Esther Breuning

Spin Crossover in a Supramolecular Fe4II [2×2] Grid Triggered by Temperature, Pressure, and Light

A multiplex electronic switch on the molecular level has been realized by using a tetranuclear FeII complex of the [2×2] grid type. The four metal ions can be switched stepwise between their high-spin and low-spin states by temperature, pressure, and light, thus representing a triple level, triple switch system as illustrated in the picture.

Two-Level Self-Organisation of Arrays of [2×2] Grid-Type Tetranuclear Metal Complexes by Hydrogen Bonding

Here we report on the synthesis and characterisation of four new complexes of the [2×2] M4II grid-type (M = Co, Fe, Zn) with oligopyridine-derived ligands. The presence of aminopyrazine and aminopyrimidine moieties at the edge of the ligands potentially enables the formation of infinite hydrogen-bonded multi-grid networks. The ligands were synthesised by subsequent stannylations and Stille-type coupling reactions. The complexes were obtained by self-assembly of the ligand with the metal salt. The single-crystal X-ray structure was determined for the Co complex 7 containing aminopyrimidine as the hydrogen-bonding moiety [P1¯; a = 15.4976(4), b = 18.2114(6), c = 31.9538(10) A, α = 86.9809(13), β = 83.4137(18), γ = 67.2828(16)°]. The crystal structure reveals hydrogen bonding in one direction, thus forming infinite chains of grids, whereas in the second direction of a layer, only weak attractive interactions are found. Anions and solvent molecules are situated between the layers, thus inhibiting any direct interaction between them. Cocrystallisation of the complementary complexes should enable the recognition-controlled alternating arrangement of grids incorporating different metal ions in a chessboard-like manner.

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.