Volatile Heterometallic Precursors for the Low-Temperature Synthesis of Prospective Sodium Ion Battery Cathode Materials

Heterometallic single-source precursors with a proper sodium:transition-metal ratio for nonoxide sodium ion battery cathode materials are reported. Heterometallic fluorinated β-diketonates NaM­(hfac)₃ (M = Mn (<b>1</b>), Fe (<b>2</b>), Co (<b>3</b>), and Ni (<b>4</b>); hfac = hexafluoroacetylacetonate) have been obtained on a large scale, in high yield using a one-step reaction that employs commercially available reagents. The complexes are stable in open air and highly volatile. The mass spectrometric investigation indicates the existence of heterometallic molecules in the gas phase. The presence of heterometallic species in solutions of several solvents has been unambiguously confirmed. Heterometallic precursors were shown to exhibit clean, low-temperature decomposition in argon atmosphere that results in phase-pure perovskite fluorides NaMF₃, the prospective cathode materials for sodium ion batteries

Mixed-Ligand Approach to Changing the Metal Ratio in Bismuth–Transition Metal Heterometallic Precursors

A new series of heteroleptic bismuth–transition metal β-diketonates [BiM­(hfac)₃(thd)₂] (M = Mn (<b>1</b>), Co (<b>2</b>), and Ni (<b>3</b>); hfac = hexafluoroacetylacetonate, thd = tetramethylheptanedionate) with Bi:M = 1:1 ratio have been synthesized by stoichiometric reactions between homometallic reagents [Bi^III(hfac)₃] and [M^II(thd)₂]. On the basis of analysis of the metal–ligand interactions in heterometallic structures, the title compounds were formulated as ion-pair {[Bi^III(thd)₂]⁺­[M^II(hfac)₃]⁻} complexes. The direct reaction between homometallic reagents proceeds with a full ligand exchange between main group and transition metal centers, yielding dinuclear heterometallic molecules. In heteroleptic molecules <b>1</b>–<b>3</b>, the Lewis acidic, coordinatively unsaturated Bi^III centers are chelated by two bulky, electron-donating thd ligands and maintain bridging interactions with three oxygen atoms of small, electron-withdrawing hfac groups that chelate the neighboring divalent transition metals. Application of the mixed-ligand approach allows one to change the connectivity pattern within the heterometallic assembly and to isolate highly volatile precursors with the proper Bi:M = 1:1 ratio. The mixed-ligand approach employed in this work opens broad opportunities for the synthesis of heterometallic (main group–transition metal) molecular precursors with specific M:M′ ratio in the case when homoleptic counterparts either do not exist or afford products with an incorrect metal:metal ratio for the target materials. Heteroleptic complexes obtained in the course of this study represent prospective single-source precursors for the low-temperature preparation of multiferroic perovskite-type oxides

Volatile Single-Source Molecular Precursor for the Lithium Ion Battery Cathode

The first single-source molecular precursor for a lithium–manganese cathode material is reported. Heterometallic β-diketonate LiMn₂(thd)₅ (<b>1</b>, thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) was obtained in high yield by simple one-step solid-state reactions employing commercially available reagents. Substantial scale-up preparation of <b>1</b> was achieved using a solution approach. The crystal structure of the precursor contains discrete Li:Mn = 1:2 trinuclear molecules held together by bridging diketonate ligands. The complex is relatively stable in open air, highly volatile, and soluble in all common solvents. It was confirmed to retain its heterometallic structure in solutions of non-coordinating solvents. The heterometallic diketonate <b>1</b> was shown to exhibit clean, low-temperature decomposition in air/oxygen that results in nanosized particles of spinel-type oxide LiMn₂O₄, one of the leading cathode materials for lithium ion batteries

Volatile Single-Source Molecular Precursor for the Lithium Ion Battery Cathode

The first single-source molecular precursor for a lithium–manganese cathode material is reported. Heterometallic β-diketonate LiMn₂(thd)₅ (<b>1</b>, thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) was obtained in high yield by simple one-step solid-state reactions employing commercially available reagents. Substantial scale-up preparation of <b>1</b> was achieved using a solution approach. The crystal structure of the precursor contains discrete Li:Mn = 1:2 trinuclear molecules held together by bridging diketonate ligands. The complex is relatively stable in open air, highly volatile, and soluble in all common solvents. It was confirmed to retain its heterometallic structure in solutions of non-coordinating solvents. The heterometallic diketonate <b>1</b> was shown to exhibit clean, low-temperature decomposition in air/oxygen that results in nanosized particles of spinel-type oxide LiMn₂O₄, one of the leading cathode materials for lithium ion batteries

