(3-Methylbenzonitrile-1κN)-cis-tetrakis(μ-N-phenylacetamidato)-1:2κ4 N:O;1:2κ4 O:N-dirhodium(II)(Rh—Rh)

The complex molecule of the title compound, [Rh2{N(C6H5)COCH3}4(NCC7H7)], has crystallographically-imposed mirror symmetry. The four acetamide ligands bridging the dirhodium core are arranged in a 2,2-cis manner with two N atoms and two O atoms coordinating to the unique RhII atom cis to one another. The Neq—Rh—Rh—Oeq torsion angles on the acetamide bridge are 0.75 (7) and 1.99 (9)°. The axial nitrile ligand completes the distorted octahedral coordination sphere of one RhII atom and shows a nonlinear coordination, with an Rh—N—C bond angle of 162.8 (5)°; the N—C bond length is 1.154 (7) Å.

The complex molecule of the title compound, [Rh 2 {N(C 6 H 5 )COCH 3 } 4 (NCC 7 H 7 )], has crystallographicallyimposed mirror symmetry. The four acetamide ligands bridging the dirhodium core are arranged in a 2,2-cis manner with two N atoms and two O atoms coordinating to the unique Rh II atom cis to one another. The N eq -Rh-Rh-O eq torsion angles on the acetamide bridge are 0.75 (7) and 1.99 (9) . The axial nitrile ligand completes the distorted octahedral coordination sphere of one Rh II atom and shows a nonlinear coordination, with an Rh-N-C bond angle of 162.8 (5) ; the N-C bond length is 1.154 (7) Å .

Experimental
Crystal data [Rh 2 (C 8 H 8 NO) 4 (C 8  We thank Dr Lee Daniels of Rigaku Americas for his training on the Rigaku XtaLAB diffractometer and his extended help in the completion of the structural determination. Support was provided by a Start Up Grant from ETSU. We thank Johnson Matthey for their generous loan of rhodium trichloride.

S2.1. Synthesis and crystallization
Approximately 10mg of cis-tetrakis [µ-N-(phenyl)acetamidato]-κ 4 N:O;κ 4 O:N dirhodium(II)] was dissolved in 18 mL of dichloromethane. 4µL of neat 3-methyl benzonitrile and 2µL of acetone were then added to this solution via a gas-tight syringe turning the solution from forest green to dark blue. Crystals grew over a two week period via vapor diffusion. The second parameter on the SHELXL weighting line has a large value (7.37) which may arise from inadequacies in the absorption correction.

supporting information
The infrared absorption spectum of compound 1 showed bands at 2338 cm -1 and 2359 cm -1 attributable to carbon-nitrogen bond stretching modes. The corresponding band for uncomplexed 3-methylbenzonitrile appears at 2228 cm -1 . This indicates that there is a shortening of the carbon-nitrogen bond and a stronger σ-interaction with the rhodium metal compared to the π-back bonding which occurs upon complexation with trans-tetrakis [µ-N-(phenyl)

Figure 1
ORTEP of the title compound with 30% probability ellipsoids. Hydrogen atoms are drawn as small spheres.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.005 Δρ max = 0.75 e Å −3 Δρ min = −0.50 e Å −3 Special details Geometry. Compound 1 is coordinated by 3-methyl benzonitrile to only one axial site. In compounds 2 through 4 there are no methyl groups on the benzonitrile ligand and each of them has a benzonitrile ligand attached in each axial site. Like compound 1, compound 5 is coordinated by 3-methyl benzonitrile to only one axial site, however compound 5 exists as the trans-acetamide isomer, whereas compound 1 is the cis-acetamide isomer. The predominance of σ-bonding in the rhodium-nitrogen-carbon bond system (and lower affect of π-back bonding) is the likely cause of this deviation from linearity for compound 1, which has a similar rhodium-nitrogen-carbon angle as compound 5. The packing diagram shows that two acetamide phenyl rings on the same rhodium are stacked upon each other. Refinement. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 σ(F 2 ) is used only for calculating R-factor (gt).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (