Utilizing proton transfer to produce molecular salts in bromanilic acid substituted-pyridine molecular complexes-predictable synthons?

pharmaceuticals and natural products

Acta Crystallographica Section C

Crystal Structure

Communications

1. Introduction

Hydrogen bonding is one of the key interactions in the ﬁeld of

crystal engineering; the directional and predictable nature of

the formation of hydrogen bonds has allowed the controlled

growth of supramolecular assemblies in a range of areas,

including pharmaceuticals (Schultheiss & Newman, 2009),

porosity (Bojdys et al., 2011) and agrochemicals (Nauha et al.,

2011). While salt formation is a well-established route for

developing new solid forms of, for example, pharmaceuticals,

with modiﬁed physical properties (Childs et al., 2007), the

charge-assisted hydrogen bond is a much less studied inter-

action as a tool in crystal engineering (Ward, 2005). The use of

proton transfer as a design tool in the creation of (ionic)

molecular complexes is thus a potentially valuable element in

the design of molecular complexes, and it is this aspect of

crystal engineering that is investigated here.

ISSN 0108-2701

Utilizing proton transfer to produce

molecular salts in bromanilic acid

substituted-pyridine molecular

complexes – predictable synthons?

Lynne H. Thomas,^a* Martin S. Adam,^bAndrew O’Neill^b

and Chick C. Wilson^a

^aDepartment of Chemistry, University of Bath, Bath BA2 7AY, England, and ^bSchool

of Chemistry, University of Glasgow, Glasgow G12 8QQ, Scotland

Correspondence e-mail: l.h.thomas@bath.ac.uk

Received 3 October 2013

Accepted 26 October 2013

Controlled introduction of proton transfer into the design of a

series of molecular complexes is described, delivering the

systematic production of ionic molecular complexes (mol-

ecular salts). The controlled production of molecular salts has

relevance as a potential strategy in the design of pharmaceu-

tical materials. In nine molecular complexes consisting of

bromanilic acid with the N-heterocyclic compounds 2-, 3- and

4-picoline [bis(2/3/4-methylpyridinium) 2,5-dibromo-3,6-di-

oxocyclohexa-1,4-diene-1,4-diolate, 2C₆H₈N⁺ꢀC₆Br₂O₄^2ꢁ], 2,3-,

2,4-, 2,5- and 3,5-lutidine [2,3/2,4/2,5/3,5-dimethylpyridinium

2,5-dibromo-4-hydroxy-3,6-dioxocyclohexa-1,4-dien-1-olate,

C₇H₁₀N⁺ꢀC₆HBr₂O₄^ꢁ], and 3-bromo-4-methylpyridine [3-bromo-

4-methylpyridinium 2,5-dibromo-4-hydroxy-3,6-dioxocyclo-

hexa-1,4-dien-1-olate, C₆H₇BrN⁺ꢀC₆HBr₂O₄^ꢁ] and 2-bromo-

3-methylpyridine [2-bromo-3-methylpyridine–2,5-dibromo-3,6-

dihydroxycyclohexa-2,5-diene-1,4-dione (1/1), C₆H₆BrNꢀ

C₆H₂Br₂O₄], proton transfer occurs readily between the

bromanilic acid molecule and the N heteroatom of the

pyridine ring, in all cases producing a charge-assisted

bifurcated N—Hꢀ ꢀ ꢀO hydrogen bond. This reinforces the

value of this motif as a design tool in the crystal engineering of

such complexes. The protonation state (and stoichiometry)

signiﬁcantly affect the supramolecular synthons obtained, but

1:2 stoichiometries reliably give rise to PBP synthons and 1:1

stoichiometries to PBBP synthons (where P indicates a

methylpyridine co-molecule and B a bromanilic acid mol-

ecule). The inﬂuence of halogen interactions on the wider

crystal packing is also discussed, with C—Hꢀ ꢀ ꢀBr and Brꢀ ꢀ ꢀO

interactions the most prevalent; only one Brꢀ ꢀ ꢀBr interaction

is found.

Chloranilic acid (2,5-dichloro-3,6-dihydroxybenzoquinone)

has been widely studied as a co-component in multicomponent

solid forms. In contrast, bromanilic acid (2,5-dibromo-3,6-di-

hydroxybenzoquinone) is much less studied. Both have the

capacity to form molecular complexes in their deprotonated

Keywords: crystal structure; crystal engineering; hydrogen

bonding; proton transfer; lutidine salts; picoline salts;

bromanilic acid.

Acta Cryst. (2013). C69, 1279–1288

doi:10.1107/S0108270113029533

# 2013 International Union of Crystallography 1279

pharmaceuticals and natural products

Table 1

Experimental details.

Bis(2-picolinium) bromanilate

Bis(3-picolinium) bromanilate

Bis(4-picolinium) bromanilate

Crystal data

Chemical formula

M_r

2C₆H₈N⁺ꢀC₆Br₂O₄

2ꢁ

484.15

Monoclinic, P2₁/c

484.15

Monoclinic, P2₁/c

484.15

Monoclinic, P2₁/c

Crystal system, space group

Temperature (K)

100

16.3604 (13), 7.7452 (6), 14.3658 (9)

100

8.9526 (7), 9.6149 (8), 10.4275 (8)

100

8.1345 (8), 6.1517 (6), 17.7868 (17)

˚

a, b, c (A)

ꢀ (^ꢃ)

100.911 (3)

1787.4 (2)

103.935 (4)

871.17 (12)

96.177 (7)

884.90 (15)

3

˚

V (A )

Z

4

4.56

2

4.68

2

4.61

ꢁ (mm^ꢁ1

Crystal size (mm)

)

0.30 ꢄ 0.25 ꢄ 0.15

0.35 ꢄ 0.25 ꢄ 0.20

Data collection

Diffractometer

Bruker APEXII CCD area-detector

diffractometer

Bruker APEXII CCD area-detector

diffractometer

Bruker APEXII CCD area-detector

diffractometer

Absorption correction

Multi-scan (SADABS; Blessing,

1995)

0.567, 1.000

Multi-scan (SADABS; Blessing,

1995)

0.671, 1.000

Multi-scan (SADABS; Blessing,

1995)

