Reaction of lithium tetrachloromanganate(II)
with
N-
n-butyldiethanolamine H
2L
3 (
3) in the presence of LiH leads tothe formation of
wheel-shaped, mixed-valent heptanuclear, neutral complex {Mn
II[Mn
II2Mn
III4Cl
6(L
3)
6]} (
4). Themanganese
wheel crystallizes in the triclinic space group
P as
4·2CHCl
3 or
4·3THF
when either diethyl ether or
n-pentane
was allo
wed to diffuse into solutions of
4 in chloroform or tetrahydrofuran. The oxidation states of eachmanganese ion in
4·2CHCl
3 or
4·3THF
were assigned on the basis of detailed symmetry, bond length, and chargeconsiderations, as
well as by the Jahn-Teller axial elongation observed for the manganese(III) ions, and
werefurther supported by cyclic voltammetry. The analysis of the SQUID magnetic susceptibility data for complex
4·2CHCl
3 sho
wed that the intramolecular magnetic coupling of the manganese(II,III) ions is dominated by ferromagneticexchange interactions. This results in an
S = 27/2 ground-state multiplet at lo
w magnetic field. At fields higherthan 0.68 T, the energetically lo
west state is given by the
mS = 31/2 component of the
S = 31/2 multiplet due tothe Zeeman effect. The ligand-field-splitting parameters
were determined by anisotropy SQUID measurements onsingle crystalline samples along the crystallographic
x,
y, and
z axes (
D = -0.055 K,
E = 6.6 mK) and byhigh-frequency electron spin resonance measurements on a polycrystalline po
wder of
4·2CHCl
3 (
D = -0.068 K,
E = 9.7 mK). The resulting barrier height for magnetization reversal amounts to
U 10 K. Finally, 2DEG Hallmagnetization measurements revealed that
4·2CHCl
3 sho
ws single-molecule magnet behavior up to the blockingtemperature of about 0.6 K
with closely spaced steps in the hysteresis because of the quantum tunneling of themagnetization.