КООРДИНАЦИОННАЯ ХИМИЯ, 2014, том 40, № 2, с. 123-128
УДК 541.49
SYNTHESIS, SPECTROSCOPIC CHARACTERIZATION, AND CRYSTAL STRUCTURES OF COPPER(I) IODIDE CLUSTERS OF N-METHYLTHIOUREA
AND 1,3-DIAZINANE-2-THIONE © 2014 T. Ahmad1, R. Mahmood2, S. C. Lee3, and S. Ahmad1, *
department of Chemistry, University of Engineering and Technology, Lahore, 54890 Pakistan 2Division of Science and Technology, University of Education, Township, Lahore, Pakistan 3Department of Chemistry, University of Waterloo, Waterloo, Canada *E-mail: saeed_a786@hotmail.com Received November 19, 2012
Two copper(I) iodide complexes, [Cu4(Metu)6I4] (I) and [Cu8(Diaz)i2I8] (II) (Metu = N-methylthiourea; Diaz = 1,3-diazinane-2-thione), have been prepared and their structures been determined by X-ray crystallography. The crystal structures show that complex I is a tetranuclear, while II is an octanuclear cluster, both having a Cu : S ratio of 2 : 3, characteristic of metallothioneins. In I, each of the four copper atoms is coordinated to three thiourea ligands and one iodide ion in a distorted tetrahedral mode adopting admantane-like structure. In II, four types of core arrangements are observed around copper(I), which include, Cu(p.-S2)I2, Cu(p.-S2)(p.-I)I, Cu(p.-S3)I, and Cu(p.-S3)S each having copper(I) tetrahedrally coordinated. The complexes were also characterized by IR and 1H and 13C NMR spectroscopy.
DOI: 10.7868/S0132344X14020017
INTRODUCTION
Copper(I) has a strong tendency to form polynu-clear aggregates and polymeric structures [1—8], which have significant importance in biological systems [8, 9] and have potential applications in catalysis [8, 10], in solar energy conversion systems, chemical sensors or display devices [11—14] and also in optical and electronic systems [14—16]. Sulfur or phosphorous containing ligands, halide ions or carbanionic organic molecules are the preferred ligands in such compounds. Among these ligand systems special attention is being given to heterocyclic thiones, which have been known to have wide ranging applications in analytical chemistry [17, 18] and metal treatment [19]. The metal—ligand interaction in such complexes has been found to be highly flexible, resulting in an extraordinary variety of molecular structures [1—3, 20—23]. Such copper(I) complexes may help to mimic bio-relevant metal sulfur interactions for example, in copper-metallothioneins the metals are coordinated by cys-teine sulfur atoms only [9, 24].
In the present study, we attempted to prepare mixed ligand copper(I) complexes of thiones and a thiolate ligand, 2-mercaptopropanoic acid, but it is interesting to note that the compounds crystallized as products [Cu4(Metu)6]I4 (I) and [Cu8(Diaz)12I8] (II) containing only thione ligands. The complex I has the adamantane structure, which is the characteristic of most of the copper(I) thiolates clusters and metal-lothioniens [7, 8, 24, 25]. The compound II is a two di-
mensional polymer with copper to sulfur ratio of 2 : 3, which is often suggested for copper(I)-metallothion-ein cluster core types, Cu6S9 and Cu8S12 [24, 25].
EXPERIMENTAL
Materials and instrumentation. Copper(I) iodide was obtained from Merck Chemicals Co. Germany. 2-Mercaptopropanoic acid and N-methylthioura from Acros Organics, Belgium. Diazinane-2-thione was prepared according to the published procedure [26].
Solid state infrared spectra in the region of 4000— 400 cm-1 were recorded as KBr pallets on a Nicolet FT-IR 6700 spectrophotometer. The 1H and 13C NMR spectra of the complexes in DMSO-d6 were obtained on a Bruker Avance 300 MHz NMR spectrometer operating at frequencies of 300.00 and 75.47 MHz, respectively at 297 K. The spectral conditions were: 32 K data points, 1.822 s acquisition time, 2.00 s pulse delay and 6.00 ^s pulse width. The 13C chemical shifts were measured relative to TMS.
Synthesis of complexes. A solution of 1 mmol of copper(I) iodide in 10 mL acetonitrile was treated with 1 mmol of 2-mercaptopropionic acid in 5 mL acetonitrile. A clear colorless solution was obtained that was stirred for 15 min. To this solution was added 2 equivalents of N-methylthiourea or diazinane-2-thione slowly. The resulting colorless solution was stirred for
Table 1. Crystallographic data and details of the structure refinement for compounds I and II
Parameter
Value
I
II
Formula weight Crystal system Space group
a, A
b, A
c, A P, deg V, A3 Z
Pcalcd g cm-1 Crystal size, mm /(000) p., mm-1 Temperature, K MMo^), A 9 Range, deg Limiting indices h, k, I Reflections collected/unique
Rint
Observed data (I > 2a(I)) T T
J min J max
Data, restraints, parameters R1, wR2, S(I> 2ct(I)) Largest diff. peak, hole, e A-3
654.35 Tetragonal
P4 n2 14.1096(6) 14.1096(6) 9.6522(9)
90
3912.4(3) 8
2.222 55 x 18 x 38 2488 5.647 296(2) 0.71073 2.89-30.04 19 < h < 19, -19 < k < 19, -27 < l< 27 57773/5730 0.0172 5226 0.559, 0.746 5730, 0, 203 0.0330, 0.0769, 1.706 1.006, -1.213
2917.93 Monoclinic
P2x/c 18.8262(8) 20.4911(9) 23.5768(10) 100.8340(10) 8933.1(7) 22 2.169 40 x 32 x 23 5600 4.959 293(2) 0.71073 2.97-30.03 -26 < h < 26, -28 < k < 28, -33 < l< 33 136015/26095 0.0270 13886 0.614, 0.746 26095, 36, 939 0.0342, 0.0755, 1.001 0.958, -1.399
30 min at room temperature. The clear solution was filtered and left for crystallization at room temperature. White crystals were obtained after 48 h, which were washed with acetonitrile and dried in air at room temperature. The yield was 40% for I (m.p. 143-144°C) and 25% for II (m.p. 168-169°C).
