Rational Design of Polynuclear Organometallic Assemblies from a Simple Heteromultifunctional Ligand

A Zr-hydroxamate metal-organic framework with intrinsic chelating sites for postsynthetic Pd metalation and Suzuki-Miyaura catalysis

A highly crystalline and robust Zr-hydroxamate metal-organic framework (MOF) was prepared from a pyrazine-based ligand, featuring abundant N,N' chelating sites. High-degree Pd(II) metalation of the MOF was achieved through straightforward postsynthetic modification, with detailed coordination chemistry elucidated spectroscopically. The Pd-functionalized MOF was then studied as a heterogeneous Suzuki-Miyaura catalyst, through combined experimental/computational methods.

Triamine and Tetramine Edge-Length Matching Drives Heteroleptic Triangular and Tetragonal Prism Assembly

Heteroleptic metal-organic capsules, which incorporate more than one type of ligand, can provide enclosed, anisotropic interior cavities for binding low-symmetry molecules of biological and industrial importance. However, the selective self-assembly of a single mixed-ligand architecture, as opposed to the numerous other possible self-assembly outcomes, remains a challenge. Here, we develop a design strategy for the subcomponent self-assembly of heteroleptic metal-organic architectures with anisotropic internal void spaces. Zn6Tet3Tri2 triangular prismatic and Zn8Tet2Tet'4 tetragonal prismatic architectures were prepared through careful matching of the side lengths of the tritopic (Tri) or tetratopic (Tet, Tet') and panels.

Assembly of Six Types of Heteroleptic Pd2L4 Cages under Kinetic Control

Heteroleptic assemblies composed of several kinds of building blocks have been seen in nature. It is still unclear how natural systems design and create such complicated assemblies selectively. Past efforts on multicomponent self-assembly of artificial metal-organic cages have mainly focused on finding a suitable combination of building blocks to lead to a single multicomponent self-assembly as the thermodynamically most stable product. Here, we present another approach to selectively produce multicomponent Pd(II)-based self-assemblies under kinetic control based on the selective ligand exchanges of weak Pd-L coordination bonds retaining the original orientation of the metal centers in a kinetically stabilized cyclic structure and on local reversibility given in certain areas of the energy landscape in the presence of the assist molecule that facilitates error correction of coordination bonds. The kinetic approach enabled us to build all six types of Pd2L4 cages and heteroleptic tetranuclear cages composed of three kinds of ditopic ligands. Although the cage complexes thus obtained are metastable, they are stable for 1 month or more at room temperature.

Tetramine Aspect Ratio and Flexibility Determine Framework Symmetry for Zn8 L6 Self-Assembled Structures

We derive design principles for the assembly of rectangular tetramines into Zn8 L6 pseudo-cubic coordination cages. Because of the rectangular, as opposed to square, geometry of the ligand panels, and the possibility of either Δ or Λ handedness of each metal center at the eight corners of the pseudo-cube, many different cage diastereomers are possible. Each of the six tetra-aniline subcomponents investigated in this work assembled with zinc(II) and 2-formylpyridine in acetonitrile into a single Zn8 L6 pseudo-cube diastereomer, however. Each product corresponded to one of four diastereomeric configurations, with T, Th , S6 or D3 symmetry. The preferred diastereomer for a given tetra-aniline subcomponent was shown to be dependent on its aspect ratio and conformational flexibility. Analysis of computationally modeled individual faces or whole pseudo-cubes provided insight as to why the observed diastereomers were favored.

