1,41-43SR,44TeR,45PR2,5x39.46 A s R ~ ~ ~which ~ ’ ~for ~ )the , bromine-bridged derivative was characterized both by X-ray d i f f r a c t i ~ nand ~ ~ by detailed infrared spectral to possess DZhsymmetry. (42) J. C. Hileman, D. K. Huggins, and H. D. Kaesz, J . Am. Chem. SOC.,83, 2953 (1961); Inorg. Chem., 1, 933 (1962). (43) M. A. El-Sayed and H. D. Kaesz, ibid., 2, 158 (1963). (44) W. Hieber and W. Schropp, Jr., Z . Naturforsch., 14b, 460 (1959); P. M. Treichel, J. H. Morris, and F. G. A. Stone, J . Chem. Soc., 720 (1963). (45) W. Hieber and ‘ I Kruck, . Chem. Ber., 95, 2027 (1962). (46) W. Hieber and W. Freyer, ibid., 92, 1765 (1959). (47) R. F. Lambert, Chem. Ind. (London), 830 (1961).
It is hoped that a neutron diffraction study of this compound can be undertaken in the near future in order to verify our proposed configuration. Acknowledgments. We are deeply indebted to Dr. Roy Hayter for the sample and for helpful discussions of the chemistry. We also wish to thank the National Science Foundation for their financial support of this work. The calculations were performed on the CDC 1604 computer at the University of Wisconsin Computing Center and on the IBM 704 computer at MURA. (48) L. F. Dah1 and C. H. Wei, Acta Cryst., 16, 611 (1963).
Structure of Ir0,Cl (CO)( P(C,H,), ) ,, the Oxygen Adduct of a Synthetic Reversible Molecular Oxygen Carrier’ Sam J. La Placa and James A. Ibers Contribution from the Chemistrv DeDartment. Brookhaven National Laboratorv. Upton, New York 11973 Received January 28,1965 ,
The structure of Ir02CI(CO)(P(C6H5)3)2, which is the oxygen adduct of the synthetic molecular oxygen carrier IrCI( CO)(P(C6H5)&, has been determined from threedimensional X-ray data collected f r o m a single crystal. The material crystallizes in space group C i 2 - P i of the triclinic system with two molecules in a cell of dimensions a = 19.02, b = 9.83, c = 9.93A.; cr = 94.0, /3 = 64.9, y = 93.2”; V = 1676 A . 3 . The crystal structure consists of the packing of discrete, monomeric molecules. The molecular structure surmised by Vaskafrom spectroscopic data has been confirmed, and, in addition, details of the attachment of molecular oxygen to iridium have been obtained. The iridium may be described as either fiveor six-coordinated: the iridium, the two oxygen atoms, the carbonyl group, and the chlorine atom lie in the basal plane, with phosphorus atoms above and below this plane. The two oxygen atoms are equidistant from the iridium atom, with an average Ir-0 distance of 2.07 A. The 0-0 bond length of 1.30 f 0.03 A. is intermediate between those characteristic of 0 2 (1.21 A.) and 0 z p 2 (1.49 A .) and corresponds closely to 02-(1.28 A .).
Introduction Knowledge of the manner in which oxygen is attached in natural molecular oxygen carriers, such as hemoglobin and hemocyanin, is obviously of great importance to our understanding of the molecular bases for such properties as reversibility of oxygen uptake and oxygen transport. No direct information on the mode of attachment is available at present, and the prospects for a direct determination by diffraction methods, though not altogether bleak, are at least not immediate. On the basis of indirect spectroscopic and magnetic measurements, several models for the mode of attachment of molecular oxygen to the iron in hemoglobin have been put f o r ~ a r d . ~ -These ~ run the gamut from a (1) Research performed under the auspices of the U. S. Atomic Energy Commission.
I
linear bonding arrangement through a bent configuration3j4 to the triangular, or a-bonding, arrangement5 in which both oxygens are equidistant from the iron. There has also been recent speculation and discussion concerning the disposition of the electrons in the bonding scheme. 4,6-8 The synthetic molecular oxygen carriers offer advantages over the natural ones in simplicity and variety. It is evident that by studying the physical and structural properties of synthetic carriers and their oxygen adducts one should be able to increase the understanding of the molecular bases for such phenomena as reversibility. Yet very few studies of a definitive nature have been carried out on these synthetic carriers or their oxygen adducts, probably because most of them are unstable or poorly chara~terized.~Vaska’s discovery lo of the 1 : 1 reversible molecular oxygen carrier IrCl(C0)(P(C6H6)&is thus of great importance, for the oxygen adduct Ir0zC1(CO)(P(C6H5)3)2 may be crystallized and is extremely stable and well characterized in comparison with previously known oxygen adducts. In a preliminary report” we gave some details of our study of the molecular structure of this remarkable compound. In this paper we present our results in full.
