An 18-membered hexanuclear manganese (MnN2)6 metalladiazamacrocycle

Article abstract of DOI:10.1515/znb-2009-0701

The macrocyclic hexanuclear manganese(III) 18-metallacrown-6, [Mn ₆(pmshz)₆(DMF)₄(C₂H ₅-OH)₂]·4DMF (1), where pmshz³-is N-propionyl-N'-5-methylsalicylhydrazide, has been synthesi

Full text of DOI:10.1515/znb-2009-0701

An 18-Membered Hexanuclear Manganese (MnN2)6
Metalladiazamacrocycle
Qi-Feng Liang
Department of Chemistry, Jiaying University, Meizhou 514015, China
Reprint requests to Qi-Feng Liang. Fax: Int. +86-753-2186853.
E-mail: liangqifeng07@yahoo.com.cn
Z. Naturforsch. 2009, 64b, 779 – 783; received March 12, 2009
The macrocyclic hexanuclear manganese(III) 18-metallacrown-6, [Mn6(pmshz)6(DMF)4(C2H5-
OH)2]·4DMF (1), where pmshz3− is N-propionyl-Nꢀ-5-methylsalicylhydrazide, has been synthesized
by self-assembly and structurally characterized. The ring is formed by the succession of six structural
moieties of the type [Mn(III)-N-N] with hydrazide N-N groups bridging the ring Mn ions. The ligand
enforces the metal ions to form the stereochemistry of a configuration with alternate...∆Λ∆Λ...-
˚
˚
type enantiomeric chiral units. The peripheral core ring is ∼18.6 A in diameter and ∼12.4 A in
thickness. The title metallacrown exhibits photoluminescent properties in the solid state and a weak
antiferromagnetic exchange interaction.
Key words: 18-Metallacrown-6, Self-assembly, Hexanuclear Complex, Photoluminescence,
Antiferromagnetic Exchange
Table 1. Crystal structure data for 1.
Formula
Introduction
C94H132Mn6N20O28
2319.8
Metallamacrocycles are an interesting class of com-
pounds because of their diverse molecular architec-
tures [1], their utilization as motifs for coordination
networks [2] and their potential as host systems in
guest inclusion chemistry [3]. Diaza-bridged metal-
ladiazamacrocycles have received considerable inter-
est because of their beautiful architecture [1, 2, 4],
unique magnetic properties [1, 2] and bioactivity [1, 2].
These compounds can be readily assembled using the
trianionic pentadentate ligand N-acylsalicylhydrazide
with metal ions such as manganese, iron, cobalt, or
gallium [1, 2]. Manganese and iron cations have re-
ceived special attention due to their ease of forma-
tion of metallamacrocycles and interesting magnetic
properties [1]. Controlling the ring size and nucle-
arity of metallamacrocycles and their properties has
recently become of interest. The results have shown
that the nature of the N-acyl substituent can influ-
ence the size and nuclearity of the macrocyclic com-
plex [1]. As part of our efforts to understand these ef-
fects on the molecular structure of the metalladiaza-
macrocycles, and to develop a better understanding
of their self-assembly and spectroscopic behavior, we
report here the structure, luminescence and magnetic
properties of a manganese 18-metallacrown-6 complex
[Mn6(pmshz)6(DMF)4(C2H5OH)2]·4DMF (1).
Mr
Crystal size, mm3
Crystal system
Space group
0.42 × 0.327 × 0.213
triclinic
¯
P1
˚
a, A
b, A
c, A
11.026(2)
16.974(3)
17.052(3)
64.49(3)
86.78(3)
71.29(3)
2715.4(9)
1
1.416
0.758
1206
11, 18, 18
25371/6914/0.0332
668
0.0612/0.1627
1.079
˚
˚
α, deg
β, deg
γ, deg
3
˚
V, A
Z
Dcalcd, g cm−3
µ(MoKα ), cm−1
F(000), e
hkl range
Refl. measured/unique/Rint
Param. refined
R1(F)/wR2(F2)a (all refls.)
GoF (F2)b
−3
˚
∆ρfin (max/min), e A
1.28/−0.94
a R1 = ꢁFo|−|Fcꢁ/Σ|Fo|, wR2 = [Σw(Fo −Fc2)2/Σw(Fo2)2]1/2, w =
2
[σ2(Fo2) + (0.0556P)2 + 16.3478P]−1, where P = (Max(Fo2, 0) +
2Fc2)/3; b GoF = [Σw(Fo −Fc2)2/(nobs −nparam)]1/2
.
