Self-assembly of melem C(6)N(7)(NH(2))(3) in hot aqueous solution leads to the formation of hydrogen-bonded, hexagonal rosettes of melem units surrounding infinite channels with a diameter of 8.9 Å. The channels are filled with strongly disordered water molecules, which are bound to the melem network through hydrogen bonds. Single-crystals of melem hydrate C(6)N(7)(NH(2))(3)⋅xH(2)O (x≈2.3) were obtained by hydrothermal treatment of melem at 200 °C and the crystal structure (R ̅3c, a=2879.0(4), c=664.01(13) pm, V=4766.4(13)×10(6) pm(3), Z=18) was elucidated by single-crystal X-ray diffraction. With respect to the structural similarity to the well-known adduct between melamine and cyanuric acid, the composition of the obtained product was further analyzed by solid-state NMR spectroscopy. Hydrolysis of melem to cyameluric acid during syntheses at elevated temperatures could thus be ruled out. DTA/TG studies revealed that, during heating of melem hydrate, water molecules can be removed from the channels of the structure to a large extent. The solvent-free framework is stable up to 430 °C without transforming into the denser structure of anhydrous melem. Dehydrated melem hydrate was further characterized by solid-state NMR spectroscopy, powder X-ray diffraction, and sorption measurements to investigate structural changes induced by the removal of water from the channels. During dehydration, the hexagonal, layered arrangement of melem units is maintained whereas the formation of additional hydrogen bonds between melem entities requires the stacking mode of hexagonal layers to be altered. It is assumed that layers are shifted perpendicular to the direction of the channels, thereby making them inaccessible for guest molecules.

Synchrotron X-ray, neutron powder diffraction, and magnetic susceptibility measurements have been used to characterize the Ln2LiRuO6 (Ln = Pr, Nd, Sm, Eu, Gd, and Tb) double perovskites. All compositions have the monoclinic P21/n superstructure with a fully ordered arrangement of Li+ and Ru5+ cations. As the Ln-size decreases, the lattice volume decreases due to the increased tilting of the octahedra, but the Li−O and Ru−O distances remain constant. Antiferromagnetic transitions with Néel temperatures in the 20−35 K range were observed for all compositions, except for Gd2LiRuO6, which does not order down to 5 K. Nd2LiRuO6 shows a field-induced ferrimagnetic transition at ∼4 Tesla. The Ln = Pr, Nd, and Tb materials have type I magnetic structures with coupled spin ordering on the Ln and Ru sublattices. Critical fits reveal that the Ln3+ sublattice magnetization shows mean field behaviour (β ≈ 0.5), whereas the Ru5+ spin order is consistent with the three-dimensional Heisenberg model (β = 0.31−0.35).

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Calcium hydrogenmelonate heptahydrate Ca[HC6N7(NCN)3]·7H2O was obtained by metathesis reaction in aqueous solution. The structure of the molecular salt was elucidated by single‐crystal X‐ray diffraction. The crystal structure consists of alternating layers of planar monopronated melonate ions, Ca2+ and crystal water molecules. The anions of adjacent layers are staggered so that no π–π stacking occurs. The melonate entities are interconnected by hydrogen bonds within and between the layers. Ca[HC6N7(NCN)3]·7H2O was investigated by solid‐state NMR and FTIR spectroscopy, TG and DTA measurements.