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Cyano‐Bridged Mn III M III Single‐Chain Magnets with M III =Co III , Fe III , Mn III , and Cr III
Author(s) -
Miyasaka Hitoshi,
Madanbashi Tomokura,
Saitoh Ayumi,
Motokawa Natsuko,
Ishikawa Ryuta,
Yamashita Masahiro,
Bahr Stefan,
Wernsdorfer Wolfgang,
Clérac Rodolphe
Publication year - 2012
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.201102738
Subject(s) - crystallography , isostructural , chemistry , monoclinic crystal system , crystal structure , manganese , steric effects , ion , space group , octahedron , stereochemistry , x ray crystallography , physics , organic chemistry , diffraction , optics
A series of isostructural cyano‐bridged Mn III ( h.s. )–M III ( l.s. ) alternating chains, [Mn III (5‐TMAMsalen)M III (CN) 6 ] ⋅ 4H 2 O (5‐TMAMsalen 2− = N , N ′‐ethylenebis(5‐trimethylammoniomethylsalicylideneiminate), Mn III ( h.s. )=high‐spin Mn III , M III ( l.s. )=low‐spin Co III , MnCo ; Fe III , MnFe ; Mn III , MnMn ; Cr III , MnCr ) was synthesized by assembling [Mn III (5‐TMAMsalen)] 3+ and [M III (CN) 6 ] 3− . The chains present in the four compounds, which crystallize in the monoclinic space group C 2/ c , are composed of an [‐Mn III ‐NC‐M III ‐CN‐] repeating motif, for which the ‐NC‐M III ‐CN‐ motif is provided by the [M III (CN) 6 ] 3− moiety adopting a trans bridging mode between [Mn III (5‐TMAMsalen)] 3+ cations. The Mn III and M III ions occupy special crystallographic positions: a C 2 axis and an inversion center, respectively, forming a highly symmetrical chain with only one kind of cyano bridge. The Jahn–Teller axis of the Mn III ( h.s. ) ion is perpendicular to the N 2 O 2 plane formed by the 5‐TMAMsalen tetradentate ligand. These Jahn–Teller axes are all perfectly aligned along the unique chain direction without a bending angle, although the chains are corrugated with an Mn‐N axis ‐C angle of about 144°. In the crystal structures, the chains are well separated with the nearest inter‐chain M⋅⋅⋅M distance being relatively large at 9 Å due to steric hindrance of the bulky trimethylammoniomethyl groups of the 5‐TMAMsalen ligand. The magnetic properties of these compounds have been thoroughly studied. MnFe and MnMn display intra‐chain ferromagnetic interactions, whereas MnCr is characterized by an antiferromagnetic exchange that induces a ferrimagnetic spin arrangement along the chain. Detailed analyses of both static and dynamic magnetic properties have demonstrated without ambiguity the single‐chain magnet (SCM) behavior of these three systems, whereas MnCo is merely paramagnetic with S Mn =2 and D / k B =−5.3 K ( D being a zero‐field splitting parameter). At low temperatures, the MnM compounds with M=Fe, Mn, and Cr display remarkably large M versus H hysteresis loops for applied magnetic fields along the easy magnetic direction that corresponds to the chain direction. The temperature dependence of the associated relaxation time for this series of compounds systematically exhibits a crossover between two Arrhenius laws corresponding to infinite‐chain and finite‐chain regimes for the SCM behavior. These isostructural hetero‐spin SCMs offer a unique series of alternating [‐Mn‐NC‐M‐CN‐] chains, enabling physicists to test theoretical SCM models between the Ising and Heisenberg limits.