Enhanced guest affinity and enantioselectivity through variation of the Gd3+ [15-metallacrown-5] side chain

Supramolecular hosts that bind guests reversibly are investigated for potential catalysis and separations applications. Chiral Ln(3+)[15-Metallacrown-5] metallocavitands bind carboxylate guests in hydrophobic cavities generated by their ligand side chains. A thermodynamic study on Gd(3+)[15-metallacrown-5] hosts with ligands bearing phenyl side chains containing 0, 1, and 2 methylene spacers (1-pgHA, 1-pheHA, 1-hpheHA, respectively) is presented to quantitatively assess how guest affinity and chiral selectivity can be enhanced through changes to the ligand side chain. Guest binding affinity was measured with cyclic voltammetry using ferrocene carboxylate as a redox probe. K(a) values between ferrocene carboxylate and 1-pgHA and 1-pheHA were 4800 ± 400 M(-1) and 4400 ± 700 M(-1), respectively. Significantly stronger binding affinity of 12,100 ± 700 M(-1) was measured with 1-hpheHA, a result of the longer side-chains more completely encapsulating the guest. A similar trend was observed with benzoate. The side chain also influenced enantioselectivity, as K(S)/K(R) values of up to 2.2 ± 0.6 were measured. The side chain dependent guest binding supports the development of highly selective Ln(3+)[15-Metallacrown-5] hosts for use in catalysis and separations through careful ligand design.     

Gd(III)[15-metallacrown-5] recognition of chiral α-amino acid analogues

Chiral Ln(III)[15-metallacrown-5] complexes with phenyl side chains have been shown to encapsulate aromatic carboxylates reversibly in their hydrophobic cavities. Given the importance of selective guest binding for applications of supramolecular containers in synthesis, separations, and materials design, the affinity of Gd(III)[15-metallacrown(Cu(II), L-pheHA)-5] hosts for a series of chiral carboxylate guests with varying substitutions on the α-carbon (phenylalanine, N-acetyl-phenylalanine, phenyllactate, mandelate, methoxyphenylacetate) has been investigated. Differential binding of S- and R-phenylalanine was revealed by X-ray crystallography, as the S-enantiomer exclusively forms associative hydrogen bonds with oxygen atoms in the metallacrown ring. Selective guest binding in solution was assessed with isothermal titration calorimetry, which measures the sequential guest binding in the hydrophobic cavity first and the hydrophilic face of the host, and a cyclic voltammetry assay, which quantifies guest binding strength in the hydrophobic cavity of the host exclusively. In solution, the Gd(III)[15-metallacrown(Cu(II), L-pheHA)-5] hydrophobic cavity exhibits modest chiral selectivity for enantiomers of phenylalanine (K(S)/K(R) = 2.4) and mandelate (K(S)/K(R) = 1.22). Weak binding constants of ～100 M(-1) were measured for neutral and -1 charged carboxylates with hydrophilic functional groups (ammonium, N-acetyl, methyl ether). Weaker binding relative to the unsubstituted guests is attributed to unfavorable interactions between the hydrophilic functionalities of the guest and the hydrophobic cavity of the host. In contrast, binding constants greater than 2000 M(-1) were measured for α-hydroxy analogues phenyllactate and mandelate. The significantly increased affinity likely arises from the guests being bound as a -2 anion upon metal-assisted deprotonation in the Gd(III)[15-metallacrown(Cu(II), l-pheHA)-5] cavity. It is established that guest binding affinity in the hydrophobic cavity of the host follows the general trend of neutral zwitterion < monoanion < dianion, with hydrophilic functional groups decreasing the binding affinity. These results have broad implications for the development of metallacrowns as supramolecular catalysts or in chiral separations.     

