MgL.cif from Investigating the geometrical preferences of a flexible benzimidazolone-based linker in the synthesis of coordination polymers

A series of new group 2 coordination polymers, <b>MgL</b> = {MgL(H₂O)(DMF)_0.75}_∞, <b>CaL</b> = {CaL(DMF)₂}_∞, <b>SrL</b> = {SrL(H₂O)_0.5}_∞ and <b>BaL</b> = {BaL(H₂O)_0.5}_∞, were synthesized using a flexible benzimidazolone diacetic acid linker (<b>L</b>) in which the two carboxylic acid binding sites are connected to a planar core via {–CH₂–} spacers that can freely rotate in solution. In a ‘curiosity-led' diversion from group 2 metals, the first row transition metal salts Mn²⁺, Cu²⁺ and Zn²⁺ were also reacted with <b>L</b> to yield crystals of <b>MnL =</b> {MnL(DMF)(H₂O)_3.33}_∞, <b>Cu₃L₂</b> = {Cu₃L₂(DMF)₂(CHO₂)₂}_∞ and <b>ZnL</b> = {ZnL(DMF)}_∞. Crystal structures were obtained for all seven materials. All structures form as two-dimensional sheets and, with the exception of <b>ZnL,</b> which displays tetrahedrally coordinated metal centres, and <b>Cu₃L_2,</b> which contains square planar coordinated metal centres and Cu paddle wheels, contain six-coordinate metal centres. In each structure, the linker adopts one of two distinct conformations, with the carboxylate groups either <i>cis</i> or <i>trans</i> to each other with respect to the plane of the core. All materials were also characterized by powder X-ray diffraction and thermogravimetric analysis.

本研究合成了一系列新型第二族配位聚合物，分别为<b>MgL</b> = {MgL(H₂O)(N,N-二甲基甲酰胺（N,N-Dimethylformamide，简称DMF）)₀.₇₅}∞、<b>CaL</b> = {CaL(DMF)₂}∞、<b>SrL</b> = {SrL(H₂O)₀.₅}∞ 及 <b>BaL</b> = {BaL(H₂O)₀.₅}∞，所用连接配体为柔性苯并咪唑酮二乙酸（<b>L</b>），其两个羧酸结合位点通过可在溶液中自由旋转的亚甲基（–CH₂–）间隔基与平面核心相连。受好奇心驱动，我们开展了针对第二族金属之外体系的研究，选用第一过渡系金属盐Mn²+、Cu²+与Zn²+与配体<b>L</b>反应，成功制备得到<b>MnL</b> = {MnL(DMF)(H₂O)₃.₃₃}∞、<b>Cu₃L₂</b> = {Cu₃L₂(DMF)₂(CHO₂)₂}∞ 及 <b>ZnL</b> = {ZnL(DMF)}∞ 的晶体。所有七种材料均解析得到了晶体结构，所有结构均形成二维片层；其中除<b>ZnL</b>（金属中心为四配位）及<b>Cu₃L₂</b>（含平面正方形配位金属中心与铜桨轮结构）外，其余材料的金属中心均为六配位。每种结构中的连接配体均存在两种不同构象：羧酸基团相对于核心平面分别呈顺式（cis）或反式（trans）排布。所有材料均通过粉末X射线衍射（PXRD）及热重分析（TGA）完成了表征。