Arenediazonium Salts as Versatile (meso-Ionic) Tectons. Charge-Transfer Intercalates and Clathrates in Unusual Crystalline Networks Self-Assembled with Neutral Aromatic π-Donors
CRYSTAL GROWTH & DESIGN 2004 VOL. 4, NO. 3 563-571
Sergey V. Lindeman and Jay K. Kochi* Department of Chemistry, University of Houston, Houston, Texas 77204-5003 Received November 13, 2003
ABSTRACT: The surprisingly uniform crystal packings of various arenediazonium salts (ArN2+X-) largely consist of two-dimensional ionic layers from various (N2+‚‚‚X-) interactions coupled with a series of antiparallel arrays of pendant aryl groups (Ar). This crystalline architecture can be deliberately modified by the introduction of different (neutral) aromatic π-donors. On the basis of the exceptional electron-acceptor strength of the (N2+) group, the principal crystal-forming interactions of the arenediazonium tecton can be dissected into (a) strong coordination to anionic and electron-rich (neutral) σ-donors within the equatorial plane, (b) enhanced capacity for (C-H‚‚‚X) hydrogen bonding, and (c) remarkable aptitude to form (noncovalent) charge-transfer bonds with aromatic π-donors. Thus, the detailed analysis of crystalline networks found in 3,5-dinitro and 4-carboethoxy derivatives of benzenediazonium salts recognizes them as remarkable intercalate and clathrate structures in which various charge-transfer interactions between the electron-deficient arene moiety and aromatic π-donors are essential for the stabilization of the unusual layered/network structures. Introduction As a robust and structurally rigid unit, the arenediazonium moiety is an unique and highly stable cation,1 in which the positive charge is largely localized on two nitrogen centers that are (linearly) appended to an aromatic center.2 Since the parent benzenediazonium cation (C6H5N2+) is also a powerful electron acceptor,3 it offers the potential to serve as an unusual tecton4 in crystal engineering based on the combination of intermolecular electrostatic and charge-transfer interactions.5 Thus, the positively charged diazonium center can function as a strong ionic attractant to various negatively charged counteranions as well as electronrich (electroneutral) nucleophiles with typical σ-donor properties.6 The presence of this cationic electronwithdrawing group also confers electron-deficiency to the tethered aromatic ring which then serves in a secondary capacity as (a) π-acceptor site for other electron-rich donors,7 and (b) effective proton donor in the formation of relatively strong intermolecular (CH‚‚‚X) hydrogen bonds8sthe electronic basis both of which is readily deduced from the major canonical (resonance) structures depicted below.
We now show how such an ambiphilic nature inherent to different arenediazonium cations leads to unusual crystalline networks via their self-assembly with neutral (uncharged) aromatic π-donors. I. Arenediazonium Salts as Versatile (meso-Ionic) Tectons Intermolecular interactions of arenediazonium cations can be dissected into three principal recognition modes * To whom correspondence should be addressed. E-mail: jkochi@ uh.edu.
Figure 1. Close interionic association extant in the crystal structures of (A) benzenediazonium chloride, (B) p-methoxybenzenediazonium nitrate, and (C) benzenediazonium tetrafluoroborate.
relevant to (A) electrostatic bindings, (B) hydrogen bonds, and (C) charge-transfer associations, as follows. A. Ionic Coordination about the Diazonium Tecton. The tight coordination of negatively charged counterions clustered around the diazonium center is inherent to many structural studies of arenediazonium salts, and this is generally acknowledged as arising from Coulombic attractions. Most importantly, the spatial distribution of the electronegative (atomic) centers about the N2 center is far from spherically isotropic. The location of anions is dictated by the cylindrical symmetry of the diazonium moiety, coupled with the steric/ electronic hindrance built up by the adjacent aryl group and the lone electron pair of the terminal nitrogen (Nβ). As a result, the counteranions only concentrate within a relatively narrow annulus in the vicinity of the equatorial plane of the linear -N2 moiety, as typically illustrated in Figure 1. Thus, in benzenediazonium chloride11 (Structure A), four chloride anions surround the diazonium group in a square-planar array at Cl‚‚‚N distances as short as 3.23 Å, which is significantly closer than the corresponding equilibrium (van der Waals) separation of 3.30 Å.12 By contrast, in p-methoxybenzenediazonium ni-
10.1021/cg034218j CCC: $27.50 © 2004 American Chemical Society Published on Web 04/10/2004
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Figure 2. Close association of aryldiazonium group with σ-donor molecular moieties: (D) 21-crown-7 and (E) acetic acid.
