1200 F. A . COTTON A N D J. 1.WTSE
l n orgun ic. Chwn istr y
radius for Tc(1V) from this structure. An upper limit would be 1.50 A, based on the long bonds Tc(l)-C1(2) and Tc(1)-Cl(3). The only other reported Tc-C1 bond length is 2.35 A for the TczCla3-ion,15in which the oxidation state of T c is V or VI. Acknowledgments.-We wish to thank Mrs. J. H . Hickford for supplying samples of the compound and (15) F. A. Cotton and W.K. Rratton, J . A m . C h m . Soc., 87,921 (1965).
Dr. J. E. Fergusson for helpful discussions concerning the bonding in the polymer. The IBM 1620 of the Mobil Computer Laboratory of the University of Canterbury was used for computations. Programs of D. van der Helm of the Institute for Cancer Research, Philadelphia, and of G. Mair, National Research Council, Ottawa, Canada, were used for part of the work. The Xew Zealand University Grants Committee supported the work in the form of grants for equiptnent.
C O N T R I B U T I O S F R O M THE L)EPARiXZEST O F CIIEMISTRY,
MASSACHIJSETTS TNSTITTJTE
OF
TRCISNOLOGY, CAMBRIDGE, MASSACITrJSr I
IS
(32139
The Crystal and Molecular Structure of Bis(2,2,6,6-tetramethylheptane-3,5-dionato)nickel(I I ) BY
F. A. COTTON
AND
J. J. WISE
Received January 12, 1966 The crystal and molecular structures of bis(2,2,6,6-tetramethylheptane-3,~-dionato)nickel(11). also called his( dipivaloylmethanido)nickel(II), Ni(DPM)2, have been determined in a single crystal X-ray diffraction study. The unit cell is 0.02 A, B = monoclinic (space group P21/a) with dimensions a = 10.70 & 0.01 A, b = 10.98 k 0.02 A, c = 10.39 113' 16' ZIC 15', and contains two formula units. As expected from earlier studies by Cotton and Fackler, the molecules are mononuclear, essentially planar, and centrosymmetric. The S i - 0 distances, 1.836 & 0.005 A, are much shorter than those in a number of complexes in which X(I1) is octahedrally coordinated by oxygen atoms. This map be explained by the absence of electrons in the antibonding u-MO with d,, symmetry. The orientation of the molecules in the unit cell is fully described for future reference in the reporting of polarized optical absorption studies of this substance and its isomorphous Cu( I1j analog.
Introduction polarized electronic spectral studies of the crystals might be made. The results of the latter studies will Studies of P-ketoenolate complexes of nickel(I1) be reported later. However, in anticipation, this and cobalt(I1) have established that while the acetylpaper will describe the molecular orientations more acetonates readily form polymeric structures by sharing explicitly and in more detail than is customary in of oxygen atoms,1-5 the replacement of the methyl reports of crystal structure studies intended purely t o groups by larger groups leads to partial2V3 or comelucidate molecular structures. plete2,3 , 6 , 7 dissociation, exclusively monomeric moleThe ligand molecule, systematically named 2,2,6,6cules being obtained when the methyl groups are retetramethylheptane-3,5-dione,has also the common placed by the very bulky t-butyl group. Spectroname dipivaloylmethane, DPM, which has been often scopic studies of the nickel2 and cobalt4n6monomeric complexes of 2,2,6,6-tetramethylheptane-3,5-dionatoused in the past. Henceforth in this paper we shall use the latter name and its abbreviation. ion lead to the conclusion that these were, respectively, square and tetrahedral, and, for the cobalt complex, Experimental Section this has been conclusively demonstrated by single Bis( dipivaloylmethanido)nickel( 11), Ni( DPM)z, was prepared crystal X-ray diffraction The present paper by the reaction of dipivaloylmethane (2,2,6,6-tetrarnethylhcpreports an X-ray study which proves conclusively the tane-3,5-dione) and nickel acetate.2 The dipivaloylmethane was prepared by the method of Adams and Hauser.8 The product planar structure of the nickel complex. of the reaction of dipivaloylmethane with nickelous aceThis study was undertaken not only to confirm this tate was a green solid, believed to be the dihydrate of bis(dipoint but to provide knoLT-ledge of the orientation of pivaloylmethanido )nickel(11). Upon drying under vacuum at the molecules in the unit cell for this compound and its looo, the green solid lost water and turned red. The red solid isomorphous Cu(I1) analog, in order that esr and was sublimed a t 120" under a pressure of approximately 0.02 mm. (1) G . J. Bullen, R. Mason, and P. Pauling, Nattlrs, 189, 291 (1961); Inoug. Chem., 4,456 (1965). (2) F. A. Cotton and J. P. Fackler, Jr., J . A m . Chem. Soc., 83, 2818 (1961). (3) J. P. Fackler, Jr., and F. A. Cotton, ibid., 83, 3775 (1961). (4) F . A. Cotton and R. H. Soderbei-g, I n o i g . Chem., 3, 1 (1964). (5) F. A. Cotton and R. C. Elder, ibid., 4, 1145 (1965). (6) F. A . Cotton and R. H. Soderberg, J . A m . Chem. Soc., 84, 872 (141i2). (7) F.A. Cotton and J. S . Wood, I n o i . ~ Chrm., . 3, 245 (1964).
