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

Abstract

Ethyl and amide zinc thioureides [L1ZnEt]2 (1), [L1*ZnEt]2 (2) and [L1Zn(N(SiMe3)2)]2 (3) have been synthesised from the equimolar reaction of thiourea ligands (HL1 = iPrN(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 β-ketoiminates (HL2 = [(Me)CN(H){iPr}–CHC(Me) Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O]), bulky aryl substituted β-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)3OH and HL4* = Me2N(CH2)3OH) and have led to the formation of the heteroleptic complexes [L1*ZnL3*] (5), [L1ZnL4]2 (6), [L1ZnL4*]2 (7), [L1*ZnL4] (8) and [L1*ZnL4*] (9). All complexes have been characterised by 1H and 13C 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 1H, 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).