Jacqueline R. Ferrer

Instituto de Nanociencia y Materiales de Aragón

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Paul M. Lahti

University of Massachusetts Amherst

Clifford George

National Institutes of Health

Guillermo Antorrena

Universidad de Zaragoza

Fernando Palacio

Fundación Universitaria Tecnológico Comfenalco Cartagena

Burak Esat

Fatih University

M. Julier

Consejo Superior de Investigaciones Científicas

Kenneth A. Marby

Edimer Pharmaceuticals (United States)

Yanbing Liu

Affiliated Hospital of Qingdao University

Chunping Xie

University of Massachusetts Amherst

Fernando Palacio

Universitat Politècnica de Catalunya

Cooperative Institutions

University of Massachusetts Amherst

Instituto de Nanociencia y Materiales de Aragón

Universidad de Zaragoza

Consejo Superior de Investigaciones Científicas

Osaka University

University of Cambridge

Universidade de São Paulo

Instituto de Ciencia de Materiales de Sevilla

Fatih University

Université de Montpellier

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ChemInform Abstract: Polymeric, H‐Bonded, and Chelatable Phenoxyl and Nitroxide Radicals

ChemInform (2000)

Paul M. Lahti Burak Esat Jacqueline R. Ferrer Yanbing Liu Kenneth A. Marby

Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

10.1002/chin.200010270

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Citations (0)

Role of Hydrogen Bonds in Benzimidazole-Based Organic Magnetic Materials: Crystal Scaffolding or Exchange Linkers?

Chemistry of Materials (2001)

Jacqueline R. Ferrer Paul M. Lahti Clifford George P.B. Oliete M. Julier

The highly stable nitroxide radicals 5(6)-chloro-2-(N-tert-butyl-N-aminoxyl)benzimidazole (4) and 5,6-dimethyl-2-(N-tert-butyl-N-aminoxyl)benzimidazole (5) were synthesized and characterized by electron spin resonance spectroscopy, crystallography, and magnetic susceptibility. Both crystallize as dimeric pairs with N−H hydrogen bond donors and N−O acceptors. This behavior contrasts to that of analogous 2-(N-tert-butyl-N-aminoxyl)benzimidazole (3), which forms hydrogen-bonded chains (Ferrer, J. R.; Lahti, P. M.; George, C.; Antorrena, G.; Palacio, F. Chem. Mater. 1999, 11, 2205−2210). Susceptibility analysis shows dimeric antiferromagnetic exchange coupling with J/k = −22 K for 4 and −24 K for 5. Density functional theory (DFT) computations support a N−O to N−O throughspace antiferromagnetic exchange mechanism as the major contributor to the overall magnetic behavior of 4 and 5. A spin−polarization exchange coupling mechanism involving a cyclic exchange path using the −N−H···O−N hydrogen bonds in the dimers is expected to yield ferromagnetic coupling between dimers, in contradiction to the experimental and DFT results. The hydrogen bonds in 4 and 5 thus act more as structural scaffolding to hold the radicals in proximity rather than as electronic exchange linkers.

Benzimidazole

10.1021/cm010322h

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Citations (33)

Heat Capacity and Antiferromagnetic Phase Transition of the Organic Free Radical Magnet, 2-tert-Butylaminoxylbenzimidazole (BABI)

The Journal of Physical Chemistry B (2002)

Yuji Miyazaki Takeshi Sakakibara Jacqueline R. Ferrer Paul M. Lahti Guillermo Antorrena

Heat capacities of the organic free radical magnet 2-tert-butylaminoxylbenzimidazole (BABI) have been measured in the 0.2−300 K range by adiabatic calorimetry for investigation of its magnetic properties from a thermodynamic viewpoint. An antiferromagnetic phase transition was observed at TN = 1.7 K. A heat capacity hump arising from short-range spin ordering characteristic of low-dimensional magnets was found around 2 K. The magnetic enthalpy and entropy were determined to be 17.4 J mol-1 and 5.34 J K-1 mol-1, respectively. The magnitude of the magnetic entropy is in good agreement with the theoretical value for the magnetic ordering of spin quantum number S = 1/2 systems, R ln 2 = 5.76 J K-1 mol-1, where R is the gas constant. The heat capacity hump above TN is well reproduced by the S = 1/2 two-dimensional antiferromagnetic bilayer Heisenberg model with the intralayer interaction J1/kB = −1.2 K and the interlayer interaction J2/kB = −1.9 K, where kB is the Boltzmann constant. The bilayer model gives a close fit to both the present calorimetric and previously reported magnetic data with very similar intra- and interlayer exchange interaction parameters. Lower dimensionality models (such as dimeric interaction) for the magnetic and heat capacity behavior are not consistent with experimental results.

10.1021/jp020630i

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Citations (14)

Polymeric, H-Bonded, and Chelatable Phenoxyl and Nitroxide Radicals

Molecular crystals and liquid crystals science technology. Section A, Molecular crystals and liquid crystals/Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals (1999)

Paul M. Lahti Burak Esat Jacqueline R. Ferrer Yanbing Liu Kenneth A. Marby

Abstract Various examples are described of a multi-strategy approach to improvement of multispin exchange design. For example, H-bonded benzimidazole 4-t-butylnitroxide shows apparent simple planar 2D-type interaction, with a Weiss constant of Θ = −4.24 K and an intraplane exchange interaction of J = −1.60 K.

Benzimidazole

Exchange interaction

Constant (computer programming)

10.1080/10587259908023326

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Citations (9)

Hydrogen-bonded benzimidazole-based tert-butylnitroxides

Polyhedron (2001)

Paul M. Lahti Jacqueline R. Ferrer Clifford George P.B. Oliete M. Julier

Benzimidazole

Heisenberg model

10.1016/s0277-5387(01)00637-4

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Citations (24)

Synthesis, Crystallography, and Magnetic Properties of 2-tert-Butylaminoxylbenzimidazole

Chemistry of Materials (1999)

Jacqueline R. Ferrer Paul M. Lahti Clifford George Guillermo Antorrena Fernando Palacio

The title nitroxide is stable at room temperature for months. ESR spectroscopy shows moderate spin delocalization from the nitroxide unit onto the benzimidazole unit. The radical crystallizes in the orthorhombic Pbca space group, forming columns that are joined by hydrogen bonds into a pseudo-2D motif. Magnetic susceptibility studies of a polycrystalline sample at low temperatures are best fit to a simple planar 2D Heisenberg model with S = 1/2 spin sites, having a Weiss constant of θ = −4.24 K and an intraplane exchange interaction of J/k = −1.60 K. Computational modeling of various close-contact dimeric interactions in the crystal structure suggest that the largest interaction in the system occurs between nearby nitroxide units related by a center of inversion and that this interaction is responsible for the overall antiferromagnetic interaction observed.

Orthorhombic crystal system

10.1021/cm990149d

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Citations (27)