CRYSTAL STRUCTURE OF I-PHENYL-I,2,3,4,5,6-HEXAMETHYLBENZOLONIUM

TETRACHLOROALUMINATE

G. I. Borodkin, Sh. M. Nagi, I. Yu. Bagryanskaya, and Yu. V. Gatilov UDC 548.737 + 541.124.16

An x-ray study has been performed on l-phenyl-l,2,3,4,5,6-hexamethylbenzolonium tetrachloroal~minate. The crystals are orthorhombic a = ii.i16(2), b = 16.923(3), c = 21.848(4)A, z = 8, space group Pbca, R = 0.088 for 2254 reflections. The AICI~ anion has an almos t ideal tetrahedral configuration, and the average dis- tance is AI--AI 2.134(3) A. The cation has idealized C s symmetry, while the bond lengths in it are close to those inohexamethylbenzolonium tetrachloroaluminate. The C(1) atom deviates by 0.105(7) A from the plane of C(2)-C(6) to the side opposite to the Ph group.

INTRODUCTION

We have previously [i] examined l-phenyl-l,2,3,4,5,6-hexamethylbenzolonium tetrachloro- aluminate (I) and have found that the sigmatropic carbocation rearrangement (scheme i) is retarded in the crystalline state by comparison with solution, which is probably due to crystalline forces*:

C6H5 1

i C6H5

To evaluate the factors influencing the carbocation rearrangement rates in the crystalline state, it is extremely important to determine the spatial structures of the salts. Here we examine the crystal structure of l-phenyl-l,2,3,4,5,6-hexamethylbenzolonium tetrachloroalumi- nate. Only very restricted information of this kind isavailable for salts of arenonium ions [2, 3].

EXPERIMENTAL AND QUANTUM-CHEMICAL CALCULATIONS

We used the following reagents: pentamethylpheno!, which was made in the experimental chemical plant at Novosibirsk Organic Chemistry Institute (content of main substance 98.4%), AICI~ of pure grade, additionally distilled, CH2C12 of pure grade, purified in accordance with [4], and ethyl acetate of chemically pure grade redistilled over P205.

The l-phenyl-l,2,3,4,5,6-hexamethylbenzolonium tetrachloroaluminate was prepared bythe following method: To a mixture of 0.403 g oY AICI~, 0.5 ml of anhydrous HCI, and 3 ml of CH2C12 we added in batches at--95~ a solution of 0.7 g of l-phenyl-4-methylene-l,2,3-5,6- pnetamethyl-2,5-cyclohexadiene [5] in 3 ml of CH2C12. The mixture was stirred at -65~ for 0.5 h and was cooled to --78~ and cautiously mixed with 6 ml of dry ethyl acetate. The crystals produced at the boundary between the two layers were separated from the mother liquor and washed at --78~ with absolute pentane, and the solvent was removed at i mm Hg. Yield 20%. Melting point 83-84~ Found %: C 53.10; 53.22; H 5.51; 5.62; CI 34.42; 34.37. C18H23AICI~. Calculated %: C 52.97; H 5.68; C1 34.74.

The x-ray structure analysis was performed with a Syntax P2~ diffractometer with Mo radiation and a graphite monochromator at about --II0~ The crystal was sealed into a glass capillary in an argon atmosphere. The crystals are orthorhombic a = 11.116(2), b = 16.923(3),

*The undenoted substituent (free valence line) in these formulas represents a CHs group.

Novosibirsk Organic Chemistry Institute, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 25, No. 3, pp. i14-i19, May-June, 1984. Original article submitted July 12, 1982.

440 0022-4766/84/2503-0440508.50 �9 1984 Plenum Publishing Corporation

TABLE i. Atomic Coordinates: x i04 for C and C1 and x I0 s for H

A t o m x y z A t o m x y z

c(l) c(2) c(3) c(4) c(5) c(6) c(7) c(8) c(9) cdo) cdl) C(12) C(13) Cd4) C(t5) cd6) c(t7) cd8) ClO) c](2) c](3) Cl(4) A1

t34t(6) t989(7) t847(8) itt6(8) 057t(6) 0678(7) 2299(8) 2144(7) 3003(7) 4014(7) 4t63(8) 3304(8) 0375(7) 273i(8) 2467(9) o9!o(8)

-o19o(8) o123(8) 3850(2) 2377(2) 2393(2) 0707(2) 2320(2)

