Supramolecular ‘flat’ Mn₉grid complexes—towards functional molecular platforms

Abstract

Flat, quantum dot like arrays of closely spaced, electron rich metal centres are seen as attractive subunits for device capability at the molecular level. Mn(II)9 grids, formed by self-assembly processes using 'tritopic' pyridine-2,6-dihydrazone ligands, provide easy and pre-programmable routes to such systems, and have been shown to exhibit a number of potentially useful physical properties, which could be utilized to generate bi-stable molecular based states. Their ability to form surface monolayers, which can be mapped by STM techniques, bodes well for their possible integration into nanometer scale electronic components of the future. This report highlights some new Mn(II)9 grids, with functionalized ligand sites, that may provide suitable anchor points to surfaces and also be potential donor sites capable of further grid elaboration. Structures, magnetic properties, electrochemical properties, surface studies on HOPG (highly ordered pyrolytic graphite), including the imaging of individual metal ion sites in the grid using CITS (current imaging tunneling spectroscopy) are discussed, in addition to an analysis of the photophysics of a stable mixed oxidation state [Mn(III)4Mn(II)5] grid. The grid physical properties as a whole are assessed in the light of reasonable approaches to the use of such molecules as nanometer scale devices.

Anion-tuning of supramolecular gel properties

“…This is probably due to the high number of heteronuclei present within a LMW gel, which is not necessarily seen in the case of other forms of gels. 94,95 Interestingly, the opposite effect was also clear. In cases where prevention of convection currents and rapid nucleation by the formation of the gel were seen, fewer crystals grew in comparison to when a pure solvent mixture was used and found to be super-saturated upon which rapid crystallisations occurred.…”

“…In cases where prevention of convection currents and rapid nucleation by the formation of the gel were seen, fewer crystals grew in comparison to when a pure solvent mixture was used and found to be super-saturated upon which rapid crystallisations occurred. 94,95 Crystallisation from these LMWGs gels often led to the thermodynamically more stable polymorph being isolated from the gel state where commonly from pure solvents often both thermodynamic and kinetic forms are found.…”

“…[91][92][93][94][95][96][97][98][99][100][101][102][103] The improved physical characteristics (optical quality, improved size and fewer defects) and preferential crystallization of the more thermally stable polymorph of the gel-grown crystals over solution-grown crystals is usually ascribed to the suppression of convection currents, sedimentation and nucleation afforded by the viscous gel milieu. 94,95 It is generally accepted that the gel does not exert large mechanical forces on the growing crystal but there has been a recent increase in the understanding of the influence of chemical interactions between the gel and the molecules of the growing crystals. In this section, crystal growth within gels of compounds 2.1a and 2.2 is investigated with specific focus on the recovery of the grown crystals using the anion initiated degradation of the gel.…”

Lanthanide Complexes of Tritopic Bis(hydrazone) Ligands: Single-Molecule Magnet Behavior in a Linear DyIII3 Complex

“…La1 is 9-coordinate, while La2 and La3 are 10-coordinate. The overall structure differs from the trinuclear Pb II derivative 8 [(2pomp-2H) 2 Gd 3 (NO 3 ) 5 (DMF)](DMF) 2 (3). Crystallographic details for 3 are listed in Table 1, and a summary of important bond distances and angles is listed in Table 2 (for the full listing, see Table S3 in the Supporting Information).…”

“…Longerrange perchlorate bridges link the halves together to form a Pb 6 aggregate structure. 8 Typically, Ln III ions are smaller (102−86.1 pm for Ce III to Lu III ) than Pb II (133 pm), and so the possibility of lanthanide [n × n] grid formation with typical ditopic and tritopic hydrazone ligands encouraged us to explore their lanthanide coordination chemistry. The close proximity of the metal ions in such structures was considered an important feature for the creation of polymetallic systems with potential single-molecule magnet (SMM) behavior.…”