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Preference for bridging versus terminal ligands in magnesium dimers

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Abstract

Magnesium dimers play important roles in inorganic and organometallic chemistry. This study evaluates the inherent bridging ability of a range of different ligands in magnesium dimers. In the first part, the Cambridge Structural Database is interrogated to establish the frequency of different types of ligands found in bridging versus terminal positions in two key structural motifs: one in which there are two bridging ligands (the D 2h “Mg2(μ-X2)” structure); the other in which there are three bridging ligands (the C 3v “Mg2(μ-X3)” structure). The most striking finding from the database search is the overwhelming preference for magnesium dimers possessing two bridging ligands. The most common bridging ligands are C-, N-, and O-based. In the second part, DFT calculations (at the B3LYP/6-311+G(d) level of theory) are carried out to examine a wider range of structural types for dimers consisting of the stoichiometries Mg2Cl3R and Mg2Cl2R2, where R = CH3, SiH3, NH2, PH2, OH, SH, CH2CH3, CH=CH2, C≡CH, Ph, OAc, F and Br. Consistent with the database search, the most stable magnesium dimers are those that contain two bridging ligands. Furthermore, it was demonstrated that the electronic effect of the bridging ligands is important in influencing the stability of the magnesium dimers. The preference for a bridging ligand, which reflects its ability to stabilize a magnesium dimer, follows the order: OH > NH2 > C≡CH > SH > Ph > Br > PH2 = CH=CH2 > CH2CH3 > CH3 > SiH3. Finally, the role that the ether solvent Me2O has on the stability of isomeric Mg2Cl2Me2 dimers was studied. It was found that the first solvent molecule stabilizes the dimers, while the second solvent molecule can either have a stabilizing or destabilizing effect, depending on the isomer structure.

A combination of database examination and DFT calculations reveals insights into the preferred number and type of bridging ligand in magnesium dimer

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Acknowledgments

We thank the Australian Research Council for financial support via Grant# DP0558430 and Victorian Institute for Chemical Sciences for the Chemical Sciences High Performance Computing Facility. We thank Associate Professor Brendan Abrahams for helping to search the Inorganic Crystal Structure Database.

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Authors and Affiliations

  1. School of Chemistry, The University of Melbourne, Melbourne, Victoria, 3010, Australia

    Hadi Lioe, Jonathan M. White & Richard A. J. O’Hair

  2. Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Melbourne, Victoria, 3010, Australia

    Hadi Lioe, Jonathan M. White & Richard A. J. O’Hair

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  1. Hadi Lioe
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  2. Jonathan M. White
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  3. Richard A. J. O’Hair
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Correspondence to Richard A. J. O’Hair.

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Lioe, H., White, J.M. & O’Hair, R.A.J. Preference for bridging versus terminal ligands in magnesium dimers. J Mol Model 17, 1325–1334 (2011). https://doi.org/10.1007/s00894-010-0834-1

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  • DOI: https://doi.org/10.1007/s00894-010-0834-1

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