Successive stepwise evolution of host layer‐stacking framework upon the intercalation of mobile vapor guests within side‐chain layers

For the ordered phases of hairy‐rod semiconductive poly(2,5‐bis(3‐tetradecylthiophene‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT) sandwiched in between crystalline platelets of hexamethylbenzene, the successive stepwise evolution of layer‐stacking framework upon guest intercalation has been studied in this research. The direct consequence of the guest intercalation into side‐chain layers is evaluated to cause the lateral shift of thiophene backbones along π–π stacking, resulting in stepwise shift of ultraviolet absorption wavelength. The thermal motions of vapor guests within disordering side‐chain layers subsequently cause progressive expansion of host stacking framework. With the increase in side‐chain length, thicker layers of disordering side chains in liquid crystals (LCs) accommodate additional vapor guests and larger amplitudes of thermal motions of guests, hence promoting the level of reversible d‐spacing change. The mixing between mobile vapor guests and aliphatic side chains is clarified as the mechanism of guest intercalation, which rationalizes successive guest intercalation during heating and the contribution of disordering side‐chain layers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1448–1456     

Synthesis, structure, and luminescent properties of microporous lanthanide metal-organic frameworks with inorganic rod-shaped building units

A series of microporous lanthanide metal-organic frameworks, Tb3(BDC)(4.5)(DMF)2(H2O)3.(DMF)(H2O) (1) and Ln3(BDC)(4.5)(DMF)2(H2O)3.(DMF)(C2H5OH)(0.5)(H2O)(0.5) [Ln = Dy (2), Ho (3), Er (4)], have been synthesized by the reaction of the lanthanide metal ion (Ln3+) with 1,4-benzenedicarboxylic acid and triethylenetetramine in a mixed solution of N,N'-dimethylformamide (DMF), water, and C(2)H(5)OH. X-ray diffraction analyses reveal that they are extremely similar in structure and crystallized in triclinic space group P. An edge-sharing metallic dimer and 4 metallic monomers assemble with 18 carboxylate groups to form discrete inorganic rod-shaped building units [Ln6(CO2)18], which link to each other through phenyl groups to lead to three-dimensional open frameworks with approximately 4 x 6 A rhombic channels along the [0,-1,1] direction. A water sorption isotherm proves that guest molecules in the framework of complex 1 can be removed to create permanent microporosity and about four water molecules per formula unit can be adsorbed into the micropores. These complexes exhibit blue fluorescence, and complex 1 shows a Tb3+ characteristic emission in the range of 450-650 nm.     

Lanthanide-transition metal chalcogenido cluster materials

[(THF)3Sm(SePh)2Zn(SePh)2]n decomposes to give a variety of products, including [(THF)8Sm4Se(SePh)8](2+)[Zn8Se(SePh)16](2-), an ionic cluster that can also be prepared in more than 60% yield by stoichiometric addition of Se to a mixture of Sm(SePh)3 and Zn(SePh)2. The isostructural Nd compound [(THF)8Nd4Se(SePh)8](2+)[Zn8Se(SePh)16](2-) was also prepared by the stoichiometric route to establish the viability of this cluster type with redox-inactive Ln. In addition, the salt [Yb(THF)6](3+)[Fe4Se4(SePh)4](3-) was isolated and structurally characterized. These ionic cluster materials illustrate the difficulties associated with doping Ln ions into covalent metal chalcogenido matrixes.     

Unprecedented NaI-CuII-LnIII heterometallic coordination polymers based on 3,5-pyrazoledicarboxylate with both infinite cationic and anionic chains

The self-assembly of 3,5-pyrazoledicarboxylic acid (H3pdc) and metal salts under hydrothermal conditions leads to the formation of a series of novel NaI-CuII-LnIII heterometallic coordination polymers, [[Na(H2O)4]2[Cu(pdc)2Ln(H2O)5]2 x 3H2O]n [Ln = La (1); Sm (2); Pr (3); Nd (4) and pdc3- = 3,5-pyrazoledicarboxylate]. X-Ray structure analyses show that these complexes all exhibit pairs of infinite, unexpected, cationic and anionic chains. It is the first successful attempt to construct unprecedented NaI-CuII-LnIII heterometallic coordination polymers with both infinite cationic and anionic chains. These four complexes show homologous thermal stabilities. The different magnetic properties of are also been reported in this paper.     

