Aerosol-assisted CVD of SnO from stannous alkoxide precursors

Heteroallene Insertions into Tin(II) Alkoxide Bonds

A series of iso-carbamate complexes have been synthesized by the reaction of [SnII(OiPr)2] or [SnII(OtBu)2] with either aryl or alkyl isocyanates, ONC-R (R = 2,4,6-trimethylphenyl (Mes), 2,6-diisopropylphenyl (Dipp), isopropyl (iPr), cyclohexyl (Cy) and tert-butyl (tBu)). In the case of aryl isocyanates, mono-insertion occurs to form structurally characterized complexes [Sn{κ2-N,O-R-NC(OiPr)O}(μ-OiPr)]2 (1: R = Mes, 2: R = Dipp) and [Sn{κ2-N,O-R-NC(OtBu)O}(μ-OtBu)]2 (3: R = Mes, 4: R = Dipp). The complicated solution-state chemistry of these species has been explored using 1H DOSY experiments. In contrast, reactions of tin(II) alkoxides with alkyl isocyanates result in the formation of bis-insertion products [Sn{κ2-N,O-R-NC(OiPr)O}2] (5: R = iPr, and 6: R = Cy) and [Sn{κ2-N,O-R-NC(OtBu)O}2] (7: R = iPr, 8: R = Cy), of which complexes 6-8 have also been structurally characterized. 1H NMR studies show that the reaction of tBu-NCO with either [Sn(OiPr)2] or [Sn(OtBu)2] results in a reversible mono-insertion. Variable-temperature 2D 1H-1H exchange spectroscopy (VT-2D-EXSY) was used to determine the rate of exchange between free tBu-NCO and the coordinated tBu-iso-carbamate ligand for the {OiPr} alkoxide complex, as well as the activation energy (Ea = 92.2 ± 0.8 kJ mol-1), enthalpy (ΔH‡ = 89.4 ± 0.8 kJ mol-1), and entropy (ΔS‡ = 12.6 ± 2.9 J mol-1 K-1) for the process [Sn(OiPr)2] + tBu-NCO ↔ [Sn{κ2-N,O-tBu-NC(OiPr)O}(OiPr)]. Attempts to form Sn(II) alkyl carbonates by the insertion of CO2 into either [Sn(OiPr)2] or [Sn(OtBu)2] proved unsuccessful. However, 119Sn{1H} NMR spectroscopy of the reaction of excess CO2 with [Sn(OiPr)2] reveals the presence of a new Sn(II) species, i.e., [(iPrO)Sn(O2COiPr)], VT-2D-EXSY (1H) of which confirms the reversible alkyl carbonate formation (Ea = 70.3 ± 13.0 kJ mol-1; ΔH‡ = 68.0 ± 1.3 kJ mol-1 and ΔS‡ = -8.07 ± 2.8 J mol-1 K-1).

AACVD system and protocol to fabricate CuO and Co3O4 nanostructured coatings for application as selective absorbent materials

In the present work, an aerosol-assisted CVD (AACVD) system is described, together with a representative example of the synthesis of nanostructured coatings, which is an attractive alternative to being implemented at the industrial level. The semi-automated AACVD system synthesizes thin films or coatings of nanostructured materials, mainly metal oxides, and noble metals. Its main components, as well as its operation, are presented here. This simple AACVD method makes it possible to produce the coatings at relatively low temperatures and in a single step. Finally, the synthesis of CuO and Co₃O₄ nanostructured coatings deposited on stainless steel substrates is reported, which are excellent candidates for use as selective absorbent materials. The CuO and Co₃O₄ coatings present high quality and purity; no further thermal treatments are required to obtain the pure and crystalline phases. The main highlights of the proposed method are as follows: a)An AACVD System for depositing thin films and coatings designed and entirely fabricated at the Centro de Investigación en Materiales Avanzados, S.C.b)A low temperature (350 °C) synthesis protocol to obtain CuO and Co₃O₄ nanostructured coatings on stainless steel substrates.c)The CuO and Co₃O₄ coatings presented the optimum characteristics to be considered selective absorbent materials.

