Cyanometallates as Halogen Bond Acceptors - Crystal Growth

Article pubs.acs.org/crystal

Cyanometallates as Halogen Bond Acceptors Published as part of the Crystal Growth & Design virtual special issue on Halogen Bonding in Crystal Engineering: Fundamentals and Applications Johnathan E. Ormond-Prout, Paul Smart, and Lee Brammer* Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, U.K. S Supporting Information *

ABSTRACT: Two families of halopyridnium hexacyanometallate salts, (3-XpyMe)3[M(CN)6] and (3,5-X2pyMe)3[M(CN)6] (X = I, Br; 3-XpyMe = N-methyl-3-halopyridinium; 3,5-XpyMe = N-methyl-3,5-dihalopyridinium; M = Cr, Fe, Co), have been synthesized and characterized by single crystal X-ray diffraction. Five of the six members of each family are characterized as isostructural compounds, two structures are reported as solvates, (3-IpyMe)3[Fe(CN)6]·2MeCN (2·2MeCN) and (3,5-Br2pyMe)3[Cr(CN)6]·4H2O (10·4H2O), and the solvate (3-IpyMe)3[Co(CN)6]·2MeCN (3·2MeCN) has been characterized in addition to the unsolvated 3. All halogens participate in halogen bonding, forming C−X···NC(M) halogen bonds and in one case a C−Br···O halogen bond (in 10·4H2O). The halogen bond distances are shorter than the corresponding sum of van der Waals radii, and stronger interactions are formed by iodine than bromine (I···N 2.789(7)−3.116(7), RIN 0.790− 0.883; Br···N 2.884(3)−3.166(2), RBrN 0.848−0.931). Longer halogen bonds are formed in 10·4H2O (Br···N 3.041(6)− 3.380(6), RBrN 0.894−0.994) due to competition from O−H···N hydrogen bonding. All halogen bonds have interaction geometries at the halogen close to linearity (most have C−X···N > 165°; smallest angle is 154.1(3)°). The geometry of interaction of the halogen bond donor (C−X) with the cyanide ligand either suggests interaction predominantly with the exo lone pair of the nitrogen atom (CN···X > 145°) or predominant involvement of the CN π-bond in the halogen bond (CN···X < 105°) acceptor role. The former are shorter interactions than the latter. Halogen bonds become shorter across each isostructural series for Cr > Fe > Co, and this is discussed in the context of metal-to-cyanide π-back-donation.

■

acceptors,11−13 following from principles established in previous work on the hydrogen bond acceptor capability of metal-bound halogens.14−16 In a series of systematic studies, it was found that the attractive nature of the interactions was dominated by electrostatics and that C−X···X′−M halogen bonds can form between both neutral and ionic molecular species.11 Halogen bonded networks of coordination compounds involving heteroditopic ligands capable of accepting halogen bonds have also recently been reported.17 Since we have clearly established that halide ligands are very effective hydrogen bond and halogen bond acceptors, we have turned our attention to other ligands that may behave similarly and thereby expand the repertoire of such interactions in inorganic chemistry leading to a broader range of applications in which these directional intermolecular interactions can play a decisive role. In this report, we focus on cyanide ligands and in particular cyanometallate complexes. This work is significant because cyanometallates have been used in magnetic materials,18 as photosensitizers in the form of polypyridyl tetracyanoruthenate complexes,19 in applications such as light harvesting units for photosynthetic systems,20 humidity sensors,21 quenchers,22 and as photosensitizers for TiO2 solar cells.23 Having the ability to predict and control the process of self-assembly offers the chance to tune the electronic properties

INTRODUCTION Supramolecular assemblies, in both the solid state and in solution, rely on a range of weak, noncovalent interactions to hold the constituent molecules together.1−3 The most common of these are hydrogen bonding interactions,2 which are relatively strong and highly directional, and thus they have highly predictable geometries and fine control of the assembly process can be achieved. An alternative interaction that has more recently been exploited as a construction tool in the field of supramolecular chemistry and crystal engineering is the halogen bond.3−13 Halogen atoms usually form a single, covalent bond with one other atom. As a result of this, halogen atoms are typically found on the periphery of a molecule, making them ideally placed for taking part in intermolecular interactions. Halogen bonds are Lewis acid−Lewis base interactions typically involving an organic halide group, C−X, or dihalogen, X−X (X = halogen) as the Lewis acid (halogen bond donor) and a Lewis base as the halogen bond acceptor (A), for example, C−X···A. The interaction is typically linear at the (organic) halogen, consistent with maximizing the two main directional attractive contributions to the interaction energy, electrostatics and charge transfer, and minimizing the exchange repulsion, which is also directional.4 Halogen bonding has found applications in a number of fields including liquid crystals,8 conducting materials,9 and structural biology10 as well as via supramolecular chemistry in anion recognition7c−e and polymerization.7a Previously, we and Willett and co-workers have established the capability of metal-bound halogens as halogen bond © 2011 American Chemical Society

Received: July 21, 2011 Revised: October 16, 2011 Published: December 16, 2011 205

dx.doi.org/10.1021/cg200942u | Cryst. Growth Des. 2012, 12, 205−216

Crystal Growth & Design

Article

which was collected by filtration and dried in a vacuum oven overnight at 60 °C. Yield: 0.9461 g, 91.94%. Found: C, 73.91; H, 4.82; N, 6.46%. Calc.: C, 73.81; H, 5.08; N, 6.62%. N-Methyl-3-iodopyridinium Iodide. 3-Iodopyridine (0.5909 g, 2.88 mmol) was placed in a sealed Schlenk tube which was degassed and placed under an atmosphere of nitrogen. Methyl iodide (0.864 mL, 14.4 mmol) and ethanol (20 mL) were added to this tube. The sealed, inert system was heated at 92 °C and stirred with a magnetic stirrer bar for 21 h. The colorless solution turned orange after a few minutes of heating, the system began to reflux, and after a few hours a colorless precipitate began to form. After 21 h the reaction was stopped and allowed to cool to room temperature. The solid was filtered, collected, and recrystallized from ethanol. Yield: 0.56 g, 56%. Elemental analysis: Found: C, 20.76; H, 1.88; N, 3.86; I, 72.94%. Calc.: C, 20.77; H, 2.03; N, 4.04; I, 73.16%. N-Methyl-3-iodopyridinium Hexafluorophosphate. N-Methyl-3-iodopyridinium iodide (0.46 g, 1.33 mmol) was dissolved in a minimum volume of hot, deionized water. (NH4)[PF6] (0.216 g, 1.33 mmol) was dissolved in a minimum volume of hot, deionized water. The two solutions were mixed. On mixing a white solid precipitated rapidly. After a couple of minutes, this turned yellow. The solid was filtered, washed with cold, deionized water, and dried. Yield: 0.478 g, 98.76%. Found: C, 19.66; H, 1.87; N, 3.77; I, 35.61%. Calc.: C, 19.74; H, 1.93; N, 3.84; I, 34.77%. N-Methyl-3-bromopyridinium Iodide. 3-Bromopyridine (0.3212 mL, 3.33 mmol) was placed in a sealed Schlenk tube which was degassed and placed under an atmosphere of nitrogen. Methyl iodide (0.864 mL, 16.67 mmol) and ethanol (20 mL) were added to this tube. The sealed, inert system was heated at 92 °C and stirred with a magnetic stirrer bar for 16 h. The colorless solution turned red after a few minutes of heating, the system began to reflux, and after a few hours a colorless precipitate began to form. After 16 h the reaction was stopped and allowed to cool to room temperature. Precipitation continued upon cooling. The solid was filtered, collected, and recrystallized from ethanol. Yield: 1.00 g, 100%. Found: C, 24.02; H, 2.09; N, 4.34; Br, 23.93; I, 42.43%. Calc.: C, 24.03; H, 2.35; N, 4.67; Br, 26.64; I, 42.31%. N-Methyl-3-bromopyridinium Hexafluorophosphate. NMethyl-3-bromopyridinium iodide (1.00 g, 3.33 mmol) was dissolved in a minimum volume of hot, deionized water. (NH4)[PF6] (0.5435 g, 3.33 mmol) was dissolved in a minimum volume of hot, deionized water. The two solutions were mixed. On mixing a white solid precipitated rapidly. After a couple of minutes this turned yellow. The solid was filtered, washed with cold, deionized water, and dried. Yield: 1.046 g, 98.7%. Found: C, 22.61; H, 2.10; N, 4.20; Br, 25.25%. Calc.: C, 22.66; H, 2.22; N, 4.40; Br, 25.13%. 3,5-Diiodopyridine.26 Anhydrous THF (30 mL) was transferred to a three-necked round-bottomed flask equipped with a magnetic stirrer. 3,5-Dibromopyridine (1.2 g, 5.07 mmol) was dissolved in the THF under a nitrogen atmosphere. The flask was placed in an acetone−CO2 ice slurry to cool the contents to −78 °C. A solution of t-BuLi in pentane (1.7 M) (11.76 mL, 20 mmol) was added to the stirring solution, dropwise over a period of 40 min, using a plastic 10 mL syringe. On addition the colorless solution turned yellow, then brown. After stirring for a further hour, I2 (5.1 g, 40.2 mmol) dissolved in dry THF (20 mL) was added dropwise to the reaction mixture, over a period of 40 min. The solution was allowed to warm to room temperature (ca. 1 h) and then poured into a 5% Na2SO3 solution (150 mL). The solution was washed twice with t-butylmethyl ether (200 mL). The combined organic layers were washed twice with brine (200 mL) and dried with MgSO4. Removal of the solvent left a brown solid in the flask. The product was purified using a silica column (50:50 pentane:CH2Cl2). Yield: 0.14 g, 8.00%. N-Methyl-3,5-diiodopyridinium Tetrafluoroborate. Trimethyloxonium tetrafluoroborate (0.0894 g, 0.471 mmol) was dissolved in acetonitrile (5 mL) under inert conditions at 0 °C. 3,5Diiodopyridine (0.14 g, 0.423 mmol) was added portion-wise to the solution with vigorous stirring. The reaction mixture was allowed to warm to room temperature and stirred for a further 6 h. The solvent

of cyanometallates. Herein we turn our attention to the use of halogen bonding. Previous studies have identified that cyanide ligands can be effective hydrogen bond acceptors24 and that such ligands can also serve as halogen bond acceptors.9,18 Recently, we reported the synthesis and study of halogen bond formation in a series of bipyridyl-tetracyanoruthenate salts with general formula (XpyMe)2[Ru(bipy)(CN)4] (where X = I, Br).25 Here we report a systematic study of a series of halopyridiunium hexacyanometallate complexes (3-XpyMe)3[M(CN)6] and (3,5X2pyMe)3[M(CN)6] (where M = Cr, Co, Fe and X = Br, I).

