On the Question of Site-Selective Ligand Exchange in Carboxylate-Substituted Metal Oxo Clusters.

Reaction of [Ti4Zr4O6(OBu)4(OMc)16] (OMc = methacrylate) with acetylacetone (acacH) resulted in dissection of the cluster and formation of [Ti(OBu)2(acac)2] and the smaller cluster [Ti2Zr4O4(OMc)16]. In contrast, the same reaction with [Zr6O4(OH)4(OOCR)12]2·6RCOOH (R = Et, CH2CH=CH2) led to site-selective substitution of two carboxylate ligands and formation of isostructural [Zr6O4(OH)4(OOCR)12-x (acac) x ]2·6RCOOH (x ≤ 1).

Synthesis and characterisation of thioether functionalised gallium and indium alkoxides.

This paper provides evidence of formerly unknown thioether coordination in metal alkoxides. The thioether functionalised alkanols serving as alcoholate ligands have been prepared by a generic route. The gallium and indium alkoxides provide the first evidence for sulphur coordination in the liquid and solid state in metal alkoxide derivatives. The presence of amines suppresses the coordination of thioether moieties leading to a well-known bonding mode in aminoalcoholates.

Retention of the Cluster Core Structure during Ligand Exchange Reactions of Carboxylato-Substituted Metal Oxo Clusters.

The exchange of the carboxylato ligands of Zr4O2(methacrylato)12 in reactions with carboxylic acids proceeds with retention of the composition and structure of the cluster core. This was concluded from exchange/re-exchange experiments and from comparison of the IR bands of the cluster core of the original and ligand-exchanged clusters. The IR bands were assigned on the basis of DFT calculations. Scrambling reactions between two Zr4O2(OOCR)12 clusters with different carboxylato ligands are a new way to prepare mixed-ligand oxo clusters.

Exploring the molecular structure of imidazolium-silica-based nanoparticle networks by combining solid-state NMR spectroscopy and first-principles calculations.

A DFT-based molecular model for imidazolium-silica-based nanoparticle networks (INNs) is presented. The INNs were synthesized and characterized by using small-angle X-ray scattering (SAXS), NMR spectroscopy, and theoretical ab initio calculations. (11)B and (31)P HETCOR CP MAS experiments were recorded. Calculated (19)F NMR spectroscopy results, combined with the calculated anion-imidazolium (IM) distances, predicted the IM chain density in the INN, which was also confirmed from thermogravimetric analysis/mass spectrometry results. The presence of water molecules trapped between the nanoparticles is also suggested. First considerations on possible π-π stacking between the IM rings are presented. The predicted electronic properties confirm the photoluminescence emissions in the correct spectral domain.

A complete series of halocarbonyl molybdenum PNP pincer complexes - Unexpected differences between NH and NMe spacers.

In the present study a complete series of seven-coordinate neutral halocarbonyl Mo(II) complexes of the type [Mo(PNPMe-Ph)(CO)2X2] (X = I, Br, Cl, F), featuring the new PNP pincer ligand N,N'-bis(diphenylphosphino)-N,N'-methyl-2,6-diaminopyridine (PNPMe-Ph), were prepared and fully characterized. The synthesis of these complexes was accomplished by different methodologies depending on the halide ligands. For X = I and Br, [Mo(PNPMe-Ph)(CO)2I2] and [Mo(PNPMe-Ph)(CO)2Br2] were obtained by reacting [Mo(PNPMe-Ph)(CO)3] with stoichiometric amounts of I2 and Br2, respectively. Alternatively, these complexes were obtained upon treatment of [MoX2(CO)3(CH3CN)2] (X = I, Br) with 1 equiv. of PNPMe-Ph. On the other hand, in the case of X = Cl, [Mo(PNPMe-Ph)(CO)2Cl2] was afforded by the reaction of [Mo(CO)4(µ-Cl)Cl]2 with 1 equiv. of PNPMe-Ph. The equivalent procedure also worked for X = Br. Finally, addition of 1 equiv. of 1-fluoro-2,4,6-trimethylpyridinium tetrafluoroborate to [Mo(PNPMe-Ph)(CO)3] yielded the analogous fluorine complex [Mo(PNPMe-Ph)(CO)2F2]. The modification of the ligand scaffold by introducing a Me group instead of H changed the properties of the PNP-Ph ligand significantly. While in the present case exclusively neutral seven-coordinate complexes of the type [Mo(PNPMe-Ph)(CO)2X2] were obtained, with the parent PNP-Ph ligand, i.e., featuring NH spacers, cationic seven-coordinate complexes of the type [Mo(PNP-Ph)(CO)3X]X were afforded. DFT calculations indicated that the reactions are under thermodynamic control. The structures of representative complexes were determined by X-ray single crystal analyses.

