[M(C 5 O 5 ) 2 (H 2 O) n ] 2− as a Building Block for Hetero- and Homo-bimetallic Coordination Polymers: From 1D Chains to 3D Supramolecular Architectures

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A series of one-dimensional (1D) coordination polymers, {[Cu(en) 2 ][M(C 5 O 5 ) 2 (H 2 O) m ]· x H 2 O} n, (M = Mn ( 1 ), m = 4, x = 2; M = Co ( 2 ), Ni ( 3 ), Cu ( 4 ), Zn ( 5 ), m = 2, x = 0; en = ethylenediamine; C 5 O 5 2− = croconate, dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione), using [M(C 5 O 5 ) 2 (H 2 O) 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(C 5 O 5 ) 2 (H 2 O) 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(C 5 O 5 ) 2 (H 2 O) n ] 2− and [Cu(en) 2 ] 2+ units. The croconate acts as a bridging ligand with three coordination modes as μ 1,3 -bismonodentate for 1, μ 1,2,3 -bidentate/monodentate for 2 and 5, and μ 1,2,4 -bidentate/monodentate for 3 and 4, respectively. In addition, a byproduct, [Cu(en)(C 5 O 5 )(H 2 O)] 2 ( 6 ), which is cocrystallized with 4, shows a dimeric structure formed through the croconate bridge with μ 1,1,2 -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.