0.576, 1.000

T_min, T_max

No. of measured, independent and

observed [I > 2ꢂ(I)] reﬂections

R_int

20956, 4883, 3506

9784, 2280, 2018

14105, 3234, 2464

0.056

29.4

0.690

0.033

28.9

0.679

0.047

32.8

0.763

ꢃ

_max(^ꢃ)

ꢁ1

˚

(sin ꢃ/ꢄ)_max(A

)

Reﬁnement

R[F²> 2ꢂ(F²)], wR(F²), S

No. of reﬂections

No. of parameters

0.033, 0.080, 1.00

4883

245

0.023, 0.061, 1.08

2280

123

0.034, 0.087, 1.06

3234

123

H-atom treatment

H atoms treated by a mixture of

independent and constrained

reﬁnement

0.64, ꢁ0.45

H atoms treated by a mixture of

independent and constrained

reﬁnement

0.45, ꢁ0.63

H atoms treated by a mixture of

independent and constrained

reﬁnement

0.82, ꢁ0.54

ꢁ3

˚

Áꢅ_max, Áꢅ_min(e A

)

2,4-Lutidinium bromanilate

2,5-Lutidinium bromanilate

3,5-Lutidinium bromanilate

Crystal data

Chemical formula

M_r

C₇H₁₀N⁺ꢀC₆HBr₂O₄

ꢁ

405.04

Monoclinic, P2₁/c

405.05

Monoclinic, P2₁/c

405.04

Monoclinic, P2₁/c

Crystal system, space group

Temperature (K)

100

8.2948 (2), 12.1560 (4), 13.9544 (5)

100

7.7357 (4), 11.1416 (6), 15.8011 (9)

100

11.6766 (5), 10.4926 (5), 11.5221 (5)

˚

a, b, c (A)

ꢀ (^ꢃ)

102.966 (2)

1371.17 (8)

94.269 (3)

1358.09 (13)

98.834 (2)

1394.92 (11)

3

˚

V (A )

Z

4

5.92

4

5.98

4

5.82

ꢁ (mm^ꢁ1

Crystal size (mm)

)

0.25 ꢄ 0.20 ꢄ 0.10

0.35 ꢄ 0.25 ꢄ 0.15

0.25 ꢄ 0.20 ꢄ 0.10

Data collection

Diffractometer

Bruker APEXII CCD area-detector

diffractometer

Bruker APEXII CCD area-detector

diffractometer

Bruker APEXII CCD area-detector

diffractometer

Absorption correction

Multi-scan (SADABS; Blessing,

1995)

0.631, 1.000

Multi-scan (SADABS; Blessing,

1995)

0.404, 1.000

Multi-scan (SADABS; Blessing,

1995)

0.684, 1.000

T_min, T_max

No. of measured, independent and

observed [I > 2ꢂ(I)] reﬂections

R_int

22482, 6064, 4537

38096, 9404, 6083

14020, 3817, 3131

0.042

36.0

0.826

0.058

42.1

0.943

0.031

31.5

0.736

ꢃ

_max(^ꢃ)

ꢁ1

˚

(sin ꢃ/ꢄ)_max(A

)

Reﬁnement

R[F²> 2ꢂ(F²)], wR(F²), S

No. of reﬂections

No. of parameters

0.032, 0.081, 1.02

6064

191

H atoms treated by a mixture of

independent and constrained

reﬁnement

0.043, 0.101, 1.03

9404

184

H-atom parameters constrained

0.027, 0.067, 1.05

3817

191

H atoms treated by a mixture of

independent and constrained

reﬁnement

H-atom treatment

ꢁ3

˚

Áꢅ_max, Áꢅ_min(e A

)

0.85, ꢁ0.56

1.34, ꢁ1.29

0.58, ꢁ0.45

3-Bromo-4-methylpyridinium

bromanilate

2,3-Lutidinium bromanilate

2-Bromo-3-methylpyridine–brom-

anilic acid (1/1)

ꢂ

1280 Thomas et al. Bromoanilate salts of picoline and lutidine

Acta Cryst. (2013). C69, 1279–1288

pharmaceuticals and natural products

Table 1 (continued)

3-Bromo-4-methylpyridinium

bromanilate

2,3-Lutidinium bromanilate

2-Bromo-3-methylpyridine–brom-

anilic acid (1/1)

Crystal data

Chemical formula

M_r

C₆H₇BrN⁺ꢀC₆HBr₂O₄

C₇H₁₀N⁺ꢀC₆HBr₂O₄

C₆H₆BrNꢀC₆H₂Br₂O₄

ꢁ

469.91

Monoclinic, P2₁/c

405.04

Monoclinic, P2₁/n

469.91

Monoclinic, P2₁/c

Crystal system, space group

Temperature (K)

100

10.2229 (4), 5.5760 (2), 24.5300 (9)

100

4.9786 (4), 23.181 (3), 12.2811 (13)

100

5.2866 (3), 13.3814 (8), 20.3576 (13)

91.556 (4)

1439.61 (15)

˚

a, b, c (A)

ꢀ (^ꢃ)

95.802 (3)

1391.12 (9)

100.794 (3)

1392.3 (2)

3

˚

V (A )

Z

4

8.71

4

5.83

4

8.42

ꢁ (mm^ꢁ1

Crystal size (mm)

)

0.25 ꢄ 0.15 ꢄ 0.10

0.20 ꢄ 0.10 ꢄ 0.05

0.25 ꢄ 0.20 ꢄ 0.10

Data collection

Diffractometer

Bruker APEXII CCD area-detector

diffractometer

Bruker APEXII CCD area-detector

diffractometer

Bruker APEXII CCD area-detector

diffractometer

Absorption correction

Multi-scan (SADABS; Blessing,

1995)

0.499, 1.000

Multi-scan (SADABS; Blessing,

1995)

0.791, 1.000

Multi-scan (SADABS; Blessing,

1995)

0.465, 1.000

T_min, T_max

No. of measured, independent and

observed [I > 2ꢂ(I)] reﬂections

R_int

19916, 4796, 3311

9783, 2053, 1664

14350, 3202, 2267

0.057

32.2

0.749

0.046

23.6

0.563

0.071

27.2

0.644

ꢃ

_max(^ꢃ)

ꢁ1

˚

(sin ꢃ/ꢄ)_max(A

)

