Nucleus-independent chemical shift analysis of the electronic states of the (CO)4, (CS)4, and (CSe)4 molecules.

ABSTRACT

NICS(1) calculations have been performed on the 8π and 10π singlet states and the 9π triplet state of (CO)4, (CS)4, and (CSe)4. The results show that transfer of electrons from the b2g σ MO into the a2u π MO decreases the NICS(1) value, indicating an increase in the diamagnetic ring current. The decreases in the calculated NICS(1) values are substantially larger in (CO)4 than in (CS)4 or (CSe)4. This finding is rationalized by the larger coefficients on the carbons in the a2u MO of (CO)4 than in the a2u MOs of (CS)4 and (CSe)4.