4428
Crystal and Molecular Structure of Dibromotris( trimethylphosphine)nickel( 11). Electronic Structures and Stereochemistries of the Complexes [Nix,( PMe3)3] James W. Dawson,l T. J. McLennan,, Ward Robinson,2 Arlette M e ~ l e , ~ Michele Dartig~enave,~ Yves Dartig~enave,~ and Harry B. Gray* Contribution No. 4849 f r o m the Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91109, f r o m the Department of Chemistry, Unicersitj of Cunterbury, Christchurch, New Zealand, and f r o m the Lahoratoire de Chimie MinPrale et Structurule, Institut de Chimie, 67-Strasbourg, France. Receiued March I , 1974 Abstract: The crystal and molecular structure of dibromotris(trimethyIphosphine)nickel(II) has been determined from three-dimensional X-ray data collected by counter methods. Full-matrix least-squares refinement of the structure has led to a final conventional R factor on F of 7.3%. The crys!als have monoclipic symmetry, space group P2&, with eight molecules in a unit cell of dimensions a = 16.519 ( 2 ) A, b = 12.956 (1) A, c = 17.482 (2) A, and /3 = 102.17 ( 2 ) " . The crystallographically derived density is 1.62 (1) g The crystal chemical unit consists of two well-separated monomeric molecules. In each of these five-coordinate molecules the nickel atoms are at the center of cis trigonal bipyramids in approximate C?,site symmetries. One nickel, one phosphorus, and two bromine atoms lie in the equatorial plane with the remaining two phosphorus atoms occupying apical positions, equidistant from the nickel atom. Solid state and solution electronic spectra of [NiXZ(PMe3)3] (X = Cl, Br, I) have been measured at 295 and 77°K. Similarities between these spectra indicate that all three compounds have a G, structure in the solid state and also in solution (at 295°K) provided an excess of PMe3 is present to prevent dissociation to rrun~-[NiX~(PMe~)~]. On cooling solutions of the bromo and iodo compounds containing excess PMe3 to 77"K, the predominant nickel species appears to be the [Ni(PMe3)s]2+cation. The difference in stereochemistry between [NiX2(PMe3)J(X = CI, Br, I) and the corresponding dicyano compound, which has a distorted D3h symmetry, is discussed in terms of the second-order Jahn-Teller effect.
I
nvestigations of diamagnetic five-coordinate nickel complexes [NiXzL3] (X = halogen or C N ; L = phosphine, phosphite, or phosphonite) have shown that the stability and stereochemistry of these compounds depend on a subtle blend of electronic and steric effect^.^ Complexes of trimethylphosphine with nickel halidesjl6 and cyanide's8 are particularly intriguing as five-coordinate structures have been found for X = C1, Br, I, and CN, and yet the geometries of these compounds are not all similar. Spectroscopic and dipole moment studies8 indicate that [Ni(CN),(PMe,),] has a distorted version of the trans trigonal bipyramidal (TBP) isomer 1. From similar experiments with
x
x
et a].,: were able to interpret the electronic spectrum of [NiBrz(PMe3)3]in terms of the TBP structure 1, but the possibility of the ground state having a cis rather than trans configuration of the bromine atoms was not ruled out. In order to obtain more pertinent information about the ground state of the compounds [NiX2(PMe&], we have examined the crystal and molecular structure of [NiBrz(PMe3)3]. Dah16 has previously measured the room temperature solution and solid state spectra of complexes [NiX2(PMe&]; in addition we have determined the low-temperature (77OK) spectra of these complexes to see if their lowest energy ligand field bands have the unusual temperature dependence found for other TBP complexes containing uni- and multidentate ligands.$
Experimental Section 1
2
3
complexes [NiX2(PMe3)3](X = C1, Br, I), however, Dahl concluded that the halogeno derivatives had cis TBP structures, although the isomers 2 and 3 could not be differentiated from electronic spectra.6 Chastain, ( I ) California Institute of Technology. ( 2 ) University of Canterbury. ( 3 ) Institut de Chimie, Strasbourg. (4) E. C. Alyea and D. W. Meek, J . Amer. Chem. Soc., 91, 5761 ( I 969), and references therein. ( 5 ) B. B. Chastain, D. W. Meek, E. Billig, J. E. Hix, Jr., and H. B. Gray, Iiiorg. Chem., 7, 2412 (1968). ( 6 ) 0. Dahl, Acta Chem. Scand., 23, 2342 (1969). (7) I 26' 6 46". A symmetric scan range of 1.20" in 28, centere4 on the calculated peak position (X(Mo K n ) 0.7107 A), was (1 1) T. C. Furnas, Single Crystal Orienter Instruction Manual, General Electric Co., Milwaukee, Wis.