2413(5) 3i82(5) 3612(5) 3316(5) 2557(5) 2100(5) 1781(5) 1 ~ 4 1 ( 4 ~

0773(5~ 0544(~ t100(5) t658(5) 2587(5) 3466(5) 4409(5) 3800(6) 2276(5) 1307(5) 43920) 25680) 39640) 4273(t) 38030)

3359(3) 3443(4) 3979t4) ~441514 I

4 4 1 b / 3 }

3904(4) 3i50(3) 26i4(3) 246t(4) 2822(4) 3350(4) 3519(4) 2852(4) 2919(4) 4048(4) 5o~o(4) 4953(4) 3838(4) t417(1) t242(1) 0066 d ~4()5(~ 10;t4 (I)

H(S) H(9) Hd0) H(tt) H(12) H(t3i) H(t32) H(t33) H(i4t) H(t42) H(143) H(i51) H(t52) H(153) H(161) H(t62)

~(163) H(171) H(172) H(173) Hd81) H(t82) H(i83)

137(7) 292(6) 469(7) 498(8) 340(6) 08t(7)

--013(7) --020(7)

286(6) 240(9) 36i (9) 300(8) 303(9) t85(8)

--ot4(7) t23(9) 13t(8)

-054(7) --Ioi(8)

025(9) 040(7) 020(6)

--077(6)

i45(5) 043(4) o18(5) lol(5) t98(4) 281(5) 2t4(4) 305(5) 307(4) 393(5) 360(6) 454(5) 444(6) 477(6) 387(4) 423(6) 355(6) t82(5) 256(6) 232(6) 100(5) to6(4) 138(4)

237(4) 205(3) 269(4) 363(5) 396(3) 24i (4) 281 (3) 306(4) 256(3) 2??(4) 300(4) 372(4) 447(4) 4t4(4) 515(3) 499(5) 539(4) 488(4) 499(4) 54i(5) 4t9(3) 348(3) 397(3)

TABLE 2. Bond Lengths (A) and Angles (deg) Used in Quantum-Chemical Calculations

c(2)-c(3) c(2)-cd4) c(3)-c(4) c(3)-cd5) c(4)-c(5)

c(5)--c(6)

C(5)--C(17) C(6) C(!8)

t,368 t ,487 1,4t6 i,524 i ,4i6

i ,368

t ,524 1,487

C(1)--C(2)--C(3) Cd)--C(6)--C(5) C(2)--C(3)--C(4) c(2)-c(3)-cd5) c(3)-c(2)-c04) C(3)--C(4)--C(i6) C(4)--C(5)--C(6) c(5)-C(4)-cd6) c(5)-c(6)-cd8) c(6)-c(5)-cd7)

i20,0 i20,0 120,4 i20,4 i23,2 il9,0 i20,4 it9,0 i23,2 t20,4

o

c = 21.848(4) A, Z = 8, dcale = 1.32 g/cm a, space group Pbca. By 2e /e scanning over the

range 20 < 50 ~ we measured 3500 independent reflections. The calculations were based on 2254 reflections having I > 30 without absorption correction. The structure was interpreted by a direct method with the MULTAN-XTL program. The positions of some of the hydrogen atoms were found from a difference synthesis, while those of the others were calculated. The structure was refined by least squares in the full-matrix anisotropic-isotropic (for the hydrogen atoms) approximation to R = 0.088 and Rw = 0.092, where w -I = OF2 + (0.01F)2 Table 1 gives the atomic coordinates.

To check that there are no polymorphic transformations, we also determined the cell parameters and space group at room temperature: a = 11.190(4), b = 17.103(10), c = 22.109(14), Z = 8, dcalc = 1.28 g/cm a, space group Pbca. A thermographic study over the range from --120

to +70~ also indicated that there were no polymorphic transformations.*

Quantum-Chemical Calculations on the l-Phenyl-l,2,3,4,5,6-hexamethylbenzoloniu m Ion. The calculations were performed by the CNDO/2 method with a BESM-6 computer on the VIKING program.* The following simplified geometry was used for the cation on the basis of the x-ray data. The atoms C(2)-C(6), C(14)--C(18) and H(141), H(151), H(171), H(182) lie in one plane, while the phenyl ring and the atoms H(133), H(161) lie in a plane perpendicular to it.

*We are indebted to Yu. M. Zelenin and Yu. A. Dyadin for recording the thermogram, and also to the team in the NMR laboratory of the Chemical Faculty at Moscow University for providing the VIKING program.

