University:
Arizona State University
Course:
CHM 101 | Introductory Chemistry
Academic year:

2021
Views:

492

Pages:

4
Author:

Prince Sampson

π acceptor ligands - back bonding ligands Halides have filled π orbitals: Can donate π electron density to the metal Other types of ligands have empty π orbitals which can accept electron density from the metal (need to have similar energy as d orbitals for overlap) Also require σ donation from ligand to empty metal orbitals (i.e. normal dative σ bond) Carbon monoxide or carbonyl, CO, is a good π acceptor ligand Bonding in M-CO complex dative σ bond with CO acting as Lewis base (donating electrons) σ donation M <- C=O empty metal σ orbital filled CO metal σ orbital donation of electron density from filled metal d orbital to empty π orbital of CO acting as Lewis acid π donation M -> C=O empty CO metal π orbital (LUMO) filled metal π type d orbital Metal and CO are both Lewis bases (electron donors) and Lewis acids (electron acceptors) M <- CO σ bonding M -> CO π bonding Back bonding/synergistic bonding: involves back donation of e- density from metal -> carbonyl Synergistic σ bonding strengthens π bonding and vice versa σ donation of σ electron density from the CO tends to make it more +ve, enhancing its ability to accept electron density via π available electron density at metal π donation from metal → CO to make CO more -ve increasing its basicity (i.e σ donor ability) MO description of back-bonding in [ML 6 ] n+ complex σ bonding is as described previously π bonding due to overlap of filled metal d - orbitals of π symmetry and empty ligand π* orbitals Bonding overlap of metal d xy with two CO π* orbitals along x axis