Tris(Pyridinium)Triazine in Crystal Synthesis of 3-Fold Symmetric

Tris(Pyridinium)Triazine in Crystal Synthesis of 3-Fold Symmetric Structures Thomas J. Podesta and A. Guy Orpen* School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K.

CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 2 681-693

Received July 6, 2004

W This paper contains enhanced objects available on the Internet at http://pubs.acs.org/crystal. ABSTRACT: A series of perchlorometalate salts of the [1,3,5-tris(R)-2,4,6-triazine]3+ trications, where R ) 4-, 3-, or 2-pyridinium, have been prepared and structurally characterized. The supramolecular motifs in these salts show striking similarities despite differences in the local position of the pyridinium NH group, the metal atom used, and the incorporation of water molecules in the structure. A supramolecular motif in which the near-planar cations are surrounded by an octahedral array of six octahedral trianions is observed in the majority of the new salts. The crystal structures of [1,3,5-tris(4-pyridinium)-2,4,6-triazine][SbCl6] (4), [1,3,5-tris(4-pyridinium)-2,4,6-triazine][BiCl6] (5), [1,3,5-tris(3-pyridinium)-2,4,6-triazine][SbCl6] (8), [1,3,5-tris(3-pyridinium)-2,4,6-triazine][BiCl6] (9), and [1,3,5tris(3-pyridinium)-2,4,6-triazine][FeCl6] (10) are essentially isostructural; [1,3,5-tris(4-pyridinium)-2,4,6-triazine]2[FeCl6][FeCl4]3 (6), [1,3,5-tris(2-pyridinium)-2,4,6-triazine][SbCl6]‚3H2O (11), and [1,3,5-tris(2-pyridinium)-2,4,6triazine][BiCl6]‚3H2O (12) show related supramolecular structural motifs. The crystal structures of all of 4, 5, 8, 9, 10, and 12 are of R3c or R3 h c symmetry and have similar cell dimensions (a ) b ) 14.6-15.2 Å, c ) 18.5-19.2 Å) reflecting the planarity and 3-fold symmetry of the cations. The structures appear to be stabilized by complementary Cl‚‚‚HN, Cl‚‚‚HO, Cl‚‚‚HC, and NH‚‚‚O hydrogen bonding, shape, and electrostatic interactions and unanticipated triazine C‚‚‚Cl interactions. Introduction We have developed a modular approach to crystal synthesis of salts of complex anions based on molecular tectonics in which the building blocks (tectons) are molecular species (typically anionic metal complexes and organic cations).1-6 Through the exploitation of the MCl2‚‚‚HN supramolecular synthon (A), we have syn-

to formation of the analogous synthon (D), and crystals with structures related to those of the [PtCl4]2- salts may be synthesized.4 To explore a wider range of organic cations and so generate an enhanced diversity of structure types, we have sought to prepare and characterize a range of metal chloride salts of triply protonated 1,3,5-tris(pyridyl)-2,4,6-triazines 1-3. They offer the possibility

thesized a range of charge-assisted hydrogen-bonded structures based on [PtCl4]2- (B) and related anionic tectons (including [PtCl6]2-, [FeCl5]2-, and [SbCl5]2-) as hydrogen bond acceptors, crystallized with a range of organic pyridinium and bipyridinium tectons.1-3,6 The robustness of A and related synthons and the possibility of synthesizing hydrogen-bonded networks with various degrees of complexity based upon the hydrogen bond donor ability of the cation used have been demonstrated. Using the anionic tecton [Ni(dithioxalate)2]2- (C) leads * Corresponding author. Mailing address: School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K. Tel: +44 (0)1179288158.Fax: +44(0)1179290376.E-mail: [email protected].

of incorporating 3-fold symmetry and three-connected nodes based on exotopic (divergent) triazine tectons into the hydrogen-bond network (see Chart 1). This in turn

10.1021/cg049783g CCC: $30.25 © 2005 American Chemical Society Published on Web 10/01/2004

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Chart 1. Schematic of (a) Branched, 3-fold-Symmetric Triazine-Based Pyridinium and (b) Linear Bipyridine-Based Tectons

Podesta and Orpen Scheme 1. Synthesis of the Tris(pyridyl)triazines 1 (py ) 4-pyridyl) and 2 (py ) 3-pyridyl)

of a mixed [MnCl5]2- chloride salt of triprotonated 3 as a hydrate has been published.24 We report here the preparation and characterization of crystalline salts 4-13 of triply protonated 1-3 with perchlorometalate anions of iron(III), antimony(III), and bismuth(III) to explore the viability of these tectons and the supramolecular synthons they form in crystal synthesis. Experimental Section

affords the likelihood of higher dimensionality nets than are formed by analogous bis(pyridinium) systems (e.g., 4,4′-bipyridinium), which do not contain a branched covalent cation framework. The extended and potentially planar tetra-aryl ring system of the triazines offers a possible further element of control over the crystal structures formed through its highly anisotropic shape. The availability of analogous 2-, 3-, and 4-isomers of the 1,3,5-tris(pyridyl)-2,4,6-triazine also offers the opportunity to explore the consequences of the different NH hydrogen bond donor location in the isomeric cations [1H3]3+, [2H3]3+, and [3H3]3+ on the structures of their salts.6 Tris(pyridyl)triazines have varied applications in supramolecular and coordination chemistry. Triazine 1 has been used for coordination polymer chemistry, in the template-assisted preparation of metal oxide networks, and in supramolecular self-assembly studies.7-12 Sanders and co-workers have reported the use of 1 for the construction of multiporphyrin arrays, capping the pyridyl units with ruthenium porphyrin units, to study the photophysical properties of the arrays produced.13 A doubly protonated derivative of 1 has been previously reported in a crystal engineering study of its hydrated [HgCl4]2-salt.14 Triazine 2 is the least studied of 1-3 and has been used in synthesis of molecular cages to encapsulate organic species.15 The synthesis of molecular cages using solventless reactions has also been reported using 2.16 No protonated derivatives of 2 seem to have been reported. Triazine 3 has been exploited in coordination chemistry. Typically two of the pyridyl nitrogen atoms and the triazine nitrogen between them chelate a metal in a merohedral fashion, as observed for terpyridine ligands. Coordination complexes of 3, in which it bridges metal centers through two or more of the pyridyl groups, and the use of 3 in preparation of coordination polymers have been reported.17-23 Protonated forms of tributyl derivatives of 3 have been reported, and the structure