■

EXPERIMENTAL SECTION

General. All reagents (purchased from Aldrich or Lancaster) and solvents were used as received, apart from those mentioned below. Single crystals of all compounds were prepared by solvent diffusion method A or B. Elemental analyses were conducted by the Elemental Analysis Service, Department of Chemistry, University of Sheffield. Crystal Synthesis Method A. Crystals were obtained at room temperature (21 °C) by layering an acetonitrile solution of the halopyridinium salt on top of a CH2Cl2 solution of the hexacyanometallate salt. A buffering layer of acetonitrile was added between the two layers. The vials were sealed with lids and Parafilm and stored in the absence of light. The acetonitrile layers slowly mix with the CH2Cl2 layer. Crystal Synthesis Method B. Crystals were obtained at room temperature (21 °C) by a method based on slow diffusion in a U-shaped glass tube (internal diameter 5 mm). An acetonitrile solution of the halopyridinium salt was prepared. A CH2Cl2 solution of the hexacyanometallate salt was prepared separately. The bottom, horizontal section of the tube was filled with a buffer layer of acetonitrile. The two solutions were placed in the separate, vertical arms of the U-tube. Both arms of the U-tube were sealed with Parafilm. (PPN)3[Cr(CN)6]·2H2O. K3[Cr(CN)6] (0.1784 g, 0.55 mmol) was dissolved in hot deionized water (1 mL). (PPN)Cl (0.9442 g, 1.645 mmol) was dissolved in 100 mL of deionized water at 80 °C. The first solution was added dropwise to the second solution and a white precipitate formed. This was filtered, collected, and dried in a vacuum oven overnight at 60 °C. Yield 0.97 g, 94.82%. Found: C, 74.17; H, 4.80; N, 6.75%. Calc.: C, 73.62; H, 5.09; N, 6.78%. (PPh4)3[Cr(CN)6]·2H2O. K3[Cr(CN)6] (0.2653 g, 0.815 mmol) was dissolved in deionized water (3 mL). (PPh4)Cl (0.9165 g, 2.445 mmol) was dissolved in 22 mL of deionized water at room temperature. The first solution was added dropwise to the second solution and a yellow precipitate formed. This was filtered, collected, and dried in a vacuum oven overnight at 60 °C. Yield: 0.967 g, 93.97%. Found: C, 74.02; H, 5.01; N, 6.58%. Calc.: C, 74.22; H, 5.11; N, 6.66%. (PPN)3[Fe(CN)6]·2H2O. K4[Fe(CN)6]·3H2O (0.2310 g, 0.547 mmol) was dissolved in 5 mL of deionized water. (PPN)Cl (0.943 g, 1.64 mmol) was dissolved in 100 mL of deionized water at 80 °C. The first solution was added dropwise to the second solution and a yellow precipitate formed. This was filtered, collected, and dried in a vacuum oven overnight at 60 °C. Because of air-oxidation of Fe(II) to Fe(III), the product formed was (PPN)3[Fe(CN)6]·2H2O rather than (PPN)4[Fe(CN)6]. Yield 0.8979 g 87.26%. Found: C, 73.96; H, 4.94; N, 5.64%. Calc.: C, 73.47; H, 5.08; N, 6.76%. (PPN)3[Co(CN)6]·2H2O. K3[Co(CN)6] (0.1815 g, 0.546 mmol) was dissolved in hot deionized water (1 mL). (PPN)Cl (0.9408 g, 1.64 mmol) was dissolved in 100 mL of deionized water at 80 °C. The first solution was added dropwise to the second solution and a white precipitate formed. This was filtered, collected, and dried in a vacuum oven overnight at 60 °C. Yield: 0.978 g, 95.98%. Found: C, 73.76; H, 4.96; N, 6.81%. Calc.: C, 73.35; H, 5.08; N, 6.75%. (PPh4)3[Co(CN)6]·2H2O. K3[Co(CN)6] (0.2695 g, 0.811 mmol) was dissolved in deionized water (3 mL). (PPh4)Cl (0.9119 g, 2.43 mmol) was dissolved in 22 mL of deionized water at 50 °C. The first solution was added dropwise to the second solution and the solution remained colorless. The mixture was heated to boiling and some of the water was driven off. Cooling yielded a white precipitate, 206



Article

(3,5-I2pyMe)3[Cr(CN)6] (7). (PPN)3[Cr(CN)6]·2H2O (7.44 mg, 0.004 mmol) was dissolved in a minimum volume of DCM (approximately 2 mL). N-Methyl-3,5-diiodopyridinium tetrafluoroborate (5 mg, 0.012 mmol) was dissolved in a minimum volume of acetonitrile (approximately 2 mL). Yellow crystals of 7 were obtained by method A after 2 days. Yield: 0.4 mg, 8.03% Found: C, 39.37; H, 2.60; N, 16.69%. Calc.: C, 39.27; H, 2.88; N, 17.17%. (3,5-I2pyMe)3[Fe(CN)6] (8). (PPN)3[Fe(CN)6]·2H2O (7.52 mg, 0.004 mmol) was dissolved in a minimum volume of DCM (approximately 2 mL). N-Methyl-3,5-diiodopyridinium tetrafluoroborate (5 mg, 0.012 mmol) was dissolved in a minimum volume of acetonitrile (approximately 2 mL). Yellow crystals of 8 were obtained by method A after 2 days. Yield: 0.8 mg, 16.00% Found: C, 25.62; H, 1.34; N, 9.43%. Calc.: C, 23.07; H, 1.45; N, 10.09%. (3,5-I2pyMe)3[Co(CN)6] (9). (PPN)3[Co(CN)6]·2H2O (7.47 mg, 0.004 mmol) was dissolved in a minimum volume of DCM (approximately 2 mL). N-Methyl-3,5-diiodopyridinium tetrafluoroborate (5 mg, 0.012 mmol) was dissolved in a minimum volume of acetonitrile (approximately 2 mL). Colorless crystals of 9 were obtained by method A after 2 days. Yield: 0.6 mg, 11.98% Found: C, 23.60; H, 1.28; N, 9.65%. Calc.: C, 23.01; H, 1.45; N, 10.06%. (3,5-Br 2 pyMe) 3 [Cr(CN) 6 ]·4H 2 O (10·4H 2 O). (PPN) 3 [Cr(CN)6]·2H2O (15.62 mg, 0.0084 mmol) was dissolved in DCM (approximately 2.5 mL) and N-methyl-3,5-dibromopyridinium hexafluorophosphate (10 mg, 0.0252 mmol) was dissolved in acetonitrile (3 mL). Yellow crystals of 10·4H2O were obtained by method A after 2 days. Yield: 1.6 mg. Found: C, 32.03; H, 1.83; N, 12.19%. Calc.: C, 27.83; H, 2.53; N, 12.17% indicates that the bulk crystalline material is not phase pure. (3,5-Br2pyMe)3[Fe(CN)6] (11). (PPN)3[Fe(CN)6]·2H2O (15.80 mg, 0.0084 mmol) was dissolved in DCM (approximately 2.5 mL) and N-methyl-3,5-dibromopyridinium hexafluorophosphate (10 mg, 0.0252 mmol) was dissolved in acetonitrile (3 mL). The two solutions were allowed to mix slowly (method B). Yellow crystals of 11 were obtained after 2 days. Yield: 2.1 mg, 25.83% Found: C, 31.57; H, 1.77; N, 12.31%. Calc.: C, 29.79; H, 1.87; N, 13.03%. (3,5-Br2pyMe)3[Co(CN)6] (12). (PPN)3[Co(CN)6]·2H2O (15.68 mg, 0.0084 mmol) was dissolved in DCM (approximately 2.5 mL) and N-methyl-3,5-dibromopyridinium hexafluorophosphate (10 mg, 0.0252 mmol) was dissolved in acetonitrile (3 mL). The two solutions were allowed to mix slowly (method B). Colorless crystals of 12 were obtained after 2 days. Yield: 2.7 mg, 33.12% Found: C, 28.49; H, 2.12; N, 11.55%. Calc.: C, 29.70; H, 1.87; N, 12.98%. Single Crystal X-ray Diffraction Studies. For compounds 1−10 a suitable crystal was mounted in a stream of cold N2 gas on a Bruker APEX-2 CCD diffractometer, equipped with graphite-monochromated Mo−Kα radiation from a sealed-tube source. For compounds 11 and 12 data were collected on a diffractometer comprising a Crystal Logic 4-circle kappa goniometer equipped with a Rigaku Saturn 724 CCD detector using synchrotron radiation (λ = 0.6998(7) Å) at beamline I19 at the Diamond Light Source. The crystal was maintained at 100 K during data collection using an Oxford Cryosystems Crystostream Plus low temperature device. CCD frame data were transformed from Rigaku to Bruker SMART format using the program ECLIPSE.27 Intensity data were indexed and integrated using the APEX II suite of programs.28 Details of the crystal, data collection, and refinement parameters are summarized in Tables 1−3. Data were corrected for absorption using empirical methods (SADABS) based upon symmetry-equivalent reflections combined with measurements at different azimuthal angles.29 The structures were solved by direct methods and refined by full-matrix least-squares on weighted F2 values for all reflections using the SHELX suite of programs.30 Non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed in calculated positions, refined using idealized geometries (riding model), and assigned fixed isotropic displacement parameters. Crystals of 3 and 10·4H2O show evidence of twinning. For 3 the best solution and refinement was obtained by using data form the major component only (ca. 75%). The structure refines as a racemic twin. For 10·4H2O the indexing and the calculation of the relative orientation of the domains