X small amount of a yellow-green paperlike solid remained after sublimation. Sublimations were repeated until no residue was observed. Melting point determinations (uncorrected) on thrice sublimed material gave 224.5-225.5' in open-tube determinations and 225.0" in closed-tube determinations. A4nalysis of the thrice sublimed sample gave 62.32% carbon and 8.927, hydro(8) J. Arlarns and G. Haiiser, J . A m . Che?iz. Soc., 66, 1220 (1044).
Vol. 5, No. 7 , July 1966
BIS(2,2,6,6-TETRAMETHYLHEPTANI3-~, 5-DIONATO)NICKEL( 11)
gen, which compares closely to the calculated values of 62.16 and 8.95%. Platelike monoclinic prisms (crystal class 2/m) were grown by sublimation under vacuum a t 100”. Using a single crystal of about 0.5 X 1.0 X 0.1 mm mounted on an axis in the plate, precession photographs were taken with Cu Kcu radiation. The unit cell was found to be monoclinic with a p angle of 113” 16’ i. 15’ and these dimensions: a = 11.70 =t 0.01, b = 10.98 i. 0.02, and c = 10.39 i. 0.02 A. The systemic absences observed were as follows: hk2 no conditions: for h02, h # 2n; for OkO, k # 212. These conditions uniquely fix the space groups as P21/a (No. 14). The density (by flotation method in a saturated solution of K I at 30’) was found to be 1.15 =t 0.02 g/cm3. Taking the molecular weight as 424.7, the calculated number of molecules in the unit cell is 2.00 =t 0.08. Intensity data were recorded photographically by the equiinclination Weissenberg method, using Cu Ka radiation and multiple film technique. The h02 through h9Z layers and the hkO through hk4 layers were recorded and the intensities were estimated by comparison with a set of timed exposures of a reflection from the same crystal. No corrections were made for absorption due to the low value of the absorption coefficient ( p = 11.8 cm-l). It was calculated that 965 independent reflections would be available with Cu K a radiation in the range 0 < sin 0 < 2-’12, and measurements were restricted to that sphere in reciprocal space. Lorentz-polarization corrections by a graphical methodlo were applied where required and necessary corrections for extension of spots on upper layer photographsll were made. It should be noted that of the approximately 965 reflections encompassed by the hO2 through h9Z layers, 248 were too weak to be recorded.
Determination of Structure I n the space group P21/a the two nickel atoms occupy special positions (0, 0, 0 ; 1/2, 0), which are inversion centers. The asymmetric unit consists of half of the nickel atom and one of the two chelate groups. It seemed likely that the position of the two oxygen atoms in the chelate ring could be obtained by a Patterson projection12 onto the 010 plane by the overlap of nickel-oxygen vectors from the oxygen atoms in the chelate ring. The projection was made using 114 nonzero h01 reflections. Two peaks lying 1.17 and 1.24 A from the origin were located. Using the bond distances observed in the analogous zinc compound for the metal-oxygen bond length8 (Zn-0, 1.96 A), trial positions for the two oxygen atoms were calculated. Using the h01 to h91 set of reflections and the positions of the nickel atom and the two oxygen atoms, a structure factor calculation was made and a threedimensional Fourier synthesis computed. The atomic scattering factors used were those of Freeman and Watson13 for nickel and those of Hoerni and Ibers14 for carbon and oxygen. The positions of the oxygen atoms were adjusted on the basis of this calculation. Three peaks were found representing the three carbon atoms in the ring. Another structure factor calculation and Fourier synthesis was made using the above atoms. Then the two carbon atoms representing the (9) Cf. “International Tables for Crystallography,” Kynoch Press, Birmingham, England, 1962, Vol. I. (10) W. Cochran, J . Sei. Instr., 26, 253 (1948). (11) D. C. Phillips, Acta C ~ y s t . ,9, 819 (1956). (12) W. G. Sly, D. P. Shoemaker, and J. H. Van den Hende, “A Twoand Three-Dimensional Crystallographic Fourier Summation Program for the IBM 709/7090 Computer-ERFR-2,” 1962. (13) A. J. Freeman and K. E. Watson, Acta Cvysl., 14, 231 (1961). (14) J. A. Hoerni and J. A. Ibers, i b i d . , 7, 744 (1854).
