Single-crystal studies of -F 2 and of ?-O 2
Single-crystal studies of -F 2 and of ?-O 2
复制标题
-F 2 和?-O 2 的单晶研究
DOI：
10.1107/s0365110x6400202x
复制
发表时间：
1964
期刊：
影响因子：
--
通讯作者：
W. Lipscomb
中科院分区：
文献类型：
--
作者：
T. H. Jordan;W. Streib;H. Smith;W. Lipscomb
Fig. 1. F1-F2和γ-O2的晶体结构。对于每个分子中心指示平面外坐标，除了在z= 0处的那些，其未标记。在000和1/2/2/2处的两个分子近似是球形无序的。其他六个分子，在1/4/2 0，0/4 {-，{。0~、-~ 1/2 0、0~ 1/2和1/2 0~显示出电子密度的扁球形分布，使得长轴与短轴的比率约为2。短轴沿着最短的分子间接触（在F2中为3.3 A，在O-中为3.4 A）沿着x（y= 1/2，z= 0）、沿着y（x= 0，z= 1/2）和沿着z（x= 1/2，y= 0）对齐。O 9的键距为1.21 A。Lipscomb，1962; Streib，Jordan & Lipscomb，1962）的计算结果，推广到50 K下的f1-F ~ 2和50 K下的~-O_2的单晶研究。令人惊讶的是，这些相具有相同的结构类型（图1）。晶胞尺寸为a= 6.67+ _0。对于fl-F~和6.83+ _0，07/~ _。05~ 05，晶胞中有8个双原子分子。当1为奇数时，hhl的系统缺失表明空间群为P43 n或Pm 3 n，但我们的结果表明Pm 3 n中存在取向无序结构.在f1-F ~中，在000或1/2/2/2处的每个F~在分子中心之间的3-7~处具有12个F2邻居。其它F2中的每一个在3.3 μ m处具有2F 8，在3.71 μ m处具有4F 8，并且在4.1 μ m处具有8 F2。如果两个Fu的分子轴垂直于接触线，则货车范德华接触为2.7 °，或者如果它们的轴沿着接触线，则范德华接触为4-1 °。因此，无序被强烈地沿着由3.3埃分开的F~-分子的无限线性链阻碍。Murphy和Rubin（1952）由于熵的不一致而怀疑存在一个主要的转变，而Hu，白色和约翰斯顿（1953）发现了这个转变，我们已经证实了它的存在，但是我们通过冷却f1-F2单晶通过45.55 K的转变点，只得到了α-F2的粉末照片。7-O~和fl-F~结构的本质一致性使得任何基于O~二聚体对7-02的描述都站不住脚（Ruhemann，1932; Vegard，1935），并进一步表明7-02不寻常的磁性（Kanda，Haseda & Otsubo，1955）并不决定其结构。无限线性链的0 - 2分子的存在是一致的非常短的范围内的相互作用怀疑I4：安达等人。（1955）（Knobler，1961; Lien &菲利普斯，1961），但是这种结构引起了关于在其他固相和溶液中存在二聚体的严重问题（刘易斯，1924; Pauling，1960）。即使是在000的近球形无序分子
Fig. 1. Crystal structure of fl-F2 and of y-O2. Out-of-plane coordinates are indicated for each molecular center, except for those at z= 0, which are unlabeled. The two molecules at 000 and ½½ ½ are approximately spherically disordered. The other six molecules, at ¼½0, 0¼ {-,{. 0~,-~ ½0, 0~ ½ and ½0~, show an oblate spheroidal distribution of electron density such that the ratio of major to minor axis is about two. Minor axes are aligned along the shortest intermolecular contacts (3.3 A in F2, 3.4 A in O~) along x (y= ½, z= O), along y (x= O, z= ½) and along z (x= ½, y= O). Bond distances of 1.21 A for O9. and 1.42 A for F2 were assumed.Lipscomb, 1962; Streib, Jordan & Lipscomb, 1962) have been extended to single crystal studies of fl-F~ at 50 K and~-O2 at 50 K. These phases have, surprisingly, the same structure-type (Fig. 1). Unit-cell dimensions are a= 6.67+ _0. 07/~ _ for fl-F~ and 6.83+ _0. 05~ for y-O2, and there are eight diatomic molecules in the unit cell. Systematic absences of hhl when 1 is odd suggest space groups P43n or Pm3n, but our results indicate an orienta-tionally disordered structure in Pm3n. In fl-F~ each F~ at 000 or at ½ ½ ½ has 12 F2 neighbors at 3-7~ between molecular centers. Each of the other F2's has 2Fg's at 3.3/~, 4Fe's at 3.71 and 8F2's at 4.1/~. Van der Waals contacts are 2.7~ if two Fu's have their molecular axes perpendicular to, or 4-1/~ if their axes are along, the line of contact. Thus, the disorder is strongly hindered along the infinite linear chains of F~ molecules separated by 3.3 A. We have verified the presence of a major transition, suspected by Murphy & Rubin (1952) because of an entropy discrepancy, and found by Hu, White & Johnston (1953), but we have obtained only powder photographs of a-F2 by cooling single crystals of fl-F2 through the transition point at 45.55 K. The essential identity of the 7-O~ and fl-F~ structures makes untenable any description of 7-02 based upon dimers of O~(Ruhemann, 1932; Vegard, 1935), and further suggests that the unusual magnetic properties of 7-02 (Kanda, Haseda & Otsubo, 1955) do not determine the structure. The presence of infinite linear chains of 0 2 molecules is consistent with the very short range inter-actions suspected by I4: anda et al.(1955)(Knobler, 1961; Lien & Phillips, 1961), but this structure raises serious questions about the existence of dimers in the other solid phases and in solution (Lewis, 1924; Pauling, 1960). Even the nearly spherically disordered molecules at 000