2,2′-Bipyridinium bis(perchlorate)

The title compound, [H₂bipy](ClO₄)₂ or C₁₀H₁₀N₂²⁺·2ClO₄⁻, was obtained at the interface between an organic (2,2′-bi­pyridine in methanol) and an aqueous phase (perchloric acid in water). The compound crystallizes in space group P and comprises discrete diprotonated trans-bipyridinium cations, [H₂bipy]²⁺, and ClO₄⁻ anions. The cations and anions are connected through N—H...O and C—H...O hydrogen bonds [distances N...O 2.817 (4) and 2.852 (4) Å, and C...O 3.225 (6)–3.412 (5)Å]. The C—C bond distance between the two rings is 1.452 (5) Å. The bipyridinium cation has a trans conformation and the N—C—C—N torsion angle is 152.0 (3)°.

S1. Comment

The conformations of 2,2'-bipyridine (bipy) and its protonated species constitute an important aspect in the understanding of the properties of this popular ligand in coordination chemistry. The 2,2'-bipyridine molecule is a nitrogen-donor ligand to metal ions (McWhinnie et al., 1969). It behaves as a weak base, often forming monoprotonated species. The stability constants are logK₁ = 4.43; log K₁ = K₂ = −0.5 (estimated)) (McWhinnie et al., 1969; Reddy et al., 1984). Hence, the [Hbipy]⁺ cation is more stable than the [H₂bipy]²⁺ dication in aqueous solution.

Recently, bipy and related bipyridines have attracted considerable attention (Howard, 1996; Lenstra et al., 1994). For bipy, the trans conformer is more stable than the cis, but the energy difference between the conformations is small (about 6 kJ mol⁻¹) and the cis/trans equilibrium can be shifted by the solvent and/or pH of the solution (Nakamoto, 1960). In the monoprotonated cation, i.e. [Hbipy]⁺, the cis conformer is more stable than the trans and the barrier for the trans/cis interconversion has been estimated to be about 14 kJ mol⁻¹ (Howard, 1996). In coordination compounds with metal ions, the cis conformer is usually found. 2,2'-Bipyridine exists in a trans conformation both in the solid state and in organic solvents (Cheng et al., 1972). The cis form of 2,2'-pyridylpyridinium can be found in 2,2'-bipyridine acidic solution. A weak N1···H—N2 hydrogen bond has been assumed to stabilize the cis conformation in the 2,2'-pyridylpyridinium cation, according to ab initio self consistent-field (SCF) calculations (Howard, 1996).

The crystal structures of 2,2'-bipyridine (Merritt et al., 1956; Felix et al., 1965) and 2,2'-pyridylpyridinium, [Hbipy](ClO₄) (Lipkowski et al., 1976), have been studied previously. Two crystal structure determinations of the diprotonated cation, i.e. [H₂bipy]²⁺, have been published with bromide (Nakatsu, 1972) and chloride (Troyanov et al., 1989). Usually, in coordination chemistry studies in aqueous solution, counter-anions are used which do not coordinate to the metal ion so that the equilibrium between the metal ion and the studied ligand (here bipy) is not disturbed. Therefore, in the present study, the diprotonated cation in its perchlorate compound was determined.

A crystal of 2,2'-bipyridinium diperchlorate, [H₂bipy](ClO₄)₂, (I), was obtained at the interface of a methanol and an aqueous solution. The C—C bond distance between the two rings is 1.452 (5) Å. The corresponding distance is 1.50 Å in 2,2'-bipyridine and 1.462 Å in 2,2'-pyridylpyridinium ion (see Fig. 1). The C—N—C angle increases by 7–9° on protonation from pyridyl to pyridinium (cf. Fig. 1). The C—N—C angles in the two rings of the 2,2'-bipyridinium cation increase by 7.1 and 7.6° compared with 2,2'-bipyridine. It is in good agreement with previous studies (Gillespie et al., 1957; Merritt et al., 1956; Bi-Cheng et al., 1970). The N—C—C—N torsion angles are 152.2 and −14.7° for (I) and [Hbipy](ClO₄) (Lipkowski et al., 1976), respectively. These values are also in good agreement with those found in [H₂bipy]Cl₂ (Troyanov et al., 1989) and [Hbipy](PF₆) (Milani et al., 1997) of −160.5 and −18.2°, respectively. The difference between the conformations of [H₂bipy]²⁺ and [Hbipy]⁺ is probably caused by the existence of an intramolecular N—H···N hydrogen bond in [Hbipy]⁺ cation and repulsion of H⁺ in [H₂bipy]²⁺. Five hydrogen bonds (types N—H···O and C—H···O) bind the two [H₂bipy]²⁺ cations and four ClO₄⁻ anions present in the unit cell of (I) (Fig. 2). The (C)—H···Y bond distances (Y = O, N, Cl) are much shorter than the sum of the corresponding van der Waals radii, which can be considered as weak hydrogen bonding (for a discussion of the existence of C—H···O hydrogen bonds, cf. Berkovitch-Yellin & Leiserovitz, 1984; Yanliang et al., 1999; Taylor & Kennard, 1982). The C—H···O hydrogen-bond distances in (I) are of the same order of magnitude as those reported previously (Taylor et al., 1982; Berkovitch-Yellin et al., 1984).

S2. Experimental

2,2'-Bipyridine (0.09 g, 0.6 mmol) was dissolved in methanol (1 ml) and the solution was placed in a thin tube (5 mm diameter). HClO₄ (1 ml, 1.0 mol l⁻¹) was added slowly into the tube through its inside wall. White block-shaped crystals grow at the interface after a few hours.

S3. Refinement

One of the O atoms of the ClO₄⁻ anion was disordered. All H atoms were localized from difference Fourier map and refined isotropically [C—H = 0.92 (4)–1.06 (3) Å]

Computing details

Data collection: CAD-4 VAX/PC (Enraf-Nonius, 1988); cell refinement: CAD-4 VAX/PC; data reduction: JANA98 (Petricek & Dusek, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. Experimental bond lengths (Å) and angles (°) for the protonated bipyridine species in solid (a) 2,2'-bipyridine (Merritt et al., 1956; s.u.'s not given), (b) 2,2'-pyridylpyridinium (Lipkowski et al., 1976) and (c) 2,2'-bipyridinium cation (present work).
	Fig. 2. ORTEPII (Johnson, 1976) drawing of a selected fragment of the structure of (I) (displacement ellipsoids are plotted at the 50% probability level) One of the disordered O82 atom has been omitted. [Symmetry codes: (i) −x, 1 − y, 1 − z; (ii) x, y, 1 + z.]

2,2'-bipyridinium diperchlorate

Crystal data

C10H10N2^2+·2ClO4^−	Z = 2
Mr = 357.10	F(000) = 364
Triclinic, P1	Dx = 1.736 Mg m^−3
a = 7.6042 (8) Å	Mo Kα radiation, λ = 0.71073 Å
b = 9.0007 (11) Å	Cell parameters from 24 reflections
c = 10.8647 (16) Å	θ = 13.7–16.0°
α = 97.974 (19)°	µ = 0.52 mm^−1
β = 98.50 (2)°	T = 293 K
γ = 108.63 (2)°	Block, colourless
V = 683.07 (15) Å^3	0.3 × 0.2 × 0.1 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	Rint = 0.000
Radiation source: fine-focus sealed tube	θmax = 26.0°, θmin = 1.9°
Graphite monochromator	h = −9→9
ω/2θ scans	k = −11→10
2696 measured reflections	l = 0→13
2696 independent reflections	3 standard reflections every 120 min
1811 reflections with I > 2σ(I)	intensity decay: −3%