was removed under vacuum and the solid was recrystallized from methanol/chloroform to yield cream crystals. Yield: 70 mg, 38.25%. N-Methyl-3,5-dibromopyridinium Tetrafluoroborate. Trimethyloxonium tetrafluoroborate (1.0916 g, 5.75 mmol) was dissolved in nitromethane (50 mL) at 0 °C under a nitrogen atmosphere. 3,5-Dibromopyridine (0.625 g, 2.64 mmol) was added portion-wise under vigorous stirring. The solution was then allowed to warm to room temperature and then stirred for a further 6 h. The solvents were then evaporated under reduced pressure leaving a white solid, which was then recrystallized from chloroform−methanol. Yield: 1.00 g, 100%. Found: C, 21.25; H, 1.54; N, 3.82; Br, 47.41%. Calc.: C, 21.21; H, 2.08; N, 4.12; Br, 47.04%. N-Methyl-3,5-dibromopyridinium Hexafluorophosphate. NMethyl-3,5-dibromopyridinium tetrafluoroborate (1.00 g, 2.64 mmol) and NH4PF6 (0.43 g, 2.64 mmol) were separately dissolved in minimum volumes of hot, deionized water. On mixing the two solutions a white solid precipitated rapidly. The solid was filtered, washed with cold, deionized water, and dried yielding colorless crystals. Yield: 1.032 g, 98.47%. (3-IpyMe)3[Cr(CN)6] (1). (PPh4)3[Cr(CN)6]·2H2O (11.36 mg, 0.009 mmol) was dissolved in a minimum volume of CH2Cl2 (approximately 2 mL). N-Methyl-3-iodopyridinium hexafluorophosphate (10 mg, 0.027 mmol) was dissolved in a minimum volume of acetonitrile (approximately 2 mL). Yellow crystals of 1 were obtained by method A after 2 days. Yield: 3.75 mg, 47.99% Found: C, 36.62; H, 2.49; N, 13.67%. Calc.: C, 33.20; H, 2.44; N, 14.52%. Rietveld refinement of synchrotron X-ray powder diffraction data indicated a very small amount of a second phase was present. (Full details in Supporting Information.) (3-IpyMe) 3 [Fe(CN) 6 ]·2MeCN (2·2MeCN). (PPN) 3 [Fe(CN)6]·2H2O (16.93 mg, 0.009 mmol) was dissolved in CH2Cl2 (approximately 2.5 mL) and N-methyl-3-iodopyridinium hexafluorophosphate (10 mg, 0.027 mmol) was dissolved in acetonitrile (3 mL). Yellow crystals of 2·2MeCN were obtained by method A after 2 days. Yield: 4.4 mg. Found: C, 48.79; H, 3.15; N, 10.91%. Calc.: C, 35.25; H, 2.85; N, 16.15% indicates bulk crystalline sample is not phase pure. (3-IpyMe)3[Co(CN)6] (3) and (3-IpyMe)3[Co(CN)6]·2MeCN (3·2MeCN). (PPh4)3[Co(CN)6]·2H2O (11.42 mg, 0.009 mmol) was dissolved in a minimum volume of CH2Cl2 (approximately 2 mL). N-Methyl-3-iodopyridinium hexafluorophosphate (10 mg, 0.027 mmol) was dissolved in a minimum volume of acetonitrile (approximately 2 mL). Colorless crystals were obtained by method A after 2 days. From one synthesis (yield 3.1 mg) crystals selected were characterized by single crystal X-ray diffraction as 3, whereas from another (yield 5.2 mg) crystals were characterized by single crystal X-ray diffraction as 3·2MeCN. Elemental analyses indicated that the bulk crystalline material was not phase pure and it is likely that both materials are formed concomitantly. (3-BrpyMe)3[Cr(CN)6] (4). (PPh4)3[Cr(CN)6]·2H2O (13.25 mg, 0.0105 mmol) was dissolved in a minimum volume of CH2Cl2 (approximately 2 mL). N-Methyl-3-bromopyridinium hexafluorophosphate (10 mg, 0.0315 mmol) was dissolved in a minimum volume of acetonitrile (approximately 2 mL). Yellow crystals of 4 were obtained by method A after 2 days. Yield: 2.7 mg, 35.0% Found: C, 40.13; H, 2.29; N, 16.57%. Calc.: C, 39.64; H, 2.91; N, 17.34%. (3-BrpyMe)3[Fe(CN)6] (5). (PPN)3[Fe(CN)6]·2H2O (19.76 mg, 0.0105 mmol) was dissolved in a minimum volume of CH2Cl2 (approximately 2 mL). N-Methyl-3-bromopyridinium hexafluorophosphate (10 mg, 0.0315 mmol) was dissolved in a minimum volume of acetonitrile (approximately 2 mL). Yellow crystals of 5 were obtained by method A after 2 days. Yield: 2.6 mg, 33.39% Found: C, 39.19; H, 2.48; N, 15.47%. Calc.: C, 39.41; H, 2.90; N, 17.24%. (3-BrpyMe)3[Co(CN)6] (6). (PPh4)3[Co(CN)6]·2H2O (13.33 mg, 0.0105 mmol) was dissolved in a minimum volume of DCM (approximately 2 mL). N-Methyl-3-bromopyridinium hexafluorophosphate (10 mg, 0.0315 mmol) was dissolved in a minimum volume of acetonitrile (approximately 2 mL). Colorless crystals of 6 were obtained by method A after 2 days. Yield: 1.6 mg, 20.76% Found: C, 23.41; H, 1.37; N, 9.59%. Calc.: C, 23.14; H, 1.46; N, 10.12%. 207



Article

Table 1. Crystal Data, Data Collection, and Structure Refinement Parameters for 1−3

crystal color crystal size/mm crystal system space group, Z a/Å b/Å c/Å α/° β/° γ/° V/Å3 density/Mg m−3 temperature/K μ /mm−1 θ range /° reflections collected independent reflections reflections used in refinement, n L.S. parameters, p restraints, r R1(F),a I > 2.0σ(I) wR2(F2),a all data S(F2),a all data a

(3-IpyMe)3[Cr(CN)6] (1)

(3-IpyMe)3[Fe(CN)6]·2MeCN (2·2MeCN)

(3-IpyMe)3[Co(CN)6] (3)

(3-IpyMe)3[Co(CN)6]·2MeCN (3·2MeCN)

yellow 0.11 × 0.34 × 0.11 monoclinic Cc, 4 19.0572(4) 10.2321(2) 15.3048(3) 90 101.993(1) 90 2919.2(1) 1.975 100 3.595 2.19−27.54 26487 6656 [R(int) = 0.0328] 6656 332 2 0.0230 0.0466 1.087

yellow 0.22 × 0.15 × 0.06 monoclinic P21/c, 4 20.4121(15) 14.2849(10) 12.4715(9) 90 106.623(4) 90 3484.5(4) 1.819 100 3.126 1.04−27.76 63324 8107 [R(int) = 0.1280] 8107 396 0 0.0618 0.1729 1.182

colorless 0.16 × 0.12 × 0.07 monoclinic Cc, 4 18.929(4) 10.141(2) 15.118(3) 90 100.068(12) 90 2857.3(11) 2.034 100 3.873 2.19−26.65 14414 5398[R(int) = 0.0768] 5248 301 50 0.0654 0.1660 1.063

colorless 0.2 × 0.18 × 0.15 monoclinic P21/c, 4 20.2858(9) 14.2364(6) 12.4838(5) 90 106.402(2) 90 3458.6(3) 1.838 100 3.210 1.05−27.53 61242 7941 [R(int) = 0.0768] 7941 396 0 0.0378 0.0954 1.127

R1(F) = Σ(|Fo| − |Fc|)/Σ|Fo|; wR2(F2) = [Σw(Fo2 − Fc2)2/ΣwFo4]1/2; S(F2) = [Σw(Fo2 − Fc2)2/(n + r − p)]1/2.

