Halobenzene Clathrates of the Porous Metal-Organic Spin-Crossover Framework [Fe(tvp)2(NCS)2]n. Stabilization of a Four-StepTransition

Abstract

[EN] Here we show that the porous metal-organic spin crossover(SCO) framework [Fe(tvp)2(NCS)2]@4(CH3CNmiddotH2O) [1@4(CH3CNmiddotH2O)] is an excellent precursor material for the systematic synthesis, via single-crystal to single-crystal transformation, of a series of halobenzeneclathrates. Immersion of samples constituted of single crystals of1@4(CH3CNmiddotH2O)in the liquid halobenzenes PhXn,X=F(n=1-6), X = Cl(n= 1, 2), and X = Br (n= 1) at room temperature induces complete replacement of the guest molecules by PhXnto afford1@2PhXn. Single-crystal analyses of the new clathrates confirm the integrity of the porousframe work with the PhXnguests being organized by pairs via pi-stackingfilling the nanochannels. The magnetic and calorimetric data confirm the occurrence of practically complete SCO behavior in all of the clathrates. The characteristic SCO equilibrium temperatures,T1/2, seem to be the result ofa subtle balance in the host-guest interactions, which are temperature- and spin-state-dependent. The radically distinctsupra molecular organization of the PhCl2guests in1@2PhCl2affords a rare example of four-step SCO behavior following the sequence [HS1:LS0]<->[HS2/3:LS1/3]<->[HS1/2:LS1/2]<->[HS1/4:LS3/4]<->[HS0:LS1], which has been structurally characterized