Paula Sanz Camacho

Probing interactions through space using spin–spin coupling

The series of eight 5-(TeY)-6-(SePh)acenaphthenes (Y = Fp (2), Tol (3), An-p (4), An-o (5), Tp (6), Mes (7), Tip (8), Nap (9)) were prepared and structurally characterised by X-ray crystallography, solution and solid-state NMR spectroscopy and density functional theory (DFT/B3LYP) calculations. All members of the series, except 5, adopt a BA type configuration comparable to the parent compound 1 (Y = Ph), aligning the Te-C(Y) bond along the mean acenaphthene plane and promoting a nonbonded Se···Te-C(Y) 3c-4e type interaction to form to stabilise the molecule (G-dependence). 5 (Y = An-o) adopts a BC type conformation in the solid but DFT calculations show this optimises to BA. Indication of strong through-space peri-interactions between Te and Se are observed in the (77)Se and (125)Te NMR spectra, with J(Te,Se) spin-spin coupling constants (SSCCs) in the range -688 to -748 Hz. Evidence supporting the presence of this interaction was also found in solid-state NMR spectra of some of the compounds which exhibit an indirect spin-spin coupling on the same order of magnitude as observed in solution. In order to quantify the steric bulk of the aryl groups (Y), we introduce the crystallographic steric parameter (θ), the cone angle measured from the furthest H atoms lying on the edges of the cone to the Te atom located at its vertex. Modification to Y has no apparent influence over the conformation of the molecule, the degree of molecular distortion occurring in the acenaphthene backbone or the extent of 3c-4e interaction; peri-distances for all eight compounds are within 0.08 Å and no apparent correlation is observed between the steric bulk of Y (θ) and the (77)Se chemical shifts or J(Te,Se) SSCCs. In contrast, a good correlation is found between θ and (125)Te chemical shifts. DFT calculations performed on all members of the series confirm the comparable covalent bonding between Te and Se in the series, with WBIs of ca. 0.1 obtained. Natural bond orbital analysis shows a noticeable donor-acceptor interaction between a p-type lone pair on Se and a σ*(Te-C) antibonding orbital, confirming the onset of 3c-4e type bonding.

Conformational Dependence of Through‐Space Tellurium–Tellurium Spin–Spin Coupling in Peri‐Substituted Bis(Tellurides)

Three related series of peri-substituted bis(tellurides) bearing naphthalene, acenaphthene and acenaphthylene backbones (Nap/Acenap/Aceyl(TeY)2 (Nap = naphthalene-1,8-diyl N; Acenap = acenaphthene-5,6-diyl A; Aceyl = acenaphthylene-5,6-diyl Ay; Y = Ph 1; Fp 2; Tol 3; An-p- 4; An-o- 5; Tp 6; Mes 7; Tip 8) have been synthesised and their solid-state structures determined by X-ray crystallography. Molecular conformations were classified as a function of the two C9-C-Te-C(Y) dihedral angles (θ); in the solid all members adopt AB or CCt configurations, with larger Te(aryl) moieties exclusively imposing the CCt variant. Exceptionally large J((125)Te,(125)Te) spin-spin coupling constants between 3289-3848 Hz were obtained for compounds substituted by bulky Te(aryl) groups, implying these species are locked in a CCt-type conformation. In contrast, compounds incorporating smaller Te(aryl) moieties are predicted to be rather dynamic in solution and afford much smaller J values (2050-2676 Hz), characteristic of greater populations of AB conformers with lower couplings. This conformational dependence of through-space coupling is supported by DFT calculations.

Polymorphism, Weak Interactions and Phase Transitions in Chalcogen-Phosphorus Heterocycles

Abstract A series of P−E‐containing heterocycles (E=chalcogen) with aromatic backbones were synthesised and characterised by single‐crystal and powder XRD, microanalysis and mass spectrometry. Solution‐ and solid‐state 31P and 77Se NMR spectroscopy revealed significant differences between the NMR parameters in solution and in the solid state, related to conformational changes in the molecules. Many compounds were shown to exhibit a number of different polymorphic structures (identified by single‐crystal XRD), although the bulk material studied by solid‐state NMR spectroscopy often contained just one major polymorph. For the unoxidised heterocycles, the presence of weak intermolecular J couplings was also investigated by DFT calculations.