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C. Knoll, D. Müller, Jan Welch, G. Giester, M. Reissner, R. Miletich, P. Weinberger:
"1-Dimensional Fe(II) spin crossover polymers - An infight between rigidity, solvate and anion";
Vortrag: ACS Spring Meeting 2019, Orlando; 31.03.2019 - 04.04.2019; in: "Chemistry for New Frontiers", American Chemical Society (Hrg.); (2019), ISBN: 978-0-8412-3433-8; Paper-Nr. 873, 1 S.

Criteria for a technologically relevant spin crossover (SCO) material include temperature and abruptness. Two series of 1-dimensional SCO-chains, based on Fe(II), are compared, discriminating the dominating influences on the SCO-behavior: 1) rigidity of the ligand, 2) counter-anion, 3) solvent guest.
Using a 1,3-bis((1H tetrazol-1-yl)methyl)bicyclo[1.1.1]pentane ligand as scaffold, different anions show the same abrupt SCO-behavior with T_1/2 between 170 K and 187 K. These materials demonstrate that without stabilizing effects of incorporated solvents or a hydrogen bond-network, the observed cooperativity during high-spin - low-spin transition is anion independent and originates only from the rigidity and internal strain of the propellane-moiety in the ligand.
In contrast, the use of the flexible 1,4-bis((1H-tetrazol-1-yl)methyl)benzene ligand results in highly variable spin state transitions, governed by the anions size and incorporated solvent guest. Small tetrahedral anions result in the presence of acetonitrile or nitromethane solvates abrupt single step transitions, whereas propylene carbonate stabilizes an intermediate HS-LS phase. For larger octahedral anions complex multi-step spin transitions are observed for all solvates.

iron(II); spin-crossover; propellane