КООРДИНАЦИОННАЯ ХИМИЯ, 2007, том 33, № 5, с. 373-376
УДК 541.49
A ROUTE TO NOVEL STABLE SALTS CONTAINING TRANSITION
AND MAIN GROUP METALS
© 2007 F. M. A. M. Aqra and R. M. A. Q. Jamhour
Department of Chemistry, Faculty of Science, Hebron University, Hebron, West Bank, Palestin Department of Applied Chemistry, Faculty of Science, Tafila Technical University, Tafila, Jordan
Received April 5, 2006
Novel salts of the type [Cu(Dien)2][Bu3SnCl3], [Cu(Dien)2][Ph2Sna4], and [Cu(Dien)2][SnCl6] (Dien - dieth-ylenetriamine) was prepared by the reaction of [Cu(Dien)2]Cl2 with Bu3SnCl, Ph2SnCl2, and SnCl4 in MeOH in a 1 : 1 ratio, respectively, were characterized by elemental analyses, electronic, IR and ESR spectroscopy, magnetic susceptibility, electrochemistry, and conductivity measurements. The results revealed that the compounds are 1 : 1 electrolytes and the Cu ion is paramagnetic in the octahedral field. The complexes exhibit a single one-electron redox couple.
INTRODUCTION
Binuclear copper(II) compounds have evoked considerable worldwide interest in recent years and have attracted much attention [1, 2] because they are good electrocatalysts [3, 4] and have been widely used in the biomimetic chemistry of copper(II) proteins and in the substrate activation by metal centers [5, 6]. Salts containing two transition metal ions have been thoroughly investigated [7-12]. However, salts incorporating with a transition and a main group metal are probably less common, and therefore, it was considered worthwhile to prepare a series of salts containing Cu2+/Sn4+ ions that could be useful in some future applications in order to gain further insight into the above properties of di-metallic complexes.
To extend this chemistry, attempts were made to utilize the ability of tin(IV) in a salt with copper(II). Herein, we performed the synthesis and characterization of new compounds resulting from the reaction of tin(IV) species with fe(diethylenetriamine)copper(n). It is an established fact that tin(IV) is capable of extending its coordination number from four to six by accepting two ligands. However, in this project, novel type of salts made of mononuclear anionic and mononuclear cationic metal complexes are described.
Attempts to recrystallize the compounds in order to prepare single crystals for X-ray diffraction studies were unsuccessful. It was not possible to record XH, 13C, and 119Sn NMR spectra for these compounds due to the presence of paramagnetic copper(II), and this would indeed be crucial to get experimental evidence for the geometry of the tin atom in the compounds.
EXPERIMENTAL
Diethylenetriamine (Koch Light), CuCl2 (BDH), Bu3SnCl, Ph2SnCl2, and SnCl4. (Fluka) were used as received. MeOH and DMSO were distilled and dried before use. Microanalyses were made on a Carlo Erba
analyzer (model 1106). Molar conductances were measured at room temperature on a Digisun electronic conductivity bridge. The IR spectra (200-4000 cm-1) were recorded on a Carl Zeiss Specord M80 spectrometer in nujol mulls. Electronic spectra were recorded on a Shi-madzu UV Vis spectrometer (model 60). The ESR spectra were measured on a Bruker Scientific X-band spectrometer (ESP-300) using a 100 KHz field modulation and quartz sample tubes. The g values determined were calibrated with a DPPA powder (g = 2.0036). Chlorine was estimated by a gravimetric method. Tin was estimated as SnO2, whereas copper analysis was made on a Schimadzu AA-6AO atomic absorption/flame emission spectrometer. Magnetic susceptibilities were measured using a Cahn 2000 Faraday magnetic balance calibrated with Hg[Co(NCS)4] at room temperature. All reactions were carried out at room temperature under nitrogen atmosphere. Cyclic voltametric experiments were carried out on a Princeton Applied Model, 273 po-tentiostat-galvanostat using a 0.001 M solution in DMF and Et4NClO4 as supporting electrolyte. All experiments were performed under dry N2 at 25°C, using a three-electrode assembly comprising a platinum disk as the working electrode, a platinum wire as the auxiliary electrode, and a standard calomel electrode (SCE) as the reference electrode. All potentials were referred to SCE.
Synthesis of [Cu(Dien)2]Cl2 (I) was carried out by a reported method [13].
Synthesis of [Cu(Dien)2][Bu3SnCl3] (II). Bu3SnCl (3.25 g, 0.01 mol) dissolved in carbon tetrachloride (25 ml) was added dropwise to a methanolic solution (25 ml) of [Cu(Dien)2]Cl2 (3.40 g, 0.01 mol). This mixture was warmed and left at room temperature for 20 days until blue crystals precipitated. The crystals were then filtered and dried in vacuo.
Synthesis of [Cu(Dien)2][Ph2SnCl4] (III). A solution of Ph2SnCl2 (3.40 g, 0.01 mol) in CCl4 was added dropwise (25 ml) to a methanolic solution (25 ml) of [Cu(Dien)2]Cl2 (3.40 g, 0.01 mol). Solution turned from
Table 1. The elemental analyses data, molar conductances and some physical properties of compounds I-IV
Compound Yield, % M.p., °C Colour Contents(found/calcd), % A, Ohm 1 cm 2 • mol1
C H N Cu Sn Cl
[Cu(Dien)2]Cl2 (I) 80 243 Blue 28.4/28.4 7.7/7.7 24.6/24.5 18.6/18.5 20.8/20.5 200
[Cu(Dien)2][Bu3SnCl3] (II) 46 210 Blue 36.0/36.3 8.0/8.0 12.6/12.6 9.5/9.3 17.8/17.5 15.9/15.8 161
[Cu(Dien)2][Ph2SnCl4] (III) 35 123 Yellow 35.1/35.2 5.3/5.3 12.2/12.2 9.2/9.1 17.3/17.0 20.7/20.5 137
[Cu(Dien)2][SnCl6] (IV) 65 205 Green- 14.3/14.5 3.9/3.9 12.5/12.5 9.4/9.2 17.6/17.2 31.1/31.0 106
ish-yel-
low
blue to yellow, was warmed and kept standing at ambient temperature for more than three weeks until a yellow crystalline compound formed. The crystals were filtered off and dried in vacuo.
