Juan M. Gutiérrez-Zorrilla

Giant Crown-Shaped Polytungstate Formed by Self-Assembly of CeIII-Stabilized Dilacunary Keggin Fragments†

Polyoxometalates (POMs) are anionic metal–oxygen clusters with a remarkable variety of structures and potential applications (catalysis, medicine, materials science, and nanotechnology). The combination of their bifunctional activity as H/e reservoirs with the unique features of 4f ions (luminescence, magnetism, Lewis acid catalysis) is of particular interest and could afford species with enhanced properties owing to synergistic effects. Because of their oxophilicity and high coordination numbers, 4f ions display a powerful ability to link lacunary polytungstates (POTs) to build unprecedented architectures. The larger size of 4f ions compared to 3d metals prevents their full incorporation in lacunary frameworks as addendum atoms, and therefore additional sites are available for further derivatization. For monolacunary POTs, this mainly results in Peacock–Weakley sandwich POTs or in dimers and extended arrangements of 1:1 monomers. The use of diand trilacunary building blocks has led to a dramatic increase in the number and size of 4f-containing POTs in recent years. In addition to several medium to large assemblies, this approach has also resulted in a few giant species with more than 100 W atoms, which are amongst the largest POTs known. These are [As12Ce16W148O524(H2O)36] 76 , which has remained the largest POT since 1997; [Gd8As12W124O432(H2O)36] 60 , recently reported as the longest and second-largest POT; and [Ce20Ge10W100O376(OH)4(H2O)30] 56 , which contains the largest number of 4f ions besides being the fourth-largest POT. However, these assemblies are still small compared to Moblue POMs, for which a cluster as large as Mo368 is known. [5] Therefore, the search for giant POTs comparable to Mo blues is an attractive challenge, and supramolecular chemistry of 4f ions and lacunary fragments appears to be a suitable strategy that could allow rational design of tailored assemblies. Here we report [K K7Ce24Ge12W120O456(OH)12(H2O)64] (1) as the largest tungstogermanate and third-largest POT to date. Besides containing the largest number of 4f ions in a POM, 1 can be considered as the first giant POTwith a crown shape, that is, with a ring structure displaying a central cavity available for ion encapsulation in an inorganic analogue of the crown ethers, and thus a new type of topology is added to this still limited family of POMs. Recently, we reported the first 3d–4f heterometallic POM derived from the Weakley-type structure. With the aim of systematically incorporating 4f ions into this sandwich structure, we replaced half of the 3d precursor by a source of 4f ions in the direct synthesis of Weakley tungstogermanates. Instead of the expected 3d–4f POT, 1 was obtained as Na40K6[Ni(H2O)6]3[1]·nH2O (Ni-1, n 178) in moderate yield from this simple one-pot procedure. Polyanion 1 (Figure 1 a) can be viewed as the product of the K-directed self-assembly of twelve [Ce2GeW10O38] 6 subunits ({Ce2GeW10}) formed in situ, each of which is composed of a dilacunary Keggin fragment stabilized by coordination of two Ce ions on the vacant sites through four Ce O bonds (Figure 1b). As many as three distinct types of {GeW10} skeletons are observed: the enantiomeric forms b(1,8) and b(1,5) and the g(3,4) fragment, and all of them are of the anti-Lipscomb type. The vacant sites in the b forms are located at the W3O15 group and the central belt, whereas the Cs-symmetric g(3,4) form is obtained by removal of one WO6 octahedron from each rotated W3O13 triad (Figure S1, Supporting Information). Among the reported {bXW10}-containing POTs, [4c,10] only one b form displays vacancies at the belt and a W3O15 group to the best of our knowledge, namely, b(1,9). On the other hand, a single gdilacunary species was known to date: the C2v-symmetric g(1,2) form with vacancies at the two edge-sharing octahedra of the rotated triads. Therefore, all three {GeW10} fragments in 1 are completely unprecedented and they represent additional, interesting building blocks in POM chemistry. The fact that {Ce20W100}, composed of {b(4,11)-Ce2GeW10} subunits, is obtained from the [A-a-GeW9O34] 10 precursor at a similar pH suggests that a diversity of {GeW10} isomers may be formed under moderately acidic conditions regardless of the tungstogermanate source. Most likely, they are rapidly interexchangeable, highly reactive intermediates in the formation of the predominant {GeW11} species. In both cases, they could be stabilized by Ce coordination, which allowed [*] Dr. S. Reinoso, M. Gim nez-Marqu s Instituto de Ciencia Molecular (ICMol) Universidad de Valencia Catedr tico J. Beltr n 2, 46980 Paterna, Valencia (Spain) E-mail: santiago.reinoso@uv.es

