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Download file# Multimetallocenes. A Theoretical Study

journal contribution

posted on 02.04.2020, 15:48 by Alejandro Velazquez, Israel Fernández, Gernot Frenking, Gabriel MerinoQuantum chemical calculations using gradient-corrected density functional theory at the BP86 level in
conjunction with TZ2P basis sets have been carried out for the multimetallocenes CpM

*Cp, where M = Be, Mg, Ca, and Zn with*_{n}*n*= 2−5. The equilibrium geometries and energetics with respect to loss of one metal atom are theoretically predicted. The nature of the metal−ligand interactions between the M_{n}^{2+}and (Cp^{-})_{2}moieties was investigated with energy decomposition analysis (EDA). The calculations predict that the CpM*Cp species with*_{n}*n*> 2 are thermodynamically unstable with respect to loss of one metal atom except for the beryllium compounds. The beryllocenes exhibit unusual stabilities in the gas phase for the whole series CpBe*Cp up to*_{n}*n*= 5. The calculations suggest that the energy for loss of one metal atom from CpBe_{2}Cp is significantly higher than from CpZn_{2}Cp. The energy for the metal extrusion reaction of CpBe_{3}Cp is much less endothermic than for CpBe_{2}Cp but it is still more endothermic than the reaction of CpZn_{2}Cp. The thermodynamic stability of the higher members CpBe_{4}Cp and CpBe_{5}Cp toward loss of one metal atom is only slightly less than for CpBe_{3}Cp, while the other multimetallocenes, CpM_{3}Cp, CpM_{4}Cp, and CpM_{5}Cp (M = Mg, Ca, Zn), possess little extra stabilization with respect to the dimetallocenes. The calculated reaction energies which include the heats of sublimation of the metals indicate that CpBe_{2}Cp might become isolated in the condensed phase, while the prospect for CpCa_{2}Cp and CpMg_{2}Cp and for the higher members CpM_{3}Cp, CpM_{4}Cp, and CpM_{5}Cp is less likely. The analysis of the metal−ligand bonding in CpM*Cp using the EDA method suggests that the interactions between M*_{n}_{n}^{2+}and (Cp^{-})_{2}have a larger electrostatic than covalent character. The beryllocenes are more covalently bonded than the other multimetallocenes. The orbital interactions in the lower members of CpM*Cp come mainly from π orbitals, but the σ contribution continuously increases when*_{n}*n*becomes larger and eventually may become stronger than the π contributions, which become weaker in the higher members of the series.## History

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CpBe 5 Cpmembers CpBe 4 Cpmembers CpM 3 Cpmetal atomTZ 2P basis setsmultimetallocenes CpM n CpCpBe 2 CpCpZn 2 Cpseries CpBe n CpCpM n Cp speciesCpM 4 CpCpMg 2 Cpmetal extrusion reactionCpCa 2 CpCpBe 3 CpTheoretical Study Quantum chemical calculationsEDACpM n CpCpM 3 Cpenergy decomposition analysisCpM 5 CpBP 86 level