Table 2. Crystal Data, Data Collection, and Structure Refinement Parameters for 4−8 (3-BrpyMe)3[Cr(CN)6] (3-BrpyMe)3[Fe(CN)6] (3-BrpyMe)3[Co(CN)6] (3,5-I2pyMe)3[Cr(CN)6] (3,5-I2pyMe)3[Fe(CN)6] (4) (5) (6) (7) (8) crystal color crystal size/mm crystal system space group, Z a/Å b/Å c/Å α/° β/° γ/° V/Å3 density/Mg m−3 temperature/K μ/mm−1 θ range/° reflections collected independent reflections reflections used in refinement, n L.S. parameters, p restraints, r R1(F),a I > 2.0σ(I) wR2(F2),a all data S(F2),a all data a

yellow 0.38 × 0.35 × 0.23 monoclinic Cc, 4 18.8866(7) 10.1126(4) 15.0093(3) 90 104.032(2) 90 2781.0(2) 1.737 100 4.754 2.23−27.51 25415 6326 [R(int) = 0.0325] 6326

yellow 0.14 × 0.19 × 0.06 monoclinic Cc, 4 18.7217(5) 9.9933(3) 14.8638(4) 90 102.810(2) 90 2711.68(13) 1.791 100 5.009 2.23−27.48 24963 5954 [R(int) = 0.0416] 5954

colorless 0.35 × 0.22 × 0.15 monoclinic Cc, 4 18.6790(5) 9.9819(2) 14.8250(4) 90 102.239(1) 90 2701.33(12) 1.805 100 5.105 2.23−27.50 24476 6097 [R(int) = 0.0234] 6097

yellow 0.35 × 0.30 × 0.15 monoclinic C2/c, 4 19.8999(8) 15.4142(6) 12.4420(4) 90 113.878(2) 90 3489.8(2) 2.371 100 5.665 1.73−27.49 29393 4005 [R(int) = 0.0237] 4005

yellow 0.30 × 0.20 × 0.10 monoclinic C2/c, 4 19.8980(6) 15.4085(5) 12.4411(3) 90 113.893(2) 90 3487.54(18) 2.380 100 5.773 1.73−27.50 16922 4008 [R(int) = 0.0505] 4008

335 2 0.0180 0.0452 1.048

337 2 0.0363 0.0836 1.526

337 2 0.0273 0.0744 1.630

186 0 0.0211 0.0733 1.596

186 0 0.0412 0.1140 1.310

R1(F) = Σ(|Fo| − |Fc|)/Σ|Fo|; wR2(F2) = [Σw(Fo2 − Fc2)2/ΣwFo4]1/2; S(F2) = [Σw(Fo2 − Fc2)2/(n + r − p)]1/2.

■

was carried out using the program CELL_NOW.31 Two domains were found and separate orientation matrices for each domain were used in the integration. Refinements for 3 were conducted using SHELX via the OLEX-2 suite of crystallographic programs.32 Additional experimental data for 10·4H2O are given in Supporting Information (Table S1).

RESULTS

Metathesis reactions of (PPN)3[M(CN)6] or (PPh4)3[M(CN)6] (where M = Cr, Fe or Co) with halopyridinium salts (3-XpyMe)PF6, or (3,5-X2pyMe)PF6 (X = I, Br) yielded a series of compounds with the general formula (3-XpyMe)3[M(CN)6] 208



Article

Table 3. Crystal Data, Data Collection, and Structure Refinement Parameters for 9−12

crystal color crystal size/mm crystal system space group, Z a/Å b/Å c/Å α/° β/° γ/° V/Å3 density/Mg m−3 temperature/K μ/mm−1 θ range /° reflections collected independent reflections reflections used in refinement, n L.S. parameters, p restraints, r R1(F),a I > 2.0σ(I) wR2(F2),a all data S(F2),a all data

(3,5-I2pyMe)3[Co(CN)6] (9)

(3,5-Br2pyMe)3[Cr(CN)6]·4H2O (10·4H2O)

(3,5-Br2pyMe)3[Fe(CN)6] (11)

(3,5-Br2pyMe)3[Co(CN)6] (12)

colorless 0.16 × 0.16 × 0.02 monoclinic C2/c, 4 19.8874(7) 15.3305(6) 12.2069(4) 90 114.187(2) 90 3395.0(2) 2.451 100 5.992 1.74−27.51 31704 3901 [R(int) = 0.0806] 3901 186 0 0.0367 0.0972 1.464

yellow 0.18 × 0.15 × 0.04 triclinic P1̅ 8.738(2) 11.072(2) 18.798(4) 79.54(3) 84.86(3) 84.84(3) 1776.3(6) 1.937 100 7.114 1.10−27.66 15824b 4411 [R(int) = 0.0640]b 4411b 401 6 0.1047 0.3043 2.067

yellow 0.20 × 0.10 × 0.10 monoclinic C2/c, 4 18.824(5) 14.901(4) 11.831(3) 90 111.520(3) 90 3087.3(15) 2.082 100 8.286 1.79−27.60 14384 3397 [R(int) = 0.0420] 3397 186 0 0.0290 0.0635 1.183

colorless 0.20 × 0.10 × 0.10 monoclinic C2/c, 4 18.901(4) 14.878(3) 11.767(2) 90 111.617(4) 90 3076.4(10) 2.096 100 8.383 1.79−27.60 16840 3502 [R(int) = 0.0221] 3502 181 0 0.0513 0.1686 1.508

R1(F) = Σ(|Fo| − |Fc|)/Σ|Fo|; wR2(F2) = [Σw(Fo2 − Fc2)2/ΣwFo4]1/2; S(F2) = [Σw(Fo2 − Fc2)2/(n + r − p)]1/2. bValues for largest component of a two component twin (full details in Table S1, Supporting Information). a

(C−N···I 148.0(3)° and 156.9(3)°, respectively, in 1). The third halogen bond is slightly longer and has a greater deviation from linearity (e.g., C−I···N 169.8 (1)° in 1). Most notably the C−N···I angle of 102.9(3)° suggests that this interaction may involve a significant contribution from the CN π-bond in the halogen bond acceptor role. Cation−anion interactions are further propagated through a network of C−H···N hydrogen bonds. Very offset π-stacking interactions between triplets of N-methyl-3iodopyridinium cations are also present (e.g., ring centroid− centroid distances 4.59 and 4.43 Å, cf. shortest corresponding inter-ring C···C distances of 3.44 and 3.40 Å, for 1). The crystal structures of 2·2MeCN and 3·2MeCN are isostructural with each other. The structure contains two crystallographically independent anions [M(CN)6]3−, both of which are situated at an inversion center. One anion interacts via separate C−I···N halogen bonds with four N-methyl-3iodopyridnium cations (3-IpyMe+), and the other with two cations, also via C−I···N halogen bonds. Two acetonitrile molecules per anion are also included in the crystal structure but do not compete for halogen bond formation with the cyanometallate anions. The crystal structure of 2·2MeCN is shown in Figure 2. Halogen bond geometries are similar for both anions and resemble those of the shorter halogen bonds observed for 1 and 3. Thus, (C)I···N distances lie in the range 2.911(7)−2.936(5) (RIN 0.82−0.83) with close to linear halogen bond geometries (C−I···N 167.3(2)−173.9(2)°) and interaction at the cyanide ligand again suggesting predominant involvement of the nitrogen lone pair in the halogen bond acceptor role (C−N···I 148.0(6)− 161.4(5)°). As in the structure of 1 and 3, cation−anion interactions further are propagated through a network of C−H···N hydrogen bonds, and π-stacking interactions between the N-methyl-3-iodopyridinium cations are also present. The presence of MeCN solvent molecules does not interrupt halogen

or (3,5-X2pyMe)3[M(CN)6]. All were structurally characterized by single crystal X-ray diffraction. Compositional purity was confirmed by elemental analysis for most products, and phase purity was examined by X-ray powder diffraction for 1. Slow mixing of the two reactants via method A was used to prepare X-ray quality single crystals of 1−10, whereas solvent layering in a U-tube (method B) was necessary to obtain suitable crystals of 11 and 12. Two of the compounds, (3-IpyMe)3[Fe(CN)6]·2MeCN (2·2MeCN) and (3,5-Br2pyMe)3[Cr(CN)6]·4H2O (10·4H2O), were crystallized only as solvates. Compound 3 was crystallized as unsolvated crystals and as solvated 3·2MeCN. In all crystal structures the hexacyanometallate anions adopt an octahedral coordination as expected. All compounds exhibit C−X···NC(M) halogen bonding between cation and anion and thereby provide an excellent opportunity to study halogen bonding across a closely related family of compounds in which cyanide ligands serve as halogen bond acceptors. The crystal structures are discussed in more detail below. A full list of halogen bond geometries is given in Table 4. Crystal Structures of (3-IpyMe)3[M(CN)6], M = Cr (1), Co (3) and (3-IpyMe) 3 [M(CN) 6 ]·2MeCN, M = Fe (2·2MeCN), Co (3·2MeCN). The crystal structures of 1 and 3 are isostructural with each other and with their N-methyl-3bromopyridinium analogues (vide infra). The three unique cations form C−I···NC(M) halogen bonds involving three of the six cyanide ligands of each anion, as depicted in Figure 1. Halogen bond distances (I···N) range from 2.911(4)−3.114(6) Å (RIN 0.83 − 0.88)31 in 1 and 2.913(14)−3.059(14) Å (RIN 0.83−0.86) in 3. The two shortest halogen bonds show only a small distortion from the preferred linear halogen bond geometry (e.g., C−I···N 177.1(1)° and 173.4(1)°, respectively in 1). Interaction geometries at the cyanide acceptor groups suggest the primary interaction is with the nitrogen lone pair 209



Article

Table 4. Halogen Bond Geometries for Compounds 1−12 compound (3-IpyMe)3[Cr(CN)6] (1)

(3-IpyMe)3[Fe(CN)6]·2MeCN (2·2MeCN)

(3-IpyMe)3[Co(CN)6] (3)

(3-IpyMe)3[Co(CN)6]·2MeCN (3·2MeCN)

(3-BrpyMe)3[Cr(CN)6] (4)

(3-BrpyMe)3[Fe(CN)6] (5)

(3-BrpyMe)3[Co(CN)6] (6)

(3,5-I2pyMe)3[Cr(CN)6] (7)

(3,5-I2pyMe)3[Fe(CN)6] (8)

(3,5-I2pyMe)3[Co(CN)6] (9)

(3,5-Br2pyMe)3[Cr(CN)6]·4H2O (10·4H2O)