Beyond Platonic: How to Build Metal-Organic Polyhedra Capable of Binding Low-Symmetry, Information-Rich Molecular Cargoes

The field of metallosupramolecular chemistry has advanced rapidly in recent years. Much work in this area has focused on the formation of hollow self-assembled metal-organic architectures and exploration of the applications of their confined nanospaces. These discrete, soluble structures incorporate metal ions as 'glue' to link organic ligands together into polyhedra.Most of the architectures employed thus far have been highly symmetrical, as these have been the easiest to prepare. Such high-symmetry structures contain pseudospherical cavities, and so typically bind roughly spherical guests. Biomolecules and high-value synthetic compounds are rarely isotropic, highly-symmetrical species. To bind, sense, separate, and transform such substrates, new, lower-symmetry, metal-organic cages are needed. Herein we summarize recent approaches, which taken together form the first draft of a handbook for the design of higher-complexity, lower-symmetry, self-assembled metal-organic architectures.

Coordination-Driven Selective Formation of D2 Symmetric Octanuclear Organometallic Cages

The coordination-driven self-assembly of organometallic half-sandwich iridium(III)- and rhodium(III)-based building blocks with asymmetric ambidentate pyridyl-carboxylate ligands is described. Despite the potential for obtaining a statistical mixture of multiple products, D₂ symmetric octanuclear cages were formed selectively by taking advantage of the electronic effects emanating from the two types of chelating sites - (O,O') and (N,N') - on the tetranuclear building blocks. The metal sources and the lengths of bridging ligands influence the selectivity of the self-assembly. Experimental observations, supported by computational studies, suggest that the D₂ symmetric cages are the thermodynamically favored products. Overall, the results underline the importance of electronic effects on the selectivity of coordination-driven self-assembly, and demonstrate that asymmetric ambidentate ligands can be used to control the design of discrete supramolecular coordination complexes.

Programmable Synthesis of Silver Wheels

The synthesis of sandwich-shaped multinuclear silver complexes with planar penta- and tetranuclear wheel-shaped silver units and a central anion, [Ag_n(2-HPB)₂(A^-)](OTf^-)_n-1, nAg^A, n = 4 or 5 and A^- = OH^- or F^- or Cl^-, is reported, along with complete spectroscopic and structural characterization. An NMR mechanistic study reveals that silver complexes were formed in the following order: 2Ag → 3Ag^H₂O → 5Ag^OH → 4Ag^OH. The central hydroxides in 4Ag^OH and 5Ag^OH exhibit exotic physical properties due to the confined environment inside the complex. The size of these silver wheels can be tuned by changing the central anion or extracting/adding one silver atom. This study provides the facile way to synthesize discrete wheel-shaped multinuclear silver complexes and provides valuable insights into the dynamics of the self-assembly process.

Russian-Doll-Like Molecular Cubes

Nanosized cage-within-cage compounds represent a synergistic molecular self-assembling form of three-dimensional architecture that has received particular research focus. Building multilayered ultralarge cages to simulate complicated virus capsids is believed to be a tough synthetic challenge. Here, we synthesize two large double-shell supramolecular cages by facile self-assembly of presynthesized metal-organic hexatopic terpyridine ligands with metal ions. Differing from the mixture of prisms formed from the inner tritopic ligand, the redesigned metal-organic hexatopic ligands bearing high geometric constraints that led to the exclusive formation of discrete double-shell structures. These two unique nested cages are composed of inner cubes (5.1 nm) and outer huge truncated cubes (12.0 and 13.2 nm) with six large bowl-shape subcages distributed on six faces. The results with molecular weights of 75 232 and 77 667 Da were among the largest synthetic cage-in-cage supramolecules reported to date. The composition, size and shape were unambiguously characterized by a combination of ¹H NMR, DOSY, ESI-MS, TWIM-MS, TEM, AFM, and SAXS. This work provides an interesting model for functional recognition, delivery, and detection of various guest molecules in the field of supramolecular materials.

Coordination assembly and host–guest chemistry of a triply interlocked [2]catenane

Triply catenated systems composed of two or more discrete coordination-metal cages through mechanical bonds exhibit excellent host–guest behaviors, which can be potentially applied in drug delivery systems.

