Gerhard Baum

THE DESIGN AND GENERATION OF INORGANIC CYLINDRICAL CAGE ARCHITECTURES BY METAL-ION-DIRECTED MULTICOMPONENT SELF-ASSEMBLY

The multicomponent self-assembly of ditopic linear ligands, circular ligands and copper(I) or silver(I) ions leads to the exclusive formation of a series of cylindrical inorganic architectures containing an internal cavity whose height may be modulated by the nature of the ligands used (see picture: 1: 20 A; 2: 33 A). The same reactions with tritopic and tetratopic linear ligands and circular tritopic ligands generates tri- (3) and tetracompartmental (4) cylindrical architectures of nanometric size in one stroke by a process involving the spontaneous positioning of up to 19 particles and the formation of up to 48 coordination bonds.

Self-Assembly and Structure of Interconverting Multinuclear Inorganic Arrays: A [4×5]-AgI20 Grid and an AgI10 Quadruple Helicate

Coordination of the pentatopic ligand 3 with AgI leads to the simultaneous self-assembly of two polynuclear architectures: a [4×5] grid-type species 10 and a quadruple-helicate 11, which contain twenty and ten silver ions, respectively. Their structures have been established by X-ray diffraction analysis of the crystals obtained as a mixture on crystallisation. Complex 10 contains two [2×5]-AgI10 rectangular subgrids located on opposite sides of an array of parallel ligands of 3 that are twisted into a transoid N=CC=N arrangement around the central CC bond; it may thus be formulated as a grid of grids: [2×(2×5)]. Complex 11 is an inorganic quadruple helicate that consists of two sets of two parallel ligands of 3 connected by an array of ten silver ions. Both compounds 10 and 11 are novel types of polynuclear complexes that are composed of two subunits. Their formation points to the possibility of generating specific arrays of metal ions by self-assembly, involving, in particular, a combination of subunits within the overall entity. They represent organised patterns of ion dots of special significance in view of their formal relationship to quantum dots.

Adaptive Self-Assembly: Environment-Induced Formation and Reversible Switching of Polynuclear Metallocyclophanes

Ligand 3 has been shown to self-assemble under coordination of copper(II) cations in a 1:1 ratio in acetonitrile to give equilibrating mixtures of a [2 x 2] grid-type tetranuclear structure 1 and a hexanuclear achitecture of hexagonal shape 2. The latter was confirmed by determination of the crystal structure which further indicated that 2 contained acetonitrile molecules and hydroxo groups bound to the copper(II) centers, which are therefore five-coordinate. The structures assigned to 1 and 2 were further supported by the spectral (mass, UV/Vis) data. The self-assembly process is strongly dependent on the conditions of the medium. An increase in concentration in acetronitrile increases the relative amount of hexamer 2, which appears to be the favored entity at the highest concentrations that can be reached before precipitation occurs. On the other hand, in nitromethane only the tetranuclear complex 1 was detected by mass spectrometry. Replacement of nitromethane by acetonitrile and vice versa indicated the reversible switching between a solution containing either 1 alone or an equilibrium mixture of 1 and 2, respectively. In conclusion, the system described presents several remarkable features: 1) self-assembly with substrate binding, 2) dynamic combinatorial structure generation, and 3) environment-induced structural switching amounting in effect to a process of adaptive self-assembly.

The Designed Self‐Assembly of Multicomponent and Multicompartmental Cylindrical Nanoarchitectures

The multicomponent self-assembly of ditopic linear ligands, circular ligands and copper(I) or silver(I) ions leads to the exclusive formation of a series of cylindrical inorganic architectures containing an internal cavity whose height may be modulated by the nature of the ligands used (see picture: 1: 20 A; 2: 33 A). The same reactions with tritopic and tetratopic linear ligands and circular tritopic ligands generates tri- (3) and tetracompartmental (4) cylindrical architectures of nanometric size in one stroke by a process involving the spontaneous positioning of up to 19 particles and the formation of up to 48 coordination bonds.

Stereoselective Double‐Helicate Assembly from Chiral 2,2′:6′,2″:6″,2′′′‐Quaterpyridines and Tetrahedral Metal Centres

PorMhelicates are formed in diastereoselective reactions of chiral 2,2′:6′,2″:6″,2′′′-quaterpyridine ligands with copper(I) and silver(I) salts.

SELF-ASSEMBLY AND CHARACTERIZATION OF MULTIMETALLIC GRID-TYPE LEAD(II) COMPLEXES

The formation of grid-type inorganic architectures of [2×2], [3×3], and [4×4] size (depicted here) occurs by self-assembly from lead(II) ions and ligands containing tridentate binding sites. Well-defined inorganic architectures of high complexity may thus be obtained in a single overall step by a spontaneous but controlled process.

Self-Assembly of Multicomponent Multimetallic Lead(II) Complexes of Cylindrical Architecture

Multicomponent self-assembly of two cylindrical inorganic architectures is achieved from ligands containing terpyridine-type coordination subunits and PbII cations. This extends such processes to a new class of ligands and of metal ions.

Self-Assembly, Structure, and Physical Properties of Tetranuclear ZnII and CoII Complexes of [2 × 2] Grid-Type

The tretrametallic [2 × 2] grid-type complexes 1–4 are formed by self-assembly of the bis(tridentate) ligands 5 and 6 with ZnII and CoII cations. They have been characterized by spectroscopic studies in solution as well as by crystal structure determination. The substituents in the central pyrimidine ring play an important role in terms of geometry and physical properties of the complexes. They induce an orthogonal orientation of the ligand in the complexes which is critical for the formation of ordered monolayers and extended self-organized arrays of grids. The physical properties of the complexes such as metal–metal interaction and π-π* stacking between the ligands may be modulated by changing these substituents.

A Novel Synthetic Approach to Highly Reactive Intermediates Containing a Metal-Phosphorus Triple Bond

A new synthetic route providing access to the highly reactive intermediate [Cp*(CO)2WPW(CO)5] with a tungsten-phosphorus triple bond is presented (see scheme). The intermediate is formed by thermolysis of [Cp*P{W(CO)5}2] by Cp* migration from the phosphorus to give 5 coordination at the transition metal. Addition of other reactive molecules to solutions conatining the intermediate provides a simple approach to novel W/P-containing ligands.

Recognition‐Directed Supramolecular Assemblies of Metal Complexes of Terpyridine Derived Ligands with Self‐Complementary Hydrogen Bonding Sites

The synthesis and X-ray structures of three metal complexes with terpyridine-derived ligands that contain amino-pyrimidine and amino-pyrazine moieties are presented. They have been designed in view of directing their self-assembly into specific supramolecular arrays through molecular recognition interactions. The solid-state structures indeed reveal extensive hydrogen-bonded networks. The Co complex 4a with PF6- counterions builds a two-dimensional infinite interwoven grid through strong double hydrogen bonds (d(N-H-N) =2.918-3.018 A) between the amino groups and the N atoms of the rings, with all H-bonding sites saturated. Changing the anions to BF4- in 4b leads to a similar infinite but partially broken grid with a quarter of the H-bonding sites unsaturated (d(N-H-N)=2.984-3.206 A). In the case of the Zn complex 12 with triflate anions, half of the hydrogen bonds are formed. Only one of the two orthogonal ligands has hydrogen bonds (d(N-H-N) = 3.082, 3.096 A) to the neighbouring complexes and thus builds linear, supramolecular, polymeric chains. These structural differences are mainly attributed to crystal-packing effects caused by the different anions. The data presented here may also be regarded as a prototype for the generation of organised arrays through sequential self-assembly processes.