Exploration of Solid-State vs Solution-State Structure in Contact Ion Pair Systems: Synthesis, Characterization, and Solution-State Dynamics of Zinc Diphenyl Phosphate, [Zn{O2P(OPh)2}2], Donor-Base-Supported Complexes

A family of zinc phosphate complexes supported by nitrogen donor-base ligands have been synthesized, and their molecular structures were identified in both the solid (X-ray crystallography) and solution state (DOSY NMR spectroscopy). [Zn{O₂P(OPh)₂}₂]_∞ (1), formed from the reaction of Zn[N(SiMe₃)₂]₂ with HO(O)P(OPh)₂ coordinates to donor-base ligands, i.e., pyridine (Py), 4-methylpyridine (4-MePy), 2,2-bipyridine (bipy), tetramethylethylenediamine (TMEDA), pentamethyldiethylenetriamine (PMDETA), and 1,3,5-trimethyl-1,3,5-triazacyclohexane (Me₃-TAC), to produce polymeric 1D structures, [(Py)₂Zn{O₂P(OPh)₂}₂]_∞ (2) and [(4-MePy)₂Zn{O₂P(OPh)₂}₂]_∞ (3), the bimetalic systems, [(Bipy)Zn{O₂P(OPh)₂}₂]₂ (4), [(TMEDA)Zn{O₂P(OPh)₂}₂]₂ (5), and [(Me₃-TAC)Zn{O₂P(OPh)₂}₂]₂ (7), as well as a mono-nuclear zinc bis-diphenylphosphate complex, [(PMDETA)Zn{O₂P(OPh)₂}₂] (6). ¹H NMR DOSY has been used to calculate averaged molecular weights of the species. Studies are consistent with the disassembly of polymeric 3 into the bimetallic species [(Me-Py)₂·Zn₂{O₂P(OPh)₂}₄], where the Me-Py ligand is in rapid exchange with free Me-Py in solution. Further ¹H DOSY NMR studies of 4 and 5 reveal that dissolution of the complex results in a monomer dimer equilibrium, i.e., [(Bipy)Zn{O₂P(OPh)₂}₂]₂ ⇆ 2[(Bipy)Zn{O₂P(OPh)₂}₂] and [(TMEDA)Zn{O₂P(OPh)₂}₂]₂ ⇆ 2[(TMEDA)Zn{O₂P(OPh)₂}₂], respectively, in which the equilibria lie toward formation of the monomer. As part of our studies, variable temperature ¹H DOSY experiments (223 to 313 K) were performed upon 5 in d₈-tol, which allowed us to approximate the enthalpy [ΔH = -43.2 kJ mol^-1 (±3.79)], entropy [ΔS = 109 J mol^-1 K^-1 (±13.9)], and approximate Gibbs free energy [ΔG = 75.6 kJ mol^-1 (±5.62) at 293 K)] of monomer-dimer equilibria. While complex 6 is shown to maintain its monomeric solid-state structure, ¹H DOSY experiments of 7 at 298 K reveal two separate normalized diffusion coefficients consistent with the presence of the bimetallic species [(TAC)_2-xZn₂{O₂P(OPh)₂}₄], (x = 1 or 0) and free TAC ligand.

Weakly Bound Dimer of a Diaryloxygermylene Derived from a tBuPh2Si-Substituted 2,2′-Methylenediphenol

Novel diaryloxygermylenes have been prepared by the reaction of Lappert’s germylene, Ge[N(SiMe3)2]2, with 2,2′-methylenediphenols bearing different substituents. The bulkiness of the substituents on the ortho positions of the phenolic oxygen (6 and 6′ positions) affects the structure of the products both in the solid-state and in solution. When the ortho substituents are SitBuPh2, the diaryloxygemylene crystalizes as a weakly bound dimer with intermolecular Ge…O distances of ca. 3.0 Å and exists as a monomer in solution. In contrast, the germylene with SiMePh2 groups as the ortho substituents form a tightly bound dimer featuring a Ge2O2 rhombus with cis-oriented terminal aryloxy groups in the crystalline state, which is confirmed to be maintained in solution through the VT (variable-temperature)-1H NMR studies. To the best of our knowledge, the former dimeric structure is unprecedented in the family of dioxytetrylenes.

Novel Heteroleptic Tin(II) Complexes Capable of Forming SnO and SnO2 Thin Films Depending on Conditions Using Chemical Solution Deposition

