Titanium phosphorus oxides (TiPOs) are promising energy-conversion materials, but most are of tetravalent titanium (TiIV), with the trivalent TiIIIPOs less explored because of instability and obstacles in synthesis. In this study, we used a simple synthetic strategy and prepared three new TiIIIPOs with different phosphorus oxoanions: the phosphate Ca2Ti(HPO4)2(PO4)·H2O (1), the phosphite CaTi2(H2O)(HPO3)4·H2O (2), and the hypophosphite Ti(H2PO2)3 (3). Each possesses different structures in one, two, and three dimensions, yet they are related to one another because of their infinite chains. Compound 1 exhibits proton-coupled electron transfer (PCET) reactivity in a solid state, losing one proton from its own HPO4 in oxidation to yield Ca2Ti(HPO4)(PO4)2·H2O (designated as 1 O ), while compound 2 also exhibits PCET reactivity in which the octahedral core [TiIII(H2O)]3+ gives off two protons to become a titanyl unit [TiIVO]2+ under oxidation, yielding CaTi2O(HPO3)4·H2O (2 O ). Both 1 O and 2 O retain their original frameworks from before oxidation, but there are some changes in the hydrogen and Ti–O bonds that affect the IR absorption and powder X-ray diffraction patterns. Compound 3 represents the first titanium hypophosphite, and two polymorphs were discovered that show structures related to 1 and 2. This work demonstrates a simple strategy that is effective for preparing titanium(III) compounds in a pure phase; further, new findings in the pathways of solid-state PCET reactions promote a greater understanding of the self-sustaining oxidation behavior for TiIIIPO solid materials.
The formation of unique nanometer-sized organic supramolecular assemblies was observed in the lamellar space of metal phosphate host lattices. Two new chiral and achiral organic-inorganic hybrid materials, zinc phosphate, (H 3 tren) 2 [Zn 3 (PO 4 ) 4 ] . 2NDA(ZnP-NDA) and zinc-cobalt phosphate, (H 3 tren) 2 [Zn 1.6 Co 1.4 (PO 4 ) 4 ] . 2NDA (ZnCoP-NDA) have been synthesized under hydrothermal conditions. The crystalline host framework was built with corner-sharing MO 4 (M=Zn or Zn/Co) and PO 4 tetrahedra. In between these framework layers, aromatic dicarboxylic acid, 2,6-Naphthalene dicarboxylic acids (NDA) are held together by means of strong hydrogen bonding and π-π stacking interactions resulting in infinite supramolecular zigzag chains. After incorporating the cobalt into inorganic host lattice, astonishingly, the chiral structure tuns achiral. The crystal structures were elucidated by single crystal X-ray diffraction and characterized by powder XRD, elemental analysis, thermogravimetry and photoluminescence measurements.
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