Design and self-assembly of wide and robust coordination cages

Tailoring Secondary Coordination Sphere Effects in Single-metal-site Catalysts by Surface Immobilization of Supramolecular Cages

Controlling the coordination sphere of heterogeneous single-metal-site catalysts is a powerful strategy for fine-tuning their catalytic properties but is fairly difficult to achieve. To address this problem, we immobilized supramolecular cages where the primary- and secondary coordination sphere are controlled by ligand design. The kinetics of these catalysts were studied in a model reaction, the hydrolysis of ammonia borane, over a temperature range using fast and precise online measurements generating high-precision Arrhenius plots. The results show how catalytic properties can be enhanced by placing a well-defined reaction pocket around the active site. Our fine-tuning yielded a catalyst with such performance that the reaction kinetics are diffusion-controlled rather than chemically controlled.

A Practice of Reticular Chemistry: Construction of a Robust Mesoporous Palladium Metal-Organic Framework via Metal Metathesis

Constructing stable palladium(II)-based metal-organic frameworks (MOFs) would unlock more opportunities for MOF chemistry, particularly toward applications in catalysis. However, their availability is limited by synthetic challenges due to the inertness of the Pd-ligand coordination bond, as well as the strong tendency of the Pd(II) source to be reduced under typical solvothermal conditions. Under the guidance of reticular chemistry, herein, we present the first example of an azolate Pd-MOF, BUT-33(Pd), obtained via a deuterated solvent-assisted metal metathesis. BUT-33(Pd) retains the underlying sodalite network and mesoporosity of the template BUT-33(Ni) and shows excellent chemical stability (resistance to an 8 M NaOH aqueous solution). With rich Pd(II) sites in the atomically precise distribution, it also demonstrates good performances as a heterogeneous Pd(II) catalyst in a wide application scope, including Suzuki/Heck coupling reactions and photocatalytic CO₂ reduction to CH₄. This work highlights a feasible approach to reticularly construct noble metal based MOFs via metal metathesis, in which various merits, including high chemical stability, large pores, and tunable functions, have been integrated for addressing challenging tasks.

Kinetic selection of Pd4L2 metallocyclic and Pd6L3 trigonal prismatic assemblies

The self-assembly of Pd4L2 metallocylcic and Pd6L3 trigonal prismatic assemblies are described. The selection of one species over the other has been achieved by careful choice of ancilliary ligands, which switch the dynamics of the Pd-pyridine bonds such that a highly unusual and distorted smaller assembly can be kinetically trapped en route to the more energetically favourable larger species. Both assemblies provide promise as easy to access multicavity reaction vessels.

Multicomponent Metallo-Supramolecular Nanocapsules Assembled from Calix[4]resorcinarene-Based Terpyridine Ligands

Tetrafunctionalized calix[4]resorcinarene cavitands commonly serve as supramolecular scaffolds for construction of coordination-driven self-assembled capsules. However, due to the calix-like shape, the structural diversity of assemblies is mostly restricted to dimeric and hexameric capsules. Previously, we reported a spontaneous heteroleptic complexation strategy based on a pair of self-recognizable terpyridine-based ligands and Cd^II ions. Building on this complementary ligand pairing system, herein three types of nanocapsules, including a dimeric capsule, a Sierpiński triangular prism, and a cubic star, could be readily obtained through dynamic complexation reactions between a tetratopic cavitand-based ligand and various multitopic counterparts in the presence of Cd^II ions. The dimeric capsular assemblies display the spacer-length-dependent self-sorting behavior in a four-component system. Moreover, the precise multicomponent self-assembly of a Sierpiński triangular prism and a cubic star possessing three and six cavitand-based motifs, respectively, demonstrates that such self-assembly methodology is able to efficiently enhance architectural complexity for calix[4]resorcinarene-containing metallo-supramolecules.

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.

Synthesis, luminescence, and electrochemical studies of a new series of octanuclear ruthenium(II) complexes of tolylterpyridine appended calixresorcarenes

A new series of octanuclear Ru(ii) complexes of tolylterpyridine appended calixresorcarenes [{Ru(ttpy)}8()](PF6)16 (), [{Ru(ttpy)}8()](PF6)16 (), and [{Ru(ttpy)}8()](PF6)16 () [ = 2,8,14,20-tetraethyl-4,6,10,12,16,18,22,24-octa(4'-p-benzyloxy-(2,2':6',2''-terpyridinyl))calix[4]resorcarene; = 2,8,14,20-tetraphenyl-4,6,10,12,16,18,22,24-octa(4'-p-benzyloxy-(2,2':6',2''-terpyridinyl))calix[4]resorcarene; and = 2,8,14,20-tetra-p-tolyl-4,6,10,12,16,18,22,24-octa(4'-p-benzyloxy-(2,2':6',2''-terpyridinyl))calix[4]resorcarene] have been synthesized and characterized. The tetraethyl-, tetraphenyl-, and tetra-p-tolylcalixresorcarenes (), (), and (), respectively, are characterized by single crystal X-ray diffraction: () a = 13.5771(4) Å, b = 7.9566(3) Å, c = 18.3912(6) Å, α = γ = 90°, β = 103.146(2)°, V = 1934.69(11) Å(3), Z = 2, monoclinic, P2/n; () a = 11.9710(8) Å, b = 12.7057(9) Å, c = 13.8570(9) Å, α = 94.731(2)°, β = 108.558(2)°, γ = 106.657(2)°, V = 1878.9(2) Å(3), Z = 1, triclinic, P1[combining macron]; and () a = 26.076(3) Å, b = 20.056(2) Å, c = 16.0193(19) Å, α = γ = 90°, β = 116.056(3)°, V = 7526.3(14) Å(3), Z = 4, monoclinic, C2/c, respectively. The octanuclear complexes are nonluminescent at 298 K, but exhibit (3)MLCT luminescence at 654, 649, and 646 nm, respectively, at 77 K in acetonitrile. In the solid state at 298 K they exhibit (3)MLCT luminescence at 658, 658, and 665 nm, respectively. The complexes exhibit a monoexponential decay profile in acetonitrile and in the solid state at 298 K. The redox active hosts containing eight [Ru(ttpy)2](2+) moieties undergo quasireversible one-electron oxidation at 1.25, 1.26, and 1.25 V versus Ag/Ag(+), respectively, in acetonitrile. The study demonstrates the versatility of the octanucleating calixresorcarene based ligands , , and in forming octanuclear Ru(ii) complexes.

