Watching the Conformational Changes of Maleonitriledithiolate Chromophores Inside the Inclusion Complexes with Cyclodextrins: Probed by ICD Spectra and DFT Calculations

A series of inclusion complexes between cyclodextrins (α-, β-, γ-cyclodextrin and HP-β-cyclodextrin, HP-β-cyclodextrin = 2-hydroxypropyl-β-cyclodextrin) and sodium maleonitriledithiolate (Na2mnt) were investigated by electronic spectra, induced circular dichroism (ICD) spectra, and quantum chemical studies. The inclusion complexes Na2mnt@α-cyclodextrin and Na2mnt@γ-cyclodextrin did not show any ICD signals, whereas Na2mnt@HP-β-cyclodextrin displayed two signs of splitting Cotton effects (CEs), with one positive CE couplet at 376 nm in the 365−410 nm region and the other negative at 277 nm in the 265−306 nm region. In addition, a dimeric host inclusion pattern of Na2mnt@HP-β-cyclodextrin in solution was determined by the method of continuous variation. Density functional theory (DFT) was used to assist assignment of the ICD signals in inclusion complexes Na2mnt@β-cyclodextrin and Na2mnt@HP-β-cyclodextrin in combination with the well-known Harata’s rule. The orientation of p → π* transition in Na2mnt chromophore was predicted by TD-DFT (time-dependent DFT) calculations to be along the CC double bond instead of being perpendicular. Upon titrations with Zn2+ solutions, reversals of the p → π* transition-relevant ICD peak and splitting CE were experimentally observed in the cases of Na2mnt@β-cyclodextrin and Na2mnt@HP-β-cyclodextrin, respectively, which strongly supported our hypotheses on their coconformations and the subsequent conformational changes of mnt chromophores occurring during the titration procedures. Therefore, on the basis of both the experimental data and TD-DFT calculations, the HP-β-cyclodextrin dimer host in inclusion complex Na2mnt@HP-β-cyclodextrin was disclosed, which in turn generated the exciton coupling between the two individually included guests and produced the splitting CEs as well as the reversals of CEs

A New Quasi-1D Spin System with Spin Transition Exhibiting Novel CN···π Interactions

A new molecular tecton with a flexible conformation, 1-methyl-ethyldeneaminopyridinium, was synthesized, and its corresponding compound with [Ni(mnt)2]- exhibits novel CN···π interactions and spin transition

Crystal Structures and Properties of Large Protonated Water Clusters Encapsulated by Metal−Organic Frameworks

A large ionic water cluster H(H2O)28+, consisting of a water shell (H2O)26 and an encaged species H(H2O)2+ as a center core, was trapped in the well-modulated cavity of a porous metal−organic framework (MOF) {[Co4(dpdo)12(PMo12O40)3]−}∞ and structurally characterized. Degeneration of the protonated water cluster H(H2O)28+ into a smaller cluster H(H2O)21+ and recovery of H(H2O)28+ from the resulting H(H2O)21+ cluster in a reversible way demonstrated the unusual stability of the protonated water clusters H(H2O)28+ and H(H2O)21+ in the robust crystal host. Proton transport and proton/potassium ion exchange through the channels of the crystal host have been investigated by a well-established fluorometry method. X-ray fluorescence experiments and X-ray structural analyses of the exchanged crystals confirmed the occurrence of the proton/potassium ion-exchange reaction and the transformation of the protonated water cluster H(H2O)28+ to an ionic cluster K(H2O)27+. Comparison of the H+/K+ exchange of H(H2O)28+ with that of its neighboring protonated water cluster H(H2O)27+ suggested that the abundance of hydrogen bonds associated with the hydronium/water cluster in the H(H2O)28+ cluster was essential for proton transport through the Grotthuss mechanism. On the basis of the results, our porous network could be described as a synthetic non-peptide ion channel, in terms of not only structural features but also the functions addressed. Direct observation of the structures of various large ionic water clusters trapped by porous MOFs, coupled with the proton/ion-exchange processes and the reversible dehydration/rehydration, provided valuable insights into the aqueous proton transfer and its mobility pertaining to the large protonated water clusters in the condensed phase

A New Quasi-1D Spin System with Spin Transition Exhibiting Novel CN···π Interactions

A new molecular tecton with a flexible conformation, 1-methyl-ethyldeneaminopyridinium, was synthesized, and its corresponding compound with [Ni(mnt)2]- exhibits novel CN···π interactions and spin transition

Assemblies of a New Flexible Multicarboxylate Ligand and d¹⁰ Metal Centers toward the Construction of Homochiral Helical Coordination Polymers: Structures, Luminescence, and NLO-Active Properties

