The objectives of this proposal include (1) the development of comprehensive synthetic methodology for precursors aiming at molecular switching and ultimately at information storage, (2) the introduction of an approach using complexes in which metal-ions in a five-coordinate environment enable stabilization and cycling of radicals, (3) the investigation of a series of electroactive ligands for modulation of redox and magnetic properties or (4) on the number of aromatic rings present, and (5) the use of these ligands and complexes as building blocks for bimetallic and multimetallic clusters. Here a progress report is offered:

For Goals 1 and 2 (Investigation of spectroscopic, electrochemical and magnetic properties of five-coordinate M(III) complexes  and Examination of the influence of aromatic groups on the electronic properties of five-coordinate M(III) complexes) the Verani Group has used ligand design to foster unusual geometries in trivalent metal centers and to enhance stable switching mechanisms (Inorg. Chem. 2006, 45,  955). Adding to the complex [Fe^IIIL¹], described previously, ongoing research focuses on a new class of complexes based on asymmetric ligands as prototypes for redox-driven switches. Some of the newly developed systems have shown improved redox cyclability allowing up to 100 oxidation/reduction cycles without decomposition. Characterization of these systems included multiple spectroscopic methods and a manuscript, possibly to Angewandte Chemie, is under preparation.

Expanding on the observations above, current research in molecular electronics gives considerable importance to molecules able to behave as switches when deposited onto surfaces. Therefore, efforts have been directed to functionalizing further these species in order to attain amphiphilic and self-assembly properties that allow for surface deposition and film formation. Related to Goal 3 ((Induction of redox and magnetic changes in heterospin modules by means of terminal ligands) considerable effort has been devoted to the development of metal-containing soft materials containing NN'O ligands that can later act as terminal ligands (Inorg. Chem. 2005, 44, 7414). The work has been expanded to using less labile cobalt(III) ions, and a newly developed ligand HL^t-BuLC and its first complex [Co^III(L^t-BuLC)₂]ClO₄ have been published (Dalton Trans. 2006, 2517). Owing to this initial success, an article will appear (Inorg. Chem. 2007 accepted) discussing the unexpected stabilization of cobalt(II) ions in similar NN'O environments with iodo-substituted phenolates. Both EPR and DFT approaches agree on high spin S= 3/2 electronic configurations given by [a_g¹,b_1g¹,a_g¹,b_2g²,b_3g²]. Two metallosurfactants, [Co^II(L^I-ODA)₂] and [Co^II(L^I-NOBA)₂] were obtained and exhibit amphiphilic properties, as observed by compression isotherms and Brewster angle microscopy. The monolayers of  [Co^II(L^I-ODA)₂] are only stable at low surface pressures while at higher pressures multilayer domains are present. The [Co^II(L^I-NOBA)₂] shows an improved monolayer behavior with collapse at 65 mN.m^-1. The main contribution of this article is the observation that the nature of the substituents in the phenol ring controls stabilization of Co(II) in amphiphiles. It also suggests [Co^II(L^I-NOBA)₂] as suitable for responsive monolayers. This information is pivotal for ongoing research aiming the development of (i) second-generation ligands containing distinctive rigidity to enhance the stability of monolayers at higher surface pressures, thus leading to highly ordered assemblies, (ii) precursors with different metal ions leading to specific optic (e.g. colorless Cu⁺ to green Cu²⁺) or redox (e.g. Fe²⁺/Fe³⁺) properties, as well as (iii) the manufacture of responsive Langmuir-Blodgett films on solid substrates with these materials.

While developing Goal 4 (Generation of homo/heterospin clusters with the module [Fe^IIIL²]), we have observed and pursued synthetic routes that allow for the incorporation of metal clusters into soft materials. Clusters show distinctive magnetic and redox behavior, and their capacity for forming organized films is regarded as highly useful for information technology and display. A study was accepted for publication (Chem. Eur. J. 2007) in which a general approach toward amphiphilic systems bearing multimetallic clusters, and their ability to form Langmuir-Blodgett films, is presented. The synthetic strategy to stabilize these clusters involved an N₂O-ligand HL with bilateral C₁₈-alkyl chains to obtain the [L₂Cu₄(μ₄-O)(μ₂-OAc)₄] and [L₂Cu₄(μ₄-O)(μ₂-OBz)₄], (OAc^- = acetate and OBz^- = benzoate). These species had their structures solved and it was observed that the Cu₄ cluster is antiferromagnetically coupled. The amphiphilic properties of the systems were studied by compression isotherms and allow for transfer onto solid substrates yielding homogeneous Langmuir-Blodgett films. These were characterized by atomic force microscopy and contact angle measurements. Another article was published in which one of the complexes present thermotropic mesomorphism (Inorg. Chem. 2006,  45,  7587). The main contribution of these articles was to demonstrate the synthetic feasibility of soft materials containing large clusters.

This research will pave the road to the generation of ordered responsive films composed of coordination complexes, thus pivotal for device fabrication in molecular electronics. The ACS-Petroleum Research Fund support has made possible for the PI and one graduate student to engage in this program and will be fundamental for the further development of the PI's career. All publications acknowledge the agency.