1) 118.5(1.9) 123.1(1.4) 118.4U.2) 125,6(2.1) 115.6(1 .3) 118.8(2,0)

N1-C10-C8 Nl-C10-C9 C8-ClO-C9 Ga-Ol2-C8 Ga-N21-C22 Ga-N21-C30 C22-N21-C30 N21-C22-C23 N21-C22-C31 C23-C22-C31 C22-C23-C24 C23-C24-C29 C26-C25-C29 C25-C26-C27 C26-C27-C28 C27-C28-C30 C27-C28-C32 C3eC28-032 C24-C29-C25 C24-C29-C30 C25-C29-C30 N21-C30-C28 N21-C30-C29 C28-C3O-C29 Ga-032-C28

116.1(1,8) 122.4(1.8) 121.5(1.4) 114,0(.9) 134.4(1.5) 106.7(.9) 118.8(1 , 8 ) 121.0(2.1) 117.5(1.8) 121.5(2.0) 120.3(2.3) 120.6(1.9) 119.3(2.1) 121.3(2.0) 119.3(1.9) 120,0(1.8) 121.2(1.4) 118.7(1.4) 124.8(2.1) 115.31.8) 119.7(1.9) 115.9(1,7) 123.8(1.7) 120.3(1.9) 114.3(..8)

calculated by the program ORFLS (IO) with a CDC-6400 computer. Although all the anisotropic temperature factors in the two structures are positive definite, they have little significance unless absorption corrections are made and all the hydrogen atoms are located in the two compounds (11).

(10) W. R. Busing, K. 0. Martin, and H. A. Levy, “ORFLS, A Fortran Crystallographic Least Squares Program,” U. S. Atomic Energy Commission Publication ORNL-TM-305, 1962. (11) Structure factor tables for the two compounds have been deposited with the ASIS National Auxiliary Publication Service, c/o CCM Information Corp., 909 3rd Avenue, New York, N. Y . , 10022.

Figure 2. Perspective view of the molecule GaC1(CloHsNO)z Values in parentheses (deviations in the last digit) are the estimated standard deviations of the bond distances.nThe esd’s for all the bond distances between the light atoms are 0.02 A RESULTS AND DISCUSSION Figures 1 and 2 show perspective views of the molecules VO(CloHsNO)zand GaCI(CloHsNO)z, and also the numbering schemes employed in each case. The interatomic distances together with theit estimated standard deviations in parentheses are also shown in Figures 1 and 2. The important bond angles in the two structures together with their estimated standard deviations are summarized in Tables VI and VII. Crystals of bis(2-methyl-8-quinolinolato)oxovanadium(IV) consist of discrete molecules of VO(CloHsN0)z in which the coordination polyhedrons around the vanadium atoms are distorted trigonal bipyramids (Figure 3). The two atoms in the oxovanadium group lie on a two-fold axis; the three oxygen atoms and the vanadium atom are coplanar and form the equatorial plane. The two nitrogen atoms at tha apices of the bipyramid together with the vanadium and oxovanadium oxygen atoms are also coplanar. The dihedral angle between these two planes is 84.1”, which is significantly different from 90” and accounts for most of the distortion in the bipyramid. The angles shown in Figure 3 indicate the extent of deviation of the coordination polyhedron from a trigonal bipyramid. There are two distinct

ANALYTICAL CHEMISTRY, VOL. 43, NO. 10, AUGUST 1971

1225

N Figure 3. Coordination polyhedron around the vanadium atom in VO(Cld-I~NO)~

Table VIII. Distances (A) of Atoms from the Least-Squares Planes through the 2-Methyl-8-Quinolinolato Groups Distance to Distance to Distance to Atom Plane 1 Atom Plane 2 Atom Plane 3 N1 -0.002 N21 0.000 N1 0.002 c2 -0.022 c22 0.015 c2 0.007 c3 -0.049 C23 -0.006 c3 0.028 c4 0.043 C24 -0,028 c4 -0.001 c5 -0.031 C25 0,014 c5 -0.023 C6 -0.048 C26 0.020 C6 0.002 c7 -0.006 C27 -0.017 c7 0.011 C8 0.005 C28 -0.003 C8 0.007 c9 0.015 C29 -0.002 c9 -0.007 c10 0.010 c20 0.006 c10 0.002 c11 -0.063 C31 0.007 c11 -0.022 012 -0.004 012 0.050 C32 -0.008 v4 -0.154 Gaa -0.133 Ga4 0.099 Atoms not included in the calculation of plane.