2
Experimental Section
Measurements of physical properties
All commercially available chemicals were of A. R. grade,
and all solvents used were purified by standard methods. Car-
c
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Q.-F. Liang · 18-Metallacrown-6
Scheme 1. Ligand H3pmshz and the coordi-
nation mode of its trianion in 1.
˚
˚
Table 2. Selected bond lengths (A) and angles (deg) of 1.
monochromatized MoKα radiation (λ = 0.71073 A). A
summary of crystallographic data and details of the struc-
ture refinement are listed in Table 1. The structure was
solved by Direct Methods and refined by full-matrix least-
squares techniques on F2 with all non-hydrogen atoms
treated anisotropically. The hydrogen atoms were assigned
a common isotropic displacement factor and included in
the final refinement cycles by using geometrical restraints.
All calculations were performed with the program package
SHELXTL [6]. Selected bond lengths and angles are listed in
Table 2 [7].
Mn1–O1
Mn1–N1
Mn1–O3
Mn2–O7
Mn2–N3
Mn2–O6
Mn3–O11
Mn3–N5
Mn3–O12
1.864(4)
1.944(4)
2.249(4)
1.858(4)
1.945(4)
2.233(4)
1.861(4)
1.941(5)
2.219(4)
Mn1–O2
Mn1–O4
Mn1–N2
Mn2–O5
Mn2–O8
Mn2–N4
Mn3–O9
Mn3–O10
Mn3–N6
1.923(4)
1.972(4)
2.269(4)
1.925(4)
1.961(4)
2.251(5)
1.925(4)
1.984(4)
2.267(5)
O1–Mn1–O2
O2–Mn1–N1
O2–Mn1–O4
O1–Mn1–O3
N1–Mn1–O3
O1–Mn1–N2
N1–Mn1–N2
O3–Mn1–N2
O7–Mn2–N3
O7–Mn2–O8
N3–Mn2–O8
O5–Mn2–O6
O8–Mn2–O6
O5–Mn2–N4
O8–Mn2–N4
O11–Mn3–O9
O9–Mn3–N5
O9–Mn3–O10
O11–Mn3–O12
N5–Mn3–O12
O11–Mn3–N6
N5–Mn3–N6
O12–Mn3–N6
168.68(16)
80.33(17)
93.36(15)
86.82(16)
100.09(16)
91.94(17)
99.69(17)
160.19(15)
91.13(17)
95.35(16)
172.94(16)
88.57(15)
86.71(15)
88.92(16)
75.05(16)
169.75(16)
79.95(17)
88.69(15)
89.30(16)
97.69(17)
93.13(16)
103.82(18)
158.32(16)
O1–Mn1–N1
O1–Mn1–O4
N1–Mn1–O4
O2–Mn1–O3
O4–Mn1–O3
O2–Mn1–N2
O4–Mn1–N2
O7–Mn2–O5
O5–Mn2–N3
O5–Mn2–O8
O7–Mn2–O6
N3–Mn2–O6
O7–Mn2–N4
N3–Mn2–N4
O6–Mn2–N4
O11–Mn3–N5
O11–Mn3–O10
N5–Mn3–O10
O9–Mn3–O12
O10–Mn3–O12
O9–Mn3–N6
O10–Mn3–N6
90.38(17)
96.53(16)
171.20(17)
88.43(16)
85.77(15)
95.99(17)
74.72(15)
171.03(16)
79.98(16)
93.59(15)
91.21(15)
95.97(17)
94.09(17)
101.75(17)
161.39(15)
90.43(17)
101.04(16)
168.41(16)
88.52(16)
84.23(15)
92.59(16)
74.16(15)
Preparation of the ligand
The ligand N-propionyl-Nꢀ-5-methylsalicylhydrazine
(H3pmshz) (Scheme 1) was synthesized by reacting
2-hydroxy-4-methylbenzohydrazine (1.66 g, 10 mmol)
with propionic anhydride (1.56 g, 12 mmol) in 25 mL
of chloroform at 0 ◦C. The reaction mixture was slowly
warmed to r. t. and stirred for 5 h. The resulting white
precipitate was filtered and rinsed with chloroform and
diethyl ether. It was then dried in vacuo over P2O5. Yield:
1.72 g, 77.4 %. Melting point: 215 – 216 ◦C. – Elemental
analysis data for C11H14N2O3: calcd. C 59.45, H 6.35,
N 12.60; found C 59.61, H 6.29, N 12.72. – 1H NMR
(600 MHz, [D6]DMSO, ppm): δ = 11.94 (s (br), 1H), 10.45
(s (br), 1H) (both amide NH’s), 10.05 (s, 1H, phenolic OH),
7.77 (s, 1H, o-Ar-H), 7.59 (d, 1H, p-Ar-H), 6.75 (d, 1H,
m-Ar-H), 2.30 (s, 3H, Ar-CH3), 2.20 (q, 2H, -CH2-), 1.06
(t, 3H, -CH3). – IR (KBr pellet, cm−1): v = 3334 (s), 3309
(s), 3078(br), 2975 (m), 2877 (w), 1664 (s), 1637 (s), 1618
(s), 1542 (s), 1512 (m), 1479 (s), 1419 (m), 1371 (m), 1311
(s), 1276 (w), 1249 (s), 1209 (m), 1178 (m), 1153 (w), 1120
(m), 1057 (m), 955 (m), 878 (s), 825 (m), 767 (m), 594 (s),
549 (m).
