1498 PETERPAULING
Inorganic Chemistvy
tive ligands leaving the equilibrium symmetry undisturbed. The evidence concerning the M6X1272+ions in solutions is more comp1icated.l Again it is clear that the T a polynucleus is subject to large deformations IT hile the iYb polynucleus is not. The sense of the deformations is such that it would be consistent r i t h hexasolvated complex ions with two X - and four HzO solvated to the elongated TaEX12?+ ions and four X- and two H20solvated to the flattened Ta6X124+ions. However, the spectroscopic evidence does not support this view. Robinlo and Kuebler found an identical split-
ting of the metal-metal bands for the TaoC1122+ ion when the anionic species was any one of C1-, OH-, Clod-, or CN-. If these various anions were solvating the Ta6C11z2+ion, the spectral splitting would be expected to be different in each case. Acknowledgment.-The author wishes to thank 31. B. Robin for suggesting this problem, for providing the Ta6C114'7Hz0crystals, and for helpful and stimulating discussion. (10) M. E. Robin, private communication.
C O S T R I B U T I O N F R O M THE %TILLIAM
RAMSAY AND RALPH FORSTER LABORATORIES, USIVERSITYCOLLEGE, LONDON, EXCLASD
The Crystal Structure of Bis (triphenylmethylarsonium)tetrachloronickel( 11) , [(C6HI,)3@H3As]2[NiCl,], of the Isomorphous Compounds of Mn, Fe, Co, and Zn, and of the Corresponding Bromides BY P E T E R PAULIKG
Receiired July 20, 1965 The crystal structure of bis(triplicnyl~ncthylarsonium)tetrachloronickel(11), [( C6H5)aCH3.~s]2[r\:iCliIf has becn detcrmined from the three-dimensional sharpened Patterson function and phased observed Fourier syntheses and refined by leastsquares methods. Crystals of the compound are cubic, space group T4-P213, a0 = 15.557 rt 0.004 A with four formula units per unit cell. The crystals contain the tetrachloronickel ion, [NiCla]t-, and two crystallographically distinct kinds of the triphenylmethylarsonium ion, [(CsHs)&H&] +, The arsenic and nickel atoms, one of t h e four chlorine atoms, and t h e carbon atoms of the methyl groups lie in special positions of the space group on threefold axes. All the complex ions arc tetrahedral, the three phenyl groups of each arsonium ion being crystallographically equivalent and three of the chlorine atoms of cach tetrachloronickel ion being crystallographically equivalent. The [NiC14]2- group is regularly tetrahedral t o within experimental error, the Ni-Cl distances being 2.267 i 0.008 and 2.271 =k 0.007 A and the CI-Ni-C1 angles being 109" 19' i 14' and 109" 38' =t17'. Crystals of the corresponding compounds containing t h e complex ions [MnCl4]z-, [FeCld] z - , [CoCld]z-, [ZnCla]z - , [MnBra]z - , [CoBr]2-, [NiBre]z-, and [ZnBre] z - have been shown by single-crystal and powder diffraction photographs t o be isomorphous with the compound containing t h e [NiC14]2 - ion. Crystals of the corresponding compounds of [CuCL]2 - and [CuBr4]2 - are isomorphous with each other; those of t h e chloride are orthorhombic, a = 32.27 ZIZ 0.02, b = 26.24 i 0.02, c = 8.943 rt 0.003 A%, space group Fdd2, eight formula units per unit cell. Crystals of the tetraiodides of Mil, Fe, Co, Ni. and Zn are isomorphous with each other but have a different crystal structure from the chlorides and bromides.
Introduction Of the several high-symmetry ligancy forms adopted by transition metal coordination compounds, the regularly tetrahedral form has been extensively discussed in recent years. One of the major problems is why it does not occur more often in certain electronic configurations such as d 2 or ds. According to simple chemical bond1 theory, paramagnetic tetrahedral nickel(I1) should be stable. Most of the compounds thought t o contain tetrahedral nickel(II), such as bis(acetylacetonato)nickel(II), have turned out to be polymeric and have octahedral coordination. An explanation for the difficulty3 in finding tetra(1) L. Pauling, .T. Ani. Ciieiiz. Soc., 63, 1 3 6 i (1931); I,. F a d i n g , "The Nature of the Chemical Bond," 3rd ed, Cornell University Press, Ithaca, S. Y., 1960, pp 153, 168. ( 2 ) G. J. Bullen, R. Mason, and P. Pauling, Inora. Cheiiz., 4 , 456 (196:). ( 3 ) M. A . Porai-Koshits, Russ. J . Inoig. Chem., 1, 332 (1959).
