Four N–H⋯OC bonded structures for 5,5-substituted derivatives of barbituric acid are reported, which are distinct from the eight fundamental types that have been previously described. The N–H⋯OC-bonded layer structures L-4, L-5 and L-6 are present in crystal polymorphs of 5-(2-bromoallyl)-5-isopropyl barbituric acid (L-4: 1, noctal), 5,5-dichlorobarbituric acid (L-6: 2a, L-5: 2b) and 5,5-dibromobarbituric acid (L-5: 3a). The monoclinic polymorph (3b) of the dibromo compound contains the framework F-2. In each case, the essential building block consists of two molecules which are doubly N–H⋯OC-bonded via a central R22(8) ring. The L-4 structure is closely related to the common 1D ladder topology C-4. It serves also as a building unit for the L-5 sandwich structure. The essential rings of L-4 and L-6 have the same graph-set descriptor R66(28) but are topologically distinct from one another. In the F-2 framework, ten molecules are linked together to give an L-shaped R1010(48) ring. The IR spectra of the crystal forms 1, 2a–b and 3a–b are discussed and a previously established classification scheme correlating the H-bonding of barbiturates with their IR characteristics is extended.
本文报道了四种N-H⋯OC键合结构的5,5-取代
巴比妥酸衍
生物,它们与之前描述的八种基本类型不同。N-H⋯OC键合层结构
L-4、L-5和L-6存在于5-(2-
溴烯丙基)-5-
异丙基巴比妥酸(
L-4:1,noctal)、
5,5-二氯巴比妥酸(L-6:2a,L-5:2b)和
5,5-二溴巴比妥酸(L-5:3a)的晶体多晶型中。二
溴化合物的单斜多晶型(3b)包含F-2框架。在每种情况下,基本结构单元由两个分子组成,它们通过中心
R22(8)环形成双N-H⋯OC键。
L-4结构与常见的1D阶梯拓扑结构C-4密切相关。它也是L-5三明治结构的构建单元。
L-4和L-6的基本环具有相同的图形集描述符R66(28),但在拓扑上彼此不同。在F-2框架中,十个分子连接在一起形成L形的R1010(48)环。本文讨论了晶体1、2a-b和3a-b的红外光谱,