Hydro(solvo)thermal reactions between a new flexible multicarboxylate ligand of 2,2‘,3,3‘-oxydiphthalic acid (2,2‘,3,3‘-H4ODPA) and M(NO3)2·xH2O (M = Zn, x = 6; M = Cd, x = 4) in the presence of 4,4‘-bipyridine (bpy) afford two novel homochiral helical coordination polymers {[Zn2(2,2‘,3,3‘-ODPA)(bpy)(H2O)3]·(H2O)2 for 1 and [Cd2(2,2‘,3,3‘-ODPA)(bpy)(H2O)3]·(H2O)2 for 2}. Though having almost the same chemical formula, they have different space groups (P212121 for 1 and P21 for 2) and different bridging modes of the 2,2‘,3,3‘-ODPA ligand. Two kinds of homochiral helices (right-handed) are found in both 1 and 2, each of which discriminates only one kind of crystallographical nonequivalent metal atom. 1 has a 2D metal−organic framework and can be seen as the unity of two parallel homochiral Zn1 and Zn2 helices, in which the nodes are etheric oxygen atoms. In contrast, 2 has a 3D metal−organic framework and consists of two partially overlapped homochiral Cd1 and Cd2 helices in the two dimensions. Moreover, metal−ODPA helices give a 2D chiral herringbone structural motif in both 1 and 2 in the two dimensions, which are further strengthened by the second ligand of bpy. Bulk materials for 1 and 2 all have good second-harmonic generation activity, approximately 1 and 0.8 times that of urea

Crystal Structures and Properties of Large Protonated Water Clusters Encapsulated by Metal−Organic Frameworks

A large ionic water cluster H(H2O)28+, consisting of a water shell (H2O)26 and an encaged species H(H2O)2+ as a center core, was trapped in the well-modulated cavity of a porous metal−organic framework (MOF) {[Co4(dpdo)12(PMo12O40)3]−}∞ and structurally characterized. Degeneration of the protonated water cluster H(H2O)28+ into a smaller cluster H(H2O)21+ and recovery of H(H2O)28+ from the resulting H(H2O)21+ cluster in a reversible way demonstrated the unusual stability of the protonated water clusters H(H2O)28+ and H(H2O)21+ in the robust crystal host. Proton transport and proton/potassium ion exchange through the channels of the crystal host have been investigated by a well-established fluorometry method. X-ray fluorescence experiments and X-ray structural analyses of the exchanged crystals confirmed the occurrence of the proton/potassium ion-exchange reaction and the transformation of the protonated water cluster H(H2O)28+ to an ionic cluster K(H2O)27+. Comparison of the H+/K+ exchange of H(H2O)28+ with that of its neighboring protonated water cluster H(H2O)27+ suggested that the abundance of hydrogen bonds associated with the hydronium/water cluster in the H(H2O)28+ cluster was essential for proton transport through the Grotthuss mechanism. On the basis of the results, our porous network could be described as a synthetic non-peptide ion channel, in terms of not only structural features but also the functions addressed. Direct observation of the structures of various large ionic water clusters trapped by porous MOFs, coupled with the proton/ion-exchange processes and the reversible dehydration/rehydration, provided valuable insights into the aqueous proton transfer and its mobility pertaining to the large protonated water clusters in the condensed phase

Zeolite Ionic Crystals Assembled through Direct Incorporation of Polyoxometalate Clusters within 3D Metal−Organic Frameworks

Polyoxometalate-based metal−organic frameworks {[Gd(dpdo)4(H2O)3](PMo12O40)(H2O)2CH3CN}n (2), {[Dy(dpdo)4(H2O)3](PMo12O40)(H2O)2CH3CN}n (3), {[Gd(dpdo)4(H2O)3](H3O)(SiMo12O40)(dpdo)0.5(CH3CN)0.5 (H2O)3}n (4), {[Ho(dpdo)4(H2O)3](H3O)(SiMo12O40)(dpdo)0.5(CH3CN)0.5(H2O)3}n (5), {[Ni(dpdo)2(CH3CN) (H2O)2]2(SiMo12O40)(H2O)2}n (6), and {[Ni(dpdo)3]4(PW12O40)3[H(H2O)27(CH3CN)12]}n (7) (where dpdo is 4,4‘-bipyridine-N,N‘-dioxide) were constructed via self-assembly by embedding Keggin-type polyanions within the intercrystalline voids as guests or pillars. Compounds 2 and 3 are isomorphic and exhibit three-dimensional (3D) noninterwoven 64 frameworks with distorted-honeycomb cavities occupied by the polyanions. Compounds 4 and 5 are comprised of 3D noninterwoven frameworks formed by linking the adjacent folded sheets through hydrogen bonds and π−π stacking interactions relative to the free isolated dpdo ligand. Compound 6 is a pillar-layered framework with the [SiMo12O40]4- anions located on the square voids of the two-dimensional bilayer sheets formed by the dpdo ligands and nickel(II) ions. Compound 7 is a 3D metal−organic framework formed by nickel(II) and 4,4‘-bipyridine-N,N‘-dioxide with the globular Keggin-structure [PW12O4]3-anion as the template. A large protonated water cluster H+(H2O)27 is trapped and stabilized within the well-modulated cavity