The tris(pyridyl)triazines 1 and 2 were prepared as previously reported (Scheme 1).25 The compounds were isolated as their trihydrochloride salts via recrystallization from aqueous hydrochloric acid. Triazine 3 was purchased from Aldrich and used without further purification. All metal chlorides were purchased from Aldrich or Johnson Matthey and used without further purification. Elemental analyses were performed by the School of Chemistry Microanalytical Service, University of Bristol. X-ray Diffraction. Diffraction measurements of 4, 5, 6, 7, 8, and 9 were made at -100 °C on a Bruker-AXS SMART three-circle CCD diffractometer using graphite monochromated Mo KR radiation (λ ) 0.710 73 Å). Diffraction measurements of 10 and 13 were made at -173 °C and those of 11 at room temperature on a Bruker-AXS APEX three-circle CCD diffractometer using graphite monochromated Mo KR radiation (λ ) 0.710 73 Å). Unit cell dimensions were determined from reflections taken from three sets of 10 frames (at 0.3° steps in ω), each at 10 s exposure. Data frames were referenced to a set of 10 dark frame readings each taken at n s exposures without X-rays, where n s is the time for each exposure during data collection. For crystals of monoclinic or higher crystal symmetry, a hemisphere of reciprocal space was scanned by 0.3ω steps at φ ) 0°, 88°, and 180° with the area detector center held at 2θ ) -27°. For triclinic crystals, a full sphere of reciprocal space was scanned. In all experiments, each exposure was n s (typically, 10 e n e 40 s). The reflections were integrated using the SAINT program.26 Absorption, Lorentz, and polarization corrections were applied. The structures were solved by direct methods and refined using fullmatrix least-squares against F2 using SHELXTL.27 All nonhydrogen atoms were assigned anisotropic displacement parameters and refined without positional constraints. Hydrogen atoms were included in idealized positions with isotropic displacement parameters constrained to 1.5 times the Uequiv of their attached carbon atoms for methyl hydrogens and 1.2 times the Uequiv of their attached carbon atoms for all others. Diffraction measurements for 12 were made at -173 °C on a Bruker-AXS Proteum diffractometer equipped with a CCD area detector using Cu KR radiation (λ ) 1.541 78 Å) The X-ray beam was collimated and focused. Data were collected as a series of narrow frames covering 0.3° in ω or φ and integrated using the SAINT program. The structure was solved as for SMART and APEX data. Powder X-ray diffraction measurements were performed using Cu KR radiation (λ ) 1.5418 Å) on a Bruker-AXS D8-Advance diffractometer equipped with a secondary monochromator. The data were collected in the range 5° < 2θ < 60° in θ-θ mode with a step time of n s (5 < n < 10 s) and step width of 0.02°. Powder diffraction patterns of bulk samples of 4, 5, 8, 9, 10, 11, and 12 were consistent with them having the same structure as the single-crystal samples analyzed.

Tris(Pyridinium)Triazine in Crystal Synthesis [1,3,5-Tris(4-pyridinium)-2,4,6-triazine][SbCl6], 4. To a solution of antimony(III) trichloride (0.409 g, 1.793 mmol) in concentrated hydrochloric acid (15 mL) was added, dropwise with stirring, a solution of 1 (0.373 g, 1.20 mmol) in concentrated hydrochloric acid (15 mL). Immediately upon addition, bright orange crystals of the product formed in the flask. The mixture was stirred for 20 min and then filtered. The product was washed with water (10 mL) and ethanol (10 mL) and dried at the pump (0.68 g, 87.6%, 1.05 mmol). Microanalytical data (%). Found: C, 32.99; H, 2.15; N, 12.68. Calcd: C, 33.27; H, 2.33; N, 12.93. [1,3,5-Tris(4-pyridinium)-2,4,6-triazine][BiCl6], 5. To a solution of bismuth(III) trichloride (0.311 g, 0.986 mmol) in concentrated hydrochloric acid (10 mL) was added, dropwise with stirring, a solution of 1‚3HCl (0.416 g, 0.984 mmol) in concentrated hydrochloric acid (10 mL). Immediately upon addition, a pale yellow precipitate was observed. The mixture was stirred for 1 h, and the precipitate was filtered off, washed with water (5 mL) and ethanol (5 mL), and dried at the pump (0.601 g, 82.9%, 0.815 mmol). Microanalytical data (%). Found: C, 29.24; H, 2.33; N, 10.78. Calcd: C, 29.33; H, 2.05; N, 11.40. Single crystals of the product were grown by slow diffusion in an H-tube apparatus. [1,3,5-Tris(4-pyridinium)-2,4,6-triazine] 2 [FeCl 6 ][FeCl4]3, 6. To a solution of iron(III) trichloride (0.235 g, 1.45 mmol) in concentrated hydrochloric acid (5 mL) was added, dropwise with stirring, a solution of 1‚3HCl (0.305 g, 0.723 mmol) in concentrated hydrochloric acid (5 mL). Immediately upon addition, a yellow precipitate was observed. The suspension was filtered, and the solid was washed with ice-cold water (2 mL) and ice-cold ethanol (2 mL) and dried at the pump (0.305 g, 0.723 mmol, 50.5%). Microanalytical data (%). Found: C, 29.21; H, 2.11; N, 11.46. Calcd: C, 28.98; H, 2.03; N, 11.26. Single crystals of the product were grown by slow diffusion in an H-tube apparatus. [1,3,5-Tris(4-pyridinium)-2,4,6-triazine][FeCl3(OH2)3][Cl]3[H2O]3, 7. To a solution of iron(III) trichloride (0.122 g, 0.752 mmol) in concentrated hydrochloric acid (10 mL) was added, dropwise with stirring, a solution of 1‚3HCl (0.320 g, 7.59 mmol) in concentrated hydrochloric acid (5 mL). Immediately upon addition, a yellow precipitate was observed. The suspension was heated to redissolve and reduce the volume (10 mL) and then allowed to cool to room temperature. When the solution had cooled, yellow crystals of the product were formed. The mixture was filtered, and the crystals were washed with ice-cold water (2 mL) and ice-cold ethanol (2 mL) and dried at the pump (0.382 g, 0.552 mmol, 73.4%). Microanalytical data (%). Found: C, 31.55; H, 3.61; N, 12.02. Calcd: C, 31.10; H, 3.91; N, 12.06. [1,3,5-Tris(3-pyridinium)-2,4,6-triazine][SbCl6], 8. To a solution of antimony(III) trichloride (0.159 g, 0.697 mmol) in concentrated hydrochloric acid (5 mL) was added, dropwise with stirring, a solution of 2‚3HCl (0.295 g, 0.700 mmol) in concentrated hydrochloric acid (5 mL). Upon addition, an orange precipitate was observed to appear. The mixture was stirred for 5 min and then left to stand. Orange crystals of the product were observed to grow over a few hours. The mixture was filtered, and the precipitate and crystals were washed with cold concentrated hydrochloric acid (5 mL) and ice-cold ethanol (5 mL) and dried at the pump (0.30 g, 0.461 mmol, 66%). Microanalytical data (%). Found: C, 33.28; H, 2.36; N, 12.34. Calcd: C, 33.27; H, 2.33; N, 12.93. [1,3,5-Tris(3-pyridinium)-2,4,6-triazine][BiCl6], 9. To a solution of bismuth(III) chloride (0.303 g, 0.961 mmol) in concentrated hydrochloric acid (10 mL) was added, dropwise with stirring, a solution of 2‚3HCl (0.406 g, 0.963 mmol) in concentrated hydrochloric acid (10 mL). Upon addition, a colorless precipitate was observed. The mixture was stirred for 5 min and left to stand overnight, whereupon colorless crystals were observed to form on the sides of the reaction vessel. The precipitate and crystals were isolated by filtration, washed with water (5 mL) and ethanol (5 mL) and dried at the pump (0.553 g, 0.750 mmol, 78.1%). Microanalytical data (%). Found: C, 29.03; H, 1.70; N, 11.06. Calcd: C, 29.33; H, 2.05; N, 11.40.

