@article{luo_chen_maggard_2020, title={Rare example of chiral and achiral polymorphs of a metal-oxide/organic hybrid compound}, volume={287}, ISSN={["1095-726X"]}, DOI={10.1016/j.jssc.2020.121358}, abstractNote={Hydrothermal techniques have been used to prepare two new Cu(I)/Mo(VI)-oxide hybrids that represent a rare example of crystallization of both achiral (1) and chiral (2) polymorphic structures with the composition CuMoO3(p2c) (p2c ​= ​pyrazine-2-carboxylate). Their structures were characterized by single-crystal X-ray diffraction (1 - space group: P21/c, Z ​= ​4; a ​= ​8.4965(3) Å, b ​= ​12.7471(5) Å, c ​= ​7.2850(3) Å), β ​= ​97.147(2)o, and 2 - P32, Z ​= ​3, a ​= ​7.6789(2) Å, c ​= ​10.9164(5) Å) and found to consist of highly-distorted MoO5N octahedra that are vertex-bridged to form -O-Mo-O-Mo-O- chains and connected to each other via the coordinating p2c ligands and Cu(I) cations. In the achiral structure of 1, the p2c ligands and Cu(I) cations are coordinated to a single side of the extended -O-Mo-O-Mo-O- chains. In the chiral structure of 2, by contrast, these coordinate via a helical-type arrangement down the 32 screw axis with a rotation of 120° between neighboring octahedra. The chiral polymorph is favored with higher pressure and exhibits a correspondingly higher density owing to the greater packing efficiency of the helical chains, with calculated densities (g cm−3) of 2.81 and 2.95 for 1 and 2, respectively. Both are found to have nearly identical band gaps of ~1.37 ​eV, which are significantly smaller than in other related Cu/Mo oxides . Density functional theory calculations show that 1 exhibits a slightly lower energy of ~89 ​meV per formula (or ~8.6 ​kJ ​mol−1) as compared to 2 and is thus energetically favored. Given the higher calculated energy of the chiral polymorph, 2, this suggests that the application of higher pressures can provide a convenient driving force for the crystallization of higher-density, helical-chain structures that are noncentrosymmetric.}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Luo, Lan and Chen, Yunhua and Maggard, Paul A.}, year={2020}, month={Jul} }
 @article{luo_ou_smirnova_maggard_2016, title={Synthesis of New Mixed-Metal Ammonium Vanadates: Cation Order versus Disorder, and Optical and Photocatalytic Properties}, volume={16}, ISSN={["1528-7505"]}, DOI={10.1021/acs.cgd.6b00851}, abstractNote={Two new ammonium vanadate hydrates, i.e., M3(H2O)2V8O24·2NH4 (M = Mn and Co, I and II, respectively) were synthesized using hydrothermal reaction conditions, and their structures were determined by single crystal X-ray diffraction [I: P2/m (No. 10), Z = 1, a = 8.2011(2) A, b = 3.5207(1) A, c = 9.9129(3) A, β = 110.987(2)°; II: C2/m (No. 12), Z = 2, a = 19.4594(6) A, b = 6.7554(2) A, c = 8.4747(3) A, β = 112.098(2)°]. Interestingly, the two structures are homeotypic, with the structure of I exhibiting an uncommon type of structural disorder between locally-bridging Mn(H2O)22+ (i.e., part of the oxide framework) and nonbridging NH4+ cations over the same site (1:2 ratio), wherein two NH4+ ions occupy the same site as the two H2O molecules when Mn(II) is vacant. The amount of Mn(II) in the formula of I was determined by a combination of techniques, including electron paramagnetic resonance, while the relative amounts of NH4+/H2O in its structure were determined by combined thermogravimetric-mass spectrometry...}, number={10}, journal={CRYSTAL GROWTH & DESIGN}, author={Luo, Lan and Ou, Erkang and Smirnova, Tatyana I. and Maggard, Paul A.}, year={2016}, month={Oct}, pages={5762–5770} }
 @article{dufficy_luo_fedkiw_maggard_2016, title={Vacancy-induced manganese vanadates and their potential application to Li-ion batteries}, volume={52}, ISSN={["1364-548X"]}, DOI={10.1039/c6cc02249a}, abstractNote={We report on the synthesis and characterization of a novel manganese vanadate, Mn1.5(H2O)(NH4)V4O12, with rare in situ disorder of Mn(H2O)22+/2NH4+.}, number={47}, journal={CHEMICAL COMMUNICATIONS}, author={Dufficy, Martin K. and Luo, Lan and Fedkiw, Peter S. and Maggard, Paul A.}, year={2016}, pages={7509–7512} }
