Synthesis and Specific Features of the Molecular and Crystal Structures of Cp4Ru4(µ3-CO)4 Cluster

Tetranuclear cluster [Ru(μ₃-CO)Cp]₄ (I) is synthesized as a minor product in the thermal reaction of cyclopentadiene with Ru₃(CO)₁₂ aimed at preparing ruthenium dimer [Ru(CO)₂Cp]₂. The spectral (¹³С and ¹H NMR, IR) and structural studies are carried out for cluster I. Under different conditions, the crystallization of cluster I gives dark cherry-colored crystals of two types: cluster Ia and its tetrahydrate Ib. The structures of compounds Ia and Ib are determined by X-ray diffraction (XRD) (CIF files CCDC nos. 2241197 and 2241199, respectively). A comparative analysis of the cluster geometry shows that the distortion of the Ru₄(CO)₄ cage in compound I from the ideal T_d symmetry in the structure of the pure compound is due to anisotropy of intermolecular contacts in the crystal. Specific features of chemical binding in the [Ru(μ₃-CO)Cp]₄ cluster and its iron-containing analog are studied by DFT calculations using topological analysis of the electron density comparing the energy characteristics and effective force constants of binding interactions. A necessity to use criteria of elastic deformations of interatomic interactions (force constants) for the correction description of such structural chemical phenomena as structural nonrigidity of the cage in transition metal clusters is demonstrated.