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Issue 15, 2010
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Towards Langmuir–Blodgett films of magnetically interesting materials: solution equilibria in amphiphilic iron(II) complexes of a triazole-containing ligand

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Abstract

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.

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

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Publication details

The article was received on 13 Nov 2009, accepted on 09 Feb 2010 and first published on 02 Mar 2010


Article type: Paper
DOI: 10.1039/B923923E
Citation: Dalton Trans., 2010,39, 3751-3758
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    Towards Langmuir–Blodgett films of magnetically interesting materials: solution equilibria in amphiphilic iron(II) complexes of a triazole-containing ligand

    N. G. White, H. L. C. Feltham, C. Gandolfi, M. Albrecht and S. Brooker, Dalton Trans., 2010, 39, 3751
    DOI: 10.1039/B923923E

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