trate13 (Structure B), only three nitrate ions occupy trigonal (equatorial) positions about the diazonium group making (O‚‚‚N) contacts as close as 2.83 Å compared to the equilibrium (van der Waals) separation of 3.07 Å.12 Such a coordination pattern remains unchanged even in the case of weakly nucleophilic anions14 such as BF4-. Thus, in benzenediazonium tetrafluoroborate15 (Structure C), the four complex counteranions surround the diazonium group from all sides at F‚‚‚N distances as short as 2.83 Å compared to the standard van der Waals value of 3.02 Å.12 Such a two-dimensional array of negatively charged anions around the cationic diazonium cationic group cannot be accounted as merely Coulombic attractions, since uncharged (neutral) σ-electron donors are known to displace counteranions from its coordination shell. For example, in the crown-ether complex of p-methoxybenzenediazonium tetrafluoroborate16 (Structure D, Figure 2), the ion pairing is completely disrupted by 21crown-7 at O‚‚‚N distances as close as 3.05 Å (and F‚‚ ‚N distances as long as 5.5 Å). Furthermore, carbonyl oxygens in the acetic-acid clathrate17 (as a weaker σ-electron donor) can replace even nucleophilic chloride anions as shown in structure E, in which a pair of carboxy groups replace two (out of four) chloride counteranions from the diazonium coordination sphere and make short CdO‚‚‚N contacts of 2.89-3.00 Å (resultant Cl‚‚‚N distances are of 3.17-3.32 Å). B. Hydrogen-Bonding Interactions with Arenediazonium Tectons. Polarization by the electropositive diazonium group on the aromatic (C-H) bonds is sufficient to induce hydrogen bonds with a variety of arene donors. Indeed, such intermolecular hydrogen bonds with unusually short C-H‚‚‚π interactions are effective for the supramolecular (aromatic/aromatic) organization in edge-to-face motifs,18 and these are related to the ubiquitous C-H‚‚‚X interactions8a (where X is a σ-donor) in arenediazonium crystals traced to the earliest structural studies in this field. Thus, C-H‚‚‚ Cl- contacts with H‚‚‚Cl distance of 2.47 Å (the corresponding sum of van der Waals radii is 2.95 Å12) and C-H-Cl bond angle of 152° can be found in the structure of benzenediazonium chloride (Structure A).11,19 The close CsH‚‚‚O contacts with H‚‚‚O distances 2.23 and 2.30 Å (cf. the standard 2.72 Å separation12) and C-H-O bond angles 151 and 143°, respectively, are observed in the structure of the 21-crown-7 complex of p-methoxybenzenediazonium cation (Structure D).16 Even much-shortened C-H‚‚‚F contacts with H‚‚‚F distances of 2.30-2.38 Å (as compared with the standard van der Waals value of 2.67 Å12) and C-H-F bond angles 132-173° take place in the structure of benzene-
Figure 3. Alternate π-donor/acceptor stacks of arenediazonium cations with (F) tribromide, (G) penta(carbomethoxy)cyclopentadienide, and (H) dinitratodioxo(2,4,6-trimethylphenyl)osmiate anions.
diazonium tetrafluoroborate (Structure C).15 The majority of such hydrogen bonds are formed with the orthohydrogens of the arene ring18 owing to the polarizing effect of the diazonium group chiefly on the ortho- and para-hydrogens, and to a lesser degree, meta-hydrogen atoms. Furthermore, the more numerous ortho-hydrogens are positioned in close proximity to the anions and other σ-electron donors concentrated around diazonium cationic center. Interestingly, the ortho-C-H‚‚‚X interactions are not subordinate to the corresponding ArN2+‚‚‚X donor/acceptor interactions, but rather effectively compete with them. For example, the two chloride anions involved in the C-H‚‚‚Cl- bondings in the structure of benzenediazonium chloride (Structure A)11 are coordinated much more weakly to the corresponding diazonium center (Cl‚‚‚N 3.55-3.56Å) as compared to the remaining two (Cl‚‚‚N 3.23-3.24 Å). The same is true for the structure of the 21-crown-7 complex of p-methoxybenzenediazonium (Structure D)16 in which two oxygen atoms of the crown-ether that participate in the C-H‚‚‚O bondings are further separated from the diazonium group (O‚‚‚N 3.35-3.38 Å) than the others (O‚‚‚N 3.05-3.25 Å). C. Donor/Acceptor π Interactions with Arenediazonium Tectons. The powerful electron-withdrawing effect of the cationic diazonium function confers strong π-electron acceptor properties upon the directly connected aromatic center, and this is observed as the spontaneous appearance of prominent (new) chargetransfer absorption bands in the UV-vis spectra of arenediazonium solutions upon the addition of various ionic and aromatic donors.10 Although X-ray crystallographic studies associated with such charge-transfer interactions are heretofore unknown for neutral aromatic donors, there are a handful of examples where electron-rich anionic donors form crystalline complexes with arenediazonium cations to produce characteristic heterosoric20 donor/acceptor stacks. For example, in the structure of benzenediazonium tribromide,21 the electronrich (linear) Br3- anions are positioned almost parallel (at an angle of 6.2°) to the arene moieties, overlapping them at an average distance of 3.67 Å and forming regular π-donor/acceptor stacks (Figure 3F). Also in the structure of p-nitrobenzenediazonium penta(carbomethoxy)cyclopentadienide,22 the electron-rich cyclo-
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Figure 4. Schematic representations of the two-dimensional packing of arenediazonium tectons modulated by ion size.
