[M(C<sub>5</sub>O<sub>5</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub><i>n</i></sub>]<sup>2−</sup> as a Building Block for Hetero- and Homo-bimetallic Coordination Polymers: From 1D Chains to 3D Supramolecular Architectures WangChih-Chieh KeMeu-Ju TsaiCheng-Hsiao ChenI-Hsuan LinShin-I LinTzuen-Yeuan WuLi-Mei LeeGene-Hsiang SheuHwo-Shuenn FedorovVladimir E. 2009 A series of one-dimensional (1D) coordination polymers, {[Cu(en)<sub>2</sub>][M(C<sub>5</sub>O<sub>5</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub><i>m</i></sub>]·<i>x</i>H<sub>2</sub>O}<i><sub>n</sub></i>, (M = Mn (<b>1</b>), <i>m</i> = 4, <i>x</i> = 2; M = Co (<b>2</b>), Ni (<b>3</b>), Cu (<b>4</b>), Zn (<b>5</b>), <i>m</i> = 2, <i>x</i> = 0; en = ethylenediamine; C<sub>5</sub>O<sub>5</sub><sup>2−</sup> = croconate, dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione), using [M(C<sub>5</sub>O<sub>5</sub>)<sub>2</sub>(H<sub>2</sub>O)<i><sub>n</sub></i>]<sup>2−</sup> dianion as a building block has been synthesized and characterized by the X-ray diffraction method. Structural determination reveals that, in compounds <b>1</b>−<b>5</b>, one [M(C<sub>5</sub>O<sub>5</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub><i>n</i></sub>]<sup>2−</sup> dianion coordinates via two oxygen (croconate) donors to the axial sites of two Cu(II) centers of [Cu(en)<sub>2</sub>]<sup>2+</sup> cations to form one-dimensional (1D) linear (<b>1</b>, <b>3</b> and <b>4</b>) or zigzag (<b>2</b> and <b>5</b>) chains of alternating [M(C<sub>5</sub>O<sub>5</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub><i>n</i></sub>]<sup>2−</sup> and [Cu(en)<sub>2</sub>]<sup>2+</sup> units. The croconate acts as a bridging ligand with three coordination modes as μ<sub>1,3</sub>-bismonodentate for <b>1</b>, μ<sub>1,2,3</sub>-bidentate/monodentate for <b>2</b> and <b>5</b>, and μ<sub>1,2,4</sub>-bidentate/monodentate for <b>3</b> and <b>4</b>, respectively. In addition, a byproduct, [Cu(en)(C<sub>5</sub>O<sub>5</sub>)(H<sub>2</sub>O)]<sub>2</sub> (<b>6</b>), which is cocrystallized with <b>4</b>, shows a dimeric structure formed through the croconate bridge with μ<sub>1,1,2</sub>-bidentate/monodentate coordination mode. All of their 1D frameworks (<b>1</b>−<b>5</b>) and dimeric structure (<b>6</b>) 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.