Frank Hoffmann

Solid-state studies evaluating intermolecular geometries in methylated nucleobases are not extensively explored. In the course of the present study, we have solved the crystal structures of 1-, 3- and 7-methylated adenines and guanines, including the monohydrate and sesquihydrate forms of 3-methyladenine and 3-methylguanine, respectively, by means of single-crystal X-ray diffraction and synchrotron/laboratory X-ray powder diffraction (XRPD). In situ high temperature XRPD experiments, coupled with differential thermal analysis/thermogravimetry (DTA/TG) measurements, allowed for monitoring crystallographic changes after water removal of N3-methylated compounds, and the discovery of a high temperature polymorph in the case of 3-methyladenine. Our findings indicate that H-bonding schemes describe ribbon planar motifs of molecules in the majority of cases, or linear double-bonded strands of molecules in a few cases. π-π stacking interactions were compared with existing findings of theoretical calculations and existing crystallographic data, showing how N-methylated purine bases follow the trend predicted by Hunter and Sanders, 1990. The present study provides the first systematic experimental insights into the solid state of the presented compounds.

Semiconductor nanocrystals (NCs) with high elemental and structural complexity can be engineered to tailor for electronic, photovoltaic, thermoelectric, and battery applications etc. However, this greater complexity causes ambiguity in the atomic structure understanding. This in turn hinders the mechanistic studies of nucleation and growth, the theoretical calculations of functional properties, and the capability to extend functional design across complementary semiconductor nanocrystals. Herein, we successfully deciphered the atomic arrangements of 4 different nanocrystal domains in Cu_αZn_βSn_γSe_δ (CZTSe) nanocrystals using crucial zone axis analysis on multiple crystals in different orientations. The results show that the essence of crystallographic progression from binary to multielemental semiconductors is actually the change of theoretical periodicity. This transition is caused by decreased symmetry in the crystal instead of previously assumed crystal deformation. We further reveal that these highly complex crystalline entities have highly ordered element arrangements as opposed to the previous understanding that their elemental orderings are random.

In this chapter an overview is given in which way framework-like crystalline compounds can be regarded as nets, how a net is derived out of a particular crystal structure, what nets actually are, how they can be appropriately described, what the characteristics of nets are, and how this topological approach helps to categorize framework compounds. Finally the term reticular chemistry is explained and a number of examples are given how the topology-guided approach opens up new possibilities to intentionally develop new framework structures on a rational basis.

Interpenetrated multicomponent MIL-142(Sc) MOFs were synthesised using the planar tritopic (4,4′,4′′-(1,3,5-triazine-2,4,6-triyl)tribenzoate, TATB, or 4,4′,4′′-(pyridine-2,4,6-triyl)tribenzoate, PTB) and linear ditopic (1,4-benzenedicarboxylate, BDC, or 2-amino or 2-nitro-1,4-benzenedicarboxylate (NH₂- or NO₂-BDC) linkers. Structure solution of the MIL-142(Sc)-TATB series from single crystal X-ray diffraction in space group Rm reveals regioselective ordering of bulky NO₂ groups in MIL-142(Sc)-TATB-NO₂. Use of 1,3,5-benzenetribenzoate (BTB) favours instead the mesoporous Sc-BTB, the PTB analogue of which forms in the absence of BDC. The materials are highly porous: MIL-142(Sc)-TATB-BDC has a pore volume of 0.70 cm³ g⁻¹.