Spin crossover and solvate effects in 1D feII chain compounds containing bis(dipyridylamine)-linked triazine ligands
Résumé
A series of 1D polymeric FeII spin crossover (SCO) compounds of type trans-[FeII(NCX)2(L)]·Solvent has been synthesised {L = DPPyT = 1-[4,6-bis(dipyridin-2-ylamino)-1,3,5-triazin-2-yl]pyridin-4(1H)-one for 1–4; NCX = NCS– for 1 and 2, NCSe– for 3 and 4; Solvent = 2.5CH2Cl2 for 1, 2CHCl3·0.5CH3OH for 2 and 4, CH2Cl2 for 3; L = DPT (6-phenoxy-N2,N2,N4,N4-tetra-2-pyridinyl-1,3,5-triazine-2,4-diamine) for 5; NCX = NCS– for 5; Solvent = 2CH3OH·H2O for 5; L = DQT {4-[4,6-bis(dipyridin-2-ylamino)-1,3,5-triazin-2-yloxy]phenol} for 6–8; NCX– = NCS– for 6; Solvent = 2CH2Cl2 for 6; NCX– = NCSe– for 7; Solvent = CH2Cl2·CH2ClCH2Cl for 7; NCX– = NCSe– for 8; Solvent = 1.5CH2Cl2·0.5CH3OH for 8}. Two mononuclear complexes, trans-[FeII(NCS)2(DPT)2]·2CH3OH (9) and trans-[FeII(NCSe)2(DPT)2]·2CH3OH (10), contained the L ligand in a terminal bidentate coordination mode. As well as variations made in the NCX– ligands, variations were also made in substituent groups on the s-triazine “core” of L to investigate their intermolecular/supramolecular role in crystal packing and, thus, their influence on SCO properties. All the complexes crystallised as solvates, and the influence of the latter on the magnetism and spin transitions was explored. A wide range of physical methods was employed, as a function of temperature, viz. crystallography, PXRD (synchrotron), susceptibilities, LIESST and Mössbauer effect, in order to probe magnetostructural correlations in these 1D families. New examples of half-crossovers, with ordered –LS–HS–LS–HS– intrachain states existing below T1/2, have been observed and comparisons made to related one- or two-step systems. All the observed transitions are gradual and non-hysteretic, and brief comments are made in relation to recent theoretical models for cooperativity, developed elsewhere.