58 Inorganic Chemistry, Vol. 15, No. 1, 1976
Stephen Z. Goldberg and Richard Eisenberg Contribution from the Department of Chemistry, University of Rochester, Rochester, New York 14627
Crystal and Molecular Structure of (Methyl isocyanide)bis [ 1,2-bis(diphenylphosphino)ethane]iridium(I) Perchlorate, [Ir (CNMe) (diphos)21 (C104) STEPHEN Z . GOLDBERG and RICHARD EISENBERG*
Received July 23, 1975
AIC50533A The crystal and molecular structure of the title compound has been determined frpm three-dimensional X-ray data collected by counter methods. The compound crystallizes in the triclinic space group P1 with two molecules in the unit cell. Cell dimensions are a = 13.004 (7) A, b = 17.224 (11) A, c = 12.127 (7) A, a = 106.57 (S)', 6 = 109.71 ( S ) ' , y = 79.71 (4)', V = 2440.6 (27) A3. The observed and calculated densities are 1.542 (7) and 1.537 g/cm3, respectively. Refinement on F for 6313 reflections with F o >~ 3U(Fo2) converged to conventional and weighted R factors of 0.0460 and 0.0531. The cation has a trigonal bipyramidal geometry with the isocyanide ligand in an equatorial site and each chelate bridging one axial and one equatorial position. The mean Ir-P distance is 2.328 (9) A. The isocyanide is coordinated in a linear fashion and the Ir-C bond length is 1.945 (8) A. Both five-membered chelate rings exhibit similar conformations which are of an unsymmetrical type. The details of the coordination geometry are compared with those of a number of other [ML(diphos)2]+ systems and discussed with regard to nonbonded interactions and electronic effects. The stereochemical nonrigidity of the molecule is also considered
Introduction Isocyanide complexes of the platinum group elements have been the focus of recent research activities because of the interesting chemistry which these systems exhibit, both at the metal center and the carbon donor atom of the isocyanide ligand. In 1972, Bedford and Rouschiasl reported that methyl isocyanide reacts with IrCl(CO)(PPh3)2 to yield the blue-black complex [Ir(CNMe)4]X (X = C1) which in turn undergoes photosubstitution with 1,2-bis(diphenylphosphino)ethane, diphos, to produce a stable, yellow five-coordinate cationic species of formula [Ir(CNMe)(diphos)2]+. The 1H N M R spectrum of this latter species, which was isolated as its c104salt, shows a quintet for the methyl resonance because of coupling with four equivalent phosphorus donor atoms (~JP-H = 1.6 Hz). This observation aroused our interest since it meant that the complex either adopted a square pyramidal structure with an apical methyl isocyanide ligand or was stereochemically nonrigid. The latter explanation seemed more plausible in view of the reported structure of [Ir(CO)(diphos)z]+,2and the structure of [Ru(NO)(diphos)2]+ which was then being completed in our laboratory.3 Both of these systems showed a trigonal bipyramidal coordination geometry with diphos ligands spanning axial and equatorial positions and the monodentate ligand occupying the remaining equatorial site. Based on bonding considerations in nitrosyl chemistry,3-6 it was thought that [Ru(NO)(diphos)2]+ should be stereochemically nonrigid, a proposal confirmed by Caulton,7 and that nitrosyl bending should help lower the energy of the square pyramidal transition state proposed for the rearrangement process in this system. However, since methyl isocyanide exhibits no tendency toward bent coordination, stabilization of an analogous square pyramidal transition state through apical ligand bending should not occur in the isoelectronic system [Ir(CNMe)(diphos)2]+. In order to unequivocally establish the molecular structure of [Ir(CNMe)(diphos)2]+ and to possibly shed light on the dynamics of bis chelated five-coordinate complexes, a single crystal structure determination of this complex as its perchlorate salt has been performed. Collection and Reduction of the X-Ray Data Single crystals of [Ir(CNMe)(diphos)z]CI04 were provided by Dr. George Rouschias. Zero and upper level precession photographs revealed that the Laue symmetry was 1. Reflections with h + k , k I , and h I = 2n + 1 were systematically absent, thus indicating that a face-centered cell had been chosen. A cell reduction was carried
