Faculté des sciences

Towards Langmuir–Blodgett films of magnetically interesting materials: solution equilibria in amphiphilic iron(II) complexes of a triazole-containing ligand

White, Nicholas G. ; Feltham, Humphrey L. C. ; Gandolfi, Claudio ; Albrecht, Martin ; Brooker, Sally

In: Dalton Transactions, 2010, vol. 39, p. 3751-3758

As a first step towards amphiphilic spin crossover (SCO) systems where the hydrophobic part of the system is introduced by a non-coordinating anion (i.e. where no modification of the ligands to introduce hydrophobic substituents is required), [FeII(OH₂)₂(C₁₆SO₃)₂] and [CoII(OH₂)₂(C₁₆SO₃)₂] have been prepared and reacted with the... Plus

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    Summary
    As a first step towards amphiphilic spin crossover (SCO) systems where the hydrophobic part of the system is introduced by a non-coordinating anion (i.e. where no modification of the ligands to introduce hydrophobic substituents is required), [FeII(OH₂)₂(C₁₆SO₃)₂] and [CoII(OH₂)₂(C₁₆SO₃)₂] have been prepared and reacted with the triazole-containing ligands adpt and pldpt (C₁₆SO₃ = hexadecanesulfonate anion, adpt = 4-amino-3,5-bis(2-pyridyl)-1,2,4-triazole, pldpt = 4-pyrrolyl-3,5-bis(2-pyridyl)-1,2,4-triazole). In the solid state, two HS complexes of the form [FeII(Rdpt)₂(C₁₆SO₃)₂] and two of the form [CoII(Rdpt)₂(CH₃OH)₂](C₁₆SO₃)₂ are obtained, even when a six-fold excess of ligand is used (Rdpt = adpt or pldpt). In solution, the cobalt complexes remain in this form as evidenced by colour, Visible/NIR and IR spectroscopy. For the iron complexes, there is an equilibrium in solution between the neutral high-spin form of the complex [FeII(Rdpt)₂(C₁₆SO₃)₂] and the dicationic low-spin tris form [FeII(Rdpt)₃](C₁₆SO₃)₂. Polar solvents favour the dicationic form, while less polar solvents favour the neutral form (as evidenced by solution colour and solution IR spectroscopy). Visible/NIR spectroscopy and Evans'method NMR spectroscopy show the equilibrium can be shifted towards the [FeII(Rdpt)₃](C₁₆SO₃)₂ form by adding additional ligand to the solution. The X-ray crystal structures of [FeII(adpt)₂(C₁₆SO₃)₂] and [CoII(adpt)₂(CH₃OH)₂](C₁₆SO₃)₂·1.33CH₃OH are presented. [FeII(adpt)₂(C₁₆SO₃)₂] has a 2D bilayer structure with alternating layers of polar Fe(adpt)₂ centres, and hydrophobic alkyl chains. The complex cations in [CoII(adpt)₂(CH₃OH)₂](C₁₆SO₃)₂·1.33CH₃OH form 1-D columns in the solid state. The capacity of the amphiphilic complexes [FeII(pldpt)₂(C₁₆SO₃)₂] and [FeII(adpt)₂(C₁₆SO₃)₂] to self-assemble has been probed at the air–water interface using Langmuir techniques. The pertinent pressure-area isotherms reveal only a low tendency of the complexes to form films.