Phase Transition of [2,2]‐Paracyclophane – An End to an Apparently Endless Story

Abstract

In this contribution, the solid-state low-temperature phase structure of [2,2]-paracyclophane is unambiguously characterised by single-crystal X-ray analysis. Additionally, a heat capacity measurement was undertaken, which proves the existence of a λ-type phase transition at 45 K, a transition that is connected with the formation of a secondary Cp/T feature at 60 K. The low-temperature phase (<45 K) crystallises in the lower symmetry space group P4n2, whereas the high-temperature phase (>60 K) crystallises in space group P4(2)/mnm. This proves what has been postulated both by experimental and theoretical chemists but has repeatedly been dismissed as speculation many times.

Indeno[1,2‐b]fluorene‐Based [2,2]Cyclophanes with 4n/4n and 4n/[4n+2] π Electrons: Syntheses, Structural Analyses, and Excitonic Coupling Properties

“…The rings C′ in 7 and 8 are defined as the benzene ring facing the IF scaffold. The values of θ 1 and d 2 for 1 , 6 , 7 , and 8 are larger than those for PCP ( θ 1 ≤12.8°, d 1 =2.99 Å, d 2 =0.158 Å), and the d 1 values of 6 and 7 exceed those of 1 , 8 , and PCP. The degree of bending of an IF scaffold is specified by the dihedral angle θ 2 between the mean‐square planes of two peripheral six‐membered rings (A and A′), and 1 (11.0°) and 6 (10.7°) had the highest values.…”

Influencing the Self‐Sorting Behavior of [2.2]Paracyclophane‐Based Ligands by Introducing Isostructural Binding Motifs

“…[13] To study chiral self-sorting behavior, we decided to use ap seudo-meta-substituted [2.2]paracyclophane backbonea sac hiral substitute for the central metafunctionalized benzene ring, which also arrangesi ts functional groups at an angle of about 1208 designed to construct discrete coordination architectures.A dditionally,t his scaffold comes with some adaptability due to ap ossible twist of approximately 128 between the aromatic decks. [14] Considering that we wanted to study two different ligands with essentially equal size and shape, we decided to use nitrile and isonitrile groups (bond length of the CN bond in nitriles 1.5 and in isonitriles 1.7 ,r espectively), [15] whicha re formally isoelectronic to carbon monoxide and have been employedp reviously to construct metallosupramolecular architectures. [9f, 16] It is worth mentioning, though, that multitopico ligoisonitrilel igands have-to the best of our knowledge-not been used for the self-assembly of discrete cyclic or cage-like metallosupramolecular aggregates so far.B oth nitrilesa nd isonitriles represent very slim metal-binding motifs.…”

“…Crystallographic data for (S p )-L nit ,( S p )-L iso ,[(dppp)Pd{(R p )-L nit }] n (OTf) 2n ,[ (dppp) 2 Pd 2 {(S p )-L nit }{(R p )-L nit }] n (OTf) 4n and [(dppp)Pd{(S p )-L iso }] n (OTf) 2n . Flack parameter x 0.3(2)0.1(7) À0.016(4) 0.004 (14) À0.036(7) P2(true) value0.990 1.000 -1.000 torsion angles bindingu nits [8] 119…”

Benchmarking Quantum Chemical Methods: Are We Heading in the Right Direction?

“…The episode was only concluded after a further experiment confirmed the theoretical result 3. Since then, there have been several cases where theory has made predictions which were only later confirmed by experiment,4, 5, 6, 7, 8, 9 and many more where theory played an essential role in the interpretation of experimental results.…”