Silver(I) tetraiodoethylene complexes with twisted olefin moiety

www.elsevier.nl/locate/ica Inorganica Chimica Acta 290 (1999) 251 – 255

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Silver(I) tetraiodoethylene complexes with twisted olefin moiety Liang Ping Wu, Megumu Munakata *, Takayoshi Kuroda-Sowa, Masahiko Maekawa, Yusaku Suenaga, Yoshinobu Kitamori Department of Chemistry, Kinki Uni6ersity, Kowakae, Higashi-Osaka, Osaka 577 -8502, Japan Received 4 September 1998; accepted 31 December 1998

Abstract The reactions of silver perchlorate and tetraiodoethylene in different solvents, namely, benzene and toluene, isolated two silver(I)–iodocarbon complexes, [Ag(C2I4)(C6H6)2(ClO4)] (1) and [Ag(C2I4)(ClO4)] (2). Both compounds contain intact iodoalkenes which coordinate via s-donation of a halogen lone pair and retain their carbon – iodine bonds. Owing to the participation of the benzene molecules in coordination, complex 1 is found to be a discrete monomer in which the five-coordinate geometry of the silver ion is comprised of two benzene molecules, one C2I4 group and one perchlorate ion. In contrast, the unsaturated coordination environment of the metal ion in 2 is filled by the second iodocarbon group leading to a two-dimensional framework. The coordinated tetraiodoethylene molecules involve severe twisting of the CC double bond, causing the CC stretching band to move to a lower frequency. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Crystal structures; Silver complexes; Iodocarbon complexes

1. Introduction Although halocarbon – metal bonds have long been suspected to be important intermediates in organometallic chemistry, it is recognized only recently that they constitute a unique type of ligand in coordination chemistry [1–10]. A number of coordination compounds containing simple alkyl and aryl halides have been structurally characterized. Among them the iodocarbon binding to the silver ion is found to be stable in the solid state presumably due to the match of the soft acid and soft base [9,10]. Notable examples of silver complexes containing simple diiodocarbons include I(CH2)n I (n =1, 3) and I(C6H4)I, which function as bridging ligands in the infinite linear chain and spiral chain frameworks of the metal ions [10]. In spite of this, information is lacking for halogen derivatives of ethylene. We now report silver(I) complexes of te* Corresponding author. Tel.: +81-6-721 2332; fax: +81-6-723 2721. E-mail address: [email protected] (M. Munakata)

traiodoethylene in an attempt to explore the coordination behavior of the alkene halides. Tetraiodoethylene is known as an antiseptic agent [11], and it is also reported to form a charge-transfer complex with pyrazine [12,13]. We have found that the ready binding of this iodocarbon species to silver(I) ions makes it an especially interesting candidate for formation of polynuclear coordination compounds.

2. Experimental Preparation was performed using usual Schlenk techniques. All solvents were dried and distilled by standard methods before use. Tetraiodoethylene and silver perchlorate were purchased from Aldrich. AgClO4 · H2O was dried at 40°C under reduced pressure for 5 h before use. Other standard chemicals were obtained from Wako, Japan, and used without further purification. Infrared spectra were measured as KBr disks on a JASCO FT/IR-8000 spectrometer. Caution: Although no problems were encountered during the

0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 9 9 ) 0 0 1 5 0 - 4

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preparation of the perchlorate salt described below, suitable care and precautions should be taken when handling such potentially hazardous compounds.

2.1. Synthesis of [Ag(C2I4)(C6H6)2(ClO4)] (1) To a benzene solution (10 ml) containing silver perchlorate (90.1 mg, 0.4 mmol) was added tetraiodoethylene (212.7 mg, 0.4 mmol). The mixture was stirred for 10 min and filtered. A portion of the filtrate (3 ml) was transferred to a 7 mm diameter glass tube and gently layered with 3 ml of n-pentane as a diffusion solvent. After standing for 3 days at room temperature pale yellow prism crystals were obtained. The product is unstable when dried in vacuo and even trying to remove excess solvent with a slow stream of dry argon resulted in loss of coordinated benzene and loss of transparency of the crystals at room temperature. Therefore, the theoretical value of elemental analysis and the isolated yields (120 mg, 41%) for 1 are based on the formula without benzene molecules. Anal. Calc. for C2I4AgClO4: C, 3.25; H, 0.00. Found: C, 3.24; H, 0.22%.