(3,5-Br2pyMe)3[Fe(CN)6] (11)

(3,5-Br2pyMe)3[Co(CN)6] (12)

a

halogen bond

X···N (Å)

C−X···N (deg)

(M)CN···X (deg)

rX + rNa (Å)

RXNa

I41···N13 I31···N11 I21···N15 I21···N11 I31···N14 I41···N12 I41···N13 I31···N11 I21···N15 I21···N11 I31···N14 I41···N12 Br41···N13 Br31···N11 Br21···N15 Br41···N13 Br31···N11 Br21···N15 Br41···N13 Br31···N11 Br21···N15 I31···N12 I22···N13 I21···N11 I31···N12 I22···N13 I21···N11 I31···N12 I22···N13 I21···N11 Br32···N16 Br42···N13 Br22···N15 Br21···N16 Br31···N15 Br31···N12 Br22···N13 Br21···N11 Br31···N12 Br22···N13 Br21···N11

2.911(4) 2.985(4) 3.114(6) 2.911(7) 2.930(6) 2.932(6) 2.927(16) 2.987(14) 3.073(15) 2.920(5) 2.935(5) 2.936(5) 2.966(2) 2.997(2) 3.166(2) 2.952(5) 3.012(5) 3.116(5) 2.941(2) 3.043(2) 3.095(2) 2.821(3) 3.044(3) 3.108(3) 2.807(6) 3.043(6) 3.116(7) 2.789(7) 3.021(6) 3.062(7) 3.042(6) 3.177(6) 3.178(6) 3.326(6) 3.380(6) 2.889(3) 2.948(3) 3.030(3) 2.884(3) 2.950(3) 3.012(3)

177.1(1) 173.4(1) 169.8(1) 171.0(3) 173.9(2) 168.1(2) 176.0(6) 173.0(6) 172.8(5) 170.08(19) 173.66(18) 167.33(18) 177.93(8) 171.11(7) 164.05(7) 176.0(2) 171.0(2) 166.5(2) 175.81(8) 170.98(8) 167.31(7) 176.8(1) 167.5(1) 171.8(1) 177.1(2) 167.2(3) 171.9(2) 176.6(3) 168.2(3) 173.5(2) 172.2(3) 154.2(3) 164.1(3) 161.2(2) 165.8(2) 175.5(1) 167.9(1) 170.0(1) 177.2(1) 167.8(1) 169.9(1)

148.0(3) 156.9(3) 102.9(3) 159.8(6) 151.3(6) 148.0(6) 147.2(13) 157.1(13) 104.1(11) 161.4(5) 151.5(5) 149.0(5) 146.2(2) 160.3(2) 100.5(2) 146.2(4) 159.5(4) 103.3(4) 145.7(2) 159.1(2) 104.0(2) 170.2(4) 104.0(3) 97.1(3) 170.2(6) 104.4(5) 96.9(5) 170.4(6) 105.0(5) 100.2(5) 146.6(5) 91.5(5) 139.1(5) 84.0(5) 79.8(5) 167.2(3) 104.0(2) 95.9(3) 167.2(3) 103.7(3) 98.2(2)

3.53 3.53 3.53 3.53 3.53 3.53 3.53 3.53 3.53 3.53 3.53 3.53 3.40 3.40 3.40 3.40 3.40 3.40 3.40 3.40 3.40 3.53 3.53 3.53 3.53 3.53 3.53 3.53 3.53 3.53 3.40 3.40 3.40 3.40 3.40 3.40 3.40 3.40 3.40 3.40 3.40

0.825 0.846 0.882 0.825 0.830 0.831 0.829 0.846 0.871 0.827 0.831 0.832 0.882 0.882 0.931 0.868 0.886 0.916 0.865 0.895 0.910 0.799 0.862 0.880 0.795 0.862 0.883 0.790 0.856 0.867 0.894 0.935 0.935 0.978 0.994 0.850 0.867 0.891 0.848 0.868 0.886

See ref 33 for definition of reduced bond length, RXN, and source of van der Waals radii, rX and rN.

(C−Br···N in the range 164.1(1)−167.3(2)°) with an interaction geometry at the cyanide indicative of significant involvement of the CN π-bond in the halogen bond acceptor role (C−N···Br in the range 100.5(2)−104.0(2)°). As in previous structures, a network of C−H···N hydrogen bonds between cations and anion is observed as are offset π-stacking interactions between the cations (e.g., ring centroid−centroid distances 4.39 and 4.39 Å, cf. shortest corresponding inter-ring C···C distances of 3.40 and 3.38 Å, for 4). Crystal Structures of (3,5-I2pyMe)3[M(CN)6] M = Cr (7), Fe (8), Co (9). The crystal structures of 7−9 are mutually isostructural (Figure 4) and are also isostructural with their N-methyl-3,5-dibromopyridnium counterparts (vide infra). The hexacyanometallate anions have crystallographic inversion symmetry, and each cyanide ligand participates in a C−I···NC(M) halogen bond with a separate N-methyl-3,5-diiodopyridnium cation. All cations form halogen bonds to two neighboring

bond formation; each is involved in weak C−H···N hydrogen bond interactions with the anions and cations. Crystal Structures of (3-BrpyMe)3[M(CN)6], M = Cr (4), Fe (5), Co (6). The crystal structures of 4−6 are mutually isostructural (see Figure 3), but also isostructural with the N-methyl-3-iodopyridinium salt analogues 1 and 3. Interestingly, in this case the hexacyanoferrate(III) salt was isolated in its unsolvated form. For structures 4−6, halogen bond distances (Br···N) range from 2.966(2)−3.166(2) Å (RBrN 0.88−0.93) in 4, 2.952(5)−3.116(5) Å (RBrN 0.87−0.92) in 5 and 2.941(2)−3.095(2) Å (RBrN 0.87−0.91) in 6. The two shortest halogen bonds in each case have geometries closest to linearity (C−Br···N in the range 171.0(1)−177.9(1)°) and exhibit interaction geometries at the cyanide ligand consistent with substantial involvement of the nitrogen lone pair (C− N···Br in the range 145.7(2)−160.3(2)°). The longest halogen bond in each structure shows greater deviation from linearity 210



Article

Figure 1. Crystal structure of (3-IpyMe)3[Cr(CN)6] (1) showing C−I···N halogen bonds. Compound 3 is isostructural with 1.

Figure 2. Crystal structure of (3-IpyMe)3[Fe(CN)6]·2MeCN (2·2MeCN) showing C−I···N halogen bonds. Compound 3·2MeCN is isostructural with 2·2MeCN.

Figure 3. Crystal structure of (3-BrpyMe)3[Cr(CN)6] (4) showing C−Br···N halogen bonds. Compounds 5 and 6 are isostructural with 4.

anions leading to a halogen-bonded network that propagates throughout the structures (Figure S2, Supporting Information). There are two independent cations, one of which forms halogen bonds with slightly different geometry to two anions,

and the other has 2-fold symmetry and therefore forms identical halogen bonds to two anions. The latter cation forms the shortest halogen bonds with (C)I···N distances of 2.821(3) Å (RIN 0.80) for 7 (Cr), 2.807(6) Å (RIN 0.80) for 8 (Fe), and 211



Article

Figure 5. Crystal structure of (3,5-Br2pyMe)3[Co(CN)6] (12) showing C−Br···N halogen bonds. Compound 11 is isostructural with 12.

Figure 4. Crystal structure of (3,5-I2pyMe)3[Co(CN)6] (9) showing C−I···N halogen bonds. Compounds 7 and 8 are isostructural with 9.

2.789(7) Å (RIN 0.79) for 9 (Co). These halogen bonds are close to linear in geometry (C−I···N 176.6(3)−177.1(2)°) and lie close to coaxial with the cyanide ligand (C−N···I 170.2(6)− 170.4(6)°). Halogen bonds involving the other cation are longer, with (C)I···N distances in the range 3.021(6)−3.116(7) Å (RIN 0.86−0.88), and deviate more from linearity (C−I···N 167.2(3)−173.5(2)°). These halogen bonds lie almost orthogonal to the cyanide ligands (C−N···I 96.9(5)− 105.0(5)°) indicating significant involvement of the CN π-bond in the halogen bond acceptor role. Crystal Structures of (3,5-Br2pyMe)3[M(CN)6], M = Fe (11), Co (12) and (3,5-Br 2 pyMe) 3 [Cr(CN) 6 ]·4H 2 O (10·4H2O). The crystal structures of 11 and 12 (Figure 5) are isostructural with each other and the N-methyl-3,5diiodopyridinium analogues 7−9. All cations form C−I···N halogen bonds to two anions via the two iodo substituents, each halogen bond involving a separate cyanide ligand. This results in a halogen bonded network that persists throughout the crystal (Figure S2, Supporting Information). The shortest halogen bonds (involving the 2-fold symmetric cation) have geometries of (C)Br···N 2.889(3) Å (RBrN 0.85), 2.884(3) Å (RBrN 0.85); C−Br···N 175.5(1), 177.2(1)°; C−N···Br 167.2(3), 167.2(3)° for 11 (Fe) and 12 (Co), respectively. The longer halogen bonds (involving cation situated in a crystallographic general position) have geometries of (C)Br···N 2.948(3)−3.030(3) Å (RBrN 0.87−0.89); C−Br···N 167.8(1)− 170.0(1)°; C−N···Br 95.9(3), 104.0(2) ° In the crystal structure of 10·4H2O, [Cr(CN)6]3− anions interact with the three 3,5-Br2pyMe+ cations via five C−Br···N halogen bonds (Figure 6) and with three of the four independent water molecules via five O−H···N hydrogen bonds. Halogen bond distances lie in the range 3.042(6)− 3.380(6) Å (RBrN 0.89−0.99). These are generally longer than for the other structures studied and show correspondingly