1201
centers of the t-butyl groups were located. From a further structure factor and Fourier calculation the positions of the six remaining carbon atoms were located. Three cycles of least-squares refinement15 in which the atom positions and the film scale factors were varied while fixed, arbitrary isotropic temperature factors were used lowered the unweighted residual from 0.36 to 0.27. The residual is defined as Zwl1 FoI ~ F o ~ \ / Z w ~inF owhich ~, F, and F, are the observed and calculated structure factors and w is the weight, set equal to unity for all Fo values in calculating an “unweighted” residual. Three additional cycles of refinement in which scale factors, atomic parameters, and temperature factors were allowed to vary lowered the residual to 0.21. At this point it became obvious that the large number of unobserved reflections was to be a problem. I n order to reduce the number of unobserved reflections and to improve the data, the second set of reflections taken along the c axis, the hkO through hk4 layers, was utilized. All reflections were corrected for Lorentz and polarization factors and spot extension and then put on the same relative scale by correlating intensities on the hkO through hk4 films with those on the h01 through h91 films. The corrected intensities obtained on the hkO through hk4 levels were averaged with the corresponding intensities observed on the h01 through h91 films. All unobserved reflections were assigned intensities of one-half the minimum value16 and were corrected for Lorentz and polarization factors and spot elongation in the same manner as the observed reflections. The number of nonobserved reflections was reduced from 248 to 201 after inclusion of the c axis data. The reflections were now weighted. Those for which readings from both films were available were assigned a weight equal to the standard deviation uFo of the average intensity ( F o ) . Using the theory of very small samples, the standard deviation was computed as being 0.89 of the difference between the two observed v a 1 ~ e s . l ~A plot of uFo against Fo was made for all reflections with two observed values. It was assumed that those reflections for which only one value was available would follow the same relationship and uFowas estimated from the plot for these reflections. For the unobserved reflections, which had been assigned an intensity of one-half the minimum observable (Fmin),a weight of ( 1 / d 2 ) F m i nwas assigned on the basis of statistical considerations. A correction of the atomic scattering factors for nickel for the real part of the anomalous dispersion was made according to the method of Dauben and Templeton.I8 The imaginary term was neglected. Two cycles of isotropic refinement were run and small adjustments made to positional parameters on the basis of a three-dimensional Fourier synthesis. Two fur(15) C. T. Prewitt, “A Full Matrix Crystallographic Least Squares Piogram for the I B M 709/7090 Computer,” 1962 (16) A. J. C. Wilson, Acta Cryst., 2, 318 (1949). (17) J. A. Ibers, t h d , 9, 652 (1956). (18) C. H. Dauben and D. H. Templeton, Sbzd , 8, 841 (1955).
1202 F. A. COTTON AND J. J. WISE
Inorganic Chemistry
TABLE I FINAL ATOMICP A R A M E T E R S FOR
-
-Atomic coordinatesa--Y/b
X/a
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811 552 360 38' 1129 384
.... . .. -9
6
1
-670
ther cycles of refinement in which scale factors as well as isotropic temperature and positional parameters were varied reduced the weighted residual to 0.156.
