F. Albert Cotton

Bio: F. Albert Cotton is an academic researcher from Florida State University. The author has contributed to research in topics: Extended metal atom chains & Magnetic susceptibility. The author has an hindex of 14, co-authored 15 publications receiving 769 citations. Previous affiliations of F. Albert Cotton include Sun Yat-sen University & University of Miami.

Molecular and Electronic Structures by Design: Tuning Symmetrical and Unsymmetrical Linear Trichromium Chains

Abstract: The preparation, properties, and crystal structures of 12 trichromium extended metal atom chain (EMAC) compounds of the type Cr3(L)4X2 (L = equatorial ligands dipyridylamide (dpa) or di-4,4‘-ethyl-2,2‘-pyridylamide (depa), and X = axial ligands, e.g., halide or pseudohalide ions) with large variations in metal−metal distances are reported here. These complexes, which belong to a broad class of fundamentally interesting trinuclear molecules over which the electrons may or may not be delocalized, pose significant theoretical and experimental challenges which are dealt with in this report. Complexes with strongly donating axial or equatorial ligands tend to favor a symmetrical (D4) molecular structure, while more weakly donating ligands give rise to unsymmetrical (C4) structures; the physical properties of these two classes of compounds are discussed fully, and important comparisons with a reported DFT model of the electronic structures of the compounds are made.

Additional Steps toward Molecular Scale Wires: Further Study of Ni510/11+ Chains Embraced by Polypyridylamide Ligands

Abstract: This paper presents two advances in the development of the chemistry of extended metal atom chains (EMACs) that employ di(2-pyridyl)amide (dpa) and its higher homologues (loosely called polypyridylamides). As EMACs employing these ligands are extended to greater lengths, low solubility becomes an increasingly difficult problem. Also, increased stability would be desirable. We have employed a method, which is designed to be applicable to chains of any length, to introduce stabilizing substituents (ethyl groups) on some of the pyridyl rings. We illustrate this here by the synthesis and characterization of the pentanickel complexes Ni5(etpda)4Cl2·6CHCl3 and [Ni5(etpda)4](PF6)3·4Me2CO, etpda = the anion of N,N‘-bis(4-ethylpyridyl)-2,6-diaminopyridine. As we had previously predicted, on the basis of the behavior of Ni3(dpa)4Cl2 and [Ni3(dpa)4](PF6)3, oxidation causes marked changes in structure and magnetic behavior indicative of a change of electronic structure that would cause an insulator−conductor transfor...

Observation of Symmetry Lowering and Electron Localization in the Doublet-States of a Spin-Frustrated Equilateral Triangular Lattice: Cu3(O2C16H23)·1.2C6H12

Abstract: Cu3(O2C16H23)6·1.2C6H12, containing a Cu36+ core in an equilateral triangle geometry, has been found to be a versatile model system for investigating the spin-frustration phenomenon in a triangular lattice. It affords well-resolved EPR spectra from both of the two possible (Stotal = 1/2 and 3/2) spin states of the Cu36+ core. From 295 to 100 K, the spectra consist of a triplet, but with the central line overlapped by an additional, sharp peak, which replaces the triplet at 30 K and below. The triplet was thus assigned to the excited state with Stotal = 3/2, located at 324 ± 5 K (∼225 cm-1), with the zero-field parameters D = −535 G, E = 0, g∥ = 2.209 and g⊥ = 2.057. The singlet was attributed to the Stotal = 1/2 state, with gxx = 2.005, gyy = 2.050, gzz = 2.282, and, surprisingly, a hyperfine splitting arising from a single Cu2+ nucleus, with Azz = 157 G. The detailed magnetic measurements on a three-electron, equilateral triangular system, and the observation of symmetry lowering in the doublet ground st...

Modeling spin interactions in a cyclic trimer and a cuboidal Co4O4 core with Co(II) in tetrahedral and octahedral environments.

Abstract: The X-ray crystallographic structures, the magnetic susceptibilities from 2 to 300 K, and a theoretical analysis of the magnetism for a triangular and a tetranuclear molecule consisting of linked high-spin cobalt(II) centers are described. The interpretation of the magnetic data for the triangular compound [Co(depa)Cl]3 (depa is the anion of 2,2‘-(bis-4-ethylpyridyl)amine), which has tetrahedrally coordinated Co2+ ions, entails isotropic antiferromagnetic exchange interaction and antisymmetric exchange acting within the two low-lying spin doublets. Two strong isotropic ferromagnetic interactions have been modeled in the cuboidal compound Co4(DPM)4(CH3O)4(CH3OH)4 (DPM represents the anion of dipivaloylmethane), which has octahedral coordination, and the system can be approximately considered as two weakly coupled S = 3 species.