Figure 6. Crystal structure of (3,5-Br2pyMe)3[Cr(CN)6]·4H2O (10·4H2O) showing C−Br···N and C−Br···O halogen bonds. Hydrogen-bonded water molecules are not shown.

greater deviations from linearity (C−Br···N angles 154.2(3)− 172.2(3)°). Three of the interactions are side-on to the cyanide ligand (Br···C−N angles 79.8(5)−91.5(5)°) suggesting description as a C−Br···π(NC) halogen bond is appropriate, whereas two of the halogen bond geometries suggest greater involvement of the nitrogen lone pair (Br···C−N angles 139.1(5) and 146.6(5)°). Hydrogen bonds have O···N distances in the range 2.808−2.917 Å. Further hydrogen bonds between water molecules (O···O 2.697−2.851 Å) provide a hydrogen-bonded network that includes eight water 212



Article

bond has an I···N separation of 2.789(7) Å (RIN 0.79) in 9 and the longest are mostly associated with 10·4H2O in which hydrogen bonding by water molecules competes with halogen bonding by the 3,5-Br2pyMe+ cations for interactions with the cyanide ligands. Comparison between C−X···N halogen bond geometries in the isostructural series (3-BrpyMe)3[M(CN)6] (M = Cr (4), Fe (5), Co (6)) and (3,5-I2pyMe)3[M(CN)6] (M = Cr (7), Fe (8), Co (9)) reveals that X···N distances of two of the three independent halogen bonds decrease in the order Cr > Fe > Co. For compounds 4−6 the third X···N distance shows the opposite trend, and for 7−9 the third X···N distance decreases in the order Fe > Cr > Co. However, there is a net decrease in halogen bond lengths in both series, a point supported by corresponding changes in the pair of isostructural compounds (3,5-Br2pyMe)3[M(CN)6] (M = Fe (11), Co (12)), but which is less convincing in the pair (3-IpyMe)3[M(CN)6] (M = Cr (1), Co (3)).34 These decreases in halogen bond length are accompanied by decreases in unit cell volume and indeed for all unit cell lengths.35 The trend in decreasing halogen bond lengths suggests increasing strength of halogen bonds and correlates well with increasing metal d-electron count, which results in increased population of t2g energy levels and therefore greater π-back-donation to the cyanide ligands.36 Increased π-back-donation will increase the partial negative charge and therefore negative electrostatic potential associated with the cyanide ligand, and in particular the nitrogen atom, which is the dominant contributor to the CN π* orbital. The increase in negative charge at the nitrogen atoms provides a rationale for formation of stronger halogen bonds. Average CN distances for cyanide ligands that form halogen bonds are slightly shorter than those for noninteracting cyanides, but the differences (approx 0.005 Å) are insignificant compared to errors in the CN bond length determinations (0.003−0.010 Å) (see Table S1, Supporting Information). Of the 41 C−X···N halogen bonds characterized all but one37 have interaction geometries at the cyanide nitrogen that suggest either predominant involvement of the nitrogen lone pair (CN···X > 145°) or predominant involvement of the CN π-bond in the halogen bond (CN···X < 105°) acceptor role.38 Throughout the series of compounds studied the shorter halogen bonds are formed through interaction with the nitrogen lone pair suggesting that this is the better halogen bond acceptor site. The difference in average CN bond lengths associated with end-on vs side-on halogen bonding interactions is very small (e.g., in 7−9, 11, 12, CN(av) 1.150 Å for cyanide ligands involved in end-on halogen bonds, and 1.153 Å for those involved in side-on halogen bonds) and comparable to the errors associated with these determinations. Previously we have reported the structures of cyanoruthenate salts (3-IpyMe)2[Ru(bipy)(CN)4]·0.5MeCN, (3,5-I2pyMe)2[Ru(bipy)(CN)4], (3-BrpyMe)2[Ru(bipy)(CN)4]·2H2O, and (3,5-Br2pyMe)2[Ru(bipy)(CN)4]·5H2O,25 in which the former pair exhibit C−I···N halogen bonding, but the latter hydrated compounds predominantly exhibit O−H···N hydrogen bonds involving cyanide ligands. The C−I···N halogen bonds have I···N separations in the range 2.79−2.97 Å (RIN 0.79−0.84), comparable with compounds 1−3 and 7−9 herein, and similarly have geometries consistent with the formation of stronger halogen bonds involving the nitrogen lone pair than those involving the CN π-bond. Two C−Br···N halogen bonds are formed in (3,5-Br2pyMe)2[Ru(bipy)(CN)4]·5H2O; both are weak sideon interactions with Br···N separations of 3.19−3.29 Å

molecules and six anions as shown in Figure 7. Three of the four independent water molecules donate two and accept one

Figure 7. Crystal structure of (3,5-Br2pyMe)3[Cr(CN)6]·4H2O (10·4H2O) showing hydrogen bond network involving water molecules and C−Br···O halogen bonds. Hydrogen atoms are omitted for clarity.

hydrogen bond. Interestingly, the other water molecule does not interact with the anions, but donates two O−H···O hydrogen bonds and accepts a C−Br···O halogen bond from the one Br atom that also does not interact with the anions (Br···O 2.860(5) Å, RBrO 0.85; C−Br···O 176.6(2)°).

■

DISCUSSION The close structural relationships between the compounds studied provide an opportunity to examine halogen bonding in some detail and specifically to assess such interactions involving cyanide ligands as halogen bond acceptors, that is, C− X···NC(M). Two isostructural families have been characterized, (3-XpyMe)3[M(CN)6] and (3,5-X2pyMe)3[M(CN)6] (X = I, Br; M = Cr, Fe, Co). For each family, five of the six members have been crystallographically characterized and the sixth member has been characterized as a solvate, namely, (3-IpyMe)3[Fe(CN)6]·2MeCN (2·2MeCN) and (3,5-Br2pyMe)3[Cr(CN)6]·4H2O (10·4H2O). Solvate 3·2MeCN was characterized in addition to the unsolvated (3-IpyMe)3[Co(CN)6] 3. Halogen bond geometries (Table 4) exhibit some informative trends. It is notable that of the 42 crystallographically independent C−X groups in these 13 crystal structures, 41 form C−X···NC(M) halogen bonds, all with X···N distances below the sum of van der Waals radii for the two interacting atoms (rX + rN), the other forming a C−Br···O halogen bond to a water molecule in 10·4H2O. Of the 41 C−X···N halogen bonds, 24 have C−X···N greater than 170° and only four are below 165°, consistent with the preferred linear geometry of halogen bonds. Comparison of isostructural pairs in which only the halogen has been changed shows that some C−I···NC(M) halogen bonds are shorter than their C−Br···NC(M) and some are longer. It is therefore instructive to consider these interaction distances, normalized to the sum of van der Waals radii, RXN.33 In all cases, RIN is smaller than RBrN, indicating that the halogen bonds involving iodine are stronger than those involving bromine, consistent with observations for halogen bonds involving other acceptor groups. The normalized distances RXN lie in the range 0.825− 0.882 for the 3-IpyMe+ systems (1−3), 0.865−0.931 for the 3-BrpyMe+ salts (4−6), 0.790−0.883 for the 3,5-IpyMe+ systems (7−9), and 0.848−0.891 for 3,5-Br2pyMe+ systems (11−12), but 0.894−0.994 for 10·4H2O. The shortest halogen 213



Article

and even the electronic properties of cyanometallate. This study provides such insight for halogen bonds.

(RBrN 0.94−0.97). All compounds were crystallized from nonpolar solvents as in the present work, but in both studies the starting cyanometallate salt is a hydrate and in neither study were rigorous efforts to exclude water made. It is interesting that as for the cyanoruthenates, water is absent when C−I···N halogen bonding is present, but unlike the cyanoruthenates only one of the five bromopyridinium salts is hydrated. This reflects the formation of short (strong) C−Br···N halogen bonds for compounds 4−6, 11, and 12, perhaps as a result of the overall charge on the anion, which is higher than in the cyanoruthenates.39 In (3-BrpyMe)2[Ru(bipy)(CN)4]·2H2O as in 10·4H2O a C−Br···O halogen bond is formed to a water molecule. Notably the halogen bond in the latter is much shorter, by some 0.4 Å. It is particularly interesting to note the involvement of water molecules in halogen bonding in these studies of cyanometallates as we have previously noted the propensity for water molecules to engage in hydrogen bonds in preference to halogen bonds in studies of halometallates.12g The observed C−I···NC(M) halogen bond geometries in the present study are also consistent with those reported for molecular semiconductor materials comprising iodo-substituted tetrathiofulvalene radical cation salts of cyanometallates (often [Au(CN)4]−).18 Very few other structures containing C−Br···NC(M) halogen bonds have been published,40 and halogen bonding has often been overlooked by the original authors.

■

ASSOCIATED CONTENT S Supporting Information * X−ray crystallographic information files (CIFs) for compounds 1, 2·MeCN, 3, 3·MeCN, 4−9, 10·4H2O, 11, 12. Details of Rietveld refinement of X-ray powder diffraction data for 1. Table of CN bond lengths for all crystallographically characterized compounds. Figure showing halogen-bonded network for compounds 7−9, 11, and 12. UV−visible spectra for 3, 6, 9, 12. This material is available free of charge via the Internet at http://pubs.acs.org.