Assemblies of a New Flexible Multicarboxylate Ligand and d¹⁰ Metal Centers toward the Construction of Homochiral Helical Coordination Polymers: Structures, Luminescence, and NLO-Active Properties

Hydro(solvo)thermal reactions between a new flexible multicarboxylate ligand of 2,2‘,3,3‘-oxydiphthalic acid (2,2‘,3,3‘-H4ODPA) and M(NO3)2·xH2O (M = Zn, x = 6; M = Cd, x = 4) in the presence of 4,4‘-bipyridine (bpy) afford two novel homochiral helical coordination polymers {[Zn2(2,2‘,3,3‘-ODPA)(bpy)(H2O)3]·(H2O)2 for 1 and [Cd2(2,2‘,3,3‘-ODPA)(bpy)(H2O)3]·(H2O)2 for 2}. Though having almost the same chemical formula, they have different space groups (P212121 for 1 and P21 for 2) and different bridging modes of the 2,2‘,3,3‘-ODPA ligand. Two kinds of homochiral helices (right-handed) are found in both 1 and 2, each of which discriminates only one kind of crystallographical nonequivalent metal atom. 1 has a 2D metal−organic framework and can be seen as the unity of two parallel homochiral Zn1 and Zn2 helices, in which the nodes are etheric oxygen atoms. In contrast, 2 has a 3D metal−organic framework and consists of two partially overlapped homochiral Cd1 and Cd2 helices in the two dimensions. Moreover, metal−ODPA helices give a 2D chiral herringbone structural motif in both 1 and 2 in the two dimensions, which are further strengthened by the second ligand of bpy. Bulk materials for 1 and 2 all have good second-harmonic generation activity, approximately 1 and 0.8 times that of urea

Four d¹⁰ Metal Coordination Polymers Containing Isomeric Thiodiphthalic Ligands: Crystal Structures and Luminescent Properties

Two versatile ligands, 2,3,2‘,3‘-tdpa and its isomer 2,3,3‘,4‘-tdpa, have been introduced to construct novel metal−organic frameworks with interesting structural motifs and good function. By hydrothermoreactions with d10 metals (Zn and Cd), four coordination polymers were obtained and characterized. 1 is a 3D framework embodying two distinct types of helical chains. 2 features a 2D lamellar structure with helices and 14-membered rings in every layer. 3 is a 3D framework bearing the (62.83.10)(62.8)(6.8.10) topology and has chiral layers in it. 4 shows a quasi-2D structure with 1D binuclear zinc chains and less common monocoordinated 4,4‘-bipyridine ligands. All four of these coordination polymers exhibit intense blue fluorescence emissions (1 at 429 nm, 2 at 473 nm, 3 at 451 nm, and 4 at 492 nm) and may be suitable as excellent candidates of blue fluorescent materials

Zeolite Ionic Crystals Assembled through Direct Incorporation of Polyoxometalate Clusters within 3D Metal−Organic Frameworks

Polyoxometalate-based metal−organic frameworks {[Gd(dpdo)4(H2O)3](PMo12O40)(H2O)2CH3CN}n (2), {[Dy(dpdo)4(H2O)3](PMo12O40)(H2O)2CH3CN}n (3), {[Gd(dpdo)4(H2O)3](H3O)(SiMo12O40)(dpdo)0.5(CH3CN)0.5 (H2O)3}n (4), {[Ho(dpdo)4(H2O)3](H3O)(SiMo12O40)(dpdo)0.5(CH3CN)0.5(H2O)3}n (5), {[Ni(dpdo)2(CH3CN) (H2O)2]2(SiMo12O40)(H2O)2}n (6), and {[Ni(dpdo)3]4(PW12O40)3[H(H2O)27(CH3CN)12]}n (7) (where dpdo is 4,4‘-bipyridine-N,N‘-dioxide) were constructed via self-assembly by embedding Keggin-type polyanions within the intercrystalline voids as guests or pillars. Compounds 2 and 3 are isomorphic and exhibit three-dimensional (3D) noninterwoven 64 frameworks with distorted-honeycomb cavities occupied by the polyanions. Compounds 4 and 5 are comprised of 3D noninterwoven frameworks formed by linking the adjacent folded sheets through hydrogen bonds and π−π stacking interactions relative to the free isolated dpdo ligand. Compound 6 is a pillar-layered framework with the [SiMo12O40]4- anions located on the square voids of the two-dimensional bilayer sheets formed by the dpdo ligands and nickel(II) ions. Compound 7 is a 3D metal−organic framework formed by nickel(II) and 4,4‘-bipyridine-N,N‘-dioxide with the globular Keggin-structure [PW12O4]3-anion as the template. A large protonated water cluster H+(H2O)27 is trapped and stabilized within the well-modulated cavity