How Strong is a Reverse Dative Bond? Compliance Constants as Unique Bond Strength Descriptors

Area of Science:

• Computational Chemistry
• Inorganic Chemistry
• Physical Chemistry

Background:

• Bond strength and bond order are fundamental chemical concepts.
• Quantifying local mechanical bond strengths in large molecules presents significant challenges.
• Previous studies on {FeNO}¹⁰ complexes have explored metal-ligand interactions.

Purpose of the Study:

• To evaluate the strength of a (reverse) dative Fe···B bond in a synthesized low-spin {FeNO}¹⁰ complex.
• To critically assess the reliability of computational methods used for determining mechanical bond strengths, specifically force constants.

Main Methods:

• Analysis of a synthesized low-spin {FeNO}¹⁰ complex featuring an ambiphilic trisphosphineborane ligand.
• Examination of the Fe-B force constant derived from spectroscopic and electronic structure calculations.
• Investigation of potential numerical ambiguities in rigid real-space force constant calculations.

Main Results:

• A strong (reverse) dative Fe···B bond was previously reported for the complex.
• A high Fe-B force constant (1.56 mdyn/Å) was a key criterion for this conclusion.
• Potential numerical ambiguities in calculating rigid real-space force constants may affect the accuracy of this value.

Conclusions:

• The reported high Fe-B force constant might be subject to computational artifacts.
• This potential flaw in force constant calculations could impact numerous studies combining spectroscopy and electronic structure.
• Further investigation is needed to validate mechanical bond strength measurements in complex molecular systems.