π−π Interactions Affect Coordination Geometries - Crystal Growth

DOI: 10.1021/cg100265d

π-π Interactions Affect Coordination Geometries

2010, Vol. 10 1892–1896

Hamid Reza Khavasi* and Mahmood Azizpoor Fard Department of Chemistry, Shahid Beheshti University, G. C., Evin, Tehran 1983963113, Iran Received January 1, 2010

ABSTRACT: We explore the effect of π-π interactions in the complexes of mercury halides containing the N-(naphthyl)-2pyrazine carboxamide ligand (L1) in the coordination geometry of the central metal. Results show molecular packing features have a dramatic effect on coordination geometries and that the π-π stacking interaction affects the geometry around the mercury.

Introduction Crystal engineering is the planning and construction of the structure and properties of crystal structures by designing molecular building blocks.1 This planning contains both the crystal structure design that is suitable for specific reactions or functions and control of the molecular assemblies in the solid state on the basis of molecular structures. In this regard, the design of the molecules has been progressing according to the metal coordination and the concept of supramolecular synthons.2 Understanding the nature of intermolecular interactions, which assemble the building blocks according to supramolecular synthons, is important in developing methodologies for crystal synthesis. The packing of molecules in the crystal structures generated by conventional hydrogen bonds has been well studied.3 Interactions of the type C-H 3 3 3 π provide weak but directional packing motifs, which aid in the evaluation of molecular assemblies.4 Other than the C-H 3 3 3 π interactions and the hydrogen bonds, the π-π interactions undoubtedly play important roles in determining the crystal packing, molecular assemblies,5 and structure of large biological systems.6 Aromatic rings can interact in different geometrical arrangements, for example, face-toface, offset, and point-to-face,7 and have been found to be a useful tool in the manipulation of the molecular components in crystals.8 According to variable orientations of the involved moieties in these interactions for the maximizing of the electrostatic attraction between the σ skeleton and π density of the aromatic rings, π-π interaction generally is a weak force in the formation of the crystal packing. So, unlike hydrogen bonding, π-π interaction is very difficult to control due to the lack of strength and directionality. The role of hypervalent,9 hydrogen,10 and C-H 3 3 3 π4c bonding effects on coordination geometries has been analyzed for complexes containing flexible ligands such as dithionate and crown ethers. Even though there are some examples reported in the literature describing the influence of π-π interactions in the secondary structure-directing in the formation of special arrangements,11 to the best of our knowledge, the study of the π-π stacking effect on the primary structuredirecting coordination geometry has not been thoroughly discussed. As part of a study on π-π interactions, we became interested in designing N-(naphthyl)-2-pyrazine carboxamide *Corresponding author. Tel.: þ98 21 29903105. Fax: þ98 21 22431663. E-mail: [email protected]. pubs.acs.org/crystal

Published on Web 03/16/2010

Figure 1. The molecular structure of (a) [HgCl2(L1)2], 1, (b) [HgBr2(L1)], 2, and (c) [HgI2(L1)], 3.

ligand (L1)12 with well-defined coordination modes that would facilitate formation of π-π stacking which affect the coordination geometries. For this purpose, we explore the effect of π-π interactions in the complexes of mercury halides containing L1 in the coordination geometry of the central metal. X-ray diffraction analysis of these coordination compounds13 give details about their three-dimensional organizations (Figure 1). Results and Discussion In [HgCl2(L1)2], 1, Figure 1a, the molecule contains one Hg(II) and two L1 ligand, while the metal ion is octahedrally coordinated to the two pyrazine nitrogen atoms, two chlorine atoms in the equatorial position, and two carbonyl oxygen atoms at the axial sites. The Hg-N distance of 2.844(4) A˚, Table 1, is slightly longer than other Hg-N distances previously reported,14 and it seems that it is outside the range of a covalent interaction. To get an idea about the nature of this distance, a Cambridge Structural Database (CSD) search was carried out with help of Vista program (version 2.1f) in the November 2008 release of the CSD version 5.29.15 A search on Hg-N distances that resulted in 1079 hits shows that 38 hits r 2010 American Chemical Society