For C12H36N12S6I4Cu4 (I)
anal. calcd., %: C, 11.06; H, 2.79; N, 12.90. Found, %: C, 11.67; H, 2.82; N, 13.41.
For C48H96N24S12I8Cu8 (II)
anal. calcd., %: C, 19.76; H, 3.32; N, 11.52. Found, %: C, 21.50; H, 3.59; N, 12.75.
X-ray crystallography. Single crystal X-ray diffraction analyses of compound I and II was carried out on a Bruker SMART APEX diffractometer processed with the Bruker APEX2 software package [27]. The structure was solved by direct methods with SHELXS-97 [28] and refined by full-matrix least
squares procedures on F2 with all measured reflections using SHELXL-97 [28]. The details of the crystallo-graphic data and refinement parameters are provided in Table 1. Supplementary material for structures I and II has been deposited with the Cambridge Crystallographic Data Centre (nos. 907221 and 907222, respectively; deposit@ccdc.cam.ac.uk or http://www. ccdc.cam.ac.uk).
RESULTS AND DISCUSSIONS
Reactions of CuI with Metu and Diaz in a 1 : 2 molar ratio in the presence of 2-mercaptopropionic acid resulted in the formation of products of empirical composition [Cu(L)15I]. The selected IR bands of the ligands and their copper(I) complexes are given in Table 2. In IR spectrum of thiones, the characteristic bands are expected in three frequency regions; v(C=S) appears around 600 or 500 cm-1, v(C-N) bands at about 1500 cm-1 and v(N-H) is observed near 3200 cm-1. The N-H bending vibration appears
KOOP^HH^HOHHAtf XHMHfl TOM 40 № 2 2014
SYNTHESIS, SPECTROSCOPIC CHARACTERIZATION, AND CRYSTAL STRUCTURES
125
Table 2. Selected IR frequencies (cm 1) and NMR (1H & 13C) chemical shifts (in DMSO) of free ligands and their cop-per(I) complexes
Compound IR frequencies NMR shifts
v(C=S) v(N-H) v(C-N) S(N-H) S(C=S) S(N-C)
Metu 634 3163, 3245 1488 6.95, 7.45, 7.65 181.10, 184.10 29.93, 31.10
[Cu4(Metu)6I4] 610 3170, 3218, 3340 1440 7.22, 7.68, 7.97 176.532, 180.773 30.08, 31.06
Diaz 510 3200 1450 7.81 175.62 39.76 (19.19)*
[Cus(Diaz)12Is] 520 3215 1440 8.16 170.88 39.96 (18.65)*
* Signals due to C(5) carbons.
around 1600 cm-1. The N—H bending vibrations in I appeared at 1540 and 1596 cm-1, while in II at 1522 cm-1. As shown in Table 2, the shifts in the v(C=S), v(N—H), and v(C—N) bands in IR spectra of the complexes are indicative of coordination of the ligands to the metal center in the solid state.
The 1H and 13C chemical shifts of the complexes in DMSO-d6 are summarized in Table 2. In 1H NMR spectra of the complexes, the N—H signal of thioureas became less intense upon coordination and shifted down field from their positions in free forms. The appearance of N—H signal shows that the ligands are coordinated to copper(I) via the thione group. Table 2 shows that N—H protons of Metu are non-equivalent (NH2 appears as a doublet) [29].
In 13C NMR, the >C=S resonance of the ligands in the complexes is shifted upfield by about 4-5 ppm as compared to their positions in uncomplexed form in accordance with the data observed for other complexes of d10 metals with thiones [29, 30]. An upfield shift of
this magnitude is a diagnostic test for thione sulfur donation. A small deshielding effect is observed in N—C carbon atoms, which is due to an increase in n character of the C—N bond. Metu gives two signals for both >C=S and N—CH3 carbons showing that the compound exists in two isomeric forms [29].
The molecular structures of[Cu4(Metu)6I4] (I) and [Cu8(Diaz)12I8] (II) with the atomic numbering schemes are depicted in figure. Selected bond distances (A) and bond angles (deg) for I and II are given in Table 3. In complex I, four copper(I) iodide and six Metu ligands are combined through ^-bridging sulfur atoms to form a tetranuclear core Cu4S6I4. In the tetranuclear core, each copper is tetrahedrally coordinated to three sulfur atoms of Metu and with one iodide in the terminal position. The angles around Cu vary over a range of 107.02°—113.47(5)° representing a nearly regular tetrahedral geometry. The Cu—S (2.2825(12) to 2.3613(14) A) and Cu—I ((2.2825(12) to 2.3613(14) A) bond distances are unequal. Howev-
The molecular structure of I (a) and II (b) with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.
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Table 3. Selected bond distances (Â) and bond angles (deg) for compounds I and II
Bond d, Â Bond d, Â
Cu(1)—S(1) Cu(1)-S(2) Cu(1)-S(3) Cu(1)-I(1) Cu(2)-S(4) Cu(2)-S(1) Cu(1)-S(1) Cu(1)-I(1) Cu(1)-I(2) Cu(1)-S
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