Synthesis, chemical characterization, X-ray crystal structure and magnetic properties of oxalato-bridged copper(II) binuclear complexes with 2,2′-bipyridine and diethylenetriamine as peripheral ligands

Abstract Two new μ-oxalato binuclear copper(II) complexes, [{Cu(NO3)(H2O)(bipy)}2(ox)] (1) and [{Cu(dien)}2(ox)](NO3)2 (2), with ox=oxalate, dien=diethylenetriamine and bipy=2,2′-bipyridine, have been synthesized and their crystal and molecular structures have been determined by single-crystal X-ray diffraction methods. The crystal structure of 1 consists of centrosymmetric neutral dimers where the copper atoms lie in a strongly elongated octahedral environment, surrounded by two nitrogen atoms of a bipy molecule and two oxygen atoms of the bridging oxalato group in the equatorial plane and oxygen atoms of water molecules and nitrate ions in the axial positions. Crystal structure of 2 is made up of non-coordinated nitrate anions and asymmetric binuclear cations in which copper atoms are in a distorted square–pyramidal coordination with three atoms of a diethylenetriamine ligand and an oxygen atom of the asymmetrically coordinated oxalato bridge building the basal plane and the other oxygen atom of the oxalato ligand filling the apical position. Both compounds have been also characterized by Fourier transform infrared (FT-IR) and electron spin resonance (ESR) spectroscopies, thermal analysis and variable temperature magnetic susceptibility measurements. The two compounds exhibit antiferromagnetic exchange with a singlet–triplet separation of −382 and −6.5 cm−1 for 1 and 2, respectively. Magnetic and ESR results are discussed with respect to the crystal structure of the compounds.

Cation-Directed Dimeric versus Tetrameric Assemblies of Lanthanide-Stabilized Dilacunary Keggin Tungstogermanates

Reaction of mid- to late lanthanide ions with GeO2 and Na2WO4 in NaOAc buffer results in a library of [Ln2 (GeW10O38)](6-) clusters (Ln2), which consist of dilacunary Keggin fragments stabilized by the insertion of 4f atoms in the vacant sites and show the ability to undergo cation-directed self-assembly processes. In the presence of Na(+), two β-Ln2 subunits assemble by means of Ln-O(WO5)-Ln bridges to form the chiral [Ln4(H2O)6(β-GeW10O38)2](12-) dimeric anions (ββ-Ln4, Ln = Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). When Cs(+) is present, two Ln4-like dimers further assemble into the [{Ln4(H2O)5(GeW10O38)2}2](24-) species (Ln8, Ln = Ho, Er, Tm, Yb, Lu). Two types of tetramers coexist in the solid state: One shows a full ββ-Ln8 architecture, whereas the other one is a mixed αβ-Ln8 assembly in which each β-subunit is linked to its corresponding α-Ln2 derivative. Regardless of differences in isomeric forms and the relative arrangement of Ln2 subunits, all anions display virtually identical {Ln4} cores as a common structural feature. A combination of ESI mass spectrometry and (183)W NMR spectroscopy experiments indicates that Ln8 tetramers fragment into Ln4 dimers upon dissolution, which undergo partial dissociation into Ln2 monomers and slow dimer/monomer equilibration. This is most likely followed by β-to-α isomerization of Ln2 clusters with consequent reassembly, as indicated by isolation of three additional αα-Ln4 derivatives. Magnetic and photoluminescence properties in the Na-ββ-Ln4 series are also discussed.