Reﬁnement

R[F²> 2ꢂ(F²)], wR(F²), S

No. of reﬂections

0.041, 0.101, 1.04

4796

0.028, 0.065, 1.02

2053

0.039, 0.086, 1.03

3202

No. of parameters

No. of restraints

H-atom treatment

190

0

182

0

188

1

H atoms treated by a mixture of

independent and constrained

reﬁnement

1.23, ꢁ1.13

H atoms treated by a mixture of

independent and constrained

reﬁnement

H atoms treated by a mixture of

independent and constrained

reﬁnement

0.77, ꢁ0.67

ꢁ3

˚

Áꢅ_max, Áꢅ_min(e A

)

0.45, ꢁ0.32

Computer programs: APEX2 (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL2013 (Sheldrick, 2008) and SHELXL97 (Sheldrick, 2008).

forms, through the loss of protons from one or both of the

–OH groups. Bromanilic acid has been studied as a co-

component in a number of multicomponent molecular

complexes containing basic N heteroatoms to generate

extended hydrogen-bonded architectures [pyrazines (Tomura

& Yamashita, 2000), dipyridyls (Zaman et al., 2001), 2,2⁰-bi-

pyrimidine (Zaman et al., 2004) and self-contained isolated

supramolecular units such as 2-acetylpyridine (Thomas et al.,

2009)]. The ferroelectric properties of bromanilic complexes

have also been probed [phenazine (Horiuchi et al., 2005, 2009;

Kumai et al., 2007); 2,3,5,6-tetrakis(pyridin-2-yl)pyrazine

(Horiuchi et al., 2008)].

A previous study of the molecular complexes of chloranilic

acid with picolines (methylpyridines) focused speciﬁcally on

the use of proton transfer from chloranilic acid to the N atom

of the pyridine ring to form bifurcated charge-assisted

hydrogen bonds (Adam et al., 2010). The systematic transfer of

a proton within this hydrogen-bond motif was established as a

reproducible factor in predictable supramolecular synthons;

these synthons were not extended, with the primary hydrogen-

bonding interactions saturated within the supramolecular unit.

The synthons obtained were related to the stoichiometry (and

therefore the protonation state of the chloranilic acid mol-

ecule), with PCP units (where P denotes picoline, or more

generally in the present work the relevant methylpyridine, and

C denotes chloranilic acid) formed for 2:1 stoichiometries

(double deprotonation of the chloranilic acid) and PCCP units

formed for 1:1 stoichiometries and single deprotonation of the

chloranilic acid. This work is extended here to complexes of

bromanilic acid with substituted pyridines [including picolines

(methylpyridines), lutidines (dimethylpyridines) and bromo-

substituted variants], allowing a comparison to be made with

the complexes formed with chloranilic acid. While the primary

hydrogen-bonding interactions are saturated within the

synthons, the additional functionality of the halogen atoms

gives them the potential to inﬂuence the wider crystal packing.

Halogen interactions have been successfully utilized as addi-

tional directional interactions in the assembly of crystal

structures (Priimagi et al., 2013) and the effect of the Br atoms

in these complexes can be assessed. The introduction of

additional halogen substituents to the co-molecules also

allows the effect of competing intermolecular interactions

involving halogens to be assessed.

2. Experimental

2.1. Synthesis and crystallization

Bromanilic acid is a solid at room temperature. The co-

molecules are all volatile liquids at room temperature. Crystals

were therefore grown using an excess of the co-molecule.

Bis(2-picolinium) bromanilate crystals were grown by slow

evaporation of a methanol solution containing bromanilic acid

(12 mg) and 2-picoline (75 mg) at room temperature.

ꢂ

Acta Cryst. (2013). C69, 1279–1288

Thomas et al.

Bromoanilate salts of picoline and lutidine 1281

pharmaceuticals and natural products

Bis(3-picolinium) bromaniliate crystals were grown by slow

evaporation of a methanol–water solution (50:50 v/v) con-

taining bromalinic acid (8 mg) and 3-picoline (50 mg) at

278 K.

Bis(4-picolinium) bromanilate crystals were grown by slow

evaporation of a methanol–water solution (50:50 v/v) con-

taining bromanilic (8 mg) acid and 4-picoline (50 mg) at

278 K.

3. Results and discussion

Bromanilic acid is a strong acid and contains two protic –OH

groups. In molecular complexes, a variety of supramolecular

synthons can be formed, inﬂuenced by the multiple deproto-

nation states which bromanilic acid can adopt. It can exist as a

neutral molecule (BAH₂), a singly deprotonated negatively

charged anion (BAH^ꢁ) and a doubly deprotonated doubly

negatively charged anion (BA^2ꢁ).

2,3-Lutidinium bromanilate crystals were grown by slow

evaporation of a propan-2-ol solution containing bromanilic

acid (6 mg) and 2,3-lutidine (16 mg) at room temperature.

2,4-Lutidinium bromanilate crystals were grown by slow

evaporation of a methanol–water solution (50:50 v/v) con-

taining bromanilic acid (10 mg) and 2,4-lutidine (26 mg) at

room temperature.

2,5-Lutidinium bromanilate crystals were grown by slow

evaporation of a methanol–water solution (50:50 v/v) con-

taining bromanilic acid (8 mg) and 2,5-lutidine (22 mg) at

room temperature.

3,5-Lutidinium bromanilate crystals were grown by slow

evaporation of a propan-2-ol solution containing bromanilic

acid (10 mg) and 3,5-lutidine (26 mg) at room temperature.

2-Bromo-3-methylpyridine bromanilic acid crystals were

grown by slow evaporation of a methanol solution containing

bromanilic acid (10 mg) and 2-bromo-3-methylpyridine

(14 mg) at 278 K.

3-Bromo-4-methylpyridinium bromanilate crystals were

grown by slow evaporation of a methanol–water solution

(50:50 v/v) containing bromanilic acid (10 mg) and 3-bromo-4-

methylpyridine (14 mg) at room temperature.

