[M(C₅O₅)₂(H₂O)_<i>n</i>]²⁻ as a Building Block for Hetero- and Homo-bimetallic Coordination Polymers: From 1D Chains to 3D Supramolecular Architectures

A series of one-dimensional (1D) coordination polymers, {[Cu(en)2][M(C5O5)2(H2O)m]·xH2O}n, (M = Mn (1), m = 4, x = 2; M = Co (2), Ni (3), Cu (4), Zn (5), m = 2, x = 0; en = ethylenediamine; C5O52− = croconate, dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione), using [M(C5O5)2(H2O)n]2− dianion as a building block has been synthesized and characterized by the X-ray diffraction method. Structural determination reveals that, in compounds 1−5, one [M(C5O5)2(H2O)n]2− dianion coordinates via two oxygen (croconate) donors to the axial sites of two Cu(II) centers of [Cu(en)2]2+ cations to form one-dimensional (1D) linear (1, 3 and 4) or zigzag (2 and 5) chains of alternating [M(C5O5)2(H2O)n]2− and [Cu(en)2]2+ units. The croconate acts as a bridging ligand with three coordination modes as μ1,3-bismonodentate for 1, μ1,2,3-bidentate/monodentate for 2 and 5, and μ1,2,4-bidentate/monodentate for 3 and 4, respectively. In addition, a byproduct, [Cu(en)(C5O5)(H2O)]2 (6), which is cocrystallized with 4, shows a dimeric structure formed through the croconate bridge with μ1,1,2-bidentate/monodentate coordination mode. All of their 1D frameworks (1−5) and dimeric structure (6) are extended to three-dimensional (3D) supramolecular architectures by the intermolecular π−π interaction among croconates and intermolecular hydrogen bonds among the en, croconate, and coordinated water molecules.一系列一维（1D）配位聚合物{[Cu(en)₂][M(C₅O₅)₂(H₂O)ₘ]·xH₂O}ₙ（其中M=Mn(1)时，m=4，x=2；M=Co(2)、Ni(3)、Cu(4)、Zn(5)时，m=2，x=0；en=乙二胺（ethylenediamine），C₅O₅²⁻=方酸根（croconate），即4,5-二羟基环戊-4-烯-1,2,3-三酮的二价阴离子），以[M(C₅O₅)₂(H₂O)ₙ]²⁻二阴离子作为构筑单元，已被合成并通过X射线衍射（X-ray diffraction）方法进行了结构表征。结构测定结果表明，在化合物1~5中，一个[M(C₅O₅)₂(H₂O)ₙ]²⁻二阴离子通过两个来自方酸根的氧原子作为给体，与[Cu(en)₂]²⁺阳离子中两个Cu(II)中心的轴向位点配位，交替连接[M(C₅O₅)₂(H₂O)ₙ]²⁻与[Cu(en)₂]²⁺单元，形成一维线性链（化合物1、3、4）或锯齿形链（化合物2、5）。方酸根作为桥联配体，具有三种配位模式：化合物1为μ1,3-双单齿配位，化合物2、5为μ1,2,3-双齿/单齿配位，化合物3、4为μ1,2,4-双齿/单齿配位。此外，与化合物4共结晶的副产物[Cu(en)(C₅O₅)(H₂O)]₂(6)呈现二聚体结构，该结构通过μ1,1,2-双齿/单齿配位模式的方酸根桥联形成。所有化合物1~5的一维骨架以及化合物6的二聚体结构，均通过方酸根之间的分子间π-π相互作用，以及乙二胺、方酸根与配位水分子之间的分子间氢键拓展为三维（3D）超分子架构。