Rationalizing polymorphism with local correlation-based methods: a case study of pnictogen molecular crystals

A computational workflow is proposed to quantify and rationalize the relative stability of different structures of molecular crystals using cluster models and quantum chemical methods. The Hartree-Fock plus London Dispersion (HFLD) scheme is used to estimate the lattice energy of molecular crystals in various structural arrangements. The fragment-pairwise Local Energy Decomposition (fp-LED) scheme is then employed to quantify the key intermolecular interactions responsible for the relative stability of different crystal structures. The fp-LED scheme provides also in-depth chemical insights by decomposing each interaction into energy components such as dispersion, electrostatics, and exchange. Notably, this analysis requires only a single interaction energy computation per structure on a suitable cluster model. As a case study, two polymorphs of each of the following are considered: naphthyl-substituted dipnictanes (with As, Sb, and Bi as the pnictogen atom) and tris(thiophen-2-yl)bismuthane. The approach outlined offers high accuracy as well as valuable insights for developing design principles to engineer crystal structures with tailored properties, opening up new avenues in the study of molecular aggregates, potentially impacting diverse fields in materials science and beyond.

Synthesis and Structural Studies of peri-Substituted Acenaphthenes with Tertiary Phosphine and Stibine Groups

Two mixed peri-substituted phosphine-chlorostibines, Acenap(PiPr2)(SbPhCl) and Acenap(PiPr2)(SbCl2) (Acenap = acenaphthene-5,6-diyl) reacted cleanly with Grignard reagents or nBuLi to give the corresponding tertiary phosphine-stibines Acenap(PiPr2)(SbRR') (R, R' = Me, iPr, nBu, Ph). In addition, the Pt(II) complex of the tertiary phosphine-stibine Acenap(PiPr2)(SbPh2) as well as the Mo(0) complex of Acenap(PiPr2)(SbMePh) were synthesised and characterised. Two of the phosphine-stibines and the two metal complexes were characterised by single-crystal X-ray diffraction. The peri-substituted species act as bidentate ligands through both P and Sb atoms, forming rather short Sb-metal bonds. The tertiary phosphine-stibines display through-space J(CP) couplings between the phosphorus atom and carbon atoms bonded directly to the Sb atom of up to 40 Hz. The sequestration of the P and Sb lone pairs results in much smaller corresponding J(CP) being observed in the metal complexes. QTAIM (Quantum Theory of Atoms in Molecules) and EDA-NOCV (Energy Decomposition Analysis employing Naturalised Orbitals for Chemical Valence) computational techniques were used to provide additional insight into a weak n(P)→σ*(Sb-C) intramolecular bonding interaction (pnictogen bond) in the phosphine-stibines.

Bisstibane-distibane conversion via consecutive single-electron oxidation and reduction reaction

peri-Substituted naphthalene complexes (Trip₂Pn)₂Naph (Pn = Sb 1, Bi 2) were synthesised and their redox behaviour investigated. Oxidation of 1 with [Fc][BAr^F] (BAr^F = B(C₆F₅)₄) yielded [(Trip₂Sb)(TripSb)Naph][BAr^F] (3) containing the stibane-coordinated stibenium cation [(Trip₂Sb)(TripSb)Naph]⁺. Subsequent reduction of 3 with KC₈ yielded distibane (TripSb)₂Naph (4). 1-4 were characterised by NMR (¹H, ¹³C) and IR spectroscopy as well as single-crystal X-ray diffraction (sc-XRD), while their electronic structures were analysed by quantum chemical computations.