Article

Crystal Growth & Design, Vol. 10, No. 4, 2010

1893

Table 1. Selected Bond Distances (A˚) and Angles (°) complex 1 bond distance

bond angle

Hg-X

2.2931(11)

Hg-O 2.964(4) Hg-N 2.844(4)a X-Hg-X 180.00b X-Hg-O 88.1(5) 91.9(4) X-Hg-N 89.1(5) 90.4(5) O-Hg-N 89.2(5) CdO-Hg 104.73(6)

2

3

2.4244(11) 2.4260(13) 2.807(6) 2.584(6)c 165.24(11) 88.0(5) 101.6(6) 97.30(16)c 95.78(16) 76.8(6) 116.24(13)

2.6014(9) 2.6257(9) 3.0493(13)d 2.498(7) 157.46(3) 85.5(6)d 103.3(5)d 100.57(9) 101.87(9) 73.18(10)d 120.10(11)

a Symmetry code: X, -1 þ Y, Z. b -X, -Y, -Z. c 1 - X, -Y, -Z. d 1 X, 2 - Y, 1 - Z.

have a distance longer than 2.800 A˚ (for a histogram plot of distribution of Hg-N bond distance see Figure S1, Supporting Information). In this complex, the Hg ions are linked by L1 to give a one-dimensional (1D) chain in the b-direction. For [HgBr2(L1)], 2, Figure 1b, and [HgI2(L1)], 3, Figure 1c, the structures consist of two ligands and two Hg ions bonded to form dimeric complexes. Each metal is four coordinated and bonded to two halogen atoms, one pyrazine nitrogen atom, and one carbonyl oxygen atom from the second ligand. The resulting polyhedron can be realized as a distorted octahedron with two adjacent vertices being removed and the two adjacent complexes approaching each other to form a Hg 3 3 3 Hg contact of 4.541(8) and 4.657(9) A˚ for 2 and 3, respectively. In these complexes, the Hg-N bonds are in the range of 2.498-2.584 A˚, Table 1, comparable to those found in previously reported pyrazine-coordinated mercury(II) complexes.16 For 3, the Hg-O bond distance of 3.0493(13) A˚, Table 1, is smaller than the sum of the revised van der Waals radii of Hg(II)17a and O17b that are 1.71 A˚ and 1.52 A˚ respectively. As it is clear from the histogram plot of distribution of Hg-O bond distances, Figure S2, Supporting Information, that there are more than 100 reports for distances longer than 3.00 A˚ for Hg-O bonds. Other bond distances are in normal ranges. All three structures are stabilized by an ordered network of intermolecular π-π interactions that exist between pyrazine and naphthalene rings, Figure 2. As shown in Figure 3a, we have defined three parameters that relate the amount of slippage of naphthalene and pyrazine rings involved in the π-π interactions. The parameters of C-C and P-P are ring centroid to ring centroid distance and naphthalene plane to pyrazine plane angle, respectively, while the P-CC, displacement angle, defines the angle between the C-C direction and pyrazine ring normal vector. CSD searches based on the C-C distance, P-P angle, and P-CC displacement angle are shown in Figures 4, S3, and 5, respectively. As it is clear from these histograms, the C-C distances of 3.559 and 3.813 A˚ for 1, 3.880 and 3.868 A˚ for 2, and 3.780 and 4.071 A˚ for 3 are near the relative maximum in the number of examples around 3.7 A˚. The same trend is found for P-CC displacement angles of 16.58° and 26.54° for 1, 26.91° and 27.36° for 2, and 26.46° and 30.05° for 3. Most examples lie between 10° to 45°, but the relative maximum in the number of examples is found between 15° to 30°. In all three compounds, the displacement angle values lie in this normal range. For all three packing, the P-P angle is near zero (0.52°, 1.90° and 1.18° for 1, 2, and 3 respectively, Figure S3, Supporting Information) which is normal for the formation of the π-π interactions. The greater part of the intermolecular plane contact is close to parallel to

Figure 2. View along the crystallographic b-axis showing layers of interacting molecules of (a) [HgCl2(L1)2], 1, (b) [HgBr2(L1)], 2, and (c) [HgI2(L1)], 3.

each other. A correlation between the centroid to centroid distance (C-C) and the displacement angle (P-CC) is illustrated in Figure 6. Compounds reported here are around the maximum distribution area in this scatter-gram. These geometrical analyses clearly show the presence of π-π interactions between adjacent aromatic rings. In these compounds, the layers stack in an ABABA fashion, Figure 2.