Organoammonium diphosphopentamolybdates(VI): influence of organic cations and anion protonation on crystal packing and geometrical features of polyanion

Abstract Four organoammonium diphosphopentamolybdate(VI) with the formulae (C5H7N2)6[P2Mo5O23]·5H2O (1), (C2H10N2)3[P2Mo5O23]·6H2O (2), Al(C4H15N3)4[HP2Mo5O23]2Cl·10H2O (3) and (C4H12N)4[H2P2Mo5O23]·5H2O (4) have been synthesized. The crystal structures have been determined by means of single crystal X-ray diffraction data. The geometrical characteristics of the [HnP2Mo5O23](6−n)− heteropolyanions have been compared with those described in the literature for other salts. Several relationships between the protonated state and topological changes in the heteropolyanions have been found. The crystal structure in compound 1 is stabilized by electrostatic forces, an extensive network of hydrogen contacts involving anions, cations and water molecules and π–π interactions among 4-aminopyridinium cations. The anions of compound 2 are arranged in layers perpendicular to the [ 1 10] direction. The interactions between anions are established through hydrogen contacts which involve water molecules and ethylenediammonium cations. The monohydrogendiphosphopentamolybdate(VI) anions in the crystal structure of compound 3 are joined along the [010] direction by means of strong O–H⋯O interactions (d(O⋯O)=2.529(10) A) which lead to a polymeric structure of [HP2Mo5O23]5− polyanions. Likewise, a similar anion polymeric arrangement is found in compound 4 in which the diprotonated polyanions are held together by means of two strong hydrogen bonds (d(O⋯O)=2.591(6) and 2.596(6) A).

Synthesis, vibrational study, crystal structure and density functional calculations of [Ni(dien)2]2+ complexes. Configurational and conformational study of [M(dien)2]n+ complexes

Abstract Two new complexes containing the complex cation [Ni(dien)2]2+ (dien=diethylenetriamine) have been synthesised [Ni(dien)2]CA·2H2O (CA=chloranilate) (1) and [Ni(dien)2][Ni(CN)4]·2H2O (2). The structures of compounds have been determined by single crystal X-ray diffraction methods. In the cationic unit of compound 1, the ligand geometry around nickel(II) is nearly octahedral. Two chelating tridentate diethylenetriamine molecules with terminal amino groups in cis and secondary amino groups in trans position define the s-fac geometry. The conformations of the two independent chelate rings are enantiomeric with each other. The nickel atom of [Ni(dien)2]2+ unit in compound 2 also shows a distorted octahedral environment, but the two tridentate dien molecules are coordinated meridionally. Crystallographic observations of fused five-membered ring of bis(dien) complexes, retrieved from Cambridge Structural Database, have been mapped and classified using principal component analysis. Several density functional calculations of the geometry of the s-fac and mer isomers of the complex cation [Ni(dien)2]2+ have been carried out, and the results have been compared to the crystallographic data.

Effects of protonation in decavanadates: crystal structure of tetrakis(n-hexylammonium) dihydrogendecavanadate(V)

The crystal structure of a new dihydrogendecavanadate(V) of n-hexylammonium has been determined by means of X-ray diffraction data. Empirical bond length/bond number calculations have located the protonation sites in two triply-linked oxygen atoms which reinforce theoretical results of relative basicities of the oxygen sites in decavanadate anions. The crystal structure is stabilised by electrostatic forces and an extensive network of hydrogen contacts among anions and cations. The dihydrogendecavanadate(V) anions are located on the (001) plane and are joined via hydrogen bonding, d(O ⋯ O)= 2.63 and 2.64 A, giving evidence of strong O ⋯ O interactions. Infrared spectroscopy and thermoanalytical methods have been applied in order to confirm structural properties.

Reactions of MoO3 with diethylenetriamine (dien): Syntheses, solid-state characterization and thermal behaviour. Molecular and crystal structure of a second polymorph of (H3dien)2[Mo7O24]·4H2O

Abstract The reaction of MoO3 with diethylenetriamine in aqueous solution yields four compounds: two polymorphs of bis(diethylenetriammonium) heptamolybdate(VI) tetrahydrate, (H3dien)2[Mo7O24·4H2O (1 and 2), bis(3-aza-1,5-pentamethylenediammonium) octamolybdate(VI) hexahydrate, (H2dien)2[Mo8O26]·6H2O (3), and the oxocomplex diethylenetriaminetrioxomolybdenum(VI), [MoO3(dien)] (4). The compounds were characterized by means of thermal analyses and IR spectroscopy. The crystal structure of 1 was determined by X-ray diffraction. Compounds 1 and 2 are an unprecedented case of polymorphism in discrete polyoxomolybdates and their syntheses experimentally confirm the ability of polyoxometallates to promote the stacking of a large number of organic molecules by means of an extended network of hydrogen contacts. Both structures contain discrete[Mo7O24]6− polyanions, diethylenetriammonium cations and water molecules connected through hydrogen bonding interactions which are responsible for a different crystal packing in both compounds. In 1 the Mo(5)O(17) bond length, 2.675(4) A, is significantly longer than those observed for other organoammonium heptamolybdates that exhibit photochemical properties and antitumour activity. This long molybdenum—oxygen distance may play an important role in the possible photochromism and anticancer activity of this compound.

