An easily synthesised Sn(II) bis(ureide) derivative is shown to be a single-source precursor for the aerosol-assisted CVD of SnO, providing unprecedented levels of oxidation state control at temperatures as low as 250 °C.

The stannous alkoxides [Sn(OR)] [R = i-Pr, t-Bu, C(Et)Me, CHPh, CPh] have been synthesised by reaction of Sn(NR') with two equivalents of HOR [R' = Me, R = i-Pr; R' = SiMe, R = t-Bu, C(Et)Me, CHPh, CPh]. Single crystal X-ray diffraction analysis of the bis(diphenylmethoxide) (4) and bis(triphenylmethoxide) (5) species have shown them to comprise three-coordinate Sn(ii) centres through dimerisation in the solid state with the alkoxide units adopting transoid and cisoid configurations across the {SnO} cores respectively. Thermogravimetric analysis indicates clean decomposition and some evidence of volatility at temperatures >200 °C for all three aliphatic alkoxides, whereas both the diphenyl- and triphenylmethoxide compounds provide higher decomposition temperatures and, for the triphenylmethoxide derivative, a residual mass consistent with the formation of a carbon-containing residue. The previously reported iso-propoxide (1) and tert-butoxide (2) derivatives have been utilised in toluene solution to deposit SnO thin films by aerosol-assisted chemical vapour deposition (AACVD) on glass at temperatures between 300 and 450 °C. While SnO is deposited under hot wall conditions as the only identifiable phase by p-XRD and Raman spectroscopy for both precursors, morphological analysis by SEM reveals inferior substrate coverage in comparison to previously reported ureide-based precursor systems.

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.

No abstract