Tiia-Riikka Tero

Template-Free Supracolloidal Self-Assembly of Atomically Precise Gold Nanoclusters: From 2D Colloidal Crystals to Spherical Capsids

We report supracolloidal self-assembly of atomically precise and strictly monodisperse gold nanoclusters involving p-mercaptobenzoic acid ligands (Au102 -pMBA44 ) under aqueous conditions into hexagonally packed monolayer-thick two-dimensional facetted colloidal crystals (thickness 2.7 nm) and their bending to closed shells leading to spherical capsids (d ca. 200 nm), as controlled by solvent conditions. The 2D colloidal assembly is driven in template-free manner by the spontaneous patchiness of the pMBA ligands around the Au102 -pMBA44 nanoclusters preferably towards equatorial plane, thus promoting inter-nanocluster hydrogen bonds and high packing to planar sheets. More generally, the findings encourage to explore atomically precise nanoclusters towards highly controlled colloidal self-assemblies.

Dynamic Stabilization of the Ligand–Metal Interface in Atomically Precise Gold Nanoclusters Au68 and Au144 Protected by meta-Mercaptobenzoic Acid

Ligand-stabilized, atomically precise gold nanoclusters with a metal core of a uniform size of just 1-3 nm constitute an interesting class of nanomaterials with versatile possibilities for applications due to their size-dependent properties and modifiable ligand layers. The key to extending the usability of the clusters in applications is to understand the chemical bonding in the ligand layer as a function of cluster size and ligand structure. Previously, it has been shown that monodispersed gold nanoclusters, stabilized by meta-mercaptobenzoic acid (m-MBA or 3-MBA) ligands and with sizes of 68-144 gold atoms, show ambient stability. Here we show that a combination of nuclear magnetic resonance spectroscopy, UV-vis absorption, infrared spectroscopy, molecular dynamics simulations, and density functional theory calculations reveals a distinct chemistry in the ligand layer, absent in other known thiol-stabilized gold nanoclusters. Our results imply a low-symmetry C1 ligand layer of 3-MBA around the gold core of Au68 and Au144 and suggest that 3-MBA protects the metal core not only by the covalent S-Au bond formation but also via weak π-Au and O═C-OH···Au interactions. The π-Au and -OH···Au interactions have a strength of the order of a hydrogen bond and thus are dynamic in water at ambient temperature. The -OH···Au interaction was identified by a distinct carbonyl stretch frequency that is distinct for 3-MBA-protected gold clusters, but is missing in the previously studied Au102(p-MBA)44 cluster. These thiol-gold interactions can be used to explain a remarkably low ligand density on the surface of the metal core of these clusters. Our results lay a foundation to understand functionalization of atomically precise ligand-stabilized gold nanoclusters via a route where weak ligand-metal interfacial interactions are sacrificed for covalent bonding.

Influence of lower rim C-methyl group on crystal forms and metal complexation of resorcinarene bis-crown-5

C-Methyl resorcinarene bis-crown-5 (1) with pendant methyl groups at the lower rim was prepared and crystallized in various solvent mixtures with and without selected metal salts. The crystal structures of two polymorphic forms of unsolvated 1 (1-I and 1-II), three solvates (acetonitrile, chloroform and dichloromethane–methanol), and three metal complexes with silver and cesium salts were obtained. The lower rim methyl groups and the block shape of the host promote crystal packing in brick-wall type assemblies, in which the binding cavities are efficiently filled by the crown bridges. Thus, solvents are found in the interstitial space or coordinated to the crown bridges on top of the cavity, whereas more strongly binding metal cations are able to occupy the cavity. The chloroform solvate proved to be a relatively labile crystal form, which transformed to unsolvated form (1-I) over time. Resorcinarene mono-crown-5 (2) was obtained as a minor product of the bridging reaction. Two solvate structures (acetonitrile and chloroform–water) of 2 are also reported, providing an example of the effect of the missing crown bridge on the solvate structures.

The missing member of the partially O-alkylated resorcinarene family: synthesis and conformation of methyl tetramethoxy resorcinarene.

An improved Lewis acid catalyzed synthesis method for methyl tetramethoxy resorcinarene is described, which produced the missing lower rim methyl derivative of this partially O-alkylated resorcinarene family. Structural characterization by means of variable temperature NMR experiments and single crystal X-ray diffraction studies furthermore revealed that the resorcinarene core adopts different conformations in the solid state and in solution.

The effect of halogen bonding on the packing of bromine-substituted pyridine and benzyl functionalized resorcinarene tetrapodands in the solid state

The synthesis and characterization of new bromine-substituted pyridine and benzyl functionalized tetramethoxy resorcinarene tetrapodands are described and their solid-state structural properties and interactions were studied by single crystal X-ray crystallography. Three different crystal structures were obtained for the pyridine derivative and one for the benzyl derivative, which revealed that the interactions of the bromine substituent have an explicit effect on the crystal packing of the resorcinarene molecules. One of the structures obtained had very interesting halogen–halogen interactions with the same geometry as is generally found for compounds used in nonlinear optical studies.

Solid state halogen bonded networks vs. dynamic assemblies in solution: explaining N⋯X interactions of multivalent building blocks

Tetrapyridine functionalized resorcinarene macrocycles were used as multivalent building blocks for the construction of halogen bonded networks with aryl halide linkers. In the solid state, resorcinarene macrocycles and aryl halide linker molecules assembled into interpenetrated, multidimensional halogen bonded networks with porous structure caused by the 3D block scaffold of the resorcinarenes. 19F NMR spectroscopy proved halogen bond formation also in solution, as either upfield or downfield shifts were observed depending on the bivalent or monovalent halogen bond binding mode. The binding mode in solution was explained by density functional theory computations.

4,4-Di­fluoro-2,3;5,6-bis­(tetra­methylene)-4-bora-3a,4a-di­aza-s-indacene (LD540)

The title compound, C18H21BF2N2, is a lipophilic dye based on a BODIPY fluorophore backbone, which was developed for microscopic imaging of lipid droplets; the molecule has a planar BODIPY core [dihedral angle between the pyrrole rings = 2.3 (3)°] and two tetramethylene substituents at the 2,3- and 5,6-positions in a half-chair conformation. One of the tetramethylene substituents is disordered over two two sets of sites with site occupancies of 0.5. In the crystal, pairs of C—H⋯F interactions link the molecules into inversion dimers. Neighbouring dimers are linked by further C—H⋯F interactions, forming an infinite array. C—H⋯π and π–π [centroid–centroid distance = 4.360 (3) Å] interactions are observed between the BODIPY core and the tetramethylene substituents of neighbouring dimer pairs.