Crystal Growth & Design, Vol. 5, No. 2, 2005 683 [1,3,5-Tris(3-pyridinium)-2,4,6-triazine][FeCl6], 10. To a solution of iron(III) chloride (0.125 g, 0.771 mmol) in concentrated hydrochloric acid (5 mL) was added, dropwise with stirring, a solution of 2‚3HCl (0.325 g, 0.771 mmol) in concentrated hydrochloric acid (10 mL). Upon addition, an oily precipitate was observed. The orange mixture was heated to redissolve this precipitate and reduce the volume (5 mL). When the mixture had cooled, orange prisms of the product crystallized, which were isolated by filtration, washed with ice-cold water (2 mL) and ethanol (2 mL), and dried at the pump (0.172 g, 0.294 mmol, 38.2%). Microanalytical data (%). Found: C, 37.76; H, 2.39; N, 13.99. Calcd: C, 37.03; H, 2.59; N, 14.39. [1,3,5-Tris(2-pyridinium)-2,4,6-triazine][SbCl 6 ][H2O]3, 11. To a solution of antimony(III) chloride (0.328 g, 1.44 mmol) in concentrated hydrochloric acid (10 mL) was added, dropwise with stirring, a solution of 3 (1.44 mmol) in concentrated hydrochloric acid (10 mL). After addition was complete, the resulting pale yellow solution was heated to reduce the volume (12 mL) and left to cool to room temperature. When the solution had cooled the product crystallized as red needles, which were filtered off, washed with ice-cold water (5 mL) and ethanol (5 mL), and dried at the pump (0.864 g, 1.23 mmol, 85.2%). Microanalytical data (%). Found: C, 31.14; H, 2.80; N, 11.74. Calcd: C, 30.72; H, 3.01; N, 11.94. [1,3,5-Tris(2-pyridinium)-2,4,6-triazine][BiCl6][H2O]3, 12. To a solution of bismuth(III) chloride (0.234 g, 0.742 mmol) in concentrated hydrochloric acid (10 mL) was added, dropwise with stirring, a solution of 3 (0.233 g, 0.746 mmol) in concentrated hydrochloric acid (10 mL). Upon addition, a pale yellow precipitate was observed. The mixture was stirred for 1 h and left to stand overnight. The precipitate was isolated by filtration, washed with water (5 mL) and ethanol (5 mL), and dried at the pump (0.445 g, 0.563 mmol, 75.8%). Upon closer examination, the precipitate was found to be small crystals of 12. Microanalytical data (%). Found: C, 27.51; H, 2.86; N, 10.90. Calcd: C, 27.33; H, 2.68; N, 10.62. [1,3,5-Tris(2-pyridinium)-2,4,6-triazine][FeCl4][Cl]2, 13. To a solution of iron(III) chloride (0.112 g, 0.69 mmol) in concentrated hydrochloric acid (10 mL) was added, dropwise with stirring, a solution of 3 (0.216 g, 0.691 mmol) in concentrated hydrochloric acid (15 mL). Upon addition, a pale yellow precipitate was observed. The mixture was heated to redissolve, and the volume was reduced (10 mL). When the mixture had cooled, pale yellow plates of the product crystallized. The crystals were isolated by filtration, washed with icecold ethanol, and dried at the pump (0.226 g, 0.387 mmol, 56.1%). Microanalytical data (%). Found: C, 36.88; H, 2.67; N, 14.50. Calcd: C, 37.03; H, 2.59; N, 14.39.

Results Reaction of SbCl3 with 1‚3HCl led immediately to precipitation of orange needles of 4 in high yield. The salt crystallized in the rhombohedral space group R3c (see Table 1 for crystal data) and has the formula [1H3][SbCl6]. The cations are of expected dimensions and close to planar (see Table 2). The [SbCl6]3- anions in the structure have exact (crystallographic) C3 (and approximate C3v) symmetry and two significantly different Sb-Cl bond lengths (2.5156(11) and 2.8645(12) Å) in a fac arrangement. The Cl-Sb-Cl angles are distorted correspondingly; the angle between the longer Sb-Cl bonds is 98.36(4)°, that between the long and short bonds is 84.36(3)°, while that between the short bonds is 89.89(4)°. All trianions are therefore deformed from octahedral symmetry, essentially by a translation of the Sb atoms parallel to the crystallographic c axis. Together with the polarity of the space group, this distortion implies that the crystal has a permanent dipole (pyroelectricity). In fact, the crystal studied is twinned with twin components indistinguishable from

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Table 1. Crystallographic Data for Salts of [1H3]3+ chemical formula crystal system space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 T, K Z µ, mm-1 reflns collected independent reflns Rint final R1 [I > 2σ(I)]

4

5

6

7

C18H15N6SbCl6 rhombohedral R3c 14.6255(15) 14.6255(15) 18.848(3) 90 90 120 3491.6(7) 173(2) 6 1.894 7110 1742 0.0450 0.0380

C18H15N6BiCl6 rhombohedral R3 hc 14.5986(11) 14.5986(11) 19.062(2) 90 90 120 3518.3(5) 173(2) 6 8.220 7144 904 0.0391 0.0198

C36H30N12Fe4Cl18 monoclinic P21/c 13.8577(19) 15.899(2) 25.332(3) 90 95.302(2) 90 5557.2(13) 173(2) 8 1.931 35 621 12771 0.0565 0.0391

C18H27N6O6FeCl6 triclinic P1 h 7.5722(10) 14.333 20(19) 14.7870(19) 63.068(2) 86.965(2) 87.724(2) 1428.5(3) 173(2) 2 1.133 15 022 6472 0.0268 0.0335

Table 2. Inter- and Intramolecular Geometric Data for Salts of [1H3]3+ salt

interaction

A‚‚‚H, Å

D‚‚‚A, Å

∠DHA, deg

∠MCl‚‚‚H, deg

3.02 2.43 2.67

3.57 3.14 3.32

121.9 138.4 129.4

119.4 112.9 106.4

4

MCl‚‚‚HN

5

MCl‚‚‚HN

6

MCl‚‚‚HN

2.25 2.25 2.21 2.24 2.30 2.34

3.09 3.11 3.06 3.11 3.14 3.18

160.4 165.3 160.8 167.0 161.4 159.9

114.6 100.2 112.1 97.5 92.9 90.6

7

MCl‚‚‚HN MCl‚‚‚HO Cl-‚‚‚H

2.89 2.37 2.37 2.14 1.78 2.22 2.29 2.33 1.76 1.91 2.05 2.45 2.32 2.22 2.35 2.36

3.45 3.17 3.11 2.99 2.63 3.02 3.07 3.08 2.04 2.71 2.76 3.19 3.18 3.07 3.08 3.14

123.0 167.1 141.3 163.4 163.4 163.7 165.8 172.9 167.3 171.6 150.9 164.9 159.8 174.0 174.4 163.5

119.6 103.0

NH‚‚‚O MOH2‚‚‚ClMOH2‚‚‚OH2 OH2‚‚‚Cl-

0.5 (Flack parameter 0.56(3)), showing that it is not macroscopically polar but has almost exactly equal amounts (presumably domains) of each polarity with respect to the c axis. Alternative refinement models were evaluated in the centrosymmetric space group R3 h c, all of which resulted a poorer outcomes with higher residuals (R1 > 0.08) and nonpositive definite atoms in the cation. The crystal structure of 4 contains a 3-dimensional network of Cl‚‚‚HN hydrogen bonds (see Table 2) in which layers of cations, parallel to the crystallographic ab plane, are linked by anions (see Figure 1). Thus cation layers contain sets of three fac chloride ligands from a given anion so that the antimony atoms lie approximately midway between the cation layers (see Figure 1).