pentadienyl anions (as aromatic π-donors) overlap with the arenediazonium moiety at a dihedrlal angle of 8.4° and average interplanar distances of 3.33 and 3.42 Å to form quasi-regular heterosoric stacks (Figure 3G). Very similar alternate stacks of 2,4,6-trimethylbenzenediazonium cations and dinitratodioxo(2,4,6-trimethylphenyl)osmiate anions can also be found (Figure 3H)23 in which dihedral angle between the donor and acceptor benzene rings is 7.6° and the average interplanar distances are 3.46 and 3.61 Å. II. Molecular Networks with Arenediazonium Tectons The diverse (binary) interactions inherent to the arenediazonium tecton, as described above, result in a surprisingly uniform series of (crystal-packing) networks as follows. A. Two-Dimensional Ionic Layers - General Structural Features. Tight interionic coordination governs the formation of various molecular networks with the characteristic two-dimensional layers depicted in Figure 4. The formation of either tetragonal or hexagonal layers is dictated by the size of the counteranion relative to the cylindrically shaped diazonium cation. For example, the formation of tetragonal layers (Figure 4A) is promoted by the rather small chloride anion in the crystal structure of benzenediazonium chloride.11 Thus, each cylindrically symmetrical diazonium cation is surrounded by four chlorides, which in turn participate in coordination to four diazonium centers. By contrast, the larger tetrachloroferrate (FeCl4-) produces hexagonal layers (Figure 4B) as in the o-methoxybenzenediazonium crystal,24 in which each spherically symmetrical anion coordinates three cylindrical diazonium centers. Both tetragonal and hexagonal packings are observed with anions of intermediate size, as shown by tetrafluoroborate (BF4-) which leads to tetragonal layers in the benzenediazonium crystals,15 but hexagonal layers in the p-bromobenzenediazonium crystals.25 Interionic association in the layers is complemented by extensive hydrogen-bonding between ortho-hydrogens and neighboring anions (vide supra), but these can be deformed or even broken when they are overwhelmed by stronger steric/electronic interactions. The latter can be influenced either by (a) bulky ortho-substituents as in o-dimethylaminobenzenediazonium tetrafluoroborate,26 or (b) uncharged (but strongly coordinating) σ-donor groups such as morpholinyl,27 acetic acid,17 or a crown-ether,16 or both, as in o-carboxybenzenediazo-
Figure 5. Two-dimensional ionic layers with different degrees of folding in the structures of (A) benzenediazonium chloride and (B) benzenediazonium tetrafluoroborate.
nium chloride monohydrate.28 Furthermore, planar (nonspherical) anions, such as nitrate, can complicate the layered structure,13 although it still persists with such odd-shaped anions as bis(trifluoromethanesulfonyl)methanide29 or o-benzenedisulfonimide.30 The faces of such ionic layers are framed with adjacent arene moieties lying perpendicular to the layer planes, as shown in Figure 5 by the remarkable contrast between the intense interionic/hydrogen-bonding interactions within the two-dimensional layers and the much weaker arene-arene interactions between the layers. Although the arene-arene interactions are hydrophobic, some stacking and dipole/dipole interactions between the bordering antiparallel benzene rings can contribute to interlayer adhesion. B. Intercalation of Aromatic Guests between Ionic Layers. The persistence of strongly bonded twodimensional interionic layers allows the introduction of appropriate guests between the layers to form intercalated complexes.31 Thus, the majority of arenediazonium structures shows ionic layers partially interpenetrated in the “ziplock” fashion that is schematically illustrated in Figure 6A, and intercalates of aromatic donors in this (and a related) manner are shown in Figure 6B,C. Indeed, both types of intercalated structures have been observed with 3,5-dinitrobenzenediazonium tetrafluoroborate in its interionic/charge-transfer associa-
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Figure 6. Interpenetrated ionic layers in arenediazonium crystals showing (A) the “ziplock” arrangement and (B) intercalated with arene donors. (C) Alternative intercalation of arene donors between overlapped layers.
Figure 7. Details of the interionic and π-donor/acceptor association in the crystal structures of 3,5-dinitrobenzenediazonium tetrafluoroborate with (J) naphthalene, and (K) p-dimethoxybenzene.10
tions with 1,4-dimethoxybenzene and naphthalene guests.10 In these structures, the electron-deficient 3,5dinitrophenyl center is responsible for the strong donoracceptor interactions with the aromatic donors 1,4dimethoxybenzene and naphthalene, the details of which are presented in Figure 7, panels J and K, respectively.32 Otherwise, the overall array of intermolecular ionic interactions follows the pattern described above. In both complexes, the diazonium group is surrounded by four BF4- counterions making close F‚‚‚N interionic contacts shortened to 2.7-2.8 Å. Also, these counteranions participate in hydrogen bonds with the ortho-H-atoms of the arene moiety (H‚‚‚F distances of 2.14-2.37 Å, angles C-H‚‚‚F of 136-161°). As a result of such strong interionic/charge-transfer interactions, intercalation of the aromatic guests between the two-dimensional layers leads to the unusual crystalline network shown in Figure 8, in which the dinitrophenyl center is alternately positioned over the aromatic faces of the naphthalene and p-dimethoxybenzene donors. Thus, the interionic layers do not show the usual ziplock interpenetration as in Figure 6A, but the aromatic donors fill out the spaces between the pendant dinitrophenyl (acceptor) groups as in Figure 6B,C.33 The relative positioning of the naphthalene donor and arenediazonium acceptor shown in Figure 7J at a short interplanar distance (av. 3.25 Å) and small dihedral angle (5.7°) suggests an important charge-transfer interaction. Interestingly, the approaching naphthalene donor almost replaces one of BF4- counterions from the coordination sphere of the arenediazonium moietysthus
Figure 8. Formation of donor/acceptor intercalates in the layered structures of 3,5-dinitrobenzenediazonium tetrafluoroborate with (A) naphthalene and (B) p-dimethoxybenzene.
