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X-ray structural analysis of bis(guanidinium) disodium hypodiphosphate heptahydrate, (CH 6 N 3 ) 2 Na 2 (P 2 O 6 )·7H 2 O revealed close Na + ...guanidinium [Na...N 3.0366 (6) Å] and water...guanidinium O-H...N [H...N 2.07 Å, O...N 3.0401 (9) Å] contacts, the nature of which is explored with the use of electron density distribution and Hirshfeld surface analysis. The crystal structure is governed by coordination interactions to Na + cations and an extensive network of hydrogen bonds, in which guanidinium cations, hypodiphosphate ions and water molecules are involved. Na + cations are in tetragonal pyramidal or octahedral environment, which was proved by continuous shape measures. From ∇ 2 ρ(r c ) and bond degree values, the character of P-P bonds are classified as shared shell or covalent bond types, whereas P-O bonds are of transit closed shell or polarized covalent types. Despite the lack of a lone electron pair on the N atom and positive charge of the guanidinium cation, the existence of an O-H...N hydrogen bond was confirmed by electron density studies.

The synthesis of [2]rotaxanes stoppered with one or two dipyrromethane groups has opened a route for the construction of mechanically interlocked molecules incorporating various porphyrinoid stations. The exploitation of those precursors allowed the creation of [3]rotaxanes and [2]catenanes based on the calix[4]phyrin motif, presenting intriguing molecular dynamics. The intrinsic flexibility of the porphyrinoid allowed the introduction of a new type of molecular motion within the rotaxanes, termed fluttering. The latter involved a bending of the axle, interconverting two angular-shaped stereoisomers of the rotaxane through a planarised transition state. Simple chemical transformations, i.e. methylation and (de)protonation of the [3]rotaxane and [2]catenane allowed controllable transformations within the conformationally flexible calix[4]phyrin-incorporated mechanically interlocked porphyrinoids., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)