Two binuclear Ni-inserted polyoxotantalates based on {NiTa10O32} units with catalytic activity.

Two Ni-inserted polyoxotantalates, K5.5Na2H0.5[Ni(H2O)2{NiTa10O30(OH)2}]·21H2O (1) and K6Na4[Ni(en){NiTa10O32}]·22H2O (2, en = ethanediamine), were synthesized in this work. Crystallographic data analyses reveal that 1 and 2 have similar configurations. A minor difference between these two structures is that the {Ni(H2O)2} unit in 1 is replaced by {Ni(en)} unit in 2. Notably, the other Ni in 1 and 2 is located as a heteroatom at the center of the {Ta10} unit, which is reported in POTas for the first time. Moreover, 2 exhibits excellent catalytic performance in transesterification reactions in a preliminary exploration of the catalytic ability of the synthesized POTas.

Polyoxotantalate chemistry: from synthetic strategies to structural diversity and applications.

Since the famous Swedish chemist Scheele described molybdenum blue for the first time in 1778, polyoxometalate (POM) chemistry has made significant progress in its more than 200-year history. Compared with the POM chemistry of Mo, W and V, significant improvement of polyoxotantalates (POTas) occurred mainly during the last few years. In this paper, complexes with different structures, including isopolyoxotantalates (IPOTas), organic-inorganic hybrid POTas, Ta/W mixed POMs and heteropolyoxotantalates (HPOTas) with their derivatives, are reviewed, aiming at providing some useful guidance for further exploration and discovery of more exciting POTas with innovative architectures and excellent performances. Herein, we highlight and discuss the structural features of POTas according to various structural types. In addition, the synthesis strategies and related applications, especially in photocatalysis, are reviewed.

Three Types of Lanthanide-Containing Polyoxoniobates and Their Luminescence Properties.

Fourteen lanthanide (Ln)-containing hetero selenato-phosphato-peroxopolyoxoniobates in three series: (1) Cs2{[Ln(H2O)4][H4P2Se2Nb6(O2)6O22]}2·nH2O [Ln = Ce (I-Ce), Pr (I-Pr), Sm (I-Sm), Eu (I-Eu), Gd (I-Gd); I-Ce, I-Pr, I-Eu, I-Gd n = 12; I-Sm n = 16]; (2) Cs2K3{[Ln(H2O)6][H2.5P2Se2Nb6(O2)6O22]}2·nH2O [Ln = Dy (II-Dy), Tm (II-Tm), Yb (II-Yb), Lu (II-Lu); II-Dy n = 14; II-Tm n = 24; II-Yb, II-Lu n = 13]; (3) Cs5K2Hm{[Ln(H2O)6][P2Se2Nb6(O2)6O22]}2{[Lnx(H2O)y]2[P2Se2Nb6(O2)6O22]}·nH2O [Ln = Ho (III-Ho), Er (III-Er), Tm (III-Tm), Yb (III-Yb), Lu (III-Lu), III-Ho-III-Yb m = 5, x = 1; y = 5; III-Lu m = 6.5; x = 0.75; y = 4; III-Ho-III-Tm n = 19, III-Yb n = 34; III-Lu n = 31], have been isolated by a one-pot reaction and structurally characterized by various physical and chemical analyses. These compounds represent the first group of Ln-functionalized polyoxoniobates with mixed heteroatoms. In addition, the photoluminescence properties of compounds I-Sm, I-Eu, and II-Dy were measured, and the time-resolved emission spectra showed that the {P2Se2Nb6} segment contributed to the energy transfer from the polyoxoniobate units to the Ln3+ center, which effectively promoted the emission of the Ln3+ center.

Synthesis, structures and stability of three V-substituted polyoxoniobate clusters based on [TeNb9O33]17- units.