hedrally coordinated nickel(I1) compounds has been put forward by Orge14 by a consideration of the interaction of the electrostatic field of the ligands and the d electrons of the metal. For this effect alone the tetrahedral configuration is destabilized relative to the octahedral configuration because of the splitting of the d electron shells by the cubic fields. Furthermore, according to the theory of Jahn and Teller,j wherever there might exist degeneracy in the electronic states with a symmetric structure, there exists a more stable nondegenerate state with a less symmetric structure. Therefore, since regularly tetrahedrally coordinated nickel(I1) is degenerate in d, electronic states we expect the configuration to distort in some manner as to remove this degeneracy. (4) I,. E. Orgel, Report t o the X t h Solvay Council, Brussels, 1956, pp 289-338. (5) H. A . Jahn and E. Teller, Pvoc. R o y . Soc. (London), A161,220 ( l Y 3 i ) .
Vol. 5, No. 9, SeFtember 1966
CRYSTAL STRUCTUREOF [(CcH&CH,Asl2 [NiCl,]
1499
axis parallel to the axis of each branch. The branches are developed similarly to the trunk consisting of three crystals. Sometimes the trunk and three branches grow together to form a regular tetrahedron. Single crystals are optically isotropic. Powder diffraction photographs of the nine compounds taken on a 114.83-mm diameter Philips Debye-Scherrer camera with Cu K a radiation are almost identical, showing that the several compounds are isomorphous. Powder and single-crystal diffraction photographs show that the [ C U C ~ ~and ] ~ - [CuBr4I2- compounds are isomorphous with each other but have a different structure from that of the nine other compounds. Weissenberg and precession photographs (Cu KCY) of the [CuC14]2 - compound are of Laue group mmm and can be indexed in terms of an orthorhombic unit cell: a = 32.27 1 0.02, IJ = 25.24 =!= 0.02, c = 8.943 =!= 0.003A. Thesystematicabsences uniquely determine the space group as Fdd2. The unit cell volume of 7330 A3 compared to 3765 A8 for the cubic [NiCl4lZ- compound indicates eight molecules per unit cell. This implies that the sixteen [(C6H6)zCH&]+ groups are crystallographically equivalent and lie in the general position of the space group and that the Cu atoms of the [CuCl4]*- group lie in the unique special position 8a2 of the space group. The coordination polyhedron or polygon of the Cu atom therefore has symmetry 2. This restriction is not sufficient to indicate the nature of the coordination polyhedron as all the simple polyhedra including the tetrahedron have a twofold axis as a symmetry element. Crystals of compounds of the form [( C E H ~ ) Z C H ~[M1II4] AS]~ with MI1 = Mn, Fe, Co, Ni, and Zn are isomorphous as shown by powder diffraction photographs. Crystals of the [ZnId]2 compound are flat, approximately hexagonal plates and appear to belong to class 3 or 32 with developed faces (0001 } and one form of { h k i l } . The poor diffraction data available indicate the crystals are twinned or trilled. The observed systematic absences are not consistent with trigonal space group theory. The measured trigonal unit cell is a = 19.14, c = 20.19 A. Small pieces of single crystal of the compounds [( CEHG)SCHSAs]2[M11C14] were cut from the dome-end portion of sections of multiple crystals and were mounted with one twofold axis parallel to the rotation axis. The crystals were dipped several times in a 2% solution of Formvar 15/19E (polyvinylformal, Monsanto) in dry ethylene dichloride to protect them from atmospheric hydration. Single-crystal zero-layer and first-layer Weissenberg photoExperimental Section graphs taken with unfiltered copper radiation about a twofold rotation axis and about a threefold rotation axis of the five chloCrystals of [(C~H~)&!H~]z[Mr1X4] were prepared by Dr. Naida rides are identical except for small lattice changes. The effect Gill by the evaporation of an alcohol solution of stoichiometric of anomalous dispersion was not observed though the series of quantities of (C6H5)aCHsAsX and MIIX2. The compounds of metals includes the absorption edge for Cu KCY radiation. chlorine, bromine, and iodine have been prepared with the diThe diffraction symmetry is Th-m3. The only systematic valent metals manganese, iron, cobalt, nickel, copper, and zinc, 1. Reflections in except for the compounds containing [FeBrl]2 - and [ C U I ~ ] ~ - . ~ absences are the planes (hOO) with h = 2% approximately the positions of (500) and (900) appear with weak The nine substances [ ( C B H G ) ~ C H ~ A S ] ~ [ Mwhere I I X ~X ] , is chlointensity. The apparent reflection (500) was interpreted as rine or bromine and MI1 is manganese, iron, cobalt, nickel, or radiation due arising from the strong reflection (400) with Fe KCY zinc, except [FeBrc]2 - , crystallize as dendrites. The similarity to contamination of the X-ray tube, and the apparent reflection between these dendrites and conical fir trees is striking. The (900) was interpreted as arising from (10.0.0) with Cu Kp ratrunk is a long thick needle consisting of three crystals grown diation. From these data and from the fact that it was difficult together with reentrant angles about a threefold axis parallel to fit the contents of the unit cell into the other space groups in to the trunk axis. The developed faces parallel to the trunk are the Laue group M 3 (P23 and Pm3) the space group T4-P213 was planes of the form { 110) and cyclic permutations, each crystal assigned. This space group assignment was subsequently of the three having as its major development one of these planes confirmed from the Patterson function by a consideration of the and being terminated a t the edge by the other two. The trunk various possible Harker sections. is terminated a t the top by a point being the intersection of the The cell parameter of the nickel compound is 15.557 1 0.004 A three planes of the form { 100) taken two a t a time to form domes as determined by measurement of (600) a t 1 2 0 on the diffractomthat terminate the three crystals. Attached to the trunk are eter ( A Cu KCY= 1.54178). The density of [(CBH5)3CH3A~]2[Withree groups of branches a t an angle of 120" from each other and Cla] measured by pycnometer is 1.46 g/cm3; that calculated for a t an angle of 109" 28' from the trunk, with another threefold four formula units per unit cell is 1.49 g/cm3. Three-dimensional diffraction data to a limit of 20 = 90' with (6) J. D. Dunitz and L. E. Orgel, Advan. Inovg. Chem. Radiochem., 2, 1 (1960). nickel-filtered Cu KCYradiation of a single crystal of [(Cg&)3' (7) L. M. Venanzi, Pvoc. Chem. SOL.,6 (1958). CHaAs]2[NiC14] of approximately cubic shape with edge 0.5 mrn (8) N. S. Gill and R. S. Nyholm, J . Chem. Sac., 3997 (1959); N. S. Gill, were collected with the four-circle proportional counter diffractoi b i d . , 3512 (1961). meter built by U . W. Arndt in the Davy Faraday Research Labo(9) M. Kotani, J . Phys. SOC.Japan, 4, 293 (1949).
Duiiitz and OrgeP have shown that a distortion of the tetrahedron from 23 symmetry to 3 symmetry will do so. This is the pseudosymmetry shown by the series of compounds dihalobis(triphenylphosphine)nickel(II) with chlorine, bromine, and iodine prepared and analyzed by Venanzi.' The LCAO molecular orbital treatment is able t o give the relative order of the energy of the molecular orbitals for each of the coordination types, but has not so far been able to predict the coordination expected for any particular compound. Arguments similar to those applicable to the ds nickel(11) case are also applicable with somewhat different conclusions t o d5 Mn(II), ds Fe(II), d7 Co(II), d 9 Cu(11), and d10 Zn(I1). A series of compounds of the form l(c6H5)3CH3As]2[M"X4J where M" is Mn, Fe, Co, Nil Cu, or Zn and X is C1, Br, or I has been prepared by Gill and Nyholm.8 The physical properties of these compounds suggested that they are tetrahedral coordination complexes. They are 2 : 1 electrolytes in organic solvents, light in color, and spin free. A preliminary diffraction investigation showed the tetrachlorocobalt compound, which is expected to be stable as a tetrahedral complex, to be isostructural with the tetrachloronickel compound. The high magnetic moment of the tetrachloronickel compound (3.89 BM) is a large increase on the spinonly value of 2.83 BM and suggests that the complex ion is regularly tetrahedral. The excess magnetic moment over the spin-only value can be explained by a large orbital contributionQresulting from regularity. An investigation of the crystal structure of the compound bis(triphenylmethy1arsonium)tetrachloronickel(11), a blue paramagnetic salt, has been undertaken in order t o determine the stereochemistry of the tetrachloronickel ion and of the other complex ions of this series.
