Tetrapositive Hafnium-Diamide Complexes in the Gas Phase: Formation, Structure and Reaction
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J. Am. Soc. Mass Spectrom. (2019) DOI: 10.1007/s13361-019-02328-x
RESEARCH ARTICLE
Tetrapositive Hafnium-Diamide Complexes in the Gas Phase: Formation, Structure and Reaction Xiuting Chen,1,2 Yu Gong1 1
Department of Radiochemistry, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, 201800, China School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing, 100049, China
2
Abstract. Tetrapositive hafnium complexes in the form of Hf(TMPDA)34+ and Hf(TMOGA)34+ were produced by ESI of acetonitrile solutions of Hf(ClO4)4/TMPDA and Hf(ClO4)4/TMOGA respectively. Analogous Hf(TMGA) 3 4 + and Hf(TMTDA)34+ were not observed when the Hf(ClO4)4/TMGA and Hf(ClO4)4/TMTDA solutions were subjected to ESI under similar conditions. Geometry optimizations on these four tetrapositive complexes revealed that the Hf(TMPDA)34+ and Hf(TMOGA)34+ complexes possess C3 and D3 geometries respectively with the Hf4+ center coordinated by nine atoms. Similar geometries were found for Hf(TMGA)34+ and Hf(TMTDA)34+, but both are sixcoordinate complexes, which should account for their absence in the gas phase. In addition, no tetrapositive hafnium ion was observed when methanol was used as a solvent instead of acetonitrile. The much stronger affinity of Cl− toward Hf4+ than ClO4− should be the reason why tetrapositive hafnium ions were not observed when HfCl4 was used as the hafnium source. CID of the Hf(TMPDA)34+ and Hf(TMOGA)34+ complexes resulted in the formation of Hf(TMPDA)(TMPDA-H)3+ and Hf(TMOGA)(TMOGA-H)3+ respectively as the major products. The most stable structures of both tripositive hafnium products arise from the deprotonation of CH3 cis to Ocarbonyl, and the Hf(IV) center in both cases is six coordinate. Compared with the loss of protonated ligand observed in the experiments, it is much higher in energy for either Hf(TMPDA)34+ or Hf(TMOGA)34+ to lose neutral or cationic ligand on the basis of DFT calculations. Keywords: Tetracation, Hafnium, Diamide, Formation, Gas phase Received: 22 June 2019/Revised: 13 August 2019/Accepted: 15 August 2019
Introduction
M
ultiply charged metal cations especially tripositive and tetrapositive ions are prevalent species in solution and solid state chemistry [1, 2], but the chemistry of these highly charged cations in the gas phase is limited due to the fact that the 3rd and 4th ionization energies (IEs) of most metals lie above the IEs of common neutral ligands. As a result, charge reduction through coulomb explosion usually occurs when complexes of
Electronic supplementary material The online version of this article (https:// doi.org/10.1007/s13361-019-02328-x) contains supplementary material, which is available to authorized users. Correspondence to: Yu Gong; e-mail: [email protected]
M3+ and M4+ are transferred into the gas phase [3, 4]. In spite of the challenges, several techniques [4], such as charge-stripping, electron ionization, and electrospray ionization (ESI), have been employed to produce a series of complexes of M3+ lig
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