Barthen Peter, Frank Walter
Institut für Anorganische Chemie und Strukturchemie, Lehrstuhl II: Material- und Strukturforschung, Heinrich-Heine-Universität Düsseldorf, Universitätsstrasse 1, D-40225 Düsseldorf, Germany.
Acta Crystallogr E Crystallogr Commun. 2019 Oct 31;75(Pt 11):1787-1791. doi: 10.1107/S2056989019014312. eCollection 2019 Nov 1.
Highly Brønsted-acidic boron trifluoride monohydrate, a widely used 'super acid-catalyst', is a colourless fuming liquid that releases BF at room temperature. Com-pared to the liquid com-ponents, boron trifluoride monohydrate and 1,4-dioxane, their 1:1 adduct, BFHO·CHO, is a solid with pronounced thermal stability (m.p. 401-403 K). The crystal structure of the long-time-stable easy-to-handle and weighable com-pound is reported along with new preparative aspects and the results of H, B, C and F spectroscopic investigations, particularly documenting its high Brønsted acidity in aceto-nitrile solution. The remarkable stability of solid BFHO·CHO is attributed to the chain structure established by O-H⋯O hydrogen bonds of exceptional strength {O2⋯H1-O1 [O⋯O = 2.534 (3) Å] and O1-H1⋯O3 [2.539 (3) Å] in the concatenating unit >O2⋯H1-O1-H2⋯O3<}, taking into account the mol-ecular (non-ionic) character of the structural moieties. Indirectly, this structural feature documents the outstanding acidification of the HO mol-ecule bound to BF and reflects the super acid nature of BFHO. In detail, the (7) zigzag chain system of hydrogen bonding in the title structure is characterized by the double hydrogen-bond donor and double (κ,κ') hydrogen-bond acceptor functionality of the aqua ligand and dioxane molecule, respectively, the almost equal strength of both hydrogen bonds, the approximatety linear arrangement of the dioxane O atoms and the two neighbouring water O atoms. Furthermore, the approximately planar arrangement of B, F and O atoms in sheets perpendicular to the axis of the ortho-rhom-bic unit cell is a characteristic structural feature.
高布朗斯特酸性的三水合三氟化硼是一种广泛使用的“超强酸催化剂”，是一种在室温下会释放出BF的无色发烟液体。与液体成分三水合三氟化硼和1,4 - 二氧六环相比，它们的1:1加合物BFHO·CHO是一种具有明显热稳定性的固体（熔点401 - 403 K）。报道了这种长期稳定、易于处理和称量的化合物的晶体结构，以及新的制备方法和H、B、C和F光谱研究结果，特别证明了其在乙腈溶液中的高布朗斯特酸度。固体BFHO·CHO的显著稳定性归因于由强度非凡的O - H⋯O氢键建立的链状结构{在连接单元>O2⋯H1 - O1 - H2⋯O3<中，O2⋯H1 - O1 [O⋯O = 2.534 (3) Å]和O1 - H1⋯O3 [2.539 (3) Å]}，同时考虑到结构部分的分子（非离子）特性。间接地，这种结构特征证明了与BF结合的HO分子的显著酸化，并反映了BFHO的超强酸性质。详细地说，标题结构中(7)之字形氢键链系统的特征在于水配体和二氧六环分子分别具有双氢键供体和双（κ,κ'）氢键受体功能、两个氢键强度几乎相等、二氧六环O原子与两个相邻水O原子近似线性排列。此外，在垂直于正交晶胞轴的平面中，B、F和O原子近似平面排列是一个特征结构特征。
