Phase transitions affecting intramolecular electron transfer in mixed-valence trinuclear iron acetate complexes

Calorimetric investigations of phase transitions in which electrons are directly involved

“…The (76,77) [Mn 3 O(O 2 CCH 3 ) 6 (py) 3 ] · (py) (2), (78,79) [ (80,81) [Fe 3 O(O 2 CCH 3 ) 6 (4-Me-py) 3 ] · (CHCl 3 ) (4), (82) [Fe 3 O(O 2 CCH 3 ) 6 (3-Me-py) 3 ] · (3-Me-py) (5), (83) 3 ] · (toluene) (6), (84) 8). (85) The complexes 1-4 commonly crystallize into an identical rhombohedral crystal system with the space group R32 in the valencedetrapped high temperature phases.…”

“…The spectrum eventually becomes a single doublet above about T = 190 K. This fact indicates that the rate of intramolecular electron-transfer exceeds the rate of 10 7 s −1 which the Mössbauer technique can sense. Figure 19 (76,77) shows the molar heat capacity of this complex. This complex exhibits essentially two kinds of phase transitions: one is a first-order phase transition at about T = 112 K and the other is a higher-order phase transition around T = 190 K. Interestingly, the low-temperature phase transition takes place at the temperature at which the first change in the Mössbauer spectrum occurs and the peak temperature of the high-temperature phase transition is identical with the temperature where the Mössbauer spectrum becomes a single average doublet.…”

Magnetic Field Effects in Charge-Ordered Mixed-Valence Trimeric Clusters

“…Taking into account the strong screening of the cluster cations by ligands, we further employ the approximation of nearest neighbour sites and consider only the interaction of a MV molecule with six other molecules in the neighbouring stacks as it occurs in basic transition metal acetates [29][30][31][32][33][34]. In this approximation for the molecular field parameters we obtain L xx ¼ L yy ¼ L, L xy ¼ 0.…”

“…The charge-ordered state is identified in crystals of dialkylbiferrocenium triiodide with substituent ions X ¼ H, CH 2 CH 3 , (CH 2 ) 2 CH 3 , (CH 2 ) 3 CH 3 , and in crystals of dihalobiferrocenium triiodide and dibromiodide with the substituent ions X ¼ Br, I [20][21][22][23][24][25][26][27][28]. The phenomenon of charge ordering was also detected in trinuclear MV metal acetate compounds [M 3 O(O 2 CCH 3 ) 6 (L) 3 ]S [29][30][31][32][33][34], where M is a transition metal element such as iron or manganese, L is a ligand, and S is a solvate molecule. Charge ordering was investigated using Mö ssbauer spectroscopy, electron paramagnetic resonance, as well as with the help of a series of other methods [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34].…”

“…The phenomenon of charge ordering was also detected in trinuclear MV metal acetate compounds [M 3 O(O 2 CCH 3 ) 6 (L) 3 ]S [29][30][31][32][33][34], where M is a transition metal element such as iron or manganese, L is a ligand, and S is a solvate molecule. Charge ordering was investigated using Mö ssbauer spectroscopy, electron paramagnetic resonance, as well as with the help of a series of other methods [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. The vast experimental material induced the appearance of a new trend within the MV theory: the investigation of interacting clusters.…”