A fourth polymorph of manganese phosphate, δ-Mn3(PO4)2, crystallizes in the monoclinic space group P21/c with lattice parameters a = 8.9234(6) Å, b = 9.1526(6) Å, c = 8.6587(5) Å, β = 111.6670(10)°, V = 657.21(7) Å3, and Z = 4. Its structure features planes of [MnO5] pentahedra edge- and corner-shared with [PO4] tetrahedra, resulting in a three-dimensional framework containing sub-nanometer channels. Both hydrothermal and solid-state synthesis routes can yield δ-Mn3(PO4)2. In one method, the hydrothermal treatment of Mn5(PO4)2(PO3OH)2·4H2O (hureaulite) at 250 °C for 1–6 h yields δ-Mn3(PO4)2 microcrystals; changing the precursor to Mn3(PO4)2·3H2O nanosheets leads to δ-Mn3(PO4)2 nanoplates. A time study of δ-Mn3(PO4)2 formation under hydrothermal conditions suggests a dissolution–nucleation mechanism. Alternatively, the solid state reaction of LiMnPO4 and β′-Mn3(PO4)2 in a 1:2 molar ratio under air-free conditions at 1000 °C produces δ-Mn3(PO4)2. Differential scanning calorimetry and variable temperature X-ray diffraction measurements show that δ-Mn3(PO4)2 is stable to 735 °C, beyond which it transforms into β′-Mn3(PO4)2. The δ-Mn3(PO4)2 → β′-Mn3(PO4)2 conversion also occurs by hydrothermal treatment at 250 °C for 24 h.

We report 1–2 unit-cell-thick CaF2 nanosheets, which can be converted topochemically into LaF3–2xOx nanosheets that scroll spontaneously. The formation of CaF2 nanosheets is achieved through interlayer confinement and templating within CaSi2 during reaction with aqueous HF. The structure and morphology of these nanosheets are characterized by HRTEM, AFM, and powder XRD. Solid-state MAS and solution 19F NMR spectroscopies provide further information about interstitial fluoride sites within CaF2 nanosheets as well as help identify side products of the CaSi2 + HF reaction. CaF2 nanosheets react with lanthanide salts at room temperature to yield nanostructured hexagonal LnF3 (Ln = Ce, Pr, Nd, Sm, Eu), orthorhombic LnF3 (Ln = Gd, Dy, Ho, Er, Yb), and cubic YbF3–x products. Furthermore, the reaction of CaF2 nanosheets with lanthanum salts is unique in producing LaF3–2xOx. The evidence for this composition includes powder XRD, EDS, XPS, and 19F NMR data. The structure of LaF3–2xOx differs from hexagonal LaF3 only in the replacement of two fluorides by one oxygen. While this topochemical transformation preserves the two-dimensional morphology it also causes lattice strain that initiates scrolling. The resulting product consists of remarkable ∼20 × 5 nm scroll-like tubes of LaF3–2xOx that are unique among metal fluoride materials. These results demonstrate novel metal fluoride nanochemistry and a new scrolling mechanism.

Nanosheets of Bi2WO6 with lateral dimensions of 1–2 μm and thicknesses of 5–15 nm were prepared using Cs4W11O362− nanosheets as the tungsten oxide precursor and lateral template. The formation of these nanosheets was followed by electron microscopy and powder X-ray diffraction techniques. The isolated Bi2WO6 nanosheet product was characterized with respect to structure, morphology, spectroscopic properties, and optical properties. The bandgap energy of Bi2WO6 nanosheets is relatively large at ∼3.1 eV. The chromism of these sheets with respect to UV irradiation and Li+ intercalation was examined in detail. The UV-induced photochromism of dispersed Bi2WO6 nanosheets is highly dependent on the solvent environment, and the initial color change from white to black is reversible. The photochromic properties of “flowerlike” and single crystal Bi2WO6 were evaluated as well. Another color change, pale yellow to brown-black, occurred when lithium ions were intercalated into the Bi2WO6 lattice using n-butyl lithium. Reaction of lithiated Bi2WO6 with water yielded nanofragments of Bi2WO6 rather than nanosheets.

We describe monolayer nanosheets of calcium copper tetrasilicate, CaCuSi4O10, which have strong near-IR luminescence and are amenable to solution processing methods. The facile exfoliation of bulk CaCuSi4O10 into nanosheets is especially surprising in view of the long history of this material as the colored component of Egyptian blue, a well-known pigment from ancient times.

Nanosheets of Bi2WO6 with lateral dimensions of 1–2 μm and thicknesses of 5–15 nm were prepared using Cs4W11O362− nanosheets as the tungsten oxide precursor and lateral template. The formation of these nanosheets was followed by electron microscopy and powder X-ray diffraction techniques. The isolated Bi2WO6 nanosheet product was characterized with respect to structure, morphology, spectroscopic properties, and optical properties. The bandgap energy of Bi2WO6 nanosheets is relatively large at ∼3.1 eV. The chromism of these sheets with respect to UV irradiation and Li+ intercalation was examined in detail. The UV-induced photochromism of dispersed Bi2WO6 nanosheets is highly dependent on the solvent environment, and the initial color change from white to black is reversible. The photochromic properties of “flowerlike” and single crystal Bi2WO6 were evaluated as well. Another color change, pale yellow to brown-black, occurred when lithium ions were intercalated into the Bi2WO6 lattice using n-butyl lithium. Reaction of lithiated Bi2WO6 with water yielded nanofragments of Bi2WO6 rather than nanosheets.