Directed coordination study of [Pd(en)(H2O)2]2+ with hetero-tripeptides containing C-terminus methyl esters employing NMR spectroscopy

Alkylation of the C-terminus acids in small peptides allows direction to amine and amide coordination, while changing the peptide composition to form tetradentate κ⁴[n,5,5], where n = 5-, 6-, 7-, or 8-membered ring coordination geometries, can be achieved. The alkylated tripeptide ligands, TrpAlaGly(OMe), β-Asp(OtBu)AlaGly(OMe), Asp(OtBu)AlaGly(OMe), and the fully methylated GSH, γ-Glu(OMe)Cys(SMe)Gly(OMe), were synthesized and their coordination properties to [Pd(en)(H₂O)₂]²⁺ were studied. pH-dependent coordination was analyzed by NMR spectroscopy and the coordination to the alkylated tripeptides at selected pH values inferred from their NMR spectra. If selective coordination of amine/amide donors results in metal complexation, allowing for flexible and adjustable ligand frameworks, then this strategy could potentially be extended to other metal ions and peptide system.

Thermotropic Liquid-Crystalline Materials Based on Supramolecular Coordination Complexes

Liquid crystals are among us, in living organisms and in electronic devices, and they have contributed to the development of our modern society. Traditionally developed by organic chemists, the field of liquid-crystalline materials is now involving chemists and physicists of all domains (computational, physical, inorganic, supramolecular, electro-chemistry, polymers, materials, etc.,). Such diversity in researchers confirms that the field remains highly active and that new applications can be foreseen in the future. In this review, liquid-crystalline materials developed around coordination complexes are presented, focusing on those showing thermotropic behavior, a relatively unexplored family of compounds.

Palladium(II)-Based Self-Assembled Heteroleptic Coordination Architectures: A Growing Family

Metal-driven self-assembly is one of the most effective approaches to lucidly design a large range of discrete 2D and 3D coordination architectures/complexes. Palladium(II)-based self-assembled coordination architectures are usually prepared by using suitable metal components, in either a partially protected form (PdL') or typical form (Pd; charges are not shown), and designed ligand components. The self-assembled molecules prepared by using a metal component and only one type of bi- or polydentate ligand (L) can be classified in the homoleptic series of complexes. On the other hand, the less explored heteroleptic series of complexes are obtained by using a metal component and at least two different types of non-chelating bi- or polydentate ligands (such as L^a and L^b ). Methods that allow the controlled generation of single, discrete heteroleptic complexes are less understood. A survey of palladium(II)-based self-assembled coordination cages that are heteroleptic has been made. This review article illustrates a systematic collection of such architectures and credible justification of their formation, along with reported functional aspects of the complexes. The collected heteroleptic assemblies are classified here into three sections: 1) [(PdL')_m (L^a )_x (L^b )_y ]-type complexes, in which the denticity of L^a and L^b is equal; 2) [(PdL')_m (L^a )_x (L^b )_y ]-type complexes, in which the denticity of L^a and L^b is different; and 3) [Pd_m (L^a )_x (L^b )_y ]-type complexes, in which the denticity of L^a and L^b is equal. Representative examples of some important homoleptic architectures are also provided, wherever possible, to set a background for a better understanding of the related heteroleptic versions. The purpose of this review is to pave the way for the construction of several unique heteroleptic coordination assemblies that might exhibit emergent supramolecular functions.

A coordination polymer-derived Co3O4/Co-N@NMC composite material as a Zn-air battery cathode electrocatalyst and microwave absorber

