The average Rh-CO bond distance in [(n6 C6H6)Rh(CO)2]+
is 1.88 Å, while [Rh(CO)4]+ has an average
Rh-CO bond distance of 1.95 Å. Is the longer Rh-CO distance in [Rh(CO)4]+ consistent with what the IR
stretching frequencies are telling you? Discuss.
Carbonyl stretching peaks generally fall between 1900 and 1600 cm-1 (assume all peak positions hereafter are in wavenumber units), a relatively unique part of the IR spectrum. This area is sometimes referred to as the carbonyl stretching region as a result.