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.048	Hydrogen site location: difference Fourier map
wR(F^2) = 0.148	Refine
S = 1.01	Calculated w = 1/[σ^2(Fo^2) + (0.0914P)^2] where P = (Fo^2 + 2Fc^2)/3
2696 reflections	(Δ/σ)max < 0.001
248 parameters	Δρmax = 0.30 e Å^−3
0 restraints	Δρmin = −0.45 e Å^−3

Special details

Experimental. 0.09 g (0.6 mmol) 2,2'-bipyridine was dissolved in 1 ml me thanol and the solution was placed in a thin tube(5 mm diameter). 1 ml 1.0 mol/L HClO₄ was slowly added into the tube through its inside-wall. White block crystals grow at the interface after few hours. One of the oxygen atoms ClO₄⁻ anion is disordered. All hydrogen atoms were localized from difference Fourier map and refine isotropically. Data collection: CAD-4 diffractometer (Enraf–Nonius). Data reduction: JANA-98 (Petricek, 1997). Program(s) used to solve the structure: SHELXS97 (Sheldrick, 1997a). Program used to refine structure: SHELXL97 (Sheldrick, 1997b). Molecular graphics: ORTEPII (Johnson, 1976). Software used to prepare material for publication: SHELXL97.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cl1	0.28745 (12)	0.52491 (9)	0.13366 (8)	0.0343 (2)
Cl2	0.19968 (13)	1.04083 (11)	0.37742 (9)	0.0405 (3)
O1	0.1115 (4)	0.5413 (3)	0.1554 (3)	0.0548 (8)
O2	0.4398 (4)	0.6480 (4)	0.2205 (3)	0.0681 (9)
O3	0.2914 (5)	0.3757 (3)	0.1544 (4)	0.0764 (11)
O4	0.3044 (5)	0.5404 (5)	0.0082 (3)	0.0765 (10)
O5	0.0948 (5)	1.1438 (4)	0.3636 (3)	0.0742 (10)
O6	0.0781 (6)	0.8828 (4)	0.3200 (4)	0.0944 (13)
O7	0.2660 (5)	1.0497 (4)	0.5089 (3)	0.0631 (9)
O81	0.358 (3)	1.108 (4)	0.323 (3)	0.097 (8)	0.50
O82	0.343 (4)	1.050 (5)	0.315 (3)	0.144 (13)	0.50
N1	0.1677 (4)	0.7730 (3)	0.8978 (3)	0.0335 (7)
N2	0.2367 (4)	0.7546 (4)	0.5796 (3)	0.0341 (7)
C1	0.1674 (6)	0.8641 (5)	1.0045 (4)	0.0418 (9)
C2	0.2400 (5)	1.0272 (4)	1.0200 (4)	0.0396 (9)
C3	0.3139 (5)	1.0913 (4)	0.9226 (4)	0.0402 (8)
C4	0.3177 (5)	0.9932 (4)	0.8144 (3)	0.0344 (8)
C5	0.2423 (4)	0.8298 (4)	0.8016 (3)	0.0305 (7)
C6	0.2424 (4)	0.7133 (4)	0.6948 (3)	0.0275 (7)
C7	0.2465 (6)	0.6608 (5)	0.4750 (4)	0.0409 (9)
C8	0.2582 (5)	0.5136 (4)	0.4809 (3)	0.0384 (8)
C9	0.2616 (5)	0.4648 (4)	0.5960 (4)	0.0393 (8)