7 1010
-5 -5 -5 -5 -5
-1
734
*3
L IO15 6 ,370
-4
1057 1081 I201 768 668 Lll -124 5 f... 1616 -1418 2 i L l -1730 590 -318 3% -51 b22 536 675 163 *7a 201 1325 1266 165 292 787 PI5 2 7 5 1 2751 l W 7 1151
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1841 2138 1910
0 1525 -1321
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3 1122 b ?139 1697 i ab19 2 2 5 5 0 'I -2.0 I 1 2 2 5 1078 2 986 -1090 3 loel 938 L 1876 1666 5 1081 1137 6 1249 1269 7 1273 -1114 1 331 181 2 1114 -1227 5 2 1 3 6 -1928 .I6 -227 5 51* -515
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1.69 i46 .3 I56 -350 1 1935 -1874 2 235 111 3 2381 1925 C 1885 1331 5 545 621 6 696 -656 7 46340 8 71. 669 1 3.73 -+363 2 4 2 P -121 3 997 799 4 PI15 169. 5 932 795 6 327 -21 7 560 -669 8 3 7 6 -154 0 llS5 19*5 i 3522 % l a 2 1711 i * b 9
FCAL
loll 0 2257 -2010 1 1711 -1870 2 793 -&*e 3 621 -66 i 446 826 5 171 46 i 1513 1601 2 6L5 655 3 1190 - 2 6 7
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-851 -73 -509 1 2 7 8 -1171 i i 2 -561 1377 -1L87 *51 701 447 679 ab0 1099 1918 1570 1377 l*ii 1180 1198 1131 , 1 6 2 1131 1291 1303 1506 125c 1211 467 - 1 0 3 467 -699 1352 -1321 2336 - 9 8 0 631 - 6 2 9 a67 -81
0
368 606 1819 -1787 295 -531 1013 123 6 3 9 -I98
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822
TABLE I1 OBSERVEDA N D CALCULATED STRUCTURE FACTORS
-9 -9 -9
2
x
-6
Z/C
0.000 0.000 0,000 39 0.072 (1) 0.071 (1) 137 0,034 (1) 0.131 (1) 0.928 (1) 50 0,054 (1) 12 0.236 (1) 0.994 (1) 0.097 (1) 0.111 (1) 0.261(1) 0.129(1) 66 0.085 (2) 0.077(1) 0.215(2) 96 0.323(1) 1.7 0.131 (1) 0.901 (1) 130 0.095(2) 0.203 (1) 0.361 (1) 201 0.977 (3) 0.196 (3) 0.376 (3) 0.159 (3) 0.320 (2) 0.419 (2) 508 159 0.180 ( 2 ) 0.109 (2) 0.462 ( 2 ) 0 . 173 ( 2 ) 0.446 (1) 0.978(1) 90 0.236 (2) 0.264 (1) 189 0.878 (2) 104 0.019 (2) 0.344 (1 ) 0.767 (2) a ATumbers in parentheses are the standard deviations which occur in the last ably somewhat low as explained in the text.
I....
UNIT
2 1915 -2113
3 159* -1529
-1 2
21 -2 -2
4
*I8
5
715
6 0
797
700
903
I 211.1 1 685
1171 1695 2292 $67
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to atomic positions were calculated by standard methods. l9 Anisotropic motion was indicated on the difference
Vol. 5, No. 7, July 1966
BIS(2,2,6,6-TETRAMETHYLHEPTANE-3,5-DIONATO) NICKEL (I I)
-
0
I
1203
2
Scale, A
Figure 1.-The Ni(DPM)z molecule projected onto the mean molecular plane. The numbering of the atoms corresponds to that in Tables I , 111, and IV.
map. Further refinement was made in which positional parameters and anisotropic temperature factors were varied. On the first cycle of refinement the weighted residual fell to 0.151. After some unsuccessful attempts to locate hydrogen atoms were abandoned, full-matrix refinement, varying all parameters, though not all on every cycle, was resumed. When the weighted residual had dropped to 0.12, positional parameters had ceased to change significantly and a difference Fourier map showed no anomalies. It was noticed only later that, apparently due to an overflow problem in the computer, standard deviations of the temperature factors were not obtained. It was not deemed worthwhile to resume computations to obtain these. It should be noted that due to the neglect of absorption corrections, the anisotropic temperature factors are not to be taken as having strict physical significance. Undoubtedly, they have compensated for some of the absorption errors. The six carbon atoms of the t-butyl groups presumably do have high temperature parameters due to librational motion, but not so high as those obtained for C(6) and C(7). It should then also be true that the calculated standard deviations are underestimates, by perhaps a factor of 2 . The final coordinates and thermal parameters are reported in Table I. The calculated structure factors
Figure 2.-The Ni(DPM)%molecule projected onto a plane perpendicular to the mean molecular plane. The nearly perfect all atoms but methyl planarity of the molecular skeleton ( k , carbon atoms) is evident.
