De Novo Structure-Based Design of Ion-Pair Triple-Stranded Helicates

We present a generalized approach toward the design of ion-pair ML₃A helicates assembled by coordination of metal cations (M) and anions (A) by ditopic chelating ligands (L). This computational approach, based on de novo structure-based design principles implemented in the HostDesigner software, led to identification of synthetically accessible ditopic ligands that are structurally encoded to form charge-neutral ion-pair helicates with FeSO₄ or LnPO₄

Tetraureas versus Triureas in Sulfate Binding

By mimicking the scaffolds of oligopyridine-based ligands, triurea and tetraurea receptors have been developed for sulfate binding. The triureas (L1, L2) show stronger binding of sulfate than tetraureas (L3, L4) in DMSO because of their better conformational complementarity with sulfate, while the tetraureas display better “water tolerance” benefiting from the chelate effect and hydrophobic effect

Tetraureas versus Triureas in Sulfate Binding

By mimicking the scaffolds of oligopyridine-based ligands, triurea and tetraurea receptors have been developed for sulfate binding. The triureas (L1, L2) show stronger binding of sulfate than tetraureas (L3, L4) in DMSO because of their better conformational complementarity with sulfate, while the tetraureas display better “water tolerance” benefiting from the chelate effect and hydrophobic effect

Chloride Coordination by Oligoureas: From Mononuclear Crescents to Dinuclear Foldamers

A series of acyclic oligourea receptors which closely resemble the scaffolds and coordination behavior of oligopyridines have been synthesized. Assembly of the receptors with chloride ions afforded mononuclear anion complexes or dinuclear foldamers depending on the number of the urea groups

Anion-Dependent Formation of Helicates versus Mesocates of Triple-Stranded M₂L₃ (M = Fe²⁺, Cu²⁺) Complexes

A series of dinuclear triple-stranded complexes, [Fe2L3⊃X]­X6 [X = BF4– (1), ClO4– (2)], [Fe2L3⊃SO4]2(SO4)5 (3), [Fe2L3⊃Br]­(BPh4)6 (4), Fe2L3(NO3)­Br6 (5), and [Cu2L3⊃NO3]­(NO3)6 (6), which incorporate a central cavity to encapsulate different anions, have been synthesized via the self-assembly of iron­(II) or copper­(II) salts with the N,N′-bis­[5-(2,2′-bipyridyl)­methyl]­imidazolium bromide (LBr) ligand. X-ray crystallographic studies (for 1–4 and 6) and elemental analyses confirmed the cagelike triple-stranded structure. The anionic guest is bound in the cage and shows remarkable influence on the outcome of the self-assembly process with regard to the configuration at the metal centers. The mesocates (with different configurations at the two metal centers) have formed in the presence of large tetrahedral anions, while helicates (with the same configuration at both metal centers) were obtained when using the relatively smaller spherical or trigonal-planar anions Br– or NO3–

Anion-Dependent Formation of Helicates versus Mesocates of Triple-Stranded M₂L₃ (M = Fe²⁺, Cu²⁺) Complexes

A series of dinuclear triple-stranded complexes, [Fe₂L₃⊃X]­X₆ [X = BF₄^– (<b>1</b>), ClO₄^– (<b>2</b>)], [Fe₂L₃⊃SO₄]₂(SO₄)₅ (<b>3</b>), [Fe₂L₃⊃Br]­(BPh₄)₆ (<b>4</b>), Fe₂L₃(NO₃)­Br₆ (<b>5</b>), and [Cu₂L₃⊃NO₃]­(NO₃)₆ (<b>6</b>), which incorporate a central cavity to encapsulate different anions, have been synthesized via the self-assembly of iron­(II) or copper­(II) salts with the <i>N</i>,<i>N</i>′-bis­[5-(2,2′-bipyridyl)­methyl]­imidazolium bromide (LBr) ligand. X-ray crystallographic studies (for <b>1</b>–<b>4</b> and <b>6</b>) and elemental analyses confirmed the cagelike triple-stranded structure. The anionic guest is bound in the cage and shows remarkable influence on the outcome of the self-assembly process with regard to the configuration at the metal centers. The mesocates (with different configurations at the two metal centers) have formed in the presence of large tetrahedral anions, while helicates (with the same configuration at both metal centers) were obtained when using the relatively smaller spherical or trigonal-planar anions Br^– or NO₃^–

Full- or Half-Encapsulation of Sulfate Anion by a Tris(3-pyridylurea) Receptor: Effect of the Secondary Coordination Sphere

Self-assembly of the [Fe(DABP)3]SO4 (DABP = 5,5′-diamino-2,2′-bipyridine) or [Fe(bipy)3]SO4 (bipy = 2,2′-bipyridine) complex with a tripodal tris(3-pyridylurea) ligand (L) results in a layered structure that includes a sulfate anion in the cleft of one L molecule. The two compounds, [Fe(DABP)3][SO4⊂L]·10H2O (2) and [Fe(bipy)3][SO4⊂L]·9H2O (3), show very similar sheets formed by the anionic units [SO4⊂L]2− and cationic building blocks ([Fe(DABP)3]2+ or [Fe(bipy)3]2+). However, there are different water clusters that link the adjacent layers in the two products, that is, water parallelograms and quasi “water cubes” in 2 versus single water molecules, water dimers, and hexamers in 3. The half-encapsulation of sulfate by a single L molecule contrasts with the previously reported full-encapsulation of the sulfate ion by two L molecules in [M(H2O)6][SO4⊂L2] (1). This different anion encapsulation is traced to the hydrogen-acceptor properties of the pyridyl groups of L together with the hydrogen-bonding properties of the cation secondary coordination sphere for a solid-state packing optimization. In 1 the direct hydrogen bonding from the secondary coordination sphere of octahedral [M(H2O)6]2+ to L-pyridyl helps in the formation of an octahedral cation−anion coordination in the NaCl-type structure. In 2 and 3, crystal water instead of the cations has to satisfy the hydrogen-accepting demands of L. Consequently, a non-spherical and only partly water-surrounded half-encapsulated [SO4⊂L]2− anion allows for a closer approach of the [Fe(DABP)3]2+ or [Fe(bipy)3]2+ cations than the [SO4⊂L2]2− anion. Then, the similar cation and anion size in 2 and 3 with the Coulomb attraction confined to a two-dimensional plane leads to the formation of a hexagonal BN (or graphite) lattice. Competition experiments with different anions for compound 2 reveal that SO42− can be selectively crystallized against NO3−, OAc−, or ClO4−

