Solution and solid state coexistence of head–head and head–tail isomers in dimeric Pd(<scp>ii</scp>) and Pt(<scp>ii</scp>) complexes of the type [M<sub>2</sub>(a–a)<sub>2</sub>(µ-L-N<sup>3</sup>N<sup>4</sup>)<sub>2</sub>]<sup>2+</sup>with a bridging triazolopyrimidine ligand and chelating bidentate diamines
作者:Mohammad Abul Haj、Miguel Quirós、Juan M. Salas
DOI:10.1039/b207263g
日期:——
Six palladium and one platinum compound containing dimeric dinuclear cations of the type [M2(aâa)2(µ-7tpO-N3,N4)2]2+ are presented, aâa representing a bidentate chelating amine and 7tpOâ being the anionic form of the ligand 4,7-dihydro-7-oxo[1,2,4]triazolo[1,5-a]pyrimidine, which bridges the metal atoms through its nitrogen atoms in positions 3 and 4. Two linkage isomers are possible for such complexes, so called headâhead and headâtail. According to 1H- and 195Pt-NMR data, both isomers are present in dmso-d6 solution and display analogous stability. An exhaustive assignment of the 1H signals has been made. The crystal structure of three of these compounds has been determined by single-crystal X-ray diffraction. For two of them, those with bispyrimidine as auxiliary ligand, the headâhead and headâtail isomers coexist even in the solid state, both being present in the same crystal in a disordered scheme. This situation is explained by the almost symmetric external shape of the bridging ligand, which is expected to interact with neighbouring species in a similar way even if rotated 180 degrees.
本文介绍了六种钯化合物和一种铂化合物,它们含有类型为 [M2(a–a)2(µ-7tpO-N3,N4)2]²⁺ 的二聚体双核阳离子,其中 a–a 代表一种双齿配位胺,7tpO⁻ 是配体 4,7-二氢-7-氧代[1,2,4]三唑[1,5-a]嘧啶的阴离子形式,该配体通过其在 3 位和 4 位的氮原子连接金属原子。这种配合物可能存在两种链接异构体,称为头-头和头-尾。根据 1H 和 195Pt-NMR 数据,这两种异构体均存在于 DMSO-d6 溶液中,并显示出类似的稳定性。对 1H 信号进行了详尽的归属。通过单晶 X 射线衍射法确定了其中三种化合物的晶体结构。对于其中两种化合物,即以双嘧啶作为辅助配体的那两种,头-头和头-尾异构体甚至在固态下也共存,二者均存在于同一晶体中,呈现无序结构。这种情况可以用桥接配体几乎对称的外部形状来解释,即使旋转 180 度,该配体预计也会以类似的方式与相邻物种相互作用。