441

TABLE 3. Bond Lengths,

At--CI(I) A1--Cl(2) A1--Cl(3) A1--CI(4) C(t)--C(2) C(t)--C(6) C(I)--C(7) c(1)-c(13) c(2)-c(3) c(2)-c(14) c(a)--c(4) c(3)--c05) c(4)-c(5) c(4)-c(16) c(5)-c(6) C(5)--C(t7) c(6)-c(18) c(7)-c(8) c(7)-c(12) c(8)--c(9) c(8)-~][(8) c(9)--c0o) C(9)--H(9)

2,t40(3) 2,t40(3) 2,,t33(3) 2,t23(4) t,498(tt} 1,498(1i) 1,577(11) 1,571(1t) 1,372(tt) t,490(12) t,4t0(t2) t,525(t2) t,422(t2) 1,497(t3) t,365(ti) t ,524(t2) i ,484(12) 1,398(tl) t,394(12) t ,396(11) 1,02(8) t,390(12) 1,07(6)

C(10)--C(tt) C(10)--H(10) C(11)--C(12) C(it)--H(lt) C(12)--H(12) C(i3)--H(13i) C(13)--H(I32) C(13)--H(t33) C(14)--H(i41) C(t4)--H(t42) C(t4)--H(143) C(15)--H(151) C(i5)--H(152) C(15)--H(153) C(16)--H(161) C(16)--H(162) C(16)--H(163) 0(17)--H(171) C(t7)--H(172) C(t7)--H(t73) c(t8)--Kg8t) C(18)--H(182) C(18)--H(i83)

1 397(t2) 1,tt(8) t,392(12) t,t'. ~) i,t" 7) t,1~ B) 0;9~ 3) 1,t", ~) 1,0~ 7) 0,9: a) I,o,~ to) 0,9~ 2) t , i l (9) 0,94(9) i,21(8) o,81(1o) 1,o3(9) 0,88(7) 1,03(9) :t ,~_lOo) 0,98(7) 0,89(6)

,04(7)

TABLE 4. Some Bond and Torsion Angles, deg

CI(i)--AI--CI(2) i10,4(I) Cl(i)--Al--Cl(3) t08,0(t) CI(t)--A1--CI(4) 1t0,3(1) CI(2)--AI--CI(3) t09,5(1) CI(2)--AI--CI(4) i07,3(i) CI(3)--A1--CI(4) 11i,3{t) C(i)--C(2)--C(3) i20,5(7) C(t)--C(2)--C(t4) t16,8(7) C(I)--C(6)--C(5) i19,5(7) C(t)--C(6)--C(18) 116,6(7)

C(1)--C(7)--C(8) t2t,4(7) C(t)--C(7)--C(t2) 1i8,4(7) C(2)--C(1)--C(6) 1t6,5(6) C(2)--C(i)--C(7) t07,5(6)

C(2)--C(t)--C(t3) 104,7(6) C(2)--C(3)--C(4) 119,8(8) C(2)--C(3)--C(i5) 120,7(7) C(3)--C(2)--C(14) 122,5(7)

C(2)--C(I)--C(7)--C(12) 56,0 C(6)--C(I)--C(7)--C(12) --7i,0 C(2)--C(1)--C(7)--C(8) --125,i C(6)--C(I)--C(7)--C(8) t07,9 C(6)--C(t)--C(13)--H(t3t) --178,9

C(3)--C(4)--C(5) t22,0(8) C(3)--C(4)--C(I6) t20,1(8) C(4)--C(3)--C(15) tt9,5(7) c(4)-c(5)-c(6) t2t,0(7) c(4)-c(5)-c(t7) tt8,8(7) C(5)--C(4).-C(16) li7,9(7) C(5)--C(6)--C(i8) 123,8(7) c(6)-c0)--c(7) i08,8(6) c(6)-c(I)-c03) i06,9(6) c(6)-c(5)-c(17) 120,1 (7) c(7)-c(i)-c(i3) 112,6(6) c(7)-c(8)-c(9) 1t8,8(7) C(7)--C(12)--C(II) tt9,8(8) C(8)--C(7)--C(t2) t20,3(7) C(8)--C(9)--C(I0) 121,7(7) C(9)--C(10)--C(II) 118,5(8) C00)--C(II)--C(12) 120,9(8)

