Stabilization of Lantern-Type Metal-Organic Cages (MOCs) by Protective Control of Ligand Exchange Rates

Self-assembling systems in nature display remarkable complexity with assemblies of different sub-units to generate functional species. Synthetic analogues of such systems are a challenge, often requiring the ability to bias distributions that are under thermodynamic assembly control. Using lantern-type MOCs (metal-organic cages) as a prototypical self-assembling system, herein we explore the role that steric bulk plays in controlling the exchange rate of ligands in paddlewheel-based assemblies, and thus the stability of cages, in competitive self-assembling scenarios. The effective lifetime of the lantern-type MOCs varies over an order of magnitude depending on the steric bulk proximal to the metal nodes with lifetimes of the cages ranging from tens of minutes to several hours. The bulk of the coordinating solvents likewise reduces the rate of ligand exchange, and thus yields longer-lived species. Understanding this subtle effect has implications for controlling the stability of complex assemblies in competitive environments with implications for guest release and application.

Organoamine-induced isomerism of calixarene-based complexes: from 1D to 2D

Two isomers of the calixarene-based cobalt complex [Co₄Cl(TC4A)(BCPT)₂]⁻ (H₄TC4A = p-tert-butylthiacalix[4]arene; H₂BCPT = 3,5-bis (4′-carboxy-phenyl)-1,2,4-triazole) were obtained under the solvothermal conditions with tetramethylammonium/tetraethylammonium hydroxide (CIAC-236) and triethylamine (CIAC-237). Single crystal X-ray diffraction reveals that CIAC-236 has a 1D zigzag aggregate constructed by bridging the shuttlecock-like Co₄–TC4A secondary building units (SBUs) with two pairs of opposite V-shaped BCPT ligands while CIAC-237 possesses a 2D layer assembly with each Co₄–TC4A SBU bonded by four BCPT ligands in a same direction (clockwise or counterclockwise), which indicates that different shapes of the organoamines lead to different assembly of the BCPT ligands and the formation of different extended aggregates. For comparison, only the 1D structure ([Fe₄Cl(TC4A)](BCPT)₂]⁻, CIAC-238) was obtained for the iron complexes with all these three organoamines, which would be attributed to different property and coordination of iron element. Magnetic properties of all these three compounds were studied.

Two isomers of the calixarene-based cobalt complex, 1D aggregate and 2D network, were obtained with different organoamine templates.

Investigating the geometrical preferences of a flexible benzimidazolone-based linker in the synthesis of coordination polymers

A series of new group 2 coordination polymers, MgL ={MgL(H₂O)(DMF)_0.75}_∞, CaL = {CaL(DMF)₂}_∞, SrL = {SrL(H₂O)_0.5}_∞ and BaL = {BaL(H₂O)_0.5}_∞, were synthesized using a flexible benzimidazolone diacetic acid linker (H₂L) in which the two carboxylic acid binding sites are connected to a planar core via {-CH₂-} spacers that can freely rotate in solution. In a 'curiosity-led' diversion from group 2 metals, the first row transition metal salts Mn²⁺, Cu²⁺ and Zn²⁺ were also reacted with L to yield crystals of MnL = {MnL(DMF)(H₂O)_3.33}_∞, Cu₃L₂  = {Cu₃L₂(DMF)₂(CHO₂)₂}_∞ and ZnL = {ZnL(DMF)}_∞. Crystal structures were obtained for all seven materials. All structures form as two-dimensional sheets and contain six-coordinate centres, with the exception of ZnL, which displays tetrahedrally coordinated metal centres, and Cu₃L₂ , which contains square planar coordinated metal centres and Cu paddle-wheels. In each structure, the linker adopts one of two distinct conformations, with the carboxylate groups either cis or trans with respect to the planar core. All materials were also characterized by powder X-ray diffraction and thermogravimetric analysis.

Two cadmium coordination polymers based on tris(p-carboxyphenyl) phosphane oxide with highly selective sensing of nitrobenzene derivatives and Hg2+ cations

Based on the tris(p-carboxyphenyl)phosphane oxide ligand, two Cd(ii) CPs were obtained which could highly sense nitrobenzene derivatives and Hg²⁺ cations.

Crystal structure of poly-[diaqua-bis(μ2-2-((1H-1,2,4-triazol-5-yl)thio)acetato-κ2N:O) cadmium(II)], C8H8CdN6O6S2

C8H8CdN6O6S2, monoclinic, P21/c (no. 14), a = 7.4175(11) Å, b = 13.786(2) Å, c = 7.4934(11) Å, β = 93.835(2)°, V = 3972.0(12) Å3, Z = 2, Rgt(F) = 0.0193, wRref(F2) = 0.0581, T = 296(2) K.

Hetero-bimetallic metal–organic polyhedra

Porous metal–organic polyhedra (MOPs), constructed from heterometallic Pd^II–M^II (M = Cu, Ni, Zn) paddlewheel nodes and 5-tert-butyl-1,3-benzenedicarboxylate organic links, were prepared in which the Pd^II ions preferentially line the inner surface of the cage molecules.