given by these parameters and the observed values are given in Table 11. Three low-order structure factors were believed to suffer from extinction and were excluded from the final refinement. These are indicated by an asterisk in Table 11. The structure factors in the table are scaled up from the true structure factors in electrons by a factor of 59.4. Discussion Molecular Structure.-The chelate rings and, indeed, the whole molecule were found to be essentially planar. A projection of the molecule onto the mean plane of the chelate ring is shown in Figure 1. The atoms are numbered according to the system used in the tables. Atoms with a prime are related to the unprimed atoms by a center of symmetry a t the nickel atom. Figure 2 shows a projection of the molecule onto a plane perpendicular to the plane of the chelate ring and passing through the Ni and C(2) atoms. In this projection the orientation of the two independent t-butyl groups can be clearly seen. Both t-butyl groups have about the same orientation with respect to the chelate ring. I n each of the two groups one carbon atom, C(7) and C(9), lies close to the plane of the ring. It is interesting t o note that the orientation with respect to the ring of the t-butyl group in Ni(DPM)z is just the reverse ( k , -180" rotation about the threefold axis of the t-butyl group) of that found7 in Zn(DPM)z. I n the case of Zn(DPM)zit is proposed
1204 F.A. COTTON AND J. J. WISE
lnorganic Chernistry
that thc observed orientation is the result of niininiization of interaction between the ring hydrogen atom and the methyl groups. Apparently in Ni(DPM)2 other considerations are dominant. One possible explanation may be minimization of intramolecular repulsions between t-butyl groups attached to opposite chelate rings. If the t-butyl groups were rotated lSO", the shortest distance between the methyl groups would be -3.5 A (ZJS. -5.5 A in the observed orientation) The generally accepted van der Waals radius for a methyl group is 2 A. Barring packing considerations, it would seem likely that the observed orientation of the t-butyl groups is the result of minimization of intramolecular contacts between methyl groups on opposite ligands. h calculation of all intermolecular distances up to 5.5 A was made.2o The list of all nearest intermolecular contacts in Table I11 s h o w that the intermolecular contacts are all on the order of the usual van der IVaals lengths or greater. Some of the methyl group-methyl group contacts, however, are somewhat shorter than the usually accepted value of 4 A, but no significance is attached to this. Further discussion will be restricted to intramolecular parameters. TABLE
111
TADLE IV BONDLESGTHSI S -%SYMMETRIC
UNIT
Length, A
Sickel-Oxygen Si-O( I ) Si-O( 2)
1.836 f 0.O07 1.836 f 0 . 0 0 7 Xv. 1.836 i 0 , 0 0 5
Oxygen to Ring Carbon O( 1)-C(3) 1.299&0.013 0(2)-C( 1) 1.328f0.014 .iv. 1,314 f 0,010
Ring Carbon to Ring Carbon C( 1)-C(2) 1.380f0.017 C(3)-C(2) 1.399 1.0.017 Av. 1.390 f 0.012 Riug to t-Butyl Carbon C(1)-C(4) 1.527dz0.016 C(3)-C( 5) 1.502f0.019 Av. 1.574 f 0.012 &Butyl Carbon-Carbon C( 5)-C( 6) C( 5)-C( 7 ) C( 5)-C( 8) Av. C(4)-C(9) C(4)-C( 10) C(4)-C( 11)
1 . 4 5 5 i 0.025 1.486f0.026 1.524 f 0 . 0 3 4 1.488 f 0.016
1.545zk 0.014 1.486 f 0.022 1.510 10.020 h v . 1,514 =t0.011
SHORTEST I S T E R M O L E C U L A R rJISTBNCES
Distance, A
Nearest neighbors
Si-C(9) O( 1)-C(9) 0(2)-C(9) C(1)-C( 10) C(2)-C(6) C(3)-C( 10) C(4)-ivi C(5)-C(6) C(6)-C(7) C(7)-C(8) C(8)-C(7) C(9)a-O( 2) C( l O ) b - 0 ( 2 ) C( 11)-C(8) a Distance t o nearest methyl C( 10) nearest methyl C( 11) = 4.09 A.
=
3.78 3.90 3.58 3.91 4.05 4.25 4.4F 4.54 3.92 3.65 3.65 3.58 3.73 4.01 3.77 A . * Distance to
From the parameters in Table I, the intramolecular bond lengths and angles were The bond lengths and angles and their averages over chemically equivalent but crystallographically independent bond lengths and angles are listed in Tables I V and V. It was found that all chemically equivalent bonds and angles except for the angles mithin the t-butyl groups were equivalent to within three standard deviations from their mean. While the average of the angles within the t-butyl groups was close to that expected for a tetrahedral array, several angles showed significant deviations from the mean. These deviations are probably the result of packing stresses. The essential planarity of the entire chelate ring 11 a5 (20) D . P. Shoemaker, "Distan-Crystcrllog~-aphic Bond Uistance, Bond Angle, and Dihedral Angle Computer Program," 1Y63. (21) J. S. W o o d , "~lGEOM--Molecular Geometry Program for t h e I B M 709/7090/7094 Computer," 1964.
TABLE V BONDANGLESIS XSYMXXTKIC USIT
Angle, deg
Ring Angles 0-N-O Xi-O( 1)-C(3) Si-O(2)-C( 1)
0(2)-C( 1)-C(2) O( 1 )-C(3)--C(2)
C( l)--C(2)-.C(3)
94.6 f 0 . 4 128.0 f 0.8 126.2 i 0 . 7 =Iv. 1 2 7 . 1 1 . 0 . 5 124.5 f 1 . 3 123.3 f 1 . 3 Xv. 123.9 f 0 . 9 123.1 f 1 . 3
Ring t o &Butyl 9ngles 124.4f1.1 C(B)-C( 3)-C(5) 123.8+ 1 . 2 C(Z)-C( 1)-C(4) Av. 124.1 f 0 . 8 t-Butyl A4ngles C(3)-C( 5)-C( 6) C(3)-C( 5)-C(7) C(3)--C(5)-C(8) C( 7)-C( 5),-C(8) C(6)-C( 5)-C( 8) C( 6)-C( 5)-C( 7 ) Xv. C( 1)-c(4)-c(9) C( l)-C(4)-c( 10) C(l)-C(4)-C( 11) C(9)-C(4)-C( 10) C(9)-C(4)-C( 11) C( lO)-C(4)-C( 11) Av.