M-L, Å [MCl6]32.5156(11) 2.8645(12) 2.7073(7) [MCl6]32.3711(9) 2.3732(9) 2.3803(9) 2.3970(9) 2.4080(9) 2.4144(9)

M-Cl 2.3000(6) 2.3178(6) 2.3277(6)

[MCl4]2.1728(12) 2.1912(11) 2.1919(11) 2.1951(11) 2.1694(11) 2.1825(13) 2.1866(11) 2.1897(12) 2.1777(11) 2.1796(11) 2.2117(10) 2.2181(10) M-OH2 2.0595(14) 2.0682(14) 2.0814(15)

torsion angle, deg

C‚‚‚Cl, Å

2.72

3.35 3.37 3.41

0.28 4.60 5.75 6.06 4.60 10.49 3.22

0.62 16.63 8.56

Figure 1. The layer structure present in 4. W A 3D rotatable image in PDB format is available.

Each triazine trication is hydrogen-bonded to six [SbCl6]3- units in a octahedral array with antimony centers alternately above and below the plane of the triazine cations (see Figure 2). The array of anions formed has Sb‚‚‚Sb distances of 9.009 Å. The 4-pyridinium groups in 4 form asymmetric bifurcated Cl2‚‚‚HN interactions (lengths Cl‚‚‚H 2.43 and

Tris(Pyridinium)Triazine in Crystal Synthesis

Crystal Growth & Design, Vol. 5, No. 2, 2005 685

Figure 2. The pattern of NH‚‚‚Cl and CH‚‚‚Cl contacts around each [triazine3H]3+ unit in salt 4.

Figure 3. The NH‚‚‚Cl hydrogen-bonding pattern around each [SbCl6]3- trianion in 4.

W A 3D rotatable image in PDB format is available.

W A 3D rotatable image in PDB format is available.

3.02 Å, see Figure 2), a supramolecular synthon that we have previously noted in the structure of [4,4′bipyH2][PtCl6] and related salts.3 A further set of interion interactions of the form CH‚‚‚Cl2Sb is notable, in which the CH groups ortho to the NH groups interact with two chloride ligands on the same anion (Cl‚‚‚H 2.59-2.88 Å; see Figure 2). In combination, these interactions give rise to a synthon of form E, coupled

Scheme 2. Ion Network in 4 (and NaCl) Showing One Layer of Cations with Neighboring Layers of Anions

so that each pyridinium group links two anions with in a slightly distorted version of motif F with the asymmetric NH distances noted above. Each [SbCl6]3- trianion is hydrogen-bonded to a total of six triazine cations, three from the cation layers above and below the plane containing the Sb atoms (see Figures 1 and 3). The SbCl‚‚‚HN contacts are of two lengths (2.43 and 3.02 Å) as noted above. The shorter contacts are associated with the longer Sb-Cl bonds (2.8645(12) Å), and all three short Cl‚‚‚HN bonds are in the same cation plane (conversely the long, 3.02 Å, SbCl‚‚‚HN contacts are also in a single cation plane). The hydrogen-bond network is therefore composed of six connected ionic tectons. The network is of 41263 topology28,29 and of the R-polonium form (or NaCl if the alternation of charge on the nodes of the net is accounted for). The analogy with NaCl is emphasized by the cartoon shown in Scheme 2 in which the ion network is represented schematically. Note the NaCl structure (normally given as F-centered cubic with cell dimension a ) 5.632 Å) can be transformed in to an obverse rhombohedral cell (on hexagonal axes) of dimensions a

) 3.982, c ) 9.754 Å (i.e., c/a ratio of 2.404; cf. the cell in 4 for which the c/a ratio is 1.289). The much reduced c/a ratio in 4 corresponds to the large planar aspect of the triazine trications, which is parallel to the ab plane of the unit cell in 4. In addition to the Sb-Cl‚‚‚pyridinium hydrogen bonds within the cation layers, a further motif is present in which each [SbCl6]3- lies directly above and below the central C3N3 unit of a cation and vice versa (see Figures 1 and 4). The Sb‚‚‚Sb distances in this stack run parallel to the c axis and are of length c/2 () 9.424 Å). The SbCl bonds approximately eclipse the radial interaryl C-C bonds, and short Cl‚‚‚C contacts result of length 3.353.37 Å (cf. sum of van der Waals radii of C and Cl ) 3.45 Å, see Table 2). Similarly short Cl‚‚‚C contacts are present in the hydrated [HgCl4]2- salt of doubly protonated 1.12 Reaction of BiCl3 with 1‚3HCl led to immediate precipitation of 5 as a white powder of formula [1H3][BiCl6]. Single crystals were grown by slow mixing

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Figure 4. The stack motif present in 4. W A 3D rotatable image in PDB format is available.

methods. In contrast to its antimony analogue 4, 5 crystallizes in the space group R3 h c with the Bi atoms on sites of exact C3i and approximate D3d symmetry. In other respects, the structures of 4 and 5 are almost identical including the cell dimensions (see Tables 1 and 2). In concert with the higher symmetry present in 5, there is a single Bi-Cl distance (2.7073(7) Å). In addition, the structure is centrosymmetric, so the polarity effects noted for 4 above are absent in 5. In 5, motif F is symmetrical with both the NH‚‚‚Cl hydrogen-bond distances equal to 2.69 Å, close to the average of the two different distances present in 4. The Bi‚‚‚Bi distance in the stack in 5 is 9.531 Å, and that in the octahedral arrangement around each cation is 9.007 Å. The distance between the cation layers is approximately 3.18 Å. Reaction of 1 with FeCl3 in aqueous HCl solution leads to the formation of two different products. Upon mixing, salt 6, of formula [1H3]2[FeCl6][FeCl4]3, precipitates as a bright yellow powder. Single crystals of 6 were grown by slow mixing methods. Redissolution of 6 by heating the mixture of crystals and mother liquor, followed by crystallization by evaporation, leads to the isolation of orange crystals of mixed salt 7 of formula [1H3][FeCl3(OH2)3][Cl]3[H2O]3. Compound 6 crystallizes in space group P21/c with two crystallographically independent [1H3]3+ cations in the asymmetric unit. While the overall structure of 6 is different from that present in 4 and 5, recognizable motifs remain. In 6, each [FeCl6]3- unit is hydrogenbonded to six triazine cation units in a manner similar to that seen in 4 and 5. In 6 however, each [1H3]3+ is only hydrogen-bonded to three [FeCl6]3- units (see Figure 5a,b). Therefore the three-dimensional net structure of 4 and 5 is not completed, rather a double layer

