title: A Sequential Method to Prepare Polymorphs and Solvatomorphs of [Fe(1,3-bpp)2 ](ClO4 )2 ⋅nH2 O (n=0, 1, 2) with Varying Spin-Crossover Behaviour.
abstract: Two polymorphs of the spin crossover (SCO) compound [Fe(1,3-bpp)2 ](ClO4 )2 (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 H2 O molecules from the solvatomorph [Fe(1,3-bpp)2 ](ClO4 )2 ⋅2 H2 O (2⋅2 H2 O), using single-crystal-to-single-crystal (SCSC) transformations. Hydrate 2⋅2 H2 O is obtained through the same reaction as 1, now with 2.5 % of water added. Compounds 2 and 2⋅2 H2 O are unstable in the atmosphere and absorb or lose one equivalent of water, respectively, to both yield the stable solvatomorph [Fe(1,3-bpp)2 ](ClO4 )2 ⋅H2 O (2⋅H2 O), 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 T1/2↑ =279/316 K and T1/2↓ =276/314 K (near 40 K of shift) and different cooperativity.
authors.affiliation: Departement de Inorgánica, Universitat de Barcelona, Diagonal 645, 08028, Barcelona, Spain. carlos.bartual@qi.ub.es.
authors.forename: Carlos
authors.identifier: http://orcid.org/0000-0003-1547-8018
authors.initials: C
authors.lastname: Bartual-Murgui
authors.affiliation: Departement de Inorgánica, Universitat de Barcelona, Diagonal 645, 08028, Barcelona, Spain.
authors.forename: Carlota
authors.initials: C
authors.lastname: Codina
authors.affiliation: Instituto de Ciencia de Materiales de Aragón (ICMA), CSIC and, Universidad de Zaragoza, Plaza San Francisco s/n, 50009, Zaragoza, Spain. roubeau@unizar.es.
authors.forename: Olivier
authors.identifier: http://orcid.org/0000-0003-2095-5843
authors.initials: O
authors.lastname: Roubeau
authors.affiliation: Departement de Inorgánica, Universitat de Barcelona, Diagonal 645, 08028, Barcelona, Spain. guillem.aromi@qi.ub.es.
authors.forename: Guillem
authors.identifier: http://orcid.org/0000-0001-9821-3650
authors.initials: G
authors.lastname: Aromí
keywords: iron; polymorphism; single-crystal-to-single-crystal; solvatomorphs; spin crossover