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Hysteretic Spin Crossover above Room Temperature and Magnetic Coupling in Trinuclear Transition‐Metal Complexes with Anionic 1,2,4‐Triazole Ligands
Author(s) -
Gómez Verónica,
BenetBuchholz Jordi,
Martin Eddy,
GalánMascarós J. R.
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201304537
Subject(s) - superexchange , antiferromagnetism , spin crossover , crystallography , transition metal , spin transition , chemistry , metal , crystal structure , spin states , transition temperature , stereochemistry , condensed matter physics , inorganic chemistry , physics , catalysis , biochemistry , superconductivity , organic chemistry
The reaction of 4‐(1,2,4‐triazol‐4‐yl)ethanesulfonate ( L ) with Zn 2+ , Cu 2+ , Ni 2+ , Co 2+ , and Fe 2+ gave a series of analogous neutral trinuclear complexes with the formula [M 3 (μ‐ L ) 6 (H 2 O) 6 ] ( 1 – 5 ). These compounds were characterized by single‐crystal X‐ray diffraction, thermogravimetry, and elemental analysis. The magnetic properties of compounds 2 – 5 were studied. Complexes 2 – 4 show weak antiferromagnetic superexchange, with J values of −0.33 ( 2 ), −9.56 ( 3 ), and −4.50 cm −1 ( 4 ) (exchange Hamiltonian H =−2 J ( S 1 S 2 + S 2 S 3 )). Compound 5 shows two additional crystallographic phases ( 5 b and 5 c ) that can be obtained by dehydration and/or thermal treatment. These three phases exhibit distinct magnetic behavior. The Fe 2+ centers in 5 are in high‐spin (HS) configuration at room temperature, with the central one exhibiting a non‐cooperative gradual spin transition below 250 K with T 1/2 =150 K. In 5 b , the central Fe 2+ stays in its low‐spin (LS) state at room temperature, and cooperative spin transition occurs at higher temperatures and with the appearance of memory effect ( T 1/2 ↑=357 K and T 1/2 ↓=343 K). In the case of 5 c , all iron centers remain in their HS configuration down to very low temperatures, with weak antiferromagnetic coupling ( J =−1.16 cm −1 ). Compound 5 b exhibits spin transition with memory effect at the highest temperature reported, which matches the remarkable features of coordination polymers.