Nine molecular complexes of bromanilic acid with substi-

tuted pyridines have been synthesized with varying stoichio-

metries and protonation states. These substituted pyridines

reﬂect a range of basicity and a range of steric bulk

surrounding the N-heterocycle. In general, anilic acid mol-

ecules readily donate H atoms to basic N atoms in multi-

component molecular complexes, and stoichiometry and the

consequent protonation state have a signiﬁcant effect on the

supramolecular synthons obtained. The nine molecular

complexes presented here ﬁt into three families: picoline

isomers (methylpyridines), lutidine isomers (dimethyl-

pyridines) and bromomethylpyridines. The picolines prefer-

entially crystallize with bromanilic acid in 2:1 stoichiometries,

whereas the lutidine isomers tend to crystallize in 1:1 stoi-

chiometries and consequently tend to form different supra-

molecular synthons. The bromomethylpyridines introduce the

additional possibility of further halogen bonding and form 1:1

complexes. However, one of the two complexes reported here

shows no proton transfer and so different synthons might be

expected.

3.1. Supramolecular synthons

3.1.1. PBP supramolecular synthons. Similar to chloranilic

ˇ

acid molecular complexes (Adam et al., 2010; Molcanov &

2.2. Refinement

´

Kojic-Prodic, 2010), 2:1 picoline–bromanilic acid molecular

complexes tend to give PBP (where P denotes the methyl-

pyridine co-molecule and B the bromanilic acid) supra-

molecular synthons (Fig. 1). These units are comprised of a

central doubly deprotonated bromanilic acid molecule sand-

wiched by two protonated (at the N heteroatom) picoline

molecules (Fig. 1). Bifurcated hydrogen bonds are formed

between the picoline NH⁺group and the two O atoms of the

BA^2ꢁanion. 2:1 molecular complexes of 3-picoline/4-picoline

with bromanilic acid form centrosymmetric PBP units which

are isostructural with the equivalent previously reported

chloranilic acid–picoline molecular complexes {chloranilic

acid–3-picoline form I [Cambridge Structural Database (CSD;

Allen, 2002) refcode VURWAH] and chloranilic acid–

4-picoline (VURSUX); Adam et al., 2010}.

Crystal data, data collection and structure reﬁnement

details are summarized in Table 1. C-bound H atoms were

positioned geometrically and treated as riding, with C—H =

˚

0.96 A and U_iso(H) = 1.5U_eq(C) for methyl H atoms, and

˚

C—H = 0.93 A and U_iso(H) = 1.2U_eq(C) otherwise. Except as

described below, N- and O-bound H atoms were located in

difference Fourier maps and reﬁned isotropically. For the 3,5-

and 2,3-lutidinium salts, the N- and O-bound H atoms were

positioned geometrically and treated as riding, with N—H =

˚

0.86 A and U_iso(H) = 1.2U_eq(N), and with O—H = 0.82 A and

U_iso(H) = 1.5U_eq(O). In the case of the 2-bromo-3-methyl-

pyridine complex, one hydroxy H atom (H1) was reﬁned with

˚

an O—H distance restraint of 0.82 (2) A and with U_iso(H) =

1.2U_eq(O).

Figure 1

PBP supramolecular synthons formed in 2:1 picoline–bromanilic acid complexes. Right to left: 2-picoline, 3-picoline and 4-picoline. Displacement

ellipsoids are drawn at the 50% probability level.

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1282 Thomas et al. Bromoanilate salts of picoline and lutidine

Acta Cryst. (2013). C69, 1279–1288

pharmaceuticals and natural products

Figure 2

The PBBP supramolecular synthon where the bromanilic acid molecule has been singly deprotonated. Top left: 2,4-lutidine; top right: 2,5-lutidine;

bottom left: 3,5-lutidine; bottom right: 3-bromo-4-methylpyridine. Displacement ellipsoids are drawn at the 50% probability level.

The bromanilic acid–2-picoline 1:2 complex represents an

anomaly in this series, where the PBP synthon is noncen-

trosymmetric; one 2-picoline molecule lies approximately in

the plane of the bromanilic acid molecule and the second is

signiﬁcantly twisted from the plane. In the CSD (Version 5.34,

with the November update), of 345 hits in which the chlor-

anilic acid molecule is doubly deprotonated, only three PCP

units are noncentrosymmetric [refcode EWOWUI (Ishida,

2004), pyrrolidinium; IZIHAA (Akhtaruzzaman et al., 2004),

4,7-bis(pyridin-4-yl)-2,1,3-benzothiadiazole trihydrate; and

TUQMAU (Hakim Al-arique et al., 2010), lansoprazole].

There are no reported noncentrosymmetric bromanilic acid

PBP units in the CSD, but there are considerably fewer

bromanilic acid complexes reported of any sort. There is no

obvious correlation between the co-molecules which give rise

to noncentrosymmetric units.

The relative orientations of the picoline molecules

compared with the bromanilic acid molecules are difﬁcult to

predict. It might be expected that a signiﬁcant relative rotation

of the rings would be found where the sterically bulky methyl

group is adjacent to the N heteroatom in the 2-position.

However, in this series of three complexes, the 2-picoline

complex has one 2-picoline molecule which is in approxi-

mately the same plane as the bromanilic acid molecule. This

results in a slightly longer bifurcated hydrogen bond on this

side of the bromanilic acid molecule and an additional Brꢀ ꢀ ꢀO

interaction is formed to the O atom with the strongest

hydrogen bond, in addition to a weak intra-synthon C—Hꢀ ꢀ ꢀO

hydrogen bond from the methyl group of the 2-picoline mol-

ecule. This synthon is also unusual as the major hydrogen

bonds comprising the bifurcated hydrogen bond are directed

towards two O atoms adjacent to the same Br atom; the

inversion centre dictates that this cannot be the case for the

other molecular complexes.

3.1.2. PBBP supramolecular synthons. Where the broma-

nilic acid is in its singly deprotonated state, a PBBP supra-

molecular synthon tends to be formed, with a centrosymmetric

bromanilic acid dimer ﬂanked by two co-molecules on either

side (Fig. 2). The relative orientations of the lutidine mol-

ecules on either side of the bromanilic acid dimer again do not

appear to be inﬂuenced by the steric bulk of a methyl group

adjacent to the N heteroatom, as all three of the lutidine

isomers (2,4-, 2,5- and 3,5-lutidine) lie in approximately the

same plane as the bromanilic acid dimer. In fact, the least

sterically inﬂuenced 3,5-lutidine shows the most signiﬁcant

shift from coplanarity and this may suggest that the weak

hydrogen bond formed between the methyl group and one of

the O atoms of the bromanilic acid molecule is a favourable

interaction and can only be formed where the methyl group is

adjacent to the N heteroatom, forcing the molecules to be

approximately coplanar.

