A Novel Family of Structurally Characterized Lithium Cobalt Double Aryloxides and the Nanoparticles and Thin Films Generated Therefrom

The reaction between LiN(SiMe3)2 and Co(N(SiMe3)2)2 in THF followed by the addition of
an aryl alcohol (HOAr) yielded:  [Co[(μ-OAr)2Li(THF)x]2 [where x = 2:  OAr =:  OC6H4Me-2
(oMP, 1), OC6H4(OCHMe2)-2 (oPP, 2), OC6H3(Me)2-2,6 (DMP, 3); where x = 1:  OAr = OC6H3(OCHMe2)2-2,6 (DIP, 4)]. Undertaking the same synthesis in pyridine (py) led to the same
general structure with py molecules substituted for the THF solvent molecules:  [Co[(μ-OAr)2Li(py)2]2 (OAr = oMP (5), oPP (6)]. For 1−6, the tetrahedrally (Td) bound Co atom
bridges two OAr ligands to each of the Li atoms. The Li atom adopts a Td or trigonal
bipyramidal (TBP) geometry, as determined by the number of bound solvent molecules. For
the more sterically demanding ligands with py as the solvent, the mononuclear monometallic
species [Co[(μ-OAr)2(py)x]2 (OAr = DMP (7), x = 2; DIP (8), x = 3) were observed adopting
a Td or TBP geometry, respectively, based on the number of bound solvent molecules.
Increasing the steric bulk of the OAr to OC6H3But2-2,6 (DBP) in either THF or py led to the
isolation of the previously characterized [Li(DBP)(solv)]2. Calculated XRD powder patterns
were generated from the single-crystal structure of 1−8 and used to verify the identity of
the bulk powder. Attempts to use these compounds for MOCVD applications were not
successful due to low volatility of these compounds. Attempts to generate nanoparticles of
the spinel phase of LiCoO2 by injecting a py solution of 5 or 6 into boiling methyl-imidazole
(MeIm)/H2O 95:5) led to nanoparticles of Co(OH)2 only, as characterized by XRD and TEM.
Thin films of the spinel phase of LiCoO2 were formed by spin-cast deposition methods using
5 or 6 dissolved in a py/toluene mixture onto platinized silicon wafers followed by firing at
700 °C. Cyclic voltammetry revealed two irreversible oxidation processes followed by one
reversible process, the latter of which is found to occur at about 4.2 V. XRD analysis of the
thin film, both before and after electrochemical cycling, revealed only minimal variations in
the crystal structure of the film after cycling. This family of compounds, even though
stoichiometrically incorrect, have been shown to be useful for single-source applications in
the solid and liquid techniques.

将双(三甲基硅基)氨基锂（LiN(SiMe3)2）与双(三甲基硅基)氨基钴(II)（Co(N(SiMe3)2)2）在四氢呋喃（THF）中反应，随后加入芳醇（HOAr），可得到产物[Co[(μ-OAr)2Li(THF)x]2，其中当x=2时，OAr分别为2-甲基苯氧基（oMP，化合物1）、2-异丙氧基苯氧基（oPP，化合物2）、2,6-二甲基苯氧基（DMP，化合物3）；当x=1时，OAr为2,6-二异丙氧基苯氧基（DIP，化合物4）。
在吡啶（py）中进行相同合成反应，可得到结构相似的产物，仅四氢呋喃溶剂分子被吡啶取代，产物为[Co[(μ-OAr)2Li(py)2]2，其中OAr分别为2-甲基苯氧基（oMP，化合物5）、2-异丙氧基苯氧基（oPP，化合物6）。
对于化合物1-6，四面体配位（Td）的钴原子通过两个桥联芳氧基配体分别连接两个锂原子；锂原子的配位构型为四面体或三角双锥（TBP），其具体构型由结合的溶剂分子数目决定。
当采用吡啶作为溶剂且配体空间位阻更大时，可得到单核单金属物种[Co[(μ-OAr)2(py)x]2，其中OAr为2,6-二甲基苯氧基（DMP，化合物7，x=2）、2,6-二异丙氧基苯氧基（DIP，化合物8，x=3），二者分别呈现四面体与三角双锥配位构型，配位构型由结合的溶剂分子数目决定。
当芳氧基配体的空间位阻进一步增大至2,6-二叔丁基苯氧基（DBP）时，无论在四氢呋喃还是吡啶溶剂中，均可分离得到此前已表征的二聚体[Li(DBP)(solv)]2。
基于化合物1-8的单晶结构计算得到其X射线衍射（XRD）粉末衍射图谱，用于验证体相粉末的物相一致性。
尝试将该系列化合物用于金属有机化学气相沉积（MOCVD）应用，但因化合物挥发性较低未获成功。
尝试将化合物5或6的吡啶溶液注入沸腾的95:5（体积比）甲基咪唑（MeIm）/水混合体系中，以制备尖晶石相LiCoO2纳米颗粒，但最终仅得到氢氧化钴（Co(OH)2）纳米颗粒，相关结果通过XRD与透射电子显微镜（TEM）表征确认。
采用旋涂沉积法，将溶解于吡啶/甲苯混合溶剂中的化合物5或6涂覆于镀铂硅片上，随后在700℃下焙烧，即可制备得到尖晶石相LiCoO2薄膜。
循环伏安测试显示存在两步不可逆氧化过程，随后为一步可逆氧化过程，该可逆过程的电位约为4.2 V。
对电化学循环前后的薄膜进行XRD分析，结果表明循环后薄膜的晶体结构仅发生极小变化。
尽管化学计量比存在偏差，但该系列化合物已被证实可用于固相与液相技术中的单源前驱体应用。