Molecular Tectonics of Four-Connected Network Topologies by Regulating the Ratios of Tetrahedral and Square-Planar Building Units

Assembly
of the 4-connected building units leads to three three-dimensional
frameworks, {[Cd­(TPPBDA)­(OH)2]·2H2O·4DMA}n (1), {[Cd­(TPPBDA)1/2(tpdc)]·DMF}n (2),
and {[Zn­(TPPBDA)1/2(bpdc)]·3H2O·3DMF}n (3) (TPPDBA = N,N,N′,N′-tetrakis­(4-(4-pyridine)-phenyl) biphenyl-4,4′-diamine,
H2tpdc = 4,4″-dicarboxyl-(1,1′,3′,1″)-terphenyl),
H2bpdc = biphenyldicarboxylic acid, DMF = N,N-dimethylformamide, DMA = N,N-dimethylacteamide), which are based on different ratios
of tetrahedral (T) and square-planar (S) building units. For compound 1, T and S nodes are in the ratio of 1:1, which is the feature
of pts. While T/S is 2:1 in compound 2 to form a bbf
framework, for compound 3, the TPPBDA ligand and the
metal center are both in tetrahedral configuration, which constructs
a dia net with the ratio of 2:0 (T/S). In addition, the compound 2 exhibits high selectivity for CO2 over CH4, showing a hysteretic sorption–desorption loop.

四连接构筑单元的组装可得到三种三维骨架配合物，分别为{[Cd­(TPPBDA)­(OH)₂]·2H₂O·4DMA}ₙ (1)、{[Cd­(TPPBDA)₁/₂(tpdc)]·DMF}ₙ (2)以及{[Zn­(TPPBDA)₁/₂(bpdc)]·3H₂O·3DMF}ₙ (3)。其中，TPPBDA（N,N,N′,N′-四(4-(4-吡啶基)苯基)联苯-4,4′-二胺，N,N,N′,N′-tetrakis(4-(4-pyridine)phenyl)biphenyl-4,4′-diamine）、H₂tpdc（4,4''-二羧基-(1,1′,3′,1''')-三联苯，4,4''-dicarboxyl-(1,1′,3′,1''')-terphenyl）、H₂bpdc（联苯二甲酸，biphenyldicarboxylic acid）、DMF（N,N-二甲基甲酰胺，N,N-dimethylformamide）以及DMA（N,N-二甲基乙酰胺，N,N-dimethylacetamide）为相应的配体或溶剂分子，上述骨架基于四面体（T）与平面正方形（S）构筑单元的不同比例构筑得到。对于配合物1，其T节点与S节点的比例为1:1，这是pts拓扑的典型结构特征；配合物2的T/S比例为2:1，据此构建出bbf骨架；配合物3中，TPPBDA配体与金属中心均为四面体构型，由此构筑出T/S比例为2:0的dia拓扑网络。此外，配合物2对二氧化碳（CO₂）相较于甲烷（CH₄）表现出优异的吸附选择性，其吸附-脱附过程呈现滞后环。