1894

Crystal Growth & Design, Vol. 10, No. 4, 2010

Khavasi and Azizpoor Fard

Figure 3. (a) Definition of π-π interaction geometry. C-C is centroid to centroid distance, dashed line is ring normal and P-CC is the displacement angle that is angle between the ring normal and the centroid to centroid vector. (b) Definition of the angle (θ) between the plane (containing ligand L1) normal and Hg-O vector.

Figure 6. Scatter-gram for a correlation between the centroid to centroid distance (C-C) and the displacement angle (P-CC). The black spots represent the values of C-C and related P-CC for 1, 2, and 3.

Figure 4. Histogram for the centroid to centroid distance between naphthalene and pyrazine rings from a CSD search. The C-C distance (A˚) was constrained to an intermolecular contact between 3.2 A˚ and 4.2 A˚ for the search. The green, red, and violet columns are shown the related values for [HgCl2(L1)2], 1, [HgBr2(L1)], 2, and [HgI2(L1)], 3, complexes, respectively.

Figure 7. Histogram for the angle (θ, deg) between the plane (containing ligand L1) normal and Hg-O vector from a CSD search. The related values for [HgCl2(L1)2], 1, [HgBr2(L1)], 2, and [HgI2(L1)], 3, complexes are shown in the figure.

Figure 5. Histogram for the displacement angle (deg), P-CC defined as the angle between the ring centroid vector (CC) and the ring normal to pyrazine ring from a CSD search. The green, red, and violet columns are shown the related values for [HgCl2(L1)2], 1, [HgBr2(L1)], 2, and [HgI2(L1)], 3, complexes, respectively.

The naphthalene rings involved in the π-π stacking interactions, with the pyrazine rings, are arranged in such a way that the θ angle (the angle between the plane normal and

Hg-O vector), Figure 3b, is reached about 14.73°, 26.24°, and 30.10° for 1, 2, and 3, respectively. It is noteworthy that a search of the CSD for the geometry of X2CdO-Hg, Figure 7, shows that there are only eight reports18 for the θ range of 0-35° that in all cases the X is a non-aromatic group, while 85 reports are found with greater values of θ angle. The histogram plot of distribution of the θ range (35.01-90°), Figure 7, shows that the most frequent value for the θ is found in the range of 80-90°. As it is clear from Figure 3b and the geometry of the L1, the naphthalene and pyrazine rings are in-plane with the carbonyl CdO group (the maximum deviation from mean plane through naphthalene and pyrazine ring is less than 0.172 A˚) and formation of parallel stacks of the adjacent ligands influence the CdO-Hg angles, Table 1. It seems that the naphthalene-pyrazine-carbonyl mean plane takes an abnormal geometry in the coordination of Hg to

