Di­carbonyl­(tropolonato)­rhodium(I), a redetermination

The mol­ecules of the title complex, [Rh(Trop)(CO)₂] (Trop is 2-hydroxycyclo­hepta-2,4,6-trienonate, C₇H₅O₂), exhibit symmetrical but non-crystallographic square-planar molecular geometry, with Rh—C distances of 1.825 (10) and 1.826 (9) Å, Rh—O distances of 2.021 (5) and 2.032 (5) Å, and an O—Rh—O bite angle of 79.4 (2)°. Strong Rh...Rh and Rh...C intermolecular interactions of 3.683 (3) and 3.650 (5) Å, respectively, are also observed.

S1. Comment

The first known crystal structure of a rhodium tropolonato-type compound was reported for the title compound, (I) (Manojlovic-Muir & Muir, 1975), but unfortunately the authors did not publish the atomic coordinates. As a result of our interest in tropolonate tertiary aryl phosphine compounds of rhodium(I) (Steyl et al., 2001 & Roodt et al., 2003, Steyl & Roodt, 2004), the current investigation was undertaken to clarify the solid-state behaviour of (I).

Dicarbonyl(tropolonato)rhodium(I) crystallizes in the monoclinic crystal system with one molecule per asymmetric unit. The molecular geometry is distorted square planar, with an O—Rh—O bite angle of 79.4 (2)° and an intra-carbonyl C—Rh—C angle of 88.3 (4)°. The molecule displays non-crystallographic internal symmetry that approaches C_2v, with Rh—C bond distances of 1.825 (10) and 1.826 (9) Å, and Rh—O bond distances of 2.021 (5) and 2.032 (5) Å. A minor distortion in symmetry is observed for the tropolone C—O bond distances [1.267 (9) and 1.324 (8) Å, as listed in Table 1]. High anisotropy is observed for the carbonyl C and O atoms lying on the periphery of the molecule, thus allowing for high flexibility of the carbonyl group.

The whole molecule, including the tropolone ring, is close to planar, as was established by calculating the least-squares plane containing all the non-H atoms. The mean deviation of the fitted atoms is 0.052 Å, with a maximum deviation of 0.104 (6) Å for carbonyl atom O02. The shortest intermolecular contact, between atoms H3 and C4 (-x, 0.5 + y, 0.5 − z) [1.941 (8) Å], illustrates the efficient packing in the unit cell.

Theoretical calculations were performed on the system using B3LYP/Lan2DZ (Gaussian 03 W; Frisch et al., 2003) with no symmetry restraints on the optimization. The stationary point was characterized as a minimum by means of frequency analysis. An r.m.s. overlay of the calculated and solid-state structures gave an error of less than 0.142 Å. A comparison of the geometric parameters for the the solid-state data in Table 1 and the calculated structure (values in parantheses) for the coordinated ligands to the metal centre (Rh—C = 1.872 and 1.872 Å, Rh—O = 2.061 and 2.061 Å, O—Rh—O = 78.6°, C—Rh—O = 94.7 and 94.7°, and C—Rh—C = 92.0°) shows a good correlation. The absence of large-scale distortions in the crystal structure indicates that packing effects do not play a major role in the solid state.

The structure is similar to those of other Rh complexes of this type in that close intermolecular Rh···Rh contacts, roughly perpendicular to the molecular plane, are present. The molecules stack as infinite chains along the the a axis, with an Rh···Rh distance of 3.683 (3) Å (Fig. 2). This is longer than examples that have been observed to date (see Table 2), but the Rh···Rh interactions are not perfectly perpendicular to the molecular planes as a result of the monoclinic stacking. Because of this offset, a second close intermolecular contact, that between Rh and C02 of 3.650 (5) Å, is also observed (Fig. 2).

A further deviation from the stacking pattern normallly observed in other crystal structures, listed in Table 2, is the unique occurrence of head-to-head stacking in the title compound. All the other complexes pack in a head-to-tail pattern or a close variant thereof. This effect is illustrated by the range of O—Rh···Rh—O dihedral angles listed in Table 2 and could be the result of the small steric demand of the tropolonate moiety, which is indicated by the fact that the bidentate bite angle (O—Rh—O) in (I) is small compared with that in other dicarbonyl complexes.

