Mixed-valence compounds based on heterometallic-oxo-clusters containing Sb(III,V): crystal structures and proton conduction

Two isostructural Co(Cd)-antimony-oxo tartrate cluster-based compounds with a one-dimensional (1-D) belt-like structure, namely H9.2[Co(H2O)6]{M0.5(H2O)3.5{M'(H2O)4[SbVO6[Co4.2(H2O)5SbIII6(μ3-O)2(tta)6]]}}2·nH2O (M = Co, M' = Co, n = 9 (1); M = Cd0.39/Co0.61, M' = Cd0.24/Co0.76, n = 7 (2); H4tta = tartaric acid), have been synthesized by solvothermal methods. It is noteworthy that the relatively rare mixed-valence Sb(III,V) exists in the structures. The anionic clusters in both compounds appear to be in a sandwich configuration; the top and bottom layers are based on {Sb3(μ3-O)(tta)3} brackets, and the intermediate layer is occupied by {SbVO6[Co4.2(H2O)5]}. The title compounds have been characterized by single-crystal X-ray diffraction, powder X-ray diffraction, elemental analyses, thermogravimetric analyses, and UV-Vis spectroscopy. We chose compound 2 as a representative to test its proton conductivity, and the results show that the conductivity can reach 1.42 × 10-3 S cm-1 at 85 °C under 98% relative humidity.

Structural Evolution and Properties of Praseodymium Antimony Oxochlorides Based on a Chain-like Tertiary Building Unit

Unveiling the structural evolution of single-crystalline compounds based on certain building units may help greatly in guiding the design of complex structures. Herein, a series of praseodymium antimony oxohalide crystals have been isolated under solvothermal conditions via adjusting the solvents used, that is, [HN(CH2CH3)3][FeII(2,2′-bpy)3][Pr4Sb12O18Cl15]·EtOH (1) (2,2′-bpy = 2,2′-bipyridine), [HN(CH2CH3)3][FeII(2,2′-bpy)3]2[Pr4Sb12O18Cl14)2Cl]·N(CH2CH3)3·2H2O (2), and (H3O)[Pr4Sb12O18Cl12.5(TEOA)0.5]·2.5EtOH (3) (TEOA = mono-deprotonated triethanolamine anion). Single-crystal X-ray diffraction analysis revealed that all the three structures feature an anionic zig-zag chain of [Pr4Sb12O18Cl15−x]n as the tertiary building unit (TBU), which is formed by interconnections of praseodymium antimony oxochloride clusters (denoted as {Pr4Sb12}) as secondary building units. Interestingly, different arrangements or linkages of chain-like TBUs result in one-dimensional, two-dimensional layered, and three-dimensional structures of 1, 2, and 3, respectively, thus demonstrating clearly the structural evolution of metal oxohalide crystals. The title compounds have been characterized by elemental analysis, powder X-ray diffraction, thermogravimetric analysis, and UV-Vis spectroscopy, and the photodegradation for methyl blue in an aqueous solution of compound 1 has been preliminarily studied. This work offers a way to deeply understand the assembly process of intricate lanthanide-antimony(III) oxohalide structures at the atomic level.

Single-Crystal Superstructures via Hierarchical Assemblies of Giant Rubik's Cubes as Tertiary Building Units

Intricate superstructures possess unusual structural features and promising applications. The preparation of superstructures with single-crystalline nature are conducive to understanding the structure-property relationship, however, remains an intriguing challenge. Herein we put forward a new hierarchical assembly strategy towards rational and precise construction of intricate single-crystal superstructures. Firstly, two unprecedented superclusters in Rubik's cube's form with a size of ≈2×2×2 nm³ are constructed by aggregation of eight {Pr₄ Sb₁₂ } oxohalide clusters as secondary building units (SBUs). Then, the Rubik's cubes further act as isolable tertiary building units (TBUs) to assemble diversified single-crystal superstructures. Importantly, intermediate assembly states are captured, which helps illustrate the evolution of TBU-based superstructures and thus provides a profound understanding of the assembly process of superstructures at the atomic level.