+
+
outs to obtain the primitive reduced cell. The cell reduction confirmed the triclinic symmetry of the lattice. All further work was performed in the primitive reduced cell. The crystal was transferred to the diffractometer for the precise determination of lattice constants and data collection. The original mounting was such that b* was nearly parallel to the diffractometer 4 axis but prior to further examination the goniometer head arcs were adjusted to reduce the danger of collisions. In the final orientation the b* axis was offset from 4 by about 7.5'. Precise cell constants at 22'C were determined from a least-squares refinement9 of the setting angles of 12 well-resolved reflections (sin O/X > 0.34) which were carefully centered (using MoKai radiation, X = 0.709261 A) on a Picker FACS-I diffractometer equipped with a graphite monochomator. The lattice constants are a = 13.004 (7) A, b = 17.224 (11) A, c = 12.127 (7) A, 01 = 106.57 (5)O, 0 = 109.71 (5)', y = 79.71 (4)', V = 2440.6 (27) A3. The experimental density of 1.542 (7) g/cm3 as determined by flotation in CC14-petroleum ether is in excellent agreement with a value of 1.537 g/cm3 calculated for two molecules of [Ir(CNMe)(diphos)2]ClO4 per unit cell. The quality of the crystal was checked by means of narrow source, open counter w scans.I0 The full widths at half-maximum for typical strong reflections were in the range 0.05-0.0S0. Intensities were measured by the 8-20 scan technique. The takeoff angle for the X-ray tube was set at 1.5' so that the intensities of typical strong reflections were roughly 80% of their maximum value as a function of takeoff angle. Data were collected dt a scan rate of 2'/min with scans being made from 0.75' below the Kai peak to 0.75' above the Kaz peak. Background counts of 4 :iec were made at each end of the scan. Attenuator foils were automatically inserted when the intensity of the diffracted beam reached 10,000 counts/sec. The pulse height analyzer was set for a 90% window centered on Mo KCXradiation. Data were collected for the hemisphere with I 2 0 for 3 5 20 5 50'. Three standards were monitored after every 60 observations. The standards showed no change in intensities during data collection. A total of 9190 reflections were measured. The values of I and G(I) were obtained using the expressions previously described.11 The value of p used in the expression for the variance was chosen as 0.05. Values by application of of I and &(I) were converted to F2 and &(P) Lorentz and polarization corrections.8 Since the absorption coefficient for Mo K E radiation is 31.35 cm-1, an absorption correction was made. The crystal faces were indexed by a comparison of diffractometer setting angles with optical goniometric measurements. Crystal dimensions were carefully measured with a Zeiss travelling hairline eyepiece.12 The absorption correction was made analytically using the method of De Meulenaer and Tompa.s.13 Transmission coefficients ranged from 0.265 to 0.766 with the me.n being 0.644. On the assumption that the correct space group was PI equivalent reflections (those with I = 0) were averaged. The R factor for averaging was 2.4%. The final data set consisted of 8667 independent reflections of which only the 631 3 with F o >~ 30(Fo2)