Molecular complexes of chloranilic acid with 2,4-lutidine

and 2,5-lutidine have been reported previously (Ishida &

Kashino, 2002); the molecular complex of chloranilic acid with

Figure 3

Exceptions to the 1:1 or 2:1 patterns. Left: 2,3-lutidine 1:1; middle and right: 2-bromo-3-methylpyridine 1:1. Displacement ellipsoids are drawn at the 50%

probability level.

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Acta Cryst. (2013). C69, 1279–1288

Thomas et al.

Bromoanilate salts of picoline and lutidine 1283

pharmaceuticals and natural products

Table 2

Bond lengths (A) for the bromanilic acid molecule contrasting bromanilic

acid in its neutral form (CSD refcode VAGTUS; Robl, 1987) with the

doubly deprotonated bromanilic acid in 1:2 complexes with the picoline

isomers.

The 1:1 complex of 2-bromo-3-methylpyridine is the

exception in all of the complexes studied. In this case, there is

no proton transfer and this has a signiﬁcant impact on the

supramolecular synthons obtained. A PBP-type supramole-

cular unit is formed, similar to those complexes in which there

is a 2:1 stoichiometry, with a hydrogen bond formed between

the hydroxy groups on the bromanilic acid molecule and the N

heteroatom of the 2-bromo-3-methylpyridine molecule (Fig. 3,

middle). This unit is centrosymmetric and the H atom is pulled

away from the intramolecular hydrogen bond with the other O

atom of the bromanilic acid molecule. A second independent

bromanilic acid molecule forms hydrogen bonds to the

bromanilic acid molecule in the PBP unit and this forms chains

of bromanilic acid molecules along the b axis (Fig. 3, right).

˚

The numbering scheme is as in Fig. 4 and does not necessarily relate to the CIF

entries as some molecules have internal inversion symmetry. Entries marked

with an asterisk (*) are related by inversion symmetry to the other half of the

bromanilic acid molecule.

VAGTUS BAH₂2-Picoline BA^2ꢁ3-Picoline BA^2ꢁ4-Picoline BA^2ꢁ

C1—Br1 1.868 (4)

C1—C2 1.347 (6)

C2—O1 1.323 (5)

C2—C3 1.504 (5)

C3—O2 1.225 (5)

C3—C4 1.449 (5)

C4—Br2 1.868 (4)*

C4—C5 1.347 (6)*

C5—O3 1.323 (5)*

C5—C6 1.504 (5)*

C6—O4 1.225 (5)*

C1—C6 1.449 (5)*

1.905 (2)

1.394 (4)

1.260 (3)

1.547 (4)

1.251 (3)

1.402 (4)

1.905 (3)

1.400 (4)

1.249 (3)

1.559 (4)

1.249 (3)

1.407 (4)

1.9025 (18)

1.387 (2)

1.262 (2)

1.548 (3)

1.238 (2)

1.414 (2)

1.9025 (18)*

1.387 (2)*

1.262 (2)*

1.548 (3)*

1.238 (2)*

1.414 (2)*

1.902 (2)

1.399 (3)

1.246 (2)

1.554 (3)

1.246 (3)

1.405 (3)

1.902 (2)*

1.399 (3)*

1.246 (2)*

1.554 (3)*

1.246 (3)*

1.405 (3)*

3.2. The effect of deprotonation on the conjugation of the

bromanilic acid molecule

Regardless of whether the bromanilic acid molecule is

singly or doubly deprotonated, the delocalization of charge is

not located between two O atoms on the same side of the

molecule, but rather passes across, through the O1—C2—

C1—C6—O4 (and/or O2—C3—C4—C5—O3) linkage (Fig. 4,

left), as evidenced by variations in the bond lengths (Tables

2–4). In all cases, a clear C—C single bond is indicated by the

C2—C3 and C5—C6 bond lengths. In fact, these bond lengths

are elongated relative to the neutral molecule found in pure

bromanilic acid (CSD refcode VAGTUS; Robl, 1987), despite

the discrepancies between the structure determination

temperatures (100 K for the structures reported here, room

temperature for VAGTUS). For singly deprotonated broma-

nilic acid molecules (Table 3), one of the C—O distances

remains consistent with a single bond and can thus be deﬁned

as the remaining –OH group. Where deprotonation has

occurred, the C—O single-bond length shortens considerably

to somewhere intermediate between those expected for a

2,5-lutidine is isostructural with the equivalent bromanilic acid

complex. However, whilst the same supramolecular unit

(PCCP) is formed in the 2,4-lutidine–chloranilic acid complex,

the molecules are not coplanar and the bifurcated hydrogen

bond is signiﬁcantly more asymmetric [Nꢀ ꢀ ꢀO = 2.698 (3) and

˚

3.263 (3) A, cf. 2.847 (2) and 2.975 (2) A].

The 3-bromo-4-methylpyridine bromanilic acid molecular

complex does not form a coplanar PBBP supramolecular unit,

with the two molecules twisted by ꢅ80^ꢃrelative to each other.

3.1.3. Exceptions to the predictable supramolecular

synthons. The 1:1 molecular complex of 2,3-lutidine with

bromanilic acid is an exception to the 1:1 supramolecular

synthons: while a bifurcated hydrogen bond is still formed on

the deprotonated side of the bromanilic acid molecule, the

bromanilic acid homodimer does not form (Fig. 3, left).

Instead, the hydroxy group forms a stronger intramolecular

hydrogen bond (C—Oꢀ ꢀ ꢀH angle ꢅ105^ꢃversus ꢅ112^ꢃin a

PBBP complex) and forms weak interactions to a neigh-

single or a double bond. In addition, at least one of the C

O

double bonds increases (only one increases where there is only

a single deprotonation), and in some cases where there is

double deprotonation it is approximately equal in length to

the other C—O bond. When the molecule is neutral, C1—C2

˚

bouring Br atom [Oꢀ ꢀ ꢀBr = 3.422 (2) A]. The C O double

bond forms a bifurcated hydrogen bond with two C—H

groups on a neighbouring lutidine molecule.

Table 3

Bond lengths (A) for the bromanilic acid molecule contrasting bromanilic acid in its neutral form (CSD refcode VAGTUS; Robl, 1987) with the singly

deprotonated bromanilic acid in 1:1 complexes with the lutidine isomers.