Collection and Reduction of the X-Ray Data Excellent light orange crystals of IrOZCl(CO)(P(C6H6)3)2 were very kindly supplied by L. Vaska. These crystals were stable in air during the X-ray photography, (2) L. Pauling and C. D. Coryell, Proc. Natl. Acad. Sci. U. S., 22, 210 (1936). (3) L. Pauling, “Hemoglobin, Sir Joseph Barcroft Memorial Symposium,” Butterworth and Co. (Publishers) Ltd., London, 1949, p. 57. (4) L. Pauling, Nature, 203, 182 (1964). ( 5 ) J. S. Griffith, Proc. Roy. SOC.(London), A235, 23 (1956). (6) J. J. Weiss, Norure, 202, 83 (1964). (7) J. J. Weiss, ibid., 203, 183 (1964). (8) R. 0. Viale, G. M. Maggiora, and L. L. Ingraham, ibid., 203, 183 (1964). (9) See L. H. Vogt, H. M. Faigenbaum, and S. E . Wiberley, Chem. Rev., 63, 269 (1963), for a review of synthetic carriers. (10) L. Vaska, Science, 140, 809 (1963). (11) J. A. Ibersand S. J. La Placa, ibid., 145, 920(1964).
La Placa, Ibers 1 Structure of IrO,Cl(CO)(P(C$-I6)&
2581
and although they did darken gradually, no detectable changes in X-ray intensities resulted. The crystals were assigned to the triclinic system as a result of an optical examination and preliminary X-ray photography. A Delaunay reduction failed to suggest the presence of hidden symmetry. The cell chosen is a primitive one of dimensions a = 19.02 f 0.03, b = 9.83 i 0.02, c = 9.93 f O.O2A.., a = 94.0 f 0.1, p = 64.9 f O.,’, y = 93.2 f 0.1”. The unit cell volume is 1676 A . 3 and the calculated density is 1.61 g . / ~ mfor . ~ two molecules in this cell. A very sensitive test for a piezoelectric effect was kindly performed for us by F. Holtzberg; no effect was found. Accordingly the space group Ci2-PT was assumed in this work, and this assumption seems justified in view of the excellent agreement obtained between observed and calculated structure amplitudes. Since there are two molecules in P i , no crystallographic symmetry conditions need be imposed on the molecules. Integrated intensity data were collected at room temperature by the equi-inclination Weissenberg technique. Zirconium-filtered Mo K a radiation was employed. The layers h01 through h61 were photographed. The intensities of 1128 independent reflections within the limiting sphere Ohlo 5 18” were estimated visually. (About 60 % of the accessible reflections were sufficiently strong to be estimated reliably.) The usual Lorentz polarization factor was applied to these intensities to yield Fo2 values (where F, is the observed structure amplitude), and these were then corrected for absorption. In order to carry out the absorption correction, the eight faces on the crystal used in the X-ray photography were identified by optical goniometry and their dimensions were carefully determined. The volume of the crystal used is approximately 0.0021 mmS3and has a calculated weight of only 3.2 gg. Yet because the crystal is not of equant habit, but has linear dimensions of approximately 0.31 X 0.09 X 0.08 mm., the absorption corrections are important. Using a linear absorption coefficient of 44.3 cm.-’, we find the transmission coefficients vary from 0.50 to 0.75.12 The F, values were subsequently brought to an approximate common scale through a modification of Wilson’s procedure. Solution and Refinement of the Structure The positions of the Ir and P atoms were evident from inspection of the three-dimensional Patterson function. The positions of the two oxygen atoms and of the ring carbon atoms were easily found in a subsequent difference Fourier synthesis, based on structure factors phased by the Ir and P contributions. The two most prominent peaks on this map corresponded to reasonable positions for the C1 and CO, but they were similar in shape and height and in neither were the C and 0 of the CO group resolved. A disordered arrangement of CO and C1 was suspected and was confirmed in later calculations. The structure was refined by the least-squares method. The function minimized was Zw(F,, - Fc)2, where the weights w were assigned in the following way: I (the raw intensity) 5 16, w = (Z/32F)2; I > 16, w = (2F)-2. The atomic scattering factors for the neutral (12) In addition to a varlety of local programs for the IBM 7090, the following were employed in the calculations : local modifications of Burnham’s GNABS absorption program, Zalkin’s FORDAP Fourier program, and the Busing-Levy ORFLS least-squares program.
