第六族 (鉬、鎢) 與碲羰基團簇化合物之合成、結構、反應性及半導體性質之探討

Abstract

Te−Mo/W−CO 系統 由不同比例的 Te 粉末、M(CO)6 (M = Mo, W) 和 Et4NBr 在 KOH/MeCN/MeOH 溶液中以一鍋反應合成得到一系列新穎的多核含碲之第六族過渡金屬羰基簇。它們包含籠狀 [Et4N]4[Te7Mo6(CO)20] ([Et4N]4[1])、籃狀 [Et4N]4[Te6Mo6(CO)15] ([Et4N]4[2a−Mo(CO)3]) 與碗狀 [Et4N]4[Te6W5(CO)12] ([Et4N]4[2b]) 化合物。化合物 1、 2a−Mo(CO)3 與 2b 皆具有高氧化活性並可與碘 (I2) 進行反應。當化合物 1 與 1：1 莫爾比的 I2並利用四氫夫喃 (Tetrahydrofuran, THF) 與乙腈 (Acetonitrile, MeCN) 作為反應溶劑，可得高產率之車輪狀化合物 [Et4N]2[Te8Mo6(CO)18] ([Et4N]2[3])。若化合物 3 與 I2 或 [Cu(MeCN)4] 進行氧化則不反應，顯示其車輪狀結構之高穩定性。此外，當籃形 2a−Mo(CO)3 或碗形 2b進一步與 1、1.5 或2.5 莫爾比的 I2 反應後，可以獲得一系列氧化產物：碗狀 [Et4N]2[Te6W5(CO)12] ([Et4N]2[4b])、扭曲三立方烷簇 [Et4N]2[Te12M10(CO)24] (M = Mo, [Et4N]2[5a]; W, [Et4N]2[5b]) 與中性化合物之 [Te12M10(CO)24] (M = Mo, 6a; W, 6b)，其中碗狀化合物 [Et4N]4[Te6Mo5O2(CO)12] (2a−O2) 由 2a−Mo(CO)3 與氧氣反應所獲得，並以X光單晶繞射儀 (Single Crystal X−ray Diffractometer, SC−XRD) 證實其存在。此外中性化合物 6a 與 6b 進一步由高解析質譜 (High Resolution Mass Spectrometer, HRMS)、元素分析與X光單晶繞射儀證實。除氧化反應外，本研究亦將化合物 5a/5b 與 KOH 進行還原反應，根據紅外光譜及元素分析其產物為 Te12M10 (M = Mo, W) 基底的高負價產物 [Te12M10(CO)24]n‒ (M = Mo, 7a; W, 7b; n>2)。此多核 Te−Mo/W−CO 系列化合物的氧化價態與電子結構均藉由X 光電子能譜 (X−ray photoelectron spectroscopy, XPS)、125Te NMR 輔以理論計算研究。最後由固態反射式 UV−vis 光譜可知此系列化合物具有0.57−0.98 eV的低能隙與可調式之電導率 (8.95×10−8‒4.67×10−6 S/cm)，它們良好的半導體特性可利用其結構與分子間弱作用力進行解釋。Te−Mo/W−CO systemA novel series of polynuclear tellurium−containing group 6 transition metal carbonyl clusters were synthesized from one−pot reactions with different stoichiometric ratios of Te powder, M(CO)6 (M = Mo, W), and Et4NBr in KOH/MeCN/MeOH solution. These products included the cage−like [Et4N]4[Te7Mo6(CO)20] (1), the basket−like [Et4N]4[Te6Mo6(CO)15](2a−Mo(CO)3), and the bowl−like [Et4N]4[Te6W5(CO)12](2b). Compounds 1, 2a−Mo(CO)3, and 2b showed high oxidation activity toward I2. When complex 1 reacted with I2 in mixed THF/MeCN solutions, the paddle−wheel−shaped compound [Et4N]2[Te8Mo6(CO)18] (3) was obtained in high yields. Compound 3 can not react with I2 or [Cu(MeCN)4]+ due to its high stability. Further, if compounds 2a−Mo(CO)3 and 2b were treated with I2 at a molar ratio of 1, 1.5 or 2.5, a new sequence of the oxidized products were formed, namely the bowl−like [Et4N]2[Te6W5(CO)12](4b), the distorted tricubane−like clusters [Et4N]2[Te12M10(CO)24] (M = Mo, 5a; W, 5b), and the Mo‒Mo−bonded neutral tricubane−like products [Te12M10(CO)24](M = Mo, 6a; W, 6b). The bowl−like compound [Et4N]4[Te6Mo5O2(CO)12](2a−O2) was obtained by setting 2a−Mo(CO)3 in air, and its existence was confirmed by single−crystal X−ray diffraction. The neutral compounds 6a and 6b were characterized by single−crystal X−ray diffraction, elemental analysis (EA), and the high−resolution mass spectroscopy (HR−MS). In addition to the oxidation reactions, the reduction of compound 5a or 5b with KOH was conducted to yield the Te12M10−based (M = Mo, W) complexes, [Te12M10(CO)24]n‒ (M = Mo, 7a; W, 7b with n>2), as evidenced by infrared spectroscopy (IR), elemental analyses, and energy−dispersive X−ray spectroscopy (EDX). The oxidation state and electronic structures of this series of polynuclear Te−Mo/W−CO compounds were studied by X−ray photoelectron spectroscopy (XPS), 125Te NMR, and DFT calculations. Finally, the diffuse reflectance UV−vis spectra showed that this series of compounds possessed low energy gaps (0.57−0.98 eV) and tunable conductivities (8.95×10−8−4.67×10−6 S/cm), where their goodsemiconducting characteristics were explained by their structural features and weak intermolecular interactions in the solid state.