TY - JOUR
T1 - High-Spin Molecules
T2 - (NBu
II
4
)[Mn
8
O
6
Cl
6
(O
2
CPh)
7
(H
2
O)
2
] (S = 11) and [Mn
9
Na
2
O
7
(O
2
CPh)
15
(MeCN)
2
] (S = 4)
AU - Tsai, Hui-Lien
AU - Hendrickson, David N.
AU - Wang, Sheyi
AU - Folting, Kirsten
AU - Streib, William E.
AU - Christou, George
PY - 1995/1/1
Y1 - 1995/1/1
N2 -
The syntheses and electrochemical and magnetochemical properties of (NBu
n
4
)[Mn
8
O
6
Cl
6
(O
2
CPh)
7
-(H
2
O)
2
]·XCH
2
C1
2
(2·xCH
2
Cl
2
) and [Mn
9
Na
2
O
7
(O
2
CPh)
15
(MeCN)
2
]·3MeCN (3·3MeCN) are reported. Both complexes were prepared from reactions involving (NBu
n
4
)[Mn
4
O
2
(H
2
O)(O
2
CPh)
9
] (1). Complex 2 was obtained in 45–60% yield on treatment of complex 1 with 4 equiv of Me
3
SiCl in CH
2
C1
2
. Complex 2·
3
/
2
CH
2
Cl
2
·2H
2
O crystallizes in triclinic space group P1 with the following cell parameters at –169 °C: a = 16.104(4) Å, b = 21.501(6) Å, c = 14.843(4) Å, a = 94.24(1)°, β = 105.96(1)°, y = 89.07(1)°, V = 4927.79 Å
3
, and Z = 2. The structure was refined by employing 10 108 unique reflections with F > 3.0σ(F) to give R = 0.0912 and R
w
= 0.0944. Complex 2 contains a [Mn
8
O
6
Cl
4
]
8+
core (8Mn
III
) that may be conveniently described as resulting from the fusion of two [Mn
4
O
2
] butterfly units by sharing one “body” or “hinge” Mn. An eighth Mn
III
ion is connected to the resultant [Mn
7
O4] unit by two additional bridging O
2–
ions. Complex 3 was obtained in 31% yield from the treatment of complex 1 with 1 equiv of benzoyl peroxide in MeCN, followed by addition of NaClO
4
. Complex 3·3MeCN crystallizes in triclinic space group P1 with the following cell parameters at –170 °C: a = 15.116(2) Å b = 27.903(4) Å, c = 15.007(2) Å, α = 102.40(1)°, β = 112.36(1)°, γ = 84.17(1)°, V = 5715.26 Å
3
, and Z = 2. The structure was refined by employing 12 020 unique reflections with F > 3σ(F) to give R = 0.0514 and R
w
= 0.0525. Complex 3 possesses a mixed-metal undecanuclear [Mn
9
Na
2
O7]
15+
core (9Mn
III
); the Mn
9
O
7
subcore again comprises a [Mn
7
O4] unit constructed from the fusion, in the same manner as for complex 2, of two [Mn
4
O
2
] butterfly units. There are now two additional Mn
III
ions connected to the [Mn
7
O
4
] unit, by three additional bridging O
2–
ions. The Na
+
ions are bound to bridging O
2–
ions of the [Mn
9
O
7
] core, supporting a heterometallic-aggregate description rather than an ion-pairing description. Complex 2 displays reversible redox couples when examined by cyclic voltammetry in CH
2
C1
2
; an oxidation and a reduction are observed at 0.91 and 0.12 V, respectively, vs ferrocene. Complex 3 displays no reversible processes. Variable-temperature and variable-field dc magnetic susceptibility data were collected for polycrystalline samples of complexes 2 and 3. In a 10.0 kG field, χ
M
T for complex 2 increases with decreasing temperature from 23.7 cm
3
K mol
–1
(μ
eff
= 13.8 μ
B
) at 300.0 K to a maximum of 53.2 cm
3
K mol
–1
(μ
eff
= 20.6 μ
B
) at 15.0 K, whereupon there is a decrease to 39.3 cm
3
K mol
–1
(μ
eff
=17.7 μ
B
) at 5.01 K. The shape of this χ
M
T vs temperature curve reflects the population of a S = 11 ground state at low temperature. Least-squares fitting of reduced magnetization vs HIT data for complex 2 in the 2.0—30.0 K and 5.00—50.0 kG field range confirms that complex 2 has a S = 11 ground state with g = 1.92 and axial zero-field splitting of D = —0.04 cm
–1
. The ac susceptibility data measured in zero external field for complex 2 in the 2.0—30.0 K range also indicate a S = 11 ground state. No out-of-phase ac magnetic susceptibility signal was observed for complex 2 in the 2.0—30.0 K range in spite of its large-spin ground state. The absence of an out-of-phase ac signal is attributable to a very small zero-field splitting in the S = 11 ground state, and the small D-value results from a near cancellation of single-ion zero-field interactions at the eight Mn
III
ions in complex 2. Complex 3 exhibits dc and ac magnetic susceptibility data consistent with a S = 4 ground state. In a 10.0 kG field μ
eff
decreases gradually from 12.23 μ
B
at 320 K to 6.94 μ
B
at 5.01 K. Even though there are some similarities in molecular structure between complexes 2 and 3, differences in the nature of spin frustration result in a S = 11 ground state for complex 2 and a S = 4 ground state for complex 3.
