Abstract
Reaction of cadmium perchlorate and the prototypical linear bridging ligand 4,4’-bipyridine (4,4’-bipy) in an ethanol/water mixture affords the one-dimensional coordination polymer, [{Cd(m-4,4’-bipy)(4,4’-bipy)2(H2O)2}(ClO4)2 × 2 4,4’-bipy × 4.5 H2O]n (1). The Cd2+ ions adopt an octahedral coordination sphere and are joined into linear chains by 4,4’-bipy via two trans coordination sites. The remaining two trans sites in the equatorial plane carry terminally monodentate-bound 4,4’-bipy ligands, resulting in a molecular antenna arrangement. The two axial sites of each Cd2+ ion are occupied by aqua ligands. Compound 1 crystallizes in the non-centrosymmetric, monoclinic space group C2 with three similar, crystallographically independent, cationic coordination polymer strands in the unit cell, which essentially differ only in the conformations of the 4,4’-bipyridyl ligands. Consistent with the similarity of the local coordination environments of the three independent Cd atoms in the structure, 113Cd MAS NMR spectroscopy reveals a single resonance line at 89 ppm.
Highlights
Coordination polymers have attracted increasing attention since the early 1990s. This interest is largely due to their fascinating structures and potential applications in such fields as ion exchange, gas storage, separation, polymerization, heterogeneous catalysis, luminescence, non-linear optics and magnetism [1,2,3,4,5,6,7,8,9,10,11]. 4,4’-Bipyridine (4,4’-bipy) is a prototypical exo-bidentate, rigid linear bridging ligand and has been widely used in crystal engineering of coordination polymers [12]
We discovered a new example of the molecular antenna 1D coordination polymer, viz. [{Cd(μ-4,4’-bipy)(4,4’bipy)2(H2O)2}(ClO4)2 ⋅ 2 4,4’-bipy ⋅ 4.5 H2O]n (1)
Since 1 was isolated from 1:1, 1:2 and 1:4 molar mixtures of cadmium perchlorate and 4,4’-bipy, it appears that the molecular antenna is a preferred product under various reaction conditions
Summary
Coordination polymers have attracted increasing attention since the early 1990s. This interest is largely due to their fascinating structures and potential applications in such fields as ion exchange, gas storage, separation, polymerization, heterogeneous catalysis, luminescence, non-linear optics and magnetism [1,2,3,4,5,6,7,8,9,10,11]. 4,4’-Bipyridine (4,4’-bipy) is a prototypical exo-bidentate, rigid linear bridging ligand and has been widely used in crystal engineering of coordination polymers [12]. If we exclude the potentially structure-determining influence of non-solvent organic molecules [18,19] other than 4,4’-bipy, the number of coordination polymers decreases to about a dozen These include (4,4) square grid (Scheme 1(d)) [20,21,22,23,24] and ‘T-shape’ [20] 2D coordination networks, as well as linear chain (Scheme 1(a)) [19,20,25,26] and molecular antenna [19,21] 1D coordination polymers.
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