Controlling transformations in the assembly of polyoxometalate clusters: {Mo11V7}, {Mo17V8} and {Mo72V30}

The reaction of molybdate with vanadium(V) in the presence of sulfite anions is explored showing how, via cation control, stepwise assembly through the {Mo(11)V(7)} cluster yields a {M(25)} cluster-based compound, [Mo(VI)(11)V(V)(5)V(IV)(2)O(52)(μ(9)-SO(3))(Mo(VI)(6)V(V)O(22))](10-) (1a), which was first discovered using cryospray mass spectrometry, whereas switching the cation away from ammonium allows the direct formation of the spherical 'Keplerate' {Mo(72)V(30)} cluster.     

From platonic templates to Archimedean solids: successive construction of nanoscopic {V16As8}, {V16As10}, {V20As8}, and {V24As8} polyoxovanadate cages

Supramolecular coordination cages provide unique restricted inner cavities that can be exploited for molecular recognition purposes and catalysis. Their syntheses often involve complex self-organization processes and rely on the identification of preorganized, kinetically stable building units that provide ligand-accessible coordination sites. Here we report a highly effective protocol for the successive buildup of symmetrical nanoscopic polyoxometalate (POM) cages. Our methodology takes advantage of a supramolecular templating effect and utilizes the structure-directing influence of octahedral {X(x)(H(2)O)(6-x)} (X = Br(-), Cl(-); x = 2, 4, 6) assemblies that reside inside the hollow cluster shells and determine the arrangement of di- and tetranuclear vanadate units. The approach allows the preparation of a series of high-nuclearity POM cages that are characterized by {V(16)As(8)}, {V(16)As(10)}, {V(20)As(8)}, and {V(24)As(8)} core structures. In the latter cluster cage, the vanadium centers adopt a truncated octahedral topology. The formation of this Archimedean body is the direct result of the assembly of six square {V(4)O(8)} units that cap the vertices of the encapsulated Platonic {Cl(6)} octahedron. To the best of our knowledge, this {V(24)As(8)} cage is the largest hybrid vanadate cluster reported to date.     

Exploring the structure and properties of transition metal templated {VM17(VO4)2} Dawson-like capsules

Vanadate(V)-templated Dawson-type capsules {V(IV)M(VI)(17)(VO(4))(2)} (M = Mo, W; 1-2) have been synthesized and investigated by electrochemical methods in aqueous and organic media using spectroscopic techniques, EPR, UV-vis/NIR, IR, and CSI-MS (cryospray ionization mass spec.), and the clusters have been examined in the solid state by magnetic studies. The collision-induced dissociation (CID-MS) studies confirmed the solution structures as well as helped pinpoint the position of the vanadium ion on the {VM(17)}-type shell, which was corroborated by EPR and theoretical studies.     

Structural Variety of Niobium(V) Polyoxo Clusters Obtained from the Reaction with Aromatic Monocarboxylic Acids: Isolation of {Nb2O}, {Nb4O4} and {Nb8O12} Cores

The reactivity of aryl monocarboxylic acids (benzoic, 1- or 2-naphtoic, 4’-methylbiphenyl-4-carboxylic, and anthracene-9-carboxylic acids) as complexing agents for the ethoxide niobium(V) (Nb(OEt)₅ precursor has been investigated. A total of eight coordination complexes were isolated with distinct niobium(V) nuclearities as well as carboxylate complexation states. The use of benzoic acid gives a tetranuclear core Nb₄(μ₂-O)₄(L)₄(OEt)₈] (L=benzoate ( 1 )) with four Nb−(μ₂-O)−Nb linkages in a square plane configuration. A similar tetramer, 7 , was obtained with 2-naphtoic acid by using a 55 % humid atmosphere synthetic route. Two types of dinuclear brick were identified with one central Nb−(μ₂-O)−Nb linkage; they differ in their complexation state, with one bridging carboxylate ([Nb₂(μ₂-O)(μ₂-OEt)(L)(OEt)₆], with L=1-naphtoate ( 3 ) or anthracene-9-carboxylate ( 5 )) or two bridging carboxylate groups ([Nb₂(μ₂-O)(L)₂(OEt)₆], with L=4’-methylbiphenyl-4-carboxylic ( 4 ) or anthracene-9-carboxylate ( 6 )). An octanuclear moiety [Nb₈(μ₂-O)₁₂(L)₈(η₁-L)_4−x(OEt)_4+x] (with L=2-naphtoate, x=0 or 2; 8 ) was obtained by using a solvothermal route in acetonitrile; it has a cubic configuration with niobium centers at each node, linked by 12 μ₂-O groups. The formation of the niobium oxo clusters was characterized by infrared and liquid ¹H NMR spectroscopy in order to analyze the esterification reaction, which induces the release of water molecules that further react through oxolation with niobium atoms, in different {Nb₂O}, {Nb₄O₄} and {Nb₈O₁₂} nuclearities.     