vanadium-oxygen distances in the molecule, a short V-0 (13) distance of 1.60 A and a long V-0 (12) distance of 1.92 A. The former bond clearly has double bond character and is within the range of previously observed V=O bong distances in tetragonal pyramidal complexes: e.g., 1.62 A in diammonium oxotetrakisisothiocyanatovanadate(12) and (12) A. C. Hazell, J. Chem. SOC.,5745 (1963). 1226

1.57 A in bis(2,4-pentanedionato) oxovanadium(1V) (13, 14). The long V-0 bond distance of 1.92 A is slightly shorter than the V-0 bond distances in other oxovanadium(1V) chelates. The only chelates for which structural data are (13) R. P. Dodge, D. H. Templeton, and A. Zalkin, J. Chem. Pliys., 35, 5 5 (1961). (14) P. K. Hon, R. L. Belford, and C . E. Pfluger, ibid., 43, 3111 (1965).

ANALYTICAL CHEMISTRY, VOL. 43, NO. 10, AUGUST 1971

Figure 4. Packing of molecules of VO(CloHsN0)2in the unit cell viewed down the c-axis

Figure 5. Packing of molecules of VO(CloHsN0)2in the unit cell viewed down the b-axis ANALYTICAL CHEMISTRY, VOL. 43, NO. 10, AUGUST 1971

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NI

available for comparison are the acetylacetonates; e.g., in the oxovanadium(1V) chelate of acetylacetonates, the V-0 distance is 1.97 A (13, 14) and is a substituted acetylacetone chelate the V-0 distances lie between 1.95 and 1.98 (15). The V-N distance (2.14 A) is within the range of V-N distances found in oxovanadium complexes with monodentate ligands with nitrogen donors, 2.04 A in (NH4)~[VO(NCS),(HzO)1 (12) and 2.23 A in VCI3(NMe3)* (16). All the interatomic distances in the 2-methyl-8quinolinol molecule are normal : the C(2)-C(11) distance is 1.53 A which is the expected value for a carbon-carbon single bond distance. The rest of the bond distances in the molecule follow the alternating pattern that has been observed before in the aluminum(II1) chelate of 2-methyl-8quinolinol (5). The equation of the least-squares plane of the 2-methyl-8-quinolinolato group (CloHsNO) with respect to the crystallographic axes is:

A

cI

+

+

-0.365X 0.927Y 0.0092 = -1.214 (Plane 1) where X, Y , and 2 are in A. The deviations of all the atoms are less than 0.03 A from this plane, the maximum deviation being that of the carbon atom C(3) which has a deviation of 0.028 A from the plane (Table VIII). The vanadium atom, which is not included in the calculation of the least-squares plane, is at a distance of -0.154 A from the plane. The dihedral angle between the two planes of the 2-methyl-8-

Nzt Figure 6. Coordination polyhedron around the gallium atom in GaCI(ClaHsNO)z

1228

(15) P. K. Hon, R. L. Belford, and C. E. Pfluger, J. Chem. Phys., 35, 1323 (1965).

(16) P. T. Greene and P. L. Orioli, J. Chem. Soc., 1969, 1621.