Volatile Single-Source Precursors for the Low-Temperature Preparation of Sodium–Rare Earth Metal Fluorides

Heterometallic single-source precursors for the preparation of sodium–rare earth metal fluorides are reported. Fluorinated β-diketonates NaRE­(hfac)₄ (RE = Y (<b>1</b>), Er (<b>2</b>), and Eu (<b>3</b>); hfac = hexafluoroacetylacetonate) have been obtained on a large scale, in high yield, via one-pot reaction that utilizes commercially available starting reagents. The solid-state structures of the title complexes consist of 1D polymeric chains with alternating [Na] and [RE­(hfac)₄] units. Compounds <b>1</b>–<b>3</b> are highly volatile and exhibit a fair stability in open air. Mass spectrometric investigation indicates the presence of heterometallic fragments in the gas phase. The presence of heterometallic species in solutions of coordinating solvents has also been confirmed. Decomposition of heterometallic precursors in argon atmosphere was shown to yield phase-pure sodium–rare earth metal fluorides. Low decomposition temperature effectively allows for a high degree of control over the formation of both kinetic α-phases and thermodynamic β-phases of target NaREF₄ (RE = Y, Er, and Eu) materials

Mixed-Ligand Approach to Design of Heterometallic Single-Source Precursors with Discrete Molecular Structure

Heterometallic single-source precursors for the Pb/Fe = 1:1 oxide materials, PbFe­(β-dik)₄ (β-dik = hexafluoroacetylacetonate (hfac, <b>1</b>), acetylacetonate (acac, <b>2</b>), and trifluoroacetylacetonate (tfac, <b>4</b>)), have been isolated by three different solid-state synthetic methods. The crystal structures of heterometallic diketonates <b>1</b>, <b>2</b>, and <b>4</b> were found to contain polymeric chains built on alternating [Fe­(β-dik)₂] and [Pb­(β-dik)₂] units that are held together by bridging M–O interactions. Heterometallic precursors are highly volatile, but soluble only in coordinating solvents, in which they dissociate into solvated homometallic fragments. In order to design the heterometallic precursor with a proper metal/metal ratio and with a discrete molecular structure, we used a combination of two different diketonate ligands. Heteroleptic complex Pb₂Fe₂­(hfac)₆­(acac)₂ (<b>5</b>) has been obtained by optimized stoichiometric reaction of an addition of homo-Fe­(acac)₂ to heterometallic Pb₂Fe­(hfac)₆ (<b>3</b>) diketonate that can be run in solution on a high scale. The combination of two ligands with electron-withdrawing and electron-donating groups allows changing the connectivity pattern within the heterometallic assembly and yields the precursor with a discrete tetranuclear structure. In accord with its molecular structure, heteroleptic complex <b>5</b> is soluble even in noncoordinating solvents and was found to retain its heterometallic structure in solution. Thermal decomposition of heterometallic precursors in air at 750 °C resulted in the target Pb₂­Fe₂O₅ oxide, a prospective multiferroic material. Prolonging the annealing time or increasing the decomposition temperature leads to another phase-pure lead–iron oxide Pb­Fe₁₂O₁₉ that is a representative of the important family of magnetic hexaferrites

Volatile Single-Source Precursors for the Low-Temperature Preparation of Sodium–Rare Earth Metal Fluorides

Heterometallic single-source precursors for the preparation of sodium–rare earth metal fluorides are reported. Fluorinated β-diketonates NaRE­(hfac)₄ (RE = Y (<b>1</b>), Er (<b>2</b>), and Eu (<b>3</b>); hfac = hexafluoroacetylacetonate) have been obtained on a large scale, in high yield, via one-pot reaction that utilizes commercially available starting reagents. The solid-state structures of the title complexes consist of 1D polymeric chains with alternating [Na] and [RE­(hfac)₄] units. Compounds <b>1</b>–<b>3</b> are highly volatile and exhibit a fair stability in open air. Mass spectrometric investigation indicates the presence of heterometallic fragments in the gas phase. The presence of heterometallic species in solutions of coordinating solvents has also been confirmed. Decomposition of heterometallic precursors in argon atmosphere was shown to yield phase-pure sodium–rare earth metal fluorides. Low decomposition temperature effectively allows for a high degree of control over the formation of both kinetic α-phases and thermodynamic β-phases of target NaREF₄ (RE = Y, Er, and Eu) materials

Expanding the Structural Motif Landscape of Heterometallic β‑Diketonates: Congruently Melting Ionic Solids

