| Autor: |
Spitsyna NG; Institute of Problems of Chemical Physics, RAS, Chernogolovka, 142432, Russia., Blagov MA; Institute of Problems of Chemical Physics, RAS, Chernogolovka, 142432, Russia., Lazarenko VA; National Research Center, Kurchatov Institute, Moscow 123182, Russia., Svetogorov RD; National Research Center, Kurchatov Institute, Moscow 123182, Russia., Zubavichus YV; Synchrotron Radiation Facility SKIF, Boreskov Institute of Catalysis, SB RAS, Koltsovo 630559, Russia., Zorina LV; Institute of Solid State Physics, RAS, Chernogolovka, 142432, Russia., Maximova O; Lomonosov Moscow State University, Moscow 119991, Russia., Yaroslavtsev SA; Lomonosov Moscow State University, Moscow 119991, Russia., Rusakov VS; Lomonosov Moscow State University, Moscow 119991, Russia., Raganyan GV; Lomonosov Moscow State University, Moscow 119991, Russia., Yagubskii EB; Institute of Problems of Chemical Physics, RAS, Chernogolovka, 142432, Russia., Vasiliev AN; Lomonosov Moscow State University, Moscow 119991, Russia. |
| Abstrakt: |
A potassium salt of the N 2 S 2 O 2 -coordination Fe(III) anion K[Fe(5Cl-thsa) 2 ] ( 1 ) (5Cl-thsa - 5-chlorosalicylaldehyde thiosemicarbazone) is synthesized and characterized structurally and magnetically over a wide temperature range. Two polymorphs of salt 1 characterized by the common 2D polymer nature and assigned to the same orthorhombic Pbcn space group have been identified. The molecular structure of the minor polymorph of 1 was solved and refined at 100, 250, and 300 K is shown to correspond to the LS configuration. The dominant polymorph of 1 features K + cations disordered over a few crystallographic sites, while the minor polymorph includes fully ordered K + cations. The major polymorph exhibits a complete three-step cooperative spin-crossover transition both in the heating and cooling modes: The first step occurs in a temperature range from 2 to 50 K; the second abrupt hysteretic step occurs from 200 to 250 K with T 1/2 = 230 K and a 6 K hysteresis loop. The third gradual step occurs from 250 to 440 K. According to 57 Fe Mössbauer, XRPD, and EXAFS data, the spin-crossover transition for the dominant polymorph is quite peculiar. Indeed, the increase in the HS concentration by 57% at the second step does not result in the expected significant increase in the iron(III)-ligand bond lengths. In addition, the final step of the spin conversion (Δγ HS = 26%) is associated with a structural phase transition with a symmetry lowering from the orthorhombic ( Pbcn ) to the monoclinic ( P 2 1 / n ) space group. This nontrivial phenomenon was investigated in detail by applying magnetization measurements, electron spin resonance, 57 Fe Mössbauer spectroscopy, and DFT calculations. These results provide a new platform for understanding the multistep spin-crossover character in the Fe(III) thsa-complexes and related compounds. |
