Spin Crossover and Solvate Effects in 1D FeII Chain Compounds Containing Bis(dipyridylamine)-Linked Triazine Ligands

A series of 1D polymeric Fe-II spin crossover (SCO) compounds of type trans-[Fe-II(NCX)(2)(L)]center dot 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 = 2.5CH(2)Cl(2) for 1, 2CHCl(3)center dot 0.5CH(3)OH for 2 and 4, CH2Cl2 for 3; L = DPT (6-phenoxy-N-2,N-2,N-4,N-4-tetra-2-pyridinyl-1,3,5-triazine-2,4-diamine) for 5; NCX = NCS- for 5; Solvent = 2CH(3)OH center dot 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 = 2CH(2)Cl(2) for 6; NCX- = NCSe- for 7; Solvent = CH2Cl2 center dot CH2ClCH2Cl for 7; NCX- = NCSe- for 8; Solvent = 1.5CH(2)Cl(2)center dot 0.5CH(3)OH for 8}. Two mononuclear complexes, trans-[Fe-II(NCS)(2)(DPT)(2)]center dot 2CH(3)OH (9) and trans-[Fe-II(NCSe)(2)(DPT)(2)]center dot 2CH(3)OH (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 Mossbauer 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 T-1/2, 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.