+
113.4 1 . 4 114.0 & 1 . 5 109.5+1.1 1 0 2 . 7 11 . 6 106.0f 1.5 110.4 f 1 . 6 109.3 f 0 . 6 109.8 f 0 . 9 104.9 i 1 . 1 109.1 i 0 . 9 111.1 f 0 . 9 109.0 + 0 . 9 112.8 1. 0 . 9 109.4 10 . 4
checked quantitatively by computing the "best plane" using least squares for the OCCCO and the plane of the Ob10 portions of the ring. The dihedral angle between the O X O and mean OCCCO planes was 179.3 f 0.5°. No atom falls more than three stand-
BIs(2,2,6,Ci-TETRAMETHYLHEPTAN~-3,5-DIONATO)NICKEL(II) 1205
Vol. 5,No. 7, July 1966
TABLE VI COMPARISON OP MOLECULAR DIMENSIONS OF CHELATERINGSIN SOME SELECTED DIKET TOE NO LATE COMPLEXES -Angles
7
--Bonds
Compound
M-0
Grim-
in ring, A---
c-0
c-c
OM0
caliph
Ni (DPM)2 Cu(acac)z
1.836 1.92
1.314
...
Four-Coordinate Planar 1.390 1.514 94.6 ... ... 93.5
Zn (DPM)z
1.962
1.274
Zn(acac)*.HzO VO(acac)J
2.02 1.97
MOC
127.1
in ring, deg----------
occ
ccc
123.9
123.1
Dihedral anglea
Ref
179.5 178
22
...
...
Four-Coordinate Tetrahedral 1.405 1.157 94.7
121.8
125.8
127.0
180
12
1.291 1.285
Five-Coordinate 1.395 1.510 88.5 1.397 1.52 87.5
127.1 129.1
124.2 123.7
125.9 123.8
168 168
31 33
2.055 2.015
1.275 1.272
Six-Coordinate Monomeric 1.420 1.48 92.0 1.412 1.510 92.4
123.4 123.5
124.9 125.5
127.9 126.6
164 167
27 35
2.055 2.210 2.021 2.01
1.277
Six-Coordinateb Polymeric 1.469 1.565 ...
...
...
...
168
29
1.245 1.33
1.421 1.55
...
...
... ...
172
28 2
... ...
...
...
...
...
...
...
Eight-Coordinate 2.198 1.270 1.399 1.517 75.0 133.1 123.7 34 Zr (acac)c 127.5 158 a Sngle in degrees between O M 0 plane and mean plane through OCCCO. * Second entry in M-0 column is metal to shared oxygen bond length.
ard deviations out of the “best” plane for the entire ring. It has been observed in all of the structural determinations on metal complexes with @-ketoenolatesthat the OCCCO portion of the ring is planar or almost planar. The O M 0 plane, however, is often canted to the mean plane of the ligand atoms. It has been shown7 that while this tendency is common it is not a necessary condition. I n the structural determination on Zn(DPM)2it was found that the entire chelate ring was required to be rigorously planar on the basis of crystallographic symmetry of the space group. It is apparent from inspection of the dihedral angles listed in Table VI that only in the four-coordinate complexes are the chelate rings planar. All of the more highly coordinated complexes have dihedral angles between -158 and -172”. Specific explanations, based on various kinds of intermolecular interactions, have been proposed in individual cases, but it may be that a more general discussion could be given based upon intramolecular forces. Comparison of Results to Those for Other @-Ketoenolates and Related Metal Complexes.-Metal complexes with (3-ketoenolates have been studied by X-ray diffracti~n~~ previously. ~ * ~ ~ - ~ ~A comparison of the (22) L. Dahi, private communication to T.S. Piper, Mol. Phys., 5, 169 (1962). (23) H. Koyama, Y. Saito, and H. Kuroya, J. Inst. Polylech. Osaka City Uniu., C 4 , 43 (1953); Chem. Abstr., 48, 2097a (1954). (241 E. A. Shugam, Dokl. Akad. Nauk SSSR, 81, 853 (1951); Ckem. Abslr., 46, 3894d (1952). ( 2 5 ) V. M. Padmanabhan, Proc. Indian Acad. Sci., 47, 329 (1958). (26) L. M. Shkol’nikova and E. A. Shugam, Kristallografiya, 5, 32 (1960). (27) G. J. Bullen, Acta Cryst., 18, 703 (1959). (28) F. A. Cotton and R. C. Elder, to be published. (29) F. A. Cotton a n d R. C. Elder, Inorg. Chem., 4, 1145 (1965). (30) V. Amirthalingam, V. M. Padmanabhan, and J. Shankar, Acta Ciysl., 18, 201 (1960). (31) H. Montgomery and E. Lingafelter, ibid., 16, 748 (1963).