2.2. Synthesis of [Ag(C2I4)(ClO4)] (2) This compound was synthesized in a similar manner to that for 1 with toluene in place of benzene as the solvent. After standing for 2 weeks at room temperature the mixed solution of silver perchlorate and C2I4 gave yellow prism crystals of 2 (131 mg, 44%). Anal. Calc. for C2I4AgClO4: C, 3.25; H, 0.00. Found: C, 3.29; H, 0.08%.

2.3. X-ray data collection and structure determination Diffraction data were collected on a Rigaku AFC7R four-circle diffractometer using graphitemonochromated Mo Ka (l= 0.71069 A, ) radiation and a 12 kW rotating anode generator. A summary of crystallographic data is given in Table 1. A suitable single crystal was mounted on a glass fiber for 2 and enclosed in a glass capillary together with mother liquor for 1. Unit cell parameters were obtained from a least-squares analysis of the setting angles of 25 high-angle reflections in which the appropriate cell angles were constrained to their ideal values. Intensity data were collected by using standard scan techniques (v – 2u). Space groups were selected on the basis of systematic absences and intensity statistics which in both cases led to satisfactory refinements. In the case of 2, the intensities of three standard reflections, monitored at 150 reflection intervals throughout data collection, remained con-

stant within experimental error, indicating crystal and electronic stability. Thus, no decay correction was applied. However, over the course of data collection for 1, the standards decreased by 28.9% because the solvent molecule was omitted from the lattice. A linear correction factor was applied to the data to account for this phenomenon. For both 1 and 2, an empirical absorption correction based on azimuthal scans of several reflections was applied which resulted in transmission factors ranging from 0.93 to 1.00 for 1 and from 0.55 to 1.00 for 2. The diffracted intensities were corrected for Lorentz and polarization effects. The structures were solved by a direct method [14] and expanded using Fourier techniques [15]. All non-H atoms were refined with anisotropic thermal parameters, except for some disordered benzene C-atoms in 1. The hydrogen atoms for benzene in 1 are excluded. Final refinements for all the structures were performed on these data having I\ 3s(I) and included anisotropic thermal parameters for non-hydrogen atoms. Reliability factors are defined as R= S( Fo − Fc )/S Fo and wR= {Sw( Fo − Fc )2/S w Fo 2}1/2. Atomic scattering factors and anomalous dispersion terms were taken from the usual sources [16]. All crystallographic computations were performed on a VAX computer using the program system TEXSAN [17].

Table 1 Crystallographic data for 1 and 2

Formula Formula weight Crystal system Space group a (A, ) b (A, ) c (A, ) b (°) U (A, 3) Dc (g cm−3) Z F(000) m(Mo Ka) (cm−1) Crystal size (mm) No. reflections measured No. reflections observed [I\ 3.00s(I)] No. of variable parameters R wR Goodness-of-fit Max./min. peaks in final diffraction map (e A, −3)

1

2

C14H12AgI4ClO4 895.19 monoclinic P21/c 10.907(5) 9.860(3) 20.615(2) 104.76 2143(1) 2.773 4 1616 68.39 0.40×0.40

C2AgI4ClO4 738.96 monoclinic P21/c 7.092(1) 21.489(2) 8.0775(9) 109.49(1) 1160.4(3) 4.229 4 1280 125.84 0.30×0.30×0.20

×0.40 5455 2460

2946 2286

217 0.067 0.081 2.62 0.90, −0.90

109 0.042 0.057 2.38 1.96, −2.58

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Table 2 Selected bond distances (A, ) and angles (°) for 1 and 2

Fig. 1. Labeling scheme and structure of [Ag(C2I4)(C6H6)2(ClO4)].

