Spacer separated donor-acceptor complexes [D→C6F4→BF3] (D = Xe, CO, N2) and the dication [Xe→C6F4←Xe]2+. A theoretical study.

Quantum chemical calculations using density functional theory at the BP86/TZ2P+ level and ab initio calculations at MP2/def2-TZVPP have been carried out for the donor-acceptor complexes [D→C(6)F(4)→BF(3)] (D = Xe, CO, N(2),) and the dication [Xe→C(6)F(4)←Xe](2+). The calculations predict rather short D→C(6)F(4)(BF(3)) and (D)C(6)F(4)→BF(3) bonds in the neutral systems which indicate rather strong binding interactions. The calculated partial charges which give large positive values for the donor moieties and negative values for the acceptor fragments and the large bond indices also suggest very strong donor-acceptor interactions D→C(6)F(4)→BF(3) and Xe→C(6)F(4)(2+)←Xe. An energy decomposition analysis suggests very strong intrinsic interactions for both systems. The donor-acceptor bonds in [D→C(6)F(4)→BF(3)] are much stronger than the direct donor-acceptor interactions D→BF(3) which are only weakly bonded van der Waals complexes. The calculated donor-acceptor interactions D→C(6)F(4)(BF(3)) are 26.1 kcal/mol for D = Xe, 121.5 kcal/mol for D = CO, and 86.9 kcal/mol for D = N(2). The strength of the intrinsic (D)C(6)F(4)→BF(3) interactions are calculated to be between 51.1-51.6 kcal/mol. The theoretical bond dissociation energies for the decomposition of [D→C(6)F(4)→BF(3)] yielding D + C(6)F(4) + BF(3) suggests that the xenon compound [Xe→C(6)F(4)→BF(3)] is metastable but may become stabilized in the condensed phase by intermolecular interactions. The complexes [OC→C(6)F(4)→BF(3)] and [N(2)→C(6)F(4)→BF(3)] are predicted to be thermodynamically stable. It is suggested that the above adducts are examples of spacer-separated donor-acceptor complexes [D→S→A] which are a hitherto unrecognized class of molecules.