Santiago Reinoso

Heterometallic 3d-4f Polyoxometalate Derived from the Weakley-Type Dimeric Structure

Polyanion [{Ce(H(2)O)(2)}(2)Mn(2)(B-alpha-GeW(9)O(34))(2)](8-) (1) constitutes the first example of a heterometallic 3d-4f cluster related to the Weakley-type dimeric structure, and it contains an unprecedented Ce(III)(2)Mn(III)(2)O(20) rhomblike moiety displaying dominant Ce(III)-Mn(III) ferromagnetic interactions.

New Type of Heterometallic 3d-4f Rhomblike Core in Weakley-Like Polyoxometalates

The first heterometallic copper-cerium polyoxometalate, [{Ce(IV)(OAc)}Cu(II)(3)(H(2)O)(B-α-GeW(9)O(34))(2)](11-) (1), is composed of an unprecedented copper(II)-trisubstituted Weakley-type tungstogermanate subunit stabilized by coordination of a {Ce(OAc)}(3+) group at the vacant position. The title species contains a central {Ce(IV)Cu(II)(3)O(18)} rhomblike cluster that belongs to a new {(4f(ext))(3d(ext))(3d(int))(2)} type and magnetically behaves as a triangular Cu(3) system with overall antiferromagnetic exchange affected by the structural distortions the vicinity of diamagnetic Ce(IV) induces.

Phenyltin-substituted 9-tungstogermanate and comparison with its tungstosilicate analogue.

Reaction of (C 6H 5)SnCl 3 with Na 10[ A-alpha-GeW 9O 34] in water results in the monomeric, trisubstituted Keggin species [{(C 6H 5)Sn(OH)} 3( A-alpha-GeW 9O 34)] (4-) ( 1), constituting the first organotin derivative of a trilacunary Keggin tungstogermanate. Polyanion 1 could be obtained as two different cesium salts depending on the applied isolation strategy: Cs 3Na[{(C 6H 5)Sn(OH)} 3( A-alpha-GeW 9O 34)].9H 2O ( CsNa-1) and Cs 3[{(C 6H 5)Sn(OH)} 3( A-alpha-HGeW 9O 34)].8H 2O ( Cs-H1). The monomeric phenyltin-containing tungstosilicate [{(C 6H 5)Sn(OH)} 3( A-alpha-SiW 9O 34)] (4-) ( 2) and the dimeric, sandwich-type derivative [{(C 6H 5)Sn(OH)} 3( A-alpha-H 3SiW 9O 34) 2] (8-) ( 3) have also been isolated as the cesium salts Cs 3Na[{(C 6H 5)Sn(OH)} 3( A-alpha-SiW 9O 34)].9H 2O ( CsNa-2), Cs 4[{(C 6H 5)Sn(OH)} 3( A-alpha-SiW 9O 34)].13H 2O ( Cs-2), and Cs 8[{(C 6H 5)Sn(OH)} 3( A-alpha-H 3SiW 9O 34) 2].23H 2O ( Cs-3), respectively. We have investigated in detail the similarities and differences in the reactivity of (C 6H 5)Sn (3+) with [ A-alpha-GeW 9O 34] (10-) vs [ A-alpha-SiW 9O 34] (10-). All five compounds have been characterized in the solid state by means of elemental analysis, infrared spectroscopy, thermogravimetry, and single-crystal X-ray diffraction, representing the first structural analysis for polyanions 1- 3. A full solution characterization of 1 by multinuclear NMR spectroscopy ( (1)H, (13)C, (119)Sn, and (183)W) has also been performed. The monomeric polyanions 1 and 2 are closely associated in the solid state through (Sn)O-H...O t (O t: terminal oxygen atom) hydrogen bonds reinforced by weak C-H...O t contacts to form 2-dimensional ( CsNa-1 and CsNa-2) or 1-dimensional ( Cs-H1) arrangements, and also dimeric entities ( Cs-2) depending on the network of intermolecular interactions.

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.

