Markus W. Schneider

Porous organic cage compounds as highly potent affinity materials for sensing by quartz crystal microbalances.

Porosity makes powerful affinity materials for quartz crystal microbalances. The shape-persistent organic cages and pores create superior affinity systems to existing ones for direct tracing of aromatic solvent vapors. A shape and size selectivity for the analytes is observed. These organic cages can be processed to thin films with highly reproducible sensing properties.

Periphery‐Substituted [4+6] Salicylbisimine Cage Compounds with Exceptionally High Surface Areas: Influence of the Molecular Structure on Nitrogen Sorption Properties

The synthesis of various periphery-substituted shape-persistent cage compounds by twelve-fold condensation reactions of four triptycene triamines and six salicyldialdehydes is described, where the substituents systematically vary in bulkiness. The resulting cage compounds were studied as permanent porous material by nitrogen sorption measurements. When the material is amorphous, the steric demand of the cages exterior does not strongly influence the gas uptake, resulting in BET surface areas of approximately 700 m(2)  g(-1) for all cage compounds 3 c-e, independently of the substituents bulkiness. In the crystalline state, materials of the same compounds show a strong interconnection between steric demand of the peripheral substituent and the resulting BET surface area. With increasing bulkiness, the overall BET surface area decreases, for example 1291 m(2)  g(-1) (for cage compound 3 c with methyl substituents), 309 m(2)  g(-1) (for cage compound 3 d with 2-(2-ethyl-pentyl) substituents) and 22 m(2)  g(-1) (for cage compound 3 e with trityl substituents). Furthermore, we found that two different crystalline polymorphs of the cage compound 3 a (with tert-butyl substituents) differ also in nitrogen sorption, resulting in a BET surface area of 1377 m(2) g(-1), when synthesized from THF and 2071 m(2) g(-1), when recrystallized from DMSO.

Post-Modification of the Interior of Porous Shape-Persistent Organic Cage Compounds†

Cage compounds are fascinating molecules for several reasons. They are defined molecular reaction vessels for “uncommon” products, or used to stabilize highly reactive species in their interior. Recently, materials made from purely organic cage compounds showed remarkable permanent porosities, with very high surface areas and good gassorption properties, both, in crystalline as well as amorphous phases. A feature that distinguishes the porous materials derived from cage compounds from those derived from extended network structures (such as metal organic frameworks (MOFs) and covalent organic frameworks (COFs)) is, that the intrinsically porous building units (the cage molecules) are soluble. This creates several possibilities, which cannot be easily achieved for extended network structures or are even impossible. For instance, Cooper et al. reported on the co-crystallization of organic cage compounds in a binary or even ternary fashion to create porous organic alloys. 11] Very recently, this property was exploited to grow microporous cage crystals in mesoporous silica. Another example of “processable” porosity has been demonstrated by our group: various cage compounds, which are highly porous in the bulk, can be deposited as thin films on quartz crystal microbalances (QMBs) by spray-coating. The modified QMBs showed very good affinities for several aromatic analytes. In 2008, we introduced the one-pot synthesis of the endofunctionalized [4+6] cage compound 3 by reacting four molecules of triamine 1 and six molecules of salicyldialdehyde 2 (Scheme1). What distinguishes this type of cage compounds from others, is that it bears six hydroxy groups pointing to the center of the cage cavity. This structural motif is very rare for organic cage compounds, and the functionalization of the cages interiors through reaction at the hydroxy groups was to date unsuccessful. Herein we present a facile method for the post-synthetic modification of the intrinsic voids in the cage compound, which allows the pore structure of the resulting material to be “fine-tuned” in the solid state. Initially, we attempted to directly synthesize 5 a by the reaction of O-methylated salicyldialdehyde 4a with triamine 1 (Method A in Scheme 1). Unfortunately, only a small amount of cage 5a was detected in the crude product by the MALDI-TOF mass spectroscopy. However, cage 5a could not be isolated by chromatographic methods. Further optimization of the reaction conditions did not offer a decent route to synthesize 5 a in reasonable yield (never exceeding 17 %). H NMR analysis of the crude product (Figure 1b) exemplifies the high complexity of the resulting mixture. Similarly, reactions of triamine 1 with other salicyldialdehyde ethers 4b–4d failed too. These unsuccessful experiments forced us to switch to an indirect approach (see Scheme 1. Synthesis of cavity-modified cage compounds 5a–5e by two different approaches. Method A: direct route by 12-fold imine condensation. Method B: Post-synthetically modification by sixfold Williamson ether formation. For reaction conditions, results, and yields, see Table 1 and Supporting Information.