confirming the strength of the π-donor/acceptor interaction. In the complex with dimethoxybenzene donor, the relative positioning of the donor and acceptor moieties (Figure 7K) is not as favorable. Although they make close van der Waals contact, the value of dihedral
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Figure 9. Details of the interionic, σ- and π-donor/acceptor associations in the structures of p-carboethoxybenzenediazonium hexafluorophosphate complexed to p-xylene (L) and benzodioxole (M).
angle between them (20.1°) is far from an optimal. As a result, the anionic shell around diazonium cation remains unperturbed in this complex. C. Clathrate Networks from π/σ Associations. The foregoing description of the interplay between ionic/ charge-transfer interactions emphasizes how the “pure” ionic layers described in Figures 4 and 5 can be systematically disrupted. In the case of p-carboethoxybenzenediazonium hexafluorophosphate, the combination of interionic forces versus π/σ charge-transfer interactions results in a remarkable series of rather porous crystalline associates that readily embed a variety of aromatic π-donors (as well as solvents) in the form of clathrate networks. The ester carbonyl groups in p-carboethoxybenzenediazonium exhibits an exceptionally strong coordination toward adjacent diazonium centers. In all six symmetrically independent units found in the four crystal structures studied, the carbonyl oxygens always coordinate a neighboring diazonium group, without exception. As a result, the most typical coordination pattern of this arenediazonium tecton is comprised of three PF6anions and one neutral carbonyl σ-donor (which replaces the fourth counteranion from the coordination shell); the details are shown in Figure 9.34 In an almost identical manner, three PF6- anions approach the diazonium acceptor center at typical distances F‚‚‚N of 2.8-3.1 Å and the carbonyl group at the close O‚‚‚N distances of 2.78-2.98 Å in the crystal structures with p-xylene (Figure 9L) and benzodioxole donor (Figure 9M). Notably, the lone electron pair of the carbonyl oxygens is well oriented toward the diazonium acceptor, as follows from the large values of the bond angles CdO‚‚‚N of 140-153°. Also, the coordination environment around the diazonium moiety is enhanced by the formation of C-H‚‚‚F bonds with participation of the ortho-hydrogen atoms; the typical distances H‚‚‚F are 2.27-2.57 Å with C-H‚‚‚F angles within the range 123-148°. The incursion of the ester carbonyl group inevitably prevents this arenediazonium cation from forming continuous two-dimensional ionic layers. Instead, double ionic chains are formed, as schematically presented in Figure 10. Effectively, these planar double chains represent exact replica “strips” cutoff from the corresponding two-
Figure 10. Schematic representations of the ionic layers of p-carboethoxybenzenediazonium tectons showing two alternative dispositions of the pendant p-carboethoxyphenyl centers.
Figure 11. Schematic representations of the σ-coordination of an ester substituent with a neighboring syn-chain (A) and anti-chain (B), as described in the text.
dimensional ionic layers (compare the schematic representations in Figures 4 and 10). Depending on the direction of the fragmentation (either along or across the rows of alternately protruding aryl groups), two different kinds of the chains are possible, either with a uniform orientation of the aryl groups along the chain or with an alternating arrangement, described as the syn and anti forms in Figure 10A,B, respectively. Indeed, both types of ionic chains are found in the crystal structures of p-carboethoxybenzenediazonium hexafluorophosphate complexed with aromatic donors, viz. the uniformly formed syn-chains (Figure 10A) with benzodioxole, and the alternately formed anti-chains (Figure 10B) with p-xylene. These ionic chains are arranged in the crystals in a parallel fashion, so that the carbonyl group coordinates the open edge of the neighboring chain. [In Figure 11, each ionic chain (viewed in perspective) is schematically represented as a rectangle, and each protruding aryl group with a terminal carbonyl by a bent arrow. Arrows of different thickness correspond to groups at different distances from the viewer.] Most importantly, the σ-coordination of the pendant p-carboethoxyphenyl groups to the neighboring ionic chains leads to unusually open molecular networks. Although both packing modes of the syn- and antichains appear to be of the same (low) packing density, the distribution of the void space is distinctively differentsthe channels between the cross-linked synchains (ovals in Figure 11A) being twice as large (and twice less numerous) as the channels between the cross-
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Figure 12. Crystal structures of p-carboethoxybenzenediazonium hexafluorophosphate complexes with (A) benzodioxole and (B) p-xylene in projection along the ionic chains (cf. Figure 11, panels A and B, respectively).
