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ARTICLE
DOI: 10.1002/zaac.201100316
Formation of Cocrystals between Alkali Triazine Tricarboxylates and
Cyanuric Acid – Reactivity Considerations and Structural Characterization
of the Adduct Phases M3[C3N3(CO2)3][C3N3O3H3]·H2O (M = K, Rb)
Sophia J. Makowski,[a] Evelyn Calta,[a] Monika Lacher,[a] and Wolfgang Schnick*[a]
Keywords: Alkali metals; Carbon nitrides; Cocrystals; Crystal structure; s-Triazine
Abstract. The reactivity of cyanuric acid towards alkali triazine K3[C3N3(CO2)3][C3N3O3H3]·H2O (3a) and Rb3[C3N3(CO2)3][C3N3O3H3]·
tricarboxylates was investigated and the first triazine-triazine adduct H2O (3b). In comparison to metal free triazine-triazine adduct phases
phases comprising alkali metal ions were synthesized and charac- in these compounds the assembly of molecules in the crystal is mainly
terized by single-crystal X-ray diffraction and thermal analysis. An determined by Coulomb interactions and only to a certain degree by
investigation of the reaction between the alkali triazine tricarboxylates
hydrogen bonds and dispersive interactions. In the crystal the s-triazine
M3[C3N3(CO2)3]·xH2O (M = Li, Na, K, Rb, Cs) and cyanuric acid
units exhibit a layered structure with triazine tricarboxylate and isocy-
showed that the degree of ion transfer from triazine tricarboxylate to anuric acid being arranged in zigzag strands within the layers and
cyanuric acid increases gradually from the lithium to the cesium salt stacked in columns perpendicular to the layers. Thermal analysis re-
reflecting an increasing basicity of the triazine tricarboxylates. vealed a quite weak cohesion between triazine tricarboxylate and cya-
The reaction of potassium and rubidium triazine tricarboxylate dihy-
drate with cyanuric yielded the novel co-crystals
nuric acid upon heating.
metric rosette-like arrangement.[4,6] Further adduct phases of
s-triazine (C3N3) and s-heptazine (C6N7) compounds were ob-
tained from solutions comprising both building blocks[5] or un-
der solvent free conditions as intermediates during the thermal
condensation of s-triazine precursors.[7] However, to the best
of our knowledge no structurally characterized compound is
known so far, in which two different s-triazine molecules are
present together with metal ions. In contrast to the above men-
tioned adduct phases in such systems not only hydrogen bonds
and dispersive interactions but also Coulomb and coordination
interactions will determine the assembly of molecules in the
crystal.
In order to obtain a system, in which the effect of various
types of non covalent interactions on the arrangement of
s-triazine molecules as well as the mutual influence of these
diverse types of interactions can be studied we tried to com-
bine s-triazine based salts with further s-triazine compounds
capable of metal coordination. For this purpose we used alkali
triazine tricarboxylates M3[C3N3(CO2)3] (M = Li, Na, K, Rb,
Cs), an interesting class of compounds that has been studied
in detail only recently,[8,9] as molecular s-triazine based salts
and cyanuric acid as further ligand (see Scheme 1). In this con-
tribution the reactivity of different alkali triazine tricarb-
oxylates (TTC) towards cyanuric acid is investigated and the
synthesis and crystal structure of the co-crystals
K3[C3N3(CO2)3][C3N3O3H3]·H2O (3a) and Rb3[C3N3(CO2)3]-
[C3N3O3H3]·H2O (3b) is presented. The influence of hydrogen
bonding and π–π stacking interactions in comparison to Cou-
lomb interactions on the arrangement of the s-triazine building
blocks in these adduct phases is discussed and the strength of
Introduction
In the last decades the concept of crystal engineering for the
rational design of new solid materials with desired physical
and chemical properties has attracted considerable interest.[1]
For the directed preparation of solids with specific architecture
and properties a detailed understanding of the factors that af-
fect the arrangement of molecular building blocks in the solid
state is an indispensable prerequisite. The assembly of mole-
cules and ions in the crystal is determined by several types of
non covalent interactions such as hydrogen bonding, coordina-
tion interactions, or π–π stacking interactions.[1,2] In this re-
gard we are especially interested in such non covalent interac-
tions between molecular carbon nitride compounds. Even
though recent research in the field of carbon nitrides is mainly
focused on synthesis, characterization, and application of co-
valently bound frameworks[3] also several adduct phases, in
which the cohesion between molecular carbon nitrides is solely
achieved by various types of non covalent interactions, were
investigated.[4–7] The most prominent example is probably the
adduct between the s-triazine compounds melamine and cya-
nuric acid, in which the self-assembly of two molecules with
a threefold symmetry leads to the formation of a highly sym-
* Prof. Dr. W. Schnick
Fax: +49-89-2180-77440
E-Mail: wolfgang.schnick@uni-muenchen.de
[a] Department Chemie
Lehrstuhl für Anorganische Festkörperchemie
Ludwig-Maximilians-Universität München
Butenandtstraße 5–13 (D)
81377 München, Germany
88
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2012, 638, (1), 88–93