Synthesis, solution dynamics and chemical vapour deposition of heteroleptic zinc complexes via ethyl and amide zinc thioureides

Ethyl and amide zinc thioureides [L(1)ZnEt](2) (1), [L(1)*ZnEt](2) (2) and [L(1)Zn(N(SiMe(3))(2))](2) (3) have been synthesised from the equimolar reaction of thiourea ligands (HL(1) = (i)PrN(H)CSNMe(2) and HL(1)* = PhN(H)CSNMe(2)) with diethyl zinc and zinc bis[bis(trimethylsilyl)amide] respectively. New routes towards heteroleptic complexes have been investigated through reactions of 1, 2 and 3 with β-ketoiminates (HL(2) = [(Me)CN(H){(i)Pr}–CHC(Me)[double bond, length as m-dash]O]), bulky aryl substituted β-diiminates (HL(3) = [(Me)CN(H){Dipp}–CHC(Me)[double bond, length as m-dash]N{Dipp}] (Dipp = diisopropylphenyl) and HL(3)* = [(Me)CN(H){Dep}–CHC(Me)[double bond, length as m-dash]N{Dep}] (Dep = diethylphenyl)) and donor-functionalised alcohols (HL(4) = Et(2)N(CH(2))(3)OH and HL(4)* = Me(2)N(CH(2))(3)OH) and have led to the formation of the heteroleptic complexes [L(1)*ZnL(3)*] (5), [L(1)ZnL(4)](2) (6), [L(1)ZnL(4)*](2) (7), [L(1)*ZnL(4)] (8) and [L(1)*ZnL(4)*] (9). All complexes have been characterised by (1)H and (13)C NMR, elemental analysis, and the X-ray structures of HL(1)*, 1, 2, 6 and 7 have been determined via single crystal X-ray diffraction. Variable temperature (1)H, COSY and NOESY NMR experiments investigating the dynamic behaviour of 5, 6 and 7 have shown these molecules to be fluxional. On the basis of solution state fluxionality and thermogravimetric analysis (TGA), alkoxyzinc thioureides 6 and 7 were investigated as single-source precursors for the deposition of the ternary material zinc oxysulfide, Zn(O,S), a buffer layer used in thin film photovoltaic devices. The aerosol-assisted chemical vapour deposition (AACVD) reaction of 7 at 400 °C led to the deposition of the heterodichalcogenide material Zn(O,S), which was confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX), with optical properties investigated using UV/vis spectroscopy, and surface morphology and film thickness examined using scanning electron microscopy (SEM).