TRIIRON CLUSTERS CONTAINING MIXED BRIDGING LIGANDS FOR THE STUDY OF DINITROGEN REDUCTION
Ricardo B. Ferreira and Leslie J. Murray
Center for Catalysis, Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, United States
Biological systems employ polynuclear clusters for the biological activation of small molecule substrates in a way to promote multi-electron redox reactions. For instance, biological N2 fixation is a process that involves a six-electron reduction and it is catalyzed by a family of metalloenzymes called nitrogenases. The most abundant nitrogenase is the molybdenum-dependent nitrogenase found in diazotrophs that contains the iron-molybdenum cofactor (FeMoco) in its active site – a cluster composed of seven Fe and one Mo atoms bound through bridging sulfides. There are evidences for the presence of hydride bridges in the FeMoco during the N2 reduction and such ligands are believed to act as sites for storage of electron and proton equivalents, having an essential role in the N2-binding and reduction. For these reasons, we are investigating the synthesis and reactivity of bromide- and sulfide-bridged triiron clusters and specifically, that of mixed sulfide-hydride systems. In this work, we will discuss our ongoing efforts to synthesize and examine the reactivity of such clusters.
CONDUCTING CHARGE TRANSFER SALTS of Fe(II) COMPLEXES WITH TCNQ RADICALS
Okten Ungor, Hoa Phan, and Michael Shatruk
Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA
Fe(II) complexes with ligands of an intermediate ligand field strength show magnetic bistability, i.e. switching between the high-spin and low-spin electronic configurations driven by changes in temperature, pressure, or photoexcitation. We are interested in designing multi functional materials that exhibit both spin crossover (SCO) and conductivity by combining para-magnetic Fe(II) cationic complexes and TCNQ·– anion radicals. It is expected that the latter should provide conducting pathways via the formation of p-p interacting stacks in the solid state structure. The synthetic strategy toward such hybrid materials is two-pronged: first, the TCNQ·– anions can coordinate to Fe(II) ions that are partially protected by blocking ligands, in order to limit fast precipitation of extended structures; second, these anions can be co-crystallized with completely blocked Fe(II) centers. In both approaches, the goal is to obtain a hybrid crystal structure that features both conducting stacks of fractionally charged organic radicals and SCO Fe(II) complexes. We report the synthesis of several such complexes, which demonstrate significant conductivity values and, in some cases, SCO behavior.
Preparation of New Akoxy-Derivatives of the Carborane Anion, CB11H12
Christos Douvris, Austin Harris, Phoenix Sconzert, Kiran Boggavarapu
Department of Chemistry, McNeese State University
The carborane anion CB11H12 and its derivatives have received widespread attention in the recent years due to its weakly coordinating nature. This allows it to support highly reactive counterions such as H+, CH3+, R3Si+, and also make it able to mask empty coordination sites in the coordination sphere of transition metals. With this work, we report synthetic routes for the preparation of alkoxy derivatives, RO- with R = Me, Et, Pr, Bu, of the carborane anion and we explore the possibility for their application in non-coordination chemistry
Investigation of Magnetic Phase Transitions in CuFe2–xCoxGe2
Zachary P. Tener1, Sebastian Stoian2, Michael Shatruk1
1Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA
2National High Magnetic Field Laboratory, E. Paul Dirac Dr, Tallahassee FL, USA
A recent experimental investigation of CuFe2Ge2 revealed that this compound exhibits weak itinerant antiferromagnetism,1 in agreement with the earlier theoretical prediction.2 Based on the similarity of the electronic band structure of CuFe2Ge2 and recently discovered superconductor, YFe2Ge2,3 it has been suggested that proper doping into the former structure might suppress the antiferromagnetic ordering and lead to the superconducting state.2 Guided by the electronic structure calculations performed at the DFT level of theory, we pursued electron doping by exploring the entire range of isostructural solid solutions, CuFe2–xCoxGe2, with an incremental (0.2) increase in the Co content across the series. Magnetic measurements do reveal a gradual suppression of the AFM behavior with the increase in the Co content (x). The low-temperature investigation of the materials that appear at the borderline of AFM ordering might result in the discovery of a superconducting phase transition.
- May, A. F.; Calder, S.; Parker, D. S.; Sales, B. C.; McGuire, M. A. Sci. Rep. 2016, 6, 35325.
- Shanavas, K. V.; Singh, D. J. PLoS One 2015, 10, 1.
- Zou, Y.; Feng, Z.; Logg, P. W.; Chen, J.; Lampronti, G.; Grosche, F. M. Phys. Status Solidi - Rapid Res. Lett. 2014, 8, 928.
Family of Mn-Ce Clusters from Reductive Aggregation: Unusual Long Range Coupling through Ce(IV)
Sayak Das Gupta, Shreya Mukherjee, Khalil A. Abboud, and George Christou
Department of Chemistry, University of Florida, Gainesville FL 32611-7200, USA
Developing new synthetic routes to high nuclearity MnIII,IV clusters has been an integral part of the research in our group. Several years ago we reported a new synthetic method involving ‘reductive aggregation’ of MnO4- ions in the presence of excess RCO2H in MeOH. This approach gave several new Mn12 and Mn16 clusters. However, to date reductive aggregation has not been employed for the synthesis of heterometallic Mn clusters, and this has stimulated our present interest in extending this method to Mn-Ce chemistry. Using reductive aggregation, we have now obtained a family of related Mn-Ce clusters. This presentation will describe their structures and magnetic properties, including the identification of unusual long-range coupling between Mn ions separated by diamagnetic Ce(IV).
Multi-Iron Clusters as Functional Models for FeMo Cofactor: Exploring the Reactivity of Triiron-Hydride Clusters and Expanding the Ligand Toolbox
Brian Knight, Kevin J. Anderson, and Leslie J. Murray*
University of Florida
As a means to interrogating the fundamental chemical transformations effected by the iron-molybdenum cofactor (FeMoco), we have explored the development of novel ligands designed to generate multiiron compounds and the reactivity profiles of the resultant complexes. In particular, our reported triiron(II) tri(μ-hydride) species provides a platform to understand the reactivity of hydrides bound to high spin iron clusters. To that end, recent results on reductive elimination and oxidative addition, hydride transfer reactivity, and bond activation will be discussed. Notably, these reactivity manifolds are commonly invoked in catalytic cycles for biological metal cluster cofactors.