Crystal Structures of Rubidium and Cesium Anthranilates and Salicylates

Abstract

In an attempt to probe a potential template role of the large alkali-metal cations rubidium and cesium in the organization of biorelevant ligands, salicylate and anthranilate complexes of the two elements were prepared and structurally investigated. The studies were also expected to show the marked structural differences compared to the corresponding thallium(I) compounds. Rubidium anthranilate and cesium salicylate could be crystallized as the monohydrates Rb(Anth)(H(2)O) and Cs(Sal)(H(2)O). Both have layer structures containing the cations and the polar groups of the ligands in core domains sandwiched by the aromatic rings above and below. The metal atoms have coordination numbers 7 and 8, respectively, with an irregular coordination sphere made up exclusively of oxygen atoms. Crystalline material with a 1:2 stoichiometry, Cs[H(Anth)(2)], is obtained from aqueous solutions of Cs(Anth) upon absorption of carbon dioxide with concomitant formation of cesium bicarbonate, Cs(HCO(3)). The crystal structure of Cs(HCO(3)) was redetermined to obtain precise benchmark data for cesium carbonates and carboxylates. The cesium hydrogen bisanthranilate also has a layer structure with eight-coordinate cesium atoms. The coordination sphere includes one nitrogen donor atom. The organization of all layer structures appears to be governed mainly by steric effects and electrostatic forces with very little directional influence of the cations. This result suggests that the large alkali metals have no efficient template effect for the organization of biological substrates and can explain the low toxicity of rubidium and cesium salts.

Solid state nuclear magnetic resonance as a tool to explore solvent-free MALDI samples

“…In particular, the high field shift in 133 Cs NMR spectrum is consistent with a coordination of the Cs ϩ cation by oxygen atoms. Chemical shift measured in Figure 1b suggests approximately eight to ten oxygen atoms around the Cs ϩ cation [31], which is consistent with the irregular coordination sphere of Cs ϩ ion reported for caesium salicylate crystal [32], exclusively consisting of eight oxygen atoms. However, although CsF is a highly hygroscopic salt, observed 133 Cs chemical shifts are neither compatible with surface hydrated species (expected at 74 ppm and 101 ppm) nor with fully hydrated species (usually observed near 45 ppm).…”

Crystal structure of caesium(I) hydrogen maleate, Cs(C4H3O4)

“…The anion is linked to two caesium cations, while the Cs + cation is surrounded by seven organic ligands, three of which are coordinated by employing both Oatoms and the other four are coordinated solely by Oatoms. The Cs-Odistances are in the range from 3.196 (2) to 3.466 (2) Å,which are well within the range reported in the literature for other caesium complexes [10][11][12]. In the crystal structure, intramolecular hydrogen bonds occur, linking carboxylate Oatoms.…”

Synthesis, spectroscopy, thermal studies and supramolecular structures of two new alkali-earth 4-nitrobenzoate complexes containing coordinated imidazole

“…In this context, a rich structural chemistry of the biologically relevant alkali and alkali-earth metals has been recently developed with amino as well as mercapto benzoic acids. [9][10][11][12][13][14][15] As part of an ongoing programme, we are investigating the chemistry of metal complexes of 4-nitrobenzoic acid (4-nbaH) to exploit the H-bonding capabilities of the nitro functionality. [16][17][18] The versatile ligational behaviour of the 4-nitrobenzoate (4-nba) ligand is well documented in the literature.…”