Synthesis of [Cu(Dien)2][SnCl6] (IV). This compound was synthesized by a slow addition of SnCl4 (0.01 mol) dissolved in CCl4 (25 ml) to a methanolic solution (25 ml) of [Cu(Dien)2]Cl? (3.40 g, 0.01 mol). The resulting precipitate was then stirred for 30 min, filtered off, washed twice with MeOH, and dried under vacuo.
The elemental analyses data, molar conductances and some physical properties of compounds are given in Table 1.
RESULTS AND DISCUSION
Copper(II) chloride reacts with diethylenetriamine (Dien) in a 1 : 2 ratio in MeOH to yield [Cu(Dien)2]Cl2 (Eq. 1), which in turn reacts efficiently with tin(IV) tetrachloride and organotin(IV) chlorides to yield polycrystal-line [Cu(Dien)2][Bu3SnCl3], [Cu(Dien)2][Ph2SnCl4], and [Cu(Dien)2][SnCl6] (Eq. 2).
CuCl2 + 2Dien
[ Cu( Dien)2 ] Cl2 (1) (I)
SnCl4
Bu3SnCl > [Cu(Dien)2][Bu3SnCl3]
(II)
[Cu(Dien)2]Cl2 MeOH( Ph2SnCl2 ■ [Cu(Dien)2][Ph2SnCl4].
(III) (2)
l4 - [Cu(Dien)2][SnCl6] (IV)
The elemental analyses are in good agreement with the proposed composition of the compounds. They are slightly hygroscopic in nature and highly soluble in water. The molar conductances of these salts in DMSO at room temperature show that they are 1 : 1 electrolytes [14]. These compounds are suggested to be formed by the transfer of two chloride ions from [Cu(Dien)2]Cl2 to tin(IV) tetrachloride or organotin(IV) chlorides. In this
way, the fe(diethylenetriamine)copper(II) cation is stabilized by tin(IV) anionic species.
At the room temperature ESR spectra of all the polycrystalline samples (figure) are similar, showing a signal with g = 2.268 and g±= 2.056 (g0 = 2.13), in agreement with the tetragonally distorted stereochemistry of the Cu2+ ion [15]. The nuclear hyperfine coupling is observed in the g signal with three of the four components resolved, the last one being obscured by the g± component. At lower temperature (110 K), narrower signals with the same values are observed. Therefore, the orbital ground state of copper(II), which contains an unpaired electron, would be basically dx2_y2 and the CuN6 would statistically be distorted (N is a donor atom in a macrocyclic complex).
The electronic absorption spectra for [Cu(Dien)2]Cl2 and for the newly synthesized copper species were recorded in MeOH and DMSO at 25C°, respectively, and expanded wherever possible. The electronic spectral bands of compounds in a ranges 200-400 and 400-750 nm are 256, 302, 300, 295 and 620, 600, 589, 585, respectively. The electronic spectrum of [Cu(Dien)2]Cl2 exhibits a high intensity charge-transfer band at 256 nm. A clear d-d band observed at 620 nm is characteristic of 2Eg —» 2T2g transition in the distorted octahedral environment of Cu2+ ion. The electronic absorption spectra of the salts exhibit a band at ~302 nm assignable to the ligand-to-metal charge transfer [16]. The d-d bands centered at ~600 nm are characteristic of the d 2 2 —- d 2
x - y z
transition in the d9 system of the Cu2+ ion in a hexacoor-dinated configuration.
The observed magnetic moments of all compounds are ~1.78 due to the presence of one spin electron. Since the Cu+2 ion is always d9, it can hardly be to imagined what an alternative expectation to paramag-netism might be. The diene ligand normally forms octahedral complexes and, therefore, it is claimed that the Cu2+ ion maintains an octahedral geometry. On this basis, it is not surprising to say that the presence of tin(IV) in these salts does not change the paramagnetism of the Cu2+ ion, and therefore, rules out the possibility of an-tiferromagnetic exchange because Sn(IV) contains no unpaired electron. Thus, the metal sites in such a salt
MeOH
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A ROUTE TO NOVEL STABLE SALTS CONTAINING TRANSITION AND MAIN GROUP METALS
(a) gii (b)
g||
i_i_i_i_i_i_i_i_i_ i_i_i_i_i_i_i_i_l_
DPPH
(c)
(d)
Y
(H = 3322 G)
2700 2800 2900 3000 3100 3200 3300 3400 3500 2700 2800 2900 3000 3100 3200 3300 3400 3500
H, G
ESR spectra of polycrystalline samples of the compounds: I (a), II (b), III (c), and IV(d).
would not be expected to exhibit any interaction with one anther, and experimentally they do not.
The IR spectral bands of all the compounds are given in Table 2. The IR spectrum of [Cu(Dien)2]Cl2 shows two adjacent bands at 3230 and 3145 cm-1 attributable to v(RNH) of the primary
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