Orientational isomerism and binding ability of nonsymmetrical guests encapsulated in a self-assembling heterodimeric capsule

The ability of a guest to induce the assembly of tetracarboxyl-cavitand 1 and tetra(3-pyridyl)-cavitand 2 into a heterodimeric capsule 12, and the orientational isomerism of nonsymmetrical p-disubstituted-benzene guests encapsulated in 12, are described. For example, the ability of a guest to induce the assembly of guest subset(12) increases in the order p-iodoaniline< or =p-chloroanisole < p-bromoanisole < N-methyl-p-iodoaniline < p-iodoanisole. For these five guests encapsulated in 12, the halogen atoms are specifically oriented with respect to the cavity of the 2 unit. By contrast, the orientational isomeric selectivities of p-chloroiodobenzene, p-bromoiodobenzene, and p-methylanisole encapsulated in 12 are quite low, in the range of 1:1.7 to 1:1. The ortho-fluoro derivatives of these three guests, however, are encapsulated in 12 with a highly selective orientation, in which the substituent next to the fluorine atom greatly prefers the cavity of the 2 unit to that of the 1 unit.     

Making amines strong bases: thermodynamic stabilization of protonated guests in a highly-charged supramolecular host1

A highly charged, cavity-containing supramolecular assembly formed by metal-ligand interactions acts as a host to dramatically shift the effective basicity of encapsulated protonated amine guests. The scope of encapsulated protonated amine and phosphine guests shows size selectivity consistent with a constrained binding environment. Protonation of the encapsulated guests is confirmed by (31)P NMR studies, mass spectrometry studies, and the pH dependence of guest encapsulation. Rates of guest self-exchange were measured using the selective inversion recovery method and were found to correlate with the size rather than with the basicity of the guests. The activation parameters for guest self-exchange are consistent with the established mechanism for guest exchange. The binding constants of the protonated amines are then used to calculate the effective basicity of the encapsulated amines. Depending on the nature of the guest, shifts in the effective basicities of the encapsulated amines of up to 4.5 pK(a) units are observed, signifying a substantial stabilization of the protonated form of the guest molecule and effectively making phosphines and amines strong bases.     

Incorporating distinct metal clusters to construct diversity of 3D pillared-layer lanthanide-transition-metal frameworks

Three novel 3D pillared-layer heterometallic lanthanide-transition-metal (hetero-Ln-TM) compounds, namely, Ln2Cu7I6(ina)7(H2O)6.H2O [ina=isonicotinic acid; Ln=Ce (1), Sm (2)] and Er4(OH)4Cu5I4(ina)6(na)(2,5-pdc).0.3H2O (3; na=nicotinic acid, 2,5-pdc=2,5-pyridinedicarboxylic acid), have been obtained by incorporating different metal clusters as building blocks under hydrothermal conditions. Compounds 1 and 2 are isostructural and consist of two distinct building units of dimeric [Ln2(ina)6] cores and inorganic 2D [Cu8I7]nn+ layers based on the [Cu3I3] and [Cu4I3]+ clusters. Compound 3 is constructed from decanuclear [Cu10I8]2+ clusters and inorganic 1D [Er4(OH)4]n8n+ cluster chain-based layers, which represent the first example of a 3D hetero-Ln-TM constructed by the combination of two distinct types of metal cluster units of a 1D [Er4(OH)4]n8n+ cluster polymer and a transition-metal cluster. It is interesting that decarboxylation occurred in the ortho position and 2,5-pdc2- was partially transformed into na- under hydrothermal conditions. Compounds 1-3 represent good examples of using different metal cluster units to construct fascinating 3D hetero-Ln-TM frameworks.     