bon, nitrogen and hydrogen analyses were performed using
a Vario EL elemental analyzer. IR spectra were recorded on
a Nicolet Avatar 360 FT-IR instrument using KBr discs in
the 400 – 4000 cm−1 region. 1H NMR spectra were mea-
sured on an FT-600A spectrometer in [D6]DMSO solution,
with TMS as internal standard. Fluorescence measurements
were made on a Hitachi F-4500 spectrophotometer. The ex-
citation and emission slit widths were 1 nm. Temperature-
dependent magnetic susceptibility measurements were car-
ried out on powdered samples between 2 and 300 K using a
Quantum Design MPMS-7XL SQUID magnetometer. Field-
cooled magnetization data were collected at H = 1000 Oe.
Preparation of [Mn6(pmshz)6(DMF)4(C2H5OH)2]·4DMF
(1)
H3pmshz (0.22 g, 1.0 mmol) was dissolved in 20 mL
DMF and ethanol (3 : 1), and 0.20 g (1.0 mmol) of MnCl2·
4H2O (0.20 g, 1.0 mmol) in DMF was added at r. t. The mix-
ture was stirred for 10 min, then the dark brown solution was
filtered. Mn(II) is oxidized to Mn(III) by atmospheric oxy-
gen. After standing for 18 days, crystals of 1 were obtained
Crystal structure determination
The intensity data of 1 were collected at 296 K on from the filtrate as dark brown blocks. Yield: 52 %. M. p. >
a Rigaku R-AXIS RAPID diffractometer with graphite- 300 ◦C (dec.). – Elemental analysis for C94H132Mn6N20O28
:
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Q.-F. Liang · 18-Metallacrown-6
781
(a)
calcd. C 48.49, H 5.58, N 11.70; found C 48.61, H 5.49,
N 11.78 %. – IR (KBr pellet, cm−1): v = 3445 (br), 3066
(w), 2939 (w), 1655 (s), 1608 (s), 1575 (s), 1558 (s), 1498
(s), 1458 (w), 1423 (s), 1389 (s), 1354 (m), 1325 (m), 1244
(m), 1176 (w), 1120 (w), 1014 (w), 962 (w), 887 (w), 862
(w), 814 (w), 763 (w), 748 (w), 698 (w), 676 (w), 669 (m),
626 (w), 592 (w), 543 (w), 432 (w).
Results and Discussion
IR spectra
The IR spectrum of 1 shows the band of C=O
shifted to lower frequencies as compared with the
ligand suggesting the coordination of the carbonyl
oxygen atom to the Mn3+ ion. The stretching vibra-
tion bands v(N-H) are significantly weakened in the
spectra of 1 indicating the deprotonation of the hy-
drazine group and coordination of the hydrazide nitro-
gen atoms to Mn3+ ions. The bands v(C-N) at 1276
and 1311 cm−1 are shifted to 1558 cm−1 due to the
deprotonation of the NH group.