■ ■

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. ACKNOWLEDGMENTS We are grateful to the EPSRC for funding for PS and JEO (EP/ F00141X/1) and for X-ray diffraction facilities at Sheffield (GR/T26047/01). STFC and CCDC are also thanked for support of PS. We are grateful to Diamond Light Source for access to beamlines I19 and I11 for single crystal and powder X-ray diffraction, respectively, and to Dr. David Allan and Dr. Stephen Thompson for their assistance at these beamlines. We thank Harry Adams (University of Sheffield) for helpful discussions.

■

CONCLUSIONS Synthesis and crystallographic characterization of two series of cyanometallate salts (3-XpyMe)3[M(CN)6] (X = I, Br; M = Cr, Fe, Co) and (3,5-X2pyMe)3[M(CN)6] (X = I, Br; M = Cr, Fe, Co) has enabled a systematic study of cyanide ligands as halogen bond acceptors. Ten of the 12 compounds were isolated as unsolvated salts, one also as its acetonitrile solvate (3·2MeCN),41 whereas two were isolated only as solvates (2·2MeCN and 10·4H2O). The absence of hydrates is notable given the propensity of cyanometallate salts to form hydrates due to the excellent hydrogen bond acceptor capability of the cyanide ligands. However, the longest halogen bonds are found in 10·4H2O presumably due to competition between halogen bonds and hydrogen bonds for interaction with the cyanides. Across the 13 crystal structures 56 of the 57 halogen groups form C−X···N halogen bonds (41 of 42 symmetry independent halogens), the other forming a C−Br···O halogen bond in 10·4H2O. All halogen bonds are close to linearity at the halogen and as is typical of such interactions. Interactions involving iodine are stronger than those involving bromine as is well established from studies of other halogen bond acceptors.3b,e Interaction geometries at the cyanide ligand suggest either the nitrogen lone pair (CN···X > 145°) or the CN π-bond (CN···X < 105°) predominates in the halogen bond acceptor role, with shorter halogen bonds being formed when the nitrogen lone pair is involved. The choice of metal also appears to play a role in the strength of the halogen bonds. In isostructural series of compounds (3,5-X2pyMe)3[M(CN)6] (X = I, Br; M = Cr, Fe, Co), there is a net decrease in halogen bond length for a given halogen in the sequence Cr > Fe > Co. The trend is less clear-cut for the (3-XpyMe)3[M(CN)6] salts. Since cyanometallates are used as components in the construction of magnetic and conducting materials and in often display interesting optoelectronic properties, it is desirable to have an understanding of their propensity to form tunable intermolecular interactions that may influence the structure of solid state forms

■

REFERENCES

(1) (a) Philp, D.; Stoddart, J. F. Angew. Chem., Int. Ed. Engl. 1996, 35, 1154. (b) Swiegers, G. F.; Malefetse, T. J. Coord. Chem. Rev. 2002, 225, 91. (c) Fujita, M.; Tominaga, M.; Hori, A.; Therrien, B. Acc. Chem. Res. 2005, 38, 369. (d) Fiedler, D.; Leung, D. H.; Bergman, R. G.; Raymond, K. N. Acc. Chem. Res. 2005, 38, 349. (e) Ward, M. D. Chem. Soc. Rev. 1997, 26, 365. (f) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311. (g) Steed, J. W.; Atwood, J. L. Supramolecular Chemistry; Wiley: New York, 2000. (2) (a) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48. (b) Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond; Oxford University Press: Oxford, 1999. (3) (a) Desiraju, G. R.; Parthasarathy, R. J. Am. Chem. Soc. 1989, 111, 8725. (b) Metrangolo, P.; Neukirch, H.; Pilati, T.; Resnati, G. Acc. Chem. Res. 2005, 38, 386. (c) Metrangolo, P.; Meyer, F.; Pilati, T.; Resnati, G.; Terraneo, G. Angew. Chem., Int. Ed. 2008, 47, 6114. (d) Rissanen, K. CrystEngComm 2008, 10, 1107. (e) Brammer, L.; Mínguez Espallargas, G.; Libri, S. CrystEngComm 2008, 10, 1712. (f) Parisini, E.; Metrangolo, P.; Pilati, T.; Resnati, G.; Terraneo, G. Chem. Soc. Rev. 2011, 40, 2267. (4) (a) Clark, T.; Hennemann, M.; Murray, J. S.; Politzer, P. J. Mol. Model. 2007, 13, 291. (b) Politzer, P.; Murray, J. S.; Clark, T. Phys. Chem. Chem. Phys. 2010, 12, 7748. (c) Legon, A. C. Angew. Chem., Int. Ed. 1999, 38, 2686. (d) Legon, A. C. Phys. Chem. Chem. Phys. 2010, 12, 7736. (5) (a) Castellote, I.; Morón, M.; Burgos, C.; Alvarez-Builla, J.; Martin, A.; Gómez-Sal, P.; Vaquero, J. J. Chem. Commun. 2007, 1281. (b) Bouchmella, K.; Boury, B.; Dutremez, S. G.; van der Lee, A. Chem.Eur. J. 2007, 13, 6130. (c) Lu, Y.-X.; Zou, J.-W.; Wang, Y.-H.; Yu, Q.-S. Chem. Phys. 2007, 334, 1. (d) Lucassen, A. C. B.; Karton, A.; Leitus, G.; Shimon, L. J. W.; Martin, J. M. L.; van der Boom, M. E. Cryst. Growth Des. 2007, 7, 386. (e) Laurence, C.; QueignecCabanetos, M.; Dziembowska, T.; Queignec, R.; Wojtkowiak, B. J. Am. Chem. Soc. 1981, 103, 2567. (f) Laurence, C.; QueignecCabanetos, M.; Wojtkowiak, B. J. Chem. Soc., Perkin Trans. II 1982, 1605. (g) Lu, Y.-X.; Zou, J.-W.; Wang, Y.-H.; Jiang, Y.-J.; Yu, Q.-S. J. Phys. Chem. A 2007, 111, 10781. (h) Lu, Y.-X.; Zou, J.-W.; 214



Article

(17) Lapadula, G.; Judaš, N.; Frišcǐ ć, T.; Jones, W. Chem.Eur. J. 2010, 16, 7400. (18) (a) Imakubo, T.; Tajima, N.; Tamura, M.; Kato, R.; Nishio, Y; Kajita, K. J. Mater. Chem. 2002, 12, 159. (b) Ueda, K.; Sugimoto, T.; Faulmann, C.; Cassoux, P. Eur. J. Inorg. Chem. 2003, 2333. (c) Ouahab, L.; Setifi, F.; Golhen, S.; Imakubo, T.; Lescouëzec, R.; ́ Lloret, F.; Julve, M.; Swietlik, R. C. R. Chim. 2005, 8, 1286. (d) Imakubo, T.; Shrahata, T.; Kibune, M.; Yoshino, H. Eur. J. Inorg. Chem. 2007, 4727. (19) Bignozzi, C. A.; Chiorboli, C.; Indelli, M. T.; Rampi Scandola, M. A.; Varani, G.; Scandola, F. J. Am. Chem. Soc. 1986, 108, 7872. (20) Loiseau, F.; Marzanni, G.; Quici, S.; Indelli, M. T.; Campagna, S. Chem. Commun. 2003, 286. (21) Evju, J. K.; Mann, K. R. Chem. Mater. 1999, 11, 1425. (22) Simpson, N. R. M.; Ward, M. D.; Morales, A. F.; Ventura, B.; Barigelletti, F. J. Chem. Soc., Dalton Trans. 2002, 2445. (23) Argazzi, E.; Bignozzi, C. A.; Yang, M.; Hasselmann, G. M.; Meyer, G. J. Nano Lett. 2002, 2, 625. (24) (a) Ferlay, S.; Félix, O.; Hosseini, m. W.; Planeix, J.-M.; Kyritsakas, M. Chem. Commun. 2002, 702. (b) Ferlay, S.; Holokovsky, R.; Hosseini, M. W.; Planeix, J.-M.; Kyritsakas, M. Chem. Commun. 2003, 1224. (c) Ferlay, S.; Bulach, F.; Félix, O.; Hosseini, M. W.; Planeix, J.-M.; Kyritsakas, M. CrystEngComm 2002, 4, 447. (d) Crawford, P. C.; Gillon, A. L.; Green, J.; Orpen, A. G.; Podesta, T. J.; Pritchard, S. V. CrystEngComm 2004, 6, 419. (25) Derossi, S.; Brammer, L.; Hunter, C. A.; Ward, M. D. Inorg. Chem. 2009, 48, 1666. (26) Winkler, M.; Cakir, B.; Sander, W. J. Am. Chem. Soc. 2004, 126, 6135. (27) (a) Dawson, A.; Allan, D. R.; Parsons, S.; Ruf, M. J. Appl. Crystallogr. 2004, 37, 410. (b) The program has recently been modified to include the frame format transformation capability. (28) APEX2, v. 2.1-0; Bruker AXS: Madison, Wisconsin, USA. (29) (a) Sheldrick, G. M. SADABS, Empirical Absorption Correction Program; University of Göttingen: Germany; based upon the method of Blessing.29b (b) Blessing, R. H. Acta Crystallogr. 1995, A51, 33. (30) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112. (31) Sheldrick, G. M. CELL_NOW; University of Göttingen: Göttingen. (32) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339. (33) (a) RXN = d(X···N)/(rX + rN), where rX and rN are the van der Waals radii33b of the halogen atom, X, and nitrogen, respectively, following the definition of Lommerse et al.33c (b) Bondi, A. J. Phys. Chem. 1964, 68, 441. (c) Lommerse, J. P. M; Stone, A. J.; Taylor, R.; Allen, F. H. J. Am. Chem. Soc. 1996, 118, 3108. (34) The crystal structure of 3 was determined from a twinned crystal (see Experimental Section) and could only be modeled by using data only from the major component (75%), which is itself a racemic twin. This may introduce small systematic errors that make detailed comparison of intermolecular interaction geometries between structures less reliable for 3. (35) It is important to note that all crystal structures were determined at 100 K. The only exception to this trend in unit cell dimensions across all 10 unsolvated compounds that are compared is the increase in the a dimension from compound 11 to compound 12. (36) (a) Increased effective nuclear charge felt by the t2g orbitals across the series Cr, Fe, Co will reduce the t2g orbital energy and render π-back donation less effective. However, this should be more than compensated for by the increased electron count in the t2g orbitals. It should be noted that there is not a simple relationship between metal-cyanide π-back bonding and CN bond strength (and stretching frequency) as is explained by Jones.36b (b) Jones, L. H. Inorg. Chem. 1963, 2, 777. (37) In 10·4H2O, one CN···X angle is 139.1(5)°. The cyanide ligand involved also accepts another C−Br···N halogen bond and an O−H···N hydrogen bond. (38) A similar range of geometries has been observed for C−I··· NC halogen bonds in a series of adducts of tetraalkylammonium