A coordination polymer with unusual structural features from imidazolylbutyric acid and titanium isopropoxide.

ABSTRACT: The coordination polymer [Ti(OiPr)3(OOCCH2CH2CH2C3N2H3)] n was prepared from 4-(imidazol-1-yl)butyric acid and titanium isopropoxide. The structure of the compound is remarkable, as the carboxylate group is coordinated in a chelating manner and no dimerization of the Ti(OiPr)3 groups through OR bridges was observed.

Heterolytic Cleavage of Dihydrogen by an Iron(II) PNP Pincer Complex via Metal-Ligand Cooperation.

The bis-carbonyl Fe(II) complex trans-[Fe(PNP-iPr)(CO)2Cl]+ reacts with Zn as reducing agent under a dihydrogen atmosphere to give the Fe(II) hydride complex cis-[Fe(PNP-iPr)(CO)2H]+ in 97% isolated yield. A crucial step in this reaction seems to be the reduction of the acidic NH protons of the PNP-iPr ligand to afford H2 and the coordinatively unsaturated intermediate [Fe(PNPH-iPr)(CO)2]+ bearing a dearomatized pyridine moiety. This species is able to bind and heterolytically cleave H2 to give cis-[Fe(PNP-iPr)(CO)2H]+. The mechanism of this reaction has been studied by DFT calculations. The proposed mechanism was supported by deuterium labeling experiments using D2 and the N-deuterated isotopologue of trans-[Fe(PNP-iPr)(CO)2Cl]+. While in the first case deuterium was partially incorporated into both N and Fe sites, in the latter case no reaction took place. In addition, the N-methylated complex trans-[Fe(PNPMe-iPr)(CO)2Cl]+ was prepared, showing no reactions with Zn and H2 under the same reaction conditions. An alternative synthesis of cis-[Fe(PNP-iPr)(CO)2H]+ was developed utilizing the Fe(0) complex [Fe(PNP-iPr)(CO)2]. This compound is obtained in high yield by treatment of either trans-[Fe(PNP-iPr)(CO)2Cl]+ or [Fe(PNP-iPr)Cl2] with an excess of NaHg or a stoichiometric amount of KC8 in the presence of carbon monoxide. Protonation of [Fe(PNP-iPr)(CO)2] with HBF4 gave the hydride complex cis-[Fe(PNP-iPr)(CO)2H]+. X-ray structures of both cis-[Fe(PNP-iPr)(CO)2H]+ and [Fe(PNP-iPr)(CO)2] are presented.

Synthesis and Characterization of Hydrido Carbonyl Molybdenum and Tungsten PNP Pincer Complexes.

In the present study the Mo(0) and W(0) complexes [M(PNP)(CO)3] as well as seven-coordinate cationic hydridocarbonyl Mo(II) and W(II) complexes of the type [M(PNP)(CO)3H]+, featuring PNP pincer ligands based on 2,6-diaminopyridine, have been prepared and fully characterized. The synthesis of Mo(0) complexes [Mo(PNP)(CO)3] was accomplished by treatment of [Mo(CO)3(CH3CN)3] with the respective PNP ligands. The analogous W(0) complexes were prepared by reduction of the bromocarbonyl complexes [W(PNP)(CO)3Br]+ with NaHg. These intermediates were obtained from the known dinuclear complex [W(CO)4(µ-Br)Br]2, prepared in situ from W(CO)6 and stoichiometric amounts of Br2. Addition of HBF4 to [M(PNP)(CO)3] resulted in clean protonation at the molybdenum and tungsten centers to generate the Mo(II) and W(II) hydride complexes [M(PNP)(CO)3H]+. The protonation is fully reversible, and upon addition of NEt3 as base the Mo(0) and W(0) complexes [M(PNP)(CO)3] are regenerated quantitatively. All heptacoordinate complexes exhibit fluxional behavior in solution. The mechanism of the dynamic process of the hydrido carbonyl complexes was investigated by means of DFT calculations, revealing that it occurs in a single step. The structures of representative complexes were determined by X-ray single-crystal analyses.

Dioximate- and Bis(salicylaldiminate)-Bridged Titanium and Zirconium Alkoxides: Structure Elucidation by Mass Spectrometry.

