Three at a Time: Step by Step to Heterotermetallic Molecules

New structural motifs in ternary metal alkoxides are demonstrated through synthetic strategies that enable overcoming statistical barriers and solution equilibrium. Tetradentate dimetalate unit, {M₂(O<i>i</i>Pr)₉}⁻ (M = Hf (<b>1</b>), Zr (<b>2</b>)), used to sequester the coordination sphere of the central metal atom (Ba), allowed step-by-step construction of termetallic molecules [{M′(O<i>i</i>Pr)₄}­(HO<i>i</i>Pr)­Ba­{M₂(O<i>i</i>Pr)₉}] (M′ = Al (<b>3</b>), Ga (<b>4</b>), M = Hf; M′ = Al, M = Zr (<b>5</b>)). In contrast to a common “coordinative-fit” approach mainly used for bimetallic compounds, this stepwise rational construction using fast successive salt metathesis reactions circumvents general challenges in the syntheses of termetallic alkoxides by avoiding the thermodynamically preferred formation of bimetallic alkoxide molecules. The presented compounds exhibit for the first time gas phase stable termetallic alkoxide frameworks

Monomeric Iron Heteroarylalkenolates: Structural Design Concepts and Investigations on Their Application in Chemical Vapor Deposition

Aryl substituted β-alkenol 1-(dimethyl-1,3-thiazol-2-yl)-3,3,3-trifluoropropenol (DMTTFP) was employed as an efficient metal chelator to obtain volatile monomeric precursors containing Fe^II and Fe^III centers. [Fe­(DMTTFP)₂] (<b>1</b>) and [Fe­(DMTTFP)₂­(OBu^<i>t</i>)] (<b>2</b>) were synthesized by reacting suitable starting materials with DMTTFP. The molecular structures were elucidated by single-crystal X-ray diffraction analyses, which revealed a distorted tetrahedral and a trigonal-bipyramidal arrangement of ligands around iron atoms in <b>1</b> and <b>2</b>, respectively. Magnetic investigations confirmed [Fe­(DMTTFP)₂] to exhibit a thermally populated spin-state transition that becomes apparent below 10 K. The high-spin state was gradually transferred to a low-spin state on cooling, suggesting a nonmagnetic ground state. [Fe­(DMTTFP)₂­(OBu^<i>t</i>)] exhibited enhanced stability, sufficient volatility, and decomposition behavior serving as an efficient Fe^III precursor for the growth of iron oxide layers on an Al₂O₃ substrate via chemical vapor deposition

Synthesis, Characterization, and Gas Sensing Properties of Porous Nickel Oxide Nanotubes

A novel approach was employed to synthesize porous NiO nanotubes with controllable interior voids based on an effective interplay of Kirkendall effect and volume change upon phase transformation. For this purpose, nickel nanowires were chemically converted into Ni₃S₂/Ni core–shell structures, followed by a controlled oxidation, whereby the associated volume change (Ni → NiO conversion) resulted in 1D porous structure with voids. The voids between the Ni core and Ni₃S₂ shell could be controlled by adjusting the oxidation conditions that enabled fabrication of hollow and double-walled morphologies. Phase composition, morphological evolution, and porosity of double-walled NiO nanotubes were analyzed by X-ray diffraction, scanning and transmission electron microscopy, and N₂ adsorption–desorption studies. Gaseous sulfur oxides formed during the oxidation of Ni₃S₂/Ni structures resulted in a perforated structure with multiple voids with pores ranging between 1 and 14 nm. The unique complex structure with the interpenetrating voids and the surface porosity resulted in a high specific surface area of 161.6 m²·g^–1. The gas sensing property of such double-walled structure was found to vary as a function of the concentric void between the core and the shell. Gas-sensing measurements in hollow porous core–shell NiO nanotubes exhibited excellent sensitivity toward ethanol, originating from efficient adsorption of target molecules in the interior voids and their rapid diffusion and transport through the porous structures

Octakis(<i>tert</i>-butoxo)dicerium(IV) [Ce₂(O^<i>t</i>Bu)₈]: Synthesis, Characterization, Decomposition, and Reactivity