+
1500 PETERPAULING
Inorganic Chemistry
9
8
1,
NO
, I
1000
6
I
4
I
0
I
2 0
40
I
I
60
80
100
13.0
140
160
180
I
I
200
220
I
I
3 0 0
310
I
240
260
280
I
340
360
u/*Figure 1.-A plot of the measured intensity of (002) as a function of @ showing thc effect mostly of absorption and of all measured intensities of the standardizing reflection (006) as a function of 6 showing the effect of absorption and variation with time of the counting system. ratory of the Royal Institution of Great Britain. The instrument had the geometry described by Furnas and Harker'O and used a semiautomatic stepped w scan. The maximum diffraction angle of the instrument was limited to 90' by mechanical interference. The three diffractometer angles were determined using the analog computer of Arndt arid Phillips," arid the instrument was set by hand. The angular coordinates of the intensity maximum for each measured reflection were determined experimentally by observing the counting rate. The nieasurenietit was made by counting the background l o in d2to one side of the reflection maximum for 10,000 monitor counts, stepping w through twenty steps of 0.1' each, counting at each stationary point for 1000 monitor counts, and counting the background at the end of the scan for 10,000 monitor counts. A% total of 890 measurements were taken over a period of 10 days, 117 reflections being too small to be observed. Of these 890, 180 were standardizing counts of the plane (006). 'rhe total count for each reflection was corrected for background by subtracting thc two background counts and for Lorentz and polarization factors by means of a chart showing the combined correction as a function of 28. The linear absorption coefficient of the substance is about 56 cm-', and the data were empirically corrected for absorption and variation in counter sensitivity by applying a correction based on the measurement of the plane (006) as a function of the angular parameter @12 and time. The plane (006) is in the reflecting position with x = 90' and is independent of @, and variations in its measured intensity give a measurement of the absorption of the crystal as a function of @. The three-dimensional data were measured in lines of constant @ oarallel to the crystal twofold axis 6 , and at the time of taking the data along any such line, the plane (006) was measured with (10) T. C. Furnas and D. Earker, Rev. Sci. Isti,., 26, 149 (1055). (11) U. W.A r n d t a n d 11. C. Phillips, A d a Ci,ysl., 10,508 (1067). (12) U. W. Arndt and D. C. Phillips, ibid., 11, 50Y (195s).
the value of @ of the linc. These measurements and those of (002) as a function of @ are shown in Figure 1. The data along any line were multiplied by the ratio of a standard valuc of (006) to the value of (006) measured with the line. The average over-all temperature factor and the absolute scale of the data were determined roughly by use of the statistical method of The data were scaled and sharpened by the function 0.71d4 38 by plotting as a function of (h2 k 2 f Z2) and calculating ( h * k2 1 2 ) by inspection for each planc. A threefold multiplication of the unique data was generated by hand through the cyclic permutation of the indices, and the sharpened three-dimensional Patterson function was calculated on a Ferranti Pegasus computcr with an mmm Fourier program especially written by Dr. D . W. Green.
+ +
+
Analysis and Refinement The space group assignment was confirmed by the observation t h a t the Harker peaks for the heavy atonis appear in the plane P(x, y , From the space group and the contents of the unit cell, the two arsenic atoms, the nickel atom, and one chlorine atom must lie in the special position of P&3 on one of the four nonintersecting threefold axes. The location of these atoms was determined primarily by a study of the plane in the Patterson function P(x, - x,z ) being the locus of all points from one threefold axis of the space group to another nonintersecting threefold axis. The image of each set of atoms along a threefold axis reflected through each atom along another axis should appear in a symmetric fashion in t n o directions in this section of the (13) A J C Wilson, .\atwe, 150, 152 (1942)
Vol. 5, No. 9, September 1966