 @article{luo_zeng_li_luo_smirnova_maggard_2015, title={Manganese-Vanadate Hybrids: Impact of Organic Ligands on Their Structures, Thermal Stabilities, Optical Properties, and Photocatalytic Activities}, volume={54}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.5b00931}, abstractNote={Manganese(II)-vanadate(V)/organic hybrids were prepared in high purity using four different N-donor organic ligands (2,6:2',2″-terpyridine = terpy, 2,2'-bipyrimidine = bpym, o-phenanthroline = o-phen, and 4,4'-bipyridine = 4,4'-bpy), and their crystalline structures, thermal stabilities, optical properties, photocatalytic activities and electronic structures were investigated as a function of the organic ligand. Hydrothermal reactions were employed that targeted a 1:2 molar ratio of Mn(II)/V(V), yielding four hybrid solids with the compositions of Mn(terpy)V2O6·H2O (I), Mn2(bpym)V4O12·0.6H2O (II), Mn(H2O)(o-phen)V2O6 (III), and Mn(4,4'-bpy)V2O6·1.16H2O (IV). The inorganic component within these hybrid compounds, that is, [MnV2O6], forms infinite chains in I and layers in II, III, and IV. In each case, the organic ligand preferentially coordinates to the Mn(II) cations within their respective structures, either as chelating and three-coordinate (mer isomer in I) or two-coordinate (cis isomers in II and III), or as bridging and two coordinate (trans isomer in IV). The terminating ligands in I (terpy) and III (o-phen) yield nonbridged "MnV2O6" chains and layers, respectively, while the bridging ligands in II (bpym) and IV (4,4'-bpy) result in three-dimensional, pillared hybrid networks. The coordination number of the ligand, that is, two- or three-coordinate, has the predominant effect on the dimensionality of the inorganic component, while the connectivity of the combined metal-oxide/organic network is determined by the chelating versus bridging ligand coordination modes. Each hybrid compound decomposes into crystalline MnV2O6 upon heating in air with specific surface areas from ∼7 m(2)/g for III to ∼41 m(2)/g for IV, depending on the extent of structural collapse as the lattice water is removed. All hybrid compounds exhibit visible-light bandgap sizes from ∼1.7 to ∼2.0 eV, decreasing with the increased dimensionality of the [MnV2O6] network in the order of I > II ≈ III > IV. These bandgap sizes are smaller by ∼0.1-0.4 eV in comparison to related vanadate hybrids, owing to the addition of the higher-energy 3d orbital contributions from the Mn(II) cations. Each compound also exhibits temperature-dependent photocatalytic activities for hydrogen production under visible-light irradiation in 20% methanol solutions, with threshold temperatures of ∼30 °C for III, ∼36 °C for I, and ∼40 °C for II, IV, and V4O10(o-phen)2. Hydrogen production rates are ∼142 μmol H2 g(-1)·h(-1), ∼673 μmol H2 g(-1)·h(-1), ∼91 μmol H2 g(-1)·h(-1), and ∼218 μmol H2 g(-1)·h(-1) at 40 °C, for I, II, III, and IV, respectively, increasing with the oxide/organic network connectivity. In contrast, the related V4O10(o-phen)2 exhibits a much lower photocatalytic rate of ∼36 H2 g(-1)·h(-1). Electronic structure calculations based on density-functional theory methods show that the valence band edges are primarily derived from the half-filled Mn 3d(5) orbitals in each, while the conduction band edges are primarily comprised of contributions from the empty V 3d(0) orbitals in I and II and from ligand π* orbitals in III. Thus, the coordinating organic ligands are shown to significantly affect the local and extended structural features, which has elucidated the underlying relationships to their photocatalytic activities, visible-light bandgap sizes, electronic structures, and thermal stabilities.}, number={15}, journal={INORGANIC CHEMISTRY}, author={Luo, Lan and Zeng, Yuhan and Li, Le and Luo, Zhixiang and Smirnova, Tatyana I. and Maggard, Paul A.}, year={2015}, month={Aug}, pages={7388–7401} }