linked anti-chains (circles in Figure 11B). The bigger channels are filled out by pairs of antiparallel benzodioxole molecules (Figure 12A), and the smaller channels by discrete p-xylene donor molecules (Figure 12B). Both types of donors make short van der Waals contacts with acceptor “walls” of the channels as shown in Figure 9L,M, with dihedral angles between the corresponding donor and acceptor benzene rings av. 11.8° (p-xylene), and 3.8° (benzodioxole), and with average interplanar donor/acceptor distances av. 3.34 Å (p-xylene), and 3.50 Å (benzodioxole).35 The remarkable molecular networks that are derived from p-carboethoxybenzenediazonium tecton and aromatic donors, as typically illustrated in Figure 12, underscore the versatility of ionic/donor/acceptor interactions for crystal engineering. The π-donor/acceptor interactions play a definitive role in the formation of the networked crystals of this arenediazonium salt. Thus, the incorporation of p-xylene donor substantially distorts the pristine structure of the complex,36 and the clathration with benzodioxole causes a significant rearrangement of the ionic network (but at the same time leaving the principal structural elements unchanged). Even more dramatic structural changes take place in the toluene clathrate. The apparently “innocent” replacement of an acetonitrile solvent with the weak
Figure 13. Schematic presentations of the complex interionic, σ- and π-donor/acceptor interactions of p-carboethoxybenzenediazonium hexafluorophosphate with toluene, as described in the text.
toluene donor causes the complete rearrangement of entire ionic network. The main structural unit of this network represents a product of incomplete degradation of ionic layers, not into the double ionic chains (like in the other structures), but into the more extended ionic bands (illustrated in Figure 13) where half of arenediazonium units (inside the bands) are coordinated in the usual manner by four anions (see Figure 14N; N‚‚‚F
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Summary and Conclusions
Figure 14. Interionic, σ- and π-donor/acceptor association of two symmetrically independent aryldiazonium units in the structure of the toluene complex of p-carboethoxybenzenediazonium hexafluorophosphate.
2.77-3.08 Å) but the other half of the cations (bordering the bands) are coordinated by three counteranions and two carbonyls from the neighboring bands (see Figure 14P; N‚‚‚F 2.88-3.07 Å, N‚‚‚O 2.89 and 2.90 Å). In both cases, ortho-hydrogens enhance the coordination by being involved in short C-H‚‚‚F interactions (H‚‚‚F 2.37-2.63 Å). The neighboring bands partially share some PF6anions (dashed circles in Figure 13A,B), which act like “joints” to assemble the ionic bands into a threedimensional grid schematically depicted in Figure 13B. The grid is substantially interwoven by the carbonyl links between the orthogonal bands (broken arrows in Figure 13C) and contains empty cells (shaded circles in Figure 13C) of sufficient size to house the disordered toluene donor molecules. Most important, the toluene donors are in a favorable position for the π-donor/ acceptor interactions (Figure 14P) since they are separated from the acceptor (aromatic) plane by only 3.47 Å at a dihedral angle of 9.3°.
Arenediazonium salts as tectonic building elements for crystal engineering possess a unique array of binding properties, including: (a) strong acceptor affinity toward electronegative or neutral σ-donors; (b) enhanced C-H acidity for extensive formation of C-H‚‚‚X bonds; and (c) π-acceptor properties of the electron-deficient arene substituent for charge-transfer complex formation with appropriate aromatic π-donors. The σ-acceptor properties are associated with the positively charged NR atom, and result in tight coordination of counteranions and neutral nucleophilic σ-donor groups within the equatorial plane of the diazonium group in crystals. The hydrogen-bonding properties are the result of significant activation/polarization of aromatic C-H groups due to the strong electron-withdrawing effect of the diazonium group. Electronically and statistically, ortho-hydrogens are most involved in hydrogen bonds formation, preferably with counterions and other σ-donor species surrounding the adjacent diazonium center. The π-acceptor properties are associated with the electron-deficient benzene ring and lead to charge-transfer complexes with aromatic π-donors in solution and in crystals. The tight σ-donor/acceptor association of arenediazonium salts (enhanced by the hydrogen bonding) typically results in the formation of two-dimensional ionic layers with antiparallel (close) packing of the polarized arene groups between them. This type of crystal packing is usually highly unfavorable for the incorporation of neutral π-donors into the crystals, albeit negatively charged π-donors readily form corresponding chargetransfer stacking motifs with arenediazonium acceptors. However, the deliberate use of various crystal-engineering tools allow us to explore the π-acceptor facet of the arenediazonium tecton to its fullest. Thus, increasing bulkiness of the arene groups can impair their close association between the ionic layers in the diazonium crystals and allows intercalation of some π-donor aromatic molecules between the layers. In particular, the introduction of a pair of nitro-substituents in the 3- and 5-positions of the arene ring results in the formation of crystalline intercalated π-donor/acceptor complexes of the 3,5-dinitrophenyldiazonium tetrafluoroborate with naphthalene and p-dimethoxybenzene molecules. Al-
Table 1. Crystal Data and Structure Refinement Details for Compounds Investigated compound
I‚naph
I‚pdmb
II‚pxyl
II‚bdox
II‚tolu
II‚acnt
empirical formula M crystal system space group a/Å b/Å c/Å β/° V/Å3 Z Dc/g cm-3 µ(Mo KR)/mm-1 crystal size/mm3 2θmax/° total rflns rflns obsd [I > 3σ(I)] total variables R ) Σ||Fo| - |Fc||/Σ|Fo| Rw ) [Σ(|Fo| - |Fc|)2/Σ|Fo|2]1/2 residual peak/e Å3