Exo-Functionalized Shape-Persistent [2+3] Cage Compounds: Influence of Molecular Rigidity on Formation and Permanent Porosity

It was demonstrated recently that shape-persistent organic cage compounds with defined cavities can form porous materials in the solid state. With specific surface areas of up to 2071 m g , these new materials complement existing systems of polymeric porous structures, for example, metal– organic frameworks (MOFs), covalent organic frameworks (COFs), and amorphous porous organic polymers. One method to synthesize organic cage compounds in high yields is the reversible formation of multiple imine bonds. Nevertheless, only some of those cage compounds have been reported to be permanently porous. One of the first examples was introduced by the Cooper group, who synthesized Td-symmetric cage compounds by condensation of four molecules of 1,3,5-triformylbenzene and six molecules of various 1,2-diamines (such cage compounds are usually termed [4+6] cages). The Brunauer– Emmett–Teller (BET) surface areas of these first systems were 624 m g . These materials could selectively adsorb various gases, for example, H2, CO2, or CH4. Very recently, the same group synthesized a porous [4+6] cage compound with a much higher specific BET surface area (1333 m g ) by enlarging the trialdehyde used. We used a complementary approach to synthesize [4+6] cage compounds. Triptycene triamine 1 was reacted with salicyldialdehydes to give endo-functionalized adamantoid cage compounds. These cage compounds show permanent porosity in the crystalline phases, with highly accessible BET surface areas of up to 2071 m g . These cage compounds could also selectively adsorb CO2 (9.4 wt %) over methane (0.98 wt %). The above-mentioned unique systems tend to have shape-persistent cavities due to the intrinsic rigidity of the tetrahedral molecular scaffold. Recently, another type of connection was used to generate porous shape-persistent molecules through an imine condensation of trisamines and dialdehydes or trisaldehydes and diamines, respectively, to give [2+3] cage compounds. However, the reported BET surface areas (10 m g 1 and 99 m g ) of these [2+3] cage compounds are significantly lower than for the [4+6] cage compounds, though a good selectivity for the adsorption of CO2 over N2 was reported. [7,8] The described [2+3] cage compounds contain flexible linking units within the molecules that allow the molecular structure of the cage compounds to twist so that the trigonal planar subunits preferentially interact through p–p stacking and almost close the cavities, which leaves insufficient space inside the cage compound interior for gas sorption. This effect might be the reason for the low measured BET surface areas. To study the influence of the rigidity of the molecular structure of [2+3] cages on their formation and gas sorption properties, we synthesized exo-functionalized [2+3] cage compounds by using two different bissalicylaldehydes as molecular precursors in the reaction with triptycene triamine 1. The more rigid of the two resulting cage compounds, 3 a, was synthesized by a sixfold imine condensation of triptycene triamine 1 and bissalicylaldehyde 2 a under reflux conditions (Scheme 1). The H NMR spectrum of the crude product in [D8]THF suggests that the main product is desired cage compound 3 a, formed in approximately 69 % yield (see Figure 1a). The byproducts could be removed through crystallisation from THF/Et2O to give pure, crystalline cage compound 3 a (Figure 1b). The other, more flexible cage compound, 3 b, was synthesized under similar conditions by using bis-salicylaldehyde 2 b as a reactant instead of 2 a. Note that the H NMR spectrum of the crude product of 3 b shows many more as-yet undefined byproducts than the spectrum of crude 3 a does (Figure 1). By integration of typical regions (around d=9 ppm) at which the imine protons resonate, we estimated that the cage compound was formed in approximately 33 % of the collected precipitate, which corresponds to about 14 % of the whole product library. It is assumed that the higher degrees of rotational freedom of the two salicylaldehydic units connected by an ethylene bridge causes a higher number of reasonable possibilities in the virtual combinatorial library, which results in a higher number of mismatched oligomeric and polymeric byproducts. From this observation, it is concluded that rigid precursors with directed functional groups are beneficial for cage formation. This finding complements suggestions for other organic cage compounds, [a] Dipl.-Chem. M. W. Schneider, Dr. M. Mastalerz Institute of Organic Chemistry II & Advanced Materials Ulm University Albert-Einstein-Allee 11, 89081 Ulm (Germany) Fax: (+49) 731-50-22840 E-mail : michael.mastalerz@uni-ulm.de [b] Prof. Dr. I. M. Oppel Institute of Inorganic Chemistry, RWTH Aachen Landoltweg 1, 52074 Aachen (Germany) Supporting information for this article (including experimental details) is available on the WWW under http://dx.doi.org/10.1002/ chem.201200032.