Enhancing the stability of trinickel molecular wires and switches: Ni36+/Ni37+

Abstract: This paper describes in detail four new compounds that contain extended metal atom chains (EMACs) of three nickel atoms wrapped by either di(2-pyridyl)amide (dpa) or the new homologous ligand with an ethyl group at the para position of each pyridyl group, depa, and compares them to the precursor Ni 3 (dpa) 4 Cl 2 (1) and the oxidized and rather unstable Ni 3 (dpa) 4 (PF 6 ) 3 (2). The new molecules are Ni 3 (depa) 4 Cl 2 (3), Ni 3 (depa) 4 (PF 6 ) 3 (4), [Ni 3 (dpa) 4 (CH 3 -CN) 2 ](PF 6 ) 2 (5), and [Ni 3 (depa) 4 (CH 3 CN) 2 ](PF 6 ) 2 (6). These compounds are fully described as to preparation, elemental composition, structure, infrared spectra, 1 H NMR spectra (where possible), electrochemistry, magnetic susceptibility, and an EPR spectrum for 4. The effects of (a) introducing the ethyl substituents on the ligands, (b) replacing axial anions by neutral axial ligands, and (c) oxidizing the Ni 3 chains are reported and discussed. The point of major interest is how oxidation profoundly alters the electronic structure of the EMAC.

Insulated molecular wires.

Abstract: An astonishing assortment of structures have been described as "insulated molecular wires" (IMWs), thus illustrating the diversity of approaches to molecular-scale insulation. These systems demonstrate the scope of encapsulation in the molecular engineering of optoelectronic materials and organic semiconductors. This Review surveys the synthesis and structural characterization of IMWs, and highlights emerging structure-property relationships to determine how insulation can enhance the behavior of a molecular wire. We focus mainly on three IMW architectures: polyrotaxanes, polymer-wrapped pi systems, and dendronized polymers, and compare the properties of these systems with those of conjugated polymers threaded through mesoporous frameworks and zeolites. Encapsulation of molecular wires can enhance properties as diverse as luminescence, electrical transport, and chemical stability, which points to applications in electroluminescent displays, sensors, and the photochemical generation of hydrogen.

Bimetallic Pd(III) complexes in palladium-catalysed carbon–heteroatom bond formation.

Abstract: Palladium is a common transition metal for catalysis, and the fundamental organometallic reactivity of palladium in its 0, I, II and IV oxidation states is well established. The potential role of Pd(III) in catalysis has not been investigated because organometallic reactions that involve Pd(III) have not been reported previously. In this article we present the formation of carbon–heteroatom bonds from discrete bimetallic Pd(III) complexes and show the synergistic involvement of two palladium atoms of the bimetallic core during both oxidation and reductive elimination. Our results challenge the currently accepted mechanism for oxidative palladium catalysis via Pd(II)–Pd(IV) redox cycles and implicate bimetallic palladium complexes in redox catalysis. The new mechanistic insight provides an opportunity to explore rationally the potential of bimetallic palladium catalysis for synthesis.

Modern Transition-Metal-Catalyzed Carbon–Halogen Bond Formation

Abstract: The high utility of halogenated organic compounds has prompted the development of a vast number of transformations which install the carbon–halogen motif. Traditional routes to these building blocks have commonly involved multiple steps, harsh reaction conditions, and the use of stoichiometric and/or toxic reagents. In this regard, using transition metals to catalyze the synthesis of organohalides has become a mature field in itself, and applying these technologies has allowed for a decrease in the production of waste, higher levels of regio- and stereoselectivity, and the ability to produce enantioenriched target compounds. Furthermore, transition metals offer the distinct advantage of possessing a diverse spectrum of mechanistic possibilities which translate to the capability to apply new substrate classes and afford novel and difficult-to-access structures. This Review provides comprehensive coverage of modern transition metal-catalyzed syntheses of organohalides via a diverse array of mechanisms. Atte...