Podesta and Orpen

(or bilayer) motif is formed in which the [FeCl6]3- anions link just two cation layers by NH‚‚‚Cl hydrogen bonds. The distance between the planes of the triazine units in the bilayer is about 3.38 Å. The [1H3]3+ cations are not as near-planar as those in 4 and 5 and have dihedral angles about the pyridyl-triazine carbon-carbon bonds of between 2.6° and 10.6°. Notably, all the NH‚‚‚Cl hydrogen bonds involve the [FeCl6]3- anions. The bilayers in 6 have formula {[1H3][FeCl6]}3+. The [FeCl4]- counteranions lie between the bilayers (see Figure 6) and do not form NH‚‚‚Cl hydrogen bonds but rather CH‚‚‚Cl interactions of lengths in the range 2.72-2.95 Å. They therefore fill the space between the bilayers, which are ca. 3.38 Å apart, with the iron atoms lying approximately midway between the cation layers and the chloride ligands of the [FeCl4]- ions lying close to the cation layers (see Figure 6). In 6, the shortest Fe‚‚‚Fe distance between [FeCl6]3units is 10.516 Å; there are other shorter distances between the [FeCl6]3- and the [FeCl4]- units, 6.89-7.85 Å. The [FeCl4]- units are more closely packed with Fe‚ ‚‚Fe distances in the range 5.149-5.814 Å. As in 4 and 5, there are short Cl‚‚‚HC contacts between the trianions and the CH groups of the cations ortho to the NH moieties of lengths in the range 2.65-2.79 Å. There are also Cl‚‚‚HC contacts between the [FeCl4]- anions and the cations of lengths in the range 2.69-2.95 Å. Complex salt 7 crystallizes in the space group P1 h and contains the neutral complex fac-[FeCl3(OH2)3] (see Figure 7), three chloride ions per [1H3]3+ cation, as well as water of solvation. These individual units are involved in hydrogen bonding, which links them into a complex three-dimensional net. The triazine cations are again arranged in parallel layers, linked by NH‚‚‚O and NH‚‚‚Cl hydrogen bonds to the solvate water molecules and chloride ions. These cation layers surround and are linked by chains of the [FeCl3(OH2)3] molecules, further water molecules, and chloride ions (see Figures S2 and S3, Supporting Information). The triazine units in 7 are slightly twisted from planarity with triazine-pyridyl dihedral angles in the range 0.8°-17.39°. The Fe(III) complex [FeCl3(OH2)3] has apparently only previously been structurally characterized in its meridional form in a complex salt [trienH2][FeCl3(OH2)3][Cl]2. 30 This compound was prepared by a method similar to 7, except that iron(II) chloride was used (rather than iron(III) chloride as in the present work). Reaction of 2‚3HCl with SbCl3 in concentrated HCl solution led to immediate precipitation of a mixture of orange powder and crystals of 8 suitable for X-ray diffraction study. Salt 8 crystallizes in space group R3 hc and has stoichiometry [2H3][SbCl6], identical to 4. The structure of 8 contains the same overall three-dimensional anion-linked layer motif as 4 and 5 and has very similar cell dimensions to those structures (see Tables 1 and 3). In contrast to 4, the anions in 8 have exact C3i (and approximate D3d) symmetry with Sb-Cl bonds all being of length 2.6552(4) Å. As in 4, each [SbCl6]3unit is hydrogen-bonded to six triazine cations and vice versa. The different position of the pyridinium NH+ group (now in the 3-site) relative to the triazine ring leads to some differences of detail in the NH‚‚‚Cl hydrogen-bond network. In 8, the NH group is hydrogenbonded to two chloride ligands on a single [SbCl6]3- unit



Figure 5. Panel a presents the bilayer motif in 6. Panel b presents the {[1H3]2[FeCl6]}3+ bilayer motif in 6 viewed parallel to the cation layers. W A 3D rotatable image of panel A in PDB format is available.

Figure 6. The layer structure of 6 showing the incorporation of [FeCl4]- units in the spaces between {[1H3][FeCl6]}3+ bilayers.

Figure 7. The neutral [FeCl3(OH2)3] moiety present in 7.

in a bifurcated fashion (i.e., occupying the same site as the ortho CH groups in 4). However in 8, the NH+ group is disordered across the two possible 3-positions on each pyridinium ring, giving the overall effect of hydrogen bonding to all six [SbCl6]3- units (see Figure 8). It is therefore more accurate to say that the hydrogen bonds

observed (lengths 2.464 and 2.940 Å) are spatially averaged NH‚‚‚C and CH‚‚‚Cl interactions, which collectively form a motif of form F (see Figure 8). In other respects, the structure of 8 is very similar to those of 4 and 5. Thus a stack of anions above cations with short Cl‚‚‚C contacts parallel to the crystallographic c axis is again formed with Sb‚‚‚Sb distances in the stack equaling 9.544 Å. The Sb‚‚‚Sb distances in the octahedral array shown in Figure 8 are 9.052 Å. The spacing between cation layers is 3.18 Å. Reaction of 2‚3HCl with BiCl3 in aqueous HCl solution leads to immediate precipitation of salt 9, [2H3][BiCl6] as a colorless powder. Single crystals were grown by slow-mixing methods. The salt 9 is isostructural with 8, having the same space group and essentially identical tecton arrangement and metrics. Salt 9 has Bi‚‚‚Bi distances in the stack motif of 9.614 Å and in the octahedral array perpendicular to the c axis of 9.072 Å. The layer spacing is 3.20 Å.

688


Podesta and Orpen

Figure 8. NH‚‚‚Cl and CH‚‚‚Cl hydrogen bonding from the disordered 1,3,5-tris(3-pyridinium)-2,4,6-triazine unit in 8, 9, and 10. Table 3. Crystallographic Data for Salts of [2H3]3+ 8 chemical formula crystal system space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 T, K Z µ, mm-1 reflns collected independent reflns Rint final R1 [I > 2σ(I)]

9

10

C18H15N6SbCl6 C18H15N6BiCl6 C18H15N6FeCl6 rhombohedral R3 hc 14.6781(6) 14.6781(6) 19.0874(10) 90 90 120 3561.4(3) 173(2) 6 1.857 11 688 920

rhombohedral R3 hc 14.7004(12) 14.7004(12) 19.228(2) 90 90 120 3598.5(6) 173(2) 6 8.037 3916 844

rhombohedral R3 hc 14.6022(9) 14.6022(9) 18.5768(16) 90 90 120 3430.3(4) 100(2) 6 1.308 3634 877

0.0310 0.0108

0.0300 0.0246

0.0238 0.0370

Reaction of 2‚3HCl with FeCl3 in aqueous HCl solution followed by evaporation gives orange crystals of [2H3][FeCl6], 10. In contrast to the corresponding reaction for 1, only one product (10), which is isostructural with both 8 and 9, having the same space group and essentially identical tecton positions and slightly smaller cell dimensions (see Table 3) as a consequence of the smaller metal-chloride bond lengths (see Table 4), was isolated. Salt 10 has Fe‚‚‚Fe distances in the stack of 9.288 Å and in the octahedral array perpendicular to the c axis of 8.981 Å. The spacing between cation layers is 3.10 Å.