Flexible and shape-selective guest binding at Cu(II) axial sites in 1-dimensional Cu(II)-1,2-bis(4-pyridyl)ethane coordination polymers

A series of guest-binding Cu(II) coordination polymers, {[Cu(bpetha)2(acetone)2].2PF6}n (bpetha = 1,2-bis(4-pyridyl)ethane) (1), {[Cu(bpetha)2(DMF)2].2PF6}n (2), {[Cu(bpetha)(2)(MeCN)(2)].2PF6.2MeCN}n (3), {[Cu(bpetha)2(H2O)2].2PF6.3THF.2H2O}n (4), {[Cu(bpetha)2(H2O)2].2PF6.3dioxane}n (5), and {[Cu(bpetha)2(H2O)2].2PF6.2-PrOH.2H2O}n (6), have been synthesized and crystallographically characterized. Their framework stabilities and guest-exchange properties have also been investigated. All compounds form a similar framework motif, a "double chain", in which the bpetha ligands bridge Cu(II) centers to form 1-D [Cu(bpetha)2]n double chains. A variety of Lewis base guest molecules, such as H2O, acetone, DMF, MeCN, THF, dioxane, and 2-PrOH, are incorporated into the assembly of the 1-D double chains. These chains flexibly change their forms of assembly in a guest-dependent manner. Interestingly, acetone, DMF, and MeCN guests with a carbonyl or cyanide group coordinate directly to the axial sites of the Cu(II) centers; in contrast, THF, dioxane, and 2-PrOH guests with an ether or alcohol group are incorporated into the frameworks not via coordination bonds but via weak interactions (hydrogen bonds and van der Waals forces). This selectivity is probably due to steric effects at coordinated oxygen or nitrogen atoms of the guests. Crystal-to-crystal transformations triggered by guests are observed, during which guests coordinated to the Cu(II) axial sites are readily removed and replaced by other guests.     

Copper(II)-mediated chiral helicity amplification and inversion of meta-ethynylpyridine polymers with metal coordination sites

meta-Ethynylpyridine polymers bearing metal coordination sites associate with alkyl glycoside guests to show induced circular dichroism (ICD) bands. The addition of a Cu(II) ion changed the intensity or the sign of these ICD bands. The changes suggested chiral helicity amplification or inversion of the polymers by Cu(II)-mediated cross-linking at the coordinating side chains.     

Inclusion behavior of water-soluble thiacalix- and calix[4]arenes towards substituted benzenes in aqueous solution

Inclusion abilities of thiacalix- and calix[4]arenetetrasulfonate (3 and 4) towards mono-substituted benzenes were investigated in neutral aqueous solution. In general, the hosts regioselectively encapsulated the guests from the aromatic moiety except the complexation of toluene by 4, in which the guest penetrated from either the aromatic or the methyl group. Stabilities of the inclusion complexes increased with the electron-withdrawing ability of the substituent on the guest, suggesting pi-pi electronic interaction between the host and guest. In spite of the lower electron density of the aromatic ring, thiacalix[4]arene 3 showed higher inclusion ability than calix[4]arene 4, suggesting that the size rather than the electron density of the calix framework is a more important factor in determining the inclusion ability.     

Two distinct Ln(III)-Cu(I) cyanide extended arrays: structures and synthetic methodology for inclusion and layer complexes

Encapsulation complexes formulated as {[La(DMF)(9)](2)[Cu(12)(CN)(18)].2DMF}(infinity), 1, and {[Ln(DMF)(8)][Cu(6)(CN)(9)].2DMF}(infinity) (Ln = Eu, 2; Gd, 3; Er, 4) were obtained from the one step reaction of LnCl(3) (Ln = La, Eu, Gd, Er) with CuCN and KCN in DMF. They consist of a three-dimensional Cu-CN anionic array with pockets occupied by the cation, [Ln(DMF)(x)](3+) (x = 8, 9). These complexes are believed to be the first examples of encapsulated Ln(3+) cations, and the zeolite-like anionic network is unique. A two step procedure that employs the same components generates the layer structure {Ln(DMF)(4)Cu(2)(CN)(5)}(infinity) (Ln = La, 5; Gd, 6; Er, 7) in which the five-membered ring repeating unit has Cu-CN-Ln and Cu-CN-Cu linkages which are also without precedent. Encapsulation complexes can also be prepared from CuCl, reacting with LnCl(3) and KCN. The crystal structure of {K(DMF)(2)Cu(CN)(2)}(infinity) (8) provides insight into the proposed reaction pathways for forming these two different structural types.     