C10	0.2562 (5)	0.5653 (4)	0.7045 (4)	0.0355 (8)
H1	0.117 (6)	0.681 (5)	0.892 (4)	0.061 (14)*
H2	0.113 (5)	0.823 (4)	1.069 (4)	0.042 (10)*
H3	0.234 (5)	1.088 (5)	1.094 (4)	0.047 (11)*
H4	0.383 (5)	1.212 (4)	0.938 (3)	0.038 (10)*
H5	0.355 (5)	1.024 (4)	0.728 (3)	0.031 (9)*
H6	0.227 (5)	0.850 (5)	0.572 (4)	0.049 (11)*
H7	0.235 (5)	0.707 (4)	0.395 (4)	0.045 (11)*
H8	0.287 (5)	0.447 (4)	0.407 (3)	0.030 (9)*
H9	0.268 (5)	0.360 (5)	0.592 (4)	0.046 (11)*
H10	0.256 (5)	0.542 (5)	0.784 (4)	0.048 (11)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.0427 (5)	0.0304 (4)	0.0315 (5)	0.0126 (3)	0.0110 (3)	0.0083 (3)
Cl2	0.0453 (5)	0.0477 (6)	0.0378 (5)	0.0239 (4)	0.0137 (4)	0.0144 (4)
O1	0.0447 (15)	0.0452 (16)	0.072 (2)	0.0124 (13)	0.0250 (14)	−0.0015 (14)
O2	0.0582 (18)	0.061 (2)	0.062 (2)	−0.0032 (15)	0.0065 (15)	−0.0012 (16)
O3	0.088 (2)	0.0407 (17)	0.113 (3)	0.0299 (17)	0.029 (2)	0.0269 (18)
O4	0.078 (2)	0.131 (3)	0.0409 (19)	0.050 (2)	0.0254 (17)	0.035 (2)
O5	0.076 (2)	0.0569 (19)	0.092 (3)	0.0391 (17)	−0.0090 (19)	0.0115 (17)
O6	0.120 (3)	0.048 (2)	0.101 (3)	0.032 (2)	−0.003 (2)	−0.0105 (18)
O7	0.103 (3)	0.0573 (18)	0.0339 (16)	0.0312 (17)	0.0124 (16)	0.0194 (13)
O81	0.034 (5)	0.201 (18)	0.067 (10)	0.026 (7)	0.035 (6)	0.072 (12)
O82	0.086 (13)	0.29 (4)	0.086 (11)	0.085 (18)	0.053 (10)	0.036 (16)
N1	0.0455 (17)	0.0234 (15)	0.0307 (17)	0.0088 (13)	0.0154 (13)	0.0023 (12)
N2	0.0464 (17)	0.0330 (15)	0.0263 (15)	0.0192 (13)	0.0060 (12)	0.0053 (12)
C1	0.053 (2)	0.042 (2)	0.037 (2)	0.0167 (17)	0.0240 (18)	0.0118 (16)
C2	0.049 (2)	0.039 (2)	0.030 (2)	0.0190 (17)	0.0082 (17)	−0.0029 (15)
C3	0.046 (2)	0.0280 (18)	0.039 (2)	0.0082 (16)	0.0058 (16)	−0.0036 (14)
C4	0.0454 (19)	0.0300 (17)	0.0273 (18)	0.0115 (15)	0.0138 (15)	0.0011 (13)
C5	0.0309 (16)	0.0364 (18)	0.0271 (18)	0.0129 (14)	0.0095 (13)	0.0095 (14)
C6	0.0286 (16)	0.0300 (16)	0.0214 (16)	0.0097 (13)	0.0030 (12)	0.0000 (12)
C7	0.057 (2)	0.046 (2)	0.028 (2)	0.0246 (18)	0.0179 (17)	0.0093 (16)
C8	0.054 (2)	0.0376 (19)	0.029 (2)	0.0240 (17)	0.0094 (16)	0.0035 (15)
C9	0.054 (2)	0.0349 (19)	0.034 (2)	0.0229 (17)	0.0108 (16)	0.0035 (15)
C10	0.0426 (19)	0.040 (2)	0.0282 (19)	0.0188 (15)	0.0091 (15)	0.0090 (15)

Geometric parameters (Å, º)

