In-Hyeok Park

Distortional Supramolecular Isomers of Polyrotaxane Coordination Polymers: Photoreactivity and Sensing of Nitro Compounds†

Distortional isomers, or bond-stretch isomers, differ only in the length of one or more bonds, which is due to crystallographic disorder in most cases. The term distortional isomerism is introduced to describe the structures of polyrotaxane 2D coordination polymers (CPs) that differ only by the relative positions in the neighboring entangled axles. A large ring and a long spacer ligand in 2D CPs yielded four different supramolecular isomers, of which two have an entangled polyrotaxane structure. One pair of C=C bonds in the spacer ligand is well-aligned in one isomer and undergoes [2+2] cycloaddition reaction, whereas the other isomer is photoinert. They also have different sensing efficiency for several aromatic nitro compounds. However, both isomers show selective PL quenching for the Bradys reagent. Structurally similar supramolecular isomers with different photochemical reactivity and sensing abilities appear to be unprecedented.

Metal–Organic Organopolymeric Hybrid Framework by Reversible [2+2] Cycloaddition Reaction†

Organic polymers are usually amorphous or possess very low crystallinity. The metal complexes of organic polymeric ligands are also difficult to crystallize by traditional methods because of their poor solubilities and their 3D structures can not be determined by single-crystal X-ray crystallography owing to a lack of single crystals. Herein, we report the crystal structure of a 1D Zn(II) coordination polymer fused with an organic polymer ligand made in situ by a [2+2] cycloaddition reaction of a six-fold interpenetrated metal-organic framework. It is also shown that this organic polymer ligand can be depolymerized in a single-crystal-to-single-crystal (SCSC) fashion by heating. This strategy could potentially be extended to make a range of monocrystalline metal organopolymeric complexes and metal-organic organopolymeric hybrid materials. Such monocrystalline metal complexes of organic polymers have hitherto been inaccessible for materials researchers.

Formation of a Syndiotactic Organic Polymer Inside a MOF by a [2+2] Photo-Polymerization Reaction†

Getting suitable crystals for single-crystal X-ray crystallographic analysis still remains an art. Obtaining single crystals of metal-organic frameworks (MOFs) containing organic polymers poses even greater challenges. Here we demonstrate the formation of a syndiotactic organic polymer ligand inside a MOF by quantitative [2+2] photopolymerization reaction in a single-crystal-to-single-crystal manner. The spacer ligands with trans,trans,trans-conformation in the pillared-layer MOF with guest water molecules in the channels, undergo pedal motion to trans,cis,trans-conformation prior to [2+2] photo-cycloaddition reaction and yield single crystals of MOF containing two-dimensional coordination polymers fused with the organic polymer ligands. We also show that the organic polymer in the single crystals can be depolymerized reversibly by cleaving the cyclobutane rings upon heating. These MOFs also show interesting photoluminescent properties and sensing of small organic molecules.

Cooperative effect of anion and mole ratio on the coordination modes of an NO2S3-donor macrocycle.

Synthesis of an NO2S3-macrocycle (L) incorporating a pyridine subunit and its anion and/or mole ratio-dependent coordination modes in the formations of mercury(II) complexes is reported. When the mercury(II) salts with different anions (ClO4(-) or Br(-)) were reacted with L, the Hg(ClO4)2 afforded a typical endocyclic complex [HgL](ClO4)2 (1). Meanwhile, the HgBr2 gave an exocyclic complex [HgLBr2] (2) in which the metal ion exists outside the macrocyclic cavity. The observed anion effect on the coordination modes can be explained by the anion coordination ability toward the metal cation. In the mole ratio variation experiments, notably, the use of 1.5 equiv or above of HgBr2 in the same reaction condition gave a unique endo/exocyclic dumbbell-type complex 3, [Hg4L2Br6][Hg2Br6]. However, the formation of the endocyclic Hg(ClO4)2 complex 1 shows no mole ratio dependency. To monitor the observed mole ratio-dependent exocoordination products as well as their reactivities and reversibility, systematic powder X-ray diffraction (PXRD) analysis was also applied. From single crystal X-ray and PXRD analyses, it was found that endocyclic complex 1 is not reactive, but complexes 2 and 3 are reactive and show the reversibility between them in the presence of the corresponding reactants.

Anion-dependent coordinative networking of macrocycle with copper(I) halides

An O2S2-macrocycle L incorporating three aromatic subunits was synthesized and structurally characterized by X-ray analysis. Four coordination polymers of L with copper(I) halides (Cl, Br and I) adopting different topologies and network patterns depending on the anions are reported. Reactions of L with copper(I) chloride and copper(I) bromide yielded a single-stranded one-dimensional (1D) coordination polymer [CuCl2(L)(CH3CN)]n (1) with an oxidized copper(II) centre and a double-stranded 1D coordination polymer [(Cu2Br2)(L)2]·4CH2Cl2]n (2), with each strand linked by a rhomboid-type Cu2Br2 unit. However, the reaction with copper(I) iodide under the same conditions gave an emissive mixture of supramolecular isomers with an identical composition {[Cu4I4(L)2]·CH2Cl2}n, adopting a regular (3a) and a tilted (3b) square-grid-type 2D coordination polymers via cubane-type Cu4I4 linking. The XRPD results also confirmed the binary mixture. The conformational diversity in the ligand leads to a variation in overall structural motifs of the supramolecular isomers.