Zn-air batteries, promising energy storage equipment with high energy density, light weight and a compact structure, are a perfect power source for electric vehicles. For a Zn-air battery, the activity of the air cathode electrocatalyst plays an important role in its performance. Here, employing a coordination polymer as a precursor, a composite material built from Co3O4 and Co-N active centres with nitrogen-doped mesoporous carbon as a matrix has been synthesized successfully. This composite material possesses outstanding activity and stability in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) processes. It possesses a small half-wave potential (ORR1/2 = 0.786 V) and low overpotential (OER10 = 1.575 V) for the ORR and OER, respectively. With this composite material as an air cathode electrocatalyst, a rechargeable Zn-air battery was assembled successfully. During the discharge process, the maximum power density of this Zn-air battery is 122 mW cm-2 at 0.76 V. The specific capacity of this battery is 505 mA h g-1 at 25 mA cm-2. The voltage gap between the charge and discharge processes is only 0.744 V at 10 mA cm-2 and 1.308 V at 100 mA cm-2. This rechargeable battery also shows promising stability after long-term charge-discharge experiments. Furthermore, the composite material also exhibits outstanding microwave adsorption properties. Its maximum reflection loss (RL) arrives at -13.9 dB with a thickness of only 1.0 mm. Thus, we find that coordination polymers are an ideal precursor for Zn-air battery cathode electrocatalysts and microwave absorbers.

Resolution of minor size differences in a family of heteroleptic coordination cages by trapped ion mobility ESI-MS

We report a complex system of heteroleptic coordination cages based on the combination of four bis-monodentate ligands whose backbones only slightly differ in shape and length. cis-[Pd2L2L'2] assemblies cleanly form after addition of PdII cations to a 1 : 1 mixture of two shape-complementary ligands, each. When three or even all four ligands are used in combination, the unambiguous discrimination of all individual species in the product mixture becomes difficult by conventional NMR spectroscopic and mass spectrometric methods. Due to steric constraints, the system is restricted to the formation of ten different coordination cages in total, two of which are isomeric. We show that high-resolution trapped ion mobility mass spectrometry (TIMS) allows the clear differentiation of all ten species. Observed size trends could be readily reproduced by the calculation of theoretical values for collisional cross sections (CCS) from geometry-optimized models.

A new family of {Co4Ln8} metallacrowns with a butterfly-shaped structure

A series of cobalt–lanthanide metallacrowns (MCs) {CoIII4Ln₈} (Ln = Dy³⁺1, Ho³⁺2 and Tm³⁺3) based on pyrazinehydroxamic acid (H₂pyzha) and pyrazinic acid (Hpyzic) ligands have been synthesized.

Versatility and trends in the interaction between Pd(ii) and peptide hydroxamic acids

The interaction between di- and tripeptide hydroxamic acids and Pd(ii) (as a Pt(ii) model but with faster ligand exchange reactions) was studied in aqueous solution in the presence of chloride ions by pH-potentiometric and NMR methods revealing ligand-dependent competition between the coordinative and hydrolytic processes.

Self-assembly of manganese(i) based thiolato bridged dinuclear metallacycles: synthesis, characterization, cytotoxicity evaluation and CO-releasing studies

Manganese(i) based thiolato bridged dinuclear metallacycles were assessed as anticancer agents along with myoglobin assay for CO-releasing studies.

Rational Design of an Amphiphilic Coordination Cage-Based Emulsifier

Self-assembled, porous coordination cages with a functional interior find application in controlled guest inclusion/release, drug delivery, separation processes, and catalysis. However, only few studies exist that describe their utilization for the development of self-assembled materials based on their 3-dimensional shape and external functionalization. Here, dodecyl chain-containing, acridone-based ligands (L^A) and shape-complementary phenanthrene-derived ligands (L^B) are shown to self-assemble to heteroleptic coordination cages cis-[Pd₂(L^A)₂(L^B)₂]⁴⁺ acting as a gemini amphiphile (CGA-1; Cage-based Gemini Amphiphile-1). Owing to their anisotropic decoration with short polar and long nonpolar side chains, the cationic cages were found to assemble into vesicles with diameters larger than 100 nm in suitable polar solvents, visualized by cryo-TEM and Liquid-Cell Transmission Electron Microscopy (LC-TEM). LC-TEM reveals that these vesicles aggregate into chains and necklaces via long-range interactions. In addition, the cages show a rarely described ability to stabilize oil-in-oil emulsions.