Encapsulated guest-host dynamics: guest rotational barriers and tumbling as a probe of host interior cavity space

The supramolecular host assembly [Ga(4)L(6)](12-) (1; L = 1,5-bis[2,3-dihydroxybenzamido]naphthalene) encapsulates cationic guest molecules within its hydrophobic cavity and catalyzes a variety of chemical transformations within its confined interior space. Despite the well-defined structure, the host ligand framework and interior cavity are very flexible and 1 can accommodate a wide range of guest shapes and sizes. These observations raise questions about the steric effects of confinement within 1 and how encapsulation fundamentally changes the motions of guest molecules. Here we examine the motional dynamics (guest bond rotation and tumbling) of encapsulated guest molecules to probe the steric consequences of encapsulation within host 1. Encapsulation is found to increase the Ph-CH(2) bond rotational barrier for ortho-substituted benzyl phosphonium guest molecules by 3 to 6 kcal/mol, and the barrier is found to depend on both guest size and shape. The tumbling dynamics of guests encapsulated in 1 were also investigated, and here it was found that longer, more prolate-shaped guest molecules tumble more slowly in the host cavity than larger but more spherical guest molecules. The prolate guests reduce the host symmetry from T to C(1) in solution at low temperatures, and the distortion of the host framework that is in part responsible for this symmetry reduction is observed directly in the solid state. Analysis of guest motional dynamics is a powerful method for interrogating host structure and fundamental host-guest interactions.     

Lanthanide complexes with acetylacetonate and 5,10,15,20-tetra[para-(4-chlorobenzoyloxy)-meta-ethyloxy]-phenyl porphyrin

Lanthanide complexes of acetylacetonate and 5, 10, 15, 20-tetra[para-(4-chloro-benzoyloxy)-meta-ethyloxy]phenyl porphyrin having the general formula Ln[(ClBOEP)₄P]acac (where Ln=Tb, Dy, Ho, Er; ClBOEP=[para-(4-chlorobenzoyloxy)-meta-ethyloxy]phenyl; Hacac=acetylacetone; P=porphyrin) have been prepared and characterized. A structure is proposed in which one 5, 10, 15, 20-tetra[para-(4-chloro-benzoyloxy)-meta-ethyloxy]phenyl porphyrin is coordinated to a rare earth ion in a tetradentate fashion, while one acetylacetonate is coordinated to the same metal ion in a bidentate fashion.     

Inclusion of Two PhP(O)(OH) 2 Guest Molecules into the Cavity of Macrocyclic Cavidand Cucurbit[8]uril

A new inclusion compound which is a supramolecular adduct of cucurbit[8]uril with two guest molecules of phenylphosphonic acid, PhP(O)(OH)₂, included into the cavity as ``two guests in host'' is reported. The guests match both size and hydrophilicity/hydrophobicity requirements. Two phenyl groups of molecules of PhP(O)(OH)₂ are directed toward the center of the large hydrophobic cavity whereas the PO(OH)₂ groups are outward-looking and bound with each hydrophilic portal of cucurbit[8]uril by a short hydrogen bond.     

