A Chiral [2+3] Covalent Organic Cage Based on 1,1'-Bi-2-naphthol (BINOL) Units.

A [2+3] chiral covalent organic cage is produced through a dynamic covalent chemistry approach by mixing two readily available building units, viz. an enantiopure 3,3'-diformyl 2,2'-BINOL compound (A) with a triamino spacer (B). The two enantiomeric (R,R,R) and (S,S,S) forms of the cage C are formed nearly quantitatively thanks to the reversibility of the imine linkage. The X-ray diffraction analysis of cage (S,S,S)-C highlights that the six OH functions of the BINOL fragments are positioned inside the cage cavity. Upon reduction of the imine bonds of cage C, the amine cage D is obtained. The ability of the cage D to host the 1-phenylethylammonium cation (EH+) as a guest is evaluated through UV, CD and DOSY NMR studies. A higher binding constant for (R)-EH+ cation (Ka=1.7 106±10 % M-1) related to (S)-EH+ (Ka=0.9 106±10 % M-1) is determined in the presence of the (R,R,R)-D cage. This enantiopreference is in close agreement with molecular dynamics simulation.

Strapping a benzaldehyde-appended 2,2'-bis-dipyrrin Zn(ii) double-stranded helicate using imine bond formation.

A novel linear binuclear Zn(ii)/2,2'-bis-dipyrrin double-stranded helicate bearing peripheral p-benzaldehyde moieties has been strapped by formation of imine bonds upon reaction with m-xylylenediamine and characterized by 1H- and 13C-NMR spectroscopy, UV-Visible spectroscopy and high-resolution mass spectrometry.

Symmetrical or non-symmetrical luminescent turnstiles based on hydroquinone stators and rotors bearing pyridyl or p-dimethylaminopyridyl coordinating units.

The design and synthesis of a novel family of molecular turnstiles T1-T5 were achieved. All five turnstiles are based on a stator and a rotor covalently interconnected. While turnstiles T1-T2 are based on a symmetric stator equipped with two coordinating pyridyl units and a rotor bearing either a pyridyl or p-dimethylaminopyridyl coordinating moiety, the two non-symmetric turnstiles T4 and T5 are based on a stator bearing only a single pyridyl unit and the same rotor as T1 and T2 mentioned above. The switching between the open (T1-T5) and the closed (T-M) states of the turnstiles by metal cations (M = Ag+ or Pd2+) was investigated in solution by using 1D and 2D NMR techniques. The locking of the rotational movement leading to the closed state of the turnstile was achieved upon addition of the Ag+ cation through its simultaneous binding by both pyridyl moieties of the stator and the rotor. The unlocking process leading back to the open state was achieved by the addition of Et4NBr. For the symmetric turnstiles T1 and T2, bearing two pyridyl units on the stator, the binding of the Ag+ cation leads to an oscillating phenomenon between the two energetically equivalent closed states. However, in the case of turnstile T1, the oscillating process could be prevented by blocking the rotational movement using PdCl2 as the locking agent. Owing to the emissive nature of the stator, the open and closed states of the turnstiles were investigated by steady state and time-resolved photophysical methods. The photo-excitation of the turnstiles in their open state leads to an intense near-UV to deep-blue emission with short-lived excited states and a singlet intra-ligand charge transfer (1ILCT) character. Upon binding of the Ag+ cation, sizeable bathochromic shifts and a substantial decrease of PLQY were observed. Finally, the coordination of PdCl2, which possesses lower-lying excited states with metal-centered (MC) and ligand-to-metal charge transfer (LMCT) character, completely quenches the photoluminescence.

From sequential to one-pot synthesis of dipyrrin based grid-type mixed metal-organic frameworks.

Both sequential and one-pot strategies for the preparation of a series of grid-type mixed metal-organic frameworks (MM'MOFs) based on dipyrrin ligands appended with either a pyridyl or a phenyl-imidazolyl moiety have been investigated. For the stepwise approach, the differentiation between the two coordination sites (nature, charge, and denticity) was exploited for the synthesis of a family of five discrete Zn(II), Cu(II), and Pd(II) complexes. Acting as metallatectons, these construction building blocks lead to the formation of a series of MM'MOFs upon self-assembly with CdCl2. In these rhombic grid-type architectures, four consecutive metallatectons are bridged by Cd(II) cations adopting an octahedral coordination geometry with the chloride anions occupying apical positions, thus behaving as square nodes. The shape of the rhombus grids as well as the way they are packed (stacking or interpenetration) in the crystalline phase are controlled by the nature of metallatectons and the solvent molecules present in the crystals. Consequently, the heterometallic assemblies display different accessible voids, although they are built on layers with the same connectivity. More interestingly, as demonstrated by X-ray diffraction on both single crystals and microcrystalline powders, the same MM'MOFs were obtained by a one-pot strategy through direct combinations of dipyrrin derivatives with the corresponding metal salts. This one-pot approach is efficient and more convenient than the sequential alternative, since the isolation, purification, and characterization of the, sometimes insoluble, metallatectons are not required.

Stepwise construction of grid-type Cu(II)-Cd(II) heterometallic MOFs based on an imidazole-appended dipyrrin ligand.

An imidazole-appended dipyrrin ligand yields, upon coordination to Cu(II) cations, a linear metallatecton that self-assembles with Cd(II) salts to afford 2D grid-type MOFs which, upon parallel stacking, lead to porous crystals offering 1D channels.