˚

The numbering scheme is as in Fig. 4 and does not necessarily relate to the CIF entries as some molecules have internal inversion symmetry. Entries marked with an

asterisk (*) are related by inversion symmetry to the other half of the bromanilic acid molecule.

VAGTUS BAH₂

2,3-Lutidine BAH^ꢁ

2,4-Lutidine BAH^ꢁ

2,5-Lutidine BAH^ꢁ

3,5-Lutidine BAH^ꢁ

C1—Br1

C1—C2

C2—O1

C2—C3

C3—O2

C3—C4

C4—Br2

C4—C5

C5—O3

C5—C6

C6—O4

C1—C6

1.868 (4)

1.347 (6)

1.323 (5)

1.504 (5)

1.225 (5)

1.449 (5)

1.868 (4)*

1.347 (6)*

1.323 (5)*

1.504 (5)*

1.225 (5)*

1.449 (5)*

1.889 (4)

1.338 (5)

1.332 (4)

1.522 (6)

1.242 (4)

1.409 (6)

1.897 (4)

1.397 (5)

1.255 (5)

1.542 (6)

1.220 (5)

1.455 (6)

1.8753 (18)

1.353 (2)

1.3204 (19)

1.511 (2)

1.248 (2)

1.405 (2)

1.8907 (17)

1.405 (2)

1.2499 (19)

1.545 (2)

1.217 (2)

1.455 (2)

1.8792 (17)

1.352 (2)

1.3235 (19)

1.519 (2)

1.2495 (19)

1.398 (2)

1.8868 (17)

1.403 (2)

1.238 (2)

1.881 (2)

1.349 (3)

1.329 (3)

1.522 (3)

1.240 (3)

1.412 (3)

1.888 (2)

1.395 (3)

1.245 (2)

1.554 (3)

1.219 (3)

1.447 (3)

1.554 (2)

1.2224 (19)

1.447 (2)

ꢂ

1284 Thomas et al. Bromoanilate salts of picoline and lutidine

Acta Cryst. (2013). C69, 1279–1288

pharmaceuticals and natural products

between the relative orientations of the two molecules and the

degree of asymmetry in the bifurcated hydrogen bond.

In the cases where the bromanilic acid molecule is only

singly deprotonated, the major component of the bifurcated

N—Hꢀ ꢀ ꢀO hydrogen bond is directed towards the charged

side of the bromanilic acid molecule (indicated with the bond

angle closest to 180^ꢃ), with one exception, the complex with

2,5-lutidine. In this case, the most linear of the two hydrogen

bonds is towards the neutral half of the molecule and the

C

O double-bonded O atom. However, the shorter of the

two bond lengths is between the N—H group and the charged

side of the bromanilic acid molecule.

Figure 4

Left: labelling scheme used in Tables 2–4. Atom O1 is protonated when

the bromanilic acid molecule is singly deprotonated, and atoms O1 and

O3 are protonated when the bromanilic acid molecule is neutral. Middle:

charge delocalization for a singly deprotonated bromanilic acid molecule.

Right: charge delocalization for a doubly deprotonated bromanilic acid

molecule.

These singly deprotonated bromanilic acid molecules all

form a PBBP synthon, except the complex with 2,3-lutidine,

where two bromanilic acid molecules form a dimer connected

by two O—Hꢀ ꢀ ꢀO hydrogen bonds. There is some competition

between this intermolecular hydrogen bond and an intra-

molecular O—Hꢀ ꢀ ꢀO hydrogen bond within the bromanilic

acid molecule. The intermolecular hydrogen bond is the most

linear in all cases and the longest of the two interactions, with

one exception, the 2,4-lutidine complex, where the intra- and

intermolecular hydrogen bonds are approximately the same.

Again, there is no obvious relationship between the strengths

of these hydrogen bonds and the co-molecules.

The 2,3-lutidine bromanilic acid complex is the exception, in

which an N—Hꢀ ꢀ ꢀO bifurcated hydrogen bond is formed to

one side of the molecule but the bromanilic acid homodimer is

not formed. Instead, a shorter intramolecular O—Hꢀ ꢀ ꢀO

hydrogen bond is formed, along with a weak O—Hꢀ ꢀ ꢀBr

intermolecular hydrogen bond to a second bromanilic acid

molecule.

The 2-bromo-3-methylpyridine–bromanilic acid molecular

complex is the only one which does not show any proton

transfer and the bromanilic acid molecule is present in its

neutral state. One-dimensional hydrogen-bonded chains of

bromanilic acid molecules are formed, similar in both orien-

tation and strength to those found in pure bromanilic acid

(VAGTUS; Robl, 1987). There are two independent neutral

molecules. The ﬁrst has a shorter intramolecular O—Hꢀ ꢀ ꢀO

and C4—C5 are shorter, reﬂecting their double-bond char-

acter. On single deprotonation of O3, C3—C4 and C4—C5

equalize in length and C4—Br2 lengthens slightly, reﬂecting

the delocalization of charge across O2—C3—C4—C5—O3.

Where double deprotonation occurs, C1—C2 and C1—C6 also

equalize, reﬂecting the presence of two regions of negative

charge.

3.3. Hydrogen bonding within the supramolecular synthons

While there is some predictability in the supramolecular

synthons obtained in bromanilic acid complexes, the relative

orientation of the two co-molecules and the directionality of

the bifurcated hydrogen bonds is less easy to predict. Where

the molecules are far from coplanar, the N—H group of the

pyridine is able to approach closer to the bromanilic acid

molecule and the resulting bifurcated hydrogen bond is more

asymmetric (Table 5). This is well illustrated in the 2-picoline

complex, where an approximately coplanar and a twisted

conformation of the co-molecule are adopted within the same

supramolecular unit. However, there is no simple correlation

Table 4

Bond lengths (A) for the bromanilic acid molecule contrasting bromanilic acid in its neutral form (CSD refcode VAGTUS; Robl, 1987) with the doubly

deprotonated bromanilic acid in 1:1 complexes with the bromomethylpyridine isomers.

˚

The numbering scheme is as in Fig. 4 and does not necessarily relate to the CIF entries as some molecules have internal inversion symmetry. Entries marked with an

asterisk (*) are related by inversion symmetry to the other half of the bromanilic acid molecule. (i) and (ii) represent the two independent bromanilic acid

molecules in the 2-bromo-3-methylpyridine molecular complex.