AB -
The syntheses and electrochemical and magnetochemical properties of (NBu
n
4
)[Mn
8
O
6
Cl
6
(O
2
CPh)
7
-(H
2
O)
2
]·XCH
2
C1
2
(2·xCH
2
Cl
2
) and [Mn
9
Na
2
O
7
(O
2
CPh)
15
(MeCN)
2
]·3MeCN (3·3MeCN) are reported. Both complexes were prepared from reactions involving (NBu
n
4
)[Mn
4
O
2
(H
2
O)(O
2
CPh)
9
] (1). Complex 2 was obtained in 45–60% yield on treatment of complex 1 with 4 equiv of Me
3
SiCl in CH
2
C1
2
. Complex 2·
3
/
2
CH
2
Cl
2
·2H
2
O crystallizes in triclinic space group P1 with the following cell parameters at –169 °C: a = 16.104(4) Å, b = 21.501(6) Å, c = 14.843(4) Å, a = 94.24(1)°, β = 105.96(1)°, y = 89.07(1)°, V = 4927.79 Å
3
, and Z = 2. The structure was refined by employing 10 108 unique reflections with F > 3.0σ(F) to give R = 0.0912 and R
w
= 0.0944. Complex 2 contains a [Mn
8
O
6
Cl
4
]
8+
core (8Mn
III
) that may be conveniently described as resulting from the fusion of two [Mn
4
O
2
] butterfly units by sharing one “body” or “hinge” Mn. An eighth Mn
III
ion is connected to the resultant [Mn
7
O4] unit by two additional bridging O
2–
ions. Complex 3 was obtained in 31% yield from the treatment of complex 1 with 1 equiv of benzoyl peroxide in MeCN, followed by addition of NaClO
4
. Complex 3·3MeCN crystallizes in triclinic space group P1 with the following cell parameters at –170 °C: a = 15.116(2) Å b = 27.903(4) Å, c = 15.007(2) Å, α = 102.40(1)°, β = 112.36(1)°, γ = 84.17(1)°, V = 5715.26 Å
3
, and Z = 2. The structure was refined by employing 12 020 unique reflections with F > 3σ(F) to give R = 0.0514 and R
w
= 0.0525. Complex 3 possesses a mixed-metal undecanuclear [Mn
9
Na
2
O7]
15+
core (9Mn
III
); the Mn
9
O
7
subcore again comprises a [Mn
7
O4] unit constructed from the fusion, in the same manner as for complex 2, of two [Mn
4
O
2
] butterfly units. There are now two additional Mn
III
ions connected to the [Mn
7
O
4
] unit, by three additional bridging O
2–
ions. The Na
+
ions are bound to bridging O
2–
ions of the [Mn
9
O
7
] core, supporting a heterometallic-aggregate description rather than an ion-pairing description. Complex 2 displays reversible redox couples when examined by cyclic voltammetry in CH
2
C1
2
; an oxidation and a reduction are observed at 0.91 and 0.12 V, respectively, vs ferrocene. Complex 3 displays no reversible processes. Variable-temperature and variable-field dc magnetic susceptibility data were collected for polycrystalline samples of complexes 2 and 3. In a 10.0 kG field, χ
M
T for complex 2 increases with decreasing temperature from 23.7 cm
3
K mol
–1
(μ
eff
= 13.8 μ
B
) at 300.0 K to a maximum of 53.2 cm
3
K mol
–1
(μ
eff
= 20.6 μ
B
) at 15.0 K, whereupon there is a decrease to 39.3 cm
3
K mol
–1
(μ
eff
=17.7 μ
B
) at 5.01 K. The shape of this χ
M
T vs temperature curve reflects the population of a S = 11 ground state at low temperature. Least-squares fitting of reduced magnetization vs HIT data for complex 2 in the 2.0—30.0 K and 5.00—50.0 kG field range confirms that complex 2 has a S = 11 ground state with g = 1.92 and axial zero-field splitting of D = —0.04 cm
–1
. The ac susceptibility data measured in zero external field for complex 2 in the 2.0—30.0 K range also indicate a S = 11 ground state. No out-of-phase ac magnetic susceptibility signal was observed for complex 2 in the 2.0—30.0 K range in spite of its large-spin ground state. The absence of an out-of-phase ac signal is attributable to a very small zero-field splitting in the S = 11 ground state, and the small D-value results from a near cancellation of single-ion zero-field interactions at the eight Mn
III
ions in complex 2. Complex 3 exhibits dc and ac magnetic susceptibility data consistent with a S = 4 ground state. In a 10.0 kG field μ
eff
decreases gradually from 12.23 μ
B
at 320 K to 6.94 μ
B
at 5.01 K. Even though there are some similarities in molecular structure between complexes 2 and 3, differences in the nature of spin frustration result in a S = 11 ground state for complex 2 and a S = 4 ground state for complex 3.
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U2 - 10.1021/ja00114a013
DO - 10.1021/ja00114a013
M3 - Article
AN - SCOPUS:0000300569
VL - 117
SP - 2503
EP - 2514
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 9
ER -