Ewa Hodorowicz

Complexation between molybdenum(VI) and citrate: structural characterisation of a tetrameric complex, K4[(MoO2)4O3(cit)2]·6H2O

The complex anion obtained by crystallisation from an aqueous solution of molybdate and citric acid (H3cit) at pH ca. 3 is of the type (i), [(MoO2)4O3(cit)2]4−, as determined by X-ray analysis of the salt K4[Mo4O11(cit)2]·6H2O. Principal dimensions [ranges or means; estimated standard deviation (e.s.d.) 0.005 A] are: MoO 1.692–1.734; Mo–O(bridging) 1.886–1.948; Mo–O(hydroxy) 1.972(5); Mo–O(carboxylate) (unidentate) 2.185–2.318, (bridging) 2.296–2.333 A. The crystals are triclinic, space group P, a = 8.966(4), b = 12.319(6), c = 15.962(9) A, α = 89.34(4), β = 99.80(4), γ = 107.04(4)°, R = 0.041 for 4 399 observed [I/σ(I) 2.0] reflections. The complex is tetranuclear with the citrato-ligands co-ordinated through the deprotonated hydroxy group and the α-carboxy group to form five-membered chelate rings. One of the oxygens of the β-carboxylate groups bridges between two Mo atoms [Mo(1)–Mo(2) and Mo(3)–Mo(4)] whereas the other oxygen bridges between these dimers. The other β-carboxylate group is not co-ordinated to molybdenum but is protonated. The i.r. and Raman solid-state spectra are in agreement with this structure as well as a study in solution (Raman, 1H and 13C n.m.r. spectroscopy, molecular weight determination).

1:1 Molybdenum(VI) citric acid complexes

SummaryThe complexes obtained by crystallisation from an aqueous solution of molybdate and citric acid (H4cit) at pH 4–8 have Mo:cit ratio 1∶1. The new complexes have been characterised by a variety of methods in the solid state and in solution. On this basis two dimeric species, [(MoO2)2O(citH)2]4− and [(MoO2)2O(cit)2]6−, and a monomeric species [MoO3(cit)OH2]4− are proposed.

Studies on water bonding in potassium paradodecatungstate

Abstract Investigations of crystalline potassium paratungstate B by means of IR and NMR spectroscopy indicate that 2 water molecules and 2 OH groups are coordinated in the anion and the formula of the polytungstate is: K 10 [W 12 /OH/ 2 /H 2 O/ 2 O 40 ]·6H 2 O.

Polytungstates with the organic cation—I. Synthesis and chemical properties of sodium—tetramethylammonium decatungstate

Abstract Sodium-tetramethylammonium decatungstate has been obtained and investigated. On the basis of X-ray, thermogravimetric and IR spectroscopic measurements its chemical formula has been discussed.

Polytungstates with the organic cation—II NMR studies of sodium-tetramethylammonium decatungstate☆

Studies on water bonding in the crystalline sodium-tetramethylammonium decatungstate were performed by wide-line proton magnetic resonance technique. The results indicate that the formula of the compound is Na6[N(CH3)4]3[W10O34(OH)]×8H2O.

Synthesis and characterization of sodium-tetramethylammonium decamolybdate

Abstract Sodium-tetramethylammonium decamolybdate in acidified solution has been crystallized. Chemical analysis, thermogravimetric and X-ray studies have been performed.