(b)
Structure description
Mn1
Compound 1 crystallizes in the triclinic space group
Mn2
¯
P1 with Z = 1. The molecular structure is shown
in Fig. 1. The ligand H3pmshz that exists in solu-
tion in its enol form has three replaceable protons
and hence can coordinate as a trianion via three oxy-
gen atoms and two hydrazinic nitrogen atoms. Six
Mn(III) ions and six deprotonated pmshz3− ligands
construct a planar 18-membered ring based on the Mn-
N-N-Mn linkages of the title azametallacrown. Each
manganese ion is in a distorted octahedral environ-
ment. While the O2, N2 and O3 atoms of a given lig-
and bind to one manganese atom, O4 and N1 bind
to the adjacent manganese atom in a back-to-back
fashion leading to a cyclic structure consisting of 6
manganese metal ions with successive metal centers
in an alternating...∆Λ∆Λ...-type chiral configuration
(Fig. 1). The remaining coordination site of each man-
ganese atom is satisfied by the oxygen atom of a DMF
or EtOH solvate molecule. The distances for Mn–N-
Mn3
Fig. 1. (a) Molecular structure of 1 with crystallographic
atom labeling adopted. H atoms and free solvent molecules
are omitted for clarity. (b) The ring is formed by the succes-
sion of six structural moieties of the type [Mn(III)-N-N] with
hydrazide N-N groups bridging the ring Mn cations (color
online).
(diazine), Mn–O(phenolate), and Mn–O(carbonyl) are cyclic structure, while the rest of them (green) are be-
in the ranges 1.941– 2.269, 1.858– 1.864, and 1.961– low. In the [Mn-N-N]6 ring the Mn···Mn interatomic
˚
˚
1.984 A, respectively. The Mn(III)–O (CH3CH2OH) distances of neighboring atoms are 4.896(2) A, while
distance is 2.249 A, the Mn(III)–O(DMF) distances the Mn···Mn···Mn angles are 114.65◦. The average
˚
˚
˚
are 2.219 and 2.233 A. The solvent molecules in the axial manganese-oxygen/nitrogen distance of 2.248 A
complex are directed away from the ring. The terminal in 1 is approximately 0.328 A longer than the average
alkyl groups of the tails of 3 ligands (red) are above the basal Mn–O/N distance of 1.920 A. This typical Jahn-
˚
˚
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782
Q.-F. Liang · 18-Metallacrown-6
Fig. 2. Emission spectrum of 1 in the solid state at room tem-
perature (EX slit = 1.0 nm).
Fig. 3. Plot of χm T and χ−1 vs. T of polycrystalline 1.
Teller elongation along the z axis of the manganese(III) of χm T and the inverse magnetic susceptibility χ−1
ion was also observed in other manganese(III) com- versus T are shown in Fig. 3. They point to a typical,
pounds [5]. The manganese ions in the ring of 1 adopt weakly coupled antiferromagnetic behavior. The
a propeller configuration, despite the Jahn-Teller dis- values of χm T decrease slightly with decreasing
tortion of high-spin d4 manganese(III) ions. The core temperature from 20.953 cm3 K mol−1 at 300 K to
of the disc-shaped hexanuclear metallamacrocycle is 14.861 cm3 K mol−1 at 50 K. Below 50 K, χm T
∼2.1 nm in diameter and ∼1.0 nm in thickness. There decreases rapidly and reaches 1.000 cm3 K mol−1 at
are no solvent molecules in the ‘host’ cavity of the 2 K. This behavior is similar to that reported for other
metallacrown. The presence of aliphatic groups at the manganese metalladiazamacrocycles [2].
core of the molecular disc and its outer areas provides
Conclusion
a non-polar nature to this neutral molecule.
In conclusion, a novel 18-metallacrown-6 molecule,
[Mn6(pmshz)6(DMF)4(C2H5OH)2]·4DMF (1), has
been synthesized and structurally characterized.
Photoluminescent and magnetic properties of [Mn6-
(pmshz)6(DMF)4(C2H5OH)2]·4DMF in the solid
state were studied. Further attempts to optimize the
factors that govern nuclearity and size of metalladi-
azamacrocycles and their photoluminescent behavior
are being pursued in our group, and the results will be
communicated later.
Photoluminescent properties
The photoluminescent properties of 1 were investi-
gated. A solid sample of 1 displayed a strong photolu-
minescence emission band at 390 nm (λex = 244 nm)
at room temperature (Fig. 2), which can be proposed
to originate from the coordination of H3anhz to the Mn
atoms (ligand-to-metal charge transfer, LMCT).
Magnetic properties
The variable-temperature magnetic susceptibility
data of 1 were recorded between 300 and 2 K. Plots
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