A new heteroleptic complex series of tin was synthesized by the salt metathesis reaction of SnX₂ (X = Cl, Br, and I) with aminoalkoxide and various N-alkoxy-functionalized carboxamide ligands. The complexes, [ClSn(dmamp)]₂ (1), [BrSn(dmamp)]₂ (2), and [ISn(dmamp)]₂ (3), were prepared from the salt metathesis reaction of SnX₂ with one equivalent of dmamp; [Sn(dmamp)(empa)]₂ (4), [Sn(dmamp)(mdpa)]₂ (5), and [Sn(dmamp)(edpa)]₂ (6) were prepared via the salt metathesis reaction using complex 2 with one equivalent of N-alkoxy-functionalized carboxamide ligand. Complexes 1-5 displayed dimeric molecular structures with tin metal centers interconnected by μ₂-O bonding via the alkoxy oxygen atom. The molecular structures of complexes 1-5 showed distorted trigonal bipyramidal geometries with lone pair electrons in the equatorial position. Using complex 6 as a tin precursor, SnO _x films were deposited by chemical solution deposition (CSD) and subsequent post-deposition annealing (PDA) at high temperatures. SnO and SnO₂ films were selectively obtained under controlled PDA atmospheres of argon and oxygen, respectively. The SnO films featured a tetragonal romarchite structure with high crystallinity and a preferred growth orientation along the (101) plane. They also exhibited a lower transmittance of >52% at 400 nm due to an optical band gap of 2.9 eV. In contrast, the SnO₂ films exhibited a tetragonal cassiterite crystal structure and an extremely high transmittance of >97% at 400 nm was observed with an optical band gap of 3.6 eV.

Tin(II) Ureide Complexes: Synthesis, Structural Chemistry, and Evaluation as SnO Precursors

In an attempt to tailor precursors for application in the deposition of phase pure SnO, we have evaluated a series of tin (1-6) ureide complexes. The complexes were successfully synthesized by employing N,N'-trialkyl-functionalized ureide ligands, in which features such as stability, volatility, and decomposition could be modified with variation of the substituents on the ureide ligand in an attempt to find the complex with the ideal electronic, steric, or coordinative properties, which determine the fate of the final products. The tin(II) ureide complexes 1-6 were synthesized by direct reaction [Sn{NMe₂}₂] with aryl and alkyl isocyanates in a 1:2 molar ratio. All the complexes were characterized by NMR spectroscopy as well as elemental analysis and, where applicable, thermogravimetric (TG) analysis. The single-crystal X-ray diffraction studies of 2, 3, 4, and 6 revealed that the complexes crystallize in the monoclinic space group P2(1)/n (2 and 4) or in the triclinic space group P-1 (3 and 6) as monomers. Reaction with phenyl isocyanate results in the formation of the bimetallic species 5, which crystallizes in the triclinic space group P-1, a consequence of incomplete insertion into the Sn-NMe₂ bonds, versus mesityl isocyanate, which produces a monomeric double insertion product, 6, under the same conditions, indicating a difference in reactivity between phenyl isocyanate and mesityl isocyanate with respect to insertion into Sn-NMe₂ bonds. The metal centers in these complexes are all four-coordinate, displaying either distorted trigonal bipyramidal or trigonal bipyramidal geometries. The steric influence of the imido-ligand substituent has a clear effect on the coordination mode of the ureide ligands, with complexes 2 and 6, which contain the cyclohexyl and mesityl ligands, displaying κ²-O,N coordination modes, whereas κ²-N,N' coordination modes are observed for the sterically bulkier tert-butyl and adamantyl derivatives, 3 and 4. The thermogravimetric analysis of the complexes 3 and 4 exhibited excellent physicochemical properties with clean single-step curves and low residual masses in their TG analyses suggesting their potential utility of these systems as MOCVD and ALD precursors.

Evaluation of Sn(II) aminoalkoxide precursors for atomic layer deposition of SnO thin films

We have successfully prepared and structurally characterized a family of eight tin(II) heteroleptic complexes, [Sn(NR₂)(ON)]_x (NR₂ = NMe₂ (1a-d) or N(SiMe₃)₂ (2a-d); x = 1 or 2) and four homoleptic systems, [Sn(κ²-ON)₂] (3a-d) from a series of aminoalcohols and fluorinated aminoalcohols (H{ON}) having a different number of methyl/trifluoromethyl substituents at the α-carbon atom, [HOC(R¹)(R₂)CH₂NMe₂] (R¹ = R² = H (H{dmae}) (a); R¹ = H, R² = Me (H{dmap}) (b); R¹ = R² = Me (H{dmamp}) (c); R¹ = R² = CF₃ (H{Fdmamp}) (d)). The synthetic route used reactions of either [Sn{N(SiMe₃)₂}₂] or [Sn(NMe₂)₂] with one or two equivalents of the aminoalcohols (a-d) in dry aprotic solvents leading to elimination of amines and formation of the Sn(II) species 1a-d, 2a-d and 3a-d respectively. All complexes were thoroughly characterized by NMR spectroscopy (¹H, ¹³C, ¹⁹F, and ¹¹⁹Sn) as well as single-crystal X-ray diffraction studies. In all case the solid state molecular structures of the complexes have been unambiguously established: the solid state structures 1a-b and 1c are dimeric with central {Sn₂N₂} cores resulting from bridging {μ²-NMe₂} units, in which the Sn(II) atoms are four-coordinate. In contrast, the solid state structures of complexes 1c and 2a-c possess similarly dimeric structures, with four-coordinate Sn(II) atoms, in which the oxygen atoms of the {ON} ligand bridge two Sn(II) centres to form dimers with a central {Sn₂O₂} core. Uniquely in this study, 2d, [Sn(κ²-O,N-OCMe₂CH₂NMe₂){N(SiMe₃)₂}] is monomeric with a three coordinate Sn(II) centre. The homoleptic complexes 3a-d are all isostructural with monomeric four-coordinate structures with disphenoidal geometries. Solution state NMR studies reveal complicated ligand exchange processes in the case of the heteroleptic complexes 1a-d and 2a-d. Contrastingly, the homoleptic systems 3a-d show no such behaviour. While complexes 1a-d and 2a-d displayed either poor thermal stability or multistep thermal decomposition processes, the thermal behaviour of the homoleptic complexes, 3a-d, was investigated in order to determine the effects, if any, of the degree of fluorination and asymmetry of the aminoalkoxide ligands on the suitability of these complexes as ALD precursors for the deposition of SnO thin films.

