Portalone Gustavo
Chemistry Department, "Sapienza" University of Rome, P. le A. Moro 5, I-00185 Rome, Italy.
Acta Crystallogr E Crystallogr Commun. 2020 Nov 6;76(Pt 12):1823-1826. doi: 10.1107/S2056989020014553. eCollection 2020 Dec 1.
A third crystalline form of the title compound, CHO, crystallizing in the centrosymmetric monoclinic space group 2/, has been identified during screening for co-crystals. The asymmetric unit comprises a non-planar independent mol-ecule with a synplanar conformation of the OH group. The sterically bulky -meth-oxy substituents force the carb-oxy group to be twisted away from the plane of the benzene ring by 74.10 (6)°. The carb-oxy group exhibits the acidic H atom disordered over two sites between two O atoms. A similar situation has been found for the second tetra-gonal polymorph reported [Portalone (2011 ▸). . E, o3394-o3395], in which mol-ecules with the OH group in a synplanar conformation form dimeric units strong O-H⋯O hydrogen bonds. In contrast, in the first ortho-rhom-bic form reported [Swaminathan (1976 ▸). . B, 1897-1900; Bryan & White (1982 ▸). . B, 1014-1016; Portalone (2009 ▸). . E, o327-o328], the mol-ecular components do not form conventional dimeric units, as an anti-planar conformation adopted by the OH group favors the association of mol-ecules in chains stabilized by linear O-H⋯O hydrogen bonds.
在共晶体筛选过程中，已鉴定出标题化合物CHO的第三种晶体形式，其结晶于中心对称单斜空间群2/。不对称单元包含一个非平面独立分子，其OH基团呈共平面构象。空间位阻较大的甲氧基取代基迫使羧基从苯环平面扭转74.10 (6)°。羧基的酸性H原子在两个O原子之间的两个位置上无序分布。在报道的第二种四方多晶型物中也发现了类似情况[波塔洛内（2011▸）。。E，o3394 - o3395]，其中OH基团呈共平面构象的分子形成二聚体单元，存在强O - H⋯O氢键。相比之下，在报道的第一种正交晶型中[斯瓦米纳坦（1976▸）。。B，1897 - 1900；布赖恩和怀特（1982▸）。。B，1014 - 1016；波塔洛内（2009▸）。。E，o327 - o328]，分子组分不形成传统的二聚体单元，因为OH基团采用的反平面构象有利于通过线性O - H⋯O氢键稳定的分子链中的分子缔合。
