Magnetic tuning of all-organic binary alloys between two stable radicals.
Mixtures of 2-(4,5,6,7-tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (F4BImNN) and 2-(benzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (BImNN) crystallize as solid solutions (alloys) across a wide range of binary compositions. (F4BImNN)(x)(BImNN)((1-x)) with x < 0.8 gives orthorhombic unit cells, while x ≥ 0.9 gives monoclinic unit cells. In all crystalline samples, the dominant intermolecular packing is controlled by one-dimensional (1D) hydrogen-bonded chains that lead to quasi-1D ferromagnetic behavior. Magnetic analysis over 0.4-300 K indicates ordering with strong 1D ferromagnetic exchange along the chains (J/k = 12-22 K). Interchain exchange is estimated to be 33- to 150-fold weaker, based on antiferromagnetic ordered phase formation below Néel temperatures in the 0.4-1.2 K range for the various compositions. The ordering temperatures of the orthorhombic samples increase linearly as (1 - x) increases from 0.25 to 1.00. The variation is attributed to increased interchain distance corresponding to decreased interchain exchange, when more F4BImNN is added into the orthorhombic lattice. The monoclinic samples are not part of the same trend, due to the different interchain arrangement associated with the phase change.
Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003, USA.
Gonca
G
Seber
Rafael S
RS
Freitas
Joel T
JT
Mague
Armando
A
Paduan-Filho
Xavier
X
Gratens
Valdir
V
Bindilatti
Nei Fernandes
NF
Oliveira
Naoki
N
Yoshioka
Paul M
PM
Lahti
D005609:Free Radicals / Q000737:chemistry; D008280:Magnetics; D008958:Models, Molecular; D015394:Molecular Structure; D009930:Organic Chemicals / Q000737:chemistry*; D013696:Temperature
D005609:Free Radicals; D009930:Organic Chemicals