Article

Crystal Growth & Design, Vol. 10, No. 4, 2010

generate π-π stacking interactions, and the θ angle will be decreased to less than 31°. These low angles are undoubtedly due to the π-π interactions in the packing of these crystals. To the best of our knowledge, such an effect has not been thoroughly discussed. It is notable that there are some differences in the molecular structures of these compounds, but the same influence of π-π interaction on the coordination geometry is found in all three complexes in the crystal structures. Conclusions In conclusion, it is clear that molecular design, considering the many possible weak interactions, is imperative in crystal engineering. The results herein show that molecular packing features have a dramatic effect on the coordination geometries. The π-π stacking interaction of the naphthalene and pyrazine rings has affected the geometry around the mercury ion. To gain some insight into the understanding of this effect, we used the set of CSD structures. Comparing the X2CdOHg angle of the related molecules discussed here with others shows that mercury takes an abnormal geometry to obtain stronger π-π interactions. Further studies are in progress to utilize the same complexes containing more expanded aromatic ligands, for clarification of the influence of the π-π interaction in the coordination geometries. Experimental Details For materials, experimental details of synthesis of N-(1-naphthyl)2-pyrazinecarboxamide (ligand L1), and X-ray crystallography see Supporting Information. Synthesis of [HgCl2(L1)2], 1, [HgBr2(L1)], 2, and [HgI2(L1)], 3. To a solution of 0.2 mmol of mercuric (II) halide (HgX2, X = Cl, Br, and I) in 5 mL of methanol, a solution of 0.2 mmol of N-(1-naphthyl)-2pyrazinecarboxamide (ligand L1) in 5 mL of methanol was added with stirring. The mixture was heated at 313 K for about 10 min and then filtered. Upon slow evaporation of the filtrate at room temperature, colorless needle, colorless plate, and yellowish block crystals for [HgCl2(L1)2],13 [HgBr2(L1)],13 and [HgI2(L1)]13 complexes, respectively, suitable for X-ray analysis were obtained after several days (The ORTEP diagrams of asymmetric unit of 1, 2 and 3 are shown in Figures S4-S6, Supporting Information). Yield ca. 63% for [HgCl2(L1)2] and 50% for [HgBr2(L1)] and 55% for [HgI2(L1)]. Melting points are 487 K for [HgCl2(L1)2] and about 418 K for [HgBr2(L1)] and 425 K for [HgI2(L1)]. It is notable that using 2:1 molar ratio of HgCl2 to L1 ligand resulted in the same product of using 1:1 molar ratio. Anal. Calcd for 1 (C30H22Cl2HgN6O2): C, 46.79; H, 2.88; N, 10.91. Found: C, 46.83; H, 2.81; N, 10.96. IR (CsI pellet, cm-1): 3363s, 3058, 1694s, 1545, 1501, 1408s, 1019s, 797s, 773s. 1H NMR (DMSO, δ from TMS): 9.3867(s, 1H), 8.8850(d, 1H), 8.8232(d, 1H), 8.0282(m,1H), 7.9332(m,2H), 7.8329(m, 1H), 7.5628(m, 3H). 13C NMR (DMSO, δ from TMS): 162.809 (CdO), 148.285, 145.315, 144.382, 143.952, 143.151, 133.260, 128.740, 128.681, 126.752, 126.663 (two overlapped peak), 126.065, 123.032, 122.989. Anal. Calcd for 2 (C30H22Br4Hg2N6O2): C, 29.55; H, 1.82; N, 6.89. Found: C, 29.62; H, 1.89; N, 6.80. IR (CsI pellet, cm-1): 3359s, 3054, 1687, 1545, 1501s, 1397s, 1023s, 799s, 773s. 1H NMR (DMSO, δ from TMS): 9.3876(s, 1H), 8.8851(d, 1H), 8.8209(d, 1H), 8.0279(m,1H), 7.9393(m,2H), 7.8320(m, 1H), 7.5519(m, 3H). 13C NMR (DMSO, δ from TMS): 162.770 (CdO), 148.226, 145.313, 144.337, 143.985, 143.131, 133.228, 128.717, 128.680, 126.756, 126.681 (two overlapped peak), 126.068, 123.022, 122.979. Anal. Calcd for 3 (C15H11I2HgN3O): C, 25.60; H, 1.58; N, 5.97. Found: C, 25.49; H, 1.62; N, 5.90. IR (CsI pellet, cm-1): 3336s, 3058, 1677, 1552, 1500s, 1409s, 1019s, 794s, 775s. 1 H NMR (DMSO, δ from TMS): 9.3916(s, 1H), 8.8838(d, 1H), 8.8264(d, 1H), 8.0323(m,1H), 7.9387(m,2H), 7.8347(m, 1H), 7.5504(m, 3H). 13C NMR (DMSO, δ from TMS): 162.715 (CdO), 148.193, 145.305, 144.318, 143.981, 143.121, 133.206, 128.689, 128.669, 126.731, 126.694 (two overlapped peak), 126.080, 122.940 (two overlapped peak).

1895

Acknowledgment. We would like to thank the Graduate Study Councils of Shahid Beheshti University, G. C., for financial support. Supporting Information Available: Detailed synthesis of L1, full crystallographic data for 1, 2, and 3, asymmetric units of 1, 2 and 3, and histograms for Hg-N, Hg-O, and P-P angles. This material is available free of charge via Internet at http://pubs.acs.org.