The first example of ionic β-diketonates in which both the cation and anion are octahedral coordinatively saturated metal diketonate moieties are reported. Heterometallic tin–transition-metal heteroleptic diketonates were obtained through solid-state redox reactions and are formulated as {[Sn^IV(thd)₃]⁺[M^II(hfac)₃]⁻} (M^II = Mn (<b>1</b>), Fe (<b>2</b>), Co (<b>3</b>); thd = 2,2,6,6-tetramethyl-3,5-heptanedionate, hfac = hexafluoroacetylacetonate). X-ray single-crystal structural investigations along with DART mass spectrometry, multinuclear NMR, and magnetic susceptibility measurements have been used to confirm an assignment of metal oxidation states in compounds <b>1</b>–<b>3</b>. Ionic compounds were found to melt congruently at temperatures below the decomposition point. As such, they represent prospective materials that can be utilized as ionic liquids as well as reagents for the soft transfer of diketonate ligands. An unexpected volatility of ionic compounds <b>1</b>–<b>3</b> was proposed to occur through a transport reaction, in which the transport agent is one of the products of their partial decomposition in the gas or condensed phase

Dirhodium Paddlewheel with Functionalized Carboxylate Bridges: New Building Block for Self-Assembly and Immobilization on Solid Support

A new dirhodium­(II,II) paddlewheel complex, [Rh₂(O₂CC₆H₄COOC₂H₅)₄] (<b>1</b>), has been synthesized using a predesigned functionalized carboxylate, namely, 4-(ethoxycarbonyl)­benzoate. The target product has been crystallized from the acetone solution and structurally characterized as a bis-acetone adduct, [Rh₂(O₂CC₆H₄COOC₂H₅)₄(OCMe₂)₂]·C₆H₁₄ (<b>2</b>). By utilizing the ability of dangling ester groups to coordinate to open axial ends of neighboring dirhodium units, <b>1</b> can self-assemble to form 2D networks upon crystallization from solutions of noncoordinating solvents such as chlorobenzene and chloroform. The resulting [Rh₂(O₂CC₆H₄COOC₂H₅)₄]·2C₆H₅Cl (<b>3</b>) and [Rh₂(O₂CC₆H₄COOC₂H₅)₄]·2CHCl₃ (<b>4</b>) products have microporous solid state structures with the pores filled with the corresponding disordered solvent molecules. Notably, <b>3</b> and <b>4</b> represent unique examples of 2D extended frameworks based on dirhodium tetracarboxylate paddlewheel units devoid of any exogenous ligands. In solution, the dangling ends of carboxylate bridges of <b>1</b> have been successfully utilized for condensation reaction with the selected solid support, benzylamine-functionalized polystyrene, allowing successful heterogenization of dirhodium units through the equatorial covalent attachment to the substrate. The resulting solid product was tested as a catalyst in the cyclopropanation reaction of styrene with methyl phenyldiazoacetate to show good yields and diastereoselectivity

Dirhodium Paddlewheel with Functionalized Carboxylate Bridges: New Building Block for Self-Assembly and Immobilization on Solid Support

A new dirhodium­(II,II) paddlewheel complex, [Rh₂(O₂CC₆H₄COOC₂H₅)₄] (<b>1</b>), has been synthesized using a predesigned functionalized carboxylate, namely, 4-(ethoxycarbonyl)­benzoate. The target product has been crystallized from the acetone solution and structurally characterized as a bis-acetone adduct, [Rh₂(O₂CC₆H₄COOC₂H₅)₄(OCMe₂)₂]·C₆H₁₄ (<b>2</b>). By utilizing the ability of dangling ester groups to coordinate to open axial ends of neighboring dirhodium units, <b>1</b> can self-assemble to form 2D networks upon crystallization from solutions of noncoordinating solvents such as chlorobenzene and chloroform. The resulting [Rh₂(O₂CC₆H₄COOC₂H₅)₄]·2C₆H₅Cl (<b>3</b>) and [Rh₂(O₂CC₆H₄COOC₂H₅)₄]·2CHCl₃ (<b>4</b>) products have microporous solid state structures with the pores filled with the corresponding disordered solvent molecules. Notably, <b>3</b> and <b>4</b> represent unique examples of 2D extended frameworks based on dirhodium tetracarboxylate paddlewheel units devoid of any exogenous ligands. In solution, the dangling ends of carboxylate bridges of <b>1</b> have been successfully utilized for condensation reaction with the selected solid support, benzylamine-functionalized polystyrene, allowing successful heterogenization of dirhodium units through the equatorial covalent attachment to the substrate. The resulting solid product was tested as a catalyst in the cyclopropanation reaction of styrene with methyl phenyldiazoacetate to show good yields and diastereoselectivity