Structures and Photoluminescence Properties of Four Cadmium(II) Coordination Polymers Synthesized by Rigid Ligands and N-Donor Ligands

Four metal–organic coordination polymers, [Cd2(dna)2(2,2′-bpy)2]n (1), {[Cd4(dna)4(im)3]·5H2O}n (2), {[Cd2(dna)2(4,4′-bpy)(H2O)2]·2EtOH}n (3), and {[Cd4(dna)4(1,3-dpp)4(H2O)4]·2H2O}n (4) (H2dna = 4,6-dimethyl-5-nitroisophthalic acid; 2,2′-bpy = 2,2′-bipyridine; im = imidazole; 4,4′-bpy = 4,4′-bipyridine; 1,3-dpp = 1,3-di(4-pyridyl)propane; and EtOH = ethanol, have been solvothermally synthesized and characterized. Compound 1 displays a one-dimensional (1D) ladder structure and the neighbouring ladders are further stabilized by π···π interactions to form a two-dimensional (2D) layer. Compound 2 forms a 2D layer based on infinite 1D [Cd2(COO)4]n chain and the im ligands act as terminal ligands, preventing expansion of the dimensionality. Compound 3 features a 2D 44-sql layer based on binuclear [Cd2(COO)4] secondary building units as 4-connected nodes, and is further linked to be an unusual three-dimensional (3D) supramolecular architecture by hydrogen bonds involving the coordinated water molecules, carboxylate groups, and lattice ethanol molecules. Compound 4 possesses a 2-fold interpenetrated dia net. The diverse structures and topologies of compounds 1–4 indicate that the N-containing ligands have significant effects on the formation of the final network structures. In addition, the thermal stabilities, structure comparison, and photoluminescence properties of the complexes have been investigated.

A two-dimensional Cd(II) coordination polymer with 2,2'-(disulfanediyl)dibenzoate and 1,10-phenanthroline ligands

In poly[[μ3-2,2'-(disulfanediyl)dibenzoato-κ(5)O:O,O':O'',O'''](1,10-phenanthroline-κ(2)N,N')cadmium(II)], [Cd(C14H8O4S2)(C12H8N2)]n, the asymmetric unit contains one Cd(II) cation, one 2,2'-(disulfanediyl)dibenzoate anion (denoted dtdb(2-)) and one 1,10-phenanthroline ligand (denoted phen). Each Cd(II) centre is seven-coordinated by five O atoms of bridging/chelating carboxylate groups from three dtdb(2-) ligands and by two N atoms from one phen ligand, forming a distorted pentagonal-bipyramidal geometry. The Cd(II) cations are bridged by dtdb(2-) anions to give a two-dimensional (4,4) layer. The layers are stacked to generate a three-dimensional supramolecular architecture via a combination of aromatic C-H···π and π-π interactions. The thermogravimetric and luminescence properties of this compound were also investigated.

A new one-dimensional nickel metal-organic framework: catena-poly[[[diaquabis(4-{[(1-phenyl-1H-tetrazol-5-yl)sulfanyl]methyl}benzoato-κO)nickel(II)]-μ-4,4'-bipyridine-κ(2)N:N'] monohydrate]

The title complex, {[Ni(C15H11N4O2S)2(C10H8N2)(H2O)2]·H2O}n, was synthesized by the reaction of nickel chloride, 4-{[(1-phenyl-1H-tetrazol-5-yl)sulfanyl]methyl}benzoic acid (HL) and 4,4'-bipyridine (bpy) under hydrothermal conditions. The asymmetric unit contains two half Ni(II) ions, each located on an inversion centre, two L(-) ligands, one bpy ligand, two coordinated water molecules and one unligated water molecule. Each Ni(II) centre is six-coordinated by two monodentate carboxylate O atoms from two different L(-) ligands, two pyridine N atoms from two different bpy ligands and two terminal water molecules, displaying a nearly ideal octahedral geometry. The Ni(II) ions are bridged by 4,4'-bipyridine ligands to afford a linear array, with an Ni...Ni separation of 11.361 (1) Å, which is further decorated by two monodentate L(-) ligands trans to each other, resulting in a one-dimensional fishbone-like chain structure. These one-dimensional fishbone-like chains are further linked by O-H...O, O-H...N and C-H...O hydrogen bonds and π-π stacking interactions to form a three-dimensional supramolecular architecture. The thermal stability of the title complex was investigated via thermogravimetric analysis.

A one-dimensional cadmium metal-organic chain based on a [Cd4(COO)4] secondary building unit and a flexible dicarboxylic acid ligand

An infinite one-dimensional cadmium metal-organic chain, namely catena-poly[aquabis(μ3-2,2'-{[1,2-phenylenebis(methylene)]bis(sulfanediyl)}dibenzoato)dicadmium(II)], [Cd2(C22H16O4S2)2(H2O)]n, was synthesized by solvothermal reaction of Cd(NO3)2·4H2O and 2,2'-{[1,2-phenylenebis(methylene)]bis(sulfanediyl)}dibenzoic acid (H2L). The Cd(II) centres have six-coordinate CdS2O4 and CdSO5 geometries. Due to the flexible -CH2-S- arms, the L(2-) ligand adopts both syn and anti conformations. Four Cd(II) cations are linked by two syn L(2-) ligands to form a centrosymmetric planar tetranuclear Cd(II) core, which is further extended through bonding to the anti L(2-) ligands to form a one-dimensional metal-organic chain. Adjacent one-dimensional chains are connected by C-H···π interactions and nonclassical C-H···O hydrogen bonds to form the resultant three-dimensional supramolecular framework.

catena-Poly[[[diaquacadmium]-μ-2,2′-(1,2-phenylenedioxy)diacetato] monohydrate]

In the title coordination complex, {[Cd(C₁₀H₈O₆)(H₂O)₂]·H₂O}_n the Cd^II atom is seven-coordinated in a distorted penta­gonal–bipyramidal geometry, the penta­gonal plane comprising four O-atom donors from the 2,2′-(1,2-phenyl­enedi­oxy)diacetate chelate ligand together with a bridging carboxyl­ate O-atom donor, with the axial sites occupied by two water mol­ecules. The resulting helical chains extend along the b axis and are inter­connected by extensive O—H⋯O hydrogen-bonding inter­actions, which also involve the water mol­ecule of solvation, giving a three-dimensional structure.