A Sandwich‐Shaped Hexanuclear Silver Complex with a Giant Cavity Constructed from a Macrocycle with Inward Chelating Units

External Phosphate Binding Triggered Formation of Coordination Bridged Dimer of Macrocyclic Trinuclear Complex

Macrocyclic complexes with spatially-arranged coordination sites have the potential to create unique supramolecular systems that combine the precise switching of self-assembled structures with the coordinative recognition of specific molecules. We now report a macrocyclic trinuclear Zn complex that undergoes a unique dimerization by molecular binding from the outside. The multinuclear complex was synthesized from a trispap ligand, a designed macrocyclic trimer of an N,N,O-type tridentate chelating unit pap. This macrocyclic ligand is capable of fixing the metal centers and retaining their exchangeable coordination sites. The macrocyclic trimer reacts with zinc acetate to form the trinuclear complex, in which the coordination sites of the three zinc atoms are aligned perpendicular to the macrocyclic plane and capped with the acetates. Subsequently, phosphate anion, PO4 3-, coordinates from one side of the macrocycle in a tripodal manner. This phosphate binding produced an electrically-neutral complex moiety with available coordination sites on the other side of the macrocycle which leads to the formation of the coordination-bridged dimer.

Formation of a Metallomacrocycle Possessing Nitrogen Donors Assembled in the Cavity and Unique Water Clusters

2,2'-Bipyridyl (bpy) is widely used as a chelating unit for metal complexation but is not usually considered as a hydrogen-bonding unit. This is because the metal-free bpy units are usually in a transoid conformation, and the two nitrogen lone pairs are pointed to the opposite sides. We now report a metallomacrocycle whose three metal-free bpy units are in a cisoid conformation and are fixed in the cavity. The complexation of nickel(II) only at the salen units of the triangular bpytrisalen ligand produced this rigid and planar macrocycle. Its cavity is surrounded by hydrogen-bond acceptors (N of bpy and O of salen), and it was found that unique pentagonal prism clusters of water molecules templated by the cavity were formed in the crystal. This study has not only increased the variation of the synthetic methodologies of multinuclear complexes but has also provided the structural platform on which multiple bpy units exert hydrogen-bonding functions.

Synthesis of a macrocyclic oligomer of pyridylbenzoxazole utilizing dynamic covalent bonds and its unsymmetric conversion

A new unsymmetric macrocycle was synthesized by an effective and high yield 3-step synthesis, which was composed of macrocyclization, irreversible conversion, and desymmetrization. The dynamic nature of imine bonds as well as selective conversion based on strain release were utilized. Moreover, the unsymmetric macrocycle formed an interesting bivalve-like 2 : 1 complex with zinc.

Hexa- and octanuclear copper(II) complexes with a tetraeicosaaza amine macrocycle

One hexa- and two octanuclear Cu(II) complexes were synthesised from different metal salts and a very large (8 + 8) tetraeicosaaza macrocycle. These nitrate, chloride and sulphate coordination compounds were characterised by taking elemental analysis, spectroscopy, crystallography and magnetic susceptibility measurements. Their crystal structures revealed different interesting coordination modes of Cu(II) cations and nuclearity in these centrosymmetric complexes. For the sulphate complex two different, homo- vs. heterochiral, arrangements of the same macrocycle L3 around the same Cu(II) cations take place.

Site-Selective Ligand Bridging among Multiple Internal Coordination Sites of a Metallomacrocycle and Its Conformational Regulation

Metallomacrocycles with internal coordination sites have a high potential to precisely control the positions of the guest ligands and the overall shape of the assemblies by utilizing the directionality and reversibility of the coordination bonds. However, when such coordinative hosts possess multiple coordination sites, it was difficult to control to which coordination sites the incoming guest ligands bind, because such systems often result in a random, uncontrolled mixture. The metallomacrocycle that we now report, a hexanuclear palladium complex of hexapap possessing six internal coordination sites, can take two different conformations depending on the guests. One is an Alternate conformation, in which six coordination sites of pap alternatively point to Up-Down-Up-Down-Up-Down. The other is a Twisted conformation, in which the coordination sites direct Up-Middle-Down-Up-Middle-Down. Interestingly, linear ditopic α,ω-diamines are captured in three distinct cross-linking modes, and regulations between the two macrocyclic conformations have been realized by the lengths of the diamines. Furthermore, the heteroleptic site-selective bridging of two kinds of diamines has been achieved. It has been demonstrated that a slight difference in the diamine lengths leads to a significant change in the structure and selection of the produced host-guest macrocyclic complexes.

Multinuclear Ni(II) and Cu(II) complexes of a meso 6 + 6 macrocyclic amine derived from trans-1,2-diaminocyclopentane and 2,6-diformylpyridine

Four hexanuclear chloride and sulphate Ni(II) and Cu(II) complexes 1, 2, 4 and 5 and one tetranuclear nitrate Cu(II) complex 3 have been synthesised from appropriate metal salts and 6 + 6 octadecaaza macrocyclic ligands. All obtained coordination compounds have been characterised by elemental analysis, spectroscopic methods (ESI MS, NMR and EPR), magnetic susceptibility measurements and X-ray crystallography. Their X-ray crystal structures reveal different coordination modes of metal cations involved in the obtained centro-symmetrical coordination compounds. The conformational folding of the macrocyclic ligand adopted in the respective complexes depends on the number of metal cations bound within the macrocycle but not on their type. The cavities of these multinuclear complexes might be occupied by solvent molecules and counter anions bound by hydrogen bonds or might be empty in the case where the macrocyclic ring of the ligand is squeezed in the middle. All obtained Ni(II) and Cu(II) coordination compounds are paramagnetic. This has been proved by their ¹H NMR and EPR spectra and magnetic measurements. Direct current (DC) variable-temperature magnetic susceptibility measurements on the polycrystalline samples of 1-5 were carried out in the temperature range of 1.8-300 K. The magnetic behaviour of 1 and 2 is dominated by the magnetic anisotropy of the nickel(II) ion masking the magnetic interactions between magnetic centres. The magnetic data of 3-5 reveal small antiferromagnetic interactions within the Cu₄ and Cu₆ units. EPR experiments for 3-5 show, at 9.6 and 34 GHz frequencies, that the predominant contribution to the orbitals occupied by the unpaired electrons in the ground state originates from d_x²-y².