Spin Transition in [Fe(DPEA)(NCS)(2)], a Compound with the New Tetradentate Ligand (2-Aminoethyl)bis(2-pyridylmethyl)amine (DPEA): Crystal Structure, Magnetic Properties, and Mössbauer Spectroscopy.
The new spin transition compound [Fe(II)(DPEA)(NCS)(2)], where DPEA [(2-aminoethyl)bis(2-pyridylmethyl)amine] is a new tetradentate ligand, has been synthesized, and its structure, magnetic properties, and Mössbauer spectra have been investigated. The crystal structure has been determined by X-ray diffraction at 298 K. The compound crystallizes in the monoclinic system, space group is P2(1)/c, with Z = 4,a = 9.358(1) Å, b = 11.812(2) Å, c = 17.135(2) Å, and beta = 94.5(4) degrees. The distorted [FeN(6)] octahedron is formed from four nitrogen atoms belonging to DPEA and two provided by the cis thiocyanate groups. The two pyridine rings of DPEA are in mer positions. Each molecule is linked to its neighbors by hydrogen-bonding interactions as well as by numerous van der Waals contacts supposed to be responsible for the cooperativity of the system. Variable-temperature magnetic susceptibility measurements (20-290 K) have evidenced a relatively abrupt S = 2 right harpoon over left harpoon S = 0 transition centered at T(1/2) = 138 K. The thermal variation of the high spin state fraction observed by Mössbauer spectroscopy is in agreement with that obtained from magnetic susceptibility measurements. The fitting of Mössbauer and magnetic data with the Ising-like model allowed us to determine the energy gap between the high-spin and low-spin states (Delta(eff) = 835 K) and to estimate the variation of the thermodynamic parameters upon spin transition. The calculated variations of enthalpy (DeltaH = 6.76 kJ mol(-)(1)) and entropy (DeltaS = 49 J mol(-)(1) K(-)(1)) associated with the spin transition are in agreement with those previously observed for iron(II) spin-crossover compounds. The spin conversion is found to be close to a first-order phenomenon.
Matouzenko
Galina S.
GS
Laboratoire de stéréochimie et interactions moléculaires, École normale supérieure de Lyon, 46, allée d'Italie, 69364 Lyon cedex 07, France, Laboratoire de chimie de coordination du CNRS, 205, route de Narbonne, 31077 Toulouse cedex, France, Laboratoire de reconnaissance et organisation moléculaire, Université Claude Bernard-Lyon 1, 69622 Villeurbanne cedex, France, and Laboratoire des sciences moléculaires, Institut de chimie de la matière condensée de Bordeaux, 33608 Pessac, France.
Bousseksou
Azzedine
A
Lecocq
Sylvain
S
van Koningsbruggen
Petra J.
PJ
Perrin
Monique
M
Kahn
Olivier
O
Collet
André
A