Chiral nanosized confinements play a major role for enantioselective recognition and reaction control in biological systems. Supramolecular self‐assembly gives access to artificial mimics with ...tunable sizes and properties. Herein, a new family of Pd2L4 coordination cages based on a chiral 6helicene backbone is introduced. A racemic mixture of the bis‐monodentate pyridyl ligand L1 selectively assembles with PdII cations under chiral self‐discrimination to an achiral meso cage, cis‐Pd2L1P2L1M2. Enantiopure L1 forms homochiral cages Pd2L1P/M4. A longer derivative L2 forms chiral cages Pd2L2P/M4 with larger cavities, which bind optical isomers of chiral guests with different affinities. Owing to its distinct chiroptical properties, this cage can distinguish non‐chiral guests of different lengths, as they were found to squeeze or elongate the cavity under modulation of the helical pitch of the helicenes. The CD spectroscopic results were supported by ion mobility mass spectrometry.
Chiral 6helicenes serve as building blocks for the assembly of Pd2L4 coordination cages and interpenetrated Pd4L8 dimers. Depending on the ligand length, chiral self‐discrimination and recognition of enantiomeric guests is observed. Helical pitch modulation allows the discrimination of non‐chiral guests by a combination of CD spectroscopy and ion mobility mass spectrometry.
One of the remaining challenges in single‐crystal structure refinement is the proper description of disorder in crystal structures. This paper describes a computer program that performs ...semi‐automatic modelling of disordered moieties in SHELXL Sheldrick (2015). Acta Cryst. C71, 3–8.. The new program contains a database that includes molecular fragments and their corresponding stereochemical restraints, and a placement procedure to place these fragments on the desired position in the unit cell. The program is also suitable for speeding up model building of well ordered crystal structures.
Chemists of all fields currently publish about 50 000 crystal structures per year, the vast majority of which are X‐ray structures. We determined two molecular structures by employing electron rather ...than X‐ray diffraction. For this purpose, an EIGER hybrid pixel detector was fitted to a transmission electron microscope, yielding an electron diffractometer. The structure of a new methylene blue derivative was determined at 0.9 Å resolution from a crystal smaller than 1×2 μm2. Several thousand active pharmaceutical ingredients (APIs) are only available as submicrocrystalline powders. To illustrate the potential of electron crystallography for the pharmaceutical industry, we also determined the structure of an API from its pill. We demonstrate that electron crystallography complements X‐ray crystallography and is the technique of choice for all unsolved cases in which submicrometer‐sized crystals were the limiting factor.
Electrons instead of X‐rays: An electron diffractometer was tailored and employed for de novo structure determination from submicrometer‐sized crystals. A new methylene blue derivative was analysed together with a microcrystalline extract of an active pharmaceutical ingredient from a pill. The results obtained on submicrometer‐sized samples complement X‐ray crystallography.
The combination of shape‐complementary bis‐monodentate ligands LA and LB with PdII cations yields heteroleptic cages cis‐Pd2LA2LB2 by self‐sorting. Herein, we report how such assemblies can be ...diversified by introduction of covalent backbone bridges between two LA units. Together with solvent and guest effects, the flexibility of these linkers can modulate nuclearity, topology, and number of cavities in a family of four structurally diverse assemblies. Ligand LA1, with flexible linker, reacts in CH3CN with its LB counterpart to a tetranuclear dimer D1. In DMSO, however, a trinuclear pseudo‐tetrahedron T1 is formed. The product of LA2, with rigid linker, looks similar to D1, but with a rotated ligand arrangement. In presence of an anionic guest, this dimer D2 transforms and a hexanuclear prismatic barrel P2 crystallizes. We demonstrate how controlling a ligand's coordination mode can trigger structural differentiation and increase complexity in metallo‐supramolecular assembly.
