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Five new magnetic coordination frameworks with formulas of {[Co2(HL)2(H2O)4]·4H2O}n (1), {[Ni2(HL)2(H2O)4]·4H2O}n (2), [Co(HL)(bpy)]n (3), [Co(HL)(pbim)]n (4), and [Ni(HL)(pbim)]n (5) [H3L = 2-(5-bromo-pyridin-3-yl)-1H-imidazole-4,5-dicarboxylic acid, bpy = 4,4′-bipyridine, and pbim = 1,1′-(5-methyl-1,3-phenylene)bis(1H-imidazole)] have been synthesized and structurally characterized by elemental, thermogravimetric, and X-ray diffraction analyses. In all compounds, the doubly deprotonated (HL)2– ligands adopt the same μ-kN,O:kN′,O′ coordination mode, showing very interesting coordination orientation in the construction of those coordination polymers. Complexes 1 and 2 feature (HL)2–-bridged linear chain structures. Complex 3 is a 2D network with (4,4) grids built up from the (HL)2–-bridged linear chains observed in 1 being further linked by rod-like bpy bridges replacing the coordination of water molecules. Those almost or completely linear chains formed by the bis-N,O-chelation of the imidazoledicarboxylate of (HL)2– in 1–3 are rarely observed in the complexes of 4,5-imidazoledicarboxylic acid and its derivatives, giving a typical structure model to investigate the magnetic exchange-coupling mediated by imidazoledicarboxylate. Isostructural complexes 4 and 5 are 2D helicates where (HL)2–-bridged left- and right-handed helixes are doubly linked into the mesolayer structures with 63 topology through the further coordination of angular spacers pbim. Remarkably, the formation of (HL)2–-bridged linear chains or helical chains is mainly dependent on the trans- or cis-chelation of two (HL)2– ligands around the same metal center, which could be finely tuned by the structural features of auxiliary ligands used. Magnetostructural analyses disclose that the bis-N,O-chelating imidazoledicarboxylates of (HL)2– transmit antiferromagnetic interactions along the (HL)2–-bridged metal–organic chains with the spin-coupling constants of −4.89, −17.8,–6.55, −7.35, and −19.6 cm–1 for 1–5, respectively. Notably, the μ-kN,O:kN′,O′ coordination mode of (HL)2– ligand dominates the assembly of metal–organic frameworks as well as the magnetic exchange between the paramagnetic ions in those magnetic chains, but the magnetic exchange-coupling depends strongly on the nature of the metal center. [ABSTRACT FROM AUTHOR]

Five 1-3D cadmium(II) coordination polymers, namely, [Cd(HL)(DMF)]n (1), [Cd4(HL)4(H2O)6]n (2), [Cd(HL)(phen)]n (3), [Cd2(HL)2(bpy)]n (4), and {[Cd3(HL)3(pbim)2]·H2O}n (5), have been synthesized and fully characterized [H3L = 2-(5-bromo-pyridin-3-yl)-1H-imidazole-4,5-dicarboxylic acid, DMF = N,N-dimethylformamide, phen = 1,10-phenanthroline, bpy = 4,4'-bipyridine, and pbim = 1,1'-(5-methyl-1,3-phenylene)bis(1H-imidazole)]. In those complexes, the doubly deprotonated H3L ligands and CdII ions display versatile coordination modes to construct various structures with interesting topologies. Complex 1 is a 2D helical structure with (4·82) topology built up from 3-connected (HL)2- and CdII nodes. Complex 2 containing (HL)2--bridged tetranuclear CdII subunits is a 3D helical structure where both (HL)2- and CdII adopt three coordination modes to form a rare 3-connected network with (5·8·12)2(5·12·16)2(5·82)(82·12) topology. Substituting the smaller terminal ligands DMF and water with the larger terminal ligand phen, (HL)2- ligands only use their imidazoledicarboxylate groups to bis-chelate CdII into a chain structure of 3. Complex 4 is a (3,4)-connected 3D network with (4·82)(4·82·103) topology built up from the (HL)2--bridged (4,82) mesolayer observed in 1 being further linked by rodlike bpy bridges replacing terminal ligand DMF. Complex 5 consists of (HL)2-- and pbim-bridged macrocycle chains and is a (3,4)-connected 2D novel network with (3·4·8)2(3·4·5·82·9)2(32·82·92) topology. As expected, the strongly bis-chelating coordination mode μ-kN,O:kN',O' of the imidazoledicarboxylate of (HL)2- absolutely dominates the assemblies with CdII in those complexes. Intriguingly, the additional ligands, such as smaller terminal ligands water and DMF, larger planar terminal ligand phen, as well as rodlike and V-shaped bridges bpy and pbim, exert obvious influence on the coordination modes of ligands (HL)2- and the resulting architectures. Clearly, larger terminal and bridging ligands phen and pbim could limit the coordination of the pyridyl of (HL)2- through steric hindrance. Meanwhile, the solid-state photoluminescence of those compounds at room temperature was also investigated, and the results indicate that their emissions are significantly influenced by the additional ligands incorporating into the networks. [ABSTRACT FROM AUTHOR]