C16H11BF4N4O2 410.12 monoclinic P21 7.502(2) 7.906(1) 14.769(3) 96.93(1) 869(1) 2 1.57 0.13 0.3 × 0.4 × 0.7 60 2882 2261 284 0.043 0.031 0.3
C20H16B2F8N8O10 702.06 monoclinic P21/n 7.575(1) 7.260(1) 25.733(4) 96.07(1) 1407(1) 2 1.66 0.15 0.2 × 0.5 × 0.5 50 2869 1652 263 0.048 0.038 0.5
C26H28F12N4O4P2 750.52 monoclinic P21/c 14.720(3) 13.838(3) 17.275(3) 109.98(1) 3328(3) 4 1.50 0.23 0.3 × 0.4 × 0.6 48 5774 3428 391 0.049 0.044 0.3
C16H15F6N2O4P 444.30 monoclinic P21/n 7.949(1) 18.654(3) 12.979(2) 104.69(1) 1862(2) 4 1.59 0.22 0.5 × 0.5 × 0.6 50 3632 2496 257 0.059 0.049 0.4
C43H44F24N8O8P4 1380.83 monoclinic C2/c 18.120(4) 16.453(3) 20.589(4) 108.69(1) 5814(5) 4 1.58 0.25 0.4 × 0.5 × 0.5 50 5127 3616 417 0.049 0.043 0.6
C11H12F6N3O2P2 363.23 monoclinic I2/c 17.054(3) 12.789(2) 15.606(3) 110.61(1) 3186(3) 8 1.51 0.24 0.3 × 0.5 × 0.6 50 2811 2114 206 0.049 0.043 0.4
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ternatively, the layered interionic association can be destabilized by introduction of neutral σ-donor substituents capable of the partial replacement of anions from the coordination sphere of the cationic diazonium center. We found that the introduction of an ester carbonyl group in the para-position of the arene ring not only effectively degrades the two-dimensional ionic layers but also results in the formation of various three-dimensional network structures. In the case of 4-carboethoxyphenyldiazonium hexafluorophosphate, these networks readily rearrange around appropriate π-donor templates to form diverse crystalline charge-transfer complexes with toluene, p-xylene, and benzodioxole. These results thus show that the clear understanding of structureforming abilities peculiar to this crystal-engineering tecton allows the deliberate utilization of weak crystallographic forces, even in the presence of much stronger intermolecular associations. Experimental Section The synthesis and spectroscopic properties of crystalline arenediazonium salts and those complexed to various aromatic π-donors were presented separately.10 The arenediazonium salts that are particularly pertinent to this crystallographic study are I ) 3,5-dinitrobenzenediazonium tetrafluoroborate, II ) 4-carboethoxybenzenediazonium hexafluorophosphate, and the arene π-donors are naphthalene (naph), 1,4-dimethoxybenzene (pdmb), p-xylene (pxyl), methylenedioxybenzene (1,3benzodioxole, bdox), toluene (tolu), and the acetonitrile (acnt) solvate as presented in Table 1. Crystal data are given in Table 1, together with some data collection and refinement details. Diffractional intensities for all crystals were measured at -50 °C with graphite monochromated MoKR radiation (λ ) 0.71073 Å) using a Nicolet R3m/V diffractometer. The unit cell parameters and orientation matrices were obtained by a least-squares fit of 25 randomly distributed in reciprocal space intense reflections, in all cases. The diffracted intensities were collected in ω-scan mode using a variable scan speed. Two standard reflections were monitored every 100 reflections collected, and these showed no significant change. Lorentz and polarization corrections were applied, but no absorption correction was made due to the small values of µ‚R for all the crystals (see Table 1). Extinction correction was found to be significant only for data on I‚naph, and a fixed extinction coefficient 0.01 was applied during the structure refinement. The structures were solved by direct methods. The usual sequence of refinements in isotropic and then in anisotropic approximation was followed for non-hydrogen atoms (in all cases, with weights w ) 1/[σ(F)]2), and after that all hydrogens were entered in ideal calculated positions and refined in a riding model with a common variable isotropic temperature factor (separate variable Uiso was used for aliphatic and aromatic hydrogens in structure II‚pxyl and for hydrogens of cation of II and molecule of bdox in structure of II‚bdox). Substantial disorder was found and resolved in most of the crystal structures investigated. Disorder of anions was found in structures I‚naph (two positions/orientations of the BF4anion with occupancy ratio 3:1 were treated as ideal rigid body moieties), II‚bdox (two positions/orientations of the PF6- anion with occupancy ratio 7:3 were treated as ideal rigid body moieties), and II‚tolu (two positions/orientations of the P(1)F6 group were modeled by two rigid body moieties with equal population; the P(2)F6 group occupying 2-fold axis is rotationally disordered about a common F(7)-P(2)-F(7) fragment in three orientations with occupancies 45, 45, and 10%). Disorder of guest molecules was found in structures I‚pdmb (the pdmb molecule that ocuppies two positions with equal probability was treated as a combination of separate rigid body moieties of benzene ring and methoxy groups), II‚pxyl (the pxyl molecule was treated as a combination of rigid bodies occupy-
Lindeman and Kochi ing two positions with equal probability), II‚tolu (the tolu molecule at 2-fold axis was modeled as an ideal rigid benzene ring with 50% occupancy having two different positions for the methyl group, with 25% occupancy each), and II‚acnt (two positions of the acnt molecule were refined with populations 0.6 and 0.4). All calculations were made using Nicolet’s SHELXTL Plus (1987) program package. Complete structural data are available from the Cambridge Crystallographic Data Center under the following refcodes: SOQWEA (3,5-dinitrobenzenediazonium tetrafluoroborate naphthalene complex), SOQWIE (3,5-dinitrobenzenediazonium tetrafluoroborate 1,4-dimethoxybenzene complex), SOQVID (4-carboethoxybenzenediazonium hexafluorophosphate acetonitrile solvate), SOQVOJ (4-carboethoxybenzenediazonium hexafluorophosphate toluene complex), SOQVUP (4-carboethoxybenzenediazonium hexafluorophosphate p-xylene complex), and SOQWAW (4-carboethoxybenzenediazonium hexafluorophosphate 1,3-benzodioxole complex).
