The Role of Weak Interactions in Strong Intermolecular M···Cl Complexes of Coinage Metal Pyrazolates: Spectroscopic and DFT Study

The nondestructive reversible complexation of the macrocyclic group 11 metal pyrazolates {[3,5-(CF₃)₂Pz]­M}₃ (M = Cu­(I), Ag­(I)) to the halogen atom X = Cl, Br of η³-allyliron tricarbonyl halides (η³-2-R-C₃H₄)­Fe­(CO)₃X is revealed by the variable-temperature spectroscopic (IR, NMR) study combined with density functional theory calculations. The composition of all complexes at room temperature is determined as 1:1. In the case of the [AgL]₃ macrocycle, complexes 1:2 are observed at low temperature (<260 K). The complex’s stability depends on the substituents in the allyl fragment and halide ligand as well as on the metal atom (Ag­(I), Cu­(I)) in the macrocycle. For bulky substituents (Me and Ph) the endo/exo equilibrium of the parent (η³-2-R-C₃H₄)­Fe­(CO)₃X shifts upon the complex formation in favor of the exo isomer due to additional noncovalent interactions of the substituent with macrocycle