References (1) (a) Grepioni, F.; Braga, D. Making Crystals by Design-From Molecules to Molecular Materials, Methods, Techniques, Applications; Wiley-VCH: Weinheim, Germany, 2007. (b) Desiraju, G. R. The Crystal as a Supramolecular Entity; John Wiley & Sons: New York, 1996. (c) Jean-Marie, L. Supramolecular Chemistry: Concepts and Prespectives; Wiley-VCH: Weinheim, Germany, 1995. (d) Desiraju, G. R. Crystal Engineering; The Design of Organic Solids: Elsevier: Amsterdam, 1989. (e) Steed, J. W.; Atwood, J. L. Supramolecular Chemistry; Wiley: Chichester, 2000. (f) Brammer, L. Chem. Soc. Rev. 2004, 33, 476–489. (g) Braga, D.; Brammer, L.; Champness, N. R. CrystEngComm. 2005, 7, 1–19. (h) Desiraju, G. R. Angew. Chem., Int. Ed. 2007, 46, 8342–8356. (i) Nangia, A.; Desiraju, G. R. Acta Crystallogr, Sect. A: Found. Crystallogr. 1998, 54, 934–944. (j) Desiraju, G. R. Crystal Engineering. The Design of Organic Solids; Elsevier: Amsterdam, 1989. (2) Desiraju, G. R. Angew. Chem., Int. Ed. 1995, 34, 2311–2327. (3) (a) Lehn, J.-M. Science 2002, 295, 2400–2403. (b) Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001, 101, 1629–1658. (c) Aaker€oy, C. B.; Salmon, D. J. CrystEngComm 2005, 7, 439–448. (d) Wegner, M.; Bernstein, J. Angew. Chem., Int. Ed. 2006, 45, 7966–7969. (e) Hosseini, M. W. Acc. Chem. Res. 2005, 38, 313–323. (f) Goldberg, I. Chem. Commun. 2005, 1243–1254. (g) Kuehl, C. J.; Tabellin, F. M.; Arif, A. M.; Stang, P. J. Organometallics 2001, 20, 1956–1959. (h) Braga, D.; Grepioni, F. Acc. Chem. Res. 2000, 33, 601–608. (i) Braga, D.; Grepioni, F.; Desiraju, G. R. Chem. Rev. 1998, 98, 1375– 1406. (j) Munakata, M.; Wu, L. P.; Yamamoto, M.; Kuroda-Sowa, T.; Maekawa, M. J. Am. Chem. Soc. 1996, 118, 3117–3124. (k) Desiraju, G. R. Curr. Opin. Solid State Mater. Sci. 1997, 2, 451–454. (l) Guru Row, T. N. Coord. Chem. Rev. 1999, 183, 81–100. (4) (a) Nishio, M.; Umezawa, Y.; Honda, K.; Tsuboyama, S.; Suezawa, H. CrystEngComm 2009, 11, 1757–1788. (b) Nishio, M.; Hirota, M; Umezawa, Y. The CH/π Interaction. Evidence, Nature, and Consequences; Wiley-VCH: New York, 1998. (c) Nishio, M. CrystEngComm 2004, 6, 130–158. (d) Umezawa, Y.; Tsuboyama, S.; Honda, K.; Uzawa, J.; Nishio, M. Bull. Chem. Soc. Jpn. 1998, 71, 1207–1213. (e) Nishio, M.; Umezawa, Y.; Hirota, M.; Takeuchi, Y. Tetrahedron 1995, 51, 8665–8791. (f) Desiraju, G. R.; Gavezzotti, A. J. Chem. Soc. Chem. Commun. 1989, 621–623. (5) (a) Hirsch, K. A.; Wilson, S. R.; Moore, J. S. Chem.;Eur. J. 1997, 3, 765–771. (b) Amabilino, D. B.; Stoddart, J. F. Chem. Rev. 1995, 95, 2725–2828. (6) (a) Guckia, K. M.; Schweitzer, B. A.; Ren, R.X.-F.; Sheils, C. J.; Tahmassebi, D. C.; Kool, E. T. J. Am. Chem. Soc. 2000, 122, 2213– 2222. (b) Umezawa, Y.; Nishio, M. Nucleic Acids Res. 2002, 30, 2183– 2192. (c) Weiss, M. S.; Brandl, M.; S€uhnel, J.; Pal, D.; Hilgenfeld, R. Trends Biochem. Sci. 2001, 26, 521–523. (d) Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112, 5525–5534. (7) (a) Lee, E. C.; Hong, B. H.; Kim, J. C.; Kim, Y.; Tarakeshwar, P.; Kim, K. S. J. Am. Chem. Soc. 2005, 127, 4530–4537. (b) Hunter, C. A.; Lawson, K. R.; Perkins, J.; Urch, C. J. J. Chem. Soc. Perkin Trans. 2 2001, 651–669. (c) Janiak, C. J. Chem. Soc., Dalton Trans. 2000, 3885–3896. (d) Wu, J.-Y.; Hsu, H.-Y.; Chan, C.-C.; Wen, Y.-S.; Tsai, C.; Lu, K.-L. Cryst. Growth Des. 2009, 9, 258–262. (8) (a) Serrano-Becerra, J. M.; Hernandez-Ortega, S.; Morales-Morales, D.; Valdes-Martı´ nez, J. CrystEngComm 2009, 11, 226–228. (b) Dance, I. CrystEngComm 2003, 5, 208–221. (9) Tiekink, E. R. T. Rigaku J. 2002, 19, 14–24. (10) (a) Desiraju, G. R. Acc. Chem. Res. 1996, 29, 441–449. (b) Steed, J. W.; McCool, B. J.; Junk, P. C. J. Chem. Soc., Dalton Trans. 1998, 3417–3423. (c) Steed, J. W.; Johnson, K.; Legido, C.; Junk, P. C. Polyhedron 2003, 22, 769–774. (d) Bearpark, M. J.; McGrady, G. S.; Prince, P. D.; Steed, J. W. J. Am. Chem. Soc. 2001, 123, 7736–7737. (11) (a) Yang, S.-Y.; Naumov, P.; Fukuzumi, S. J. Am. Chem. Soc. 2009, 131, 7247–7248. (b) Blanco, V.; Abella, D.; Pia, E.; PlatasIglesias, C.; Peinador, C.; Quintela, J. M. Inorg. Chem. 2009, 48, 4098– 4107. (c) Kumagai, H.; Akita-Tanaka, M.; Kawata, S.; Inoue, K.;