ANALYTICAL CHEMISTRY, VOL. 43, NO. 10, AUGUST 1971

quinolinolato groups in the same molecule is 44'1', and the distance between two of these planes that are related to each other by the center of symmetry, (I/*, 0, l/*) is 3.60 A. Intermolecular forces between these two planes play an important part in the crystal packing (Figure 4). Intermolecular contacts which are less than 3.5 A are shown in the projection of the unit cell down the 6-axis (Figure 5). There are no significant interactions between the methyl 'groups and 2-methyl-8-quinolinolato planes. The shortest intermolecular contact (3.25 A) is between the oxygen atom, 0(12), and a carbon atom, C(4), in the quinoline ring system. There are eight discrete molecules of GaC1(CloHsNO)z per unit cell in the crystals of bis(2-methyl-8-quinolinolato)chlorogallium(II1). Consequently, there are no crystallographic symmetry conditions imposed upon the molecule, and the two 2-methyl-8-quinolinolato groups that are coordinated to the gallium atom are crystallographically independent. The coordination polyhedron around the gallium atom can be considered to be a distorted trigonal bipyramid (Figure 6). The gallium atom does not lie on the equatorial plane, nor does it lie on the plane defined by the two apical nitrogen atoms and the chlorine atom. In Figure 6, the planes A , B, C, and D are each defined by three atoms in the coordination polyhedron. The angles between the planes A and B and between the planes A and D are 85.9" and 92.7",

respectively; the angles between B and C and between C and D are 94.6' and 86.8', respectively. All these dihedral angles are significantly different from 90" and so are the bond angles N(21)-Ga-C1 and N(1)-Ga-Cl (Figure 6). It is evident therefore, that the extent of distortion in the trigonal bipyramid is much greater in the gallium (111) complex than in the oxovanadium(1V) complex. It is of interest to compare the Ga-N(2.11 A) and Ga-O(1.86, 1.88 A) in this structure with the Al-N(2.10 A) and A1-0(1.80, 1.82 A) distances that were found in a p-oxo-bridged bis-chelate of 2-methyl-8-quinolinol and aluminum(II1) (5). The Ga-N and the A1-N distances are almost identical, but the Ga-0 distances are 0.06 to 0.08 A longer than the A1-0 distances. Although this bond lengthening is significant (greater than three times the esd of the bond distance), it is probably too small to account for the differences that have been observed in the reactivities of aluminum(II1) and gallium(II1) with 2-methyl-8-quinolinol in aqueous solutions (17). The Ga-Cl distance (2.20 A) is normal (18) and the bond distances between the light atoms in the (17) H. Irving and D. L. Petit, in "Proceedings of the International Symposium," Birmingham University, 1962, P. W. West, A. M. G. MacDonald, and T. S . West, Ed., Elsevier, Amsterdam, 1963. (18) A. H. Barrett and M. Mandel, Phys. Rev., 109, 1572 (1958).

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2-methyl-8-quinolinolato groups are similar to those found in the oxovanadium complex and in the aluminum(II1) complex (5). The equation of the least-squares plane, with respect to the crystallographic axes, through the 2-methyl-8-quinolinolato group defined by the atoms N(l), C(1), . , , C(11), O(12) is: 0.215X

+ 0.677Y - 0.7282 =

-4.162

(Plane 2)

and through the 2-methyl-8-quinolinolato group defined by the atoms N(21), C(22), . , . C(31), O(32) is: -0.495X

+ 0.030Y + 0.9992 = 6.242

(Plane 3)

where X , Y, and 2 are in A. The distances from the atoms in each of these groups to their respective planes are given in Table VIII. The carbon atom of the methyl group, C(11), shows the maximum deviation (0.063 A) from Plane 2, and a ring carbon atom, C(24), shows the maximum deviation (0.028 A) from Plane 3. The gallium atom which is not included in the calculation of tge least-squares planes lies 0.099 A above Plane 3 and 0.133 A below Plane 2. Although the coordinated 2-methyl-8-quinolinolato groups are approximately planar, there is considerably more distortion in this structure than in the oxovanadium(1V) structure. A comparison of the dihedral angles between the two intramolecular planes of the 2-methyl-8-quinolinolato groups reveals an important difference in the two structures. In the oxovanadium(1V) complex, the dihedral angle is 44'1 ', whereas in the gallium complex it is 69'45'. The distance between the 2-methyl-8-quinolinolato planes that are related by the 1/4, 1/4), is 3.55 A. The 2-methyl-8center of symmetry quinolinolato planes which are packed in a direction almost perpendicular to the c-axis are 3.89 A apart when related by a center of symmetry, and 3.99 A apart when related by a twofold axis (Figure 7). Intermolecular aontacts that are Iess than 3.5 A are shown in Figure 8.

