Temperature-induced reversible structural phase transition of N-chloromethyl-1,4-diazabicyclo[2.2.2]octonium trichloroaquo-manganese(II)

Thermodynamics of Proton and Electron Transfer in Tetranuclear Clusters with Mn-OH2/OH Motifs Relevant to H2O Activation by the Oxygen Evolving Complex in Photosystem II

We report the synthesis of site-differentiated heterometallic clusters with three Fe centers and a single Mn site that binds water and hydroxide in multiple cluster oxidation states. Deprotonation of Fe^III/II₃Mn^II-OH₂ clusters leads to internal reorganization resulting in formal oxidation at Mn to generate Fe^III/II₃Mn^III-OH. ⁵⁷Fe Mössbauer spectroscopy reveals that oxidation state changes (three for Fe^III/II₃Mn-OH₂ and four for Fe^III/II₃Mn-OH clusters) occur exclusively at the Fe centers; the Mn center is formally Mn^II when water is bound and Mn^III when hydroxide is bound. Experimentally determined p K_a (17.4) of the [Fe^III₂Fe^IIMn^II-OH₂] cluster and the reduction potentials of the [Fe₃Mn-OH₂] and [Fe₃Mn-OH] clusters were used to analyze the O-H bond dissociation enthalpies (BDE_O-H) for multiple cluster oxidation states. BDE_O-H increases from 69 to 78 and 85 kcal/mol for the [Fe^IIIFe^II₂Mn^II-OH₂], [Fe^III₂Fe^IIMn^II-OH₂], and [Fe^III₃Mn^II-OH₂] clusters, respectively. Further insight of the proton and electron transfer thermodynamics of the [Fe₃Mn-OH _x] system was obtained by constructing a potential-p K_a diagram; the shift in reduction potentials of the [Fe₃Mn-OH _x] clusters in the presence of different bases supports the BDE_O-H values reported for the [Fe₃Mn-OH₂] clusters. A lower limit of the p K_a for the hydroxide ligand of the [Fe₃Mn-OH] clusters was estimated for two oxidation states. These data suggest BDE_O-H values for the [Fe^III₂Fe^IIMn^III-OH] and [Fe^III₃Mn^III-OH] clusters are greater than 93 and 103 kcal/mol, which hints to the high reactivity expected of the resulting [Fe₃Mn═O] in this and related multinuclear systems.

High switchable dielectric phase transition originating from distortion in inorganic–organic hybrid materials (H2dabco-C2H5) [MIICl4] (M = Co, Zn)

Two phase transition materials (H₂dabco-C₂H₅)[ZnCl₄] and (H₂dabco-C₂H₅)[CoCl₄] were synthesized and characterized.

Two novel metal–organic coordination polymers based on ligand 1,4-diazabicyclo[2.2.2]octane N,N′-dioxide with phase transition, and ferroelectric and dielectric properties

The synthesis of two low-temperature structural phase transition compounds {[Ag₃(dabcodo)(NO₃)₃]·H₂O}n (1) and [Ca(Dabcodo)(H₂O)₄Cl₂]_n (2) are described. Compound 1 displayed ferroelectric–ferroelectric phase transition.