results of this work with other three-dimensional work of comparable accuracy is shown in Table VI. Results for the carbon-oxygen, ring carbon-ring carbon, and ring carbon-aliphatic carbon bond lengths are consistent with prior results. As has already been pointed these bond lengths correspond to bond orders of -1.3, -1.5, and -1.0, respectively, due account being taken for shortening on going from sp3 to sp2hybridization. These bond orders are consistent with the assumption of delocalized T bonding in dipivaloylmethanide and acetylacetonato rings. Nickel-Oxygen Bond Lengths.-A point of particular interest is the mean Ni-0 bond length, 1.836 0.005 A, as compared to Ni-0 bond lengths in other Ni(I1) complexes, particularly the closely related [Ni(acac)2]3 and Ni(acac)2(H20)z,in which the distances from Ni to nonbridging oxygen atoms are 2.01 k 0.07 and 2.015 A 0.01 A, respectively. There are a t least three possible explanations for this, no one of which excludes the others. One possibility is that the donor ability or basicity of the oxygen atoms in the DPM ion is much greater than that for the oxygen atoms in acac- because of the greater electron-donating effect of the t-butyl group compared to methyl groups. While this may make some contribution to the observed shortening, we doubt that it can account for more than a small fraction of it. A second effect which might operate in the right direction, but which is also considered likely to be small, is the possibility of metal-oxygen r bonding in the planar molecule by means of the metal pzorbital.
*
(32) E. L. Lippert and bl.R. Truter, ibid., 16, 752 (1963). (33) 11. P. Dodge, D. H. Templeton, and A. Zalkin, J. Chem. Phys., S I , 55 (1961). (34) J . V. Silverton and J. L. Hoard, Inorg. Chem., 2, 243 (1963). (35) H. Montgomery and E. C. Lingafelter, Acta CrysL., 17, 1481 (1904). (36) S. C. Nyburg and J. S. Wood, Inora. Chem., 3. 468 (1964).
AND J . J. ~ ’ I S E 1206 F.A. COTTON
Inorgunic Chemistry
010
001
100
\
d
110
U
Figure 3.--I-’rojections of the Ni(DPM)2molecules o n four crystal plancs.
We believe that the main cause of the short metaloxygen bonds here as compared to those in the molecules containing octahedrally coordinated Ni(I1) is the absence of electrons from the d orbital which is 0 antibonding with respect to the Ni-0 interactions. The octahedrally coordinated complexes contain highspin nickel(I1) and the two d orbitals which are antibonding in respect to the Ni-0 bonds, namely d+,, and d,,, are each occupied by one electron. In the lowspin square complex, however, the d orbital which is antibonding in respect to the Ni-0 bonds, namely d,, in the coordinate system used here, is empty. There are two main reasons for preferring this explana-
tion, or a t least assuming that it represents the predominant effect. First, the shortening effect observed here is very similar to those which occur in other cases where one or both of the first two factors mentioned are not operative. Thus, for example, the Ni-n’ distances in the param a g n e t i c bis(meso-stilbenediamino)diaquonickel(II) complex are 2.05 A, whereas those in the corresponding anhydrous, diamagnetic complex are 1.89 A. The ligand stilbenediamine cannot engage in T bonding. Thus only the third factor, the change in the populatioii of the antibonding du orbital, could apply here. Also,
Vol. 5, No. 7 , July 1966
BIS(~,~,~,~-TETRAMETHYLHEPTANE-~,~-DIONATO) NICKEL (11) 1207