二{2-{2-{9-乙基-6-[2-(8-羟基喹啉-2-基)乙烯基]咔唑-3-基}乙烯}-8-羟基喹啉}锌配合物的合成与荧光光谱特性

合成了新的N-乙基咔唑衍生物: 3,6-二[2-(8-羟基喹啉基)乙烯基]咔唑(4)及其锌配合物(5); 化合物4经质谱、红外光谱、核磁共振氢谱、元素分析表征其结构, 并测定了它的荧光光谱. 结果显示: 化合物4的荧光发射为蓝绿色光(500 nm), 其发射光谱随着溶剂极性的增大荧光光谱向长波方向移动(即发生红移); 同时, 考察了化合物5的荧光性质, 其荧光发光峰值为600 nm, 与2-甲基-8-羟基喹啉锌相比, 发生了明显的红移.     

Synthesis, structural, and magnetic studies on a redox family of tetrametallic vanadium clusters: {VIV4}, {VIII2VIV2}, and {VIII4} butterfly complexes

The synthesis, crystal structures, and magnetic properties are reported for a redox family of butterfly-type tetrametallic vanadium alkoxide clusters, namely [V2(VO)2(acac)4(RC{CH2O}3)2] (R=Me 1, Et 2, CH2OH 3), [V2(VO)2(acac)2(O2CPh)2(MeC{CH2O}3)2] (5), [(VO)4(MeOH)2(O2CPh)2({HOCH2}C{CH2O}3)2] (6), [V4Cl2(dbm)4(RC{CH2OH}3)2] (R=Me 7, Et 8, CH2OH 9), and [V4Cl2(dbm)4(MeO)6] (10). The cluster cores are {VIV4} (6), {VIII2VIV2} (1-5), and {VIII4} (7-10), with examples of both isomeric forms of the of the mixed-valence cores (either VIII or VIV ions forming the butterfly body). Magnetic studies reveal the clusters to be dominated by antiferromagnetic exchange interactions in each case. The magnetic exchange parameters are determined for representative examples of each core type. {VIV4} and {VIII4} have diamagnetic ground states. The two isomeric {VIII2VIV2} types are found to give rise to either an S=0 ground state with a number of low-lying excited states due to competing antiferromagnetic exchange interactions (VIII2 butterfly body) or to a well-isolated S=1 ground state (VIV2 butterfly body).     

A barrier-free molecular radical-molecule reaction: {^{3}C_{2} (a^{3}\Pi) {+} O_{2} (X^{3} \Sigma)}

The reaction of ³C₂ (a³Π) radical with O₂ (X³Σ) molecule has been studied theoretically using ab initio Quantum Chemistry method. Both singlet and triplet potential energy surfaces (PES) are calculated at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311+G(d) + ZPE and G3B3 levels of theory. On the singlet PES of the title reaction, it is shown that the most feasible pathway should be the O-atom of O₂ attacking the C-atom of the  ³C₂ molecule first to form the adduct 1 CCOO, followed by the O-shift to give intermediate 2 CC(OO), and then to the major products P1 (2CO). Alternatively, 1 can be directly dissociated to P1 via transition state TS1-P1. The other reaction pathways are less competitive due to thermodynamical or kinetic factors. On the other hand, the pathways on the triplet PES are less competitive than those on the singlet PES in low temperature range, whereas it is not the case in high temperature ranges. On the basis of the analysis of the kinetics of all pathways through which the reactions proceed, we expect that the competitive power of reaction pathways may vary with experimental conditions for the title reaction. The reaction heats of formation calculated are in good agreement with that obtained experimentally.     