composed of 60 steps of I-sec duration. Stationarycrystal, stationary-counter background counts of 15 sec were measured at each end of the scan range. Reflections for which counts were greater than 10,000 per second were re-collected using nickel foil attenuators to bring them within the linear response range of the scintillation counter. The counter was located with its 5 mm diameter receiving aperture 250 mm from the crystal. During data collection the intensities of three standard reflections, monitored at regular intervals, dropped to 91% of their starting values. These observations were used to place all intensities on the same relative scale.12 Data were corrected for Lorentz and polarization (Lp)13 factors and then for absorption14 (p(Mo K n ) = 59.25 cm-l) using Gaussian integration. Maximum and minimum values of transmission coefficients were 0.2044 and 0.1059, respectively. After averaging reflections recorded more than twice, and also those equivalent by symmetry, the data reduced to 2857 reflections of which 1586 had F2 > 3 4 F 2 ) , where a(F2)is defined below.l5 These were the data used in final refinements of the structure parameters. Solution and Refinement of the Structure Full-matrix least-squares refinements were based on F and the function minimized was Zw(lFol The weights w were taken as 4F0/a2(Fo2)where lFoi and IF,/ are observed and calculated structure amplitudes and dF2) = (c
+ '/4(tc/tb)'(Bl + B?) f pF2)"'
where p is a factor introduced to avoid overweighting strong reflections, in this case = 1.15, c is the scan count, B1 and Bz are the first and second background counts, and tc and f b are scan and background counting times. The atomic scattering factors for Ni, Br, P, and C were taken from a standard tabulation.'' The effects of anomalous dispersion for nickel, bromine, and phosphorus were included in FCl8using Cromer's l9 (12) Calculations were performed at the University of Canterbury using an IBM 360/44 computer with 32K words of core storage and twin disk drives. (13) The data processing program HILGOUT is based on programs DRED (J. F. Blount) and PICKOUT (R. J. Doedens). (14) Numerical absorption corrections were applied using program DABS which is a modified version of DATAPH (C. P. Coppens). Mathematical methods are fully described in "Crystallographic Computing," Munksgaard, Copenhagen, 1970. (15) P. W. R. Corfield, R. J. Doedens, and J. A . Ibers, Inorg. Chem., 6, 197 (1967). ( I 6) Structure factor calculations and least-squares refinements were carried out using program CWCLS and Fourier summations using program FOURIER. These are highly modified versions of well-known programs ORFLS (W. R. Busing, K. 0. Martin, and H. A. Levy) and FORDAP (A. Zalkin), respectively. (17) "International Tables for X-Ray Crystallography," Vol. 3, Kynoch Press, Birmingham, England, 1962. (18) J. A. Ibers and W. C. Hamilton, Acta Crystallogr., 17, 781 (1964). (19) D. J. Cromer, Acta Crystallogr., 18, 17 (1965).
