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SOLVOLTHERMAL SYNTHESIS, STRUCTURE, AND PROPERTIES OF A NOVEL DINUCLEAR ZINC(II) COMPLEX
© 2015 N. Wang1, * and X. Y. Qiu2
1Department of Public Subject, Shangqiu Medical College, Shangqiu, 476100 P.R. China 2School of Chemistry and Chemical Engineering, Shangqiu Normal University, Shangqiu, 476000 P.R. China
*E-mail: wangna_sqnu@126.com Received November 22, 2014
A novel centrosymmetric dinuclear zinc(II) complex, [Zn2L2], was prepared from 2-bromo-6-[(3-cyclohex-ylaminopropylimino)methyl]phenol (H2L), 3,5-dichlorosalicylaldehyde, and zinc acetate under solvolther-mal conditions. There occurs a rarely-seen 1,3-hydride shift reaction during the process. Structure of [Zn2L2] has been characterized by elemental analysis, IR spectra, and single crystal X-ray diffraction (CIF file CCDC no. 956057). The Zn--Zn separation is 3.163(1) A. Each Zn atom in the complex is in a trigonal-bipyramidal coordination. Thermal stability and fluorescence property of [Zn2L2] were studied. The complex displays in-traligand n—n* fluorescence and can potentially serve as photoactive material.
DOI: 10.7868/S0132344X15060092
INTRODUCTION
Schiff bases are a kind of versatile ligands in coordination chemistry which are readily synthesized from the reaction of primary amines with carbonyl-con-taining compounds. In recent years, much work has been carried out on the syntheses and properties of Schiff bases and their complexes [1—5]. You and coworkers have prepared some Schiff base complexes with solvolthermal method [6—8]. It was found that the mono-Schiffbase ligand 4-chloro-2-[(3-cyclohexylami-nopropylimino)methyl]phenol can be transformed to ¿¿s-Schiff base ligand N,N'-te(5-chlorosalicylidene)-1,3-propanediamine under solvolthermal condition [8]. Then, they reported three interesting dinuclear zinc(II) complexes derived from mono-Schiff bases bearing 2-[3-cyclohexylaminopropylimino]methyl]phe-nol backbone under solvolthermal conditions [9, 10]. It is interesting that the mono-Schiff bases underwent structural transformation during the reactions. As further investigation on this interesting reaction under solvolthermal conditions, in the present work, a new centrosymmetric dinuclear zinc(II) complex [Zn2L2], where L is the dianionic form of 2-[(3-{[1-(3-bromo-2-hydroxyphenyl)methylidene]amino}propylamino)me-thyl]-4,6-dichlorophenol (H2L), has been prepared and structurally characterized.
Cl
EXPERIMENTAL
Materials and physical measurements. 3,5-Dichloro-salicylaldehyde, 3-bromosalicylaldehyde, and N-cyclo-hexylpropane-1,3-diamine with AR grade were purchased from Lancaster. Other reagents and solvents were purchased from Shanghai Chemical Reagent Company and used as received. The mono-Schiffbase 2-bromo-6-[(3-cyclohexylaminopropylimino)methyl]phenol was prepared according to the literature method [11]. C, H, and N elemental analyses were performed on a Perkin-Elmer 240C elemental analyzer. IR spectra were measured with a Nicolet FT-IR 170-SX spectrophotometer. Thermal stability analysis was performed on a Perki-nElmer Pyris Diamond TG—DTA thermal analyses system. Luminescence spectra were reported on a JASCO FP-6500 spectrofluorimeter (solid) in the range of 200— 850 nm.
Synthesis of [Zn2L2]. 2-Bromo-6-[(3-cyclohexylami-nopropylimino)methyl]phenol (0.1 mmol, 33.9 mg), 3,5-dichlorosalicylaldehyde (0.1 mmol, 19.0 mg), and zinc acetate (0.1 mmol, 22.0 mg) were mixed in methanol. The mixture was stirred at room temperature for 10 min and transferred to a stainless steel bomb, which was sealed, heated at 150°C for 12 h, and cooled gradually to room temperature. Colorless thin needle-like single crystals of the complex, suitable for X-ray diffraction, were collected by filtration. The yield was 63%.
