title: A mononuclear iron(II) complex: cooperativity, kinetics and activation energy of the solvent-dependent spin transition.
abstract: The system [FeL2](BF4)2 (1)-EtOH-H2O (L is 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-(pyridin-2-yl)-6-methylpyrimidine) shows a complicated balance between the relative stabilities of solvatomorphs and polymorphs of the complex [FeL2](BF4)2. New solvatomorphs, 1(LS)·EtOH·H2O and β-1(LS)·xH2O, were isolated in this system. They were converted into four daughter phases, 1(A/LS), 1(D/LS), 1(E/LS)·yEtOH·zH2O and 1(F/LS). On thermal cycling in sealed ampoules, the phases 1(LS)·EtOH·H2O and β-1(LS)·xH2O transform into the anhydrous phase 1(A/LS). The hysteresis loop width for the (A/LS) ↔ (A/HS) spin transition depends on the water and ethanol contents in the ampoule and varies from ca. 30 K up to 145 K. The reproducible hysteresis loop of 145 K is the widest ever reported one for a spin crossover complex. The phase 1(A/LS) combines the outstanding spin crossover properties with thermal robustness allowing for multiple cycling in sealed ampoules without degradation. The kinetics of the 1(A/LS) → 1(A/HS) transition is sigmoidal which is indicative of strong cooperative interactions. The cooperativity of the 1(A/LS) → 1(A/HS) transition is related to the formation of a 2D supramolecular structure of the phase 1(A/LS). The activation energy for the spin transition is very high (hundreds of kJ mol(-1)). The kinetics of the 1(A/HS) → 1(A/LS) transition can either be sigmoidal or exponential depending on the water and ethanol contents in the ampoule. The phases 1(D/LS) and 1(F/LS) show gradual crossover, whereas the phase 1(E/LS)·yEtOH·yH2O shows a reversible hysteretic transition associated with the solvent molecule release and uptake.
authors.affiliation: Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciences, 3, Acad. Lavrentiev Ave., Novosibirsk, 630090, Russia. bushuev@niic.nsc.ru mark.bushuev@gmail.com and Novosibirsk State University, 2, Pirogova str., Novosibirsk, 630090, Russia.
authors.forename: Mark B
authors.initials: MB
authors.lastname: Bushuev
authors.affiliation: Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciences, 3, Acad. Lavrentiev Ave., Novosibirsk, 630090, Russia. bushuev@niic.nsc.ru mark.bushuev@gmail.com.
authors.forename: Denis P
authors.initials: DP
authors.lastname: Pishchur
authors.affiliation: Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciences, 3, Acad. Lavrentiev Ave., Novosibirsk, 630090, Russia. bushuev@niic.nsc.ru mark.bushuev@gmail.com and Novosibirsk State University, 2, Pirogova str., Novosibirsk, 630090, Russia.
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Logvinenko
authors.affiliation: Novosibirsk State University, 2, Pirogova str., Novosibirsk, 630090, Russia and N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of Russian Academy of Sciences, 9, Acad. Lavrentiev Ave., Novosibirsk, 630090, Russia.
authors.forename: Yuri V
authors.initials: YV
authors.lastname: Gatilov
authors.affiliation: Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciences, 3, Acad. Lavrentiev Ave., Novosibirsk, 630090, Russia. bushuev@niic.nsc.ru mark.bushuev@gmail.com and Novosibirsk State University, 2, Pirogova str., Novosibirsk, 630090, Russia.
authors.forename: Ilya V
authors.initials: IV
authors.lastname: Korolkov
authors.affiliation: Novosibirsk State University, 2, Pirogova str., Novosibirsk, 630090, Russia and N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of Russian Academy of Sciences, 9, Acad. Lavrentiev Ave., Novosibirsk, 630090, Russia.
authors.forename: Inna K
authors.initials: IK
authors.lastname: Shundrina
authors.affiliation: N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of Russian Academy of Sciences, 9, Acad. Lavrentiev Ave., Novosibirsk, 630090, Russia.
authors.forename: Elena B
authors.initials: EB
authors.lastname: Nikolaenkova
authors.affiliation: N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of Russian Academy of Sciences, 9, Acad. Lavrentiev Ave., Novosibirsk, 630090, Russia.
authors.forename: Viktor P
authors.initials: VP
authors.lastname: Krivopalov