S2. Experimental

The title compound, (I), was synthesized by dissolving [Rh(µ-Cl)(CO)₂]₂ (45 mg, 0.116 mmol) in methanol (30 ml), adding 2.2 equivalents of tropolone (30.9 mg, 0.253 mmol) and allowing crystallization to occur under slow evaporation (ca 1 d). Yield 58.5 mg, 90%. IR: ν_CO 2074, 2014 cm⁻¹; ¹H NMR (CDCl₃, 300 MHz): 7.55 (m, 5H).

Computing details

Data collection: PWPC (Gomm, 1998); cell refinement: PWPC (Gomm, 1998); data reduction: Xtal3.6 (Hall et al., 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg & Berndt, 2001); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. : The molecular conformation of (I), with anisotropic displacement ellipsoids shown at 30% probability level (Brandenburg & Brendt, 2001).
	Fig. 2. : Part of the unit cell of (I), showing the stacking pattern and the intermolecular Rh···Rh and Rh···C interactions.

Dicarbonyl(tropolonato)rhodium(I)

Crystal data

[Rh(C7H5O2)(CO)2]	F(000) = 544
Mr = 280.04	Dx = 2.058 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71069 Å
Hall symbol: -p 2ybc	Cell parameters from 48 reflections
a = 3.683 (1) Å	θ = 4.1–13.3°
b = 21.856 (4) Å	µ = 1.87 mm^−1
c = 11.296 (3) Å	T = 293 K
β = 96.32 (2)°	Prism, orange
V = 903.8 (4) Å^3	0.23 × 0.15 × 0.08 mm
Z = 4

Data collection

Philips PW1100 diffractometer	1049 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.085
Graphite monochromator	θmax = 26.0°, θmin = 3.3°
ω–2θ scans	h = 0→4
Absorption correction: gaussian (ABSORB in Xtal3.6; Hall et al., 1999)	k = −26→26
Tmin = 0.673, Tmax = 0.872	l = −13→13
3331 measured reflections	1 standard reflections every 50 reflections
1784 independent reflections	intensity decay: 0.0%

Refinement

Refinement on F^2	Primary atom site location: Patterson
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.051	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.120	H-atom parameters constrained
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0388P)^2] where P = (Fo^2 + 2Fc^2)/3
1784 reflections	(Δ/σ)max < 0.001
127 parameters	Δρmax = 1.26 e Å^−3
0 restraints	Δρmin = −0.61 e Å^−3

Special details

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	1.07981 (18)	0.08945 (3)	0.27514 (5)	0.0505 (3)
O11	0.8663 (16)	0.0601 (3)	0.1115 (4)	0.0561 (14)
O12	1.0294 (16)	0.1697 (2)	0.1859 (4)	0.0533 (14)
C01	1.117 (2)	0.0140 (4)	0.3447 (7)	0.055 (2)
C02	1.260 (3)	0.1223 (4)	0.4183 (7)	0.059 (2)
O01	1.146 (2)	−0.0330 (3)	0.3884 (6)	0.093 (2)
O02	1.364 (2)	0.1437 (3)	0.5083 (5)	0.081 (2)
C1	0.788 (2)	0.1018 (4)	0.0352 (6)	0.0459 (19)
C2	0.881 (2)	0.1645 (4)	0.0742 (6)	0.0455 (19)
C3	0.841 (2)	0.2167 (4)	0.0056 (7)	0.058 (2)
H3	0.9212	0.2523	0.0453	0.069*
C4	0.704 (2)	0.2252 (4)	−0.1102 (7)	0.064 (2)
H4	0.7126	0.2653	−0.1374	0.077*
C5	0.555 (2)	0.1840 (5)	−0.1920 (7)	0.066 (3)
H5	0.4707	0.1994	−0.2667	0.079*
C6	0.517 (2)	0.1215 (5)	−0.1758 (7)	0.061 (2)
H6	0.4025	0.1005	−0.2411	0.073*
C7	0.623 (2)	0.0862 (4)	−0.0778 (7)	0.056 (2)
H7	0.5766	0.0446	−0.0885	0.067*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Rh	0.0608 (5)	0.0511 (4)	0.0392 (3)	0.0018 (4)	0.0038 (3)	−0.0018 (3)
O11	0.069 (4)	0.055 (3)	0.043 (3)	−0.004 (3)	0.000 (3)	−0.009 (3)
O12	0.075 (4)	0.046 (3)	0.037 (3)	−0.005 (3)	−0.003 (3)	−0.007 (2)
C01	0.059 (6)	0.062 (6)	0.045 (5)	0.001 (5)	0.005 (4)	−0.007 (4)
C02	0.074 (7)	0.056 (5)	0.045 (5)	−0.004 (5)	0.002 (4)	0.006 (4)
O01	0.149 (8)	0.062 (5)	0.070 (4)	0.013 (5)	0.012 (4)	0.007 (4)
O02	0.127 (6)	0.064 (4)	0.047 (3)	−0.007 (4)	−0.017 (3)	0.000 (3)
C1	0.051 (5)	0.050 (5)	0.037 (4)	−0.001 (4)	0.006 (3)	−0.004 (3)
C2	0.043 (5)	0.058 (5)	0.035 (4)	−0.005 (4)	0.005 (3)	−0.011 (3)
C3	0.067 (6)	0.053 (5)	0.052 (5)	0.002 (5)	−0.001 (4)	0.002 (4)
C4	0.078 (7)	0.070 (6)	0.044 (4)	0.007 (5)	0.004 (4)	0.008 (4)
C5	0.065 (7)	0.093 (7)	0.039 (4)	0.017 (6)	0.002 (4)	0.007 (5)
C6	0.053 (6)	0.085 (7)	0.044 (4)	−0.001 (5)	−0.003 (4)	−0.012 (5)
C7	0.057 (6)	0.062 (5)	0.048 (4)	0.003 (5)	0.003 (4)	−0.013 (4)