Photocatalytic remediation of organic waste over Keggin-based polyoxometalate materials: A review

Photocatalytic remediation of industrial water pollution has courted intense attention lately due to its touted green approach. In this respect, Keggin-based polyoxometalates (POMs) as green solid acids in photocatalytic reaction possess superior qualities, viz. unique photoinduced charge-transfer properties, strong photooxidative-photoreductive ability, high chemical and thermal stability, and so forth. Unfortunately, it suffers from a large bandgap energy, low specific surface area, low recoverability, and scarce utilization in narrow absorption range. Therefore, the pollutant degradation performance is not satisfactory. Consequently, multifarious research to enhance the photocatalytic performance of Keggin-based POMs were reported, viz. via novel modifications and functionalizations through a variety of materials, inclusive of, inter alia, metal oxides, transition metals, noble metals, and others. In order to advocate this emerging technology, current review work provides a systematic overview on recent advancement, initiated from the strategized synthetic methods, followed by hierarchical enhancement and intensification process, at the same time emphasizes on the fundamental working principles of Keggin-based POM nanocomposites. By reviewing and summarizing the efforts adopted global-wide, this review is ended with providing useful outlooks for future studies. It is also anticipated to shed light on producing Keggin-based POM nanocomposites with breakthrough visible- and solar-light-driven photocatalytic performance against recalcitrant organic waste.

Proton-conducting layered structures based on transition metal oxo-clusters supported by Sb(iii) tartrate scaffolds

Two transition metal-antimony oxo-cluster based compounds, H₅{MCd(H₂O)₆[M(H₂O)₃Co₃Sb^VSb(μ₃-O)₈(l-tta)₆]}·7H₂O (1) (M = Cd_0.5 + Co_0.5) and H₃K₅(H₂O)₁₁{Cd(H₂O)₄[Cd(H₂O)Fe₄Cd₂Sb₆(μ₄-O)₅(μ₃-O)₃(l-tta)₆][Cd(H₂O)₂Fe₄Cd₂Sb₆(μ₄-O)₄(μ₃-O)₄(l-tta)₆][Cd(H₂O)₂Fe₄Cd₂Sb₆(μ₄-O)₄(μ₃-O)₄(l-tta)₆Cd(H₂O)₅]}·17H₂O (2) (L-H₄tta = l-tartaric acid) were hydrothermally synthesized and characterized. Compound 1 features a [MCo₃Sb^VSb(μ₃-O)₈(l-tta)₆(H₂O)₃]^9- cluster, while compound 2 contains three types of clusters, namely, [Cd(H₂O)Fe₄Cd₂Sb₆(μ₄-O)₅(μ₃-O)₃(l-tta)₆]^4-, [Cd(H₂O)₂Fe₄Cd₂Sb₆(μ₄-O)₄(μ₃-O)₄(l-tta)₆]^4- and [Cd(H₂O)₂Fe₄Cd₂Sb₆(μ₄-O)₄(μ₃-O)₄(l-tta)₆Cd(H₂O)₅]^2-. All the clusters are of sandwich-type with {Sb₃(μ₃-O)(l-tta)} scaffolds on the top and bottom. The Cd (and M in 1) ions interconnect the clusters into layered structures in both compounds. To the best of our knowledge, this is the first report of transition metal-antimony oxo-clusters that simultaneously contain the first-row and second-raw transition metal ions, and compound 1 represents the first example of such type of clusters that contain Sb(v). The two compounds exhibit proton conductivity with the values of 2.43 × 10^-3 and 2.95 × 10^-3 S cm^-1 at 85 °C under 98% relative humidity, respectively.

Crystal structures and spectral properties of two polyoxometalate-based inorganic-organic compounds from silver-azine building blocks with bis-bidentate and tridentate ligands

Two polyoxometalate-based inorganic-organic hybrid compounds constructed from silver(I)-L species and saturated Keggin type polyoxoanion, [Ag2L2(1)]2(SiMo12O40)·1.5DMF·0.5CH3OH⋅H2O 1 and [{Ag4L2(2)(DMF)5}(SiMo12O40)] 2 (L(1) = phenyl 2-pyridyl ketone azine, L(2) = 3-phenyltriazolo[1,5-a]pyridine), have been synthesized and structurally characterized by IR, UV, elemental analysis, XRPD and complete single crystal structure analyses, where the ligands L(1) and L(2) are bis-bidentate and tridentate azines synthesized with the same materials under different conditions. The structure of 1 exhibits a dinuclear double-helicate with [SiMo12O40](4)(-) anions as counter ions, where all of the Ag centers coordinate to bis-bidentate chelating ligands. Compound 2 displays a two-dimensional sheet formed by the Ag-organic infinite chains and the [SiMo12O40](4)(-) alternately arranged in a "rail-like" fashion. The luminescent properties of 1 and 2 in the solid state were investigated.

Syntheses, structures and photocatalytic properties of five new praseodymium–antimony oxochlorides: from discrete clusters to 3D inorganic–organic hybrid racemic compounds

Presented here are five Pr–Sb–O–Cl cluster-based compounds with structures from discrete organic-decorated cluster to 3D framework that exhibit photocatalytic H₂-evolution activity and magnetic properties.