1896

Crystal Growth & Design, Vol. 10, No. 4, 2010

Kepert, C. J.; Kurmoo, M. Cryst. Growth Des. 2009, 9, 2734–2741. (d) Banerjee, S.; Adarsh, N. N.; Dastidar, P. CrystEngComm 2009, 11, 746–749. (12) L1 is synthesized using our previous report. Sasan, K.; Khavasi, H. R.; Davari, M. D. Monatsh. Chem. 2008, 139, 773–780 (for experimental details see Supporting Information) . (13) Crystal data for 1: C30H22Cl2Hg1N6O2 (Mr = 770.03), monoclinic, space group C2/c, a = 29.762(4), b = 6.7876(6), c = 14.0678(17) A˚, β = 101.51(10)°, V = 2784.7(6) A˚3, Z = 4, Dcalc = 1.837 g cm-3, μ = 5.760 mm-1, T = 298(2) K, crystal size 0.50  0.10  0.10 mm3, R1 = 0.0333, wR2 = 0.0828, GOF = 1.090 with I > 2σ(I). CCDC No.; 754002, crystal data for 2: C30H22Br4Hg2N6O2 (Mr = 1219.32), triclinic, space group P1, a = 7.7479(8), b = 9.8027(8), c = 12.1149(10) A˚, R = 67.026(6)°, β = 71.945(7)°, γ = 76.517(7)°, V = 798.79(12) A˚3, Z = 1, Dcalc = 2.535 g cm-3, μ = 14.640 mm-1, T = 298(2), crystal size 0.20  0.20  0.06 mm3, R1 = 0.0507, wR2 = 0.1235, GOF = 1.112 with I > 2σ(I). CCDC No.; 754003, crystal data for 3: C15H11Hg1I2N3O1 (Mr = 703.66), triclinic, space group P1, a = 7.8355(10), b = 10.037(2), c = 11.988(3) A˚, R = 92.460(18)°, β = 93.142(19)°, γ = 105.051(18)°, V = 798.79(12) A˚3, Z = 2, Dcalc = 2.575 g cm-3, μ = 11.886 mm-1, T = 298(2) K, crystal size 0.22  0.10  0.04 mm3, R1 = 0.0600, wR2 = 0.1752, GOF = 1.179 with I > 2σ(I). CCDC No. 754004. (14) As examples (a) Cockrell, G. M.; Zhang, G.; Van Derveer, D. G.; Thummel, R. P.; Hancock, R. D. J. Am. Chem. Soc. 2008, 130, 1420–1430. (b) Teets, T. S.; Partyka, D. V.; Updegraff, J. B.; Gray, T. G. Inorg. Chem. 2008, 47, 2338–2346. (c) Dong, H; Yang, J.; Liu, X.; Gou, S. Inorg. Chem. 2008, 47, 2913–2915. (d) Tzeng, B.-C.; Huang, Y.-C.; Chen, B.-S.; Wu, W.-M.; Lee, S.-Y.; Lee, G.-H.; Peng, S.-M.

