A sequential method to prepare polymorphsand solvatomorphs of [Fe(1,3-bpp)2](ClO4)2·nH2O( n=0, 1, 2) with varying spin-crossover behaviour

Two polymorphs of the spin crossover (SCO) compound [Fe(1,3bpp)2](ClO4)2 (1 and 2; 1,3bpp, 2-(pyrazol-1-yl)-6-(pyrazol-3-yl)-pyridine) are prepared using a novel, stepwise procedure. Crystals of 1 deposit from dry solvents while 2 is obtained from a solid-state procedure, by sequentially removing lattice H2O molecules from the solvatomorph [Fe(1,3bpp)2](ClO4)2·2H2O (2·2H2O), using single-crystal-to-single-crystal (SCSC) transformations. Hydrate 2·2H2O is obtained through the same reaction as 1, now with 2.5% of added water. Compounds 2 and 2·2H2O are unstable in the atmosphere and absorb or lose one equivalent of water, respectively, to both yield the stable solvatomorph [Fe(1,3bpp)2](ClO4)2·H2O (2·H2O), also following SCSC processes. The four derivatives have been characterized by single crystal X-ray diffraction (SCXRD). Furthermore, the homogeneity of the various compounds as well as their SCSC interconversions have been confirmed by powder X-ray diffraction (PXRD). Polymorphs 1/2 exhibit abrupt SCO near room temperature with T1/2↑ = 279/316 K and T1/2↓ = 276/314 K (near 40 K of shift) and different cooperativity

A sequential method to prepare polymorphs and solvatomorphs of [Fe(1,3-bpp)2](ClO4)2⋅nH2O (n=0, 1, 2) with varying spin-crossover behaviour

Two polymorphs of the spin crossover (SCO) compound [Fe(1,3-bpp)](ClO)(1 and 2; 1,3-bpp=2-(pyrazol-1-yl)-6-(pyrazol-3-yl)pyridine) were prepared using a novel, stepwise procedure. Crystals of 1 deposit from dry solvents, while 2 is obtained from a solid-state procedure, by sequentially removing lattice HO molecules from the solvatomorph [Fe(1,3-bpp)](ClO)⋅2 HO (2⋅2 HO), using single-crystal-to-single-crystal (SCSC) transformations. Hydrate 2⋅2 HO is obtained through the same reaction as 1, now with 2.5 % of water added. Compounds 2 and 2⋅2 HO are unstable in the atmosphere and absorb or lose one equivalent of water, respectively, to both yield the stable solvatomorph [Fe(1,3-bpp)](ClO)⋅HO (2⋅HO), also following SCSC processes. The four derivatives have been characterised by single-crystal X-ray diffraction (SCXRD). Furthermore, the homogeneity of the various compounds as well as their SCSC interconversions have been confirmed by powder X-ray diffraction (PXRD). Polymorphs 1 and 2 exhibit abrupt SCO behaviour near room temperature with T=279/316 K and T=276/314 K (near 40 K of shift) and different cooperativity.The authors thank the Generalitat de Catalunya for the prize ICREA Academia 2008 and 2013, the ERC for Starting Grant StG-2010-258060 (GA) and MINECO through MAT2014-53961-R and MAT2015-70868-ERC (O.R.) and CTQ2012-32247 and CTQ2015-68370-P (G.A., C.B.M.).Peer Reviewe