七元瓜环与N,N′-二烷基-1,3-(4,4′-二吡啶基)丙烷衍生物的相互作用

以1,3-(4,4′-二吡啶基)丙烷为母体,合成了N,N′-二乙基\,二丁基\,二己基以及二辛基1,3-(4,4′-二吡啶基)丙烷衍生物.利用 1H NMR技术和紫外吸收光谱法,考察了Q[7]与上述链状吡啶衍生物的相互作用.实验结果表明,Q[7]与客体PC0,PC2作用,瓜环包结客体的二吡啶基丙烷部分形成1∶1的包结配合物;对于取代烷基碳链数大于4的N,N′-二烷基-1,3-(4,4′-二吡啶基)丙烷衍生物,随着主体与客体摩尔比值的增加,体系中主-客体相互作用的主导模式是Q[7]逐渐包结了客体二吡啶基丙烷部分,进而形成Q[7]包结客体两端取代烷基,甚至形成一个客体分子上"挂满"3个主体瓜环的包结物.     

七元瓜环与N,N’-二烷基-1,3-(4,4’-二吡啶基)丙烷衍生物的相互作用

以1,3-(4,4’-二吡啶基)丙烷为母体, 合成了N,N’-二乙基、二丁基、二己基以及二辛基1,3-(4,4’-二吡啶基)丙烷衍生物. 利用1H NMR技术和紫外吸收光谱法, 考察了Q[7]与上述链状吡啶衍生物的相互作用. 实验结果表明, Q[7]与客体PC0, PC2作用, 瓜环包结客体的二吡啶基丙烷部分形成1∶1的包结配合物; 对于取代烷基碳链数大于4的N,N’-二烷基-1,3-(4,4’-二吡啶基)丙烷衍生物, 随着主体与客体摩尔比值的增加, 体系中主-客体相互作用的主导模式是Q[7]逐渐包结了客体二吡啶基丙烷部分, 进而形成Q[7]包结客体两端取代烷基, 甚至形成一个客体分子上“挂满”3个主体瓜环的包结物.     

Synthesis,crystal structure and magnetic properties of a series of polymeric lanthanoid–copper complexes [Ln2Cu3{O(CH2−CO2)2}6]·nH2O (Ln=La,Nd, n=9; Ln=Er,n=6)

The reaction of diglycolic acid, O(CH2CO2H)2, with Cu(NO3)2·2H2O and lanthanoid nitrate hydrate produces a series of novel Ln–Cu mixed metal complexes, [Ln2Cu3{O(CH2CO2)2}6]·nH2O (Ln=La, Nd, n=9; Ln=Er, n=6), which have been characterized by elemental analysis, i.r. spectroscopy, magnetic measurements and X-ray crystallography. The Ln3+ and Cu2+ ions are connected by the carboxylate groups of the ligands, resulting in the formation of a complicated network.     

A series of lanthanide-transition metal frameworks based on 1-, 2-, and 3D metal-organic motifs linked by different 1D copper(I) halide motifs

Hydrothermal reactions of lanthanide(III) oxide and copper halide with isonicotinic acid (Hina) and pyridine-2,3-dicarboxylic acid (H2pdc) or 1,2-benzenedicarboxylic acid (H2bdc) lead to three novel lanthanide(III)-copper(I) heterometallic compounds, namely, [Ce2(ina)5(na)2(H2O)2][Cu5Br4] (1, na=nicotinic acid), [Er4(ina)8(bdc)2(OH)(H2O)5][Cu8I7] (2), and [Ce3(ina)8(bdc)(H2O)4][Cu7Br6] (3). Compound 1 is constructed from two distinct units of the Ln-organic double chains and inorganic [Cu5Br4]nn+ chains. Compound 2 consists of 2D Ln-organic layers and 1D [Cu8I7]nn+ cluster chains. Compound 3 can be viewed as a 1D [Cu6Br6]n chainlike motif inserted into the channels of a 3D Ln-Cu-organic motif. Compounds 1-3 exhibit three different 1D inorganic copper(I)-halide chains interconnected with metal-organic 1D chains, 2D layers, and 3D nets resulting in three mixed-motif non-interpenetrating heterometallic Cu-halide-lanthanide (Ln)-organic frameworks, which represent good examples and a facile method to construct such mixed-motif heterometallic compounds. Furthermore, the IR, TGA, and UV-vis spectra of 1-3 were also studied.