CRYSTAL STRUCTURE OF [(CSH&CH&SJZ [NiC14] 1501
three-dimensional Patterson function. Absolute coordinates for the atoms were obtained by the interpretation of the Harker peaks which appear in each image axis, The coordinates of the chlorine atom in the twelvefold general position were determined by the interpretation of the peaks in the three-dimensional Patterson function corresponding to the vectors from the two arsenic and one nickel atoms to this general chlorine atom. This was done by plotting, as projections on a major section, spherical shells in the Patterson function a t a distance 2.25 A from the peaks interpreted as vectors from the two arsenic and the nickel atoms to the nickel atom on the same threefold axis and a twofold screw-related threefold axis. A set of three coordinates for the chlorine atom in the general position was determined from these six images. No attempt was made to find the positions of the lighter atoms from the Patterson function. The trial coordinates of the heavy atoms determined from the three-dimensional sharpened Patterson function were used to phase an observed Fourier synthesis using a program specially written for the space group P213. The program calculates the noncentrosymmetric structure factors, generates the planes related to the unique planes by a threefold axis of symmetry, and sorts the resultant list either of calculated, phased observed or diflerence structure factors for one octant into an order convenient for the subsequent Fourier synthesis. This and subsequent calculations were done on the University of London Ferranti Mercury computer. The three-dimensional observed synthesis was calculated using the Fourier program of Mills.14 All the carbon atoms appear well in this synthesis except that one methyl group (C(7)) attached to an arsenic atom did not show up strongly and a ghost peak appeared along the threefold axis on the other side of the arsenic atom. Coordinates for all other carbon atoms were determined from this synthesis and the coordinates for the heavy atoms were slightly adjusted. These coordinates were used to calculate structure factors and a difference synthesis from which the position of the methyl group (C(7)) was determined and all atomic coordinates were slightly refined. The structure was refined with isotropic thermal parameters using a program written for the space group. The program calculates a 4 X 4 block matrix for positional and isotropic thermal parameters for each atom in general position, a 2 X 2 block matrix for the one positional parameter and the isotropic thermal parameter for each atom in a special position along the threefold axis, and a 2 X 2 block matrix for the scale factor and an over-all thermal parameter. The shifts were determined in the usual way, the thermal parameter shifts being determined by the relationship B Bt B i i , where B is the shift determined from the 4 X 4 or 2 X 2 atomic matrix, B i ; is the suggested shift in the
over-all temperature factor as determined using the diagonal term of the inverse 2 X 2 over-s11thermal factor and scale factor matrix, and B , is the over-all B shift using the complete 2 X 2 niatrix.16 The structure was refined by 16 rounds of least-squares refinement of this form with use of equal weight for all observed planes. The scattering factors used in this refinement were for Ni(0),16Cl(0),17As(0),17 and C(O).'* The scattering factor of nickel(0) was corrected for the real part The of the effect of anomalous dispersion ( - 3 . l ) . I 9 hydrogen atom positions were not determined in the analysis and were not used in the refinement. Full shifts were used and parameters were not restricted by interatomic distance or thermal constraints. The final shifts are less than 0.05 of the estimated standard deviation of the parameter for the heavy atoms and less than 0.08 for the carbon atonis. The final coordinates are listed in Table I along with estimated standard deviations determined from the least-squares matrices using the relationship
+
(14) 0. S. Mills and J. S. Rollett in "Computing Methods and the Phase
Problem in X-ray Crystal Analysis," R Pepinsky, J M Robertson, and
J. C. Speakman, Ed., report of the conference a t Glasgow, 1960, Peigamon Press. Oxford, 1961, pp 107-124.