2582
Journal o f t h e American Chemical Society
atoms tabulated by IbersI3 were used. The anomalous parts of the Ir, C1, and P scattering factors were obtained from Templeton’s tabulation l 4 and were included in the calculated structure factors. I5 The refinement was carried out using the group procedure discussed more fully elsewhere. 16, l7 In this manner the phenyl rings were constrained to their ~ $ 1 known geometry (Dsh symmetry, C-C = 1.392 A . , C-H = 1.08 A.) with consequent increase in convergence rate and decrease in the number of parameters and in computing time. This procedure permits the introduction of physically reasonable information, namely the phenyl ring geometry, into the refinement and this is particularly important since this geometry is known more accurately than it could be deduced from a structure determination of this sort. The variable parameters for each phenyl ring are a single, isotropic thermal parameter and six positional parameters. These are the fractional coordinates of the ring center, x,, y,, and zc, and three angles, 6 , t, and 7, which are successive counterclockwise rotations about the az’, al’, and a 3 ’ orthogonal internal axes that bring about alignment, except for translation, of this coordinate system with an orthogonal, external coordinate system A . The origin of the internal coordinate system is taken at the ring center, and a3’is normal to the plane of the ring while a l ’ intersects a vertex. The orthogonal, external coordinate system A is formed from the triclinic coordinate system a in the following way: Az is parallel to az; A1 is parallel to a2 X as; A 3 is parallel to A1 X Az. In the initial refinement, C1 scattering factors were assigned to each of the C1-CO peaks, and each of the heavy atoms was assigned a single, variable isotropic thermal parameter. This refinement of 70 individual and group positional and thermal parameters converged rapidly to a conventional R factor ( R = Z l ~ F o ~ IF,~~/ZlF,,)) of 0.085 and to a weighted R factor R ’ ( R ’ = ( 2 w ( F o - F c ) 2 / Z w F , 2 ) ’ ~ zof) 0.100. A difference Fourier synthesis based on this refinement provided no indication of an incorrect treatment of the C1-CO peaks, but did suggest that the Ir atom is vibrating anisotropically. In a final round of calculations the Ir was assigned anisotropic thermal parameters, the C1-CO positions were again approximated by a C1 scattering factor, and this time the hydrogen atom contributions on the phenyl rings were included in the calculations. This refinement of 75 positional and thermal parameters converged to values of R of 0.071 and of R’ of 0.074 and led to the final parameter values given in Table I. The standard deviations of these parameters, as estimated from the inverse matrix, are also listed in Table I. (Table 11 lists the fractional coordinates for the ring carbon atoms that can be derived from the data of Table I.) A final difference Fourier based on this refinement had density no higher than 0.9 electron/A.3, about 30% of the height of a phenyl carbon atom in this structure. The only obvious feature on this difference Fourier relates to the vibration of the phenyl rings: (13) J. A. Ibers in “International Tables for X-Ray Crystallography,” Vol. 3, Kynoch Press, Birmingham, England, 1962, Table 3.3.1. (14) D. H. Templeton, ref. 13, Table 3 . 3 . X . (15) J. A. Ibers and W. C. Hamilton, Acra Crust., 17, 781 (1964). (16) S. J. La Placa and J. A. Ibers, J . A m . Chem. Soc., 85, 3 5 0 1 (1963). (17) S . J. La Placa and J. A. Ibers, Acta C r y s t . , 18, 5 1 1 (1965).
1 87:12 1 June 20, 1969
Table I. Positional, Thermal, and Group Parameters for h o & ~ ( c o ) ( P ( c & ~ ) & Atom
0.2342(1)a 0.1335(6) 0.3430(7) 0.2873(9) 0.1467(10) 0.224( 1) 0,279(2) Group PiRi’ PiR2 PIRa P2Ri P A P2R3
0.2100(2) 0.3207( 13) 0.1266(15) 0.1153(18) 0.0293(21) 0.366(3) 0.397(3) Yc
20
0.313(2) 0.203(2) 0.635(2) 0.279(2) 0.152(2) -0.192(2)
0.195(2) 0.528(2) 0.250(1) - 0.494(2) -0.146(2) -0.281(2)
Xo
-0.033(1) 0.098(1) 0.181(1) 0.375(1) 0.496(1) 0.33q1)
Z
B, A.z
0.0068(2) 0.2136(11) -0.2024( 13) 0.1618(16) O,OO19(19) -0.117(2) -0.073(3)
3.9(3) 6 . o(4) 11.0(4) 13.6(5) 4.9(7) 8 . q 1 .O)
Y
X
b
6
e
tl
B , A.?
4.97(4) 3.04(2) 1,21(2) 4.86(2) 0.30(2) 5.34(5)
5.22(2) 5.81(2) 5,86(1) 0.29(2) 0.33(2) 5.10(2)
4.97(4) 1.69(2) 2.91(2) 5.20(2) 2,46(2) 3.85(5)
5.6(6) 5.2(5) 5 .2(5) 6.3(5) 7.2(6) 6.3(5)
Numbers in parentheses here and in succeeding tables are estimated standard deviations in the least significant digits. * Ir was refined anisotropically. The thermal ellipsoid had the form exp(-Pllh* PZ2k2 p 3 3 1 2 2PIzhk 2P13hl 2Pz3kO and the values obtained are Pll = 0.00205(6); & = 0.0088(2); P33 = 0.0085(2); Pi* = 0.00082(9); P i 3 = -0.0025(1); Pz3 = 0.0020(2). c XI and Xz refer to disordered C l C O positions. x c , y,, and z, are the fractional coordinates of the ring centers. The angles 6, c, (in radians) are defined in the text. PIRl is phosphorus l , ring l , etc.
+
Table 11. Derived Parameters for Group Carbon Atoms Group atoma
X
Y
2
0.039(1) 0.036(1) -0.036(2) -0.104(1) -0.101(1) -0.030(2)
0.317(3) 0.325(3) 0.321(3) 0.309(4) 0.302(3) 0.306(3)
0.203(4) 0.066(3) 0.058(2) 0,188(4) 0.324(3) 0.332(2)
0.111(1) 0,098(1) 0.085(1) 0.085(1) 0.098(1) 0.111(1)
0,257(3) 0.118(3) 0.063(2) 0.148(3) 0.288(3) 0,342(2)
0.394(2) 0.410(3) 0.545(3) 0.663(2) 0.646(3) 0.512(3)
0.160(2) 0 . 1 ll(1) 0,132(2) 0.202(2) 0,251(1) 0.230(2)
0.499(2) 0.601(4) 0.737(3) 0.772(2) 0.670(4) 0.534(3)
0.238(3) 0.243(3) 0.256(3) 0.263(3) 0.258(3) 0.245(3)
0.361(2) 0.435(2) 0,449(1) 0.390(2) 0.316(2) 0.302(1)
0.217(3) 0.271(3) 0.334(3) 0.342(3) 0,288(3) 0.225(3)
-0.363(3) -0.448(3) -0.579(3) -0.625(3) -0.540(3) -0.409(3)
0.431(2) 0,444(2) 0.509(2) 0.561(1) 0.548(2) 0.483(2)
0.138(4) 0.257(3) 0.271(3) 0.166 (4) 0.046(3) 0.033(3)
-0.178(3) -0.107(3) -0.075(3) -0.114(3) -0.185(3) -0.216(3)
0.333(2) 0.352(1) 0.349(2) 0.326(2) 0.307 (1)
-0.052(2) -0.102(3) -0.241(4) -0.331(2) -0.282(3)
-0.250(4) -0.396(3) -0.427(2) -0.313(4) -0.167(3) -0.136(2)
a C1 is attached t o P ; other C atoms are numbered in succession so that C, is para to C,. The standard deviations are derived from estimated standard deviations in the group parameters and are meant to be used in error analyses on inter-ring distances. Intra-ring distances, of course, are fixed (C-C = 1.392 A.).
there is a clear indication that the carbon atoms nearest to phosphorus are vibrating less than those farther
+
+
+
+
away. The differences in thermal parameters were not derived. Even in this difference Fourier there was no indication that the treatment of the disorder was improper. Although a more elaborate treatment might be desirable, it does not seem possible, since the Ir-Cl and Ir-C distances and the thermal parameters of C1, C, and 0 would have to be known in advance, and could not be refined, if one were to use a model consisting of ‘i2 C1 and CO at each position. Undoubtedly the high thermal parameters for “atoms” XI and X2 (where X designates a CI-CO composite position) are a reflection of the fact that the peak is broadened both by the composite C-0 peak and also because the C-0 peak center and the C1 peak center d o not necessarily coincide. Both for this reason and because of the excellent agreement achieved with the present model, the parameters of Table I are taken as final parameters for this structure. In Table 111 the values of F , and F, (in electrons) are given for the 1128 observed reflections. The F, values for unobserved reflections are omitted from Table 111, since none of the intensities calculated for unobserved but accessible reflections exceeds our estimate of a minimum observable intensity value. The anisotropic thermal parameters of Ir lead to principal root-mean-square amplitudes of vibratioa of 0.125 f 0.004, 0.192 f 0.002, and 0.220 f 0.003 A.
Description of the Structure The crystal structure described by the space group, the parameters of Table I, and the cell parameters consists of the packing of individual, monomeric molecules (shortest Ir-Ir distance >9 A.). A perspective drawing of a monomer molecule is shown in Figure 1 ; the molecular structure is essentially that deduced by Vaska’O from spectroscopic and magnetic data. The Ir, 01,02,XI, and X2 atoms are coplanar: the best least-squares plane through these five atoms has the equation 8 . 3 3 1 ~- 3 . 9 3 1 ~- 5.3122 = 1.089 (triclinic coordinates). The distances of these atoms from this plane are given in Table IV. Figure 2 shows part of the difference electron density in this plane. (18) W.
