TY - JOUR
T1 - Measuring the Magnetic Anisotropy of Metal-Metal Multiple Bonds
T2 - The Importance of Correcting for Ligand Effects
AU - Lastowski, R. Joseph
AU - Vogiatzis, Konstantinos D.
AU - Girolami, Gregory S.
N1 - G.S.G. thanks the National Science Foundation under Grant CHE 19-54745 for support of this research and the School of Chemical Sciences of the University of Illinois for computational resources.
PY - 2024/8/26
Y1 - 2024/8/26
N2 - We describe the synthesis and characterization of the quadruply-bonded dimer Mo2(CH2NMe2BH3)4 in which each molybdenum(II) center is bound to two chelating boranatodimethylaminomethyl (BDAM) ligands. The BDAM anions bind to the metal at one end by a metal-carbon σ bond and at the other by a three-center M-H-B interaction. Each BDAM ligand chelates to a single Mo atom so that the metal-metal bond is unbridged; the Mo-Mo distance is 2.114(2) Å. Structural and solution NMR data, analyzed via McConnell’s equation and supported by DFT calculations, show that the magnetic anisotropies associated with highly polarizable and π-bonding ligands (such as chloride groups and aryl rings) can greatly affect the NMR chemical shifts of reporter groups, so that ignoring their contributions leads to significant overestimates of the anisotropy due just to the metal-metal bond. We propose a method to quantify and correct for the magnetic anisotropy effects arising from the ligands. Application of this method to Mo2(BDAM)4 indicates that the magnetic anisotropy of the Mo-Mo quadruple bond in this molecule is about −800 × 10-36 m3 molecule-1. Anisotropies significantly higher than this value (as sometimes reported in the prior literature) are most likely incorrect.
AB - We describe the synthesis and characterization of the quadruply-bonded dimer Mo2(CH2NMe2BH3)4 in which each molybdenum(II) center is bound to two chelating boranatodimethylaminomethyl (BDAM) ligands. The BDAM anions bind to the metal at one end by a metal-carbon σ bond and at the other by a three-center M-H-B interaction. Each BDAM ligand chelates to a single Mo atom so that the metal-metal bond is unbridged; the Mo-Mo distance is 2.114(2) Å. Structural and solution NMR data, analyzed via McConnell’s equation and supported by DFT calculations, show that the magnetic anisotropies associated with highly polarizable and π-bonding ligands (such as chloride groups and aryl rings) can greatly affect the NMR chemical shifts of reporter groups, so that ignoring their contributions leads to significant overestimates of the anisotropy due just to the metal-metal bond. We propose a method to quantify and correct for the magnetic anisotropy effects arising from the ligands. Application of this method to Mo2(BDAM)4 indicates that the magnetic anisotropy of the Mo-Mo quadruple bond in this molecule is about −800 × 10-36 m3 molecule-1. Anisotropies significantly higher than this value (as sometimes reported in the prior literature) are most likely incorrect.
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U2 - 10.1021/acs.inorgchem.4c02329
DO - 10.1021/acs.inorgchem.4c02329
M3 - Article
C2 - 39141829
AN - SCOPUS:85201428272
SN - 0020-1669
VL - 63
SP - 15546
EP - 15556
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 34
ER -