Giannis S. Papaefstathiou

Supramolecular Control of Reactivity in the Solid State: From Templates to Ladderanes to Metal−Organic Frameworks

We describe how reactivity can be controlled in the solid state using molecules and self-assembled metal-organic complexes as templates. Being able to control reactivity in the solid state bears relevance to synthetic chemistry and materials science. The former offers a promise to synthesize molecules that may be impossible to realize from the liquid phase while also taking advantage of the benefits of conducting highly stereocontrolled reactions in a solvent-free environment (i.e., green chemistry). The latter provides an opportunity to modify bulk physical properties of solids (e.g., optical properties) through changes to molecular structure that result from a solid-state reaction. Reactions in the solid state have been difficult to control owing to frustrating effects of molecular close packing. The high degree of order provided by the solid state also means that the templates can be developed to determine how principles of supramolecular chemistry can be generally employed to form covalent bonds. The paradigm of synthetic chemistry employed by Nature is based on integrating noncovalent and covalent bonds. The templates assemble olefins via either hydrogen bond or coordination-driven self-assembly for intermolecular [2 + 2] photodimerizations. The olefins are assembled within discrete, or finite, self-assembled complexes, which effectively decouples chemical reactivity from effects of crystal packing. The control of the solid-state assembly process affords the supramolecular construction of targets in the form of cyclophanes and ladderanes. The targets form stereospecifically, in quantitative yield, and in gram amounts. Both [3]- and [5]-ladderanes have been synthesized. The ladderanes are comparable to natural ladderane lipids, which are a new and exciting class of natural products recently discovered in anaerobic marine bacteria. The organic templates function as either hydrogen bond donors or hydrogen bond acceptors. The donors and acceptors generate cyclobutanes lined with pyridyl and carboxylic acid groups, respectively. The metal-organic templates are based on Zn(II) and Ag(I) ions. The reactivity involving Zn(II) ions is shown to affect optical properties in the form of solid-state fluorescence. The solids based on both the organic and metal-organic templates undergo rare single-crystal-to-single-crystal reactions. We also demonstrate how the cyclobutanes obtained from this method can be applied as novel polytopic ligands of metallosupramolecular assemblies (e.g., self-assembled capsules) and materials (e.g., metal-organic frameworks). Sonochemistry is also used to generate nanostructured single crystals of the multicomponent solids or cocrystals based on the organic templates. Collectively, our observations suggest that the organic solid state can be integrated into more mainstream settings of synthetic organic chemistry and be developed to construct functional crystalline solids.

Inverted metal-organic frameworks: solid-state hosts with modular functionality

Abstract Metal–organic frameworks (MOFs) are crystalline inorganic–organic hybrid materials that consist of metal ions and organic molecules connected in space to produce an infinite one-, two-, or three-dimensional framework. The modularity of MOFs, specifically, the ability to modify the organic and/or inorganic components, offers a ready means to modify and control properties of such materials (e.g. inclusion, magnetism). This review highlights the design and synthesis of cavity-containing and porous MOFs with emphasis on methods that enable the functionalization of interior void spaces with organic groups. A relatively new class of MOFs, known as inverted metal–organic frameworks (IMOFs), which enables organic functionalization using principles of supramolecular chemistry, is discussed. We also briefly outline methods to functionalize the interior spaces of mesoporous materials (MCMs) and zeolites, and suggest that MOFs offer a diverse space within which to place a wide range of organic functionalities.

Turn‐On Luminescence Sensing and Real‐Time Detection of Traces of Water in Organic Solvents by a Flexible Metal–Organic Framework

The development of efficient sensors for the determination of the water content in organic solvents is highly desirable for a number of chemical industries. Presented herein is a Mg(2+) metal-organic framework (MOF), which exhibits the remarkable capability to rapidly detect traces of water (0.05-5 % v/v) in various organic solvents through an unusual turn-on luminescence sensing mechanism. The extraordinary sensitivity and fast response of this MOF for water, and its reusability make it one of the most powerful water sensors known.

An Inverted Metal‐Organic Framework with Compartmentalized Cavities Constructed by Using an Organic Bridging Unit Derived from the Solid State

Porous crystalline solids that employ metal-organic components as building blocks, where a rigid, linear organic bridge propagates the coordination geometry of a metal node in one-, two-, or threedimensions, are attracting much interest.[1±3] Such metal ± organic frameworks (MOFs) are designed to exhibit properties that mimic, and improve upon, more conventional porous solids, such as zeolites[4] and mesoporous materials (MCMs).[5] Many porous MOFs, however, have fallen short, in contrast to zeolites and MCMs, as robust porous solids.[2, 6] Interpenetration[6] and framework fragility[2] have hampered progress such that host cavities tend to selfinclude while guest removal often results in a collapse of host structure. Recently, however, such problems of interpenetration and framework fragility have been largely circumvented by using metal clusters, as secondary building units (SBUs), for host design.[7] SBUs (e.g. metal carboxylates) reduce the likelihood of interpenetration owing to their large sizes which can preclude filling of void spaces,[8] producing stable, porous solids able to support inclusion and catalysis.[1a±c] Although SBUs have been successfully employed for the construction of MOFs with stable pores, it can be difficult, in contrast to MCMs,[5, 9] to line the interiors of such solids with organic groups since an elaborate covalent synthesis of a linear organic bridge is often required to introduce simple (e.g. -Me) and diverse (e.g. chiral) functional groups. With this in mind, it has occurred to us that one way to circumvent this problemmay be to invert the structural role[10] of the SBU and linear organic bridge such that the SBU serves as a linear bridge and the organic ligand serves as a node. In this design, the bonds of the SBU that support the framework are minimized (i.e. two) such that the remaining coordination sites of the SBU may be filled with organic ligands that decorate the interior of the framework. Moreover, such an inverted metal-organic framework (IMOF) would enable the second sphere of a SBU to line the walls of a host, in contrast to a covalent synthesis, supramolecularly[11] where convergent[12] terminal groups may be tailored to define structure and recognition properties of the solid. Herein, we describe initial results of a strategy for the construction of such a porous IMOF that employs a molecule

