Journal
CRYSTAL GROWTH & DESIGN
Volume 18, Issue 7, Pages 4130-4139Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.cgd.8b00548
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Funding
- State Schleswig-Holstein
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Applying identical amounts of starting materials allowed the solvothermal preparation of two new polyoxoniobates by controlling the pH value of the reaction mixture. Stirring the slurries afforded crystallization of K-5[Cu(H2O)(2) (cyclam)](1.5){[Cu(cyclam)][Cu(H2O)(cyclam)](2)HSiNb18O54}(NO3)center dot 30H(2)O (I) and {[Cu(cyclam)(H2O)](2)[Cu ( cyclam)][Nb10O28]}(n)center dot 9nH(2)O (II) within short reaction times and in high yields. While compound I crystallizes from the mother liquor at room temperature after hydrothermal treatment at pH values >10.3, compound II is isolated at pH < 10.3 by filtration, i.e., II is formed at the reaction conditions applied. Time-dependent experiments demonstrate that under stirring, pure samples of both compounds can be obtained within 30 min. Syntheses without stirring the educt mixtures leads to very low yields of I and crystallization of II in comparable yields afforded about 20 h reaction time. In the structure of I, the rare [SiNb18O54](14-) anion is found, which is surrounded by [Cu(cyclam)](2+) complexes and K+ cations. The water molecules form a very unusual hydrogen bonding pattern which may be classified as a L4(2)4(4)5(4)10(4)16(6)42(14) water cluster. Compound II features the decaniobate anion [Nb10O28](6)(-), is obtained after short reaction time in high yields and exhibits a reversible release/uptake of crystal water molecules.
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