Synthesis, characterization and crystal structure of the anilinium β-octamolybdate dihydrate

Abstract The anilinium β-octamolybdate dihydrate has been prepared in acidic aqueous solution. TG, DTG, IR and 1H NMR techniques have been used to identify the compound. It belongs to a series of molybdates of alkyl-N- and -N,N-substituted anilinium cations. Single crystals have been analyzed by X-ray diffraction. Crystal data are: (C6H8N)4[Mo8O26] · 2H2O, space group P 1 , Z = 1, a = 10.007(1), b = 8.014(2), c = 14.645(8)A, α = 109.81(3), β = 108.59(2), γ = 85.44(2)°, V = 1052.9(6) A3, Do = 2.49(1), Dx = 2.52 mg m−3, R = 0.026 and Rw = 0.031 for 5297 observed reflexions. The crystal structure consists of discrete [β-Mo8O26]4− polyanions, two crystallographically independent (C6H8N)+ cations and one independent water molecule. Polyanions are linked to the cations and to the water molecules by hydrogen bonds of types NH…O and OH…O.

Preparation and solid state characterization of some alkylammonium decavanadates. Crystal structure of the hexakis(n-hexylammonium) decavanadate dihydrate

Abstract This paper deals with the syntheses and solid state characterization of three new n-alkylammonium decavanadates with general formula (BH) 6 [V 10 O 28 ] .2H 2 O, where B = n-butyl-, n-pentyl-, and n-hexylamine (hereafter abbreviated as BUTVA10, PENTVA10 and HEXVA10, respectively). The compounds have been prepared by dissolving V 2 O 5 in an aqueous solution of the respective amine and adjusting the final pH to 6.0 – 6.5. The compounds have been identified by using thermoanalytical, X-ray diffraction and IR techniques. Suitable single crystals were only obtained for the hexakis(n-hexylammonium) decavanadate(V) dihydrate and its crystal structure was determined. The compound crystallizes in the monoclinic space group P 2 1 a , M = 1605.5, a = 10.190(5), b = 18.206(4), c = 19.126(4) A , β = 105.35(3)°, V = 3447(2) A 3 , Z = 2, F(000) = 1656, μ = 26.75 cm −1 , D x = 1.56, D o = 1.57(1) Mg·m −3 , and λ( MoK α) = 0.71069 A . Final refinement led to R = 0.058, and wR = 0.068. The unit cell is made up of decavanadate anions forming layers, n-hexylammonium cations and water molecules occupying the space among them. The distinguishing feature of this compound is its extensive hydrogen bond network which contributes to the structure stabilization. n-Butylammonium decavanadate dihydrate and n-pentylammonium decavanadate dihydrate are isostructural. Space group was determined by X-ray diffraction data. Powder diffraction patterns were indexed for a monoclinic space group P 2 1 m unit cell, with parameters for BUTVA10: a = 16.91(2), b = 19.59(1), c = 16.29(2) A and β = 102.7(1)°, and for PENTVA10: a = 17.18(2), b = 20.57(2), c = 16.30(5) A , β = 101.7(2)°.

Preparation, characterization and crystal structure of N,N-dimethylanilinium β-octamolybdate dihydrate

Abstract N,N-dimethylanilinium β-ocatmolybdate dihydrate has been synthesized in acidic aqueous solution. The compound has been identified by using TG, DTG, IR and 1H NMR techniques. It crystallizes in the triclinic system, space group PĪ, Z = 1, a = 11.755(3) A, b = 11.836(5) A, c = 10.498(2) A, α = 105.29(2)°, β = 81.56(3)°, γ = 115.24(3)°, V = d1273.4(8) A, Do = 2.23(1) Mg m−3, Dx = 2.23 Mg m−3, R = 0.029 and R2 = 0.032 for 5259 observed reflexions. Two crystallographically independent [C8H12N]+ cations, one water molecule and one centrosymmetric β-octamolybdate polyanion are present in the asymmetric unit. Hydrogen bonds of types NH ···O and OH···O seem to stabilize the structure.