Wang, Y.-H.; Yu, Q.-S. J. Mol. Struct.: THEOCHEM 2006, 767, 139. (i) Rimmer, E. L.; Bailey, R. D.; Hanks, T. W.; Pennington, W. T. Chem.Eur. J. 2000, 6, 4071. (j) Padgett, C. W.; Walsh, R. D.; Drake, G. W.; Hanks, T. W.; Pennington, W. T. Cryst. Growth Des. 2005, 5, 745. (k) Pennington, W. T.; Hanks, T. W.; Arman, H. D. Struct. Bonding (Berlin) 2008, 126, 65. (l) Saha, B. K.; Nangia, A.; Jaskólski, M. CrystEngComm 2005, 7, 355. (6) (a) Corradi, E.; Meille, S. V.; Messina, M. T.; Metrangolo, P.; Resnati, G. Angew. Chem., Int. Ed. 2000, 39, 1782. (b) Metrangolo, P.; Pilati, T.; Resnati, G.; Stevenazzi, A. Chem. Commun. 2004, 1492. (c) Caronna, T.; Liantonio, R.; Lobgothetis, T. A.; Metrangolo, P.; Pilati, T.; Resnati, G. J. Am. Chem. Soc. 2004, 126, 4500. (d) Mele, A.; Metrangolo, P.; Neukirch, H.; Pilati, T.; Resnati, G. J. Am. Chem. Soc. 2005, 127, 14972. (7) (a) Sun, A. W.; Lauher, J. W.; Goroff, N. S. Science 2006, 312, 5776. (b) Shirman, T.; Arad, T.; van der Boom, M. E. Angew. Chem., Int. Ed. 2010, 49, 926. (c) Serpell, C. J.; Kilah, N. L.; Costa, P. J.; Felix, V.; Beer, P. D. Angew. Chem., Int. Ed. 2010, 49, 5322. (d) Kilah, N. L.; Wise, M. D.; Serpell, C. J.; Thompson, A. L.; White, N. G.; Christensen, K. E.; Beer, P. D. J. Am. Chem. Soc. 2010, 132, 11893. (e) Metrangolo, P.; Carcenac, Y.; Lahtinen, M.; Pilati, T.; Rissanen, K.; Vij, A.; Resnati, G. Science 2009, 323, 1461. (8) (a) Nguyen, H. L.; Horton, P. N.; Hursthouse, M. B.; Legon, A. C.; Bruce, D. W. J. Am. Chem. Soc. 2004, 126, 16. (b) Präsang, C.; Whitwood, A. C.; Bruce, D. W. Chem. Commun. 2008, 2137. (9) (a) Fourmigué, M.; Batail, P. Chem. Rev. 2004, 104, 5379. (b) Imakubo, T.; Sawa, H.; Kato, R. J. Chem. Soc., Chem. Commun. 1995, 1667. (c) Yamamoto, H. M.; Kosaka, Y.; Maeda, R.; Yamaura, J.; Nakao, A.; Nakamura, T.; Kato, R. ACS Nano 2008, 2, 143. (10) (a) Auffinger, P.; Hays, F. A.; Westhof, E.; Ho, P. S. Proc. Natl. Acad. Sci. U. S. A. 2004, 101, 16789. (b) Howard, E.; Sanishvili, R.; Cachau, R. E.; Mitschler, B.; Bart, P.; Lamour, V.; Van Zandt, M.; Sibley, E.; Bon, C.; Moras, D.; Schneider, T. R.; Joachimiak, A.; Podjarny, A. Proteins Struct. Funct. Genet. 2004, 55, 792. (11) (a) Zordan, F.; Brammer, L. J. Am. Chem. Soc. 2005, 127, 5979. (b) Mínguez Espallargas, G.; Brammer, L.; Sherwood, P. Angew. Chem., Int. Ed. 2006, 45, 435. (12) (a) Brammer, L.; Mínguez Espallargas, G.; Adams, H. CrystEngComm 2003, 5, 343. (b) Zordan, F.; Brammer, L. Cryst. Growth Des. 2006, 6, 1374. (c) Zordan, F.; Mínguez Espallargas, G.; Brammer, L. CrystEngComm 2006, 8, 425. (d) Libri, S.; Jasim, N. A.; Perutz, R. N.; Brammer, L. J. Am. Chem. Soc. 2008, 130, 7842. (e) Mínguez Espallargas, G.; Brammer, L; Allan, D. R.; Pulham, C. R.; Robertson, N.; Warren, J. E. J. Am. Chem. Soc. 2008, 130, 9058. (f) Brammer, L.; Zordan, F.; Mínguez Espallargas, G.; Purver, S. L.; Arroyo Marín, L.; Adams, H. Trans. Am. Crystallogr. Assoc. 2004, 39, 114. (g) Zordan, F.; Brammer, L. Acta Crystallogr. 2004, B60, 512. (h) Zordan, F.; Purver, S. L.; Adams, H.; Brammer, L. CrystEngComm 2005, 7, 350. (13) (a) Willett, R. D.; Awwadi, F.; Butcher, R.; Haddad, S.; Twamley, B. Cryst. Growth Des. 2003, 3, 301. (b) Awwadi, F. F.; Willett, R. D.; Haddad, S. F.; Twamley, B. Cryst. Growth Des. 2006, 6, 1833. (c) Awwadi, F. F.; Willett, R. D.; Twamley, B. Cryst. Growth Des. 2007, 7, 624. (d) Awwadi, F.; Haddad, S. F.; Willett, R. D.; Twamley, B. Cryst. Growth Des. 2010, 10, 158. (14) (a) Brammer, L.; Bruton, E. A.; Sherwood, P. Cryst. Growth Des. 2001, 1, 277. (b) Aullón, G.; Bellamy, D.; Brammer, L.; Bruton, E. A.; Orpen, A. G. Chem. Commun. 1998, 653. (c) Brammer, L.; Bruton, E. A.; Sherwood, P. New J. Chem. 1999, 23, 965. (15) (a) Brammer, L.; Swearingen, J. K.; Bruton, E. A.; Sherwood, P. Proc. Natl. Acad. Sci., U. S. A. 2002, 99, 4956. (b) Mareque Rivas, J. C.; Brammer, L. Inorg. Chem. 1998, 37, 4756. (16) (a) Lewis, G. R.; Orpen, A. G. Chem. Commun. 1998, 1873. (b) Gillon, A. L.; Lewis, G. R.; Orpen, A. G.; Rotter, S.; Starbuck, J.; Wang, X.-M.; Rodríguez-Martín, Y.; Ruiz-Pérez, C. J. Chem. Soc., Dalton Trans. 2000, 3897. (c) Angeloni, A.; Orpen, A. G. Chem. Commun. 2001, 343. (d) Dolling, B.; Gillon, A. L.; Orpen, A. G.; Starbuck, J.; Wang, X.-M. Chem. Commun. 2001, 567. 215



Article

thiocyanate salts with fluoroiodocarbon halogen bond donors. Cauliez, P.; Polo., V.; Roisnel, T.; Llusar, R.; Fourmigué, M. CrystEngComm 2010, 12, 558. (39) The charge per cyanide ligand is the same in the present hexacyanometallates and the previously reported tetracyanoruthenates.25 (40) (a) Morimoto, K.; Inabe, T. Mol. Cryst. Liq. Cryst. Sci. Technol., Sec. A. 1996, 284, 291. (b) Yamashita, Y.; Tomura, M.; Tanaka, S.; Imaeda, K. Synth. Met. 1999, 102, 1730. (c) Pan, F.; Wang, Z.-M.; Gao, S. Inorg. Chem. 2007, 46, 10221. (d) Kang, L.-C.; Chen, X.; Wang, C.-F.; Zhou, X.-H.; Zuo, J.-L.; You, X.-Z. Inorg. Chim. Acta 2009, 362, 5195. (e) Kim, J. I.; Kwak, H. Y.; Yoon, J. H.; Ryu, D. W.; Yoo, I. Y.; Yang, N.; Cho, B. K.; Park, J.-G.; Lee, H.; Hong, C. S. Inorg. Chem. 2009, 48, 2956. (f) Ababei, R.; Li, Y.G-.; Roubeau, O.; Kalisz, M.; Brefuel, N.; Coulon, C.; Harte, E.; Liu, X.; Mathoniere, C.; Clerac, R. New. J. Chem. 2009, 33, 1237. (g) Katz, M. J.; Leznoff, D. B. J. Am. Chem. Soc. 2009, 131, 18435. (41) (3-XpyMe)3[M(CN)6] was characterized in unsolvated form as 3 and solvated form as 3·2MeCN.

216


Cyanometallates as Halogen Bond Acceptors - Crystal Growth

Recommend Documents