PCCP and its isomers: a theoretical studyElectronic Supplementary Information available. See http://www.rsc.org/suppdata/cp/b1/b106927f/

Abstract

Structural and electronic features of the linear 1,4-diphosphabutadiyne PC–CP and its rhombic isomer were explored using ab initio quantum chemical methods. Portions of the lower-lying [C2P2] potential energy surfaces of both neutral and ionized states were constructed. Geometries, rotational constants, vibrational frequencies, proton affinities and heats of formation of the ground state planar structures were determined using B3LYP and CCSD(T) computations. The vertical excitation and ionization energies were evaluated using the equation of motion EOM-CCSD. Atomic basis sets of different qualities ranging from 6-311++G(d,p) to aug-cc-pV6Z, were employed. Some thermochemical parameters were evaluated as follows: heat of formation at 0 K ΔfH0(PCCP) = 413 ± 8 kJ/mol−1, adiabatic ionization energy IEa(PCCP) = 9.6 ± 0.2 eV, proton affinity PA(PCCP) = 715 ± 8 kJ mol−1. The heats of formation at 0 K of relevant species are: ΔfH0(CP) = 510 kJ mol−1 and ΔfH0(HCP) = 225 kJ mol−1, and the dissociation energies, De(H–CP) = 501 kJ mol−1 and De(PC–CP) = 606 kJ mol−1, with expected errors of ±10 kJ mol−1.