C(1)--C(2)--C(14)-- H(141) --9,7 C(2)--C(3)--C05)--H(15i) --6,0 C(3)--C(4)--C(t6!--H(t6t) i28,9 C(4)--C(5)--C(17j--H(iTi) i74,8 C(5)--C(6)--C(i8)--H(181) --542

The bond lengths and angles given in Table 2 were found by pairwise averaging of the co~re- sponding x-ray data. The C-C bond lengths in the phenyl ring were also averaged (1.395 A). All the C--H bond lengths were taken as i.ii A [6]. The bond angles of the CHS and C6H5 groups were taken as 109.5 and 120 ~ correspondingly. The other bond lengths and angles are given in Tables 3 and 4.

RESULTS

The structure of I consists of carbocations and tetrahedral AICI~ anions (Figs. 1 and 2 and Tables 3 and 4). The mean AI-CI bond length of 2.134(3) A is close to that found for heptamethylbenzolonium tetrachloroaluminate (2.120(4) A [7]). Within the experimental errors for the atomic coordinates, the carbon core of l-phenyl-l,2,3,4,5,6-hexamethylbenzolonium has symmetry C s+ The atoms C(2)=C(6) lie in a single plane (plane i in Table 5) within _+0"019

(compare [3, 7, 8]). Plane 2 contains the phenyl ring and plane 3 includes atoms C(1), C(2), C(6) for angles of 84.6 and 7.6 r corresponding with plane i. The deviations of the carbon atoms in the methyl groups from the plane C(2)-C(6) are relatively small, but C(1) deviates more substantially (Table 5). The methyl groups C(14)--C(18) are oriented in such a way that the hydrogen atoms H(141), H(151), H(162), H(171), and H(182) lie almost in the plane of the core of the ion (plane i) (Fig. i, Table 4).

442

H10

H ~ / ~ C i0

C9"~ '~'%-~tI,.Cll Hll HI81

Hs H 83 H132 "~_Cli~'~ 4 H ~2 ]L.c 17

Iq142 ~ , ~ (~I"~H 161 C i l ~ I H162

H!51 (~ I- 5'2 H153

Fig. i

0 9"~ ' . ~ % -- h I J ~ 1"I 1/4

I V < " i - - / 14 i. / . i

R \ ' 7 f.', YG I ~,.-'k C 4 " ,<./ I ! | I t c s \ �9 / , PI J L...:%o6 fc.~ ,c,,~/.. ~ . I

tx v42 J ,o i , r - - - - ' - -

c - ~ - c <~ c)l" / " / ' ' K ', ~ ' + ~ ' " h ' ].-_._J, y-i

AI ' I '~ t / " > ' , t I h' / " 2 " '<~,1

Pig. 2

Fig. io Spatial structure of the l-phenyl-l,2,3,4,5,6-hexamethylbenzo- lonium ion.

Fig. 2. The (010) projection of the structure of the salt of ion I.

TABLE 5. Equations for Certain Planes and Deviations of the Atoms from Them (in ~)

Plane 1 Plane 2 Plane 3 t

Atom $ Deviation from

plane 1

Atom $ Deviation from

plane 2

--0,8120xd-O,4277y--O,3971z-~2,4832= 0 0 , 5 0 0 3 x d - O , 6 9 i @ - - O , 5 2 1 3 z - ~ O , 2 2 3 3 = O

- -0 ,820ix~-O,4948y--O,2873z-PI ,3099= 0 c(i) 0J05(7) C(7)

--I,036(8) ads )

--0,012(9) c(l)

c(2)* c O P c(4)* c(5)* c(6)*

0,004(7) -0,0t4(8) 0,0i9(8)-0,012(7) 0,004(8) C(13) C(14) C(15). G ( 1 6 ) C(17) 1,543(8) --0,006(9) --0,064(9) 0,066(9) 0,006(9)

C(4) C(7)* (i(8)* C(9)* C(iO)*

--0,032(8) --0.339(9) --0,002(8) C(li)* C(i2)* 0,011(8) --0,007(8)

0,008@) -o,oo6(s) -0,004(8)

#Plane 3 is drawn through atoms C(1), C(2), C(6). SThe asterisks denote atoms through which the plane is drawn.

