Multiple Weak C-H Intramolecular Hydrogen Bonding as an Aid to Minimizing Bond Rotation Flexibility

The presence of 14 intramolecular interactions relevant to bond rotational flexibility in coordination compounds important in the context of crystal engineering were identified by density functional theory calculations in the crystal structure of the highly crystalline oxoimido complex [Mo(NC6H4CMe3-2)(O)-Cl-2(bipy)] (1). A combination of computational techniques including noncovalent interaction index properties and Quantum Theory of Atoms analysis which are based on the computed electron density as well as natural bond orbitals analysis, were used to uncover the nature of the interactions. Wealdy stabilizing intramolecular interactions involving electrostatic contributions were found for O center dot center dot center dot center dot HC, N center dot center dot center dot center dot HC, and CH center dot center dot center dot center dot HC, close separations involving the bipy ligand where coordination does not allow flexibility and for O center dot center dot center dot center dot HC, N center dot center dot center dot center dot HC, Cl center dot center dot center dot center dot HC, CH center dot center dot center dot center dot HC, and C center dot center dot center dot center dot HC close contacts where C-N and C-C rotations of the imido ligand would allow flexibility. Partial covalency is not a significant feature of these interactions. The inclusion of up to two molecules of CH2Cl2 solvate molecules in the structure does not affect the structural parameters. Overall, this work shows that including electronegative atoms in a structure to which multiple intramolecular weak C-H hydrogen bonding interactions can develop has the potential to prevent rotational flexibility in coordination compounds. This observation could be important in a variety of crystal engineering situations.