Di-2-pyridyl Ketone/Benzoate/Azide Combination as a Source of Copper(II) Clusters and Coordination Polymers: Dependence of the Product Identity on the Solvent

The reactions of di-2-pyridyl ketone with Cu(O2CPh)2 in the presence of NaN3 and LiOH have led to an antiferromagnetically coupled (S = 0) Cu(II)6 cluster with a novel core and to (Cu(II)8)n and (Cu(II)2)n coordination polymers (the former 1D and the latter 2D) with interesting structures. The cluster or polymer formation depends on the reaction solvent.

Chiral single-molecule magnets: a partial Mn(III) supertetrahedron from achiral components

A [Mn(III)(9)] partial supertetrahedron is a Single-Molecule Magnet (SMM) with an energy barrier to magnetisation reversal of ~30 K and represents the first chiral SMM obtained from achiral starting materials.

Insertion of Functional Groups into a Nd3+ Metal–Organic Framework via Single-Crystal-to-Single-Crystal Coordinating Solvent Exchange

Single-crystal-to-single-crystal (SCSC) transformations represent some of the most fascinating phenomena in chemistry. They are not only intriguing from a basic science point of view but also provide a means to modify or tune the properties of the materials via the postsynthetic introduction of suitable guest molecules or organic functional groups into their structures. Here, we describe UCY-2, a new flexible Nd(3+) metal-organic framework (MOF), which exhibits a unique capability to undergo a plethora of SCSC transformations with some of them being very uncommon. These structural alterations involve the replacement of coordinating solvent molecules of UCY-2 by terminally ligating solvents and organic ligands with multiple functional groups including -OH, -SH, -NH-, and -NH(2) or their combinations, chelating ligands, anions, and two different organic compounds. The SCSC coordinating solvent exchange is thus demonstrated as a powerful method for the functionalization of MOFs.

Onion-Shell Metal-Organic Polyhedra (MOPs): A General Approach to Decorate the Exteriors of MOPs using Principles of Supramolecular Chemistry

Metal-organic polyhedra with surface-exposed organic groups have been designed. The polyhedra are based on concentric shells of alternating negative-positive-negative charges and have been used to design homochiral hosts.

Diorganotin(IV) complexes of dipeptides containing the α-aminoisobutyryl residue (Aib): Preparation, structural characterization, antibacterial and antiproliferative activities of [(n-Bu)2Sn(H−1L)] (LH = H-Aib-L-Leu-OH, H-Aib-L-Ala-OH)

Two new organotin(IV) complexes with dianionic dipeptides containing the alpha-aminoisobutyryl residue (Aib) as ligands are described. The solid complexes [(n-Bu)(2)Sn(H(-1)L(A))] x 2MeOH (1 x 2MeOH) (L(A)H=H-Aib-L-Leu-OH) and [(n-Bu)(2)Sn(H(-1)L(B))] x MeOH (2 x MeOH) (L(B)H=H-Aib-L-Ala-OH) have been isolated and characterized by single-crystal X-ray crystallography and spectroscopic techniques (H(-1)L(2-) is the dianionic form of the corresponding dipeptide). Complexes 1 x 2MeOH and 2 x MeOH are monomeric with similar molecular structures. The doubly deprotonated dipeptide behaves as a N(amino), N(peptide), O(carboxylate) ligand and binds to the Sn(IV) atom. The five-coordinate metal ion has a distorted trigonal bipyramidal geometry. A different network of intermolecular hydrogen bonds in each compound results in very dissimilar supramolecular features. The IR, far-IR, Raman and (119)Sn NMR data are discussed in terms of the nature of bonding and known structures. The antibacterial and antiproliferative activities as well as the effect of the new compounds on pDNA were examined. Complexes 1 and 2 are active against the gram-positive bacteria Bacillus subtilis and Bacillus cereus. The IC(50) values reveal that the two compounds express promising cytotoxic activity in vitro against a series of cell lines.

Planar [Ni7] discs as double-bowl, pseudo metallacalix[6]arene host cavities

We report three heptanuclear [Ni7] complexes with planar disc-like cores, akin to double-bowl metallocalix[6]arenes, which form molecular H-bonded host cavities.