Stress‐Induced Domain Wall Motion in a Ferroelastic Mn³⁺ Spin Crossover Complex

Abstract

Domain wall motion is detected for the first time during the transition to a ferroelastic and spin state ordered phase of a spin crossover complex. Single‐crystal X‐ray diffraction and resonant ultrasound spectroscopy (RUS) revealed two distinct symmetry‐breaking phase transitions in the mononuclear Mn 3+ compound [Mn(3,5‐diBr‐sal 2 (323))]BPh 4 , 1. The first at 250 K, involves the space group change Cc → Pc and is thermodynamically continuous, while the second, Pc → P 1 at 85 K, is discontinuous and related to spin crossover and spin state ordering. Stress‐induced domain wall mobility was interpreted on the basis of a steep increase in acoustic loss immediately below the the Pc ‐ P 1 transition

General Landau theory of non-symmetry-breaking and symmetry-breaking spin transition materials

“…The competition between short-range elastic interaction, favoring alternation of molecules in different spin states with different volume, and long-range elastic interactions due to the global crystalline volume change, favoring molecules in the same spin state, can generate stepwise spin transition curves, 30,31,66 as reported in many Fe II , Fe III , Co II , and Mn III complexes. 28,30,31,48,61,63,[67][68][69][70][71][72][73][74][75][76][77][78] Variety of stepwise of processes were studied theoretically. 79,80 More and more systems are reported to undergo sequences of phases with a fully HS state at high temperature, an intermediate Here again the stability condition is found with: = 0 = ( + 2 2 + 2 ) = 0.…”

Modulation of Mn3+ Spin State by Guest Molecule Inclusion

“…Hydrogen-bonding is a particularly effective tool in modulating SCO and this approach was successfully used to generate an extended homochiral 2D sheet of mixed valence Fe 2+ /Fe 3+ sites, which exhibited SCO and light induced excited spin state trapping (LIESST) [36]. In our own work with the [Mn(R-sal 2 323)] + series of Schiff base complexes, we have established that thermal SCO is possible in the less studied d 4 ion Mn 3+ [37][38][39][40][41][42][43][44][45][46]. The hexadentate ligand type used in this approach results from condensation of 1,2-bis(3-aminopropylamino)ethane with a substituted 2-hydroxybenzaldehyde, and the ligand series may be abbreviated as R-Sal 2 323 to indicate the 323 alkyl connectivity in the starting tetraamine and the substitution (R) on the phenolate ring.…”

“…Complexes ( 1) and (2) crystallize isostructurally in monoclinic space group P2 1 /c with Z = 4 where the asymmetric unit contains a full [MnL 1 ] + cation and one full triflate or one full hexafluorophosphate anion, respectively, Figure 2. The hexadentate Schiff base ligand chelates the Mn 3+ centre in pseudo octahedral geometry with two trans-phenolate donors, O1 and O3, two cis-amine and two cis-imine donor atoms, in the same way as previously observed for manganese complexes with this ligand type [37][38][39][40][41][42][43][44][45][46]48]. Residual electron density in both data sets was modelled as part occupancy water molecules using Platon SQUEEZE [47].…”

Stress‐Induced Domain Wall Motion in a Ferroelastic Mn3+ Spin Crossover Complex

“…Perspective view of the LT P1( 83 K), INT Pc (110 K) and HT Cc (250 K) structures of complex 1. [34]…”