Stable Fe(ii)-based coordination polymers: synthesis, structural diversity and catalytic applications in homo-coupling reactions

Herein, we synthesize three new stable Fe(ii) coordination polymers, {[Fe3(tttmb)4(OH)(NCS)5]2CH3OH·H2O}n (1), {[Fe3(tttmb)4(NCS)6]·3H2O}n (2), and {[Fe3(tttmb)2Cl6(H2O)6]·5H2O}n (3) (tttmb = 1,3,5-tris(triazole-1-ylmethyl)-2,4,6-trimethyl-benzene) under the regulation of KSCN and solvents and use them as green heterogeneous catalysts in aryl homo-coupling reactions. The catalytic experiments show that 1 and 3 exhibit high efficiency for aryl homo-coupling reactions under an air environment with a yield of up to 80%. Furthermore, the crystal structure analysis reveals that 1 and 3 have coordinated water molecules and OH-, which are easily removed from the host materials during the reactions. In contrast, no unsaturated coordination sites are generated in 2 during the reaction process. In addition, the variable temperature magnetic susceptibilities of 1-3 prove that the metal centers of these polymers are bivalent and all of them exhibit a weak antiferromagnetic effect.

Controllable assembly of rectangular macrocycles bearing different numbers of unsaturated sites based on half-sandwich iridium fragments

A series of hexanuclear rectangular macrocycles were designed and synthesized by utilizing multifunctional pyrazine-derived (pyrazine-2,3-diamine (H4L1)) and quinoxaline-derived ligands (2,3-dihydroxy-quinoxaline (H2L2)) featuring two monodentate sites and one pair of chelating sites. X-ray crystallography in combination with 1H NMR spectroscopy elucidated that both half-sandwich iridium diimine and dihydroxy moieties are located on either side of the rectangular macrocycles, making them centrosymmetric. Thereby, the prepared diimine-functionalised complexes were found to have unsaturated metal sites on account of their strongly bound Ir-N-C-C-N arrangement. However, all the iridium atoms in the rectangular macrocycles containing dihydroxy groups were found to adopt an 18-electron coordination configuration, indicating that the O,O'-bonded iridium centers had bound additional ligands, such as Cl-, MeOH, MeCN, etc. Notably, a rare rectangular macrocycle containing a single coordinatively unsaturated metal site was achieved when the ligands H2L12- and L22- were introduced simultaneously.

Host–guest capability of a three-dimensional heterometallic macrocycle

Three-dimensional heterometallic macrocycles with half-sandwich Rh corners were studied for their ability to trap planar and non-planar guests. Furthermore, these heterometallic macrocycles can be destroyed in the presence of a soft base to form hexanuclear triangular prism complexes.

Preparation of polynuclear NHC complexes by post-synthetic modification of half-sandwich rhodium and iridium complexes bearing C-azolato ligands

Synthesis of polymetallic structures via rational N-functionalization of half-sandwich rhodium and iridium complexes featuring C-azolato ligands.

Construction of half-sandwich multinuclear complexes including tunnel architectures via C–H-activation-directed assembly

Half-sandwich bi-, tetra-, hexa- and octanuclear complexes were prepared via C–H-activation-directed assembly based on three aromatic ligands. A series of tunnel architectures were observed in the complexes, with guest molecules in certain parts.

Syntheses, Structures, and Solution Studies of Multicomponent Macrocycles and Cages Based on Versatile Ligands

Different types of multinuclear half-sandwich rhodium macrocycles and cages were designed and synthesized by using two similar multifunctional hydroxamate ligands (pyrazine-2-hydroxamic acid (NaHL¹ ) and 4,4'-bipyridine-2-hydroxamic acid (KHL² )) featuring one monodentate site and two pairs of chelating sites. The Rh^III -Pd^II heterometallic macrocycles were constructed by using the semi-open palladium(II) source [Pd(en)Cl₂ ] with two free acceptor sites. However, only one kind of macrocycle was found when the shorter ligand L¹ was used, while in for the larger ligand, various spectroscopic techniques demonstrated the coexistence of hexanuclear and octanuclear macrocycles in solution and the proportions of both components depended on concentration and temperature. The palladium salt Pd(NO₃ )₂ , as a source of "naked" Pd²⁺ , was introduced to assemble the cuboid-shaped cage composed of two types of metal ions and three types of organic ligands. In addition, two silver(I)-containing mixed-metal complexes bridged by pyrazine were obtained, in which two forms of decanuclear complex with C_2v and C_2h point symmetry cocrystallized-one is a polymeric structure and the other is a discrete cage. However, the third form, with D₂ point symmetry, was found in the larger cage.