The treatment of titanium alkoxides with 1,5-pentanedioxime or 2,5-hexanedioxime resulted in the formation of complexes [{TiL(OR)2}2] in which the dioximate ligands (L) bridge a dimeric Ti2(µ2-OR)2 unit. The structures of the complexes were determined by single-crystal structure analysis, ESI mass spectrometry, and 1D and 2D solution NMR spectroscopy. In contrast, the treatment of titanium alkoxides with dioximes bearing cyclic linkers, such as cyclohexyl or aryl groups, resulted in insoluble polymeric compounds. The treatment of various bis(salicylaldiminates) with titanium and zirconium alkoxides resulted in compounds with the same composition [{TiL(OR)2}2], in which, however, two monomeric Ti(OR)2 units are bridged by the ligands L. The two structural possibilities can be distinguished by low-energy collision-induced dissociation owing to their different fragmentation patterns.

Ionic bis-nanoparticle networks.

ABSTRACT: A newly arising challenge in the field of nanoparticle research concerns the control and the understanding of the interparticle interactions and interparticle properties. This should allow the development of materials based on nanoparticle assemblies which represents a great opportunity to exploit nanoparticle collective properties. Although some nanoparticle networks have been reported, few works are addressing the highly exciting problem of forming bis-nanoparticle assemblies in which two different types of nanoparticles are present. In this article we report an original synthesis pathway for the formation of an ionic bis-nanoparticle network, silica/silver, based on the formation of an imidazolium bridging unit. The reaction used for the formation of the bridging imidazolium can be considered as click-like chemistry. The synthesis of the metal/metal oxide hybrid composite material starts from the formation of a metal oxide nanoparticle modified with an imidazole ligand. This composite formation is therefore very general and could be extended to other metal/metal oxide composites. GRAPHICAL ABSTRACT: .

Zinc(II) Complexes with Dangling Functional Organic Groups.

Zinc(II) complexes with dangling functional organic groups were synthesized by reaction of zinc acetate with a series of bifunctional p-substituted benzene derivatives (a combination of carboxylate, oximate, amino, ß-ketoimine, and salicylaldime groups). Selective coordination to carboxylate groups was observed when the second functional group was an oxime or ß-ketoimine group. When the second group was an amine or salicylaldimine moiety, these groups were additionally coordinated. From the reaction with p-aminobenzoic acid, the compound [Zn2(OOCCH3)(OOC-C6H4-NH2)3]∞ was crystallized. It is a three-dimensional coordination polymer with bridging aminobenzoate ligands.

Tri- and tetracoordinate copper(I) complexes bearing bidentate soft/hard SN and SeN ligands based on 2-aminopyridine.

The coordination properties of the EN ligands N-(2-pyridinyl)amino-diphenylphosphine sulfide, N-(2-pyridinyl)amino-diisopropylphosphine sulfide, N-(2-pyridinyl)amino-diphenylphosphine selenide, N-(2-pyridinyl)amino-diisopropylphosphine selenide towards copper(I) precursors CuX (X = Br, I), [Cu(IPr)Cl] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), and [Cu(CH(3)CN)(4)]PF(6) were studied. Treatment of CuX with EN ligands resulted in the formation of tricoordinate complexes of the type [Cu(κ(2)(E,N)-EN)X]. The reaction of [Cu(IPr)Cl] with EN ligands, followed by halide abstraction with AgSbF(6), afforded cationic tricoordinate complexes [Cu(κ(2)(S,N)-EN)(IPr)](+), while the reaction of [Cu(CH(3)CN)(4)](+) with two equivalents of EN ligands yielded tetrahedral complexes [Cu(κ(2)(E,N)-EN)(2)](+). Halide removal from [Cu(κ(2)(S,N)-SN)I] with silver salts in the presence of L = CH(3)CN and CNtBu afforded dinuclear complexes of the type [Cu(κ(2)(S,N),µ(S)-SN)(L)](2)(2+) containing bridging SN ligands. With the terminal alkynes HC≡CC(6)H(4)Me and HC≡CC(6)H(4)OMe, complexes of the formula [Cu(κ(2)(S,N)-SN-iPr)(η(2)-HC≡CC(6)H(4)Me)](+) and [Cu(κ(2)(S,N)-SN-iPr)(η(2)-HC≡CC(6)H(4)OMe)](+) were obtained. The mononuclear nature of these compounds was supported by DFT calculations. Most complexes were also characterized by X-ray crystallography.

A facile route to difunctionalized monosubstituted octasilsesquioxanes.

A series of difunctionalized monosubstituted octasilsesquioxanes have been synthesized that bear ester, amino acid, alcohol, haloalkyl, or azido functional groups. These units are suitable nanobuilding blocks for the preparation of new organic-inorganic hybrid materials.

Directing alkyl chain ordering of functional phosphorus coupling agents on ZrO2.

