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Issue 47, 2013
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Crown-linked dipyridylamino-triazine ligands and their spin-crossover iron(II) derivatives: magnetism, photomagnetism and cooperativity

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The syntheses, crystallography and magnetic properties of a series of compounds of formula trans-[FeII(L1)2(NCX)2] (X = S, Se, BH3 (1–3)), cis-[FeII(L2)(NCX)2]·CH2Cl2 (X = S, Se, BH3 (4–6)) and trans-[FeII(L3)(NCX)2]n (X = S, Se (7–8)) are described (L1 = 6-chloro-N2,N2-diethyl-N4,N4-di(pyridin-2-yl)-1,3,5-triazine-2,4-diamine, L2 = 6,6′-(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyl)bis(N2,N2-diethyl-N4,N4-di(pyridin-2-yl)-1,3,5-triazine-2,4-diamine, L3 = 6,6′-(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyl)bis(N2,N2,N4,N4-tetra(pyridin-2-yl)-1,3,5-triazine-2,4-diamine)). The magnetostructural properties of 1–8 have been probed in detail by variable temperature magnetic measurements and crystallographic methods. 1–6 display mononuclear structures while 7 and 8 form 1-D chain structures. Complexes 4–6 have the potential to form 1D-chains via L2 bridging, but instead form mononuclear complexes. Magnetic studies show that complexes 1, 2, and 4 remain in the high-spin (HS) state at all temperatures. An aged, dry, powdered sample of 3 gives an abrupt HS to LS transition (T1/2 = 200 K), while a freshly prepared, powdered sample of 3·1.5H2O displays thermal hysteresis (Δ = 7 K). Complexes 5, 6 and 7 undergo a gradual spin transition with T1/2 values of 100 K, 150 K and 130 K, respectively. Cooperativity parameters are compared, with 3 showing cooperativity (positive C) and 5 and 6 showing anticooperativity. Photomagnetic LIESST (light induced excited spin state trapping) studies were performed on complexes 5 and 6 and reveal T(LIESST) values lower than 60 K. An attempt has been made to understand the electronic structure of complex 3 and its cooperativity behaviour using density functional methods, the calculations reproducing the sign and, in part, the magnitude of the cooperativity.

Graphical abstract: Crown-linked dipyridylamino-triazine ligands and their spin-crossover iron(ii) derivatives: magnetism, photomagnetism and cooperativity

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The article was received on 08 Jul 2013, accepted on 31 Jul 2013 and first published on 01 Aug 2013

Article type: Paper
DOI: 10.1039/C3DT51839F
Citation: Dalton Trans., 2013,42, 16494-16509
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    Crown-linked dipyridylamino-triazine ligands and their spin-crossover iron(II) derivatives: magnetism, photomagnetism and cooperativity

    H. S. Scott, T. M. Ross, N. F. Chilton, I. A. Gass, B. Moubaraki, G. Chastanet, N. Paradis, J. Lètard, K. R. Vignesh, G. Rajaraman, S. R. Batten and K. S. Murray, Dalton Trans., 2013, 42, 16494
    DOI: 10.1039/C3DT51839F

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