On the Molecular and Electronic Structures of AsP₃ and P ₄

The molecular and electronic structures of AsP₃ and P ₄ have been investigated. Gas-phase electron diffraction studies of AsP₃ have provided r_g bond lengths of 2.3041(12) and 2.1949(28) Å for the As-P interatomic distances and the P-P interatomic distances, respectively. The gas-phase electron diffraction structure of P ₄ has been redetermined and provides an updated value of 2.1994(3) Å for the P-P interatomic distances, reconciling conflicting literature values. Gas-phase photoelectron spectroscopy provides experimental values for the energies of ionizations from the valence molecular orbitals of AsP ₃ and P₄ and shows that electronically AsP₃ and P₄ are quite similar. Solid-state ⁷⁵As and ³¹P NMR spectroscopy demonstrate the plastic nature of AsP₃ and P ₄ as solids, and an extreme upfield ⁷⁵As chemical shift has been confirmed for the As atom in AsP₃. Finally, quantum chemical gauge-including magnetically induced current calculations show that AsP ₃ and P₄ can accurately be described as strongly aromatic. Together these data provide a cohesive description of the molecular and electronic properties of these two tetraatomic molecules.