Organometallics 2009, 28, 5593–5596 DOI: 10.1021/om900585y
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Synthesis and Structural Characterization of Some Alkylindium Bisphenoxides Wanda Ziemkowska*,† and Michale K. Cyra nski‡ †
Warsaw University of Technology, Faculty of Chemistry, Koszykowa 75, 00-662 Warsaw, Poland, and ‡ Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland Received July 7, 2009
Summary: Alkylindium bisphenoxides stabilized by a methoxy group, Me6In3(OMe)(EDBP) (1) and Me6In3(OMe)(MMBP) (2) (where EDBP-H2 = 2,20 -ethylidenebis(4,6-di-tert-butylphenol) and MMBP-H2 = 2,20 -methylenebis(4-methyl-6-tertbutylphenol)), have been synthesized in reaction of bulky bisphenols with Me3In and Me2InOMe in a 1:2:1 molar ratio of the reagents. In contrast, under the same conditions, 2,20 methylenediphenol forms the complex without a methoxy group, Me5In3(OC6H4CH2C6H4O)2 (3), as the only product. The molecular structures of 1-3 have been determined by X-ray crystallography.
In recent years, there has been an increasing interest in the synthesis of new indium mono-, bis-, and tris(alkoxides) complexes because of their potential use as precursors of indium and indium tin oxides, which are suitable for application in optoelectronic technologies as display panels, solar cell windows, and gas sensors.1 Although a number of indium alkoxides have been prepared,2 the chemistry of indium diolates, BINOLates (BINOL = 2,20 -dihydroxy-1,10 -binaphthyl), and bisphenoxides remains largely unexplored. This work is a continuation of our fundamental studies on the synthesis and structure of group 13 metal diolates. We report the synthesis and structural characterization of methylindium bisphenoxides containing methoxy groups, derived from bulky 2,20 -alkylenebisphenols, Me3In, and Me2InOMe. The use of a mixture of Me3In and Me2InOMe instead of just Me3In allowed us to obtain kinetically stable products. The structure and stability of indium
bisphenoxides is shown to depend on the bulkiness of the bisphenolate units. Bulky 2,20 -alkylenebisphenols, 2,20 -ethylidenebis(4,6-ditert-butylphenol) (EDBP-H2) and 2,20 -methylenebis(4-methyl-6-tert-butylphenol) (MMBP-H2), were reacted with a mixture of 2 equiv of Me3In and 1 equiv of Me2InOMe to produce the trinuclear indium complexes Me6In3(OMe)(EDBP) (1) and Me6In3(OMe)(MMBP) (2) (Scheme 1). It is noteworthy that excess Me3In and Me2InOMe remained free in the postreaction solution. The compounds 1 and 2 precipitated from the postreaction mixture as white solids in yields of 94% and 90%, respectively. They are sparingly soluble in Et2O and CHCl3, whereas they show good solubility in CH2Cl2. Crystallization from a CH2Cl2 solution of the compound 2 gave a small amount of crystals containing 0.0625 molecule of CH2Cl2 and 0.125 molecule of H2O per molecule of 2. The solvent molecules of CH2Cl2 and H2O are situated at the 42 axis. Their contents are not integers because of the static disorder that takes place in this situation. Most likely, water present in the crystal structure of the compound originated from solvents. During our studies on the hydrolysis reaction of alkylaluminum benzopinacolates3 we found that solvents purified according to standard methods contain 10-40 ppm of residual water. A small amount of crystals of 1 containing one molecule of CH3OH per molecule of 1 were obtained as described in the Experimental Section. Although methanol was not added to the solution of 1, it was, however, present in the formula unit of 1. Presumably, a small amount of methanol was formed in the reaction of residual water with Me2InOMe present in the postreaction mixture. According to Barron’s observations, the basicity (reactivity) of aluminum alkyl groups in organoaluminum compounds containing a heteroatom donor ligand (e.g., alkoxide) is significantly reduced.4 In the presence of water, a hydrolytic protonation of the heteroatom takes place rather than one of the alkyl groups. Taking into consideration similarities in the chemistry of aluminum and indium, we state that the hydrolysis reaction of Me2InOMe results in the formation of MeOH and Me2InOH. The molecular structures of 1 and 2 were determined on the basis of X-ray diffraction studies and are shown in Figures 1 and 2. Data collection and structure analysis details are given in Table S1 in the Supporting Information. Molecules of 1 and 2 consist of one bisphenolate unit bonded
*To whom correspondence should be addressed. Tel: þ48 22 2347316. E-mail:
[email protected]. (1) See for example: (a) Suh, S.; Hoffman, D. M. J. Am. Chem. Soc. 2000, 122, 9396. (b) Chou, T.-Y.; Chi, Y.; Huang, S.-F.; Liu, C.-S.; Carty, A. J.; Scoles, L.; Udachin, K. A. Inorg. Chem. 2003, 42, 6041. (c) Basharat, S.; Carmalt, C. J.; Barnett, S. A.; Tocher, D. A.; Davies, H. O. Inorg. Chem. 2007, 46, 9473. (d) Dutta, D. P.; Sudarsan, V.; Srinivasu, P.; Vinu, A.; Tyagi, A. K. J. Phys. Chem. C 2008, 112, 6781. (e) Hakam, A.; Banouq, M.; Ouboumalk, L.; Saidi, Y.; Chouiyakh, A. Ann. Chim. Sci. Mat. 1998, 23, 385. (f) Zhuang, Z.; Peng, Q.; Liu, J.; Wang, X.; Li, Y. Inorg. Chem. 2007, 46, 5179. (g) Gurlo, A.; Ivanovskaya, M.; Barsan, N.; Schweizer-Berberich, M.; Weimar, U.; G€ opel, W.; Dieguez, A. Sensors Actuators B 1997, 44, 327. (h) Gunho, J.; Hong, W.-K.; Maeng, J.; Kim, T.-W.; Wang, G.; Yoon, A.; Kwon, S.-S.; Song, S.; Lee, T. Colloids Surf., A 2008, 313-314, 308. (2) See for example: (a) Shen, Y.; Pan, Y.; Jin, X.; Xu, X.; Sun, X.; Huang, X. Polyhedron 1999, 18, 2423. (b) Bradley, D. C.; Frigo, D. M.; Hursthouse, M. B.; Hussain, B. Organometallics 1988, 7, 1112. (c) Beachley, O. T., Jr.; MacRae, D. J.; Kovalevsky, A. Y. Organometallics 2003, 22, 1690. (d) Zhao, Q.; Sun, H.-S.; Chen, W.-Z.; Liu, Y.-J.; You, X.-Z. J. Organomet. Chem. 1998, 556, 159. (e) Veith, M.; Hill, S.; Huch, V. Eur. J. Inorg. Chem. 1999, 1343. (f) Chitsaz, S.; Iravani, E.; Neum€uller, B. Z. Anorg. Allg. Chem. 2002, 628, 2279. (g) Chitsaz, S.; Neum€uller, B. Z. Anorg. Allg. Chem. 2001, 627, 2451.
(3) Ziemkowska, W.; Kucharski, S.; Koleodziej, A.; AnulewiczOstrowska, R. J. Organomet. Chem. 2004, 689, 2930. (4) (a) Niamh, C.; Barron, A. R. J. Chem. Soc., Dalton Trans. 1998, 3703. (b) Healy, M. D.; Leman, J. T.; Barron, A. R. J. Am. Chem. Soc. 1991, 113, 2776.