VAGTUS BAH₂

2-Bromo-3-methylpyridine (i) BAH₂

2-Bromo-3-methylpyridine (ii) BAH₂

3-Bromo-4-methylpyridine BAH^ꢁ

C1—Br1

C1—C2

C2—O1

C2—C3

C3—O2

C3—C4

C4—Br2

C4—C5

C5—O3

C5—C6

C6—O4

C1—C6

1.868 (4)

1.347 (6)

1.323 (5)

1.504 (5)

1.225 (5)

1.449 (5)

1.868 (4)*

1.347 (6)*

1.323 (5)*

1.504 (5)*

1.225 (5)*

1.449 (5)*

1.882 (4)

1.346 (6)

1.322 (5)

1.517 (6)

1.223 (5)

1.453 (6)

1.882 (4)*

1.346 (6)*

1.322 (5)*

1.517 (6)*

1.223 (5)*

1.453 (6)*

1.886 (4)

1.353 (6)

1.308 (5)

1.527 (6)

1.230 (5)

1.437 (6)

1.886 (4)*

1.353 (6)*

1.308 (5)*

1.527 (6)*

1.231 (5)*

1.437 (6)*

1.894 (4)

1.347 (5)

1.327 (4)

1.517 (5)

1.243 (4)

1.420 (5)

1.894 (4)

1.390 (4)

1.266 (4)

1.531 (5)

1.234 (4)

1.442 (5)

ꢂ

Acta Cryst. (2013). C69, 1279–1288

Thomas et al.

Bromoanilate salts of picoline and lutidine 1285

pharmaceuticals and natural products

Table 5

Selected hydrogen-bond parameters (A, ).

hydrogen bond, and in addition this O—H group forms an

intermolecular O—Hꢀ ꢀ ꢀO hydrogen bond to the second

bromanilic acid molecule. The second bromanilic acid mol-

ecule forms a PBP unit similar to those found in the 2:1

molecular complexes, but with the H atom clearly located on

the O atom and with the N atom of the 2-bromo-3-methyl-

pyridine molecule acting as the hydrogen-bond acceptor. This

is the strongest hydrogen bond in the complex and the H atom

is pulled out of the intramolecular hydrogen bond, weakening

the latter.

ꢃ

˚

D—Hꢀ ꢀ ꢀA

D—H

Hꢀ ꢀ ꢀA

Dꢀ ꢀ ꢀA

D—Hꢀ ꢀ ꢀA

2-Picoline

N2—H2ꢀ ꢀ ꢀO4

N2—H2ꢀ ꢀ ꢀO3

N1—H1ꢀ ꢀ ꢀO1

N1—H1ꢀ ꢀ ꢀO2

0.86 (3)

0.77 (4)

2.02 (3)

2.36 (3)

1.96 (4)

2.36 (4)

2.838 (3)

2.946 (3)

2.693 (3)

2.828 (3)

159 (3)

126 (2)

160 (4)

121 (4)

3-Picoline

N1—H5ꢀ ꢀ ꢀO1

N1—H5ꢀ ꢀ ꢀO2ⁱ

C4—H4ꢀ ꢀ ꢀBr1ⁱⁱ

0.84 (3)

0.93

1.78 (3)

2.54 (3)

2.96

2.598 (2)

3.039 (2)

3.7977 (18)

165 (3)

119 (3)

151

4-Picoline

N1—H3ꢀ ꢀ ꢀO1

3.4. Halogen interactions

0.74 (3)

2.12 (3)

2.31 (3)

2.760 (3)

2.859 (3)

145 (4)

131 (3)

N1—H3ꢀ ꢀ ꢀO2

A range of halogen interactions are observed in these

complexes (Table 6), the most prevalent being weak C—

Hꢀ ꢀ ꢀBr hydrogen bonds and Brꢀ ꢀ ꢀO halogen interactions,

which occur at similar frequencies. The Brꢀ ꢀ ꢀO contacts also

show an almost equal preference for halogen bonds to the

neutral or charge-delocalized O atoms of the bromanilic acid

molecules. The shortest Brꢀ ꢀ ꢀO contact does not involve

charge and is found in the complex with 2-bromo-3-methyl-

2,4-Lutidine

O1—H1ꢀ ꢀ ꢀO2ⁱⁱⁱ

O1—H1ꢀ ꢀ ꢀO2

N1—H2ꢀ ꢀ ꢀO3^iv

N1—H2ꢀ ꢀ ꢀO4^iv

0.68 (3)

0.72 (2)

2.03 (3)

2.26 (3)

2.14 (2)

2.56 (2)

2.6509 (18)

2.6559 (19)

2.849 (2)

151 (3)

119 (3)

168 (3)

119 (2)

2.9807 (18)

2,5-Lutidine

O1—H1ꢀ ꢀ ꢀO2^v

O1—H1ꢀ ꢀ ꢀO2

N1—H1Aꢀ ꢀ ꢀO4

N1—H1Aꢀ ꢀ ꢀO3

0.82

0.86

2.01

2.16

2.17

2.34

2.6994 (17)

2.6403 (19)

2.9794 (19)

2.883 (2)

141

117

158

122

˚

pyridine [2.851 (3) A, cf. the sum of the van der Waals radii of

˚

3.3 A; Bondi, 1964]. There is only one complex which shows

3,5-Lutidine

N1—H2ꢀ ꢀ ꢀO3^vi

N1—H2ꢀ ꢀ ꢀO4^vi

O1—H1ꢀ ꢀ ꢀO2ⁱⁱⁱ

O1—H1ꢀ ꢀ ꢀO2

0.93 (3)

0.72 (3)

1.84 (3)

2.37 (3)

2.11 (3)

2.23 (3)

2.677 (3)

3.008 (3)

2.768 (3)

2.631 (2)

148 (3)

125 (3)

152 (3)

116 (3)

Brꢀ ꢀ ꢀBr contacts, that with 2,4-lutidine; the observed Brꢀ ꢀ ꢀBr

˚

distance of 3.6195 (4) A is at the weak end of these inter-

actions but is still signiﬁcantly less than the sum of the van der

˚

Waals radii of two Br atoms (3.7 A).