Gray, et al. 1 Molecular Structure of Dibromotris(triinethylphosphine)nickel(II)
4430 Table 11. Final Positional and Thermal Parameters for [NiBr,(PMe3)#
X
Atom
0.1353 (2) 0.1196 (2) 0.2209 (2) 0.0626 ( 5 ) 0.2508 ( 5 ) 0.0347 (4) 0.6581 (2) 0.5029 (2) 0.7415 (2) 0.6865 ( 5 ) 0.6438 (4) 0.6628 ( 5 ) 0.593 (2) 0.754 (2) 0.735 (2) 0.573 (2) 0.736 (2) 0.599 (2) 0.766 (2) 0.621 (2) 0.603 (2) 0.002 (2) -0.016 (2) 0.117 (2) 0.242 (2) 0.311 (2) 0.324 (2) 0.008 (2) 0.060 (2) -0.066 (2)
values for Af’ and Af’ as
‘.
Y 0.2449 (2) 0.4361 (2) 0.2058 (2) 0.1464 (6) 0.2421 (6) 0.2735 ( 5 ) 0.2391 (2) 0.2465 (2) 0.2057 (2) 0.2665 (6) 0.0705 (5) 0.4039 (6) 0.292 (3) 0.126 (2) 0.160 (2) 0.020 (2) -0.004 (2) 0.011 (2) 0.460 (2) 0.427 (2) 0.494 (2) 0.228 (2) 0.063 (3) 0.051 (2) 0.274 (2) 0.125 (2) 0.340 (2) 0.165 (2) 0.374 (2) 0.321 (2)
Z
R
0.4068 (2) 0.3654 (2) 0.5342 (2) 0.3145 ( 5 ) 0.3622 (4) 0.4694 (4) 0.8632 (2) 0.8051 (2) 0.7652 (2) 0.9899 (5) 0.8716 (4) 0.8312 (5) 1 ,028 (2) 0.533 (2) 1.058 (2) 0.932 (2) 0.902 (2) 0.774 (2) 0.842 (2) 0.726 (2) 0.880 (2) 0.235 (2) 0.340 (2) 0.264 (2) 0.257 (2) 0.381 (2) 0.410 (2) 0.530 (2) 0.541 (2) 0.416 (2)
3.12(7) 4 . 4 (2) 3.8 (2) 3 . 6 (2) 3.10 (7) 4 . 4 (2) 3 . 6 (2) 4 . 6 (2) 8.0(9) 5 . 9 (8) 5 . 2 (7) 4.7 (6) 4 . 6 (7) 5.0(7) 5 . 8 (8) 5 . 9 (8) 5 . 7 (7) 5 . 5 (7) 7 . 1 (9) 5 . 8 (8) 5.7 (7) 4 . 7 (7) 3 . 5 (6) 5 . 1 (7) 4 . 1 (6) 5 . 2 (7)
822
P3s
PI2
PI:$
P23
0.0047 (2) 0.0085 (3) 0.0085 (3) 0.0087 (3)
0.0039 (1) 0.0024 (1) 0.0056 (2) 0.0029 (1)
0.0003 (1) 0.0011 (2) 0.0007 (2) 0.0007 (2)
-0.0001 (1) -0.0008 (1) -0.0003 (1) 0.0004 (1)
0.0016 (1) 0.0008 (1) 0.0012 (2) 0.0007 (1)
Agreement factors are defined
The data were used to obtain a set of normalized structure factors20,21(E’s). The 398 largest E’s were chosen for sign determination by the symbolic addition procedure.22 A unique consistent set of signs was obtained for 388 reflections. The resultant E map clearly revealed the positions of the four bromine and two nickel atoms. Refinement of these coordinates with isotropic temperature factors gave values for R1 and Rz of 0.319 and 0.448. From this point three difference Fourier syntheses with intermediate least-squares refinements enabled the development of a model including all 30 non-hydrogen atoms of the structure. Using isotropic temperature factors, refinement of this model gave R1 = 0.113 and Rz = 0,136. At this stage examination of electron density maps and the isotropic temperature factors suggested that the bromine atoms might be better described by anisotropic temperature factors. Refinement of this model ultimately converged (20) H. Hauptmann and I. Karle, “Solution of the Phase Problem. I The Centrosymmetric Crystal,” American Crystallographic Association Monograph, No. 3, Pittsburgh, Pa., 1953. (21) SHNORM is a program derived from NRC-4 (S. R. Hall and F.R.