Inorganic Chemistry, Vol. 15, No. I, 1976 59
[Ir( CNMe) (diphos)2] ((2104) Table I. Positional and Thermal Parameters for [Ir(CNMe)(diphos), ](ClO,) ~~
~
Atom X Y z O1lU 021 033 012 613 023 5.14 (12) Ir 0.229319 (25)b 0.254595 (19) 0.067264 (30) 34.34 (21) 18.52 (12) 41.44 (27) -1.48 (10) 11.64 (17) 8.33 (20)c 0.3182 (6) 0.4721 (8) Cl(1) 0.7168 (7) 0.5320 (8) 8.99 (23) 0.3457 (5) Cl(2) 0.7731 (7) 6.6 (10) -2.8 (8) 10.5 (13) 23.4 (8) 46.0 (18) 0.16166 (18) 37.3 (14) 0.16127 (12) P(l) 0.21122 (16) 6.6 (10) 18.3 (14) 52.7 (19) -0.7 (8) 22.2 (8) 43.2 (15) 0.14143 (12) -0.04553 (19) P(2) 0.30706 (16) 8.4 (11) 18.3 (15) 57.5 (20) -4.3 (9) 54.8 (17) 22.2 (8) 0.35332 (13) -0.01643 (20) P(3) 0.25568 (18) 17.2 (11) 2.3 (9) 14.7 (14) 28.5 (9) 66.9 (21) 41.2 (15) 0.29764 (13) -0.00405 (20) P(4) 0.04261 (17) C(1) 0.2879 (7) 0.3270 (5) 0.2248 (8) 65 (7) 24 (3) 59 (8) -5 (4) 20 (6) 8 (4) C(2) 0.3816 (12) 0.4228 (8) 0.4318 (10) 190 (16) 65 (7) 63 (10) -60 (8) 6 (10) -22 (7) 18 (5) 7 (4) 0.0584 (5) 0.0655 (7) 49 (6) 51 (7) -4 (3) 24 (3) C(3) 0.2253 (6) 0.0554 (5) 28 (6) 10 (4) 4 (31 0.0245 (7) 55 (6) C(4) 0.3247 (6) 23 (3) 69 (8) 17 (5) 0.4235 (5) 6 (4) 27 (7) -0.0337 (8) 70 (7) 25 (3) 86 (9) C(5) 0.1301 (7) 32 (5) 36 (4) 0.3767 (5) 100 (10) 10 (4) 28 (7) -0.0843 (8) 50 (6) C(6) 0.0300 (7) 67 (8) 22 (6) 0 (4) 0.3698 (5) 0.3201 (7) -18 (4) N 0.3211 (7) 104 (8) 34 (3) a The form of the anisotropic thermal ellipsoid is exp[-(h2/3,, + k2p,, + 12f13, + 2hkp12 + 2hlpI3 + 2klp2,)]. Anisotropic thermal parameters have been multiplied by lo4. In this and subsequent tables the estimated standard deviations of the least signifkant figures are given The disordered C1 atom was refined isotropically with 50% occupancy at each of two sites. The parameter given isB in the in parentheses. expression exp[-B(sin 1. Table 11. Group Parameters“ for [Ir(CNMe)(diphos), ](C104) Group XC yc ZC 6 e P 2.742 (3) 0.699 (4) 0.4012 (3) -0.7 36 (4) 0.4022 (3) 0.1303 (2) PH(1 l)b 2.488 (3) 0.893 (4) 0.2501 (3) 2.754 (4) 0.001 3 (3) 0.1717 (2) PH(12) 1.861 (3) 1.107 (12) -0.0423 (3) 2.302 (12) 0.5564 (3) 0.1467 (2) PH(21) -3.003 (4) -2.085 (4) -0.3278 (4) 0.554 (4) 0.1802 (3) 0.0677 (3) PH(22) 2.990 (3) -1.450 (4) -0.2753 (4) 1.256 (4) 0.2985 (3) 0.3098 (2) PH(31) 2.808 (4) 0.334 (5) 0.1372 (4) 0.592 (4) 0.4471 (4) 0.4722 (3) PH(32) 2.932 (4) 1.121 (4) 0.2013 (4) 2.212 (4) -0.0715 (4) 0.3963 (3) PH(41) 3.159 (4) -0.568 (4) -2.460 (4) 0.1796 (3) -0.2042 (4) PH(42) -0.1363 (3) 3.390 (16) -1.049 (13) 2.586 (14) 0.3182 0.4721 0.7168d GP(l)C 1.513 (14) 1.322 (14) 2.676 (12) 0.5320 0.3457 GP(2) 0.7731 a X,, Y,, and Z, are the coordinates of the group centers. The angles @, 0 , and p are in radians and have been previously defined (see R. The first digit indicates the P atom to which the phenylgroup is bound. GP(1) Eisenberg and J. A. Ibers,Znorg. Chem., 4,773 (1965)). Positional parameters for the oxygen tetrahedra were and GP(2) are the tetrahedra of oxygen atoms associated with Cl(1) and Cl(2). constrained to be those of the C1 with which they are associated. were used in the refinement of the structure.
