trans-Carbonyliodotris(triphenylstibine-κSb)rhodium(I)

The crystal structure of the title compound, [RhI(C₁₈H₁₅Sb)₃(CO)], represents a rare example of a crystallographically characterized five-coordinate Rh^I–SbPh₃ complex. The compound crystallizes with the I—Rh—CO core on a threefold rotation axis, with three crystallographically equivalent tri­phenyl­stibine ligands. Selected geometric parameters are: Rh—I = 2.7159 (8), Rh—Sb = 2.5962 (4), Rh—C_CO = 1.825 (6) and C_CO—O 1.153 (6) Å, and Sb—Rh—I = 89.374 (10) and Sb—Rh—C_CO = 90.626 (10)°. The cone angle of the SbPh₃ ligand was determined as 137°, according to the Tolman model.

S1. Comment

Although stibine complexes of Rh have been known since the 1950 s (Vallarino, 1957), surprisingly few crystallographic studies of these complexes have been reported to date. As has been pointed out in earlier investigations (Ugo et al., 1969; Otto & Roodt, 2002), several experimental problems may arise during the characterization of these complexes, making X-ray crystallography the method of choice. As part of our systematic investigation of these systems (Mzamane et al., 2001; Otto & Roodt, 2002), we obtained single crystals of trans-carbonyliodotris(triphenylstibine-κSb)rhodium(I), (I), and its crystal structure is presented here. \sch

Compound (I) (Fig. 1) crystallizes with an almost perfect trigonal-bipyramidal geometry in the trigonal space group P3. The packing in the crystal is governed by van der Waals forces alone; no significant intermolecular interactions are observed. The OC—Rh—I core is situated along the threefold rotation axis, resulting in three crystallographically equivalent SbPh₃ ligands around the Rh atom with angles of exactly 120°. Accordingly, the OC—Rh—I core is exactly linear and the C1—Rh—Sb and I—Rh—Sb angles are close to 90°, at 90.626 (10) and 89.374 (10)°, respectively.

An I—Rh—Sb—C11 torsion angle of 175.77 (10)° indicates phenyl ring 1 (C11—C16) points almost directly towards the CO moiety, whereas rings 2 (C21—C26) and 3 (C31—C36) are staggered with respect to the Rh—I bond, with I—Rh—Sb—C21 and I—Rh—Sb—C31 torsion angles of -63.88 (11) and 57.89 (9)°, respectively. These specific geometric orientations may account for the observation that the SbPh₃ ligands are marginally displaced towards the larger I ligand.

Based on molecular models, Tolman (1977) predicted that increasing the M—L or L—C (M is a metal, L is a ligand) bond lengths by 0.1 Å (for ligands containing other donor atoms than P) would result in a 3–5° decrease in the cone angle of the ligand. In this regard, the effective cone angle, as defined earlier (Otto et al., 2001), utilizes the observed Rh—Sb bond distance, and the cone angle for SbPh₃ in (I) was calculated as 137°. This value is in excellent agreement with both Tolman's prediction and the average of 139° for six independent SbPh₃ ligands obtained during a previous study (Otto & Roodt, 2002).

In Table 2, compound (I) is compared with related trans-[Rh(X)CO(LPh₃)_n] (n = 2 or 3, L is Sb or P) complexes from the literature, illustrating the effect of different X ligands on the geometric parameters of four- and five-coordinate SbPh₃ complexes of Rh^I. From these data, it is clear that the Rh—Sb bond length of 2.5962 (4) Å in (I) is comparable with the value of 2.5981 (5) Å found in the analogous five-coordinate Cl complex, but is slightly longer than the values of 2.568 (2) Å in the acetyl complex and 2.5655 (2) Å in the four-coordinate Cl complex. Not many Rh—I bond distances are known for complexes of this kind, but the Rh—I bond length of 2.7159 (8) Å in (I) is considerably longer than the value of 2.683 (1) Å determined for trans-[RhI(CO)(PPh₃)₂] (Basson et al., 1990). This may be a result of the increased steric crowding in the five-coordinate complex or the increased electron density introduced by the three SbPh₃ ligands. A similar observation was made in relation to the Rh—Cl bond distances of the four- and five-coordinate triphenylstibine complexes (Otto & Roodt, 2002) listed in Table 2, where an elongation of 2.315 (3)–2.4094 (18) Å was induced by the increase in coordination number.