Figure 9. CH‚‚‚Cl, CH‚‚‚O, and NH‚‚‚O interactions close to the cation plane in 11.

Reaction of 3 with SbCl3 in aqueous HCl solution followed by evaporation leads to the formation of the crystalline trihydrate salt [3H3][SbCl6][H2O]3, 11, as red needles in high yield. The salt crystallizes in the monoclinic space group P21/c with one trication in the asymmetric unit, as well as three molecules of water and one [SbCl6]3- unit. In contrast to the corresponding salts of 1 and 2, the pyridinium NH+ groups of 11 do not form NH‚‚‚Cl hydrogen bonds to the [SbCl6]3- unit. Instead, two of the NH+ groups form chelate NH‚‚‚O hydrogen bonds to a water molecule, while the third bonds to another. Some similarities between the motifs in 11 and those seen for 4, 5, 6, and 8-10 become clear. Each trication [3H3]3+ is surrounded by six [SbCl6]3- units and vice versa in a pattern similar to that in the (nonhydrate) salts 4, 5, and 8-10 with anions alternating above and below the plane of the cation (see Figure 9). Local CH ‚‚‚Cl interactions (distances 2.72-3.09 Å) are observed of form similar to the synthons E and F seen in previous examples but are here distorted due to the inclusion of water molecules, and a less symmetrical structure results. Although hydrogen atoms on the water molecules were not located, contacts between the oxygen atoms and adjacent anions and other water molecules imply the formation of a three-dimensional network with similarities to those previously identified (see Table 6 and Figure 10; indicated O‚‚‚Cl distances are in range 2.92-3.24 Å). As in the other structures, a stack motif is found with units of [SbCl6]3- above and below the plane of the

Table 4. Inter- and Intramolecular Geometric Data for Salts of [2H3]3+ salt

interaction

8

MCl‚‚‚HN

9 10

A‚‚‚H, Å

D‚‚‚A, Å

∠DHA, deg

∠MCl‚‚‚H, deg

M-L, Å

torsion angle, deg

C‚‚‚ClSb, Å

2.46 2.94 2.48 2.96 2.44 2.80

3.29 3.57 3.30 3.58 3.30 3.47

145.8 124.9 145.2 124.1 150.4 128.8

83.3 74.8 82.6 74.2 86.7 79.1

2.6552(4)

3.03

3.34

2.7223(7)

0.12

3.43

2.3979(6)

1.59

3.35



Figure 10. The stacking of layer units in 11, presumably linked through OH‚‚‚Cl hydrogen-bonding interactions. Table 5. Crystallographic Data for Salts of [3H3]3+ 11 chemical formula crystal system space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 T, K Z µ, mm-1 reflns collected independent reflns Rint final R1 [I > 2σ(I)]

12

13

C18H15N6O3SbCl6 C18H15N6O3BiCl6 C18H15N6FeCl6 monoclinic

rhombohedral

monoclinic

P21/c 9.5743(9) 15.4364(16) 17.8570(17) 90 96.185(2) 90 2623.8(4) 273(2) 4 1.695 11 504

R3 hc 15.1595(2) 15.1595(2) 19.2129(3) 90 90 120 3823.78(9) 100(2) 6 7.579 9702

Pn 6.6316(13) 28.981(6) 12.145(2) 90 98.24(3) 90 2310.0(8) 100(2) 4 1.367 16 203

3778

780

8734

0.0560 0.0404

0.0466 0.0233

0.0413 0.0468

triazine cations (see Figure 11). The Sb‚‚‚Sb distance in the stack is 9.574 Å. However, the metal atom is no longer directly above the center of the triazine, and the stack is slightly offset from linearity. The shortest C‚‚ ‚Cl distances are between 3.23 and 3.58 Å. The reaction of 3 with BiCl3 in aqueous HCl leads to the immediate precipitation of crystalline needles of hydrated salt 12 of stoichiometry [3H3][BiCl6][H2O]3. Salt 12 crystallized in the space group R3 h c and contains trianions [BiCl6]3- and trications [3H3]3+, both at sites

Figure 11. The offset stack motif in 11.

of C3i symmetry, and water molecules disordered over two sites. The positions of the NH+ groups around the pyridinium rings are disordered about the two possible 2-sites on each ring. This creates three hydrophilic pockets about each triazine cation, in which the disordered water molecules are bound (see Figure 12 and Scheme 3). The water molecules are held in the hydrophilic pockets of the triazines cation with NH‚‚‚O and CH‚‚‚ O distances of 1.95-2.52 Å. Presumably the shorter distances correspond to NH‚‚‚O contacts and the longer ones to CH‚‚‚O (see Scheme 3). These water molecules appear to be hydrogen-bonded to the [BiCl6]3- units adjacent to the ring with O‚‚‚Cl distances in the range 2.83-3.41 Å. These contacts must also be affected by

Table 6. Inter- and Intramolecular Geometric Data for Salts of [3H3]3+ A‚‚‚H, Å

D‚‚‚A, Å

∠DH‚‚‚A, deg

M-L, Å

torsion angle, deg

C‚‚‚ClSb, Å

NH‚‚‚OH2

1.92 2.14 2.01

2.73 2.98 2.84

157.0 164.6 162.5

2.4870(18) 2.5264(19) 2.6060(18) 2.6711(19) 2.839(2) 2.932(2)

2.17 6.44 2.83

3.23 3.31 3.37 3.40 3.58

12

NH‚‚‚OH2

1.95 2.59

2.83 3.44

157.1 171.6

2.7063(12)

0.06

3.40

13

NH‚‚‚Cl-

2.20 2.23 2.22 2.16 2.26 2.21

2.96 3.06 3.06 2.94 3.08 3.05

143.9 158.2 158.5 147.5 155.7 158.2

2.1830(14) 2.1965(16) 2.1991(15) 2.2109(17) 2.1831(15) 2.1855(17) 2.1956(16) 2.2034(16)

1.37 9.76 4.51 8.91 3.74 0.33

salt

interaction

11

690


Podesta and Orpen

Figure 12. The disordered [3H3]3+‚3H2O unit showing the two positions for each water molecule in hydrated salt 12.

