Two series of tetranuclear [Ln₂Co₂] clusters were built from the same [Co(CDTA)]^2– building blocks but have different metal skeletons: square 1Ln compounds {[Ln₂Co₂(CDTA)₂(μ₄-OH)(DMF)₂(H₂O)₆]·ClO₄·1.5H₂O; Ln = La, Gd, and Dy} with a μ₄-OH^– bridged Ln–Co–Ln–Co arrangement, and two μ₃-OH^–-bridged “butterfly” 2Ln compounds {[Ln₂Co₂(CDTA)₂(μ₃-OH)₂(H₂O)₆]·6H₂O; Ln = Gd, Tb, Dy, and Y} with two Ln³⁺ ions as the “body” and two Co²⁺ ions as “wings”. They were prepared from the solvothermal reactions of trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (H₄DCTA), Ln(ClO₄)₃, and Co(ClO₄)₂ in DMF/H₂O or H₂O solvent. Their syntheses are mainly controlled by the solvent and the radii of Ln³⁺ ions. Light Ln³⁺ ions with big radii are favorable for the formation of square complexes, whereas heavy Ln³⁺ ions (including Y³⁺) with small radii promote the formation of butterfly ones. Remarkably, the middle Ln³⁺ ions are favorable for the formation of both structures, and in these cases the reactions are controlled by solvent (H₂O or H₂O + DMF). Magnetic analyses reveal the antiferromagnetic interactions between the two Co²⁺ ions in 1La and 2Y. Interestingly, other butterfly clusters (2Gd, 2Tb, 2Dy) show dominant ferromagnetic interactions, whereas the other square clusters (1Gd, 1Dy) show overall antiferromagnetic interactions. Details of the magnetic interaction between the metal ions are discussed.

The application of metal–organic polyhedra as “molecular flasks” has precipitated a surge of interest in the reactivity and property of molecules within well-defined spaces. Inspired by the structures of the natural enzymatic pockets, three metal–organic neutral molecular tetrahedral, Ce-TTS, Ce-TNS and Ce-TBS (H₆TTS: N′,N′′,N′′′-nitrilotris-4,4′,4′′-(2-hydroxybenzylidene)-benzohydrazide; H₆TNS: N′,N′′,N′′′-nitrilotris-6,6′,6′′-(2-hydroxybenzylidene)-2-naphthohydrazide; H₆TBS: 1,3,5- phenyltris -4,4′,4′′-(2-hydroxybenzylidene)benzohydrazide), which exhibit different size of the edges and cavities, were achieved through self-assembly by incorporating robust amide-containing tridentate chelating sites into the fragments of the ligands. They acted as molecular flasks to prompt the cyanosilylation of aldehydes with excellent selectivity towards the substrates size. The amide groups worked as trigger sites and catalytic driven forces to achieve efficient guest interactions, enforcing the substrates proximity within the cavity. Experiments on catalysts with the different cavity radii and substrates with the different molecular size demonstrated that the catalytic performance exhibited enzymatical catalytic mechanism and occurred in the molecular flask. These amides were also able to amplify guest-bonding events into the measurable outputs for the detection of concentration variations of the substrates, providing the possibility for metal–organic hosts to work as smart molecular flasks for the luminescent tracing of catalytic reactions.

Cu²⁺-based metal-organic framework (Cu−TCA) (H₃TCA = tricarboxytriphenyl amine) having triphenylamine emitters was assembled and structurally characterized. Cu−TCA features a three-dimensional porous structure consolidated by the well-established Cu₂(O₂CR)₄ paddlewheel units with volume of the cavities approximately 4000 nm³. Having paramagnetic Cu²⁺ ions to quench the luminescence of triphenylamine, Cu−TCA only exhibited very weak emission at 430 nm; upon the addition of NO up to 0.1 mM, the luminescence was recovered directly and provided about 700-fold fluorescent enhancement. The luminescence detection exhibited high selectivity – other reactive species present in biological systems, including H₂O₂, NO₃⁻, NO₂⁻, ONOO⁻, ClO⁻ and ¹O₂, did not interfere with the NO detection. The brightness of the emission of Cu−TCA also led to its successful application in the biological imaging of NO in living cells. As a comparison, lanthanide metal-organic framework Eu−TCA having triphenylamine emitters and characteristic europium emitters was also assembled. Eu−TCA exhibited ratiometric fluorescent responses towards NO with the europium luminescence maintained as the internal standard and the triphenylamine emission exhibited more than 1000-fold enhancement.

A multifunctional lanthanide-organic framework Tb−TCA (H₃TCA = tricarboxytriphenylamine) comprising a triphenylamine moiety as an efficient luminescence sensitizer is synthesized by a solvothermal method and structurally characterized. Tb−TCA exhibits lanthanide-based emission (540 nm) and triphenylamine emission (435 nm) after excitation at 350 nm and works as a luminescent chemosensor towards salicylaldehyde with a sensitivity of 10 ppm under optimized conditions. Tb−TCA features a high concentration of Lewis acid Tb³⁺ sites and Lewis base triphenylamine sites on its internal surfaces; it thus enables both Knoevenagel and cyanosilylation reactions in a size-selective fashion. The ratiometric fluorescent response towards aldehydes (I₅₄₀/I₄₃₅) demonstrates that the absorption of the porous material is size selective, and the interactions between the aldehyde molecules and the Tb³⁺ ions play a dominant role in the absorption and activation of the aldehyde substrates. In particular, these studies provide opportunities to directly validate the sorption sites and the catalytic mechanism of the multifunctional Ln metal–organic framework material by luminescence.

An inorganic–organic silica material (SBA–P2), prepared by immobilization of the 1,8-naphthalimide-based receptor P2 within the channels of the mesoporous silica material SBA-15, is characterized by transmission electron microscopy and several spectroscopic methods. SBA–P2 features a high affinity Cu²⁺-specific fluorescence response in aqueous solution with a detection limit for Cu²⁺ of ca. 0.65 ppb (10 × 10⁻⁹ M) under optimized conditions. It can extract Cu²⁺ from the solution with only trace amounts remaining. Through isolating of the toxic ions within the mesopores of the silica, SBA–P2 has the potential to work as a toxicide for Cu²⁺ in living systems. The fluorogenical responses are reversible and do not vary over a broad (4.0 to 9.0) pH range suitable for application under physiological conditions. The fluorescence responses of Cu²⁺ in vitro (human breast cancer cells) and in vivo (five-day-old zebrafish) demonstrate the possibility of further application in biology.