Ahmed) to calculate normalized structure factors. (22) Symbolic addition was carried out using SAP, a program emanating from N R C - 4 (S. R. Hall and F. R. Ahmed).
Journal of the American Chemical Society / 96:14
with R1 = 0.074 and R2 = 0.095. However, the strong low angle reflections showed some evidence of secondary extinction and so an isotropic extinction parameter was refined until convergence was achieved with R1 = 0.073 and Rz = 0.094. Shifts in the last cycle of refinement were all less than ljl0Oth of their estimated standard deviations. The relative weighting scheme appeared satisfactory in that the average values of the minimized function appear to be independent of lFol. The error in an observation of unit weight is 1.377. Structure factor calculations for the 1271 reflections having Fo2 > 30(FO2)show only one reflection for which IFo* - FC21> 3a(FO2). The top peaks of a final difference Fourier suggested that the thermal motions of the nickel atoms might be better described by anisotropic temperature factors, but it was not considered that such expensive refinements would reveal any further points of significant chemical interest. None of the remaining peaks exceeded 25 % of the value at which the last carbon atom was located. Hydrogen atom positions were not established nor were their contributions included in any structure factor calculations. The positional and vibrational parameters obtained from the final cycle of the least-squares refinement are listed in Table 11. Derived root-mean-square amplitudes of vibration for the anisotropic atoms are listed in Table 111, and Table IV contains final values of lFol and lFcj for the 1586 reflections used in the refinement. (See paragraph at end of paper regarding supplementary material.)
July 10, 1974
443 1 Table 111. Root-Mean-Square Amplitudes of Vibration
(A)
Atom
Min
Intermed
Max
Br( 11) Br( 12) Br(21) Br(22)
0.181 ( 5 ) 0.155 (5) 0.191 (4) 0.198 (4)
0.242 (4) 0.268 (4) 0.266 (4) 0.235 (4)
0.303 (4) 0.290 (4) 0.312 (4) 0.271 (4)
Description of the Structure The crystal structure consists of well-separated molecules of [NiBr2(PMe3)3]. There are two independent molecules in the crystal chemical unit. The closest nonbonded intermolecular distance between non-hydrogen atoms (C(27). . .C(12)) is 3.62 A. Since bromine atoms are not involved, this eliminates the remote possibility of weak hydrogen bonding between the molecules. Perspective views of the independent molecules are shown in Figure l(a) and (b) which define the atom numbering scheme used throughout the text. Bond lengths are 2hown and their standard deviations 5ange from 0.004 A for the Ni(1)-Br(l2) bond to 0.04 A for the P(21)-C(21) bond, Selected bond angles are given in Table V. Each nickel atom has a distorted trigonal Table V.