3. Results and discussion Although both complexes 1 and 2 crystallize in the same monoclinic space group P21/c, they involve two distinct structures. As shown in Fig. 1, the crystal structure of 1 consists of discrete monomeric molecules of [Ag(C2I4)(C6H6)2(ClO4)] in which each silver atom displays an essentially trigonal bipyramidal environment. The two crystallized solvate benzene molecules and one iodine atom of the tetraiodoethylene group comprise the plane, while the two apical positions are occupied by one oxygen atom from the perchlorate ion and the second iodine atom of the C2I4 group with I(4) –Ag–O(1) bond angle of 156.7(5)° (Table 2). The two Ag–I bond lengths are unequal, being 3.006(2) and 2.989(2) A, for I(2) and I(4), respectively, but both are well within the range of 2.78 – 3.30 A, observed in the previously reported iodocarbon – silver complexes [9,10]. The silver–benzene p interaction is approximately symmetrical, having Ag – C distances of 2.60(2) and 2.64(2) A, for one benzene, and the same length of 2.60(2) A, for the other. The remaining silver – carbon interactions are greater than 3.31 A, , well beyond the limits from 2.47 to 2.920 A, observed in the reported silver(I)–aromatic complexes [18]. In fact, complex 1 is a rare example of monomeric silver compound with benzene and its derivatives. Normally, each benzene molecule is associated with two metal ions lying above and below the ring [19,20]. With perchlorate ions acting as spacers, such connection sometimes can generate an infinite chain structure as observed in the silver perchlorate complex of benzene [19]. X-ray structure determination of complex 2 reveals a

1 Ag–I(2) Ag–C(3) Ag–C(11) Ag–O(1) I(2)–C(1) I(4)–C(2)

3.006(2) 2.60(2) 2.60(2) 2.61(1) 2.11(1) 2.10(1)

Ag–I(4) Ag–C(4) Ag–C(13) I(1)–C(1) I(3)–C(2) C(1)–C(2)

2.989(2) 2.64(2) 2.60(2) 2.08(1) 2.10(1) 1.33(2)

I(2)–Ag–I(4) I(2)–Ag–C(4) I(2)–Ag–C(13) I(4)–Ag–C(4) I(4)–Ag–C(13) C(3)–Ag–C(11) C(4)–Ag–C(11) C(11)–Ag–C(13)

74.32(4) 106.1(5) 127.4(8) 96.3(5) 102.7(7) 124(1) 150.1(10) 28(1)

I(2)–Ag–C(3) I(2)–Ag–C(11) I(4)–Ag–C(3) I(4)–Ag–C(11) C(3)–Ag–C(4) C(3)–Ag–C(13) C(4)–Ag–C(13) I(4)–Ag–O(1)

135.0(6) 100.2(9) 96.0(5) 104.3(7) 30.0(8) 97.6(10) 126.2(9) 156.7(5)

2 Ag–I(1) Ag–I(3) Ag–O(2) I(2)–C(2) I(4)–C(2)

2.894(1) 2.812(1) 2.56(1) 2.091(9) 2.10(1)

Ag–I(2) Ag–O(1) I(1)–C(1) I(3)–C(1) C(1)–C(2)

2.924(1) 2.454(9) 2.088(10) 2.112(9) 1.32(1)

I(1)–Ag–I(2) I(1)–Ag–O(1) I(2)–Ag–I(3) I(2)–Ag–O(2) I(3)–Ag–O(2)

77.81(3) 91.6(2) 118.90(5) 89.4(3) 92.4(2)

I(1)–Ag–I(3) I(1)–Ag–O(2) I(2)–Ag–O(1) I(3)–Ag–O(1) O(1)–Ag–O(2)

126.83(4) 140.2(3) 139.9(2) 98.5(2) 74.3(4)

