Novel Heteroleptic Tin(II) Complexes Capable of Forming SnO and SnO₂ Thin Films Depending on Conditions Using Chemical Solution Deposition

A new heteroleptic complex series of tin was synthesized by the salt metathesis reaction of SnX2 (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 SnX2 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 μ2–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, SnOx films were deposited by chemical solution deposition (CSD) and subsequent post-deposition annealing (PDA) at high temperatures. SnO and SnO2 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 SnO2 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.通过SnX₂（X=Cl、Br和I）与氨基烷氧基配体以及多种N-烷氧基官能化羧酰胺配体发生复分解反应，合成了一种新型异配体锡配合物系列。配合物[ClSn(dmamp)]₂（1）、[BrSn(dmamp)]₂（2）和[ISn(dmamp)]₂（3）由SnX₂与1当量dmamp通过复分解反应制备得到；配合物[Sn(dmamp)(empa)]₂（4）、[Sn(dmamp)(mdpa)]₂（5）和[Sn(dmamp)(edpa)]₂（6）则通过以配合物2为原料，与1当量N-烷氧基官能化羧酰胺配体发生复分解反应制得。配合物1~5呈现二聚分子结构，锡金属中心通过烷氧基氧原子形成的μ₂-氧桥相互连接。配合物1~5的分子结构均为畸变三角双锥几何构型，孤对电子处于赤道位置。以配合物6作为锡前驱体，通过化学溶液沉积法（chemical solution deposition, CSD）并在高温下进行沉积后退火（post-deposition annealing, PDA），制备得到SnOₓ薄膜。在氩气和氧气氛围下分别进行控温退火，可选择性得到SnO和SnO₂薄膜。SnO薄膜为四方红锡矿（romarchite）结构，结晶度高且沿(101)晶面择优生长；其在400 nm波长处的透光率大于52%，对应光学带隙为2.9 eV。与之相反，SnO₂薄膜为四方锡石（cassiterite）晶体结构，在400 nm波长处透光率高达97%以上，光学带隙为3.6 eV。