Marcel Handke

One-dimensional networks of the well-known photosensitizer [Ru(bpy) ₃ ] ²⁺ are encapsulated in an unusual hydrogen-bonded crystalline host framework.

A new inclusion compound consisting of a guanidinium 1,3,5-tri(4-sulfophenyl)benzene (G₃TSPHB) host framework containing isophorone guests that surround isolated and seemingly inaccessible pockets was amenable to guest exchange with hexafluorobenzene (HFB) through a single crystal–single crystal transformation (SCSCT). Single-crystal X-ray diffraction of intermediate transformation states, from the parent compound G₃TSPHB·(isophorone)_3.7·(methanol)_5.4 to the final state G₃TSPHB·(isophorone)_3.1·(HFB)₂·(methanol)₂, indicated a crystal symmetry change from monoclinic to hexagonal prior to full incorporation of HFB. Optical microscopy during the SCSCT revealed the formation of lamellae, which expanded and then coalesced into a single crystal when the phase transformation was complete. In situ Raman microscopy revealed changes in the orientation of isophorone guests during the transformation that suggested a pathway for HFB entry into the host cavities. The SCSCT occurs more rapidly than expected on the basis of simple diffusion, consistent with facilitated transport along the lamellae interfaces and a reduction in the length scale for guest exchange.

The sequestration of luminophores within supramolecular polyhedral compartments of a crystalline zeolite‐like hydrogen‐bonded framework illustrates a unique approach to limiting the self‐quenching ordinarily exhibited at the high concentrations achievable in this framework. A range of differently sized luminescent guests, namely coumarin 1, coumarin 4, fluorescein, [Ru(bpy)₃]Cl₂, and rhodamine B, can be encapsulated in amounts of up to one molecule per cage, equivalent to a concentration of 0.175 m, which is significantly higher than the concentration at which aggregation‐induced quenching occurs in other media. The luminescence spectra of the encapsulated guests are consistent with the presence of isolated monomers and the absence of self‐quenching. The emission color of the single crystals can be tuned readily from blue to red through the choice of guest molecules. These observations promise an approach to organic solid‐state lasing compounds if crystals of sufficient size and quality can be prepared.

The sequestration of luminophores within supramolecular polyhedral compartments of a crystalline zeolite‐like hydrogen‐bonded framework illustrates a unique approach to limiting the self‐quenching ordinarily exhibited at the high concentrations achievable in this framework. A range of differently sized luminescent guests, namely coumarin 1, coumarin 4, fluorescein, [Ru(bpy)₃]Cl₂, and rhodamine B, can be encapsulated in amounts of up to one molecule per cage, equivalent to a concentration of 0.175 m, which is significantly higher than the concentration at which aggregation‐induced quenching occurs in other media. The luminescence spectra of the encapsulated guests are consistent with the presence of isolated monomers and the absence of self‐quenching. The emission color of the single crystals can be tuned readily from blue to red through the choice of guest molecules. These observations promise an approach to organic solid‐state lasing compounds if crystals of sufficient size and quality can be prepared.

A macrocyclic ligand (H₂L) containing two o,o′‐bis(iminomethyl)phenol and two calix[4]arene head units has been synthesized and its coordination chemistry towards divalent Ni and Zn investigated. The new macrocycle forms complexes of composition [ML] (M=Zn, M=Ni) and [ZnL(py)₂], which were characterized by elemental analysis; IR, UV/Vis, and NMR spectroscopy; electrospray ionization mass spectrometry (ESI‐MS); and X‐ray crystallography (for [ZnL(py)₂] and [NiL]). H₂L allows the sensitive optical detection of Zn²⁺ among a series of biologically relevant metal ions by a dual fluorescence enhancement/quenching effect in solution. The fluorescence intensity of the macrocycle increases by a factor of ten in the presence of Zn²⁺ with a detection limit in the lower nanomolar region.

A bitopic ligand, 4-(3,5-dimethylpyrazol-4-yl)-1,2,4-triazole (Hpz-tr) (1), containing two different heterocyclic moieties was employed for the design of copper(II)–molybdate solids under hydrothermal conditions. In the multicomponent Cu^II/Hpz-tr/Mo^VI system, a diverse set of coordination hybrids, [Cu(Hpz-tr)₂SO₄]·3H₂O (2), [Cu(Hpz-tr)Mo₃O₁₀] (3), [Cu₄(OH)₄(Hpz-tr)₄Mo₈O₂₆]·6H₂O (4), [Cu(Hpz-tr)₂Mo₄O₁₃] (5), and [Mo₂O₆(Hpz-tr)]·H₂O (6), was prepared and characterized. A systematic investigation of these systems in the form of a ternary crystallization diagram approach was utilized to show the influence of the molar ratios of starting reagents, the metal (Cu^II and Mo^VI) sources, the temperature, etc., on the reaction products outcome. Complexes 2–4 dominate throughout a wide crystallization range of the composition triangle, while the other two compounds 5 and 6 crystallize as minor phases in a narrow concentration range. In the crystal structures of 2–6, the organic ligand behaves as a short [N–N]-triazole linker between metal centers Cu···Cu in 2–4, Cu···Mo in 5, and Mo···Mo in 6, while the pyrazolyl function remains uncoordinated. This is the reason for the exceptional formation of low-dimensional coordination motifs: 1D for 2, 4, and 6 and 2D for 3 and 5. In all cases, the pyrazolyl group is involved in H bonding (H-donor/H-acceptor) and is responsible for π–π stacking, thus connecting the chain and layer structures in more complicated H-bonding architectures. These compounds possess moderate thermal stability up to 250–300 °C. The magnetic measurements were performed for 2–4, revealing in all three cases antiferromagnetic exchange interactions between neighboring Cu^II centers and long-range order with a net moment below T_c of 13 K for compound 4.

The preparation, characterization and the molecular structure of a dinuclear uranyl complex [(UO₂)₂L(OCMe₂)₂] supported by the bis-salophen ligand N,N′,N″,N′″-tetra-(3,5-di-tert-butylsalicylidene)-1,2,4,5-phenylenetetraamine (L^4–) is described. [(UO₂)₂L(OCMe₂)₂] was prepared by reaction of uranyl nitrate with the neutral, protonated form of the ligand (H₄L) in acetone. From a saturated acetone solution [(UO₂)₂L(OCMe₂)₂]·1.5(OCMe₂) crystallizes triclinically, space group P1̅ with a = 1522.7(2), b = 1751.4(2), c = 1815.4(2) Å, α = 109.16(1), β = 99.29(1), γ = 105.29(1)° and Z = 2. Each uranium atom is surrounded in a distorted pentagonal bipyramidal fashion by two O and two N atoms of the salicylidene units, one O atom of an acetone ligand, and the two oxo groups. The cyclic voltammogram of [(UO₂)₂L(OCMe₂)₂] shows two quasi-reversible redox processes centered at +0.57 V and +0.82 V vs. Fc⁺/Fc attributed to the sequential oxidation of the coordinating phenolates to phenoxyl radicals. The crystal structure of an ethanol solvate of H₄L was also determined by X-ray crystallography. H₄L·5EtOH: triclinic, space group P1̅, a = 1003.4(3), b = 1187.7(3), c = 1905.1(5) Å, α = 75.75(2), β = 78.74(2), γ = 66.66(2)°, Z = 1.