The reasons for undertaking these two structure determinations were to gain further insight into the metal complexing properties of the ligand, 2-methyl-8-quinolinoI, and to determine whether there are any differences in the bonds formed between the oxygen and nitrogen donor atoms of the ligand and the aluminum(II1) and gallium(II1) ions. The ionic radius of gallium is 0.12 A greater than the ionic radius of aluminum, but their covalent tetrahedral radii are identical (17). The bond distances in the aluminum(II1) ( 5 ) and gallium(II1) complexes indicate that the same type of bond is formed by the two metals with nitrogen, but that the galliumoxygen bond is less covalent than the aluminum-oxygen bond. This comparison however, may not be strictly valid; although the aluminum(II1) and gallium(II1) compounds have a formal resemblance since they are both five-coordinated chelates of 2-methyl-8-quinolino1, the former is a p-oxo-bridged dimer with three oxygen atoms in the equatorial plane, whereas the latter has two oxygen atoms and a chlorine atom in the equatorial plane. It is conceivable that the chlorine atom affects only the oxygen atoms in the equatorial plane and not the apical nitrogen atoms. Thus the increase in the G a - 0 bond length and the similarity of the Ga-N and A1-N bond lengths can be rationalized. Although at this stage of our investigations the effect of the 2-methyl substituent on the structural parameters of the metal chelates is not apparent, it is of interest that the three metal chelates of this ligand which can be readily isolated from solution have an approximately trigonal bipyramidal geometry. Structure determinations of the beryllium(I1) and indium(II1) chelates of this ligand should provide answers to some of the questions that have been raised (17). RECEIVED for review February 22, 1971. Accepted April 30, 1971. Work supported by a research grant from the National Science Foundation.

Use of Anion Exchange Resin-LoadedPaper in the Determination of Trace Mercury in Water by Neutron Activation Analysis D. E. Becknell, R. H. Marsh, and William Allie, Jr. Scientific Research Staff, Ford Motor Company, Dearborn, Mich. A neutron activation analysis method has been developed for the determination of mercury in water at levels of 0.05 to 250 pg. A preirradiation concentration of Hg is accomplished through the use of anion exchange resin-loaded filter disks. Hydrochloric acid is added to the water sample and mercury, as HgCI4*-, is removed from the solution by an exchange technique. Following the concentration of Hg in the resin the samples are irradiated and the Hg content is determined using a standard comparison technique on the 77-Kev gamma ray from the decay of Ig7Hg. In solutions containing up to 250 gg of Hg, 100% of the Hg is removed by the anion exchange technique. A chlorine treatment is used to degrade organomercury compounds. The method has been applied to a variety of natural water samples, the compositions of which have varied from 0.03 to 6.6 ppb of mercury.

INRECENT YEARS there has been a growing interest in a variety of analytical environmental detection techniques. One area of investigation has been the analysis of natural water 1230

supplies for certain elements present in the ppm and ppb ranges. Among these elements are Se, As, Sb, and of particular importance, Hg. To date there has not been available a method which will reliably determine Hg in water samples when present in concentrations of less than 10 ppb. A neutron activation analysis method which employs resin loaded anion exchange filter papers for a preirradiation removal of Hg from water samples has been developed. It involves the removal of Hg, as HgC14*-, from water which has been adjusted to pH 1 with HCl and subsequently passed through an anion exchange filter paper. Following this concentration step, the paper containing the Hg is irradiated along with a Hg standard, From the gamma-ray spectra of samples and standards, the Hg content in the original water sample is easily determined by the standard comparison technique. When present in amounts up to 250 pg, 100% of the Hg known to be present can be recovered by passing the solution seven times through an anion exchange resinloaded filter paper.

ANALYTICAL CHEMISTRY, VOL. 43, NO. 10, AUGUST 1971