Solution and Refinement of the Structure The structure was solved and refined using standard Patterson, Fourier, and least-squares methods.8 In all least-squares refinements the quantity minimized was C w ( l F ~ l -I F c ~where ) ~ the weights, w, were taken as (l/u(Fo))2= 4F02/4(F02). The atomic scattering factors for neutral Ir, C1, P, 0, N, and C were taken from the tabulation of Cromer and Mann.14 Corrections for anomolous dispersion of Ir, C1, and P were made using the Af’ and Af” values of Cromer and Lieberman.15 The hydrogen scattering factor was that of Stewart et a1.16 The ttree-dimensional Patterson map could be interpreted in space group P1 and the successful refinement confirms this choice. The positions of the Ir atom and the four phosphorus atoms were deduced from the Patterson map, and a difference Fourier map phased by the five-atom model revealed the remaining nonhydrogen atoms of the cation. A model was adopted in which the phenyl rings were treated as rigid groups (D6h symmetry, C-C = 1.392 A). Each group atom was refined isotropically and the nongroup atoms were refined with anisotropic thermal parameters. This model of the cation refined to convergence with R I = 0.098 and R2 = 0.147.17 The major feature of a difference Fourier computed a t this point was the presence of two strong (equally intense) peaks surrounded by a number of weaker peaks. The two intense peaks were interpreted as resulting from partial CI atoms of a disordered perchlorate. The model developed for the disordered perchlorate involved refinement of two CI sites, each with 50% occupancy. Associated with each CI site was a tetrahedron of oxygen atoms (each oxygen with 50% occupancy). The center of the tetrahedra were constrained to be at the CI sites, and the C1-0 distance was set a t 1.45 A. Inclusion of the Clod-, as just described, in the model yielded RI = 0.077 and R2 = 0.096. Prior to this point refinement had been carried out with data that had not been corrected for absorption. The use of the corrected data lowered Ri and R2 to 0.051 and 0.062, respectively. idealized positions were now calculated for the phenyl and methylene protons (C-H = 1.00 A, trigonal or tetrahedral geometry as appropriate at C), but
the methyl groups of the isocyanide ligand were omitted from consideration. The thermal parameters for hydrogen atoms were chosen to be 1 A2 larger than those of the carbon atom to which the hydrogen is bound. Two additional cycles of refinement yielded R I = 0.0460 and R2 = 0.0531. On the final cycle of refinement no parameter associated with the cation shifted by more than half of its estimated standard deviation. Despite the low final R factors the model for the disordered C l O r group is inadequate as judged by the large thermal parameters of some of the oxygen atoms, as well as a tendency for the orientational parameters to oscillate during the final cycles of refinement. A more extended treatment of the anion disorder was not attempted since the structural parameters of the cation were insensitive to inclusion of the anion in the model. A final difference Fourier map showed no peaks larger than 1.4 e-/& or 20% of the height of a typical carbon atom in this structure. The major peaks in the final difference map were all in the vicinity of the perchlorate. The estimated standard deviation of an observation of unit weight17 was 1.32 e- for 6313 reflections and 227 variables. The quantity Cw(lFol - I F C ~showed )~ no trends as a function of either IF01 or sin O/A. A listing of the observed and calculated structure factors for those reflections used in the refinement is available.l* The positional and thermal parameters obtained from the final cycle of least-squares refinement are given in Tables I and 11. The derived positional parameters for the atoms of the rigid groups are given in Table 111, along with the isotropic thermal parameters of these atoms. A table of the parameters used in calculating the hydrogen contributions to the calculated structure factors, Fc,is available.18