For C34H30N4O4Cl4Br2Zn2
anal. calcd., %: C, 41.2; H, 3.1; N, 5.7. Found, %: C, 41.0; H, 3.0; N, 5.5.
Br
Cl
(H2L)
IR data (KBr; v(C=N).
v, cm-1): 3225 w v(N-H), 1629 s
SOLVOLTHERMAL SYNTHESIS, STRUCTURE, AND PROPERTIES
X-ray crystallography. Diffraction intensities for complex I were collected at 298(2) K using Bruker SMART CCD detector with Mo^ radiation (X = = 0.71073 A). The collected data were reduced using SAINT [12], and multiscan absorption corrections were performed using SADABS [13]. The structure was solved by direct method and refined against F2 by full-matrix least-squares method using SHELXTL [14]. All non-hydrogen atoms were refined anisotropically. The amino H was located from a difference Fourier map and refined isotropically, with N—H distance restrained to 0.90(1) A. The remaining hydrogen atoms were placed in calculated positions and constrained to ride on their parent atoms. A summary of the crystal-
381
lographic data are given in Table 1. Coordinate bond lengths and angles are listed in Table 2.
Supplementary material for the structure has deposited with the Cambridge Crystallographic Data Centre (no. 956057; deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
RESULTS AND DISCUSSION
The zinc complex was prepared by reaction of the mono-Schiff base with 3,5-dichlorosalicylaldehyde and zinc acetate in methanol under solvolthermal conditions.
The possible mechanism for the reaction prepora-tion of the complex is shown below:
+ Zn:
2+
R.t.
Cl
CHO OH
Cl
Br
(I)
MeOH
150°C
N
^-•Zn^ ' tt
Cl
Br O Cl
-H2O
Cl
O
(II)
^ tzn2O<Cl>rH
-N,
Cl
(III)
3-hydride shift
Cl {
Hydrolysis
h2o '
© N-Z^O. Br
>
Cl
2
N Zn
O ^N-
H2O
n O^Zn / )
N-^T Br
C1 ZfO. N.
h2o
(IV)
Cl
H /H
A
(V)
—H2O
Cl (
H
N
N
u ^Zn, Cl B^O ^N-
)
Cl
/^Br Cl
"Zn—O.
H
382
WANG, QIU
Table 1. Crystalloraphic data and structure refinement for [Zn2L2]
Parameter Value
Fw 990.98
Crystal shape/colour Block/colorless
Crystal size, mm 0.25 x 0.23 x 0.23
Crystal system Monoclinic
Space group P2j/c
a, A 7.3839(6)
b, A 23.096(2)
c, A 10.4023(8)
P, deg 98.099(2)
V, A3 1756.3(2)
Z 2
^(MoJa), mm-1 3.991
Tmin/Tmax 0.4353/0.4604
Pcalcd g cm-3 1.874
Reflections collected 16343
Independent reflections (Rjnt) 3226 (0.0652)
Observed reflections (I > 2a(I)) 2011
Parameters refined 229
Restraints 1
Goodness of fit on F2 1.088
R1, wR2 (I> 2ct(I)) 0.0756, 0.1857
R1, wR2 (all data) 0.1302, 0.2110
^ma/APm^ e A~3 0.582/—0.905
In the presence of Zn2+ ions, the reaction underwent a 1,3-hydride shift process [9, 15—17]. Under solvolthermal conditions, 3,5-dichlorosalicylaldehyde reacted with I, generating intermediate zinc complex (II). In II, there is a condensation reaction between the coordinated 3,5-dichlorosalicylaldehyde and the
mono-Schiff base ligand, which forms an imine cationic intermediate (III). Further, III changed to the following imine cationic intermediate (IV) undergoing a 1,3-hydride shift process to give the intermediate (V), which maybe the main step of the reaction mechanism. After a serials of hydrolysis reactions, the final dinuclear zinc(II) complex, [Zn2L2], was formed.
