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[EN] The unprecedented bimetallic 2D coordination polymer {Fe[(Hg(SCN)3)2](4,4’-bipy)2}n exhibits a thermal high-spin (HS)$low-spin (LS) staircase-like conversion characterized by a multi-step dependence of the HS molar fraction gHS. Between the fully HS (gHS = 1) and LS (gHS = 0) phases, two steps associated with different ordering appear in terms of spin-state concentration waves (SSCW). On the gHS 0.5 step, a periodic SSCW forms with a HS-LS-HS-LS sequence. On the gHS 0.34 step, the 4D superspace crystallography structural refinement reveals an aperiodic SSCW, with a HS-LS sequence incommensurate with the molecular lattice. The formation of these different long-range spatially ordered structures of LS and HS states during the multi-step spin-crossover is discussed within the framework of “DevilÏs staircase”-type transitions. Spatially modulated phases are known in various types of materials but are uniquely related to molecular HS/LS bistability in this case., This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO), FEDER (CTQ2013-46275-P), Unidad de Excelencia Maria de Maeztu MDM-2015-0538, the Generalitat Valenciana through PROMETEO/2012/049. L.P.L. and F.J.V.M. thank the Universidad de Valencia and a MINECO for a predoctoral (FPI) grant. D.Z. thanks the Natural Science Foundation of China and China Scholarship Council. This work was supported by the Institut Universitaire de France, the National Research Agency (ANR-13-BS04-0002), Rennes Metropole and CNRS (Post-Doc funding of E.T.). E.C. and J.A.R. would like to thank G. Chastanet for meditations on the Devil's staircase.

Das chemische Schalten des Magnetismus in zwei Richtungen wurde in einem mikroporosen Koordinationspolymer mit Spin-Crossover-Einheiten beobachtet. M. Ohba, J. A. Real, S. Kitagawa und Mitarbeiter stellten in ihrer Zuschrift auf S. 4861 ff. magnetische Messungen vor, die belegen, dass die meisten Gastmolekule einen Ubergang des Netzwerks vom diamagnetischen Low-Spin- (rot) in den paramagnetischen High-Spin-Zustand (gelb) bewirken. Allein CS2 stabilisiert den Low-Spin-Zustand. Die induzierten Spinzustande werden auch nach Freisetzung der Gastspezies beibehalten.