Networking of macrocycles: 1D and 2D coordination polymers of dithia-18-crown-6 with copper(II) and copper(I)

CuI and CuII coordination polymers of 1,10-dithia-18-crown-6 (L) with unusual networking modes involving an exocyclic coordination are presented. The reaction of L with copper(II) nitrate gave a unprecedented ladder-type 1D coordination polymer {[(LOXOX)Cu2(NO3)2(H2O)4](LOXOX)(NO3)2·2H2O}n (1) via strong CuII–Osulfoxide bonds because L was oxidized to the disulfoxide macrocycle (LOXOX) under the present conditions. Meanwhile the parallel reaction of copper(I) iodide with L in the presence of cobalt(II) perchlorate yielded a mixture of an emissive 2D network product [(Cu4I4)(L)2]n (2) linked with cubane-type Cu4I4 clusters and a non-emissive 1D coordination polymer {[(Cu2I2)(L)2][Co(H2O)6](ClO4)2·0.5H2O}n (3) linked with rhomboidal Cu2I2 cores. In 3, hexaaquacobalt(II) complexes, anions and water molecules also exist and stabilize the 1D macrocyclic network through H-bonds.

Regioisomer-dependent endo- and exocyclic coordination of bis-dithiamacrocycles.

Syntheses of the regioisomers of bis-dithiamacrocycle and the regioisomer-controlled endo- and exocyclic coordination behaviors are reported. Direct bis-cyclization reaction of 1,2,4,5-tetra(bromomethyl)benzene with 3,6-dioxa-1,8-octanedithiol led to a mixture of two bis-dithiamacrocycle regioisomers (ortho-type; o-bis-L and meta-type; m-bis-L) which were separated by recrystallization and column chromatography. When the two isomers were reacted with AgPF6, o-bis-L gave an endocyclic one-dimensional (1-D) coordination polymer {[Ag3(o-bis-L)2(CH3CN)](PF6)3·2CH3CN}n (1) with a 3:2 (metal-to-ligand) stoichiometry, while m-bis-L afforded an exocoordination-based 1-D polymeric complex {[Ag(m-bis-L)](PF6)}n (2) with a 2:2 stoichiometry. The observed endo- and exocoordination modes depending on the isomers were discussed in terms of the S···S distances in the bis-dithiamacrocycle isomers. Due to the closer S···S distance in each macrocyclic ring, o-bis-L is suitable for the endocoordination. However, m-bis-L forms an exocyclic complex because the S···S distance between two macrocyclic rings is shorter than that in one macrocyclic ring. NMR experiments also revealed that o-bis-L and m-bis-L form the endo- and the exocyclic complexes, respectively, in solution.

Ligand-Induced Formation of Copper(I) Iodide Clusters: Exocyclic Coordination Polymers with Bis-dithiamacrocycle Isomers

A comparative study on the formation of guest clusters induced by different shapes (or sizes) of exocyclic binding sites embedded in the bis-macrocyclic host isomers is reported. CuI reacts with two regioisomers of a bis-dithiamacrocycle, o-bis-L (W-shaped binding site) and m-bis-L (U-shaped binding site), to yield one-dimensional coordination polymers {[(μ4-Cu4I4)(o-bis-L)]·2CH3CN}n (1a) and [(μ4-Cu2I2)(m-bis-L)]n (2). In 1a, the o-bis-L ligand isomer is linked by a spacious cubane [Cu4I4] cluster, while the m-bis-L ligand in 2 is linked by a smaller rhomboid [Cu2I2] cluster because of the different exocyclic binding sites. The results observed illustrate the possibility for the metal clusters including [CunIn] (n = 2 or 4) to adopt a controlled formation through the binding site alternation or design. Because of the adaptive cluster formations, the products show different photophysical properties. Additionally, sliding of the one-dimensional chains in 1a was observed upon loss of the lattice solvent molecules in ambient condition.

Hard and soft metal complexes of calix[4]-bis-monothiacrown-5: X-ray and NMR studies of discrete homodinuclear complexes and a heteromultinuclear network.

Endocyclic homodinuclear complexation and endo/exocyclic heteronuclear networking of calix[4]-bis-monothiacrown-5 (L) are reported. First, dipotassium(I) and disilver(I) complexes of L were isolated and their solid state structures characterized. To probe the complexation behavior for these same systems in solution, the competition between potassium(I) and silver(I) for L was monitored by (1)H NMR. Potassium(I) showed a higher affinity to L than silver(I) both in the solid and solution states. The reaction of L with KI in the presence of HgI2 afforded a two-dimensional coordination polymer with the endocyclic dipotassium(I) complex linked by an exocyclic mercury(II) iodide cluster backbone.

Cation-Selective and Anion-Controlled Fluorogenic Behaviors of a Benzothiazole-Attached Macrocycle That Correlate with Structural Coordination Modes

We report how the metal cation and its counteranions cooperate in the complexation-based macrocyclic chemosensor to monitor the target metal ion via the specific coordination modes. The benzothiazolyl group bearing NO2S2-macrocycle L was synthesized, and its mercury(II) selectivity (for perchlorate salt) as a dual-probe channel (UV-vis and fluorescence) chemosensor exhibiting the largest blue shift and the fluorescence turn-off was observed. In the mercury(II) sensing with different anions, except ClO4(-) and NO3(-), no responses for mercury(II) were observed with other anions such as Cl(-), Br(-), I(-), SCN(-), OAc(-), and SO4(2-). A crystallographic approach for the mononuclear mercury(II) perchlorate complex [Hg(L)(ClO4)2]·0.67CH2Cl2 (1) and polymeric mercury(II) iodide complex [Hg(L)I2]n (2) revealed that the observed anion-controlled mercury(II) sensing in the fluorescence mainly stems from the endo- and exocoordination modes, depending on the anion coordinating ability, which induces either the Hg-Ntert bond formation or not. The detailed complexation process with mercury(II) perchlorate associated with the cation sensing was also monitored with the titration methods by UV-vis, fluorescence spectroscopy, and cold-spray ionization mass spectrometry.