Functionalisation of Fe(II) compounds with long alkyl chains
: spin-crossover and structural properties

  • Blaise Geoghegan

    Student thesis: Doctoral Thesis


    Fe(II) compounds of N-(di(pyridin-2-yl)methyl)-Cn-1-amine (L1Cn) with formula [FeII(L1Cn)2](X)2·solvate (X = BF4 1C4 and 1C14, X = CF3SO3 1C6-1C12 and 1C16) pack in bilayer arrangements in the solid state, where interdigitated alkyl chains form hydrophobic regions between cations. Differential scanning calorimetry showed that 1C6 and 1C12-1C16 undergo crystallographic phase changes between 193-473 K. NMR studies of 1C4-1C16 in DMSO-d6 showed an increase in χMT upon heating but do not show the same behaviour in acetonitrile-d6 although UV-vis studies confirm that the Fe(II) species is preserved.

    Fe(II) compounds of 2-(1-R-1H-1,2,3-triazol-4-yl)-4-(X)pyridine (L2C10-L4) with formulae [FeII(L2C10)3](BF4)2 (2C10), trans-[FeII(L2C10)2(NCSe)2]·0.5H2O·0.5CH3OH (3C10), [FeII(L3C10)3](BF4)2 (4C10) trans-[FeII(L3C10)2(NCS)2] (5C10), trans-[FeII(L4)2(NCS)2] (6a and 6b) were prepared via a modulated approach. 2C10 and 4C10 are low-spin at 100 K. At 100 K 3C10 and 5C10 are high-spin, 6b is ca. 97% high-spin, whilst 6a is low-spin. Partial thermally driven spin-crossover is observed in 6b between 100-250 K in the solid state. In DMSO-d6 2C10 contains mostly high-spin Fe(II) centres, 4C10 is entirely high-spin and 6a/6b oxidise to a LS Fe(III) species.

    Fe(II) compounds of N,N-di(pyridin-2-yl)-Cx-amide (L5Cx) of formula trans-[FeII(L5Cx)2(X)2], where X = NCS (7Cx), NCSe (8Cx) or Cl (9Cx) were generally high-spin in the solid state at 100 K apart from 7C4, 7C10 and 8C10 which were low-spin. 7C4, 7C10 and 8C10 exhibit spin-crossover in the solid state with T1/2 values of 115.2, 101.8 and 152.1 K, respectively. 7C10 exhibited thermal hysteresis with ΔT = 8.8 K.

    Coordination compounds of 2-((4-decyl-1H-1,2,3-triazol-1-yl)methyl)pyridine (L6C10) of formula [FeII(L6C10)3](BF4)2·2H2O (10C10), [FeIII(L6C10)3](NO3)3 (11C10), [CuII(L6C10)2(NO3)](NO3) (12C10) and [ZnII2(L6C10)2Cl4] (13C10) were investigated. 10C10 and 11C10 form lyotropic liquid crystal phases in excess water, visible under crossed polarisers and are the first examples of water and air-stable Fe(II)-based lyotropic liquid crystals to date. 12C10 and 13C10 displayed two different coordination modes of the L6C10 ligand; the structure of the 12C10 cation is highly asymmetrical, resembling a mononuclear type II amphiphile. 13C10 forms a 1D coordination polymer with tetrahedral Zn(II) centres linked by bridging L6C10 ligands and charged balanced by two Cl- ligands per Zn(II) centre.
    Date of AwardApr 2019
    Original languageEnglish
    Awarding Institution
    • University of Brighton
    SupervisorIan Gass (Supervisor), Marcus Dymond (Supervisor) & Peter Cragg (Supervisor)

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