Metallophilic interactions in stacked dinuclear rhodium 2,2′-biimidazole carbonyl complexes

Non-covalent metallophilic interactions were studied by investigating the stacking of two neutral rhodium complexes [Rh-2(I)(R(2)bim)Cl-2(CO)(4)] (R = Et, ethyl or Pr, propyl) in the solid state. Both dinuclear complexes formed infinite arrays of square planar d(8) rhodium centres with intramolecular Rh center dot center dot center dot Rh distances of 3.1781(5) angstrom (R = Et) and 3.1469(3) angstrom (R = Pr) and the intermolecular Rh center dot center dot center dot Rh distances of 3.4345(6) angstrom (R = Et) and 3.4403(3) angstrom (R = Pr) between the adjacent molecules. The crystalline solids were stable and did not contain any solvent of crystallization. The effect of the metallophilic interactions on the absorption properties were studied using TD-DFT methods. The computational results indicate a red shift with a shortening Rh center dot center dot center dot Rh distance. Experimentally, bathochromic effects were also observed. The colour of the crystals was found to be dependent on the temperature, shape of the crystal, and the direction of the incoming light. The general appearance of the crystal was strongly affected by the linearly arranged metal atoms. Both crystalline materials had a metallic lustre typical of chain-like metal systems with metal-metal interactions.