Khavasi and Azizpoor Fard

(15) (16)

(17) (18)

Inorg. Chem. 2007, 46, 186–195. (e) Wu, D.; Huang, W.; Duan, C.; Lin, Z.; Meng, Q. Inorg. Chem. 2007, 46, 1538–1540. (f) Wu, G.; Wang, X.-F.; Okamura, T.; Sun, W.-Y.; Ueyama, N. Inorg. Chem. 2007, 45, 8523–8532. (g) Sharma, C. V. K.; Broker, G. A.; Huddleston, J. G.; Baldwin, J. W.; Metzger, R. M.; Rogers, R. D. J. Am. Chem. Soc. 1999, 121, 1137–1144. The Cambridge Crystallographic Data Center, Cambridge, UK. (a) Wang, G.-W.; Wu, W.-Y.; Zhuang, L.-H.; Wang, J. T. Acta Crystallogr. Sect. E 2008, 64, m13. (b) Nolte, M.; Pantenburg, I.; Meyer, G. Z. Anorg. Allg. Chem. 2008, 634, 362–368. (c) Lee, K.-M.; Chen, J. C. C.; Huang, C.-J.; Lin, I. J. B. CrystEngComm 2007, 9, 278– 281. (d) Dong, Y.-B.; Smith, M. D.; zur Loye, H.-C. Solid State Sci. 2000, 2, 861–870. (e) Nockemann, P.; Meyer, G. Z. Anorg. Allg. Chem. 2003, 629, 1294–1299. (a) Pyykk€ o, P.; Straka, M. Phys. Chem. Chem. Phys. 2000, 2, 2489– 2493. (b) Nyburg, S. C.; Faerman, C. H. Acta Crystallogr. Sect. B 1985, 41, 274–279. (a) Birker, P. J. M. W. L.; Freeman, H. C.; Guss, J. M.; Watson, A. D. Acta Crystallogr. Sect. B 1977, 33, 182–184. (b) Lewinski, K.; Sliwinski, J.; Lebioda, L. Inorg. Chem. 1983, 22, 2339–2342. (c) Tikhonova, I. A.; Dolgushin, F. M.; Tugashov, K. I.; Petrovskii, P. V.; Furin, G. G.; Shur, V. B. J. Organomet. Chem. 2002, 654, 123–131. (d) Beauchamp, A. L.; Olivier, M. J.; Wuest, J. D.; Zacharie, B. Organometallics 1987, 6, 153–156. (e) Tschinkl, M.; Schier, A.; Riede, J.; Gabbai, F. P. Organometallics 1999, 18, 1747–1753. (f) Jogun, K. H.; Stezowski, J. J. J. Am. Chem. Soc. 1976, 98, 6018–6029. (g) Tikhonova, I. A.; Dolgushin, F. M.; Tugashov, K. I.; Furin, G. G.; Petrovskii, P. V.; Shur, V. B. Russ. Chem. Bull. 2001, 1673–1678. (h) Baldamus, J.; Deacon, G. B.; Hey-Hawkins, E.; Junk, P. C.; Martin, C. Aust. J. Chem. 2002, 55, 195–198.