C.Hamilton, Acta. Crust., 14, 185 (1961)
Table 111. Observed and Calculated Structure Amplitudes (in Electrons) for IrOlC1(CO)(P(CeHs)B)2 H L 695 C 4 L
0 k
0 0 0
5 6 1 R 9 10 II 13
0 0
n 0 P
n 0
3 -I 4 -1 5 -1 6 -I 1-1 n -1 9 -1 in - 1 I I -I 13 - I - 4 -1 -5 - I -h - 1
-IO - 1 -11 -I -13 - I n -2 I -7 2 4 5 6
-2 -2 -?
-2 7 -2 8 -? 9 -2 1 1 -? -4 - 2 -5 - 2 -h -2 -7 -2 -9 -? -11 -7 - I 3 -2
-15 - 2 0 -7 2 -1 ? -3 4 -3 5 -7 6 -3 7 -3 8 -3 11 -3
-I
-3
14 -4
803 5 2 49 6 5 61 96 9 5 4 2 49 1 9 en I15 1 2 5 66 59 n3 n4 49 5 0 9 1 89 109 LO9 90 9 3 98 94 67 6 5 113 io1 71 7 1 57 54 5 h I? 50 46 2R5 2.41 5 1 5n 55 5 0 18 7 6 112 I20 9 0 9? O R 64 ?5 20 80 7h 142 1 3 7 bR bR 1? 9 0 4 1 5b 59 5? 51 59 49 54 110 104 11 1 4 118 115 12 6 9 40 61 1 0 66 91 89 RP 81 75 7 9 118 124 34 35 16 n9 70 01 63 65 59 6 2 44 44 0 2 51 1 1 5 ion 0 4 6) 55 5 1 LOO 93 n ? 19
-2 - ? - 3 -7 -4 - 3 -5 - 7 -6 - 7 I11 L O R -7 - 3 119 112 -8
-7
-9 - 3
W 12
,*****K.0*.*..
I * I . I.. ?? 66 bh
-11 - 3 iz 7 0 0 -4 117 113 1 -4 50 4 0 2 - 4 175 1 2 1 7 - 4 11 7 0 4 -4 49 54 9 -4 49 5n 48 4 7 -1 - 4 -2 -4 7 8 8 9 -3 -4 58 0 1 -4 -4 1 0 7 98 -5 - 4 5n 57 - 0 -4 96 105 - 1 -4 56 5 8 - 0 - 4 I 4 0 140 -9 - 4 7 5 15 P5 89 -10 - c - 1 1 -4 82 1 9 h2 hn -13 -4 0 -5 140 I27 I -5 49 4n 2 -5 50 54 3 -5 42 34 -1 - 5 3 8 36 -2 -5 137 1 3 ? -4 - 5 h? h? -6 -5 h4 10 - R -5 91 I14 -9 - 5 55 50 - 1 0 -5 119 110 - 1 1 -5 0 4 73 a -6 h i 64 -2 - h LO3 1 0 0 -4 - 6 89 91 -0 - 6 14 1 4 -8 - 6 45 50 -10 - 6 59 hR - 1 1 - h 50 65 -12 - h 51 6 h 64 79 -13 - h -7 7 0 7 0 -2 - 1 116 66 -4 - 1 9 1 n9 -6 - 1 8 1 8 h - 1 3 -7 9 4 0 5 -2 - n 61 6 7 -4 - 8 50 5 1 -6 -n 19 1 3 119 ~5 -8 - Q -9 -n 52 4 5
-5 -1
-n
-9 -10 -12
0 0
n
n
71
85
45
54 48
50
106 107 0 I 2 7 131 n 65 73 n in 80 0 52 6 0
n
-14 4
41 78
49
0 69 1 56 I 1 1 98 9 5 I 112 LO7 7 I 0 5 68 8 I 40 5 4 10 1 9 h 9 5 12 I 86 9 1 1 70 6 0 14 - 3 1 7?5 ? 5 0 33 -4 1 25 -5 1 156 1 5 8 I 55 5 5 -6 -1 I 81 92 -9 1 7 6 8 7 0 2 56 5 3 1 2 IR0 175 3 2 75 72 4 ? 17 3 2 5 7 121 110 h 7 6 1 50 7 2 9n 92 1 2 129 123 in ? 9 5 99 12 7 ni 8 9 14 2 94 91 -1 2 204 1 9 7 -? 7 189 190 -4 2 h2 hl - 5 2 168 156 - 1 ? 99 9 5 -1 2 54 50 - 1 2 2 44 4 4 1 7 114 I O 6 ? 3 54 5 4 3 3 49 4 1 1 52 49 4 5 ? Pl 1 1 6 3 87 1 5 7 ? 1?9 1 2 9 n i 171 113 9 3 6 4 bn 10 ? 7 h 1 1 I ? 7 $7 81 14 3 5 5 6 6 lh ? R4 1 0 -1 7 154 152 -2 3 29 2 1 -3 3 166 1 5 n -4 7 1n 41 3 @4 5 4 -5 - 1 1 6 n 66 -9 3 4 9 4 5 -in 3 42 43 -11 3 44 42 1 4 I14 1 0 1 5 6
.