S2. Experimental

NaI (17 mg, 0.113 mmol) was added to a nitrogen-flushed solution of the [Rh(µ-Cl)(CO)₂]₂ dimer (20 mg, 0.051 mmol) in acetone (5 ml). The reaction medium immediately took on a deep-red colour and was stirred for a further 5 min after addition. Stirring was discontinued and SbPh₃ (126 mg, 0.357 mmol) dissolved in acetone (7 ml) was added carefully to avoid the least disturbance in the solution. Deep-red rectangles of (I) soon started separating from the solution. Yields > 80% based on Rh could be obtained. Spectroscopic analysis: IR (KBr, ν): 1977 cm^-1 (CO); IR (dichloromethane, ν): 1978 cm^-1 (CO).

S3. Refinement

H atoms were treated as riding, with C—H = 0.93 Å. Is this added text OK? Even though the structure contains solvent-accessible voids of 115 ų, both the minimum and maximum residual electron density were smaller than 1 e Å^-3, indicating that no molecular fragments remain unaccounted for.

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SAINT (Siemens, 1995); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. A view of the structure of (I), showing the atom-numbering scheme and with displacement ellipsoids at the 30% probability level. H atoms have been omitted for clarity. The complex is numbered with the first digit of the phenyl rings referring to the number of the ring (1–3) and the second digit referring to the number of the atom within the ring (1–6) [symmetry codes: (i); (ii)]. Please provide missing symmetry codes.

trans-Carbonyliodotris(triphenylstibine-κSb)rhodium(I)

Crystal data

[RhI(CO)(C18H15Sb)3]	Dx = 1.737 Mg m^−3
Mr = 1316.97	Mo Kα radiation, λ = 0.71073 Å
Trigonal, P3	Cell parameters from 4642 reflections
a = 14.462 (2) Å	θ = 2.2–24.8°
c = 13.902 (3) Å	µ = 2.56 mm^−1
V = 2518.2 (7) Å^3	T = 293 K
Z = 2	Parallelepiped, dark red
F(000) = 1268	0.29 × 0.10 × 0.08 mm

Data collection

Siemens SMART CCD area-detector diffractometer	5324 independent reflections
Radiation source: rotating anode	2651 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.094
ω scans	θmax = 31.8°, θmin = 1.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −18→21
Tmin = 0.493, Tmax = 0.815	k = −20→20
24940 measured reflections	l = −20→20

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.031	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.056	H-atom parameters constrained
S = 0.86	w = 1/[σ^2(Fo^2) + (0.0154P)^2] where P = (Fo^2 + 2Fc^2)/3
5324 reflections	(Δ/σ)max = 0.003
185 parameters	Δρmax = 0.43 e Å^−3
0 restraints	Δρmin = −0.67 e Å^−3