{AsW9O33}-{Mo3S4} based polyoxometalates including a metal-metal bond with Pd or Ni. Synthesis, structure and studies in solution

Heterometallic cuboidal clusters [Mo(3)S(4)M(H(2)O)(9)Cl](3+) M = Pd or Ni react with the trivacant [AsW(9)O(33)](9-) anion to give tetramodular complexes [(H(2)AsW(9)O(33))(4){Mo(3)S(4)M(H(2)O)(5)}(2)](20-) (M = Pd for anion 2 and M = Ni for anion 3) in good yield. Both anions crystallized as single crystals of potassium salts to give K-2 and K-3 salts which have been characterized structurally by X-ray diffraction. Both compounds are isomorphous and the anions 2 and 3 are described as two dimeric moeties, associated by internal hydrogen bonds, electrostatic interactions involving four outer potassium ion and coordination bonds within a central {M(2)S(2)} unit containing a M-M metallic bond. Studies in solution reveal that the dimeric association is maintained in solution in the 2 × 10(-4)-2 × 10(-3) mol L(-1) range. Conversely, in the presence of exogeneous ligands, such as iodide or pyridine the UV-vis data are consistent with the dissociation of the anion 2 into monomer through a Pd-L coordination bond (L = I(-) or Py). Furthermore, (183)W NMR spectrum of 2 shows that molecular structure of 2 is retained in solution. Elemental analysis and IR are also supplied. Electrochemical behavior of 2 and 3 are given and compared with the Pd or Ni free parent anion. The CVs are dominated mainly by irreversible reduction or oxidation processes, where the peak potentials appear dependent upon the ionic charge of the complex. However, the CV of the Pd-containing anion (2) is consistent with the deposition of Pd metal at the electrode, which gives rise to an oxidation process into palladium oxide.     

Structures and magnetism of {Ni2Na2}, {Ni4} and {Ni6(II)Ni(III)} 2-hydroxy-3-alkoxy-benzaldehyde clusters

Three polynuclear complexes, [NiNa(μ(1,1,1)-N(3))(μ-hmb)(2)(DMF)](2), (1), [Ni(4)(μ(3)-OMe)(4)(heb)(4)(MeOH)(1.05)(H(2)O)(2.95)], (2) and [Ni(III)(OH)(6)(hmb)(6)Ni(II)(6)]·(ClO(4))(3) (3) (Hhmb = 2-hydroxy-3-methoxy-benzaldehyde; Hheb = 2-hydroxy-3-ethoxy-benzaldehyde), were prepared by reaction of the appropriate ligand with nickel(II) perchloride hexahydrate under solvothermal conditions. All compounds were characterized by elemental analysis, IR spectroscopy and X-ray single-crystal diffraction. Compound 1 exhibits a centrosymmetric heterotetranuclear cluster which represents the first nickel complex to possess two connected face-sharing cubes structure {Ni(2)Na(2)N(2)O(4)}. Compound 2 has a tetranuclear Ni cluster with a cubane topology in which the Ni(II) and the oxygen atoms from the methanol ligands occupying alternate vertices of the cube. Compound 3 consisits of a mixed-valence [Ni(III)(OH)(6)(hmb)(6)Ni(II)(6)](3+) subunits and it represents the first nickel {Ni(II)(6)Ni(III)} complex to possess a planar hexagonal disc-like structure. The results show that the minor ligand modifications or solvent change have a key role in the structural control of the self-assembly process. Magnetic properties of 1-3 in the 300-2 K have been discussed. The {Ni(2)Na(2)} (1) and {Ni(4)} (2) core display dominant ferromagnetic interactions from the nature of the binding modes through μ(3)-N(3)(-) or μ(3)-OCH(3)(-), while {Ni(II)(6)Ni(III)} core (3) displays dominant anti-ferromagnetic interactions from the nature of the binding modes through μ(3)-OH(-).     

