Two novel isostructural phosphonate-monoethylcarboxylate MOFs with the structural formula of [M₂(EtBCP)₂(DABCO)_0.5]·2DMA (M = Zn (2), Co (3); H₂EtBCP = O-ethyl-P-(4-carboxyphenyl)phosphonic acid, DABCO = 1,4-diazabicyclo[2.2.2]octane, DMA = N,N-dimethylacetamide) were synthesized and characterized. The frameworks of 2 and 3 are sustained by {Zn₂(PO₂(OEt))₂}_n metal-phosphonate- and DABCO-extended {Zn₂(COO)₄(DABCO)}_n paddle-wheel carboxylate chain-SBUs. The chains providing connectivity in three, mutually orthogonal directions are running parallel and are combined in a framework, which could be interpreted as having a pcu topology. The simple structure-organization principle, which suggests the possibility of the elongation of the bifunctional ligand with scaling in two directions, allows to view the structures of 2 and 3 as prototypes for an isoreticular series. The porosity of both compounds, based on a relatively short ligand, is low: no adsorption of N₂ was registered, however, CO₂ is adsorbed readily allowing to estimate the surface area at ∼330 m² g⁻¹ (∼900–1060 m² g⁻¹ geometric estimate). The compounds demonstrate a two-step CO₂ adsorption isotherm both at 195 K (0–1 bar) and 298 K (0–20 bar). The adsorption isotherms are characterized by a gradual (type “F-I”), albeit still relatively steep onset of the second step, associated with structural flexibility/bistability. The estimated pore volumes at the start of the transformation (195 K) for 2 and 3 are ∼0.11 (0.08P/P₀) and 0.12 cm³ g⁻¹ (0.12P/P₀) respectively, which corresponds considerably well to the geometrically calculated accessible volume of ∼0.07 cm³ g⁻¹ for the experimental structure (3.3 Å probe diameter). The structural prerequisites of the observed flexibility of the framework, which might be associated with the non-planarity of the metal-phosphonate moieties, acting as ‘levers’ for propagating mechanical stress, are discussed.

中文翻译：

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用DABCO共配体增强的Zn（II）和Co（II）的柔性双功能单乙基膦酸酯/羧酸盐：具有pcu拓扑的范例结构组织

两种新型同构膦酸盐monoethylcarboxylate的MOF具有结构式[M ₂（EtBCP）₂（DABCO）_0.5 ]·2DMA（M = Zn（上2），CO（3）; H ₂ EtBCP = ö乙基P - （合成并表征了4-羧基苯基）膦酸DABCO = 1,4-二氮杂双环[2.2.2]辛烷，DMA = N，N-二甲基乙酰胺。2和3的构架由{Zn ₂（PO ₂（OEt））₂ } _n金属膦酸酯和DABCO延伸的{Zn ₂（COO）₄（DABCO）} _n桨轮羧酸酯链-SBU。在三个相互正交的方向上提供连接的链并行运行，并在一个框架中组合在一起，这可以解释为具有pcu拓扑。简单的结构-组织原理表明双功能配体在两个方向上成比例伸长的可能性，允许将2和3的结构视为等网状系列的原型。两种化合物（基于相对较短的配体）的孔隙率都很低：未记录到N _2的吸附，但是，CO ₂易于吸附，因此可以估算约330 m的表面积² g ^-1（〜900-1060 m ² g ^-1几何估计）。这些化合物在195 K（0-1 bar）和298 K（0-20 bar）下均表现出两步式的CO ₂吸附等温线。吸附等温线的特征在于，尽管第二步骤的起步仍然比较陡峭，但逐渐变小（“ FI”型），这与结构的柔韧性/双稳性有关。对于2和3，转换开始时的估计孔体积（195 K）为〜0.11（0.08 P / P ₀）和0.12 cm ³ g ^-1（0.12 P / P ₀），这相当好地对应于实验结构（探头直径3.3Å）的〜0.07 cm ³ g ^-1的几何计算可及体积。讨论了观察到的框架柔性的结构前提，这可能与金属膦酸酯基团的非平面性有关，充当了传播机械应力的“杠杆”。