Special details

Experimental. Data completeness of 99.3% was accomplished up to θ = 30.50°. The first 50 frames were recollected at the end of the data collection to check for decay, none being found.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Rh	0.3333	0.6667	0.28356 (3)	0.03710 (11)
I	0.3333	0.6667	0.08820 (3)	0.05782 (12)
Sb	0.184189 (16)	0.467444 (16)	0.281520 (16)	0.04150 (7)
C1	0.3333	0.6667	0.4148 (4)	0.0465 (14)
O	0.3333	0.6667	0.4978 (3)	0.0674 (12)
C11	0.1435 (2)	0.3991 (3)	0.4224 (2)	0.0454 (8)
C12	0.1118 (3)	0.4465 (3)	0.4918 (3)	0.0629 (10)
H12	0.1026	0.5037	0.4753	0.075 (3)*
C13	0.0941 (3)	0.4097 (3)	0.5844 (3)	0.0716 (11)
H13	0.0710	0.4406	0.6300	0.075 (3)*
C14	0.1103 (3)	0.3275 (4)	0.6102 (3)	0.0795 (13)
H14	0.0997	0.3039	0.6736	0.075 (3)*
C15	0.1416 (3)	0.2803 (4)	0.5434 (3)	0.0788 (13)
H15	0.1521	0.2241	0.5607	0.075 (3)*
C16	0.1579 (3)	0.3167 (3)	0.4496 (3)	0.0613 (10)
H16	0.1791	0.2841	0.4039	0.075 (3)*
C21	0.0271 (2)	0.4102 (2)	0.2246 (2)	0.0441 (8)
C22	0.0133 (3)	0.4108 (3)	0.1265 (3)	0.0616 (10)
H22	0.0722	0.4375	0.0859	0.075 (3)*
C23	−0.0883 (3)	0.3718 (3)	0.0879 (3)	0.0713 (11)
H23	−0.0975	0.3719	0.0217	0.075 (3)*
C24	−0.1749 (3)	0.3331 (3)	0.1484 (3)	0.0668 (11)
H24	−0.2429	0.3065	0.1226	0.075 (3)*
C25	−0.1626 (3)	0.3332 (3)	0.2443 (3)	0.0686 (11)
H25	−0.2220	0.3070	0.2843	0.075 (3)*
C26	−0.0614 (3)	0.3724 (3)	0.2840 (3)	0.0563 (9)
H26	−0.0532	0.3733	0.3504	0.075 (3)*
C31	0.2134 (2)	0.3547 (2)	0.2094 (2)	0.0433 (8)
C32	0.3162 (3)	0.3818 (3)	0.1849 (2)	0.0529 (9)
H32	0.3722	0.4494	0.2001	0.075 (3)*
C33	0.3375 (3)	0.3095 (3)	0.1379 (3)	0.0692 (11)
H33	0.4076	0.3289	0.1227	0.075 (3)*
C34	0.2569 (4)	0.2109 (3)	0.1141 (3)	0.0758 (12)
H34	0.2711	0.1629	0.0822	0.075 (3)*
C35	0.1556 (4)	0.1834 (3)	0.1373 (4)	0.0951 (15)
H35	0.1000	0.1159	0.1213	0.075 (3)*
C36	0.1337 (3)	0.2544 (3)	0.1847 (3)	0.0775 (12)
H36	0.0633	0.2337	0.2000	0.075 (3)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Rh	0.03752 (16)	0.03752 (16)	0.0362 (3)	0.01876 (8)	0.000	0.000
I	0.06804 (18)	0.06804 (18)	0.0374 (2)	0.03402 (9)	0.000	0.000
Sb	0.03827 (13)	0.03649 (13)	0.04601 (13)	0.01590 (11)	0.00141 (11)	0.00096 (11)
C1	0.046 (2)	0.046 (2)	0.047 (4)	0.0232 (11)	0.000	0.000
O	0.079 (2)	0.079 (2)	0.043 (3)	0.0397 (10)	0.000	0.000
C11	0.0371 (18)	0.043 (2)	0.049 (2)	0.0145 (16)	0.0028 (16)	0.0047 (17)
C12	0.068 (3)	0.056 (2)	0.054 (2)	0.022 (2)	0.011 (2)	0.010 (2)
C13	0.062 (3)	0.081 (3)	0.056 (3)	0.024 (2)	0.014 (2)	−0.003 (2)
C14	0.055 (3)	0.114 (4)	0.056 (3)	0.033 (3)	0.005 (2)	0.024 (3)
C15	0.078 (3)	0.104 (4)	0.073 (3)	0.059 (3)	0.012 (2)	0.037 (3)
C16	0.054 (2)	0.077 (3)	0.063 (3)	0.041 (2)	0.011 (2)	0.017 (2)
C21	0.0385 (19)	0.0349 (18)	0.059 (2)	0.0183 (15)	−0.0024 (18)	0.0012 (16)
C22	0.046 (2)	0.069 (3)	0.064 (3)	0.024 (2)	−0.007 (2)	−0.006 (2)
C23	0.072 (3)	0.078 (3)	0.066 (3)	0.039 (2)	−0.020 (2)	−0.011 (2)
C24	0.043 (2)	0.059 (2)	0.096 (3)	0.024 (2)	−0.011 (2)	0.011 (2)
C25	0.040 (2)	0.074 (3)	0.089 (3)	0.027 (2)	0.006 (2)	0.028 (2)
C26	0.052 (2)	0.059 (2)	0.058 (2)	0.027 (2)	0.0014 (19)	0.0108 (19)
C31	0.044 (2)	0.0398 (19)	0.046 (2)	0.0207 (17)	−0.0014 (16)	0.0004 (16)
C32	0.054 (2)	0.047 (2)	0.056 (2)	0.0238 (18)	0.0038 (19)	0.0027 (18)
C33	0.077 (3)	0.075 (3)	0.075 (3)	0.053 (3)	0.008 (2)	0.005 (2)
C34	0.104 (4)	0.076 (3)	0.075 (3)	0.066 (3)	−0.010 (3)	−0.018 (2)
C35	0.079 (3)	0.053 (3)	0.148 (5)	0.028 (2)	−0.035 (3)	−0.047 (3)
C36	0.049 (2)	0.058 (3)	0.122 (4)	0.025 (2)	−0.010 (2)	−0.023 (2)