Additive-free spin coating of tin oxide thin films: synthesis, characterization and evaluation of tin β-ketoiminates as a new precursor class for solution deposition processes

The fabrication of SnOx in thin film form via chemical solution deposition (CSD) processes is favored over vacuum based techniques as it is cost effective and simpler. The precursor employed plays a central role in defining the process conditions for CSD. Particularly for processing SnO2 layers that are appealing for sensor or electronic applications, there are limited precursors available for CSD. Thus the focus of this work was to develop metalorganic precursors for tin, based on the ketoiminate ligand class. By systematic molecular engineering of the ligand periphery, a series of new homoleptic Sn(ii) β-ketoiminate complexes was synthesized, namely bis[4-(2-methoxyethylimino)-3-pentanonato] tin, [Sn(MEKI)2] (1), bis[4-(2-ethoxyethylimino)-2-pentanonato] tin, [Sn(EEKI)2] (2), bis[4-(3-methoxypropylimino)-2-pentanonato] tin, [Sn(MPKI)2] (3), bis[4-(3-ethoxypropylimino)-2-pentanonato] tin, [Sn(EPKI)2] (4) and bis[4-(3-isopropoxypropylimino)-2-pentanonato] tin, [Sn(iPPKI)2] (5). All these N-side-chain ether functionalized compounds were analyzed by nuclear magnetic resonance (NMR) spectroscopy, electron impact mass spectrometry (EI-MS), elemental analysis (EA) and thermogravimetric analysis (TGA). The solid state molecular structure of [Sn(MPKI)2] (3) was eludicated by means of single crystal X-ray diffraction (SCXRD). Interestingly, this class of compounds features excellent solubility and stability in common organic solvents alongside good reactivity towards H2O and low decomposition temperatures, thus fulfilling the desired requirements for CSD of tin oxides. With compound 3 as a representative example, we have demonstrated the possibility to directly deposit SnOx layers via hydrolysis upon exposure to air followed by heat treatment under oxygen at moderate temperatures and most importantly without the need for any additive that is generally used in CSD. A range of complementary analytical methods were employed, namely X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to analyse the structure, morphology and composition of the SnOx layers.

Synthesis, characterisation and thermal properties of Sn(ii) pyrrolide complexes

SnO is a rare example of a stable p-type semiconductor material. Here, we describe the synthesis and characterisation of a family of Sn(ii) pyrrolide complexes for future application in the MOCVD and ALD of tin containing thin films. Reaction of the Sn(ii) amide complex, [{(Me3Si)2N}2Sn], with the N,N-bidentate pyrrole pro-ligand, L1H, forms the hetero- and homoleptic complexes [{L1}Sn{N(SiMe3)2}] (1) and [{L1}2Sn] (2), respectively, bearing the 2-dimethylaminomethyl-pyrrolide ligand (L1). Reaction of [{(Me3Si)2N)}2Sn] with the pyrrole-aldimine pro-ligands, L2H-L7H, results in the exclusive formation of the homoleptic bis-pyrrolide complexes [{L2-7}2Sn] (3-8). All complexes have been characterised by elemental analysis and NMR spectroscopy, and the molecular structures of complexes 1-5 and 8 are determined by single crystal X-ray diffraction. TG analysis and isothermal TG analysis have been used to evaluate the potential utility of these systems as MOCVD and ALD precursors.