We describe the synthesis, characterization, photochemical isomerization, and rotational dynamics of a crystalline molecular gyroscope containing an azobenzene bridge (trans-2) that spans from one end of the stator to other, with the intention of exploring its function as a molecular brake. While single crystal X-ray diffraction analysis of a photochemically inactive dichloromethane solvate was used to confirm the molecular and packing structures of trans-2, a nanocrystalline pseudopolymorph was shown to be photoactive, and it was analyzed by powder X-ray diffraction (PXRD), scanning electron microscopy, and variable temperature solid state 2H NMR before and after photoisomerization. It was shown that the nanocrystalline suspension irradiated with λ = 340 nm reaches a photostationary state with 34% of cis-isomer, as compared to that observed in solution where the corresponding value is 74%. Line shape analysis of solid state 2H NMR spectra of a phenylene-d4 isotopologue, obtained as a function of temperat...

Photochromic molecular gyroscope with solid state rotational states determined by an azobenzene bridge.

The ubiquitous nature of anions has gained a bourgeoning interest among the supramolecular chemists to develop artificial receptors for the selective recognition and sensing of bioactive anions. Many excellent linear, dipodal, tripodal and multipodal anion receptors have been reported in the last two decades to recognize and detect anions of diverse geometry selectively. This review was narrated with the aim to summarize the C 3v -symmetric tripodal receptors reported for the chromogenic and fluorogenic sensing of anions using various flexible and rigid tripodal frameworks. Sensing mechanisms like ICT, PET, excimer-monomer formation, push-pull, rigidity effect etc., and the design concepts applied for the development of tripodal anion sensors have been discussed.

Optical sensing of anions using C3v-symmetric tripodal receptors

Novel calix[4]arene-based receptors with bis-squaramide moieties for colorimetric sensing of anions via two different interaction modes

Threefold intramolecular ring-closing metatheses of trans-(MCl2(P{(CH2)mCH=CH2}3)2) are effected with Grubbs' catalyst. Following hydrogenation catalyzed by (RhCl(PPh3)3), the title complexes trans-(MCl2(P((CH2)n)3P)) (n = 2m + 2; M/n = Pt/14, 4c ; Pt/16, 4d ; Pt/18, 4e ; Pd/14, 5c ; Pd/18, 5e ) and sometimes isomers partly derived from intraligand metathesis, trans-(MCl2{P(CH2)n(CH2)n}P(CH2)n)) (4'c-e, 5'e), are isolated. These react with LiBr, NaI, and KCN to give the corresponding MBr2 ,M I 2, and M(CN)2 species (58-99 %). 13 C NMR data show that the MX 2 moieties rapidly rotate within the diphosphine cage on the NMR timescale, even at � 1208C. The reaction of 4c and KSCN gives separable Pt(NCS)2 and Pt(NCS)(SCN) adducts (13 c ,2 8 %;14 c ,2 0 %), and those of 4c ,e and Ph2Zn give PtPh2 species (15 c ,6 1 %; 15 e ,9 0 %). 13 C NMR spectra of 13 c-15 c show two sets of CH2 signals (ca. 2:1 intensity ratios), indicating that MX2 rota- tion is no longer rapid. Reactions of 4c or 4'c and excess NaCCH afford the free diphosphines P{(CH2)14}3P (91 %) and (CH2)14P(CH2)14P(CH2)14 (90 %). The latter has been crystallo- graphically characterized as a bis(BH3) adduct. The crystal structures of eight complexes with P(CH2)14P linkages (PtCl2, PtBr2, PtI2, Pt(NCS)2, PtPh2, PdCl2, PdBr2, PdI2) and 15 e have been determined, and intramolecular distances analyzed with respect to MX2 rotation. The conformations of the (CH2)14 moieties and features of the crystal lattices are also discussed.

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Gyroscope-Like Molecules Consisting of PdX2/PtX2 Rotators within Three-Spoke Dibridgehead Diphosphine Stators: Syntheses, Substitution Reactions, Structures, and Dynamic Properties

Gyroscope-Like Platinum and Palladium Complexes with Trans-Spanning Bis(pyridine) Ligands

Square-Planar Palladium Complexes with Trans Di- and Tribenzylphosphine Ligands Bearing O(CH2)4CH═CH2 Substituents; Two- and Three-Fold Intramolecular Ring-Closing Metatheses

New P-bridgehead urea-based tripodal anion receptors for H2PO4− recognition

Novel Tripod L-Prolinamide Catalysts Based on Tribenzyl- and Triphenylphosphine Oxide for the Direct Aldol Reaction.

Three tripod molecules, tris(2-methoxy-5-nitrobenzyl)phosphine oxide (1), tris(2-butoxy-3-methyl-5-nitrobenzyl)phosphine oxide (2), and tris(3-nitrobenzyl)amine (TNBA), were synthesized and crystallized. The structures of 1, 2, and their comparison (TNBA) were determined by X-ray crystallography. It is noteworthy that compound 1 interacted with adjacent molecules via π-π stacking and C-H⋯π interactions to yield an open supramolecular network with the porosity P in 8.9%, whereas compound 2 gathered closely to form an open-dimer capsule by sixfold N-O⋯π and triple C-H⋯O interactions, which showed a rare example of a stable in, out-invertomer of phosphine inversion existing in open-dimers. A series of columns were built and arranged side by side by these weak interactions. By contrast, TNBA crystallized to form a 2D network maintained by C-H⋯O and C-H⋯π interactions. It seems minor changes of the chemical structure may cause large differences in the crystal structure and interactions in crystal engineering.

Tripod molecules build molecular networks and open-dimer capsules by weak interactions

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Square-Planar Palladium Complexes with Trans Di- and Tribenzylphosphine Ligands Bearing O(CH2)4CH═CH2 Substituents; Two- and Three-Fold Intramolecular Ring-Closing Metatheses

New P-bridgehead urea-based tripodal anion receptors for H2PO4− recognition

Novel Tripod L-Prolinamide Catalysts Based on Tribenzyl- and Triphenylphosphine Oxide for the Direct Aldol Reaction.

Tripod molecules build molecular networks and open-dimer capsules by weak interactions