Journal article
Direct measurement of covalent three-center, two-electron M–H–B bonding in Zr and Hf borohydrides using B K-edge XAS
Chemical science (Cambridge), Vol.16(47), pp.22333-22347
2025
DOI: 10.1039/D5SC06254C
PMCID: PMC12570076
PMID: 41170516
Appears in UI Libraries Support Open Access
Abstract
Metal borohydride complexes have long been the subject of intense fundamental interest because of their unconventional metal–ligand bonding that occurs via three-center, two-electron M–H–B bonds. This type of bonding implies significant delocalization of electron density over all three atoms, but the degree of orbital mixing between the metal and boron has been difficult to assess by direct experimental means. Herein, we demonstrate how ligand K-edge X-ray absorption spectroscopy (XAS) conducted at the B K-edge yields evidence of significant covalent M–H–B bonding with Zr and Hf. To accommodate the B K-edge XAS studies, which were conducted under ultra-high vacuum (<10 −8 torr), we prepared a series of new [Zr(RBH 3 ) 4 ] and [Hf(RBH 3 ) 4 ] complexes with substituents that attenuate volatility (R = benzyl, phenyl, mesityl, 2,4,6-triisopropylphenyl, and anthryl). 1 H and 11 B NMR spectroscopy, IR spectroscopy, and single-crystal X-ray diffraction (XRD) studies revealed metal and ligand dependent differences in the BH 3 chemical shifts that correlate to changes in M−B distances and select B–H vibrational stretching modes. The B K-edge XAS spectra of the Zr and Hf complexes yielded a pre-edge feature that was assigned as B 1s → M–H–B π* based on comparison to time-dependent density functional theory (TDDFT) calculations. The pre-edge transitions appear due to covalent mixing between boron and the metal, thereby demonstrating how B K-edge XAS can provide direct evidence of covalent three-center, two electron M–H–B bonding in borohydride complexes using boron as a spectroscopic reporter.
Details
- Title: Subtitle
- Direct measurement of covalent three-center, two-electron M–H–B bonding in Zr and Hf borohydrides using B K-edge XAS
- Creators
- Hannah M. Hansen - The University of Iowa, Department of Chemistry, E331 Chemistry Building, Iowa City, Iowa 52242, USAJoshua C. Zgrabik - University of IowaPeter A. Zacher - University of IowaJacob J. Schuely - University of IowaEmily M. Amano - Colgate UniversityMai Yer Yang - The University of Iowa, Department of Chemistry, E331 Chemistry Building, Iowa City, Iowa 52242, USADaniel K. Unruh - University of IowaLucia Zuin - Canadian Light Source (Canada)Jason M. Keith - Colgate UniversityScott R. Daly - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Chemical science (Cambridge), Vol.16(47), pp.22333-22347
- DOI
- 10.1039/D5SC06254C
- PMID
- 41170516
- PMCID
- PMC12570076
- NLM abbreviation
- Chem Sci
- ISSN
- 2041-6520
- eISSN
- 2041-6539
- Publisher
- Royal Society of Chemistry
- Grant note
- NSF: CHE-1828117, CHE-2017828, CHE-2247235 Laboratory Directed Research and Development (LDRD) program of Los Alamos National Laboratory: 20220518MFR NNSA: DE-NA0004151 National Science Foundation: OAC-2346664
HMH, PAZ, JJS, and SRD were supported by the NNSA under award DE-NA0004151. JCZ and SRD also thank the Laboratory Directed Research and Development (LDRD) program of Los Alamos National Laboratory under project number 20220518MFR for funding preliminary data collection efforts at the Canadian Light Source (CLS). MYY thanks the NSF for support (CHE-2247235). EMA and JMK thank the National Science Foundation (OAC-2346664) for the purchase of an upgraded supercomputer at Colgate University, which supported this work. XRD data were collected using the instrument supported by NSF CHE-1828117. Some of the NMR data were collected using the instrument supported by NSF CHE-2017828. We thank Benj Revis for preparing thick-walled glass ampules used to ship samples to CLS. Part of the research described in this paper was performed using beamline VLS-PGM at the Canadian Light Source, a national research facility of the University of Saskatchewan, which is supported by the Canada Foundation for Innovation (CFI), the Natural Sciences and Engineering Research Council (NSERC), the National Research Council (NRC), the Canadian Institutes of Health Research (CIHR), the Government of Saskatchewan, and the University of Saskatchewan.
- Language
- English
- Electronic publication date
- 10/29/2025
- Date published
- 2025
- Academic Unit
- Core Research Facilities; Chemistry
- Record Identifier
- 9985024147002771
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