Supramolecular Self-Assembled Polynuclear Complexes from Tritopic, Tetratopic, and Pentatopic Ligands:  Structural, Magnetic and Surface Studies

Abstract

Polymetallic, highly organized molecular architectures can be created by "bottom-up" self-assembly methods using ligands with appropriately programmed coordination information. Ligands based on 2,6-picolyldihydrazone (tritopic and pentatopic) and 3,6-pyridazinedihydrazone (tetratopic) cores, with tridentate coordination pockets, are highly specific and lead to the efficient self-assembly of square [3 x 3] Mn9, [4 x 4] Mn16, and [5 x 5] Mn25 nanoscale grids. Subtle changes in the tritopic ligand composition to include bulky end groups can lead to a rectangular 3 x [1 x 3] Mn9 grid, while changing the central pyridazine to a more sterically demanding pyrazole leads to simple dinuclear copper complexes, despite the potential for binding four metal ions. The creation of all bidentate sites in a tetratopic pyridazine ligand leads to a dramatically different spiral Mn4 strand. Single-crystal X-ray structural data show metallic connectivity through both mu-O and mu-NN bridges, which leads to dominant intramolecular antiferromagnetic spin exchange in all cases. Surface depositions of the Mn9, Mn16, and Mn25 square grid molecules on graphite (HOPG) have been examined using STM/CITS imagery (scanning tunneling microscopy/current imaging tunneling spectroscopy), where tunneling through the metal d-orbital-based HOMO levels reveals the metal ion positions. CITS imagery of the grids clearly shows the presence of 9, 16, and 25 manganese ions in the expected square grid arrangements, highlighting the importance and power of this technique in establishing the molecular nature of the surface adsorbed species. Nanoscale, electronically functional, polymetallic assemblies of this sort, created by such a bottom-up synthetic approach, constitute important components for advanced molecule-based materials.

Self‐Assembly of Alkoxy‐Substituted Bis(hydrazone)‐Based Organic Ligands and of a Metallosupramolecular Grid on Graphite

“…[18,20] For such purposes, methods of assembling addressable metallogrid units on surfaces are highly important. While deposition of grids on surfaces, such as highly oriented pyrolytic graphite (HOPG) [24][25][26][27][28] and AuA C H T U N G T R E N N U N G (111), [29,30] has indeed proved possible, there is evidence that in the absence of external functionality promoting specific interactions with the substrate surface, the adsorbed layer may be disordered, unstable and not necessarily contain the grids in the orientation desired, that is, with the mean plane of the metal cluster lying parallel to the surface ("face-on" configuration). In fact, previous studies have revealed that the physisorption of molecular grids into a faceon configuration on the basal plane of HOPG is difficult to attain.…”

A Molecular Chain of Four CoII Ions Stabilized by a Tris-Pyridyl/Bis-?-Diketonate Ligand

“…[7] This strategy has been adopted successfully by other groups, for example, to deliberately obtain ferromagnetically exchanged clusters, [8] or to prepare magnetically active molecules in the form of grids. [9,10] Our focus has been two-fold. On the one hand, some of the ligands designed in our laboratory have proven appropriate for the preparation of stable molecules that contain two semi-independent and welldefined magnetic clusters.…”

Magnetic Coupling Constants of Self‐Assembled CuII [3×3] Grids: Alternative Spin Model from Theoretical Calculations

“…Sevilla (Spain) E-mail: calzado@us.es with a well-defined suite of redox waves in a narrow potential window. [5,16,17] In fact, although the ligands are spatially extended, the coordination pockets provide small bridges between the metal ions, with efficient electronic communication pathways among them. These magnetic and electronic properties, combined with the possibility of binding these grids to a surface in an ordered array, with footprints of about 2.5 2.5 nm 2 , [18] make these systems potential candidates as highdensity spatial media for information storage.…”