Acknowledgment. We thank D. Kosynkin and J. D. Korp for synthetic and crystallographic assistance, and the National Science Foundation and the Robert A. Welch Foundation for financial support. References (1) Wulfman, D. E. in The Chemistry of Diazonium and Diazo Groups; Patai, S., Ed.; Wiley: New York, 1978. (2) (a) Zollinger, H. Diazo Chemistry; VCH: New York, 1994; Vol. 1. (b) Glaser, R.; Horan, C. J.; Lewis, M.; Zollinger, H. J. Org. Chem. 1999, 64, 902. (c) Allen, F. H.; Harris, S. E. Acta Crystallogr., Sect. B: Struct. Sci. 1995, 51, 378. (3) Kochi, J. K. Organometallic Mechanisms and Catalysis; Wiley: New York, 1978. (b) Perez, P. J. Org. Chem. 2003, 68, 5886. (c) Glaser, R.; Horan, C. J.; Zollinger, H. Angew. Chem., Int. Ed. Engl. 1997, 36, 2210. (4) (a) Tecton was coined by Wuest and co-workers4b to describe “...any molecule whose interactions are dominated by particular associative forces that induce the self-assembly of an organized network with specific architectural or functional features.” (b) Sinard, M.; Su. D.; Wuest, J. D. J. Am. Chem. Soc. 1991, 113, 4696. (c) For further elaborations of tectons, see for example (d) Hosseini, M. W. Coord. Chem. Rev. 2003, 240, 157. (e) Mann, S. Nature 1993, 365, 499. (5) (a) Foster, R. Organic Charge-Transfer Complexes; Academic: New York, 1965. (b) Briegleb, G. Electronen DonatorAcceptor Komplexe; Springer: Berlin, 1961. (6) Compare: Lindeman, S. V.; Hecht, J.; Kochi, J. K. J. Am. Chem. Soc. 2003, 125, 11597. (7) For intermolecular π-interactions of aromatic donor-acceptor pairs, see (a) Badger, B.; Brocklehurst, B. Trans. Faraday Soc. 1970, 66, 2939 and related papers. (b) Fritz, H. P.; Gebauer, H.; Friedrich, P.; Ecker, P.; Artes, R.; Schubert, V. Z. Naturforsch. 1978, 33B, 498. (c) Herwig, P. T.; Enkelman, V.; Schmelz, D.; Mullen, K. Chem. Eur. J. 2000, 6, 1834. (8) See, e.g., (a) Jakubetz, W.; Schuster, P. Tetrahedron 1971, 27, 101. (b) Viswamitra, M. A.; Radhakrishnan, R.; Bandekar, J.; Desiraju, G. R. J. Am. Chem. Soc. 1993, 115, 4868. (c) Nishio, M.; Umezawa, Y.; Hirota, M.; Takeuchi, Y. Tetrahedron 1995, 51, 8665. (d) Braga, D.; Grepioni, F.; Tedesco, E. Organometallics 1998, 17, 2669. (9) See Wulfman, D. E.; Zollinger, H. in refs 1 and 2. (10) (a) Kosynkin, D.; Bockman, T. M.; Kochi, J. K. J. Am. Chem. Soc. 1997, 119, 4846. (b) Bockman, T. M.; Kosynkin, D.; Kochi, J. K. J. Org. Chem. 1997, 62, 5811. (11) Rømming, C. Acta Chem. Scand. 1963, 17, 1444. (12) Bondi, A. J. Phys. Chem. 1964, 68, 441. (13) Hrabie, J. A.; Srinivasan, A.; George, C.; Keefer, L. K. Tetrahedron Lett. 1998, 39, 5933. (14) Caveat: Diazonium salts with halides and other strongly nucleophilic counteranions are quite unstable in dry state and can be highly explosive. On the other hand, the use of low-nucleophilic counterions such as BF4- and PF6- dramatically increases the stability of the salts, and these are commonly employed in laboratory practice. (15) Cygler, M.; Przybylska, M.; Elofson, R. M. Can. J. Chem. 1982, 60, 2852.
