European Journal of Mass Spectrometry - Abstract of Influence of solvent and counter ion on complexes of 2,5-bis(2-pyridyl)-1,3,4- oxadiazole with iron (II) and (III) studied by electrospray ionization mass spectrometry

The effect of solvent and counter ion on the complexes of 2,5-bis(2- pyridyl)-1,3,4-oxadiazole (1) with Fe⁺² and Fe⁺³ has been studied by electrospray ionization mass spectrometry (ESI/MS). As expected, upon ESI conditions the metal reduction proceeds, but it can be deduced that complexes with Fe⁺² are favored over those with Fe⁺³. When methanol is used as solvent, the formation of complexes of stoichiometry 2:1 and 1:1 with counter ion attached (monovalent anion) is favored, for example, [1₂+FeCl]⁺ ion. The use of methanol/water (1/1) as solvent favors the formation of complexes of stoichiometry 2:1 and 3:1, namely doubly charged [1₂+Fe]⁺² and [1₃+Fe]⁺² ions. The complexes containing anion of oxidative properties (ClO₄^–, NO₃^–), when the higher cone voltage is applied, yield unusual species [1_n+FeO_m]⁺ (n=1, 2; m=1, 2). The use of divalent counter ion (SO₄^–2) resulted in formation of complexes containing two iron cations, namely [1_n+Fe₂SO₄]⁺² (n=2, 3, 4) ions. These ions can be regarded as Fe-1 complexes bridged by a sulfate anion.