 @article{luo_lin_li_smirnova_maggard_2014, title={Copper-Organic/Octamolybdates: Structures, Bandgap Sizes, and Photocatalytic Activities}, volume={53}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/IC402910A}, DOI={10.1021/ic402910a}, abstractNote={The structures, optical bandgap sizes, and photocatalytic activities are described for three copper-octamolybdate hybrid solids prepared using hydrothermal methods, [Cu(pda)]4[β-Mo8O26] (I; pda = pyridazine), [Cu(en)2]2[γ-Mo8O26] (II; en = ethylenediamine), and [Cu(o-phen)2]2[α-Mo8O26] (III; o-phen = o-phenanthroline). The structure of I consists of a [Cu(pda)]4(4+) tetramer that bridges to neighboring [β-Mo8O26](4-) octamolybdate clusters to form two-dimensional layers that stack along the a axis. The previously reported structures of II and III are constructed from [Cu2(en)4Mo8O26] and [Cu2(o-phen)4Mo8O26] clusters. The optical bandgap sizes were measured by UV-vis diffuse reflectance techniques to be ∼1.8 eV for I, ∼3.1 eV for II, and ∼3.0 eV for III. Electronic structure calculations show that the smaller bandgap size of I originates primarily from an electronic transition between the valence and conduction band edges comprised of filled 3d(10) orbitals on Cu(I) and empty 4d(0) orbitals on Mo(VI). Both II and III contain Cu(II) and exhibit larger bandgap sizes. Accordingly, aqueous suspensions of I exhibit visible-light photocatalytic activity for the production of oxygen at a rate of ∼90 μmol O2 g(-1) h(-1) (10 mg samples; radiant power density of ∼1 W/cm(2)) and a turnover frequency per calculated surface [Mo8O26](4-) cluster of ∼36 h(-1). Under combined ultraviolet and visible-light irradiation, I also exhibits photocatalytic activity for hydrogen production in 20% aqueous methanol of ∼316 μmol H2 g(-1) h(-1). By contrast, II decomposed during the photocatalysis measurements. The molecular [Cu2(o-phen)4(α-Mo8O26)] clusters of III dissolve into the aqueous methanol solution under ultraviolet irradiation and exhibit homogeneous photocatalytic rates for hydrogen production of up to ∼8670 μmol H2·g(-1) h(-1) and a turnover frequency of 17 h(-1). The clusters of III can be precipitated out by evaporation and redispersed into solution with no apparent decrease in photocatalytic activity. During the photocatalysis measurements, the dissolution of the clusters in III is found to occur with the reduction of Cu(II) to Cu(I), followed by subsequent detachment from the octamolybdate cluster. The lower turnover frequency, but higher photocatalytic rate, of III arises from the net contribution of all dissolved [Cu2(o-phen)4(α-Mo8O26)] clusters, compared to only the surface clusters for the heterogeneous photocatalysis of I.}, number={7}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Luo, Lan and Lin, Haisheng and Li, Le and Smirnova, Tatyana I. and Maggard, Paul A.}, year={2014}, month={Mar}, pages={3464–3470} }
 @article{luo_maggard_2013, title={Effect of Ligand Coordination on the Structures and Visible-Light Photocatalytic Activity of Manganese Vanadate Hybrids}, volume={13}, ISSN={["1528-7505"]}, DOI={10.1021/cg401062f}, abstractNote={A new manganese–vanadate hybrid structure, Mn(H2O)(bpy)V2O6 (I; bpy = 2,2′-bipyridine), has been synthesized via hydrothermal methods and characterized by single crystal X-ray diffraction [P21/n, Z = 4, a = 6.8557(4) A, b = 10.4900(6) A, c = 19.7921(13) A, β = 96.419(4)°], infrared spectroscopy, thermogravimetric analysis, magnetic susceptibility measurements, and UV–vis diffuse reflectance. The structure is comprised of manganese vanadate layers with 2,2’-bipyridine ligands coordinated to the Mn(II) cations. The water molecules coordinated to the manganese sites can be reversibly desorbed at ∼190 °C with the formation of a new hybrid structure before then further decomposing to MnV2O6 upon heating to 300 °C. Notably, I undergoes a reversible structural transformation to Mn(bpy)V4O11(bpy) (II) under hydrothermal conditions. This structural transformation results from additional bpy-ligand coordination to 1/4 of the vanadium sites. Magnetic data indicate Mn(II) cations in both I and II are high spin (S = 5...}, number={12}, journal={CRYSTAL GROWTH & DESIGN}, author={Luo, Lan and Maggard, Paul A.}, year={2013}, month={Dec}, pages={5282–5288} }