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We would like to thank the ERC (EU FP7 Consolidator Grant 614290 “EXONMR”) and EPSRC for computational support through the Collaborative Computational Project on NMR Crystallography (CCP-NC), via EP/M022501/1 and EP/J010510/1. SEA would like to thank the Royal Society and the Wolfson Foundation for a merit award. The research data (and/or materials) supporting this publication can be accessed at DOI: 10.17630/d0b365a1-b647-4556-b6f8-24d99d0c7a8a. 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. Publisher PDF

The work in this project was supported by the Engineering and Physical Sciences Research Council (EPSRC). M.B. wishes to thank EaStCHEM and the University of St Andrews for support. 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(125Te,125Te) 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. Postprint