Ge(IV)–citrate complex formation: synthesis and structural characterisation of GeCl4(bipy) and GeCl(bipy)(Hcit) (bipy=2,2′-bipyridine, H4cit=citric acid)

Stability Constants of Tetravalent Germanium Complexes in Aqueous Solution: Small Organic Oxygen and Nitrogen Donor Ligands

The formation constants of about 100 different complexes of Ge(IV) with some 50 organic, low-molecular-weight ligands, principally bidentate oxygen and/or nitrogen donors, are determined by potentiometric titrations at 25 °C and an ionic strength of 0.1 mol L-1 (KNO3). In the few cases for which literature data are available, these older data are critically discussed and completed in light of our new experimental data. The overall picture emerging from our work is that such complexes are comparatively weak, except when a chelate effect comes into play, as is observed with aminopolyols, α-hydroxocarboxylic acids, and carbohydrate derivatives, where even quantitative chelation of Ge is possible. No binding to amino acids or peptides is detected. An important finding is our evidence for the existence of a bridged dinuclear germanium(IV) tartrate complex in the aqueous phase, whose occurrence in solids was confirmed by X-ray diffraction beforehand. Our work has implications for the general understanding of the aqueous coordination chemistry of Ge, its geochemical cycling, and its behavior in environmental and biological systems. Potentiometric raw data for use by other researchers are publicly accessible in the repository Zenodo at CERN.

Different Complexation Behavior of P-Functionalized Ferrocene Derivatives Towards SnCl2 , SnCl4 and SnPh2 Cl2 : Auto-ionization and Redox-Type Reactions

The novel phosphonyl-substituted ferrocene derivatives [Fe(η(5) -Cp)(η(5) -C5 H3 {P(O)(O-iPr)2 }2 -1,2)] (Fc(1,2) ) and [Fe{η(5) -C5 H4 P(O)(O-iPr)2 }2 ] (Fc(1,1') ) react with SnCl2 , SnCl4 , and SnPh2 Cl2 , giving the corresponding complexes [(Fc(1,2) )2 SnCl][SnCl3 ] (1), [{(Fc(1,1') )SnCl2 }n ] (2), [(Fc(1,1') )SnCl4 ] (3), [{(Fc(1,1') )SnPh2 Cl2 }n ] (4), and [(Fc(1,2) )SnCl4 ] (5), respectively. The compounds are characterized by elemental analyses, (1) H, (13) C, (31) P, (119) Sn NMR and IR spectroscopy, (31) P and (119) Sn CP-MAS NMR spectroscopy, cyclovoltammetry, electrospray ionization mass spectrometry, and single-crystal as well as powder X-ray diffraction analyses. The experimental work is accompanied by DFT calculations, which help to shed light on the origin for the different reaction behavior of Fc(1,1') and Fc(1,2) towards tin(II) chloride.

Preliminary speciation study of Co(II)-citrate system by ion pairing-reversed phase chromatography coupled to UV detector

This paper describes the ability of ion pairing-reversed phase chromatography coupled to UV detector to determine an experimental speciation of cobalt in the binary Co(II)-citrate system. A method has been developed to investigate aqueous Co(II)-citrate samples at physiological pH as a function of time, by varying metal-to-ligand ratios, concentration and temperature. Solid 1:1 dimeric and 1:2 monomeric Co(II)-citrate complexes previously described have been synthesised and their analysis by IP-RPC-UV allowed the assignation of the solution state separated species. In solution state and at Co(II) concentration of 5×10-2M, 1:2 Co(II)-citrate monomeric species are predominant forms, while 1:1 mono and dimeric complexes are the minor species. At Co(II) concentration lower than 5 mM, only species of 1:1 stoichiometry are involved in the aqueous cobalt distribution. The monitoring of the formed species as a function of time allows highlighting the high inertness of this system. At low concentration ranges, electrospray ionisation-mass spectrometry experiments were carried out to support the chromatographic data. This study is the first one establishing a link among synthetic cobalt-citrate complexes and species existing in solution.