What is synergic bonding , Bonding in metal Carbonyl , Bond order of M-C and C-O in synergic Bond

(1) Stretching frequency of CO is inversely proportional to negative oxidation state of central metal atom

(2) Extent of back bonding or back acceptance is directly proportional to negative oxidation state of central metal atom.

(3) M-C bond order is directly proportional to negative oxidation state of central metal atom

(4) C-O bond order is inversely proportional to negative oxidation state of central metal atom.

(5) d C-O bond length is directly proportional to negative oxidation state of central metal atom.

(6) Bond energy of C-O bond is inversely proportional to negative oxidation state of central metal atom 

What is synergic bonding ?

Related Questions;

(1) What is stretching frequency of C-O bond in carbonyl Complexes?

(2) What type of ligands are known ?

(3) What are pi-donors ligands give the examples?

(4) What are pi-acceptors ligands give the examples?

(5) What are sigma-donors ligands give the examples?