Geometric parameters (Å, º)

Rh—C01	1.825 (10)	C2—C3	1.378 (10)
Rh—C02	1.826 (9)	C3—C4	1.362 (10)
Rh—O12	2.021 (5)	C3—H3	0.9300
Rh—O11	2.032 (5)	C4—C5	1.360 (12)
O11—C1	1.267 (9)	C4—H4	0.9300
O12—C2	1.324 (8)	C5—C6	1.388 (13)
C01—O01	1.139 (9)	C5—H5	0.9300
C02—O02	1.145 (9)	C6—C7	1.370 (11)
C1—C7	1.394 (10)	C6—H6	0.9300
C1—C2	1.467 (10)	C7—H7	0.9300
C01—Rh—C02	88.3 (4)	O12—C2—C3	118.2 (7)
O12—Rh—O11	79.4 (2)	O12—C2—C1	115.1 (7)
C01—Rh—O12	175.6 (3)	C3—C2—C1	126.7 (7)
C02—Rh—O12	96.1 (3)	O11—C1—C7	119.4 (7)
C01—Rh—O11	96.3 (3)	O11—C1—C2	116.1 (6)
C02—Rh—O11	175.2 (3)	C7—C1—C2	124.6 (7)
C1—O11—Rh	115.3 (5)	C5—C4—C3	129.8 (9)
C2—O12—Rh	114.0 (5)	C5—C4—H4	115.1
O02—C02—Rh	178.0 (9)	C3—C4—H4	115.1
C6—C7—C1	131.2 (8)	C4—C5—C6	126.9 (8)
C6—C7—H7	114.4	C4—C5—H5	116.5
C1—C7—H7	114.4	C6—C5—H5	116.5
C4—C3—C2	131.2 (8)	C7—C6—C5	129.5 (8)
C4—C3—H3	114.4	C7—C6—H6	115.2
C2—C3—H3	114.4	C5—C6—H6	115.2
O01—C01—Rh	178.8 (9)
C01—Rh—O11—C1	177.7 (6)	O11—C1—C2—C3	176.1 (8)
O12—Rh—O11—C1	−3.0 (5)	C7—C1—C2—C3	−3.8 (14)
C02—Rh—O12—C2	−176.5 (6)	O12—C2—C3—C4	179.2 (9)
O11—Rh—O12—C2	2.2 (5)	C1—C2—C3—C4	1.7 (16)
Rh—O11—C1—C7	−176.8 (6)	C2—C3—C4—C5	1.9 (18)
Rh—O11—C1—C2	3.3 (9)	C3—C4—C5—C6	−1.6 (17)
Rh—O12—C2—C3	−179.0 (6)	C4—C5—C6—C7	−1.8 (17)
Rh—O12—C2—C1	−1.2 (9)	C5—C6—C7—C1	2.4 (16)
O11—C1—C2—O12	−1.4 (11)	O11—C1—C7—C6	−178.7 (8)
C7—C1—C2—O12	178.7 (7)	C2—C1—C7—C6	1.2 (15)