A Robust Open Framework Formed by Decavanadate Clusters and Copper(II) Complexes of Macrocyclic Polyamines: Permanent Microporosity and Catalytic Oxidation of Cycloalkanes

The first decavanadate-based microporous hybrid, namely, [Cu(cyclam)][{Cu(cyclam)}2(V10O28)]·10H2O (1, cyclam = 1,4,8,11-tetraazacyclotetradecane) was prepared by reaction of (VO3)(-) anions and {Cu(cyclam)}(2+) complexes in NaCl (aq) at pH 4.6-4.7 and characterized by elemental analyses, thermogravimetry, and X-ray diffraction (powder, single-crystal) techniques. Compound 1 exhibits a POMOF-like supramolecular open-framework built of covalent decavanadate/metalorganic layers with square-like voids, the stacking of which is aided by interlamellar cementing complexes and generates water-filled channels with approximate cross sections of 10.4 × 8.8 Å(2). The framework is robust enough to remain virtually unaltered upon thermal evacuation of all water molecules of hydration, as demonstrated through single-crystal X-ray diffraction studies on the anhydrous phase 1a. This permanent microporosity renders interesting functionality to 1, such as selective adsorption of CO2 over N2 and remarkable activity as heterogeneous catalyst toward the H2O2-based oxidation of the highly-stable, tricyclic alkane adamantane.

O,N-Chelated boron aminophenolate complexes. Crystal structure of BPh2(OC6H4(CH2NMe2)-2)

Abstract Two diphenylboron ortho-aminophenolate complexes, [BPh2(OC6H4(CH2NMe2)-2)] (2) and [BPh2(OC6H2(CH2NMe2)2-2,6-Me-4)] (6), have been prepared in a one-pot procedure approach starting from B(OMe)3. The starting material was reacted with two equivalents of phenylmagnesium bromide, followed by hydrolysis with HCl. The resulting borinic acid, BPh2(OH), was reacted with either HOC6H4(CH2NMe2)-2 or HOC6H2(CH2NMe2)2-2,6-Me-4 to give 2 or 6, respectively. An X-ray structure determination of 2 showed it to be a four-coordinate boron compound with a tetrahedral coordination geometry. The six-membered chelate ring in 2 is puckered. Variable temperature 1H-NMR analysis of 6 showed the existence of two dynamic processes in solution, i.e. one process involving flipping of the puckered chelate ring conformation (ΔG‡=41 kJ mol−1) and a second, higher energy, process (ΔG‡=65 kJ mol−1) in which exchange of coordinated and non-coordinated amine functions occurs. The exchange is (at least partly) assisted intermolecularly.

Rearrangement of a Krebs-Type Polyoxometalate upon Coordination of N,O-Bis(bidentate) Ligands

Selective coordination of 2,3-pyzdc to the Krebs-type [{Ni(H2O)3}2(WO2)2(SbW9O33)2](10-) anion promotes a skeletal rearrangement that results in the [(2,3-pyzdc)2{NaNi2(H2O)4Sb2W20O70}2](22-) (Ni4) hybrid dimer showing a novel dinickel containing a 20-tungsto-2-antimonate(III) framework stabilized by N,O-bis(bidentate) bridging ligands. The solution stability and magnetism of Ni4 is discussed.

Crown‐Shaped Tungstogermanates as Solvent‐Controlled Dual Systems in the Formation of Vesicle‐Like Assemblies