A shape-persistent exo-functionalized [4 + 6] imine cage compound with a very high specific surface area

The one-pot synthesis of an exo-functionalized [4 + 6] imine cage compound is introduced. The material derived from this compound is highly porous in its amorphous state with a specific surface area of 1037 m(2) g(-1) as determined by nitrogen sorption at 77 K.

Uniform porous nanospheres of discrete shape-persistent organic cage compounds

By mixing solutions of the reactants for shape-persistent cage compounds in a binary solvent mixture, spheres in the nanometre regime with controlled sizes can be generated, which show permanent porosities.

Expected similarity estimation for large scale anomaly detection

We propose a new algorithm named EXPected Similarity Estimation (EXPoSE) to approach the problem of anomaly detection (also known as one-class learning or outlier detection) which is based on the similarity between data points and the distribution of non-anomalous data. We formulate the problem as an inner product in a reproducing kernel Hilbert space to which we present approximations that allow its application to very large-scale datasets. More precisely, given a dataset with n instances, our proposed method requires O(n) training time and O(1) to make a prediction while spending only O(1) memory to store the learned model. Despite its abstract derivation our algorithm is simple and parameter free. We show on seven real datasets that our approach can compete with state of the art algorithms for anomaly detection.

Ln(III) complexes with triptycene based tripodal ligands: speciation and equilibria

Triaminotriptycene was used as a rigid anchoring platform for preparing several organic ligands for Ln(III) complexation. In this work we present detailed speciation studies with a tripodal ligand L6 possessing terminal carboxamide coordinating moieties. The solution speciation for different [Ln]/[L] ratios is investigated using NMR and mass spectrometry and compared with those of closely related ligands L7 and L8. A special interest is devoted to chemical equilibria in metal excess, whereby different complex species are generated through slow transformations. The effect of the ionic radius along the lanthanide series is discussed for tetranuclear and trinuclear complexes.

Kernel Feature Maps from Arbitrary Distance Metrics

The approximation of kernel functions using explicit feature maps gained a lot of attention in recent years due to the tremendous speed up in training and learning time of kernel-based algorithms, making them applicable to very large-scale problems. For example, approximations based on random Fourier features are an efficient way to create feature maps for a certain class of scale invariant kernel functions. However, there are still many kernels for which there exists no algorithm to derive such maps. In this work we propose an efficient method to create approximate feature maps from an arbitrary distance metric using pseudo line projections called Distance-Based Feature Map (DBFM). We show that our approximation does not depend on the input dataset size or the dimension of the input space. We experimentally evaluate our approach on two real datasets using two metric and one non-metric distance function.