Tin guanidinato complexes: oxidative control of Sn, SnS, SnSe and SnTe thin film deposition

A family of tin(ii) guanidinate complexes of the general form [{RNC(NMe2)NR}2Sn] (R = iPr (6), Cy (7), Tol (9) and Dipp (10)) and [{tBuNC(NMe2)NtBu}Sn{NMe2}] (8) have been synthesised and isolated from the reaction of tin(ii) bis-dimethylamide and a series of carbodiimides (1-5). The cyclic poly-chalcogenide compounds [{CyNC(NMe2)NCy}2Sn{Chx}] (Ch = S, x = 4 (11); Ch = Se, x = 4 (12), and Ch = S, x = 6 (13)) with {SnChx} rings were prepared by the oxidative addition of elemental sulfur and selenium to the heteroleptic stannylene complex [{CyNC(NMe2)NCy}2Sn] (7) in THF at room temperature. Similarly, reaction of compounds 6 and 7 with an equimolar amount of the chalcogen transfer reagents (SC3H6 and Se[double bond, length as m-dash]PEt3, respectively) led to the formation of the chalcogenide tin(iv) complexes [{RNC(NMe2)NR}Sn(Ch)] (R = Cy: Ch = S (14); R = iPr, Ch = Se (15); R = Cy, Ch = Se (16)) with terminal Sn[double bond, length as m-dash]Ch (14 and 16) and dimeric bridged seleno-tin {Sn2Se2} rings (15), respectively. The mono telluro-compounds [{RNC(NMe2)NR}Sn(Te)] (R = iPr (17); R = Cy (18)) were similarly prepared by the oxidative addition of elemental tellurium to 7 and 8, respectively. All of the tin containing compounds have been investigated by multinuclear NMR (1H, 13C 119Sn and 77Se/125Te, where possible), elemental analysis and single crystal X-ray structural analysis (7, 8, 10-13, 15-18). Thermogravimetric analysis (TGA) was used to probe the possible utility of complexes 6-8, 11-12 and 14-18 as single source Sn and SnCh precursors. The Sn(ii) compounds 6 and 7 have been utilised in the growth of thin films by aerosol-assisted chemical vapor deposition (AACVD) at both 300 and 400 °C. The thin films have been analysed by pXRD, EDS, SEM and AFM and shown to be Sn metal. Subsequent studies provided film growth at temperatures as low as 200 °C. Similarly, the mono-chalcogenide systems 14, 16 and 18 have been utilised in the AACVD of thin films. These latter studies provided films, grown at 300 and 400 °C, which have also been analysed by pXRD, Raman spectroscopy, AFM, and SEM and are shown to comprise phase pure SnS, SnSe and SnTe, respectively. These preliminary results demonstrate the potential of such simple guanidinate complexes to act as single source precursors with a high degree of oxidative control over the deposited thin films.