From Chain‐ to Graphene‐like Hydroxyl‐terminated (ZnO)_n Clusters with n≤6 Obtained via Zinc Dimethoxide Hydrolysis and Condensation: Ab initio Structural, Electronic, Vibrational and Optical Properties Calculations

Abstract

Recent reports are focusing on the structural evolution from the atomic‐scale and also at the expenses of alkyl zinc alkoxide precursors towards (ZnO)n clusters and nanostructures with different interesting motifs, but still not much is known about their electronic properties. In this manuscript, we present a theoretical study using DFT and TD‐DFT methodologies on the hydrolysis and condensation of zinc dimethoxide precursor in its monomeric, dimeric and trimeric forms towards thermodynamically stable hydroxyl‐terminated (ZnO)n clusters with novel chain‐ and graphene‐like fashions. For all cases, distinct vibrational and optical spectra features were assigned evidencing a global monotonic decrease in the opto‐electronic gap with increasing oligomerization and cyclization stages. In addition, the electron‐affinity of all clusters was also observed to be enhanced with increasing oligomerization and cyclization stages and the electronic charge localization in ‐e charged clusters was observed to be strongly related to the presence of zinc‐oxo subunits and other particular structural features. Our calculations also indicate that the stabilization through hydroxyl termination of both chain‐ and graphene‐like ZnO clusters not only could be a promising driving force to obtain larger atomic‐scale 1D and 2D nanostructures but also envisage interesting properties, particularly as electronic acceptor materials for energy applications.

Evidence of Graphene-like ZnO Nanostructures via Zinc Dimethoxide Hydrolysis–Condensation Under Ambient Conditions on a Au(111) Surface Using SERS: Simulation and Experiment

“…DFT , calculations were performed utilizing Gaussian 09 by selecting the B3LYP − exchange–correlation potential at the 6-31++g­(d,p) level of theory including frequency calculations to confirm the local minima of our cluster’s geometries and to compute the corresponding Raman activities. This level of theory has also shown reasonable results for similar clusters in the literature , and balances the computational cost for our purposes. In order to compare the theoretical and experimental Raman spectra, a scale factor of 0.964 was applied, as suggested by the Computational Chemistry Comparison and Benchmark DataBase for the current level of theory.…”

“…The presence of hydroxyl termination in our graphene-like ZnO nanosized systems is inspired by the fact that our preparation is given at ambient conditions with 50% RH and that we have already evidenced the presence of small hydroxyl-terminated zinc–oxo planar clusters derived from zinc dimethoxide early hydrolysis–condensation products. , Our nanosized systems were proposed following a rational design from a small cluster consisting of fused (ZnO) 3 planar rings growing in a triangular fashion under the typical hydrolysis–condensation scenario. The growth stages were simplified by considering the successive addition of three Zn­(OH) 2 entities at the “vertices” of the triangle-shaped clusters, yielding g-(ZnO) n [Zn­(OH) 2 ] 6 with n = 3, 6, 9 and 12, with their corresponding after-optimization structures depicted in Figure a.…”

“…33,34 We have recently reported, T h i s c o n t e n t i s both theoretically and experimentally, that the formation of small hydroxyl-terminated (ZnO) n planar clusters with n < 6 is possible via the hydrolysis−condensation of zinc dimethoxide. 35,36 However, regardless of the preparation methodology, characterizing these g-ZnO structures has so far been a hard task. It is well-known that the g-ZnO structures are reported to be stable only in their monolayered and bilayered structures while higher-order layered structures (more than 3 layers) are thermodynamically stable on Wurtzite structures based on high-resolution transmission electron or scanning tunneling microscopies.…”

“…A large variety of zinc oxide (ZnO) nanostructures, mainly in the Wurtzite polymorph, has been reported to exhibit excellent electrical, optical, and electrochemical properties in a wide range of applications. − However, recent experimental and theoretical studies have been focused on the study of atomic-scale layered ZnO nanostructures with graphene-like structures, usually abbreviated as g-ZnO. − The most common synthetic route toward g-ZnO is based on a chemical vapor deposition (CVD) process under ultrahigh vacuum conditions not only over Cu(111), Pd(111), Ag(111), − Pt(111), and Au(111) − but also over defectuous and nondefectuous graphene. − Moreover, the preparation of layered zinc oxide using zinc nitrate as a precursor in hydrothermal conditions, as well as the preparation of layered zinc hydroxide materials by the hydrolysis of diethyl zinc and zinc carboxylate at room temperature has also been explored recently. , The study of organozinc compounds such as dialkyl zinc or alkyl zinc alkoxides and their corresponding transformation toward zinc oxo–hydroxide clusters and nanostructures have been extensively studied. − More recently, Terlecki et al has shown that various reactions involving hydrolysis of organozinc precursors can provide completely different ZnO- or even Zn­(OH) 2 -based nanostructures . However, although zinc dialkoxides exhibit easier handling in air moisture conditions compared to dialkyl zinc or alkyl zinc alkoxides, only a few reports on the hydrolysis and condensation of zinc dialkoxides are reported in the literature. , We have recently reported, both theoretically and experimentally, that the formation of small hydroxyl-terminated (ZnO) n planar clusters with n < 6 is possible via the hydrolysis–condensation of zinc dimethoxide. , However, regardless of the preparation methodology, characterizing these g-ZnO structures has so far been a hard task. It is well-known that the g-ZnO structures are reported to be stable only in their monolayered and bilayered structures while higher-order layered structures (more than 3 layers) are thermodynamically stable on Wurtzite structures based on high-resolution transmission electron or scanning tunneling microscopies. − …”