Syntheses and Multi-NMR Study of <i>fac</i>- and <i>mer</i>-OsO₃F₂(NCCH₃) and the X-ray Crystal Structure (<i>n</i> = 2) and Raman Spectrum (<i>n</i> = 0) of <i>fac</i>-OsO₃F₂(NCCH₃)·<i>n</i>CH₃CN

Dissolution of the infinite chain polymer, (OsO3F2)∞, in CH3CN solvent at −40 °C followed by solvent removal under vacuum at −40 °C yielded fac-OsO3F2(NCCH3)·nCH3CN (n ≥ 2). Continued pumping at −40 °C with removal of uncoordinated CH3CN yielded fac-OsO3F2(NCCH3). Both fac-OsO3F2(NCCH3)·nCH3CN and fac-OsO3F2(NCCH3) are yellow-brown solids and were characterized by low-temperature (−150 °C) Raman spectroscopy. The crystal structure (−173 °C) of fac-OsO3F2(NCCH3)·2CH3CN consists of two co-crystallized CH3CN molecules and a pseudo-octahedral OsO3F2·NCCH3 molecule in which three oxygen atoms are in a facial arrangement and CH3CN is coordinated trans to an oxygen atom in an end-on fashion. The Os---N bond length (2.205(3) Å) is among the shortest M---N adduct bonds observed for a d0 transition metal oxide fluoride. The 19F NMR spectrum of (OsO3F2)∞ in CH3CN solvent (−40 °C) is a singlet (−99.6 ppm) corresponding to fac-OsO3F2(NCCH3). The 1H, 15N, 13C, and 19F NMR spectra of 15N-enriched OsO3F2(NCCH3) were recorded in SO2ClF solvent (−84 °C). Nitrogen-15 enrichment resulted in splitting of the 19F resonance of fac-OsO3F2(15NCCH3) into a doublet (2J(15N−19F), 21 Hz). In addition, a doublet of doublets (2J(19Fax−19Feq), 134 Hz; 2J(15N−19Feq), 18 Hz) and a doublet (2J(19Fax−19Feq), 134 Hz) were observed in the 19F NMR spectrum that have been assigned to mer-OsO3F2(15NCCH3); however, coupling of 15N to the axial fluorine-on-osmium environment could not be resolved. The nitrogen atom of CH3CN is coordinated trans to a fluorine ligand in the mer-isomer. Quantum-chemical calculations at the SVWN and B3LYP levels of theory were used to calculate the energy-minimized gas-phase geometries, vibrational frequencies of fac- and mer-OsO3F2(NCCH3) and of CH3CN. The relative stabilities of the mer- and fac-isomers have been determined and are in accordance with the solution NMR assignments.将无限链状聚合物(OsO3F2)∞于−40 ℃下溶解于乙腈（CH3CN）溶剂中，随后在−40 ℃真空条件下移除溶剂，得到面式(facial)-OsO3F2(NCCH3)·nCH3CN（n ≥ 2）。继续在−40 ℃下抽真空以移除未配位的乙腈，即可得到面式-OsO3F2(NCCH3)。面式-OsO3F2(NCCH3)·nCH3CN与面式-OsO3F2(NCCH3)均为黄褐色固体，且通过−150 ℃低温拉曼光谱（Raman spectroscopy）进行了表征。面式-OsO3F2(NCCH3)·2CH3CN的晶体结构（测试温度−173 ℃）由两个共结晶的乙腈分子，以及一个假八面体构型的OsO3F2·NCCH3分子构成：该分子中三个氧原子呈面式排布，且乙腈以端基配位方式与氧原子反位结合。Os---N键长（2.205(3) Å）属于d⁰过渡金属氧化氟所观测到的最短M---N加合键之一。(OsO3F2)∞在乙腈溶剂中（−40 ℃）的¹⁹F核磁共振（Nuclear Magnetic Resonance, NMR）谱为单峰（化学位移−99.6 ppm），对应面式-OsO3F2(NCCH3)。对¹⁵N富集的OsO3F2(NCCH3)，我们在SO2ClF溶剂中（−84 ℃）记录了其¹H、¹⁵N、¹³C及¹⁹F NMR谱。氮-15富集使得面式-OsO3F2(¹⁵NCCH3)的¹⁹F共振峰裂分为双峰（耦合常数²J(¹⁵N−¹⁹F)=21 Hz）。此外，在¹⁹F NMR谱中还观测到了两组峰：一组为双二重峰（耦合常数²J(¹⁹Fax−¹⁹Feq)=134 Hz，²J(¹⁵N−¹⁹Feq)=18 Hz），另一组为双峰（²J(¹⁹Fax−¹⁹Feq)=134 Hz），上述峰均被归属于经式(meridional)-OsO3F2(¹⁵NCCH3)；但无法观测到¹⁵N与锇中心轴向氟原子之间的耦合作用。在经式异构体中，乙腈的氮原子与氟配体呈反位配位。采用SVWN与B3LYP理论水平下的量子化学计算方法，优化得到了气相下的最低能量构型，并计算了面式-、经式-OsO3F2(NCCH3)以及乙腈的振动频率。经式与面式异构体的相对稳定性已被确定，且与溶液相NMR谱的归属结果一致。