An advanced synthesis for the homometallic derivative [Ce₂(O^<i>t</i>Bu)₈] (<b>1</b>) starting from [Ce­(O^<i>t</i>Bu)₂{N­(SiMe₃)₂}₂] was developed. Structural characterization of a cerium­(IV) complex and its decomposition products confirmed the coexistence of both ether elimination and Ce–O bond cleavage processes, which lead to the formation of [Ce₃O­(O^<i>t</i>Bu)₁₀] and [Ce₃(O^<i>t</i>Bu)₁₁] (<b>2</b>) derivatives, respectively. Variable-temperature NMR spectroscopy under strict exclusion of moisture enabled insight into the decomposition processes in noncoordinating solvents and at elevated temperature. In addition, structural analysis of the heterovalent <b>2</b> and of two new complexes of the general formula [Ce₂(O^<i>t</i>Bu)₈(L)] [L = HO^<i>t</i>Bu (<b>3</b>), OCPh₂ (<b>4</b>)] is described

Novel Air-Stable and Volatile Bis(pyridylalkenolato)palladium(II) and -platinum(II) Derivatives

Six novel homoleptic palladium­(II) and platinum­(II) complexes of donor-substituted alkenol ligands [PyCHC­(R)­OH; Py = pyridine, R = CH₃, CF₃, C₂F₅, C₃F₇] of the general formula M­[PyCHC­(R)­O]₂ (M = Pd, Pt) were synthesized by reacting the deprotonated ligands with PdCl₂ and K₂PtCl₄, respectively. Molecular structures, revealed by single-crystal X-ray diffraction analyses, showed a square-planar arrangement of ligands around palladium and platinum centers, with the pyridine-ring nitrogen atoms situated in a mutually <i>trans</i> position. The monomeric nature of the compounds in the solution state was confirmed by multinuclear (¹H, ¹³C, and ¹⁹F) NMR spectroscopy. Thermal decomposition profiles recorded under a nitrogen atmosphere suggested their potential as volatile precursors to palladium and platinum materials. The volatility was increased upon elongation of the perfluoroalkyl chain, which suppressed the intermolecular interactions, as is evident in crystal packings. The volatility of these compounds was attributed to bidentate chelation of the alkenol units and cooperativity among the electron-back-donating nitrogen atom and interplay of electron-withdrawing C_<i>x</i>F_<i>y</i> groups, resulting in an effective steric shielding of the metal atoms

Improved Stability of “Naked” Gold Nanoparticles Enabled by in Situ Coating with Mono and Multivalent Thiol PEG Ligands

Unprotected (“naked”) gold nanoparticles with high monodispersity (⟨<i>d</i>⟩, 5.5± 0.5 nm) were obtained in a facile and single-step microwave-assisted hydrolytic decomposition of the molecular precursor [NMe₄]­[Au­(CF₃)₂]. Given their chloride-free surface chemistry, the as-obtained gold nanoparticles were in situ functionalized with mono-, di-, and trivalent thiolated PEG ligands in order to study the influence of multivalent character of the ligands on the stability of the colloidal solutions. For this purpose, a novel tridentate ligand was synthesized and the previously reported syntheses of mono- and divalent thiol ligands were improved. Owing to the pristine character of the Au nanoparticles no ligand exchange was required, and the colloidal and chemical stability of the mono- and multivalent functionalized particles purely depended on the ligating ability of the thiolated groups. In situ-functionalized Au nanoparticles showed a strikingly (2 orders of magnitude higher) improved stability against small nucleophiles such as sodium cyanide compared to gold nanoparticles coated with citrate ligands and functionalized via a ligand-exchange reaction. The monovalent thiol PEG ligand produced most stable colloids against cyanide, which is explained by a strongly increased numerical ligand-density on the surface. Gold colloids stabilized by di- and trivalent ligands exhibited high stability in aqueous solutions with high NaCl concentrations (2 M) in contrast to those functionalized with the monovalent PEG ligand, which were only temporally stable in dilute NaCl solutions. The beneficial effect of the multivalence of the ligands was further demonstrated by the incorporation of an additional chelating ligand (dithiothreitol) to the colloidal dispersions

Heterobi- and Trimetallic Cerium(IV) <i>tert</i>-Butoxides with Mono‑, Di‑, and Trivalent Metals (<i>M</i> = K(I), Ge(II), Sn(II), Pb(II), Al(III), Fe(III))

