A Self‐Assembled Tetracopper Triple‐Stranded Helicate: Towards the Controlled Synthesis of Finite One‐Dimensional Magnetic Chains

Abstract

The majority of self-assembled metallic helicates contain two metal centers, whilst those containing three or more remain quite rare.[1] The limitation to synthesizing high-nuclearity helicates appears to be the design of the organic ligand, since double-and quadruple-stranded helicates containing five [2] and nine [3] metal centers, respectively, have been reported. This is in contrast to triple-stranded helicates, which have not progressed beyond the inclusion of three metal centers.[4] The apparent lack of high-nuclearity helicates has undoubtedly limited the exploitation of these systems, which is currently driven towards the development of molecular devices having predetermined properties and functions such as chirality, [5] energy transfer, [6] metal-metal bonding, [7] and DNA groove binding. [8] Surprisingly, helicates exhibiting magnetic exchange remain scarce, [9] since the adjacent metal ions are often bridged by long spacers that preclude viable superexchange pathways. However the preparation of high-nuclearity helicates with adjacent metal centers bridged by a single atom, or groups of atoms, provide an ideal opportunity to study the magnetic exchange between fixed numbers of paramagnetic metal centers in an isolated finite one-dimensional (1D) system. These systems could serve as useful models to provide further insights into the magnetic properties of infinite 1D magnetic-chain compounds, [10] which occupy an intermediate position between zero-dimensional clusters and 3D extended lattices, and as building blocks for future supramolecular devices.[11] Consequently we have embarked upon a program to exploit the helical structural

Self-Assembly of an Infinite Copper(II) Chiral Metallohelicate

“…1 During the past two decades, the study of helicates, that is, metal-containing helices, 2 has turned into an important area of supramolecular chemistry. 3,4 Helical complexes are not only the subject of much scientific interest because of aesthetic reasons but increasingly also for their potential applications in catalysis, 5 magnetochemistry, 6 or DNA groove binding. 7 From the different synthetic approaches to generate artificial, self-organized helices, the use of coordination chemistry has proven to be quite effective.…”

2-(1H-pyrazol-3-yl)pyrazine: a polytopic N-donor ligand used to construct Cu-[2+2] molecular grid: synthesis, structure, and magnetic properties

“…The choice of ligand lies in two main factors, namely, rigidity (to minimize variability) and the use of polytopic coordination sites (to ensure multiple metal centers are coordinated) (e.g. pyridazine, pyrimidine, phenoxide) [7][8][9][10][11][12][13][14]. N 3 -(2-pyridoyl)-2-pyridinecarboxamidrazone and analogs are often employed to construct homometallic or heterometallic [2þ2] molecular grids [1][2][3].…”

Aggregation of [Cu${{\bf }{{{\bf II}\hfill \atop \bf 4\hfill}}}$] Building Blocks into [Cu${{\bf }{{{\bf II}\hfill \atop \bf 8\hfill}}}$] Clusters or a [Cu${{\bf }{{{\bf II}\hfill \atop \bf 4\hfill}}}$]∞ Chain through Subtle Chemical Control

“…Such an arrangement of 3d metals is of particular interest in the study of magnetic interactions within molecular magnets, and remarkable success has been achieved in this direction with polydentate N-ligands. [13][14][15] The new ligand H 3 L possesses three ionizable protons that can be removed gradually and this has allowed the preparation of a variety of complexes with different metals featuring various nuclearities. [16][17][18][19][20] These complexes contain the ligand in its di-or trianionic form, depending on the amount of basic equivalents used in the reaction system.…”