Question

why 1st transition series complexes are mainly high spin while 3rd and 2nd series are low​

Answer 1

Answer:

There is more room for two electrons in one orbital, with less repulsion.

Answer 2

1st transition series complexes are mainly high spins while 3rd and 2nd transition series are low spins due to the high CFSE of 3rd and 2nd transition series.

• The order of CFSE of 1st, 2nd and 3rd transition series elements is 5d>4d>3d.
• Hence 1st transition series elements have a low CFSE and high pairing energy and hence form low spin complexes.
• Again 2nd and 3rd transition series elements have a high CFSE and low pairing energy once it forms high spin complexes.