Integrative self-sorting of coordination cages based on 'naked' metal ions

Coordination-driven self-assembly of metal ions and organic ligands has been extensively utilised over the past four decades to access a variety of nano-sized cage assemblies, with functions ranging from sensing and catalysis to drug delivery. Many of the reported examples, however, are highly symmetric architectures that contain one type of organic ligand carrying not more than a single functionality. This contrasts significantly with the level of structural and functional complexity encountered in biological macromolecular hosts, which are able to bind and chemically convert smaller molecules in their highly-decorated internal cavities. To address this disparity, rational approaches that facilitate heteroleptic assembly by regulating integrative self-sorting of metal ions and multiple ligand components have emerged. Among these, routes to access coordination cages from 'naked' metal cations that offer more than two coordination sites are still in early development, as the complexity of the self-sorted products in terms of composition and stereochemistry presents an entropic challenge. This feature article highlights recent progress in controlling integrative self-sorting of multi-component cage systems with a focus on structures composed of 'naked' metal cations and two different ligands. Once heteroleptic self-assembly strategies find a wider implementation in supramolecular design, the resultant interplay between tailored combinations of precisely positioned substituents promises enhanced functionality in nanoscale structures.

Controllable construction of half-sandwich octanuclear complexes based on pyridyl-substituted ligands with conjugated centers

Based on three tetradentate ligands with conjugated centers, seven half-sandwich octanuclear complexes were selectively obtained. Several subsequent structural conversions were also successfully conducted.

[Cd(H2O)6]@{Cd6Cl4(nico)12[Hg(Tab)2(μ-Cl)]2}: a heterometallic host–guest icosidodecahedron cage via hierarchical assembly

A reaction of [Hg(Tab)₂(nico)](PF₆) (Tab = 4-(trimethylammonio)benzenethiolate, nico = nicotinate) with equimolar CdCl₂·2.5H₂O afforded a unique heterometallic cage complex [Cd(H₂O)₆]@{Cd₆Cl₄(nico)₁₂[Hg(Tab)₂(μ-Cl)]₂}.

Metallosupramolecular 3D assembly of dimetallic Zn4[RuL2]2 and trimetallic Fe2Zn2[RuL2]2

A 3D trismetallo-macromolecule was assembled with a stepwise synthesized key metallo-organic ligand, which was created by a reaction on complex strategy.

Preparation, X-ray Structures, Spectroscopic, and Redox Properties of Di- and Trinuclear Iron-Zirconium and Iron-Hafnium Porphyrinoclathrochelates

The first hybrid di- and trinuclear iron(II)-zirconium(IV) and iron(II)-hafnium(IV) macrobicyclic complexes with one or two apical 5,10,15,20-tetraphenylporphyrin fragments were obtained using transmetalation reaction between n-butylboron-triethylantimony-capped or bis(triethylantimony)-capped iron(II) clathrochelate precursors and dichlorozirconium(IV)- or dichlorohafnium(IV)-5,10,15,20-tetraphenylporphyrins under mild conditions. New di- and trinuclear porphyrinoclathrochelates of general formula FeNx₃((Bn-Bu)(MTPP)) and FeNx₃(MTPP)₂ [M = Zr, Hf; TPP = 5,10,15,20-tetraporphyrinato(2-); Nx = nioximo(2-)] were characterized by one-dimensional (¹H and ¹³C{¹H}) and two-dimensional (COSY and HSQC) NMR, high-resolution electrospray ionization mass spectrometry, UV-visible, and magnetic circular dichroism spectra, single-crystal X-ray diffraction experiments, as well as elemental analyses. Redox properties of all complexes were probed using electrochemical and spectroelectrochemical approaches. Electrochemical and spectroelectrochemical data suggestive of a very weak, if any, long-range electronic coupling between two porphyrin π-systems in FeNx₃(MTPP)₂ complexes. Density functional theory and time-dependent density functional theory calculations were used to correlate spectroscopic signatures and redox properties of new compounds with their electronic structures.

