CRYSTAL FIELD THEORY

What is meant by crystal field splitting energy? On the basis of crystal field theory, write the electronic configuration of d^(4) in terms of t_(2g) and e_(g) in an octahedral field when (i) Delta_(0)gtP (ii) Delta_(0)ltP

Electronic configuration of [Cu(NH_(3))_(6)]^(2+) on the basis of crystal field splitting theory is