David J. Wolstenholme

Understanding the Electronic Structure, Reactivity, and Hydrogen Bonding for a 1,2-Diphosphonium Dication

The experimental charge density for hexamethyldiphosphonium ditriflate has been determined from low-temperature high-resolution X-ray diffraction data. These results have been compared with theoretically calculated values for the isolated gas-phase compound. Analysis of the topological and atomic basin properties has provided insight into the exact nature of the P-P bond in both the crystalline and the gas-phase structures. The rho(b)(r) and nabla2rho(b)(r) values highlight the covalent nature of the P-P bond, while the atomic charges indicate a localization of the positive charges on the two phosphorus atoms. This seems to indicate that a covalent bond is formed despite a strong electrostatic repulsion between these two heteroatoms. The topological properties and electrostatic potentials have also been shown to provide significant insight into the chemical reactivity of the title compound. A topological analysis of P2Me4, P2Me5(+), and P2Me6(+2) species has provided information about the progression of the P-P bond in the synthesis of the title compound. An investigation of the different hydrogen-bonding networks present in the crystalline and gas-phase structures, along with their affect on the electronic structure of the title compound has also been investigated. This has all led to significant new insight into the electronic structure, reactivity, and weak hydrogen bonding in prototypical 1,2-diphosphonium dications.

Investigation of I⋯S interactions by charge density studies

Crystals of S2I4 (AsF6)2 and CHI3 (S8)3 have been examined with charge density studies. The conventional structure of S2I4 (AsF6)2 and the theory of the bonding of the S2I4 2+ cation has already been published [1]. Here the S-S bond order of 2.4 was claimed to be the highest bond order known between heavy main-group elements and the structure of the cation was constructed to maximise ( bonding. There are also a multitude of I ...F and S ...F weak-interaction contacts in S2I4 (AsF6)2. The topological analysis largely confirms the theoretical studies on the S2I4 2+ cation and examines and categorises the long range contacts to F. The structure of CHI3 (S8)3 was examined [2] many years ago, the structure is in the trigonal space group R3m with the CHI3 group on the three-fold axis (C3v) and the S8 rings across the respective three mirror planes so that the structure actually contains only 8 unique atoms (C, H, I and five sulfur atoms). It was originally claimed that in the weak I ....S interactions that hold the structure together, the sulfur was the donor, the iodine the acceptor. The topological analysis suggests differently with the bond critical points (BCP) suggesting that the iodine is the donor. All the BCPs for the weak interactions, and the ring BCP for the S8 ring have been detected and characterised. They fall within the expected range of locations and values.