The reaction of <i>C</i>erium <i>A</i>mmonium <i>N</i>itrate (CAN) with varying amounts of KO^<i>t</i>Bu produced homometallic Ce­(O^<i>t</i>Bu)₄(NC₅H₅)₂ (<b>1</b>) and the heterometallic derivative KCe₂(O^<i>t</i>Bu)₁₀ (<b>3</b>) characterized by X-ray diffraction and NMR spectroscopy. The oxo-alkoxide cluster Ce₃O­(O^<i>t</i>Bu)₉ (<b>2</b>) was obtained from a solution of cerium­(IV) tetrakis­(<i>tert</i>-butoxide) in <i>n</i>-heptane under stringent precautions to avoid any adventitious hydrolysis. Lewis acid-base reactions of in situ generated Ce­(O^<i>t</i>Bu)₄(THF)₂ (THF = tetrahydrofuran) with bi- and trivalent metal alkoxides [<i>M</i>(O^<i>t</i>Bu)_<i>x</i>]_<i>n</i> (<i>M</i> = Ge, Sn; <i>x</i> = 2; <i>n</i> = 2; <i>M</i> = Pb, <i>x</i> = 2; <i>n</i> = 3; <i>M</i> = Al, Fe; <i>x</i> = 3; <i>n</i> = 2) resulted in volatile products of the general formula <i>M</i>Ce­(O^<i>t</i>Bu)_4+<i>x</i> (<i>M</i> = Al (<b>4</b>), Fe (<b>5</b>); <i>x</i> = 3; <i>M</i> = Ge (<b>8</b>), Sn (<b>9</b>), Pb (<b>10</b>); <i>x</i> = 2) in high yields. By dissolving <b>4</b> and <b>5</b> in pyridine the solvent adducts <i>M</i>Ce­(O^<i>t</i>Bu)₇(NC₅H₅) (<i>M</i> = Al (<b>6</b>), Fe (<b>7</b>)) were formed, whereas <b>8</b> and <b>9</b> reacted with Mo­(CO)₆ in boiling toluene to yield the termetallic complexes (CO)₅Mo<i>M</i>(μ₂-O^<i>t</i>Bu)₃Ce­(O^<i>t</i>Bu)₃ (<i>M</i> = Ge (<b>11</b>), Sn (<b>12</b>)). The new compounds were characterized by comprehensive spectral studies, mass spectroscopy, and single crystal X-ray diffraction analysis

Heterobi- and Trimetallic Cerium(IV) <i>tert</i>-Butoxides with Mono‑, Di‑, and Trivalent Metals (<i>M</i> = K(I), Ge(II), Sn(II), Pb(II), Al(III), Fe(III))

The reaction of <i>C</i>erium <i>A</i>mmonium <i>N</i>itrate (CAN) with varying amounts of KO^<i>t</i>Bu produced homometallic Ce­(O^<i>t</i>Bu)₄(NC₅H₅)₂ (<b>1</b>) and the heterometallic derivative KCe₂(O^<i>t</i>Bu)₁₀ (<b>3</b>) characterized by X-ray diffraction and NMR spectroscopy. The oxo-alkoxide cluster Ce₃O­(O^<i>t</i>Bu)₉ (<b>2</b>) was obtained from a solution of cerium­(IV) tetrakis­(<i>tert</i>-butoxide) in <i>n</i>-heptane under stringent precautions to avoid any adventitious hydrolysis. Lewis acid-base reactions of in situ generated Ce­(O^<i>t</i>Bu)₄(THF)₂ (THF = tetrahydrofuran) with bi- and trivalent metal alkoxides [<i>M</i>(O^<i>t</i>Bu)_<i>x</i>]_<i>n</i> (<i>M</i> = Ge, Sn; <i>x</i> = 2; <i>n</i> = 2; <i>M</i> = Pb, <i>x</i> = 2; <i>n</i> = 3; <i>M</i> = Al, Fe; <i>x</i> = 3; <i>n</i> = 2) resulted in volatile products of the general formula <i>M</i>Ce­(O^<i>t</i>Bu)_4+<i>x</i> (<i>M</i> = Al (<b>4</b>), Fe (<b>5</b>); <i>x</i> = 3; <i>M</i> = Ge (<b>8</b>), Sn (<b>9</b>), Pb (<b>10</b>); <i>x</i> = 2) in high yields. By dissolving <b>4</b> and <b>5</b> in pyridine the solvent adducts <i>M</i>Ce­(O^<i>t</i>Bu)₇(NC₅H₅) (<i>M</i> = Al (<b>6</b>), Fe (<b>7</b>)) were formed, whereas <b>8</b> and <b>9</b> reacted with Mo­(CO)₆ in boiling toluene to yield the termetallic complexes (CO)₅Mo<i>M</i>(μ₂-O^<i>t</i>Bu)₃Ce­(O^<i>t</i>Bu)₃ (<i>M</i> = Ge (<b>11</b>), Sn (<b>12</b>)). The new compounds were characterized by comprehensive spectral studies, mass spectroscopy, and single crystal X-ray diffraction analysis