' - __ 4 h? 51 3"
?3
5
4 4
31 11
6 1
4 4
5n
26 15 55
43
44
09
7
3 4
o
4
92
9 10 11 12
4
PL
07
4 4
94 41
4
Rn
-1 -1 -5
6
in1
94 49 79 9n
4
94
90
4
36
41
-6
4
-1
4
39 40 41
76 42 34
-8 -9
0
I 7
3
4 5 6
1 8 9
IO I2
14
-1 -7 -5 -6
-1 1
2 3 5 1 9 10
I2 14
-1
-3 -5 1
3 5 1 9
10
-1
> 5 1 I
9 7 4
5 6
7
2584
L R R S CAL
4 4 + 3 4n 5 49 38 5 1 1 ) I03 5 33 7a 5 11 7 8 5 ?4 4 7 5 94 9n 5 43 4 1 5 (19 71 5 01 54 5 h3 60 5 7 1 70 5 6 9 77 5 5 1 59 5 19 1 4 5 46 5 5 5 56 4 ) 5 41 37 5 43 4 1 0 84 n6 h 45 3 4 6 90 i o n h 95 89 6 11 78 h 49 5n h 5 1 55 6 47 5? 6 17 1 8 6 48 hL h 5 5 k9 h h5 54 6 53 4 9 7 5 0 50 1 10 7 2 1 R l 85 7 17 6 4 1 44 5 0 ? 45 51 7 6 0 57 1 54 49 I 4 4 48 R 17 7 3 R 56 4 9 n 51 55 - 1 146 135 -1 53 5 0 -1 69 7 1 -1 86 87 -1 91 9 8
I4 L I -1 9 -I I O -I I2 - 1 -5 - 1 -6 - 1 -a - I -9 - I -10 - I -11 - 1 -12 - I 2 -2 3 -2 4 -2 5 -2 6 -2 1-2 9 -2 9 -?
ABS C 4 L 96
ni 16 52 47 I73 51 I19
68 112 R6
17h 63
87 17 86 59 4n 131 54 122 16 114 90 t4n 64
49 n5 84 I1 74 68 72 97 9 1 ?8 32 LO - ? 75 7h - 5 -2 1 0 3 i o n -7 - I 70 l? -8 - 2 57 5 4 - 1 0 -2 9 4 9 4 - 1 1 -2 7? 19 -17 -7 76 7 5 - 1 3 -2 o n 87 1 1 13 -14 - 7 0 -7 4 4 42 2 -3 DO h4 7 -3 63 42 4 -7 44 49 5 - 7 47 4 9 14 1 1 6 -3 1 - 1 7 1 36 n - 3 71 7 9 52 4 5 10 - 3 - I -7 1 1 4 1 1 5 -2 - 3 6 3 58 -3 -3 170 131 -4 - 7 4 b 48 -5 - 1 1 4 4 134 -6 - ? h? bI - 7 - 3 lhl 167 -9 -? h9 71 - 1 1 -7 14 73 51 68 -12 - 3 47 57 -13 - 3 -14 - 1 71 15 -16 - 3 49 66 I -4 05 O h 2 -4 32 79 3 -4 87 8 h 4 -4 14 7) 6 -4 46 49 - 1 -4 4 5 50 - 3 -4 9 9 9 1 -5 -4 151 I51 -6
-4
40
*n
32
-1 - 4 -9 -4 - 1 1 -4 n -5 1 -5 7 -5 4-5 h -5 8 -5 - I -5 -3 -5 - 5 -5 -7 - 5 -R - 5 -9 - 5 - 1 1 -5 - 1 6 -5
124 1 1 7 89 9 3 1 1 82 59 5 5 121 I l l 55 5 4 38 4 5 41 70 54 51 129 1 2 1 Lh 7 3 95 90 105 106 3n 35 I ? R 121 19 11 50 7 2 -6 05 6 1 1 -h 61 61 2 -6 79 4 3 4 -0 51 5 2 - I -6 in8 1 1 3 -7 -6 112 I18 - 5 -6 1 8 n5 -7 - 6 54 67 -9 - h 8 1 96 92 9 5 -11 -0 17 7 7 - 1 2 -6 0 -7 4 1 55 - I - 1 5n 60 -2 -7 4n 37 -1 - 7 05 84 -5 -7 119 9 1 -7 -7 5 0 57 - 1 1 - 1 R5 82 -12 - 1 6 5 6 4 - 1 3 - 1 58 6 1 -7 -n 43 5 1 -5 - 8 hR 4 5 88 7 9 -1 -n -9 - 8 56 65
H
L
-12
1
-I3
I
0 1 2
3
+ 5 h i R
5 6 7
9
ii 17 -4 -6
-8 -9
-io
-11 4 5 6 7 9
It 13 15 -4
-6 -1
n
54
58
1 4 1 44 1 149 165 I 16 83 1 88 9 8 1 94 i n 2 1 43 6 7 1 9 5 I35 1 I 3 81 1 49 61 1 i n o 112 I 112 120 1 37 39
?
