Four novel ditopic ligands that have a pyrazole ring in their central unit and are useful for the generation of coordination polymers have been synthesized. Two of these ditopic ligands present two carboxylate functions as coordinating groups, while the other two are hybrid ligands having only one carboxylate function and either tetrazolate or imidazole as the remaining coordination site. The ligands have been obtained through a multi-step reaction sequence that begins with the Claisen condensation of either 4-acetylbenzonitrile or 4-(1H-imidazol-1-yl)acetophenone with diethyl oxalate and has the Knorr pyrazole ring closure as its key step. Subsequently, the tetrazolate in one of the ligands is constructed through a [3 + 2] cycloaddition of azide anion to the cyano group, while hydrolysis of the ester and the cyano substituents generates the carboxylate function(s). The structure of the intermediates and of the target ligands has been investigated by solution NMR, special attention being given to keto–enol and pyrazole tautomerism when present. The structure of two ligands and a key intermediate has also been established by single-crystal X-ray diffraction.

中文翻译：

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中央单元带有吡唑环的新型对位配体的设计与合成

已经合成了在其中心单元中具有吡唑环并且可用于生成配位聚合物的四个新颖的​​对位配体。这些对位配体中的两个呈现两个羧酸盐官能团作为配位基团，而其他两个是仅具有一个羧酸盐官能团且四唑酸酯或咪唑作为剩余配位位点的杂化配体。配体是通过多步反应序列获得的，该反应序列以4-乙酰基苄腈或4-（1 H-咪唑-1-基）苯乙酮与草酸二乙酯，并以克诺尔吡唑环闭合为关键步骤。随后，通过将叠氮化物阴离子与氰基进行[3 + 2]环加成反应，来构造配体之一中的四唑酸盐，同时酯和氰基取代基的水解产生羧酸盐官能团。中间体和目标配体的结构已通过溶液NMR进行了研究，当存在酮-烯醇和吡唑互变异构现象时要特别注意。还通过单晶X射线衍射确定了两个配体和关键中间体的结构。