Three structurally intriguing polyoxoniobates (PONbs) based on the trivacant B-type α-Keggin ion {TeNb9O33}, H4K(CN3H6)2{[Cu4(2,2'-bipy)4(H2O)2][TeNb9V2O37]}·29H2O (1, 2,2'-bipy = 2,2'-bipyridine), H0.5K5Na2.5{[Cu(en)H2O]3[TeNb9V3O39]}·10H2O (2, en = ethylenediamine), and K3Na5{[Cu(1,3-dap)H2O]3[TeNb9V3O39]}·11H2O (3, 1,3-dap = 1,3-diaminopropane), are assembled by the conventional aqueous solution methods using a series of N-containing organic ligands. In 1, each of the two {VO4} units is attached to two coplanar NbO6 octahedra on the {Nb3O13} cluster of the {TeNb9O33} unit. Differently, three {VO4} units in 2 and 3 are linked to two edge-sharing NbO6 octahedra, respectively. Compounds 1-3 represent the first oxo NbTeV clusters and also the first vanadoniobates based on the trivacant Keggin PONb units. All three compounds were characterised by single-crystal X-ray structural analysis, TGA and IR, ESI-MS and 51V NMR spectroscopy. Furthermore, the magnetic properties of compounds 1 and 2 were also studied.

Selenotungstates incorporating organophosphonate ligands and metal ions: synthesis, characterization, magnetism and catalytic efficiency in the Knoevenagel condensation reaction.

Three sandwich-type TM-containing (TM = transition metal) organophosphonate-based polyoxotungstate clusters, [TM(H2O)4(SeW6O21)2{Co(OOCCH2NCH2PO3)2}3]12- (TM = Co, Ni), have been successfully synthesized, which are the first reported TM-containing organophosphonate-based selenotungstates. They were structurally characterized by PXRD analyses, IR spectroscopy, TGA analyses, etc. Magnetic measurements show that all three compounds exhibit antiferromagnetic interactions. Besides, Co1 can be used as an efficient heterogeneous catalyst in the Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate under mild conditions (60 °C), and exhibits satisfactory conversion (93%) and high selectivity (99%).

A 1D Helical Chain Heterpolyniobate Templated by AsO33.

A novel polyoxoniobate cluster directed by AsO33-, {[Cu(phen)]5[Nb6O19][As2Nb6O22]}2 (1a), has been successfully synthesized by a "two-pot" strategy, namely, the conventional aqueous solution and diffusional methods. It incorporates two {[Cu(phen)]2Nb6O19} and two {[Cu(phen)]3As2Nb6O22} subunits. Surprisingly, by changing the reaction conditions, one of the subunits {[Cu(phen)]2Nb6O19} was isolated as a guanidinium salt. These architectures were structurally characterized by single crystal X-ray diffraction, TGA, IR, elemental analysis and PXRD, etc. Furthermore, the behavior of 1 in aqueous solution was measured by electrospray ionization mass spectrometry, and the magnetic property in the low temperature range indicates the presence of antiferromagnetic interactions.

An unprecedented [{Fe5O5(OH)2(OAc)2}2{W2O2(OH)}] cluster sandwiched in the tetravacant tungstophosphate.

A novel tungstophosphate H12Na4K3[{Fe5O5(OH)2(OAc)2}2{W2-O2(OH)}{P2W14O54}2]·36H2O (1) containing an unprecedented [{Fe5O5(OH)2(OAc)2}2{W2O2(OH)}] unit has been successfully obtained and characterized by IR, TGA, magnetic susceptibility measurements and single-crystal X-ray diffraction. It shows a decameric FeIII molecular assembly formed through two {Fe5O23} subunits bridged by a {W2O3} motif.

A novel peroxopolyoxoniobate incorporating mixed heteroatoms: [P2Se2Nb6(O2)6O22]8- .

A novel hetero selenato-phosphato-peroxopolyoxoniobate with the formula Cs4H4[P2Se2Nb6(O2)6O22]·10H2O has been successfully isolated in an acidified aqueous hydrogen peroxide solution. The synthesized cluster represents the first example of a selenium-containing polyoxoniobate. Furthermore, the ESI-MS spectra show that the polyoxoanion structural unit [P2Se2Nb6(O2)6O22]8- remains intact in aqueous solution.

The {Ni10Nb32} aggregate: a perspective on isopolyniobates as ligands.

[H4Ni10(H2O)8Nb32O102]20-, representing the first high-nuclear nickel-cation-bridged polyoxoniobate, has been synthesized. It incorporates two [{Ni2O4}(H2O)2(Nb6O19)]12- and two [Ni3(H2O)2Nb10O34]12- subunits exhibiting a rhombus-like architecture. Furthermore, the solution behaviour was examined by electrospray ionization mass spectrometry and the magnetic properties in the low temperature range indicate the presence of ferromagnetic interactions.