7 2 7 2 2 7
2 7
7
-I
2
-2 -3 -4
2 ?
-0
-1
-n
2 ?
?
2 2 2
CIL 93 5 4 47 46 46 l ? l 126 59 5 4 92 93 50 4 0 l l d 115 ne 1 9 11 6 9 91 101 43 31 1 5 11 11 15 71 no 84 15 6 4 bI 156 166 45 4 2 I R h 19h 94 98 n3
?h
-12 0
7
53 5h
1
7
04
3
3
? 7
3
h9 39 Ob 68
3
b3
4 5 b
7 8
11
3
3 3
-6
3
1
3 ?
73 47 in 61 37 7h 87 58 in
7
7 3
hI 75 63
-11 0 2 3 4 5
3
46
4 4 4 4
b8
13 -2 -4 -4
-3
0 1 ?
t'
eo 55 77 7v 35 19
4 4 4 in3 4 9? 4
4 4 4 4 5 5
94 58 39 bn 63 79 51 77
v
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Figure 1. A perspective drawing of the Ir02C1(CO)(P(C$I&)~ molecule. X1 and XZare the disordered CI-CO positions; phenyl hydrogen atoms are not shown.
This difference Fourier is based on F, values that do not include contributions from 01,02,XI, or Xz and displays the electron density at these positions. Figure 2 illustrates rather well the near equivalence of the X1 and Xz peaks and the fact that while the 01-02 peaks are readily resolved, there is no indication of CO resolution. This total disorder of the C1 and CO positions may be rationalized in the following way. Presumably the compound results from the attack above or below the square-planar IrCl(CO)(P(C6H,)3)z molecule by Oz in benzene solution, for the method of preparationlo is essentially the reaction of Oz with a benzene solution of IrCl(CO)(P(C6H,)3)z. Since the triphenylphosphine ligands are equivalent in solution, lo only one isomer is formed, and if the relative positions of C1 and CO do not affect the crystallization process, then total disorder would be expected. This is not unreasonable, for the packing is determined almost entirely by the triphenylphosphine groups: the volume per triphenylphosphine in this structure is only 15% greater than in triphenylph~sphine’~ itself. Table IV.
Distances of Atoms from Best Least-Squares Plane Atom Ir
x1 x 2
0 1 0 2
Distance, A.
0.0008(19) -0.007(15) 0.008( 18) -0.039(21) 0.063(28)
Figure 2. Electron density at the X1, Xz, 01,and 0 2 positions in the best least-squares plane containing these positions and the Ir. The Ir positio? is marked with a cross. The contour interval is 0.26 electron/A.a and contours from 1.31 to 5.24 electrons/A.S are shown.
the Cr radius is about 0.1 A. less tban the Ir radius, the average Ir-0 distance of 2.07 A. does not seem unreasonable. The triphenylphosphine geometry is similar to that found recently in other compounds, 16,2o with the C-P-C angles being somewhat larger. Table V.
Selected Intramolecular Distances and Angles Intramolec$ar distance, A.