ZrO(2) powder (6.6 m(2)/g) was modified using polymerizable phosphorus-based coupling agents (P-CAs) (i.e., phosphonic acid, phosphoric acid, and bis-phosphonic acid), resulting in densely grafted layers as determined by thermogravimetry and elemental analysis (up to 4.2 molecules/nm(2)). The applied P-CAs contained a methacrylate group, which led to the covalent incorporation of a polymerizable moiety into the grafted layer. To direct the ordering of the alkyl chains in the layer, three different approaches were evaluated with respect to their structure-directing ability by means of FT-IR and nitrogen sorption at 77 K: (i) variation of the chain length, (ii) variation of the anchoring group and (iii) comodification with a defined amount of a nonfunctional phosphonic acid (variation of the functional/nonfunctional acid ratio). It was shown that the chain length and anchoring group size have significant effects on the alkyl chain ordering and morphology of the layer.

Porous titania ionic nanoparticle networks.

Titania nanoparticle networks were synthesized by the reaction between imidazole and alkyl halide functionalized anatase nanoparticles. The reaction produced imidazolium bridging units between the nanoparticles that were observed by the means of CP MAS (15)N NMR spectroscopy. The porous characteristics of the obtained nanoparticle network were investigated with nitrogen sorption experiments. From these experiments, a high surface area originating from small mesopores was observed. These results were confirmed by small-angle X-ray diffraction experiments.

Oximate-substituted zirconium alkoxides.

The reaction of acetoxime, ethyl methyl ketoxime or cyclohexanone oxime with zirconium iso-propoxide gave dimeric alkoxo oximate derivatives [Zr(OiPr)(oximate)3]2. The oximate ligands are side-on coordinated and the alkoxo groups bridge the two metal centres. NMR spectroscopy revealed dynamic behaviour of the compounds in solution. When exposing a reaction mixture of zirconium butoxide and cyclohexanone oxime to ambient moisture, the oxo-alkoxo derivative Zr4O(OBu)8(ON=C6H10)6 was obtained.

Clusters for alkyne-azide click reactions.

The clusters Ti(6)O(4)(OPr)(8)(OOC(CH(2))(2)C[triple bond]CH)(8) and [Zr(6)O(4)(OH)(4)(OOC(CH(2))(3)C[triple bond]CH)(12)](2) with acetylenic carboxylate ligands were prepared and structurally characterized in solution and in the crystalline state. Model reactions showed that they are suitable candidates for the formation of cluster-based inorganic-organic hybrid materials by alkyne-azide click reactions.

Modification of aluminium alkoxides with dialkylmalonates.

ABSTRACT: Depending on the reaction conditions, different aluminium dialkylmalonate derivatives were obtained by reaction of aluminium alkoxides Al(OR)3 (R = Et, iPr, tBu) with dialkylmalonates, viz. Al(malonate)3 (malonate = dimethyl, diethyl, di-iso-propyl and di-tert-butyl malonate), Al2(OiPr)4(malonate)2 (malonate = di-iso-propyl and di-tert-butyl malonate), Al2(OiPr)2(di-iso-propylmalonate)4 and Al3(OH)(OEt)3(diethylmalonate)5. All compounds were characterized by NMR spectroscopy, and single crystal structure analyses are reported for each type of compound. An Al2(OiPr)2(dialkylmalonate)4 derivative was only obtained by disproportionation of Al2(OiPr)4(di-iso-propylmalonate)2, but not by reaction of Al(OiPr)3 with dialkylmalonates in the corresponding molar ratio. Reactions of Al(OtBu)3 only resulted in Al(malonate)3 derivatives, but no transesterification was observed, contrary to the reaction of Al(OiPr)3 with dimethyl or diethyl malonate.

Crosslinked hybrid polymer matrices with nanostructure directing abilities for lanthanum hydroxide growth.

Polysiloxane-PEO hybrid polymers were used as precipitation environments for La(OH)3 nanoobjects.

Ligand dynamics on the surface of zirconium oxo clusters.

The dynamics of carboxylate ligands on the surface of zirconium oxo clusters was investigated in two case studies. Zr4O2(methacrylate)12 was investigated by one- and two dimensional NMR spectra both in the solid state and in solution. In solution, the cluster is C2h symmetric; stepwise intramolecular exchange of the four non-equivalent ligands was observed when the temperature was raised from -80 degrees C to -50 degrees C. The individual exchange processes were assigned to different ligand positions. Ab initio molecular dynamics simulations were performed for Zr6(OH)4O4(formate)12 to study the trajectory for the rearrangement of three chelating ligands into bridging positions, i.e. the conversion of the C3-symmetric into an Oh-symmetric cluster. The observation of a dip in the energy barrier along the reaction coordinate was related to the intermediate formation of hydrogen bonds between the moving oxygen atom of the rearranging ligand and a micro3-OH group of the cluster. Thus, the motion of the ligand requires a concerted motion in three dimensions.