As in the case of heptamethylbenzolonium tetrachloroaluminate [7], the C(2)-C(I)--C(6) angle at 116.5 ~ differs appreciably from the tetrahedral value. A similar deviation is pre- dicted by the quantum-chemical calculations for the benzolonium ion [8]. The C(2)-C(3) and C(5)-C(6) bon~s (mean length 1.368 A) have higher orders than C(3)-C(4) and C(4)-C(5) (mean length 1.416 A), and their orders are also higher than those of the bonds in benzene (1.397 ~) [9]. The lengths of the C(I)--C(2) and C(I)--C(6) bonds are close to those expected for Csp3--Csp2 ones [9, I0]. The C(I)--C(7) and C(I)-C(13) bonds are somewhat longer than the corresponding ones in toluene and ethane (1.52 and 1.536 A correspondingly [9]), which is characteristic of compounds containing quaternary carbon atoms [2, 6]. The C--CHo3 bonds for the methyl groups in the positions ortho and para to C(1) on average are 0.034 A shorter than that in the metaposition, which is probably due to higher positive charges on C(2), C(4), C(6)

443

I \ J

Fig. 3. Schematic spatial model for l-phenyl-l,2,3,4,5,6-hexamethylbenzo- lonium ion.

[7, ii, 12]. Our CNDO/2 calculations give the following distribution for the atomic charges on the core of cation I: 0.001(CI), 0.144(C=, C~), --0.048 (C3, Cs), 0.179(C~).

The corresponding bond lengths and angles are similar in l-phenyl-l, 2, 3, 4, 5, 6- hexamethylbenzolonium tetrachloroaluminate (Tables 3 and 4) and in I, i, 2, 3, 4, 5, 6-hepta- methylbenzolonium tetrachloroaluminate [7], which indicates that the cation geometry is not very sensitive to substituent variation in the geminal bond.

Figure 2 shows a projection of the structure. The cations and anions shown by solid lines (and correspondingly dashed ones) lie approximately in the same layer. The cations and anions aregrouped into stacks arranged in chessboard order. The immediate environment of a cation includes four anions. There are the following contacts between ions shorter than normal [131: CI(1)...C(10) (i -- x, 1/2 + y, 1/2 -- z) 3.59 ~, CI(3)...C(5) (x, 1/2 -- y, --1/2 + z) 3.57 ~, CI(3)...C(15) (1/2 -- x, i -- y, --1/2 + z) 3.54 ~, CI(3)...C(17) (x, 1/2 -- y, --1/2 + z) 3.57 A. The other contacts are the usual ones.

The three-dimensional structure of the I salt shows that the most likelypath for the degenerate rearrangement lies in rotation of the six-membered benzolonium ring around the normal to the average plane (Fig. 3) via the squence of 1,2 shifts [i], which lead to the breakage and formation of the C--Ph bond. A similar mechanism has been proposed previously [14] for the degenerate rearrangement in cyclopentadiene derivatives (~I-CsHs)HgX[14]. It is very unlikely that the phenyl group would move around the six-membered benzolonium ring in the lattice because of the large volume.

LITERATURE CITED

I. G. I. Borodkin, Sh. M. Nagi, and V. G. Shubin, Izv. Akad. Nauk SSSR, Ser. Khim., 2639 (1982).

2. G. A. Olah and P. von R. Schleyer (editors), Carbonium Ions, Wiley-lnterseience, New York (1976), Vol. 5, p. 2427.

3. P. Menzel and F. Effenberger, Angew. Chem., Int. Ed. Engl., 14, 62 (1975); F. Effen- berger, P. Menzel, and W. Seufert, Chem. Ber., 112, 1660 (1979).

4. D. E. H. Jones and J. L. Wood, J. Chem. Soc., 1448 (1966A). 5. V. A. Koptyug and L. M. Mozulenko, Zh. Org. Khim., 6, 102 (1970). 6. L. V. Vilkov, V. S. Mastryukov, and N. I. Sadova, Determining the Geometrical Structures

of Free Molecules [in Russian], Khimiya, Leningrad (1978), pp. 65 and 81. 7. N. C. Baenziger and A. D. Nelson, J. Am. Chem. Soc., 90, 6602 (1968). 8. G.M. Zhidomirov, A. A. Bagatur'yants, and I. A. Abronin, Applied Quantum Chemistry [in

Russian], Khimiya, Moscow (1979), pp. 74 and 221; T. Sordo and J. Bertran, J. Chem. Soc., Perkin Trans II, 1486 (1979).