the Ni-0 bond lengths in three planar salicylaldiminato c o m p l e ~ e s ~of~ -Ni(I1) ~ ~ are in the range 1.801.84 A, whereas in bis(salicyla1dehydato)diaquonickel(11)40 the Ni-0 distances are 2.03 A. The only explanation which seems to apply to all cases, in all of which the effects are of similar magnitude, is the one concerned with changes in d orbital population. Second, the magnitude of the shortening effect, 0.15-0.20 A per change of one electron in a d orbital which is antibonding with respect to four ligands, is comparable with the changes in octahedral radii of divalent metal ions of the first transition series as electrons are added to the eg orbitals.*I Thus, R (Mn2+)> R ( V z + )by -0.25 A, where two eR electrons per six ligaiids have been added, but where the concomitant increase in nuclear charge tends to diminish the effect by about 0.05 A. Orientation of Molecules in the Unit Cell.-One important purpose for undertaking this crystal structure determination was to ascertain the orientation of the molecules in the unit cell and to calculate therefrom the relationship of the molecular axes to the various well-developed faces of the crystals. Such data were necessary for the study of the polarized crystal spectra of both the nickel and the isomorphous copper compounds and for the study of the esr spectrum of Cu(DPM)2 using Ni(DPM)2 as host. The spectroscopic investigations will be reported later. Figure 3 shows the projections of the molecules on the 010, 001, 100, and 110 crystal planes. Table VI1 gives orthogonal coordinates for each of tbe two molecules relative to axes defining tw-o of the principal planes, viz., a,b, l a (001) andc, b, IC (100). Theseare particularly useful in making the quantitative calculations required to resolve polarized spectra into polarizations appropriate to the internal molecular Cartesian coordinates. A few particular observations concerning the orientations of the molecules fnay be made. Since the two molecules are related by a twofold screw axis parallel to b, they have identical projections on the 010 plane, (37) L. Merritt, Jr., C. Guare, and A. Lessor, Acla Cryst., 0, 253 (1956). (38) J. Stewart and E. Lingafelter. ihid., l a , 842 (1959). (39) E. Vrasson, C. Panattoni, and L. Sacconi, J . Phys. Chem., 63, 1908 (1959). (40) J. Stewart, E. C. Lingafelter, and J. Breazeale, Acla C y y s t . , 14, 888 (1961). (41) L. E. Orgel, "An Introduction to Transition Metal Chemistry," John Wiley and Sons, Inc.. New York, N. Y., 1960.
TABLE VI1 ORTHOGONAL COORDINATES FOR ALL ATOMS IN ASYMMETRIC UNIT -a, U
b , l a coordinates, Ab a
--c,
c
b , Lc coordinates, A--b c
0.000 -0.306 0.921 1.164 0.773 0.108 1.944 -0.369 -1,814 0.136 0.208 2.113 3.259 1.180
Atoms of Molecule 1 0.000 0.000 0.000 0.785 1.631 1.619 1.434 -0.683 -0.992 -0.513 2.580 -0.058 2.863 1.235 0.829 1.942 2.051 1.841 3.551 -0.941 -1.633 3.311 2.233 3.445 3.590 4.015 2.152 3.514 4.001 3.622 1.301 4.405 3.965 4.902 -0.210 -1.027 2.894 -1.162 -2.355 3.778 -2.224 -2.510
0.000 0.000 0.363 0.785 0.577 1.434 1,046 2.580 1.198 2.863 0.910 1.942 1,414 3.551 1,021 2.233 2.152 -0.249 1.706 3.514 1.931 1.201 1.858 4.902 2.535 2.894 0.206 3,778
5.850 5.544 6.771 7.014 6,623 5.958 7.794 5.481 4.036 5.986 6.058 7.963 9.109 7.030
Atoms of Molecule 2 0.000 -2.309 5.490 4.706 1.631 -0.689 0.301 4.056 -0.683 -2.822 2.910 -0.058 2.627 1.235 -1.480 3.548 2.051 -0,468 1.939 -0.941 -3.942 3.258 3.445 1.002 1.706 3.338 3.590 4.001 1.313 1.976 4.289 4.405 1.656 0.588 -0.209 -3.336 2.596 -1.162 -4.664 1.712 -2.224 -4.819
5.490 5.375 4.705 --5.738 4.056 5.952 6.421 2.910 2.627 6.573 6.285 3.548 6.789 1.939 6,400 3.257 5.125 3.338 7.081 1.976 4.289 7.306 0.588 7.233 2.596 7.909 1.712 5.580
as is apparent in Figure 3. The dihedral angle between the mean planes of the two molecules is 44.9 i: 0.9", while the line passing through Ni and the carbon atoms C(2) and C(2)' (which we shall later identify with the molecular x axis in molecular orbital calculations and the interpretation of spectra) makes an angle of 24.2 i 0.8" with the b axis of the unit cell. This is most clearly shown in the 001 projection (Figure 3). Acknowledgments.-This research was supported by a contract with the United States Atomic Energy Commission. We are grateful to the Socony Mobil Oil Company for generous financial support to John J. Wise and to the M.I.T. Computation Center for use of the IBM 7094 computer.