Synthetic and Structural Investigations on the Reactivity of the Cd–I Bond in [ICd{Zr₂(OPr^<i>i</i>)₉}] to Construct New Mixed-Metal Alkoxides

New mixed-metal alkoxides of general formula [XCd­{Zr₂(OPr^<i>i</i>)₉}]_<i>n</i> (X = −C₂F₅, −C₆F₅, −C₆F₄-4-H, −NO₃, −NCO, −SO₃CF₃, −O₂CCF₃, −O₂CC₂F₅, −O₂CCH₃, −ClO₄, −CN, −SO₄; <i>n</i> = 1, 2) were obtained by the scission of the Cd–I bond in the iodo heterobimetallic isopropoxide [ICd­{Zr₂(OPr^<i>i</i>)₉}] (<b>1</b>), whereby the underlying synthetic strategies involve metathesis reactions with silver salts or Lewis acid–base interactions between the Brønsted acid [Zr­(OPr^<i>i</i>)₄(HOPr^<i>i</i>)]₂ and bis­(fluoroorgano)cadmium (Cd­(R_<i>f</i><i>)</i>₂) compounds. The new compounds were characterized by multinuclear NMR spectroscopy, elemental analysis, and mass spectrometry. The results of X-ray diffraction analysis of [(F₅C₆)­Cd­{Zr₂(OPr^<i>i</i>)₉}] (<b>2</b>), [(4-H-F₄C₆)­Cd­{Zr₂(OPr^<i>i</i>)₉}] (<b>3</b>), [(F₅C₂)­Cd­{Zr₂(OPr^<i>i</i>)₉}]₂ (<b>4</b>), [(ONO₂)­Cd­{Zr₂(OPr^<i>i</i>)₉}]₂ (<b>5</b>), [(CH₃CO₂)­Cd­{Zr₂(OPr^<i>i</i>)₉}] (<b>6</b>), [(O₂ClO₂)­(H₅C₃N)­Cd­{Zr₂(OPr^<i>i</i>)₉}] (<b>7</b>), [(μ-O₂ClO₂)­Cd­{Zr₂(OPr^<i>i</i>)₉}]₂ (<b>8</b>), [(μ-O₂CCF₃)­Cd­{Zr₂(OPr^<i>i</i>)₈(O₂CCF₃)}]₂ (<b>9</b>), [(μ-O₂CC₂F₅)­Cd­{Zr₂(OPr^<i>i</i>)₈(O₂CC₂F₅)}]₂ (<b>10</b>), [(μ­(<i>O</i>,<i>N</i>)-OCN)­Cd­{Zr₂(OPr^<i>i</i>)₉}]₂ (<b>11</b>), and [(μ-O₂SOCF₃)­Cd­{Zr₂(OPr^<i>i</i>)₉}]₂ (<b>12</b>) revealed the molecular framework to be formally constituted by tetradentate coordination of a nonaisopropoxo dizirconate unit, {Zr₂(OPr^<i>i</i>)₉}⁻, to a CdX⁺ unit. In solution and in the solid state, <b>1</b>–<b>7</b> exist as monomers, whereas compounds <b>8</b>–<b>12</b> form dimers

Single-Source Precursors for Alloyed Gold–Silver Nanocrystals - A Molecular Metallurgy Approach

Multiple silver­(I)-aurates­(I) have been prepared by salt metathesis reactions that act as efficient single-source precursors to colloidal gold silver alloys with the highest possible atom economy in the chemical synthesis of nanostructures. The CF₃ group present on the Au cation acts as an in situ reducing agent and can be converted into CO ligands by simple hydrolysis. This ligand-mediated activation and subsequent decomposition of metal–organic precursors impose a molecular control over the nucleation process, producing homogeneously alloyed (Ag–Au) nanoparticles with an atomic Au:Ag ratio of 1:1. The concept also works for the Au–Cu system and acts as a pointer to replace Au (Ag) with less expensive (Cu) metals