Description of the Structure The crystal structure consists of discrete [Ir(CNMe)(diphos)2]+ cations and disordered perchlorate anions. The cation is illustrated in Figures 1 and 2, and the unit cell is shown in Figure 3. The geometry of the cation is that of a somewhat distorted trigonal bipyramid. Each diphos ligand bridges an axial and equatorial coordination site with the isocyanide ligand occupying the remaining equatorial position. Tables I11 and IV
60 Inorganic Chemistry, Vol. 15, No. 1, 1976
Stephen Z . Goldberg and Richard Eisenberg
Table 111. Derived Positional Parameters for Group Atoms Atom
Y
X
PH(11) C(111) 0.1484 (3) 0.3182 (4) 0.2990 (3) 0.1038 (3) C(112) 0.3830 (5) C(113) 0.0858 (3) C(114) 0.4861 (4) 0.1123 (4) C(115) 0.5053 (3) 0.1569 (4) C(116) 0.4214 (4) 0.1749 (3) PH(12) C(121) 0.0881 (4) 0.1672 (3) C(122) 0.0744 (4) 0.2315 (3) 0.2360 (3) C(123) -0.0124 (5) C(124) -0.0854 (4) 0.1761 (4) C(125) -0.0717 (4) 0.1118 (3) C(126) 0.0150 (4) 0.1073 (3) PH(21) 0.4495 (3) 0.1408 (3) C(211) C(212) 0.4819 (4) 0.1118 (3) C(213) 0.5889 (5) 0.1177 (4) C(214) 0.6634 (3) 0.1526 (4) C(215) 0.6310 (4) 0.1815 (4) 0.5240 (4) 0.1756 (3) C(216) PH(22) 0.2351 (4) 0.0974 (3) C(221) 0.2592 (5) 0.0173 (3) C(222) 0.2042 (6) -0.0124 (3) C(223) 0.1252 (5) 0.0381 (4) C(224) 0.1011 (5) 0.1182 (4) C(225) 0.1561 (5) 0.1479 (3) C(226) GP(1) 0.6531 (14) 0.3084 (14) O(11) 0.7954 (12) 0.3771 (9) O(12) 0.7746 (14) 0.2407 (7) O(13) 0.6447 (13) 0.3465 (10) 0(14)
B, R 2
Z
0.3022 0.3715 0.4705 0.5002 0.4308 0.3318
(4) (5) (5) (4) (5) (5)
2.68 (14) 3.52 (17) 3.97 (18) 4.48 (20) 4.49 (20) 3.19 (16)
0.2050 (5) 0.3005 (5) 0.3456 (4) 0.2952 (5) 0.1997 (5) 0.1546 (4)
2.39 (14) 3.63 (17) 4.00 (18) 4.66 (21) 4.75 (21) 3.78 (18)
-0.0475 -0.1513 -0.1462 -0.0372 0.0666 0.0615
(5) (4) (4) (5) (4) (4)
2.72 (15) 3.77 (18) 4.25 (19) 4.36 (20) 4.42 (20) 3.56 (17)
-0.2062 -0.2641 -0.3858 -0.4495 -0.3916 -0.2699
(4) (5) (5) (4) (5) (5)
3.10 (16) 4.28 (20) 5.73 (25) 5.72 (24) 5.55 (24) 4.09 (19)
0.3459 0.5044 0.4916 0.5464
(5)
(21) (19) (15)
24.8 (19) 25.3 (13) 13.0 (8) 10.1 (6)
Y
X
PH(31) C(311) C(312) C(313) C(314) C(315) C(316) PH(32) C(321) C(322) C(323) C(324) C(325) C(326) PH(41) C(411) C(412) C(413) C(414) C(415) C(416) PH(42) C(421) C(422) C(423) C(424) C(425) C(426) GP(2) O(21) O(22) O(23) OW)
B, A'
2
0.2779 (4) 0.3811 (4) 0.4017 (4) 0.3190 (5) 0.2158 (4) 0.1953 (3)
0.3293 (4) 0.2949 (4) 0.2755 (4) 0.2903 (4) 0.3247 (4) 0.3441 (4)
-0.1647 -0.1733 -0.2839 -0.3860 -0.3774 -0.2667
(4) (4) (5) (4) (4) (5)
3.17 (16) 3.68 (17) 4.62 (21) 4.95 (22) 5.21 (22) 4.42 (20)
0.3644 (4) 0.4579 (5) 0.5406 (4) 0.5298 (5) 0.4364 (6) 0.3536 (5)
0.4206 (3) 0.3948 (3) 0.4464 (4) 0.5238 (4) 0.5496 (3) 0.4980 (4)
0.0725 0.1562 0.2209 0.2020 0.1183 0.0535
(5) (6) (5) (6) (7) (6)
3.28 4.00 4.89 6.05 7.33 5.45
-0.0247 (5) 0.0294 (4) -0.0174 (6) -0.1184 (6) -0.1725 (5) -0.1256 (5)
0.3529 (4) 0.4146 (4) 0.4581 (4) 0.4398 (4) 0.3781 (5) 0.3346 (4)
0.1115 (5) 0.2038 (6) 0.2937 (5) 0.2912 (6) 0.1988 (7) 0.1090 (6)
-0.0622 -0.1615 -0.2356 -0.2103 -0.1110 -0.0369
0.2310 (3) 0.2635 (3) 0.2121 (4) 0.1282 (4) 0.0957 (2) 0.1471 (3)
0.7231 0.8868 0.7675 0.7149
(4) (5)
(4) (5) (5) (4)
(14) 0.3855 (9) 0.3190 (11) (4) (13) 0.4024 (8) (14) 0.2760 (7)
-0.1150 -0.1822 -0.2714 -0.2934 -0.2262 -0.1370
(16) (19) (21) (26) (31) (23)
3.64 (17) 4.71 (21) 6.29 (27) 6.97 (30) 6.89 (29) 5.37 (23)
(5) (6) (6) (5) (6) (5)
3.30 (16) 5.04 (22) 5.22 (23) 5.14 (22) 4.95 (22) 3.75 (17)
0.6266 (11) 0.5858 (14) 0.4614 (14) 0.4543 (14)
13.8 (7) 12.4 (7) 10.6 (5) 26.0 (22)
Table IV. Bond Distances for [Ir(CNMe)(diphos),](ClO,)
C (31
c PI1
Atom
Atoms P Ill
IrC(1) Ir-P(l) Ir -P( 2) Ir-P(3) 1r-pj4 j
Distance, A
Atoms
Distance, A
1.945 (8)
P(1)4(3) p(2)4(4) P(3)C(5) P(4)C(6)
1.838 (8) 1.85 3 (8) 1.838 (8) 1.843 (9) Av 1.843 (4) . .
2.306 2.324 2.338 2.345 A 9 2.328
(3) (3) (3) i3j (9) .,
P(l)-C(lll) ~ (j c ii i 2 i j 1.166 (10) P(2)4(211) 1.456 (11) P(2)
