Novel Heteroleptic Tin(II) Complexes Capable of Forming SnO and SnO 2 Thin Films Depending on Conditions Using Chemical Solution Deposition.

A new heteroleptic complex series of tin was synthesized by the salt metathesis reaction of SnX ₂ (X = Cl, Br, and I) with aminoalkoxide and various N -alkoxy-functionalized carboxamide ligands. The complexes, [ClSn(dmamp)] ₂ ( 1 ), [BrSn(dmamp)] ₂ ( 2 ), and [ISn(dmamp)] ₂ ( 3 ), were prepared from the salt metathesis reaction of SnX ₂ with one equivalent of dmamp; [Sn(dmamp)(empa)] ₂ ( 4 ), [Sn(dmamp)(mdpa)] ₂ ( 5 ), and [Sn(dmamp)(edpa)] ₂ ( 6 ) were prepared via the salt metathesis reaction using complex 2 with one equivalent of N -alkoxy-functionalized carboxamide ligand. Complexes 1 - 5 displayed dimeric molecular structures with tin metal centers interconnected by μ ₂ -O bonding via the alkoxy oxygen atom. The molecular structures of complexes 1 - 5 showed distorted trigonal bipyramidal geometries with lone pair electrons in the equatorial position. Using complex 6 as a tin precursor, SnO _x films were deposited by chemical solution deposition (CSD) and subsequent post-deposition annealing (PDA) at high temperatures. SnO and SnO ₂ films were selectively obtained under controlled PDA atmospheres of argon and oxygen, respectively. The SnO films featured a tetragonal romarchite structure with high crystallinity and a preferred growth orientation along the (101) plane. They also exhibited a lower transmittance of >52% at 400 nm due to an optical band gap of 2.9 eV. In contrast, the SnO ₂ films exhibited a tetragonal cassiterite crystal structure and an extremely high transmittance of >97% at 400 nm was observed with an optical band gap of 3.6 eV.
Competing Interests: The authors declare no competing financial interest.
(© 2021 The Authors. Published by American Chemical Society.)