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

doi:10.1039/b923923e

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Journal article

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

White, Nicholas G. Department of Chemistry and MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, Dunedin, New Zealand
Feltham, Humphrey L. C. Department of Chemistry and MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, Dunedin, New Zealand
Gandolfi, Claudio Department of Chemistry, University of Fribourg, Switzerland
Albrecht, Martin Department of Chemistry, University of Fribourg, Switzerland
Brooker, Sally Department of Chemistry and MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, Dunedin, New Zealand

02.03.2010

Published in:

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

English 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), [Fe^II(OH₂)₂(C₁₆SO₃)₂] and [Co^II(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 [Fe^II(Rdpt)₂(C₁₆SO₃)₂] and two of the form [Co^II(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 [Fe^II(Rdpt)₂(C₁₆SO₃)₂] and the dicationic low-spin tris form [Fe^II(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 [Fe^II(Rdpt)₃](C₁₆SO₃)₂ form by adding additional ligand to the solution. The X-ray crystal structures of [Fe^II(adpt)₂(C₁₆SO₃)₂] and [Co^II(adpt)₂(CH₃OH)₂](C₁₆SO₃)₂·1.33CH₃OH are presented. [Fe^II(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 [Co^II(adpt)₂(CH₃OH)₂](C₁₆SO₃)₂·1.33CH₃OH form 1-D columns in the solid state. The capacity of the amphiphilic complexes [Fe^II(pldpt)₂(C₁₆SO₃)₂] and [Fe^II(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.

Faculty

Faculté des sciences et de médecine

Department

Département de Chimie

Language