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

Abstract

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 [1ⁿ + Fe₂SO₄]⁺² (n = 2, 3, 4) ions. These ions can be regarded as Fe-1 complexes bridged by a sulfate anion.

Keywords

1,3,4-oxadiazoles iron complexes electrospray ionization mass spectrometry

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