Cl1—O3	1.401 (3)	C1—H2	0.92 (4)
Cl1—O4	1.410 (3)	C2—C3	1.382 (5)
Cl1—O2	1.424 (3)	C2—H3	0.92 (4)
Cl1—O1	1.441 (3)	C3—C4	1.378 (5)
Cl2—O82	1.36 (3)	C3—H4	1.02 (4)
Cl2—O5	1.411 (3)	C4—C5	1.376 (5)
Cl2—O6	1.418 (4)	C4—H5	1.06 (3)
Cl2—O81	1.419 (17)	C5—C6	1.452 (5)
Cl2—O7	1.425 (3)	C6—C10	1.386 (5)
N1—C1	1.325 (5)	C7—C8	1.365 (5)
N1—C5	1.347 (4)	C7—H7	1.02 (4)
N1—H1	0.78 (4)	C8—C9	1.381 (5)
N2—C7	1.345 (4)	C8—H8	1.03 (4)
N2—C6	1.352 (4)	C9—C10	1.396 (5)
N2—H6	0.90 (4)	C9—H9	0.96 (4)
C1—C2	1.369 (5)	C10—H10	0.92 (4)
O3—Cl1—O4	110.5 (2)	C1—C2—H3	118 (3)
O3—Cl1—O2	109.2 (2)	C3—C2—H3	124 (3)
O4—Cl1—O2	109.6 (2)	C4—C3—C2	120.6 (3)
O3—Cl1—O1	109.61 (19)	C4—C3—H4	121 (2)
O4—Cl1—O1	109.3 (2)	C2—C3—H4	118 (2)
O2—Cl1—O1	108.62 (19)	C5—C4—C3	119.8 (3)
O82—Cl2—O5	120.0 (15)	C5—C4—H5	110.4 (18)
O82—Cl2—O6	99.1 (18)	C3—C4—H5	129.2 (18)
O5—Cl2—O6	108.0 (2)	N1—C5—C4	117.4 (3)
O82—Cl2—O81	20 (3)	N1—C5—C6	117.2 (3)
O5—Cl2—O81	103.5 (14)	C4—C5—C6	125.4 (3)
O6—Cl2—O81	117.0 (16)	N2—C6—C10	118.0 (3)
O82—Cl2—O7	109.6 (14)	N2—C6—C5	117.9 (3)
O5—Cl2—O7	109.6 (2)	C10—C6—C5	124.1 (3)
O6—Cl2—O7	109.9 (2)	N2—C7—C8	120.1 (3)
O81—Cl2—O7	108.5 (10)	N2—C7—H7	114 (2)
C1—N1—C5	124.2 (3)	C8—C7—H7	126 (2)
C1—N1—H1	115 (3)	C7—C8—C9	118.7 (3)
C5—N1—H1	121 (3)	C7—C8—H8	121.9 (19)
C7—N2—C6	123.5 (3)	C9—C8—H8	118.6 (19)
C7—N2—H6	118 (3)	C8—C9—C10	120.5 (3)
C6—N2—H6	119 (3)	C8—C9—H9	114 (2)
N1—C1—C2	119.9 (3)	C10—C9—H9	126 (2)
N1—C1—H2	123 (2)	C6—C10—C9	119.2 (3)
C2—C1—H2	117 (2)	C6—C10—H10	114 (2)
C1—C2—C3	118.0 (3)	C9—C10—H10	127 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1^i	0.78 (4)	2.13 (4)	2.862 (4)	157 (4)
N2—H6···O7	0.90 (4)	1.96 (4)	2.817 (4)	158 (4)
C4—H5···O7	1.06 (3)	2.45 (3)	3.412 (5)	151 (2)
C7—H7···O6	1.02 (4)	2.42 (4)	3.225 (6)	135 (3)
C10—H10···O4^ii	0.92 (4)	2.41 (4)	3.313 (5)	168 (3)

Symmetry codes: (i) −x, −y+1, −z+1; (ii) x, y, z+1.