Peculiar transformations in the C _xH _xP _4-x (x = 0-4) series

In the current work, we performed a systematic study of the C _xH _xP _4-x (x = 0-4) series using an unbiased CK global minimum and low-lying isomers search for the singlet and triplet P ₄-C ₄H ₄ species at the B3LYP/6-31G** level of theory. The selected lowest isomers were recalculated at the CCSD(T)/CBS//B3LYP/6-311++G** level of theory. We found that the transition from a three-dimensional tetrahedron-like structure to a planar structure occurs at x = 3, where planar isomers become much more stable than the tetrahedral structures due to significantly stronger π bonds between carbon atoms in addition to increasing strain energy at the carbon atom in the tetrahedral environment.