Die Kristallstrukturen von {Li3(12-Krone-4)2[HC(CN)2]3}, {Na(15-Krone-5)-[HC(CN)2]} und {Na[N(nBu)4][HC(CN)2]2 · THF}

The Crystal Structures of {Li₃(12-crown-4)₂[HC(CN)₂]₃}, {Na(15-crown-5)[HC(CN)₂]}, and {NaN(nBu)₄[HC(CN)₂]₂ · THF} The preparation and the crystal structures of the title compounds 1 — 3 are described. 1 forms a polymeric chain structure, in which one of the lithium ions is linked by Li…NCC(H)CN… bridges. The remaining lithium ions form (12-crown-4)Li[NCC(H)CN] units, which are coordinated by one of the nitrogen atoms of the dicyanomethanide ions with the lithium ions of the chain. 2 forms an ion pair, in which the sodium ion is coordinated by the five oxygen atoms of the crown ether molecule and by one nitrogen atom of the dicyanomethanide ion. 3 has a threedimensional network, in which the sodium ions are coordinated in a distorted tetrahedral manner by the nitrogen atoms of the dicyanomethanide ions. In the cavities of the network the tetrabutylammonium ions and the THF molecules are found.     

A two-dimensional octacyanomolybdate(V)-based ferrimagnet: {[Mn(II)(DMF)4]3[Mo(V)(CN)8]2}n

Treatment of [HNBu3]3[Mo(V)(CN)8] with manganese(II) p-toluenesulfonate in N,N'-dimethylformamide (DMF) affords {[Mn(II)(DMF)4]3[Mo(V)(CN)8]2}n (1) as a two-dimensional network. The structure of 1 consists of [cis-Mn(II)(DMF)4(mu-NC)2]2+ and [trans-Mn(II)(DMF)4(mu-NC)2]2+ units that are linked via cyanides to three-connected [Mo(V)(CN)5(mu-CN)3]3- centers in a 4:2:6 ratio, forming 12-membered rings. Magnetic measurements indicate that 1 is a ferrimagnet (TN = 8 K) that exhibits frequency-dependent behavior in chi". Heating of 1 affords an additional magnetic phase (TN = 21 K) that is absent of linkage isomerism.     

Synthesis of a new series of ditopic proligands for metal salts: differing regiochemistry of electrophilic attack at 3{5}-amino-5{3}-(pyrid-2-yl)-1H-pyrazole

An improved synthesis of 3{5}-amino-5{3}-(pyrid-2-yl)-1H-pyrazole (I) is described, which affords the compound on a multi-gram scale. Reaction of I with acid chloride and isothiocyanate electrophiles in MeCN cleanly results in attack at its amino group, yielding N-(3-{pyrid-2-yl}-1H-pyrazol-5-yl)amide and N-(3-{pyrid-2-yl}-1H-pyrazol-5-yl)thiourea products. These are good candidates as proligands for the simultaneous complexation of metal cations and anions. However, treatment of I with isocyanates under the same conditions instead yields attack at the pyrazole ring, giving 3-(pyridin-2-yl)-5-aminopyrazole-1-carboxylic acid amides as the only isolable products. The differing regiochemistries of these reactions were confirmed by ¹H NMR and X-ray crystallography.     

p-tert-Butylthiacalix[4]arene-supported high-nuclearity {Co24M8} (M=Mo or W) nanospheres and the hybrids with Keggin polyoxometalates

Two hybrid assemblies (3 and 4) with two kind of nanoscaled cluster units, the spherical [Co(24)(TC4A)(6)(MO(4))(8)Cl(6)](2+) cation (1 and 2) and Keggin-type [PM(12)O(40)](3-) anion (M = Mo (1/3), W (2/4)), were solvothermally prepared and characterized, in which the spherical units are constructed by six Co(4)-p-tert-butylthiacalix[4]arene (Co(4)-TC4A) SBUs linked by eight MO(4) tetrahedrons and present the highest nuclearity bimetallic clusters capped by cailxarenes.