g,2
=
A,,ZwA2 ~
n-s
where A i , is the diagonal term of the inverse leastsquares matrix for the appropriate parameter, ZwA2 is the sum of the squares of the residuals of the individual structure factors (scaled F, - F J 2 , w = 1, n is the number of observations (500), and s is the number of parameters (65). Observed and calculated structure factors for the parameters listed in Table I are given in Table 11. Unobserved reflections were not used in the refinement but are included in Table I1 indicated by negative Fo. The residual R = ZlAFI/ BF, for the 500 observed planes is 0.074 with the refined atomic coordinates and isotropic thermal parameters of Table I. Figure 2 shows = x w A 2 / n as a function of sin
a
n
e / A and F,. The appropriate weighting scheme for a least-squares refinement should result in vs. any variable being constant for the refined structure, and these curves indicate that other than unit weight for all planes would have been more appropriate. While data available to higher diffraction angle would be valuable, the ratio of available observations to parameters and the statistical standard deviations indicate that this analysis is not invalidated by the 90" 20 limit of the observations. A drawing showing sections of the observed electron density function through each atom is shown in Figure 3 . The drawing shows all of the atoms (except H) of the complex ions lying along the threefold axis passing through the origin, and while overlap of some phenyl rings is severe, crystallographically equivalent groups appear clearly. Interatomic distances and interatomic angles are listed in Figure 4. The varia-
a2
(15) D. W J Cruickshank, zbzd , p 43; R. A. Sparks, zbzd , p 174. (16) R E Watson and A. J Freeman, Acta Cryst., 14, 27 (1961). (17) A. J Freeman and R. E. Watson, personal communication, 1961. (18) J A. Hoerni and J. A Ibers, Acta Cvyst., 7, 744 (1954) (19) International Table, for X-ray Crystallography, Vol. 111, Kynoch Press, Birmingham, 1962, p 214
lnorganic Chemislry
1502 PETERPAULING TABLE 1 REFINED COORDINATES A N D ISOTROPIC T H E R M A L I'ARBMETERS ( A ) A S D ESTIMATED STAXDARD STRUCTURE OF [( C G H ~ ) ~ C H ~NiC141 AS]~[ r/a"
Ni CI(1) CI(2)
d
3 1
, ~
J
L12
1
a
Y/aQ
0.0597 (3) 0.0597 ( 3 ) b 0.1815(4) 0.0938 (4) d 3 - 0.0246 (4) -0.0246 ( 4 ) a 3 0.7824 ( 2 ) 0,7824 ( 2 ) C(1) 0.750 (1) 0.900 (1) C(2) 0.806 (2) 0.962 (2) 0.783 ( 2 ) 1.050 ( 2 ) c(3) 112 b 1 0.700 ( 2 ) 1.074 ( 2 ) C(4) I C(5) I 0.647 ( 2 ) 1.010 ( 2 ) 0.666 ( 2 ) 0.920 ( 2 ) ~ ( 6 ) 3 0.710 (1) 0.710 (1) C(7) 4 d 0.5092 ( 2 ) 4 d 3 0.5092 ( 2 ) As(2) 0.393 ( 1 ) 0.555 (1) C(8) 0.499 ( 2 ) C(9) 0.329 (1) 0.245 ( 2 ) 0.530 (2) C(10) b 1 0.229 ( 2 ) 0.621 ( 2 ) C(11) f C(12) 0.300 ( 2 ) 0.673 ( 2 ) 0.643 ( 2 ) 0.382 ( 2 ) (213) J C(14) 4 a 3 0.582 ( 2 ) 0.582 ( 2 ) riumbers in parcntheses are standard deviations in least significant digits. 4 12 4 4
L)EVIATIONS O F AkTOMS I S THE
CRYSTAL
z/a"
K
dB)
0.0597 (3) -0,0127 ( 4 ) -0.0246(4) 0.7824 ( 2 ) 0.770 ( 2 ) 0.793 ( 2 ) 0.790 ( 2 ) 0.761 ( 2 ) 0.738 ( 2 ) 0.740 (2) 0.710 (1) 0.5092 ( 2 ) 0.505 (1) 0.483 (2) 0.478 ( 2 ) 0.494 ( 2 ) 0.515 (2) 0.522 (2) 0.582 (2)
3.49 3.98 4.26 3.86 3.44 4.17 4.15 5.01 5.92 4.40 3.10 3.94 3.25 3.73 5.58 7.16 5.42 3.95 5.31
0 . 1;i 0.14 0.26 0.10 0.55 0.59 0.59 0.66 0.71 0.61
0.87 0.10 0.53 0.54 0.71 0.83 0.68 0.57 1.17
6000 5000
4000 3800
2000 IC00
01 0 0
Figure 2.-wA2,
I
I
50 0.05
w
=
100 0.1
I
I
150
200
0.15
0.2
F sin @ / A
1, as a function of sin O/A (triangles) and
F (circles) for the refined structure.
"'.-1,;t
C82
2 271
IOP*lP'f 14'
I'
lO9'3B'f 17'
i i n t 008
$
Figure 4.-Interatomic distances and angles with statistical estimated standard deviations (no allowance for esd of cell of CC-C [S~ ~ ~ ]distances is parameter) of [ ( C ~ H ~ ) ~ C H ~ X S ;] *esd 0.04 A.
tions in refined C-C distances show that this analysis is not of much value for determining the structure of the phenyl ring, but the standard deviations of the metalhalogen distances and angles are usefully l0\~7.
Figure 3.-Composite sections perpendicular (001) through t h e atomic centers of the observed Fourier synthesis of the compound [(CsH6)3CH&]2[NiC14]. Contours are a t 0 and 4.0 e/X3 for heavy atoms and 2.0 e/X3 for carbon atoms.