the two-site disorder of the cation and its associated water molecules. The overall structural motif is very similar to that found in 4, 5, and 8-10 with the anion-cation stack motif again present in the structure. While direct NH ‚‚‚Cl hydrogen bonds are precluded by the position of the NH+ groups on the pyridinium rings, a similar packing is present with six [BiCl6]3- around each [3H3‚3H2O]3+ trication and vice versa (see Figure 13). In this case, a distorted version of motif F is formed without the use of NH‚‚‚Cl hydrogen bonds at all (see Figure 13). The CH‚‚‚Cl contacts involved are of lengths in the range 2.85-3.10 Å. The Bi‚‚‚Bi distance in the octahedral array shown in Figure 13 is 9.320 Å, and that in the stack motif parallel to the c axis is 9.606 Å. The overall structure is similar to those of 4, 5, and 8-10 with a threedimensional anion-linked layer structure produced (see Figure 14) and the a and b cell dimensions somewhat enlarged (Table 5) as a result of inclusion of water in the structure. Thus the unit cell volume is 200-300 Å3 larger than those of the two other bismuth salts studied, 5 and 9. The corresponding reaction between 3 and FeCl3 in aqueous HCl solution leads to the formation of pale yellow crystals of 13 in the polar monoclinic space group Pn. The crystal studied appears to be slightly twinned (Flack parameter 0.16(2)). The asymmetric unit contains

Figure 13. The local arrangement of anions and disordered water molecules around cations in 12, showing CH‚‚‚Cl, NH ‚‚‚O, and water‚‚‚Cl hydrogen bonds. W A 3D rotatable image in PDB format is available.

Figure 14. The overall anion linked layer structure found in 12 viewed perpendicular to the c axis.

two [2H3]3+ cations, two [FeCl4]- anions, and four chloride anions (see Figure 15). The triazine cations in 13 form chelating NH‚‚‚Cl hydrogen bonds of lengths 2.61-2.58 Å to the chloride anions in a manner reminiscent of the hydrogen bond chelation of water molecules in 11 and 12. The supramolecular structure is defined by rows of stacks of triazine cations linked by CH‚‚‚Cl hydrogen bonds of

Scheme 3. The Two Images of the Hydrated Cations [3H3]3+‚3H2O Present in 12


Figure 15. The asymmetric unit of mixed salt 13.

Figure 16. The cation stacks and the perpendicular anion layers in 13. W A 3D rotatable image in PDB format is available.

lengths 2.67-2.92 Å to layers containing [FeCl4]- anions (see Figures 16 and 17). The distance between the triazines in the stack is between 3.31 and 3.38 Å. The Fe‚‚‚Fe distances between adjacent anions in the layers are between 5.6 and 8.4 Å. The Fe‚‚‚Fe distances between the layers are in the range 14.7-15.3 Å. Discussion The synthesis and characterization of crystal structures 4-6 and 8-12 demonstrate that these protonated triazines are viable tectons for the construction of new crystal structures. That the structures show pronounced similarities is striking. The 3- and 4-pyridinium species 4 and 5 and 8-10 are essentially isostructural,


showing six connected ions linked by a combination of NH‚‚‚Cl and CH‚‚‚Cl hydrogen bonds. The [FeCl6]3anions in 6 are also hydrogen-bonded to six cations. In the 2-pyridinium species 11-13, the tendency for endotopic (convergent) binding of hydrogen bond acceptors in a pocket formed by two pyridinium moieties is notable. In 10 and 11, this is achieved by binding water in this pocket, which in turn forms hydrogen bonds to neighboring anions. We have previously noted the ability of water when bound to pyridinium to act as a proxy hydrogen bond donor5 essentially by formation of a supramolecular cation (here of the form [3H3‚2H2O]3+ in 11 and [3H3‚3H2O]3+ in 12). In any event, the array of anions around the cations in 11 and 12 is in practice rather similar to that in 4, 5, and 8-10, albeit enlarged. In these structures, the branched covalent form of the cationic tecton has served the purpose intended in generating enhanced dimensionality of the hydrogenbond network. In practice, two-dimensional (layer) arrays of cations are formed in which the hydrogen bonds extend essentially in the plane of the triazine. These layers are then linked through the anions into a three-dimensional array. In contrast, the corresponding [MCl6]2- salts of the 4,4′-bipyridinium cation form twodimensional nets in which hydrogen-bonded ribbons are cross-linked by the anions.1 Furthermore, the 3-fold symmetry of the triazine cations is reflected in the dominant 3-fold symmetry of the product crystal structuressnotably in their space groups (4, 5, 8, 9, 10, and 12 are all R3c or R3 h c). The robustness of this structure type is emphasized by the recent characterization of a molybdenum(III) analogue of 5, [1H3][MoCl6]31 with space group R3 h c, cell dimensions a ) 14.543 Å and c ) 18.437 Å, and cell volume 3377 Å3 with Mo-Cl distance of 2.4684(5) Å. This study complements and extends previous work in which we have explored the hypothesis that hydrogen bonding is but part of the range of factors that determine the crystal structures formed by this class of organic/inorganic salts.6 The cations are close to planar in all instances. Thus in the salts 4, 5, 8, 9, 10, and 12, the torsion angles around the triazine-pyridinium bond are close to zero, while in the more complex salts 6, 7, 11, and 13, the cation shows more flexibility with the torsion angles varying between 0° and 18°. The large size and anisotropy of the cations relative to the anions is presumably at the heart of the dominance of the

Figure 17. A slab of 13 viewed perpendicular to the cation stacks showing rows of cations and anions.

692


planar layer and stacking motifs in this family of structures. The anisotropy of the cation is substantial: the NH donors of, for example, [1H3]3+ form a triangle the van der Waals surface of which is circumscribed by a circle of diameter ca. 13 Å, while the cation is of thickness ca. 3.2 Å. One consequence of this is that the hydrogen-bond network formed, although of R-Po/NaCl topology, has a highly anisotropic form compared with the cubic sodium chloride net (the rhombohedral cell c/a ratio is reduced by ca. 50%). This anisotropy is further associated with polarity and pyroelectric behavior in the ordered (but twinned) phase, 4. In this work, as in our previous efforts in synthesis of crystal structures using pyridinium species and metal complex anions, we have been guided by a heuristic model that emphasizes the NH‚‚‚anion hydrogen bonds as structure-determining. The formation of bifurcated NH‚‚‚Cl2 interactions in 4, 5, and 8-10 is perhaps to be expected given the relative dearth of strong hydrogen bond donors (three NH per formula unit; cf. six Cl, each carrying a nominal 0.5- charge). In the 4-pyridinium species 4 and 5, the bifurcated hydrogen bond involves two anions, [NH‚‚‚(ClM)2], and is identical in form (G)

to those observed in 4,4′-bipyridinium salts of octahedral hexachlorometalates.2 In contrast, in the 3-pyridinium species 8-10, a bifurcated hydrogen bond to a single anion is observed (i.e., NH‚‚‚Cl2M), identical in form to synthon A observed in square-planar tetrachlorometalates. However, it is notable that in all of these salts, the general arrangement of the [MCl6]3- unit relative to the organic cation is invariant, implying that the hydrogen bonding is not the only factor directing the supramolecular structure. Thus the pyridinium‚‚‚MCl6 contacts in 4, 5, 8, 9, and 10 have very similar gross form (F), and while the NH‚‚‚Cl hydrogen bonds distances are typically shorter than their CH‚‚‚Cl counterparts when comparing like for like, individual CH‚‚‚Cl contacts may be shorter than the NH contacts that we have presumed significant. We have previously pointed out6 the partial nature of a model focusing only on NH‚‚‚anion hydrogen bonding, and the present study further emphasizes its incompleteness. Thus it seems likely that CH‚‚‚Cl interactions are significant in these structures, as noted above. In addition, the fact that the location of the primary (NH) hydrogen bond donor has only a secondary influence on the crystal structures formed (viz., the extreme similarity of 4 and 8 and of 5 and 9) is particularly striking. That there is some influence is, however, clear. Thus 4 is polar, and 8 is not, and most notably, the 2-pyridinium species have substantially different local patterns of hydrogen bonding. The detailed metrics of the structures are also affected by NH location both locally (anion‚‚‚cation contacts) and in terms of the cell dimensions (see below). In 4, 5, 8, 9, 10, and 12, the hydrogen bond interactions between ions are complemented by an unanticipated stack motif composed of alternating [MCl6]3- and triazine units (see Figures 1, 4, and 9). Here the anions