Ir-Pl Ir-Pz Ir-XI Ir-Xz Ir-Ol Ir-Oz PI-Pz P1-x1 PI-& Pro1 P1-02 Pz-XI Pz-xz Pz-01 Pz-02
x1-xz
x1-01
XI-02 xz-01 Xz-02 01-02
P-CI (av. cf six)
2.38(1) 2.36(1) 2.42(2) 2.38(2) 2.09(3) 2.04(3) 4.73(2) 3.48(2) 3.39(2) 3.04(2) 3.11(3) 3.32(2) 3.52(2) 3.17(3) 2.96(3) 3.68(2) 4.39(3) 3.79(4) 3.61(3) 4.21(4) 1.30(3) 1.81(1)
-----Angle, P1-Ir-Pz PI-Ir-X1 Pl-Ir-Xz PI-Ir-O1 PI-Ir-OZ P2-Ir-XI Pz-Ir-X2 Pz-Ir-O, PZ-Ir-Oz X1-Ir-Xz X1-Ir-O1 X1-Ir-02 X2-Ir-Ol XZ-Ir-O2 Ol-Ir-02 C1-P-C1 ’ (av. of six)
deg.172.8(5) 93.0(5) 90.9(5) 85.4(7) 89.2(9) 87.7(5) 96,0(6) 90.6(7) 84.1(9) 100.1(6) 152.4(8) 115.9(1.0) 107,4(9) 144.q1.1) 36.7(9) 105(1)
Principal intramolecular distances and angles are The significant facts with regard to oxygen attachgiven in Table V. (All intermolecular contacts appear ment are that the two oxygen atoms are equidistant to be normal and are therefore not listed.) The intrafrom the Ir (difference in Ir-0 bond lengths is 0.061 molecular distanc$s seem normal. The average Ir-P f 0.045 A.) and the 0-0 distance of 1.30 f 0.03 b., distance of 2.37 A. may be compared with the basal while longer than that in molecular oxygen (1.21 A,), Ru-P distances of 2.39 A. ia R U C ~ ~ ( P ( C ~ Hand , ) ~with ) ~ ~ ~ is significantly less than that in a typical peroxide Rh-P distances of 2.32 A. in RhH(CO)(P(C6H5)3)3.l6 (1.49 A.).22 This equivalence of the oxygen atoms is There is no comparable Ir-02 geometry described in the consistent with Griffith’s5 model of the 7r-bonding of literature. Hpwever, the Cr-0 distances in K3Cr08 molecular oxygen to iron in hemoglobin (also a 1 : l average 1.89 A.,21 and since the Cr-02 bonding seems oxygen carrier). The facts that oxygen uptake is reversito be similar to the Ir-02 bonding found here and since ble and that the 0-0 bond length is significantly shorter (19) J. J. Daly, J . Chem. Soc., 3799 (1964). (20) S. J. La Placa and J. A. Ibers, Inorg. Chem., 4, 778 (1965). (21) J. D. Swalenand J. A. Ibers, J . Chem. Phys., 37, 17(1962).
(22) As a result of thermal motion, this bond distance of 1.30 A. is shorter than the equilibrium distance; however, we estimate that it is within 0.04 A. of the equilibrium distance.
La Placa, Ibers / Structure of I~O~CI(CO)(P(CBH&)~2585
than that in a typical peroxide are consistent with the views of Martell and Calvinz3that reversibility probably depends upon some electron transfer from metal to oxygen, but not sufficient transfer to bring about irreversible oxidation of the metal. In the present case this transfer amounts to approximately one electron, since the 0-0 distance corresponds closely to 02-(1.28 A.); thus the formal oxidation state is Ir(I1) and yet the compound is diamagnetic. Of course, in compounds of this type the concept of a formal oxidation state is not particularly useful. A less qualitative and possibly more useful description of the bonding might result from a molecular orbital calculation, although this would be more meaningful if the structures of a series of analogous compounds were known. Even the question of whether Ir is five- or six-coordinated in this structure has been tacitly ignored. (The Ir could be thought of as five-coordinated if the 0 2 molecule were counted as a single ligand, as is, for example, the ethylene molecule in Zeiss’s salt.) An analogous compound with SOz in place of 0 2 has been prepared by VaskaZ4and its structure is now under investigation.z5 The differences between the stereochemistry of the SOz and O2 com(23) A. E. Martell and M. Calvin, “Chemistry of the Metal Chelate Compounds,” Prentice-Hall, Inc., Englewood Cliffs, N. J . , 1952, p. 352. (24) L. Vaska, unpublished results. (25) NOTEADDEDIN PROOF. The SO, complex is five-coordinated, with an Ir-S bond. However, the coordination geometry is tetragonal
2586
Journal of the American Chemical Society
1 87.12
pounds should provide additional insight into the bonding in each. It is particularly interesting that the combination Fe3+.0,- has been proposed very recently by Weiss67’ as the structure of oxyhemoglobin and that a preliminary molecular orbital calculation* appears to support such a structure. It may be that the analogy between the oxyhemoglobin system and the synthetic iridium system studied here is a very good one. Nevertheless, it is obviously dangerous to extrapolate from this one structure determination and conclude that in both natural and synthetic molecular oxygen carriers T bonding of the oxygen to the metal is the rule and that the 0-0 distance approaching that of Oz- is necessary for reversibility of oxygen uptake. Clearly additional experiments are needed to discover new, synthetic oxygen carriers of sufficient stability so that additional molecular structures of their oxygen adducts can be determined. Acknowledgment. It is a pleasure to acknowledge the close cooperation we have enjoyed with L. Vaska. In addition to supplying the crystals, Professor Vaska has provided a number of very helpful discussions of the chemistry. pyramidal with S at the apex, rather than the trigonal bipyramidal complex. geometry which may be assigned to the 0 %
June 20, 1965