Discussion The [NiCl4I2- group is regularly tetrahedral to within experimental error, the observed difference in Ni-C1 distance Of 0.0°4 A being about one-ha1f Of the estimated standard deviations for these distances and
CRYSTAL STRUCTURE OF [(C6H&CH3AsI2 [NiCl,] 1503
Vol. 5, No. 9, Sepember 1966
TABLE I1 OBSERVED AND CALCULATED STRUCTURE FACTORS FOR h
k
1
Fobs
2
3 0 0
0
1409 3796 887
d 12
0 0 0
14
0
10
I
o o @
0 0 0
0
i
I I 1
4
1
o
2
a
3
9
IO 11 12
13
o o
1 1
0
1
0
1
1 1 1 1
1
o
o o 0
2
o o
i
10 9
11
2
2 2
12
2 2
14
2
1 2
3 3 3 3
3 4
a
i
: 0
o
0 0
:
: 2
0
154
o
1263
0
-182
0
611 553 454
0
-228
o
o
o
o
4
o
4 4 4
0
o 0
70 1701 1379 1187 469 442
1692 528 412
0 0
-221
13
4 4
I
5
o
5 5
o o
619 665 805 237 180
5 5 5
0
1052
@
5
294
0 0
226
5
0
177
@
342
7
10 9
I1
12
13 1 2
3 4
a
7 9 10 11
12 1 2
3 4
a
6 6
6 6 6
6 6 6 6 6 6 6
0
-228
: 2 275
o
868
0
1441
0
847 752
0 0 0
1189 1001
4"
0 0 0 0 0
-221
1291
853 437 317
0
847
0
-151
7
: :a;
11
7
12
o
0
10 9
3
: 2;
7
7 7 7 7 7
3
9
10
I1
0
218
: 2: 0 0
o 0 0
186 -207 -217
708 199
o 0 0
o o
144
936 758 289 412 651
11 2
623 975 355 1074 271 277 358 294 116
168
1 2
3
4
a
5 9
10
757 2209
1
1215
3 4
1073 1089 468 627 64
6b;
2
a
7
319 1183 1267 575 162 134
1280 111
628 558 410
50 103 1702 1410 1208
477 370 1787 539 377 709 751
9 9 9 9 9 9 9 9 9 9
0 4 4 4 0
0 0
0 0
o
o 0 0
10 10
0 0
10
0
10
lo 10
10 10 IO
0
o
o o o
I
11
o
11
0
11 11
0
a
3
li 11 11 11
1 2
12
3
12 I2
4
a
o
210
300
o
!2482 ;
0
-221
0
313
12
0 4 4 4 -224
o o
382
0 0
327 243
14
o
663
14
0
-228
256
1686 1314 1352 587
604
i
7
1
211 844
9
1 1 1 1 1
877
14
I
-228
240
2
2
299 263 315
3
2
4
2
2 3
2
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COMPOUND [( CsHs)&!HsAsI2 [ NiCla]
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Scale is 1OX absolute for one formula unit.
the observed difference in the C1-Ni-C1 angles of 19' being about equal to the estimated standard deviation for these angles. This regularity is consistent with the observed high magnetic moment of the compound,8 in which the degeneracy of the d electron levels gives rise to a high orbital contribution t o the magnetic
m ~ m e n t . The ~ distortion predicted by the theory of Jahn and Teller5 does not appear and if present a t all must be smaller than the observed experimental error of the structure. The tetrahedral arrangement of ligands in the complex anion [NiC14I2- is not stabilized in the compound
1504 PETERPAULING
Figure 5.-A
diagram of the structure of [ (C~H,)3CH8A4s]2[r\’iCl~] projected or1 (001) showing the packing environment of the anion. In order of decreasing diameter, the circles represent nickel, chlorine, arsenic, and carbon atoms
by crystal forces; that is, the forces exerted on the anion by the other components of the crystal or by these complex ions on each other do not force an otherwise unstable arrangement. Each complex group [NiCl4I2is effectively separated from other anions and shielded from the rest of the crystal by phenyl rings, which, like large flat leaves, surround the anion as shown in Figure 5 . The phenyl rings are not closely constrained and do not constrain the anions. Evidence independent of this structure analysis that the complex anion is stable is that the magnetic moment of the substance in solution in nitromethane is the same as that of the solid.*O That the environment of the complex ion in this compound is so unrestrictive caused us to consider the possibility of a larger distortion than has been indicated that cannot easily be detected by X-ray analysis. Each anion has threefold symmetry derived from the crystal symmetry. It is consistent with the crystal symmetry that each anion have 23 symmetry and be regularly tetrahedral. It mould be possible for each anion to be distorted along a twofold axis giving point symmetry 4 in a manner suggested by Dunitz and OrgeP and that the unique distortion axis resonate in time or (20) N.