Self-assembled capsules based on tetrafunctionalized calix[4]resorcinarene cavitands

The hemispherical structures of calix[4]resorcinarene cavitands are suitable for forming capsular assemblies with guest encapsulations through various intermolecular interactions.

Transporting and shielding photosensitisers by using water-soluble organometallic cages: a new strategy in drug delivery and photodynamic therapy

Skin photosensitivity remains one of the main limitations in photodynamic therapy. In this Concept article a strategy to overcome this limitation is described, in which the photosensitizer is hidden inside the hydrophobic cavity of a water-soluble organometallic cage. The metallacage not only protects the photosensitizer from light, it also facilitates its delivery to cancer cells.

Self-assembly of isomeric clamshell dimers of platinum(II)

The controlled synthesis of isomeric organoplatinum clamshell dimers [Pt(2)Me(2)(μ(2)-κ(3)-6-dppd)(2)](2+), 6-dppd = 1,4-di-2-pyridyl-5,6,7,8,9,10-hexahydrocycloocta[d]pyridazine, is reported. The new complexes are formed selectively by self-assembly from mononuclear precursors, taking advantage of the slow cis-trans isomerization at platinum(II). Thus reaction of endo-[PtClMe(κ(2)-6-dppd)] with AgOTf gave endo,endo-[Pt(2)Me(2)(μ(2)-κ(3)-6-dppd)(2)](2+), while the reaction of [PtMe(2)(κ(2)-6-dppd)] with HOTf in solvent S = Me(2)C=O or MeCN gave first a mixture of exo- and endo-[PtMe(S)(κ(2)-6-dppd)](+) and then, by loss of solvent, a mixture of exo,exo- and endo,endo-[Pt(2)Me(2)(μ(2)-κ(3)-6-dppd)(2)](2+). The endo,endo isomer slowly isomerized to the more stable exo,exo isomer in solution. Reaction of PPh(3) with endo-[PtClMe(κ(2)-6-dppd)] gave a mixture of endo- and exo-[PtMe(PPh(3))(κ(2)-6-dppd)](+) but reaction with exo,exo-[Pt(2)Me(2)(μ(2)-κ(3)-6-dppd)(2)](2+) gave exo-[PtMe(PPh(3))(κ(2)-6-dppd)](+) selectively, with retention of stereochemistry. The structures of the clamshell dimers and of key precursors are reported and equilibria are studied both experimentally and by DFT calculations.

Dimeric capsules formed by tetra-CMPO derivatives of (thia)calix[4]arenes

Thiacalix[4]arene 2, calix[4]arene 3a and its tetraether fixed in the cone conformation 3b form homo- and heterodimeric capsules in apolar solvents, which are held together by a seam of NH...O=P hydrogen bonds between carbamoylmethyl phosphine oxide functions attached to their wide rim. Their internal volume of approximately 370 A(3) requires the inclusion of a suitable guest. Although neutral molecules such as adamantane (derivatives) or tetraethylammonium cations form kinetically stable complexes ((1)H- and (31)P-time scale), the included solvent is rapidly exchanged. The internal mobility of the included tetraethylammonium cation is distinctly higher (DeltaG=42.5 and 49.7 kJ mol(-1) for 3a and 3b) than that for similar capsules of tetraurea calix[4]arenes 1. Mixtures of 1 with 2, 3a, or 3b contain only the two homodimers but the heterodimerization occurs with the tetraloop tetraurea 6, which cannot form homodimers. Two dimers with cationic guests (2.(C(5)H(5))(2)Co(+).2 and 3a.Et(3)NH(+).H(2)O.3a) were confirmed by single-crystal X-ray analysis.

Binding mechanisms in supramolecular complexes

Supramolecular chemistry has expanded dramatically in recent years both in terms of potential applications and in its relevance to analogous biological systems. The formation and function of supramolecular complexes occur through a multiplicity of often difficult to differentiate noncovalent forces. The aim of this Review is to describe the crucial interaction mechanisms in context, and thus classify the entire subject. In most cases, organic host-guest complexes have been selected as examples, but biologically relevant problems are also considered. An understanding and quantification of intermolecular interactions is of importance both for the rational planning of new supramolecular systems, including intelligent materials, as well as for developing new biologically active agents.