Podesta and Orpen

occupy positions above the center of the triazine ring with the M-Cl bonds eclipsing the triazine-pyridine C-C bonds so that the chlorine atoms lie above the triazine ring carbon atoms at distances of 3.3-3.4 Å (cf. van der Waals radius sum ) 3.45 Å). These interactions are presumably partly electrostatic in nature, given that the triazine carbon atoms carry significant partial positive charges and the chloride ligands negative charge. Such interactions are not without precedent. There are 59 cases of Cl‚‚‚CN2 interactions in structures in the Cambridge Structural Database (CSD)32 with Cl‚ ‚‚C distances in the range 3.19-3.45 Å. In all cases, the chlorine is Cl- or in M-Cl or B-Cl moieties. It is unclear whether this anion-triazine motif or the hydrogen bonds in these salts determine the structure. Nonetheless this stack motif is a potential supramolecular synthon awaiting exploitation in other synthetic studies. In practice, as ever, it is presumably the combination of these local motifs, efficient shape packing, and electrostatics that leads to the observed crystal structure.6 The coordination chemistry involved in the preparation of these structures is of interest. Presumably a variety of M(III) (M ) Sb, Bi, or Fe) species are present in solutionsobviously so in the case of iron. It is notable that the isolated products have selectively formed the trianionic hexachlorides of Sb and Bi rather than, say, the pentachloro dianions (e.g., see ref 6). This preference is presumably dictated by the formation of these “good” crystal structures. This factor is not however sufficient to force formation of the [FeCl6]3- anion in all cases (notably in the systems based on 1). The softness of 14e anions such as [MCl6]3- (M ) Sb and Bi) is well-known33 with gross distortions of geometry possible. In practice, in this work all the [BiCl6]3anions are essentially regular with all Bi-Cl lengths in the range 2.70-2.73 Å and cis Cl-Bi-Cl angles within 3° of 90°. The antimony anions show much greater variability with only that in 8 showing nearregular octahedral geometry and that in 11 being particularly distorted. Average Sb-Cl distances are 2.691 Å in 4, 2.655 Å in 8, and 2.677 Å in 11 and cis Cl-Sb-Cl angles deviate up to 8.5° from ideal octahedral values. The observation of more symmetrical geometries for the [BiCl6]3- anions than [SbCl6]3- is consistent with previous analyses of secondary bonding34,35 in the group 15 elements.36 The [FeCl6]3- anion is relatively rigid in 6 and 10 with Fe-Cl distances all in the range 2.37-2.41 Å and cis Cl-Fe-Cl angles within 3° of 90°. The identity of the metal has a significant effect on the metrics of the crystal structures even though the salts they form are near isostructural. Thus the bismuth structures are typically slightly larger than the corresponding antimony cases (by ca. 1% in volume), while the iron case is smaller (by 3.5%) in volume (in the case of 10). The structural metrics are also affected by the cation identity. Thus the 4-pyridinium species have unit cell volumes ca. 2% smaller than the 3-pyridinium cases (comparing 4 with 8 and 5 with 9). The hydrated “supramolecular” cations in 11 and 12 lead to cell volumes ca. 6-10% greater per formula unit than their nonhydrated counterparts.


Conclusions In summary, the following conclusions can be drawn from this work: (1) The triazine cations are suitable ionic tectons for synthesis of a family of closely related crystal structures of [MCl6]3- salts. (2) These salts have patterns of local hydrogen bonding in which NH‚‚‚Cl and CH‚‚‚Cl interactions, while varying in detail, appear almost interchangeable as structural elements. (3) The key hydrogen bond motif appears to be F, versions of which appear in all the triazine cation structures containing [MCl6]3- except 6. (4) The formation of motif F at each pyridinium moiety of the cations and the corresponding 6-fold pattern of hydrogen bonding around each anion leads to a six-connected hydrogen-bond network in salts 4, 5, 8, 9, 10, and 12 of the R-Po (or NaCl) form. (5) The hydrogen bond interactions between ions are complemented by an unexpected stack motif in which the M-Cl functions of anions apparently serve as electron donors to the carbon atoms of the polarized triazine moiety in the cations. (6) Compounds 4, 5, 8, 9, and 10, which all feature both of these motifs, also have similar unit cells and space groups. All have space group R3c or R3 h c with values of a () b) of between 14.6 and 14.7 Å and c between 18.5 and 19.3 Å. Compound 12, which incorporates water informing a supramolecular cation, has larger a ) 15.16 Å. This is a highly anisotropic structure with c/a ratio of ca. 50% of that of NaCl in the same setting. (7) Structure 4 is a polar structure and apparently pyroelectric although the single crystal studied is twinned. (8) The unit cell dimensions and volume are dependent on the position of the NH+ group (with 4-pyridinium salts giving smaller volumes than 3-pyridinium ones) and the metal used (in the sequence Fe < Sb < Bi). Acknowledgment. We thank the University of Bristol and the E.P.S.R.C. for financial support. Supporting Information Available: Further intermolecular geometry details (Table S1) and crystallographic (cif) data for all structures, and Figures S1-S3 giving further details regarding the structures of 6 and 7. This material is available free of charge via the Internet at http://pubs.acs.org.

References (1) Gillon, A. L.; Lewis, G. R.; Orpen, A. G.; Rotter, S.; Starbuck, J.; Wang, X. M.; Rodriguez-Martin, Y.; Ruiz-Perez, C. J. Chem. Soc., Dalton Trans. 2000, 3897-3905. (2) Dolling, B.; Gillon, A. L.; Orpen, A. G.; Starbuck, J.; Wang, X. M. Chem. Commun. 2001, 567-568. (3) Angeloni, A.; Orpen, A. G. Chem. Commun. 2001, 343-344. (4) Podesta, T. J.; Orpen, A. G. CrystEngComm. 2002, 336342. (5) Crawford, P. C.; Gillon, A. L.; Green, J.; Orpen, A. G.; Podesta, T. J.; Pritchard, S. V. CrystEngComm., in press.

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CG049783G

Tris(Pyridinium)Triazine in Crystal Synthesis of 3-Fold Symmetric

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