Inorganic Chemistry
S.Gill, personal communication.
be disordered in space among the four possible directions of the twofold axes of a regular tetrahedron and of the crystal. The effect of this distortion would not be observed in the positions of the ligands as determined by X-ray structure analysis ; the coordination polyhedron would appear perfectly regular. The only observable effect of such resonating distortion or disorder would be interpreted as an increase in the anisotropic thermal vibration parameters. The determination of thermal parameters by diffraction analysis is less precise than that of coordinate parameters. Nonetheless, an inspection of the difference synthesis calculated using the parameters of Table I in the region of the anion shown in Figtlre 6 shows that this form of distortion is not evident in this compound. The structure was refined using isotropic thermal parameters, and one would expect the anisotropy caused by normal thermal vibration alone to be largest in the direction perpendicular to the Ni-C1 bonds. This is the same direction as one would expect from the suggested distortion when mixed with the threefold symmetry of the crystal. The expected anisotropy is present but is not large, certainly small enough to indicate that this form of distortion is not present to any degree. It does indicate, however, that anisotropic
Vol. 5, No. 9, September 1966
CRYSTAL STRUCTURE OF [ (C6Hb)3CH3A~]2 [NiCld] 1505 phenyl groups is 20” 10’ for As(l)C(l)-C(B) and 22’ 50’ for As(2)C(S)-C(13). The interatomic distances and angles of the arsenic atoms to their nearest neighbors and of the phenyl rings are given in Figure 4. The cell parameters for the chlorides determined from Weissenberg photographs are listed in Table 111. The individual photographs were not calibrated, but the camera was calibrated with pure aluminum wire. The relative changes in cell parameter are small but real as shown by film-to-film comparison. TABLE I11 CUBICCELLPARAMETERS OF THE CHLORIDES [ ( C B H ~ ) ~ C H ~ A S ] ~ [for M I MI1 IC~~ =] Mn, Fe, Co, Ni, and Zn, MEASURED FROM WEISSENBERG PHOTOGRAPHS (ESD 0.01 A )
Figure 6.--Composite sections of the phased difference synthesis of the compound [(CeH5)3CH1As]z[~iC14]in the region of the anion [XiC14I2-, excluding the nickel atom section, which is indicated by the small circle. Solid contour lines are a t 0 and $0.1 e/A3.
thermal parameters for the heavy atoms could be determined from the data. The arsonium ions are regularly tetrahedral to within experimental error. The angle between the threefold axis and the axis of least inertia (all atoms given equal weight) of the (AsC6) groups is 111’ 12’ for As(l)C(l)C(6) and 110’ 38’ for As(2)C(8)-C(13). The related phenyl-arsenic-phenyl angles of the two groups are 107” 41 ’ and 108’ 17’, respectively. The differences between these angles and regularity (109” 28’) are approximately 3 u, though the estimated standard deviations of the axes of minimum inertia have not been calculated accurately. The angle between the plane defined by the axis of minimum inertia of the (AsC6) group (all atoms given equal weight) and the threefold axis and the plane of the ring (perpendicular to the axis of maximum inertia) or the pitch of the
Metal
a, A
Metal
a, A
Mn Fe
15.63 15.65
co Xi Zn
15.53 15.56 15.55
The existence of this series of compounds with definite regularly tetrahedral coordination should allow a series of experiments involving the correlation of properties and structure. Among these are the studies of optical absorption spectra,21 infrared spectra, 2 2 magnetic moment,23and heats of solution.24 Acknowledgment.-The author is grateful to Dr. Naida Gill for presenting him with the problem and with crystals of the compounds, to Dr. H. C. Carlisle of Birkbeck College for X-ray facilities, to Dr. D. C. Phillips and the Managers of the Royal Institution of Great Britain for use of the diffractometer, to Miss Carol Routledge, who measured about half the data, to Mrs. Jean Dollimore, Dr. D. W. Green, Mr. 0. S. Mills, and Dr. R. Sparks for help with computer programs or for the use of their programs, and to Professors Sir Lawrence Bragg, J. D. Dunitz, and R. S. Nyholm for continuous encouragement. (21) T. M. Dunn in “Advances in Molecular Spectroscopy,” Pergamon Press, Oxford, 1962, pp 220-226, D. M. L. Goodgame, M. Goodgame, and F. A. Cotton, J . A m . Chem. Sac., 83, 4161 (1961). (22) R. J. H. C l a r k a n d T . M. Dunn, J . Chem. Soc., 1198 (1963). (23) B. N. Figgis, J. Lewis, F. Mabbs, and G. A. Webb, Natuve, 208, 1138 (1964). (24) A. B. Blake and F. A . Cotton, Inorg. Chem., 3, 5 (1964).
