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

Ethyl and amide zinc thioureides [(LZnEt)-Zn-1](2) (1), [L-1*ZnEt](2) (2) and [(LZn)-Zn-1(N(SiMe3)(2))](2) (3) have been synthesised from the equimolar reaction of thiourea ligands (HL1 = (PrN)-Pr-i(H)CSNMe2 and HL1* = PhN(H)CSNMe2) 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 beta-ketoiminates (HL2 = [(Me) CN(H){Pr-i}-CHC(Me)]O]), bulky aryl substituted beta-diiminates (HL3 = [(Me)CN(H){Dipp}-CHC(Me)]=N {Dipp}] (Dipp = diisopropylphenyl) and HL3* = [(Me)CN(H){Dep}-CHC(Me)=]N{Dep}] (Dep = diethylphenyl)) and donor-functionalised alcohols (HL4 = Et2N(CH2)(3)OH and HL4* = Me2N(CH2)(3)OH) and have led to the formation of the heteroleptic complexes [L-1*ZnL3*] (5), [(LZnL4)-Zn-1](2) (6), [(LZnL4)-Zn-1*](2) (7), [L-1*ZnL4] (8) and [L-1*ZnL4*] (9). All complexes have been characterised by H-1 and C-13 NMR, elemental analysis, and the X-ray structures of HL1*, 1, 2, 6 and 7 have been determined via single crystal X-ray diffraction. Variable temperature H-1, 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 degrees 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).

Automated summary

Various thiosemicarbazide compounds were synthesized and used to prepare a series of heteroleptic complexes through reactions with other compounds. Some of these compounds can also serve as precursor materials for the deposition of buffer layers in thin film photovoltaic devices.