Geometric parameters (Å, º)

Rh—C1	1.825 (6)	C21—C26	1.386 (4)
Rh—Sb^i	2.5962 (4)	C22—C23	1.392 (5)
Rh—Sb	2.5962 (4)	C22—H22	0.9300
Rh—Sb^ii	2.5962 (4)	C23—C24	1.374 (5)
Rh—I	2.7159 (8)	C23—H23	0.9300
Sb—C11	2.140 (3)	C24—C25	1.346 (5)
Sb—C21	2.143 (3)	C24—H24	0.9300
Sb—C31	2.129 (3)	C25—C26	1.392 (4)
C1—O	1.153 (6)	C25—H25	0.9300
C11—C16	1.362 (4)	C26—H26	0.9300
C11—C12	1.387 (4)	C31—C36	1.370 (4)
C12—C13	1.367 (5)	C31—C32	1.378 (4)
C12—H12	0.9300	C32—C33	1.392 (4)
C13—C14	1.369 (5)	C32—H32	0.9300
C13—H13	0.9300	C33—C34	1.356 (5)
C14—C15	1.357 (5)	C33—H33	0.9300
C14—H14	0.9300	C34—C35	1.351 (5)
C15—C16	1.383 (5)	C34—H34	0.9300
C15—H15	0.9300	C35—C36	1.384 (5)
C16—H16	0.9300	C35—H35	0.9300
C21—C22	1.379 (4)	C36—H36	0.9300
C1—Rh—Sb^i	90.626 (10)	C22—C21—Sb	119.5 (2)
C1—Rh—Sb	90.626 (10)	C26—C21—Sb	121.6 (3)
Sb^i—Rh—Sb	120	C21—C22—C23	120.3 (4)
C1—Rh—Sb^ii	90.626 (10)	C21—C22—H22	119.8
Sb^i—Rh—Sb^ii	120	C23—C22—H22	119.8
Sb—Rh—Sb^ii	120	C24—C23—C22	119.5 (4)
C1—Rh—I	180	C24—C23—H23	120.3
Sb^i—Rh—I	89.374 (10)	C22—C23—H23	120.3
Sb—Rh—I	89.374 (10)	C25—C24—C23	120.9 (3)
Sb^ii—Rh—I	89.374 (10)	C25—C24—H24	119.6
C11—Sb—C21	99.57 (12)	C23—C24—H24	119.6
C11—Sb—C31	101.04 (12)	C24—C25—C26	120.3 (4)
C21—Sb—C31	96.21 (12)	C24—C25—H25	119.9
C11—Sb—Rh	112.73 (9)	C26—C25—H25	119.9
C21—Sb—Rh	124.39 (8)	C21—C26—C25	120.0 (3)
C31—Sb—Rh	118.84 (8)	C21—C26—H26	120.0
O—C1—Rh	180	C25—C26—H26	120.0
C16—C11—C12	118.2 (3)	C36—C31—C32	117.2 (3)
C16—C11—Sb	122.1 (3)	C36—C31—Sb	123.0 (3)
C12—C11—Sb	119.4 (3)	C32—C31—Sb	119.8 (2)
C13—C12—C11	120.4 (4)	C31—C32—C33	121.0 (3)
C13—C12—H12	119.8	C31—C32—H32	119.5
C11—C12—H12	119.8	C33—C32—H32	119.5
C12—C13—C14	120.3 (4)	C34—C33—C32	120.5 (4)
C12—C13—H13	119.8	C34—C33—H33	119.8
C14—C13—H13	119.8	C32—C33—H33	119.8
C15—C14—C13	120.2 (4)	C35—C34—C33	119.2 (4)
C15—C14—H14	119.9	C35—C34—H34	120.4
C13—C14—H14	119.9	C33—C34—H34	120.4
C14—C15—C16	119.3 (4)	C34—C35—C36	120.8 (4)
C14—C15—H15	120.3	C34—C35—H35	119.6
C16—C15—H15	120.3	C36—C35—H35	119.6
C11—C16—C15	121.6 (4)	C31—C36—C35	121.4 (4)
C11—C16—H16	119.2	C31—C36—H36	119.3
C15—C16—H16	119.2	C35—C36—H36	119.3
C22—C21—C26	118.9 (3)
I—Rh—Sb—C11	175.77 (10)	I—Rh—Sb—C31	57.89 (9)
I—Rh—Sb—C21	−63.88 (11)

Symmetry codes: (i) −x+y, −x+1, z; (ii) −y+1, x−y+1, z.