i need help with the inorganic chemistry question

(Q7) The pseudo-C3v complex, [Ni(CO)3L], is shown below. This complex is used to measure the socalled Tolman electronic parameter of a given ligand. When triphenylphosphine is coordinated to this complex (i.e. L=PPh3), the measured v(CO)=2068.9cm1. Given that the v(CO) of free carbon monoxide is 2143cm1, state and explain whether PPh3 is considered an electron donating or withdrawing ligand