Face and edge directed self-assembly of Pd12 tetrahedral nano-cages and their self-sorting

Reactions of a cis-blocked Pd(ii) 90° acceptor [cis-(tmeda)Pd(NO3)2] (M) with 1,4-di(1H-tetrazol-5-yl)benzene (H2L1 ) and [1,3,5-tri(1H-tetrazol-5-yl)benzene] (H3L2 ) in 1 : 1 and 3 : 2 molar ratios respectively, yielded soft metallogels G1 and G2 [tmeda = N,N,N',N'-tetramethylethane-1,2-diamine]. Post-metalation of the gels G1 and G2 with M yielded highly water-soluble edge and face directed self-assembled Pd12 tetrahedral nano-cages T1 and T2, respectively. Such facile conversion of Pd(ii) gels to discrete tetrahedral metallocages is unprecedented. Moreover, distinct self-sorting of these two tetrahedral cages of similar sizes was observed in the self-assembly of M with a mixture of H2L1 and H3L2 in aqueous medium. The edge directed tetrahedral cage (T1) was successfully used to perform Michael reactions of a series of water insoluble nitro-olefins assisted by encapsulation into the cage in aqueous medium.

A nonanuclear triangular macrocycle and a linear heptanuclear heterometallic complex based on a 2-substituted imidazole-4,5-dicarboxylate ligand

A Cp*Rh-based nonanuclear triangular macrocycle complex [(Cp*Rh)9L3(NO3)4.5(MeOH)](OTf)4.5 (1), a Cp*Ir-based trinuclear complex [(Cp*Ir)3L(MeCN)4](OTf)3 (2) and a linear heptanuclear heterometallic complex [(Cp*Ir)6ZnL2(MeCN)8(MeOH)2](OTf)8 (3) (Cp* = η(5)-pentamethylcyclopentadienyl) have been synthesized from a 2-(4-(pyridin-4-yl)phenyl)-1H-imidazole-4,5-dicarboxylic acid proligand. These complexes were further characterized by X-ray crystallography, (1)H NMR, DOSY NMR, IR spectroscopy, and elemental analyses.

Synthesis, crystal structures, and thermal and spectroscopic properties of two Cd(II) metal-organic frameworks with a versatile ligand

Two new metal-organic frameworks, namely, [Cd(L)(H2O)] n (1) and {[Cd0.5(L)(4,4′-bipy)0.5][Cd0.5(H2O)(4,4′-bipy)0.5]·H2O} n (2), where H2L = N-pyrazinesulfonyl-glycine and 4,4′-bipy = 4,4′-bipyridine, have been synthesized and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental, thermogravimetric, and photoluminescent analysis. X-ray diffraction crystallographic analyses indicate that 1 displays a distorted octahedral metal coordination in a 3-connected (4, 82) topology, while the molecular structure of 2 has a 4-connected (4, 4) topology with two perfectly octahedrally coordinated Cd centers. The L2– ligand serves as a N,N,O-tridentate, μ 2-pyrazine-bridging, and μ 2-carboxylate-bridging ligand in 1, and as a N,O-bidentate and μ 2-carboxylate-bridging ligand in 2. In the crystal, a 3D supramolecular architecture is formed by O–H···O hydrogen bond interactions in 1, but through O–H···O as well as π···π stacking in 2. The two compounds show intense fluorescence in the solid state at room temperature.