Dietzel Pascal D C, Kremer Reinhard K, Jansen Martin
Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70689 Stuttgart, Germany.
J Am Chem Soc. 2004 Apr 14;126(14):4689-96. doi: 10.1021/ja039880i.
Trimethylphenylammonium superoxide (1) and tetrabutylammonium superoxide (2) were prepared by ion-exchange reaction in liquid ammonia. Both compounds were structurally characterized by single-crystal X-ray diffraction. The crystal structure of 2 contains solvent ammonia molecules that are hydrogen bonded to the superoxide ion and therefore may influence the bonding properties of the superoxide ion. The crystal structure of 1 does not contain any solvent molecules. Therefore, it represents the best known approximation to the virtually isolated superoxide ion in the solid state to date. The O-O bond length is 1.332(2) A in 1 and 1.312(2) A in 2. Magnetization measurements show that the susceptibilities of both compounds follow an ideal Curie law down to 2 K reflecting an absence of intermolecular exchange effects between the superoxide ions. The effective magnetic moments of both compounds are larger than the spin-only value due to contributions of the orbital momentum in the superoxide ion. The values of the magnetic moment comply well with the g factors obtained from electron paramagnetic resonance spectra. The g tensors themselves reflect the anisotropic environment of the superoxide ions. The Pi(g) energy levels which are degenerate in the free superoxide ion split up in crystal fields of lower than tetragonal symmetry. The energy splitting is estimated from the diagonal elements of the g tensor of 1.
三甲基苯基铵超氧化物（1）和四丁基铵超氧化物（2）通过在液氨中的离子交换反应制备。两种化合物均通过单晶X射线衍射进行结构表征。2的晶体结构包含与超氧离子形成氢键的溶剂氨分子，因此可能会影响超氧离子的键合性质。1的晶体结构不包含任何溶剂分子。因此，它代表了迄今为止固态中几乎孤立的超氧离子的最接近已知近似结构。1中O - O键长为1.332(2) Å，2中为1.312(2) Å。磁化测量表明，两种化合物的磁化率在2 K以下均遵循理想居里定律，这反映出超氧离子之间不存在分子间交换效应。由于超氧离子中轨道动量的贡献，两种化合物的有效磁矩均大于仅自旋值。磁矩值与从电子顺磁共振光谱获得的g因子吻合良好。g张量本身反映了超氧离子的各向异性环境。在自由超氧离子中简并的π(g)能级在低于四方对称的晶体场中分裂。能量分裂由1的g张量对角元素估算得出。
