Observation of alkaline earth complexes M(CO)8 (M = Ca, Sr, or Ba) that mimic transition metals

Xuan Wu; Lili Zhao; Jiaye Jin; Sudip Pan; Wei Li; Xiaoyang Jin; Guanjun Wang; Mingfei Zhou; Gernot Frenking

doi:10.1126/science.aau0839

Observation of alkaline earth complexes M(CO)₈ (M = Ca, Sr, or Ba) that mimic transition metals

Science. 2018 Aug 31;361(6405):912-916. doi: 10.1126/science.aau0839.

Authors

Xuan Wu^#¹, Lili Zhao^#², Jiaye Jin¹, Sudip Pan², Wei Li¹, Xiaoyang Jin¹, Guanjun Wang¹, Mingfei Zhou³, Gernot Frenking^{4

5}

Affiliations

¹ Department of Chemistry, Collaborative Innovation Center of Chemistry for Energy Materials, Shanghai Key Laboratory of Molecular Catalysts and Innovative Materials, Fudan University, Shanghai 200433, China.
² Institute of Advanced Synthesis, School of Chemistry and Molecular Engineering, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing 211816, China.
³ Department of Chemistry, Collaborative Innovation Center of Chemistry for Energy Materials, Shanghai Key Laboratory of Molecular Catalysts and Innovative Materials, Fudan University, Shanghai 200433, China. mfzhou@fudan.edu.cn frenking@chemie.uni-marburg.de.
⁴ Institute of Advanced Synthesis, School of Chemistry and Molecular Engineering, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing 211816, China. mfzhou@fudan.edu.cn frenking@chemie.uni-marburg.de.
⁵ Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse, D-35043 Marburg, Germany.

^# Contributed equally.

PMID: 30166489
DOI: 10.1126/science.aau0839

Abstract

The alkaline earth metals calcium (Ca), strontium (Sr), and barium (Ba) typically engage in chemical bonding as classical main-group elements through their ns and np valence orbitals, where n is the principal quantum number. Here we report the isolation and spectroscopic characterization of eight-coordinate carbonyl complexes M(CO)₈ (where M = Ca, Sr, or Ba) in a low-temperature neon matrix. Analysis of the electronic structure of these cubic O_h -symmetric complexes reveals that the metal-carbon monoxide (CO) bonds arise mainly from [M(d_π)] → (CO)₈ π backdonation, which explains the strong observed red shift of the C-O stretching frequencies. The corresponding radical cation complexes were also prepared in gas phase and characterized by mass-selected infrared photodissociation spectroscopy, confirming adherence to the 18-electron rule more conventionally associated with transition metal chemistry.

Publication types

Research Support, Non-U.S. Gov't