9. B. P. Nikol'skii (editor), Chemist's Handbook [in Russian], Khimiya, Leningrad (1971), Vol. i, p. 354.

I0. A. I. Kitaigorodskii, P. M. Zorkii, and V. K. Bel'skii, The Structure of Organic Sub- stances [in Russian], Nauka, Moscow (1980).

ii. G. I. Borodkin, M. M. Shakirov, and B. G. Shubin, Zh. Org. Khim., 13, 2152 (1977). 12. V. A. Koptyug (editor), Current Problems in Carbonium-lon Chemistry [in Russian], Nauka,

Novosibirsk (1975), p. 5.

444

13. Yu. V. Zefirov and P. M. Zorkii, Zh. Strukt. Khim., 17, 994 (1976). 14. A. J. Campbell, C. E. Cottrell, C. A. Fyfe, and K. R. Jeffrey, Inorg. Chem., 15, 1326

(1976).

AN X-RAY STUDY OF ORGANIC LIGANDS OF COMPLEXON TYPE.

VI. CRYSTAL AND MOLECULAR STRUCTURES OF

PHENYLPHOSPHINEDIACETIC ACID

L. M. Shkol'nikova, A. V. Gasparyan, N. M. Dyatlova, J. Podlaha, and J. Podlahov~ UDC 548.737

A structure study has been performed (diffractometer, %Mo, direct method, aniso- tropic (H atoms) least squares, R = 0.049 on 1295 reflections) for phenylphos- phinediacetic acid. In accordance with IR results for the solid state and solution, it is found that the molecule does not have a betaine structure. The orientation of the phenyl ring and the two carboxyl groups with respect to the P-C bond corresponds to the crossed and gauche conformations correspondingly. The active H atoms in the ~arboxyl groups participate in 0...0 hydrogen bonds of length_2.680(6) and 2.664(5) A, which produce infinite chains of the molecules along the [i01] direction.

Phenylphosphinediacetic acid C6HsP(CH2COOH) 2 (I) is potentially a tridentate ligand and can be considered as a very simple representative of a homologous series of triphenylphosphine derivative of composition (C6Hs)nP(CH2COOH)~- n. The synthesis of I has been described in [i].

In I there is the phosphine acetate group~PCH2COOH, which is analogous to the iminoacetate

~NCH2C00H group in classical complex zones. Virtually nothing is known about the structural

aspect of complexons containing phosphine, apart from the bis-hydrobromide of ethylenediphos- phinetetraacetic acid [2]. Interest attaches to the structures of complex zones containing X donor atoms, where X = N(III), S(II), P(III), in relation to elucidating the effects of the donor atom on the conformation and coordination behavior of the ligands.

EXPERIMENTAL

Colorless crystals of I of composition CIoH~IO4P were grown from aqueous solution. The O

crystals are triclinic; a = 7.929(5), b = 8.314(3), c = 9.676(4) A, ~ = 70.35(3), $ = 76.11(4), y = 64.62(4) ~ , V = 539'3(5) A~, dcalc = 1.393 g/cm 3, Z = 2, space group P~. The data (1681

independent reflections) were obtained with a CAD-4 automatic diffractometer with Mo radiation and a graphite monochromator. The intensities were measured by ~ scanning, maximum 0 = 24 ~ The crystals are platey (linear dimensions 0.25 • 0.45 • 0.50 mm). All the calculations were based on the ENX-SDP suite with a PDP-II/t55 minicomputer. The structure was interpreted automatically on the MULTAN program. All the nonhydrogen atoms were localized in the E synthe- sis. The positional and thermal parameters were refined by block-diagonal least squares initially in the isotropic approximation and then in the anisotropic one with allowance for secondary extinctions on 1295 reflections to R = 0.070. The coordinates of all the H atoms were found from difference syntheses. After refinement in the anisotropic-isotropic (for the H atoms) approximation, the final values were R = 0.049, R = 0.055. We used the weighting

w scheme w = i/~ (F 2) in the least-squares fitting. Table 1 gives the atomic coordinates. The

All-Union Scientific-Research Institute of Chemical Reagents and Ultrapure Substances. Charles University~ Prague, Czechoslovakia. Translated from Zhurnal Strukturnoi Khimii, Vol. 25, No. 3, pp. 120--123, May-June, 1984. Original article submitted November 17, 1982.

0022-4766/84/2503-0445508.50 �9 1984 Plenum Publishing Corporation 445