Question

3. Consider the trigonal bipyramidal complex Fe(CO)4(PPh3) (Note: PPh3 is triphenylphosphine, P(C6H5)3. For symmetry purposes you can ignore the phenyl groups) a) Draw the two possible isomers for this complex and determine the point group for each. b) Consider IR data for one of the possible structures: Vco = 2052, 1978, and 1945 cm-1. Can this data be used to determine which of the two structures you drew in "a" is the correct structure? Determine the number of IR-active stretching modes you would expect for each in order to support your answer.

Answer 1

Ans. 3(b) Stretching frequency for 'co' ligand terminal co (M-co) Frequency (cm) Ico - M-co 2120-1850 enil 'co' is connected with only one metal bridging co (M2-co) (1) 1850 - 1750cm мм is connected with when to two metals (7) bridging co (Mg-co). 1730 - 1600 cut when 'col is connected with three metals Vco = 2052 ani, 1978 cm and 1945 ant can be used to determine which type of co' ligand is present in molecule [ see table above] - Fe (60), (PPhy) contains all terminal 'col ligands, which is pooved from above data. Felo) u PPhy, where P Phz is at axial position - Tre (Co), PPhy, where | PPhz is at equitorial Molecule D position IR 4 bands 3 bands A bands