When compared with those complexes prepared under common condition with Schiff bases derived from N-cyclohexylpropane-1,3-diamine [11, 18], we can observe that the cyclohexyl groups of the Schiff bases can remove away only under solvolthermal conditions.
The molecular structure of [Zn2L2] is shown in Fig. 1. X-ray crystallography reveals that the complex is a centrosymmetric phenolate O-bridged dinuclear zinc(II) species, with the inversion center located at the midpoint of the two metal atoms. The Zn---Zn separation is 3.163(1) Â.
The C(10)—N(2) bond length of 1.460(12) Â confirms it as a single C—N bond. Furthermore, the difference Fourier map of the complex reveals that there is one H atom attached to N(2). Each Zn atom in the complex is in a trigonal-bipyramidal coordination, with one amino N and two phenolate O atoms from two Schiff base ligands defining the equatorial plane, and with one imino N and one phenolate O atoms of one Schiff base ligand occupying the two axial positions. The Zn atom deviates from the least-squares plane defined by the equatorial donor atoms by 0.100(2) Â. The coordinate bond lengths in the complex are comparable to those reported in similar zinc(II) complexes [9, 10]. The ZnL unit in [Zn2L2] is butterfly-shaped, with the dihedral angle formed by the two benzene rings of 17.0(5)°. The chelate ring formed by the atoms Zn(1), N(1), C(8)-C(10), and N(2) in the complex has chair conformation. The diagonally positioned atoms, Zn(1) and C(9), are shifted from the least-squares plane defined by the atoms N(1), N(2),
Table 2. Coordinate bond lengths (Â) and angles (deg) for [Zn2L2]*
Bond d, А Bond d, А
Zn(1)—O(1) 1.981(6) Zn(1)—O(2) 2.089(6)
Zn(1)—O(2A) 2.016(5) Zn(1)—N(1) 2.110(8)
Zn(1)—N(2) 2.099(8)
Angle ю, deg Angle ю, deg
O(1)Zn(1)O(2A) 114.3(3) O(1)Zn(1)O(2) 90.5(2)
O(2)Zn(1)O(2A) 79.2(2) O(1)Zn(1)N(2) 130.3(3)
O(2A)Zn(1)N(2) 114.7(3) O(2)Zn(1)N(2) 90.5(3)
O(1)Zn(1)N(1) 86.9(3) O(2A)Zn(1)N(1) 98.5(2)
O(2)Zn(1)N(1) 175.5(3) N(2)Zn(1)N(1) 94.0(3)
* Symmetry code for A: — x, 1 — y, — z.
SOLVOLTHERMAL SYNTHESIS, STRUCTURE, AND PROPERTIES
383
C(9)
C(8) C(7)N(1
C(10) N(2)C(11) C(17)
Cl(2)
C(16) C(15)
C(5)W C(3) C(4)
Fig. 1. The molecular structure of [Zn2L2]. Thermal ellipsoids are at the 30% probability level. Hydrogen atoms except for the amino H are omitted for clarity. Atoms labeled with the suffix A or unlabeled atoms are at the symmetry position —x, 1 — y, — z.
C(8), and C(10) by -0.613(2) and 0.706(6) Â, respectively. The chelate ring formed by the atoms Zn(1), N(2), C(11)-C(13), and O(2) in the complex has boat conformation. The diagonally positioned atoms, O(2) and C(11), are shifted from the least-squares plane defined by the atoms Zn(1), N(2), C(12), and C(13) by 0.385(2) and 0.665(6) Â, respectively.
In the crystal structure of [Zn2L2], dinuclear zinc complex molecules are linked via intermolecular
200 400 600 800 1000 Temperature, °C
Fig. 3. DT-TGA curves of [Zn2L2].
N(2)-H(2)-O(
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