Full- or Half-Encapsulation of Sulfate Anion by a Tris(3-pyridylurea) Receptor: Effect of the Secondary Coordination Sphere

Self-assembly of the [Fe(DABP)3]SO4 (DABP = 5,5′-diamino-2,2′-bipyridine) or [Fe(bipy)3]SO4 (bipy = 2,2′-bipyridine) complex with a tripodal tris(3-pyridylurea) ligand (L) results in a layered structure that includes a sulfate anion in the cleft of one L molecule. The two compounds, [Fe(DABP)3][SO4⊂L]·10H2O (2) and [Fe(bipy)3][SO4⊂L]·9H2O (3), show very similar sheets formed by the anionic units [SO4⊂L]2− and cationic building blocks ([Fe(DABP)3]2+ or [Fe(bipy)3]2+). However, there are different water clusters that link the adjacent layers in the two products, that is, water parallelograms and quasi “water cubes” in 2 versus single water molecules, water dimers, and hexamers in 3. The half-encapsulation of sulfate by a single L molecule contrasts with the previously reported full-encapsulation of the sulfate ion by two L molecules in [M(H2O)6][SO4⊂L2] (1). This different anion encapsulation is traced to the hydrogen-acceptor properties of the pyridyl groups of L together with the hydrogen-bonding properties of the cation secondary coordination sphere for a solid-state packing optimization. In 1 the direct hydrogen bonding from the secondary coordination sphere of octahedral [M(H2O)6]2+ to L-pyridyl helps in the formation of an octahedral cation−anion coordination in the NaCl-type structure. In 2 and 3, crystal water instead of the cations has to satisfy the hydrogen-accepting demands of L. Consequently, a non-spherical and only partly water-surrounded half-encapsulated [SO4⊂L]2− anion allows for a closer approach of the [Fe(DABP)3]2+ or [Fe(bipy)3]2+ cations than the [SO4⊂L2]2− anion. Then, the similar cation and anion size in 2 and 3 with the Coulomb attraction confined to a two-dimensional plane leads to the formation of a hexagonal BN (or graphite) lattice. Competition experiments with different anions for compound 2 reveal that SO42− can be selectively crystallized against NO3−, OAc−, or ClO4−

Coordination Networks from Zero-Dimensional Metallomacrocycle, One-Dimensional Chain to Two-Dimensional Sheet Based on a Ditopic Diiminopyridine Ligand and Group 12 Metals

The reaction of a ditopic diiminopyridine ligand 2,6-bis(1-(2,6-diisopropyl-4-(pyridin-3-yl)phenylimino)ethyl)pyridine (L) with group 12 metal salts in various solvent systems afforded 12 metal−organic coordination complexes, including zero-dimensional (0D) metallomacrocycle, one-dimensional (1D) chain, and two-dimensional (2D) network structures: [Zn4Cl8L2]·2C7H8·2CH3COCH3·3H2O (1a), {[Zn2Cl4L]·2CH3OH·2CHCl3·2H2O}n (1b), {[ZnCl2L]·0.5CH2Cl2·0.5H2O}n (1c), {[ZnBr2L]·CH2Cl2}n (2), [ZnI2L]n (3), {[Zn(NO3)2L2·2C7H8]}n (4), {[CdCl2L2]·2CH2Cl2}n (5), {[Cd(NO3)2L2]·CH2Cl2}n (6), {[Cd(ClO4)2L2]·CH2Cl2}n (7), {[Hg4(μ2-L2)(μ2-Cl2)(μ-HgCl2)Cl6]·2H2O}n (8), {[HgBr2L]·CH3CN·0.5CH2Cl2}n (9), and {[HgI2L]·0.5CH2Cl2}n (10). In these complexes, the semirigid ligand L exhibits four kinds of coordination modes [(syn, syn, syn), (syn, syn, anti), (anti, anti, syn), (anti, anti, anti)], leading to the formation of various supramolecular structures. Complex 1a is a tetranuclear metallomacrocycle. 1b contains 1D zigzag chains propagating along two different directions, which further pack into a noninterpenetrated three-dimensional (3D) framework by hydrogen-bonding interactions. Complexes 1c, 2, 3, 9, and 10 exhibit a 1D helical chain structure, while 4, 5, 6, and 7 are 1D looped-chain coordination polymers. Complex 8 displays an unprecedented pentanuclear Hg(II)-based 2D network with both HgCl2 and Hg2Cl2 bridges. It is noteworthy that 1a and 1b are supramolecular isomers formed in different solvent systems. The effects of the solvent, metal center, and anion on the different conformations adopted by the ligand and the structure of the products have been discussed. Additionally, the luminescent properties of the complexes have been investigated in the solid state, which display increased ligand-based fluorescence emission at room temperature