COMPLEXES IN SOLUTION FORMED BY AN ORGANOMETALLIC TRIPODAL OXYGEN LIGAND WITH MONOVALENT, DIVALENT AND TRIVALENT METAL-IONS - AN ELECTROSPRAY MASS-SPECTROMETRIC STUDY

Electrospray mass spectrometry (ESMS) has been used to observe mass sp ectra for solutions of a wide variety of metal salts of the uni-negati ve tripodal oxygen donor ligand [(C5H5)Co(P(O)(OEt)2}3]-, abbreviated to L-. In aqueous/methanol solutions the sodium salt gives peaks in th e ES mass spectrum corresponding to species containing one, two and th ree ligand moieties showing that the trimeric structure known to occur in the solid state and in benzene solution is partially retained even in aqueous media. The species observed are all monocations generated by addition of protons (from the mobile phase) or sodium ions to L-, L 2(2-) or L3(3-). Addition of NaL to KCI solution gives ions correspond ing to almost global exchange of Na+ and K+, but CsCl does not give an y ions with more than one Cs+, although the oligomeric units are retai ned with additional H+ and Na+ coordinated. In contrast, Li+ competes successfully with Na+ for coordination to L-, and tbe peak intensities of the dimeric and trimeric oligomers are greatly reduced. These obse rvations are in accord with known stability constant data of these met als with L-. The Group 2 metals react with a deficiency of L- to give the protonated species [HML(OAc)]+ (the acetate is derived from the mo bile phase) and with sufficient L- present the ES mass spectra show pe aks due to the ions [HML2]+. Group 3 metals and the lanthanides give t he ions [ML(OAc)]+ and [HML(OAc)2]+ with a deficiency of L-, and exclu sively [ML2]+ with an excess of L- present. ESMS provides a convenient method for the qualitative analysis of mixtures of lanthanide and Gro up 3 elements after complexing with L-.