Reaction of early lanthanides, GeO2 , and Na2 WO4 in a NaOAc buffer results in large crown-shaped polyoxometalates based on [Ln2 GeW10 O38 ](6-) subunits. By using Ni(2+) as a crystallizing agent, [Na⊂Ln12 Ge6 W60 O228 (H2 O)24 ](35-) (Na⊂Ln12 ) hexamers formed by alternating β(1,5)/β(1,8) subunits were obtained for Ln=Pr, Nd. The addition of K(+) led to a similar anion for Ln=Sm, namely, [K⊂Sm12 Ge6 W60 O228 (H2 O)22 ](35-) (K⊂Sm12 ) and [K⊂K7 Ln24 Ge12 W120 O444 (OH)12 (H2 O)64 ](52-) (K⊂Ln24 ) dodecamers that consist of a central core identical to K⊂Sm12 decorated with six external γ(3,4) subunits for Ln=Pr, Nd. These anions dissociate in water into hexameric cores and monomeric entities, as shown by ESI mass spectrometry. The former self-assemble into spherical, hollow, and single-layered blackberry-type structures with radii of approximately 75 nm, as monitored by laser light scattering (LLS) and TEM techniques. Analogous studies performed for K⊂Nd24 in water/acetone mixtures show that the dodecamers remain stable and form in turn their own type of blackberries with sizes that increase from approximately 20 to 50 nm with increasing acetone content. This control over both the composition and size of the vesicle-like assemblies is achieved for the first time by modifying the architecture of the species that undergoes supramolecular association through the solvent polarity.

New Perspectives for Old Clusters: Anderson-Evans Anions as Building Blocks of Large Polyoxometalate Frameworks in a Series of Heterometallic 3 d-4 f Species.

A series of nine [Sb7W36O133Ln3M2(OAc)(H2O)8](17-) heterometallic anions (Ln3M2; Ln=La-Gd, M=Co; Ln=Ce, M=Ni and Zn) have been obtained by reacting 3 d metal disubstituted Krebs-type tungstoantimonates(III) with early lanthanides. Their unique tetrameric structure contains a novel {MW9O33} capping unit formed by a planar {MW6O24} fragment to which three {WO2} groups are condensed to form a tungstate skeleton identical to that of a hypothetical trilacunary derivative of the ɛ-Keggin cluster. It is shown, for the first time, that classical Anderson-Evans {MW6O24} anions can act as building blocks to construct purely inorganic large frameworks. Unprecedented reactivity in the outer ring of these disk-shaped species is also revealed. The Ln3M2 anions possess chirality owing to a {Sb4O4} cluster being encapsulated in left- or right-handed orientations. Their ability to self-associate in blackberry-type vesicles in solution has been assessed for the Ce3Co2 derivative.

Sequential single-crystal-to-single-crystal transformations promoted by gradual thermal dehydration in a porous metavanadate hybrid

TheE porous hybrid metavanadate [{Cu(cyclam)}(VO3)2]·5H2O (1) (cyclam = 1,4,8,11-tetraazacyclotetradecane) undergoes thermally-triggered sequential single-crystal-to-single-crystal (SCSC) transformations upon gradual dehydration to produce three new porous crystalline phases, namely [{Cu(cyclam)}(VO3)2]·3H2O (2), [{Cu(cyclam)}(VO3)2]·1.3H2O (3) and [{Cu(cyclam)}(VO3)2] (4). Compound 1 has a three-dimensional structure formed by metavanadate chains linked by {Cu(cyclam)} moieties in a hybrid open framework with two different types of hexagonal channels where water molecules of hydration are hosted. The SCSC transformations cause a rearrangement o/f the metavanadate chains in such a way that they contract when going from 1 to 2 and stretch back when 2 transforms into 3. The size of the channels is also modified as the hybrid dehydrates. The transition from 2 to 3 leads to the cleavage of a Cu–O bond and consequent coordination of a {Cu(cyclam)} moiety to a different {VO4} unit, which drastically decreases the size of the channel in the process. In contrast, total dehydration of 3 enlarges the channel in the anhydrous phase 4 due to the migration of another Cu atom. The reversibility of such transformations has been monitored by a combination of thermogravimetric and powder X-ray diffraction analyses. While 1 and 3 are stable in open-air conditions, 2 transforms back into 1 upon exposure to air for three weeks. The anhydrous phase 4 rapidly rehydrates into 3 when in contact with ambient moisture. Furthermore, 3 can also be transformed into the parent hybrid 1 when soaked in water for seven days. Therefore, all crystal transitions described herein are fully reversible by applying the appropriate conditions.