two-dimensional framework of metal ions bridged by both tetraiodoethylene and perchlorate ions. As shown in Fig. 2, each Ag ion adopts a five-coordinate squarepyramidal geometry comprising two I atoms of the tetraiodoethylene molecule, Ag–I 2.894(1) and 2.924(1) A, , and one O atom of two separate perchlorate ions, Ag–O 2.454(9) and 2.56(1) A, , forming the basal plane with another iodine atom of the second C2I4 group located at the apex, Ag–I(3) 2.812(1) A, . The separation between Ag and I(4) is 4.62 A, , too large to be considered effective interaction. Stereochemistry of silver(I) complexes is dominated by four- and three-coordination. In contrast, five-coordinate silver(I) compounds are unusual. The Ag atom is lifted out of the basal plane by a distance of ca. 0.24 A, in a direction towards the terminal iodine atom. Each C2I4 moiety displays a tridentate fashion bridging two metal centers giving an infinite linear chain structure. The adjacent chains are crosslinked by the perchlorate ions forming two-dimensional networks. The structure is reminiscent of silver(I) complex [Ag(NO3)(CH2I2)] in which the nitrate bridges two silver atoms via two oxygen atoms leading to a sheet array of metal ions [10]. The fact that two very different compounds were obtained from the same reactants but in different solvents indicates that the solvents play an important role

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Fig. 2. Labeling scheme and structure of [Ag(C2I4)(ClO4)].

not only in solvating the reactants for obtaining large crystals suitable for X-ray analysis but also in topological control of the metal stereochemistry by coordination of solvent molecules to the metal ions. In both 1 and 2, tetraiodoethylene is coordinated to the silver ion through the iodine atoms rather than the olefin moiety. Previously, Dahl and Hassel [13] have shown that tetrabromoethylene and tetraiodoethylene act as electron acceptor to form 1:1 adducts with pyrazine, and the packing of the acceptor molecules is left virtually unaltered after the introduction of the less voluminous pyrazine molecules into the lattice of the tetrahalogenoethylene. In the present work we have demonstrated that C2I4 can also act as a bidentate or a tridentate ligand (but not a tetradentate ligand). The most striking

feature of the two complexes is that the ligand CC double bond is severely twisted due to the coordination of the iodine atoms. The least-squares plane calculation indicates that the half plane of the C2I4 moiety is twisted against the other by 4.31° for 1 and 8.26° for 2 (Fig. 3). The most twisted olefin was observed in tetrasilylethylene due to sterically overcrowding of the molecules in the unit cell, which involves a dihedral angle of 49.6° between two C(sp2) planes and an exceedingly longer CC double bond length [21]. Likewise, the observed CC distances for the iodocarbon in 1 and 2 are 1.33(2) and 1.32(2) A, , respectively, both longer than that for the non-coordinated tetraiodoethylene (1.295 A, ) [11]. Although these two distances cannot be compared with each other (because of large standard deviations) in discussion of the dihedral angles involved in the twisting C2I4 molecules, they represent a general trend of lengthening of the CC bond with increase of twisting the double bond. It also explains why C2I4 displays a tridentate rather than tetradentate coordination fashion in complex 2 since the molecular constraint resulting from the twisting of the CC double bond repelled the ligand chelating the silver ion with I(3) and I(4) atoms. Infrared spectroscopy is a good indicator of the CC bond twisting involved in the C2I4 moiety. The free tetraiodoethylene molecule exhibits a CC stretching frequency at 1623 cm − 1. This frequency shifts to 1613 and 1609 cm − 1 for 1 and 2, respectively, indicating that the double bond strength decreases with the extent of the CC bond twisting.

4. Conclusions Tetraiodoethylene reacts favorably with silver(I) salt forming monomeric and polymeric coordination compounds. The iodocarbon binds the metal ion through the iodine atoms rather than the olefin moiety and acts as a bidentate or tridentate ligand, but not tetradentate ligand, owing to the molecular constraint resulting from twisting of the CC bond. Its coordinative versatility highlights its potential application as ligands for development of coordination antiseptic agents and other coordination materials.

5. Supplementary material

Fig. 3. Schematic view of the twisting CC bond involved in C2I4 molecules.

Complete tables of bond lengths and angles, final atomic coordinates and equivalent isotropic thermal parameters, calculated hydrogen atom parameters, anisotropic thermal parameters, and structure factors for two structures are available from the authors. Details of the crystal structure determinations of the com-

L.P. Wu et al. / Inorganica Chimica Acta 290 (1999) 251–255

pounds reported are also available upon request from the Cambridge Crystallographic Data Center (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK.

Acknowledgements This work was partially supported by a Grant-in-Aid for Science Research [Nos. 09554041, 10440201 and 10016743 (priority areas)] from the Ministry of Education, Science, Culture and Sports in Japan.

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