Arenediazonium Salts as Versatile (meso-Ionic) Tectons (16) Groth, P. Acta Chem. Scand. 1981, A35, 541. (17) Rømming, C.; Tjorhorn, T. Acta Chem. Scand. 1968, 22, 2934. (18) Lindeman, S. V.; Kosynkin, D.; Kochi, J. K. J. Am. Chem. Soc. 1998, 120, 13268. (19) The positions of the hydrogen atoms in all structures were normalized to a standard “neutronographic” value of the C-H bond length of 1.095 Å. (20) (a) In charge-transfer crystals, packing of the donor (D) and acceptor (A) units can occur either in two separate DDD and AAA stacks (homosoric) or single alternating DADA stacks (heterosoric). See, e.g., (b) Dahm, D. J.; Johnson, G. R.; Miles, M. G.; Wilson, J. D. J. Cryst. Mol. Struct. 1975, 5, 27. (21) Andresen, O.; Rømming, C. Acta Chem. Scand. 1962, 16, 1882. (22) Kompan, O. E.; Antipin, M. Y.; Struchkov, Y. T.; Mikhailov, I. E.; Dushenko, G. A.; Olekhnovich, L. P.; Minkin, V. I. Zh. Org. Khim. 1985, 21, 2032. (23) McGilligan, B. S.; Arnold, J.; Wilkinson, G.; Hussain-Bates B.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1990, 2465. (24) Polynova, T. N.; Bokii, N. G.; Porai-Koshits, M. A. Zh. Strukt. Khim. 1965, 6, 841. (25) Sasvari, K.; Hess, H.; Schwarz, W. Cryst. Struct. Commun. 1982, 11, 781. (26) Wallis, J. D.; Dunitz, J. D. Helv. Chim. Acta 1984, 67, 1374. (27) Alcock, N. W.; Greenhough, T. J.; Hirst, D. M.; Kemp, T. J.; Payne, D. R. J. Chem. Soc., Perkin Trans. 2 1980, 8. (28) Horan, C. J.; Barnes, C. L.; Glaser, R. Acta Crystallogr. Sect. C: Cryst. Struct. Commun. 1993, C49, 507. (29) Zhu, S.-Z. J. Fluorine Chem. 1993, 62, 31. (30) Barbero, M.; Crisma, M.; Degani, I.; Fochi, R.; Perracino, P. Synthesis 1998, 1171. (31) Alberti, G.; Costantino, U. Layered Solids and Their Intercalation Chemistry in Comprehensive Supramolecular Chemistry; Lehn, J.-M., Ed.; Elsevier: New York, 1996; Vol 7. (32) The formation of the charge-transfer donor/acceptor complexes in the crystals of the dinitro derivative cannot be attributed to the π-acceptor properties of the arenediazonium moiety alone (even enhanced by the presence of two nitro substituents). The majority of other arenediazonium salts do not crystallize together with organic π-donors, and the weaker π-donor/acceptor association is hardly a factor capable of the separating the ionic layers on its own.
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(33)
(34)
(35)
(36)
Instead, we believe that close-packing issues should be considered as a main origin of donor intercalation. In the majority of aryldiazonium structures, the ionic layers partially interpenetrate in a ziplock manner (Figure 6A). This observation indicates that the size of protruding aryl groups is insufficient to provide close packing over the surface of the layers, and aryl groups from a neighboring layer enter into the voids between them (and vice versa). The efficient close packing in the ziplocked hydrophobic areas obviously depends on the match between van der Waals volumes of the aryl groups and separations between them. This is normally balanced (depending on size of anions that determines the distance between axes of the aryl groups in the ionic layers) by degree of folding of the layers and by the tilt of the aryl groups (cf. Figure 5, panels A and B). However, in the case of the bulky 3,5-dinitrosubstituted arene groups, the increased size of the groups and (consequently) decreased size of the separations between them make ziplocking between the layers less efficient. To compensate for the remaining voids between aryl groups, the preferred layered architecture must be either completely rearranged or some additional (donor) guest molecules must be incorporated to stabilize the structure. Apparently, the latter takes place in the intercalated structures in Figure 8A,B. (a) Some weaker σ-donor groups can also coordinate to the diazonium acceptor and lead to the replacement of the counteranion, e.g., the nitro group from a neighboring cation replaces one BF4- anion from the diazonium coordination shell in the structure of p-nitrobenzenediazonium tetrafluoroborate (O‚‚‚N distance of 2.97 Å). See Barnes, J. C.; Butler, A.; Anderson, L. Acta Crystallogr. Sect. C: Cryst. Struct. Commun. 1990, C46, 945. (b) Note that the p-xylene complex contains two essentially identical but symmetrically independent structural units.10 The solvate structure with acetonitrile is similar (albeit not isomorphous) to the structure with p-xylene in which the two solvent molecules replace each p-xylene donor moiety. The acetonitrile solvent molecules are more distant from the aromatic acceptor planes (4.06 Å), but form relatively strong H-bonds (C-H‚‚‚N) with their edges (H‚‚‚N 2.45 Å). The complex is isostructural but not isomorphous to the corresponding acetonitrile solvate crystallized in the absence of aromatic donors;35 see experimental section.
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