r 2009 American Chemical Society
Published on Web 08/25/2009
pubs.acs.org/Organometallics
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Organometallics, Vol. 28, No. 18, 2009
Ziemkowska and Cyra nski
Scheme 1
to three four-coordinate indium atoms. Each of the indium atoms is bonded to two oxygen atoms and two methyl groups. The indium atoms In(2) and In(3) in compound 1 are bridged by the oxygen atom of the OMe group and chelated by the bisphenolate unit. The lengths of the bonds between the indium atoms and the oxygen atom of the OMe group (In(2)-O(2) = 2.168(2) A˚ and In(3)-O(2) = 2.168(2) A˚) are the same and show that the indium atoms are symmetrically bonded to the methoxy group. The atom In(3) is bonded to two oxygen atoms of the bisphenolate moiety and two methyl groups. In-O bond lengths in compound 1 are situated in the region of 2.168-2.202 A˚. They are similar to those in the indium benzopinacolate Me6In4[OC(C6H5)2C(C6H5)2O]2(OMe)2 (average In-O distance 2.18 A˚)5 and slightly longer than the average In-O distances in alkali-metal indium BINOLates [{(DME)Li}3{In((S)-BINOLate)3}] 3 2DME (2.15 A˚), [{(toluene)2K}3{In((S)-BINOLate)3}] 3 2(toluene) (1.15 A˚), and [{(DME)Li}3{In((S)-BINOLate)3}] 3 0.75THF (2.14 A˚).6 A molecule of 1 consists of a bicyclic structure formed by two rings adopting a “chairlike” conformation: an In3O3 sixmembered ring and an In2OC5 eight-membered ring (Figure S1 in the Supporting Information). A similar “chairlike” In3O3 ring was previously described for the trimeric indium hydroxo compound [{(CH3)3Si}3C(nC3H7)In(μ-OH)]3.7 The methyl groups, C(8)H3 of the ethylidene bridge and C(37)H3 of the methoxy group, are situated syn to each other. The sums ofP the angles about the oxygen atoms of the P bisphenolate unit ( [O(1)] = 357.1° and [O(3)] = 356.7°) are slightly less than 360°, which indicates a small steric strain in the molecule. The molecular structure of 2 shows a planar symmetry with the C(5), O(2), In(2), C(3), C(4), and C(6) atoms situated in the plane. The two central rings, In2OC5 and In3O3, adopt “chairlike” conformations. The bond between the indium atom and the oxygen atom of the OMe group (In(1)-O(2) = 2.144(2) A˚) is shorter than similar bonds in compound 1 (In(2)-O(2) = 2.168(2) A˚ and In(3)-O(2) = 2.168(2) A˚). The lengths of other In-O bonds in 2 are situated in a region similar to those in compound 1. The 1H NMR spectrum of 1 in solution revealed four singlets of CH3In group protons (at 0.17, 0.13, -0.42, and -1.59 ppm) in a 1:2:2:1 relative intensity ratio. Protons of the two methyl groups attached to the In(1) atom exhibited singlets at 0.17 and -1.59 ppm. The singlets at 0.13 and (5) Ziemkowska, W.; Kubiak, A.; Kucharski, S.; Wozniak, R.; Anulewicz-Ostrowska, R. Polyhedron 2007, 26, 1436. (6) (a) Chitsaz, S.; Neum€ uller, B. Organometallics 2001, 20, 2338. (b) Pauls, J.; Chitsaz, S.; Neum€uller, B. Z. Anorg. Allg. Chem. 2000, 626, 2028. (7) Walz, A.; Niemeyer, M.; Weidlein, J. Z. Anorg. Allg. Chem. 1999, 625, 547.
Figure 1. Molecular structure of 1. Thermal ellipsoids are shown at the 50% probability level. For selected bond lengths and bond angles see Figure S1 in the Supporting Information.
Figure 2. Molecular structure of 2. Thermal ellipsoids are shown at the 50% probability level. For selected bond lengths and bond angles see Figure S2 in the Supporting Information.
-0.42 ppm were assigned to protons of the four methyl groups bonded to the In(2) and In(3) atoms. The presence of these two singlets indicates the equivalence of the two InC(4)H3 and InC(5)H3 groups positioned syn to the OC(37)H3 group. The two anti InC(3)H3 and InC(6)H3 groups were also equivalent. The NMR observations in solution contrast with the solid-state structure, in which all the InMe groups units are inequivalent. There are no lowtemperature NMR spectra of the compound 1; it seems, however, that the differences are the result of fluxionality phenomena involving transitions between the two nonequivalent antisymmetric structures occurring in the fast exchange regime. 1H and 13C NMR data of 2 in solution are in agreement with the solid-state structure. Compounds 1 and 2 are kinetically stable products of the reaction of bulky bisphenols with alkylindium compounds to and can be isolated and stored without decomposition. It is
Note
Organometallics, Vol. 28, No. 18, 2009
Figure 3. Molecular structure of 3. Thermal ellipsoids are shown at the 50% probability level. For selected bond lengths and bond angles see Figure S3 in the Supporting Information. Scheme 2
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bipyramid. The bonds In(2)-O(2) (2.116(2) A˚) and In(2)-O(3) (2.130(2) A˚) are significantly shorter than other In-O (average length 2.211 A˚) bonds in 3. In summary, the first kinetically stable bulky methylindium bisphenoxides, 1 and 2, were prepared in the reaction of bulky bisphenols with Me3In and Me2InOMe. The use of dialkyl alkoxides of group 13 metals, in addition to trialkyl metals in reactions with bulky diols, BINOLs and bisphenols, can be regarded as a method of synthesis of a new class of alkylalkoxy group 13 metal complexes. We found that the structure of the products of reactions of 2,20 -alkylenebisphenols with a mixture of Me3In and Me2InOMe depends on the bulkiness of the bisphenolate units. Alkylindium bisphenolates containing additional alkoxy groups are formed in reactions of bisphenols substituted by bulky groups, whereas sterically uncrowded bisphenols (such as 2,20 -methylenediphenol) yield alkylindium bisphenoxides of the form R5In3[bisphenol-(2H)]2. In comparison with EDBP, the MMBP-bisphenolate unit is less sterically crowded; however, in both units the same bulky tBu groups are situated at the 6-position of the aromatic rings. Considering the fact that both MMBP-H2 and EDBP-H2 react with indium compounds with formation of the similar 1 and 2 structures, we conclude that the bulkiness of groups at the 6-position of the aromatic rings is the most important factor influencing the structure of alkylindium bisphenolates.
Experimental Section noteworthy that these complexes are rare examples of new structures of indium bisphenoxides.8 Surprisingly, in the presence of a mixture of Me3In and Me2InOMe, 2,20 -methylenediphenol formed a trinuclear complex, Me5In3(OC6H4CH2C6H4O)2 (3), as the only product (Scheme 2). The same compound 3 was obtained in the reaction of 2,20 -methylenediphenol with Me3In at a 2:3 molar ratio of reagents. The molecular structure of 3 was determined on the basis of an X-ray diffraction study and is shown in Figure 3. Data collection and structure analysis details are given in Table S1. In the literature, a similar structure has been found for numerous alkylaluminum and alkylgallium diolates.9 However, complex 3 is the first structurally characterized indium compound of the form R5In3[diol-(2H)]2 (where R = alkyl group and diol-(2H) = doubly deprotonated diolate unit). Complex 3 consists of two diolate units and five methyl groups bonded to three indium atoms. The two terminal indium atoms, In(1) and In(3), are four-coordinate, residing in distorted tetrahedrons. The angles O(1)-In(2)-O(4) = 159.3(1)° and O(2)-In(2)-O(3) = 93.5(1)° indicate that the coordination sphere geometry of the central indium atom In(2) can be regarded as a distorted trigonal bipyramid with the basal plane consisting of O(2), O(3), and C(5) atoms. The O(1) and O(4) atoms are situated in the axial positions of the (8) For very recently reported indium bisphenoxides see: Peckermann, I.; Kapelski, A.; Spaniol, T. P.; Okuda, J. Inorg. Chem. 2009, 48, 5526. (9) (a) McMahon, C. N.; Obrey, S. J.; Keys, A.; Bott, S. G.; Barron, A. R. Dalton Trans. 2000, 2151. (b) Ziemkowska, W. Coord. Chem. Rev. 2005, 249, 2176. (c) Ziemkowska, W.; Buzniak, M.; Kwasniewska, S.; Starowieyski, K. B.; Anulewicz-Ostrowska, R. J. Organomet. Chem. 2003, 688, 246. (d) Ziemkowska, W.; Anulewicz-Ostrowska, R.; Cyranski, M. Polyhedron 2008, 27, 962.
Reagents and General Procedures. All manipulations were carried out using standard Schlenk techniques under an inert gas atmosphere. The solvents were distilled over a blue benzophenone-K complex. All bisphenols were purchased from Aldrich. Me3In was synthesized as described in the literature.10 1 H and 13C NMR spectra were obtained on a Mercury-400BB spectrometer. 1H NMR spectra were recorded at 400.09 MHz. Chemical shifts were referenced to the residual proton signals of CDCl3 (7.26 ppm). 13C NMR spectra were acquired at 100.60 MHz (standard: chloroform 13CDCl3, 77.20 ppm). Elemental analyses of compounds 1-3 were obtained on a PerkinElmer 2400 analyzer. Synthesis of Me6In3(OMe)(EDBP) (1). A solution of methanol (0.016 g, 0.5 mmol) in Et2O (5 cm3) was added to a stirred solution of Me3In (0.240 g, 1.5 mmol) in Et2O (10 cm3) at -76 °C. The reaction mixture was warmed to room temperature. A mixture of Me3In and Me2InOMe (n a 2:1 molar ratio, on the basis of the integration ratio of the signals at -0.14 ((CH3)3In) and 3.49 ppm ((CH3)2InOCH3) in the 1H NMR spectrum) was obtained.11 Then a solution of EDBP-H2 (0.219 g, 0.5 mmol) in Et2O (10 cm3) was added to the mixture of Me3In and Me2InOMe at 0 °C. The reaction mixture was warmed to room temperature. Evolution of gases was observed during the course of the reaction. A white solid of complex 1 (0.420 g, 94% yield) precipitated immediately from the postreaction mixture. An excess of Me3In and Me2InOMe had no influence on formation of the product 1. 1H NMR (CDCl3): δ 7.48 (2H, d, 4JHH = 2.3 Hz, Harom), 7.04 (2H, d, 4JHH = 2.3 Hz, Harom), 5.36 (1H, q, 3JHH = 7.1 Hz, C(H)CH3), 3.45 (3H, s, OCH3), 1.55 (3H, d, 3JHH = 7.1 Hz, C(H)CH3), 1.33 (18H, s, C(CH3)3), 1.28 (18H, s, C(CH3)3), 0.17 (3H, s, InCH3), 0.13 (6H, s, InCH3), -0.42 (6H, s, InCH3), -1.59 ppm (3H, s, InCH3). 13C NMR (CDCl3): δ 154.47, 142.79, 138.31, 137.34, 122.74, 121.03 (Carom), 51.90 (OCH3), 35.20, 34.39 (C(CH3)3), 31.78, 31.66 (10) Todt, E.; Dotzer, R. Z. Anorg. Allg. Chem. 1963, 321, 120. (11) For the 1H NMR spectrum of Me2InOMe see: Mann, G.; Olapinski, H.; Ott, R.; Weidlein, J. Z. Anorg. Allg. Chem. 1974, 410, 195.
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(C(CH3)3), 28.63 (C(H)CH3), 23.93 (C(H)CH3), -3.07, -3.19, -6.52, -7.43 ppm (InCH3). Anal. Calcd for C37H57In3O3: C, 49.64; H, 6.37. Found: C, 50.02; H, 6.30. The NMR spectra and elemental analysis of complex 1 precipitated from the postreaction mixture indicated the absence of solvents. A small amount of X-ray-quality crystals of 1 3 CH3OH (containing one molecule of CH3OH per one molecule of 1) was grown as follows: the solvent was removed from the postreaction mixture by decantation, and a white solid of compound 1 was obtained. This product was suspended in n-C6H14. Then CH2Cl2 was carefully added until the dissolution of the solid. The solution was placed at -25 °C. Crystals of 1 were obtained after 1 month. Crystal data for 1: C37H65In3O3 3 CH3OH, triclinic, space group P1, a = 10.9913(3) A˚, b = 12.4873(2) A˚, c = 17.0108(5) A˚, Z = 2, Rint = 0.0250, R1 = 0.0264 (I > 2σ(I)), wR2 = 0.0744 (all data). Mp (crystals): the compound became yellow at 140 °C and underwent slow decomposition without melting while the temperature was increased to 300 °C. Synthesis of Me6In3(OMe)(MMBP) (2). The reaction of MMBP-H2 with Me3In and Me2InOMe was carried out as described for compound 1, using 0.170 g (0.5 mmol) of MMBP-H2, 0.240 g (1.5 mmol) of Me3In, and 0.016 g (0.5 mmol) of MeOH. A solution of MMBP-H2 in Et2O was added to a mixture of Me3In and Me2InOMe at -76 °C. A white solid precipitated immediately from the postreaction mixture. The solid was filtered, washed with Et2O, and dried under vacuum. Pure compound 2 (without solvents in the structure) was obtained (0.361 g, 90% yield). 1H NMR (CDCl3): δ 7.17 (d, 4JH-H=2.0 Hz, 2H, Harom), 6.89 (d, 4JH-H = 2.0 Hz, 2H, Harom), 4.67 (δA), 3.27 (δB) (dd, 2JH-H = 13.2 Hz, 2H, CH2, AB pattern), 3.39 (s, 3H, OCH3), 2.26 (s, 6H, CH3), 1.32 (s, 18H, C(CH3)3), 0.18 (s, 3H, InCH3), 0.13 (s, 6H, InCH3), -0.50 (s, 6H, InCH3), -1.29 (s, 3H, InCH3). 13C NMR (CDCl3): δ 154.69, 138.71, 134.20, 129.58, 129.50, 126.13 (Carom), 51.54 (OCH3), 34.96 (CH2), 31.79 (C(CH3)3), 31.70 (C(CH3)3), 21.16 (CH3), -3.02, -3.62, -5.83, -7.46 ppm (InCH3). Anal. Calcd for C30H51In3O3: C, 44.76; H, 6.34. Found: C, 44.41; H, 6.46. A small amount of X-ray -quality crystals of 2 was grown as follows: 10 cm3 of Et2O was added to the solid compound 2. A suspension was formed. When a white solid precipitated, the solution was carefully decanted. The solvent was removed from the solution under reduced pressure, and a small amount of the product, soluble in Et2O, was obtained. Crystals of 2 were grown from a solution of 2 in CH2Cl2 at -25 °C. Crystal data for 2: (C30H51In3O3)0.5 3 0.0625CH2Cl2 3 0.125H2O, tetragonal,
Ziemkowska and Cyra nski space group P42cm, a = 19.7811(3) A˚, b = 19.7811(3) A˚, c = 9.1039(2) A˚, Z = 8, Rint = 0.0173, R1 = 0.0202 (I > 2σ(I)), wR2 = 0.0541 (all data). Mp (crystals): 186-188 °C. Reaction of 2,20 -Methylenediphenol with Me3In and Me2InOMe. Synthesis of Me5In3(OC6H4CH2C6H4O)2 (3). The reaction of 2,20 -methylenediphenol with Me3In and Me2InOMe was carried out as described for compound 1, using 0.200 g (1 mmol) of 2,20 -methylenediphenol, 0.480 g (3 mmol) of Me3In, and 0.032 g (1 mmol) of MeOH. A solution of 2,20 -methylenediphenol in Et2O was added to a mixture of Me3In and Me2InOMe at -76 °C. The reaction mixture was warmed to room temperature. A white solid of pure compound 3 precipitated at 0 °C (0.355 g, 87% yield based on 2,20 -methylenediphenol). 1H NMR (CDCl3): δ 7.21 (m, 4H, Harom, broad), 7.09 (m, 4H, Harom), 6.83 (m, 4H, Harom), 6.73 (m, 4H, Harom, broad), 4.18 (δA1), 3.54 (δB1) (dd, 2JH-H = 15.2 Hz, 4H, CH2, AB pattern), 0.19 (s, 6H, InCH3), -0.02 (s, 3H, InCH3), -0.49 (s, 6H, InCH3). 13C NMR (CDCl3): δ 131.04, 127.77, 118.64 (Carom, broad signals), 32.21 (CH2), -0.89, -3.39 (InCH3) ppm. Anal. Calcd for C31H35In3O4: C, 45.59; H, 4.29. Found: C, 45.25; H, 4.39. X-ray-quality crystals were grown from a CH2Cl2 solution of 3 at -25 °C. Crystal data for 3: C31H35In3O4, monoclinic, space group P21/c, a=14.9064(5) A˚, b=12.5295(4) A˚, c=19.9118(8) A˚, Z = 4, Rint = 0.0727, R1 = 0.0313 (I > 2σ(I)), wR2 = 0.0832 (all data). At 260 °C the crystals of 3 become brown and undergo decomposition. Compound 3 was also synthesized, in the absence of Me2InOMe, in the reaction of 2,20 -methylenediphenol with Me3In in a 2:3 molar ratio of the reagents. A solution of 0.250 g (1.6 mmol) of Me3In in Et2O (5 cm3) was added to a stirred solution of 2,20 -methylenediphenol (0.200 g, 1 mmol) in Et2O (5 cm3) at -76 °C. The reaction mixture was warmed to room temperature. A white solid precipitated from the postreaction mixture. It was confirmed on the basis of NMR spectra that the solid consists of the pure compound 3 (0.363 g, yield 89%).
Acknowledgment. We thank the Warsaw University of Technology for financial support. We gratefully acknowledge Dr Romana Anulewicz-Ostrowska for her kind assistance. Supporting Information Available: Text, figures, and a table giving crystal data and data collection parameters. This material is available free of charge via the Internet at http://pubs.acs.org.