Rich structural variety in shape‐complementary metallo‐supramolecular assemblies is achieved by bridging ligands via their backbones. A series of unprecedented heteroleptic assemblies ranging from dimeric cages over a prismatic structure to a pseudo‐tetrahedron were obtained. The influence of linker flexibility, solvent and presence of guest molecules was studied.
A strategy to implement four members of the classic coal‐tar dye family, Michler's ketone, methylene blue, rhodamine B, and crystal violet, into Pd2L4 self‐assemblies is introduced. Chromophores were ...incorporated into bis‐monodentate ligands using piperazine linkers that allow to retain the auxochromic dialkyl amine functionalities required for intense colors deep in the visible spectrum. Upon palladium coordination, ligands with pyridine donors form lantern‐shaped dinuclear cages while quinoline donors lead to strongly twisted Pd2L4 helicates in solution. In one case, single crystal X‐ray diffraction revealed rearrangement to a Pd3L6 ring structure in the solid state. For nine examined derivatives, showing colors from yellow to deep violet, CD spectroscopy discloses different degrees of chiral induction by an enantiomerically pure guest. Ion mobility mass spectrometry allows to distinguish two binding modes. Self‐assemblies based on this new ligand class promise application in chiroptical recognition, photo‐redox catalysis and optical materials.
A family of classic organic dyes, known since the advent of modern chemistry, was integrated into 3‐dimensional, self‐assembled nano‐objects via a novel piperazine‐based linker strategy that conserves the auxochromic substituents. The dynamic nature of the lantern‐shaped cages and helicates allows to recognize enantiopure guests via chirality transfer to the host, detected by circular dichroism response far in the visible region.
Control over the integrative self-sorting of metallo-supramolecular assemblies opens up possibilities for introducing increased complexity and function into a single self-assembled architecture. ...Herein, the relationship between the geometry of three ligand components and morphology of three self-sorted heteroleptic Pd2L2L'24+ cages is examined. Pd-mediated assembly of two bis-monodentate pyridyl ligands with native bite angles of 75° and 120° affords a cis-Pd2L2L'24+ cage while the same reaction with two ligands with bite angles of 75° and 60° gives an unprecedented, self-penetrating structural motif; a trans-Pd2(anti-L)2L'24+ heteroleptic cage with a "doubly bridged figure eight" topology. Each heteroleptic assembly can be formed by cage-to-cage conversion of the homoleptic precursors and morphological control of Pd2L2L'2 cages is achieved by selective ligand displacement transformations in a system of three ligands and at least six possible cage products.
A strategy to engineer the stacking of diketopyrrolopyrrole (DPP) dyes based on non‐statistical metallosupramolecular self‐assembly is introduced. For this, the DPP backbone is equipped with ...nitrogen‐based donors that allow for different discrete assemblies to be formed upon the addition of Pd(II), distinguished by the number of π‐stacked chromophores. A Pd3L6 three‐ring, a heteroleptic Pd2L2L′2 ravel composed of two crossing DPPs (flanked by two carbazoles), and two unprecedented self‐penetrated motifs (a Pd2L3 triple and a Pd2L4 quadruple stack), were obtained and systematically investigated. With increasing counts of stacked chromophores, UV/Vis absorptions red‐shift and emission intensities decrease, except for compound Pd2L2L′2, which stands out with an exceptional photoluminescence quantum yield of 51 %. This is extraordinary for open‐shell metal containing assemblies and explainable by an intra‐assembly FRET process. The modular design and synthesis of soluble multi‐chromophore building blocks offers the potential for the preparation of nanodevices and materials with applications in sensing, photo‐redox catalysis and optics.
Stacking of one, two, three, or four diketopyrrolopyrrole (DPP) dyes was achieved by employing recent progress in Pd(II)‐mediated self‐assembly. Two unprecedented self‐penetrated motifs have been identified: a Pd2L3 triple and a Pd2L4 quadruple stack. With increasing stack size, the absorption bathochromically shifts and emission quenches, except for Pd2L2L′2, which stands out with an exceptional luminescence quantum yield of 51 %.
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