Magnetic Properties of 1:2 Mixed Cobalt(II) Salicylaldehyde Schiff-Base Complexes with Pyridine Ligands Carrying High-Spin Carbenes (Scar = 2/2, 4/2, 6/2, and 8/2) in Dilute Frozen Solutions: Role of Organic Spin in Heterospin Single-Molecule Magnets
dataset
posted on 2014-06-02, 00:00 authored by Satoru Karasawa, Kimihiro Nakano, Daisuke Yoshihara, Noriko Yamamoto, Jun-ichi Tanokashira, Takahito Yoshizaki, Yuji Inagaki, Noboru KogaThe
1:2 mixtures of Co(p-tolsal)2, p-tolsal = N-p-tolylsalicylideniminato,
and diazo-pyridine ligands, DXpy; X = 1, 2, 3l, 3b, and 4, in MTHF solutions were irradiated at cryogenic temperature
to form the corresponding 1:2 cobalt–carbene complexes Co(p-tolsal)2(CXpy)2, with Stotal = 5/2, 9/2, 13/2, 13/2, and 17/2, respectively.
The resulting Co(p-tolsal)2(CXpy)2, X = 1, 2, 3l, 3b, and 4, showed magnetic
behaviors characteristic of heterospin single-molecule magnets with
effective activation barriers, Ueff/kB, of 40, 65, 73, 72, and 74 K, for reorientation
of the magnetic moment and temperature-dependent hysteresis loops
with a coercive force, Hc, of ∼0,
6.2, 10, 6.5, and 9.0 kOe at 1.9 K, respectively. The relaxation times,
τQ, due to a quantum tunneling of magnetization (QTM)
were estimated to be 1.6 s for Co(p-tolsal)2(C1py)2, ∼2.0 × 103 s for Co(p-tolsal)2(C2py)2, and >105 s for Co(p-tolsal)2(CXpy)2; X = 3b, 3l, and 4. In heterospin
complexes, organic
spins, carbenes interacted with the cobalt ion to suppress the QTM
pathway, and the τQ value increased with increasing
the Stotal values.