Bond Angles (deg) for [NiBr2(PMea),]
Angles around Ni(1) 96.3 (3) P(ll)-Ni(l)-P(l2) 96.3 (3) P(ll)-Ni(l)-P(l3) 110.1 (2) P(l1)-Ni(1)-Br(l1) 132.3 (3) P(ll)-Ni(l)-Br(l2) 167.3 (3) P(l2)-Ni(l)-P(l3) 87.7 (2) P(l2)-Ni(l)-Br(ll) 86.6 (2) P(l2)-Ni(l)-Br(l2) 86.3 (2) P(l3)-Ni(l)-Br(ll) 8 6 . 3 (2) P(l3)-Ni(l)-Br(l2) 117.6 (2) Br(ll)-Ni(l)-Br(l2) Angles around F(11) 103 (1) C(l1)-P(l1)-C(l2) 105 (1) C(l1)-P(l1)-C(l3) 110 (1) C(l1)-P(l1)-Ni(1) C(12)-P(ll)-C(l3) 99 (1) 118 (1) C(l2)-P(ll)-Ni(l) 120 (1) C(l3)-P(ll)-Ni(l) Angles around P(12) 106 (1) C(14)-P(12)-C(15) 102 (1) C(14)-P(12)-C(16) 117 (1) C(l4)-P(l2)-Ni(l) 103 (1) C(15)-P(12)-C(16) 116 (1) C(l5)-P(l2)-Ni(l) 111 (1) C(l6)-P(l2)-Ni(l) Angles around P(13) C(17)-P(13)-C(18) 101 (1) C(17)-P(13)-C(19) 104 (1) C(l7)-P(l3)-Ni(l) 117 (1) 99 (1) C(18)-P(13)-C(19) C(l8)-P(l3)-NI(l) 113 (1) 120 (1) C(l9)-P(l3)-Ni(l)
Angles around Ni(2) P(21)-Ni(2)-P(22) 95.5 (3) P(21)-Ni(2)-P(23) 9 5 . 0 (3) P(21)-Ni(2)-Br(21) 112.2 (3) 134.5 (3) P(21)-Ni(2)-Br(22) P(22)-Ni(2)-P(23) 169.3 (3) P(22)-Ni(2)-Br(21) 87.2 (2) P(22)-Ni(2)-Br(22) 87.5 (2) P(23)-Ni(2)-Br(21) 87.1 (2) P(23)-Ni(2)-Br(22) 86.5 ( 2 ) Br(21)-Ni(2)-Br(22) 113.2 (2) Angles around P(21) C(21)-P(21)-C(22) 101 (1) C(31)-P(21)-C(23) 100 (1) C(21)-P(21)-Ni(2) 112 (1) C(22)-P(21)-C(23) 99 (1) C(22)-P(21)-Ni(2) 121 (1) 119 (1) C(23)-P(21)- Ni(2) Angles around P(22) 104 (1) C(24)-P(22)-C(25) 101 (1) C(24)-P(22)-C(26) 119 (1) C(24)-P(22)-Ni(2) C(25)-P(22)-C(26) 101 (1) 117 (1) C(25)-P(22)-Ni(2) C(26)-P(22)-Ni(2) 112 (1) Angles around P(23) C(27)-P(23)-C(28) 100 (1) C(27)-P(23)-C(29) 106 (1) C(27)-P(23)-Ni(2) 116 (1) C(28)-P(23)-C(29) 103 (I) C(28)-P(23)-Ni(2) 113 (1) C(29)-P(23)-Ni(2) 116 (1)
bipyramidal coordination environment with cis bromine atoms in the equatorial plane. Thus the nickel sites have approximate C2? symmetry and not D 3 h as had been considered more likely. There are, however, statistically significant deviations from this implied idealized molecular shape and, furthermore, these are observed in each of two independent molecules. The range of Ni-P bond lengths (2.19-2.21 A) is smaller than those found in other five-coordinate comGray, et al.
Figure 1. Perspective drawings of the two independent molecules of [NiBr2(PMe,),].
plexes, such as 2.13-2.22 in [Ni12(PHPh2)3],23 2.22 in [N~(CGCP~~)(PE~& 2; ]19-2.29 ,~~ in [Ni(CN),( PPh(OEt)2]3],25and 2.22-2.26 A in [Ni(CN),(PPhMe?)a]. 2 G It is apparent from the diagrams, and from Table V, that the nickel atoms do not lie on a straight line joining the apical phosphorus atoms. This is certainly due to the apical groups experiencing greater repulsion from the nonbonded equatorial PMe3 groups than from the equatorial bromine ligands. Deviations from ideal trigonal equatorial plane geometry are difficult to explain without detailed knowledge of hydrogen atom positions. Shortest nonbonded (23) J. A. Bertrand and D. L. Plymale, Inorg. Chem., 5, 879 (1966). (24) W. A. Spoffard, 111, P. P. Carfagna, and E . L. Amma, I m r g . Chem., 6, 1553 (1967). ( 2 5 ) J. I