3-Bromo-4-methylpyridine

O1—H1ꢀ ꢀ ꢀO2^vii

Bromomethylpyridines were chosen as co-molecules with

the expectation that increasing the number of Br atoms might

increase the number of halogen interactions, speciﬁcally

favouring halogen–halogen interactions. However, in the two

complexes reported here, no Brꢀ ꢀ ꢀBr interactions are found

and the 2-bromo-3-methylpyridine complex only shows one Br

interaction with an O atom, with two of the three Br atoms not

participating in any interactions. The 3-bromo-4-methyl-

pyridine complex contains three independent Br atoms and

each one participates in one Br interaction, one very weak C—

0.87 (5)

0.79 (5)

1.97 (5)

2.12 (4)

1.91 (5)

2.53 (5)

2.717 (3)

2.637 (4)

2.675 (4)

2.915 (4)

144 (4)

118 (4)

161 (5)

112 (4)

O1—H1ꢀ ꢀ ꢀO2

N1—H5ꢀ ꢀ ꢀO3^viii

N1—H5ꢀ ꢀ ꢀO4^viii

2,3-Lutidine

O1—H1ꢀ ꢀ ꢀO2

O1—H1ꢀ ꢀ ꢀBr1^ix

N1—H1Aꢀ ꢀ ꢀO3^x

N1—H1Aꢀ ꢀ ꢀO4^x

0.82

0.86

2.13

2.82

1.93

2.54

2.611 (4)

3.423 (3)

2.777 (4)

3.043 (4)

117

132

168

119

2-Bromo-3-methylpyridine

O1—H1ꢀ ꢀ ꢀO4

0.857 (19)

0.92 (5)

2.01 (3)

2.15 (5)

1.73 (5)

2.794 (4)

2.638 (5)

2.619 (5)

151 (5)

115 (4)

163 (5)

O1—H1ꢀ ꢀ ꢀO2^xi

˚

Hꢀ ꢀ ꢀBr hydrogen bond [Cꢀ ꢀ ꢀBr = 3.940 (4) A] and two Brꢀ ꢀ ꢀO

O3—H2ꢀ ꢀ ꢀN1

contacts.

Symmetry codes: (i) ꢁx + 1, ꢁy + 1, ꢁz; (ii) ꢁx + 1, y + ¹₂, ꢁz + ₂¹; (iii) ꢁx + 1, ꢁy, ꢁz + 1;

(iv) x ꢁ 1, y, z; (v) ꢁx, ꢁy, ꢁz; (vi) ꢁx, ꢁy + 1, ꢁz + 1; (vii) ꢁx, ꢁy, ꢁz + 2; (viii) ꢁx + 1,

y ꢁ ¹₂, ꢁz + ₂³; (ix) x + ₂¹, ꢁy + ¹₂, z + ¹₂; (x) x + 1, y, z; (xi) ꢁx + 1, ꢁy + 1, ꢁz + 1.

3.5. Crystal packing

While the functional groups differ and are in different

relative positions on the co-molecule, there are some simila-

rities in the global packing of these nine molecular complexes.

All of them show layers of alternating bromanilic acid and co-

molecule, the thickness of which varies depending on the

stoichiometries and the relative orientations of the molecules

(Fig. 5). Some of the layers are interwoven (e.g. 2,4-lutidine

and 3,5-lutidine) and some take a wave-like form (4-picoline,

2,3-lutidine, 3,5-lutidine and 3-bromo-4-methylpyridine).

The primary hydrogen-bonding interactions are contained

within the supramolecular units (PBP or PBBP), with the

exception of the 2-bromo-3-methylpyridine complex which

features extended bromanilic hydrogen-bonded chains. The

interactions within the extended structures are therefore

primarily weak in nature and, in addition to the halogen

Table 6

A summary of the Br interactions in the molecular complexes with

bromanilic acid.

Brꢀ ꢀ ꢀBr Brꢀ ꢀ ꢀO

C—Hꢀ ꢀ ꢀBr Brꢀ ꢀ ꢀꢆ O—Hꢀ ꢀ ꢀBr

VAGTUS (Robl,

1987)

2-Picoline

3-Picoline

4-Picoline

2,3-Lutidine

2,4-Lutidine

2,5-Lutidine

3,5-Lutidine

2-Bromo-3-methyl-

pyridine

Yes

ꢄ

Yes

ꢄ

Yes

ꢄ

Yes

ꢄ

Yes (ꢄ2)

ꢄ

Yes

ꢄ

Yes

ꢄ

Yes

ꢄ

Yes

ꢄ

Yes (ꢄ4)

Yes (ꢄ2)

ꢄ

Yes

ꢄ

3-Bromo-4-methyl-

pyridine

ꢄ

Yes (ꢄ2) Yes

ꢄ

ꢂ

1286 Thomas et al. Bromoanilate salts of picoline and lutidine

Acta Cryst. (2013). C69, 1279–1288

pharmaceuticals and natural products

Figure 5

The crystal packing in the nine title bromanilic acid molecular complexes, coloured by symmetry-equivalent molecules. All molecular complexes show a

layered structure, with some showing more interweaving of the layers than others. 2-Picoline is viewed along the b axis, with bromanilic acid blue, and

2-picoline molecules red (twisted) and green (coplanar). 3-Picoline and 4-picoline are viewed along the c axis, with bromanilic acid blue and picoline

green. For the lutidines, bromanilic acid is shown in green, and lutidine blue. 2,3-Lutidine and 2,4-lutidine are viewed along the a axis, 2,5-lutidine along

the b axis and 3,5-lutidine along the c axis. 2-Bromo-3-methylpyridine is viewed along the a axis, with bromanilic acid green and blue, and 2-bromo-3-

methylpyridine red. 3-Bromo-4-methylpyridine is viewed along the c axis, with bromanilic acid green and 3-bromo-4-methylpyridine blue. (All colours

refer to the electronic version of the paper.)

interactions (discussed in x3.4), feature C—Hꢀ ꢀ ꢀO, C—Hꢀ ꢀ ꢀꢆ

and ꢆ–ꢆ interactions.

only C—Hꢀ ꢀ ꢀꢆ and Oꢀ ꢀ ꢀꢆ interactions are found. There are

also no ꢆ–ꢆ interactions in the 3-picoline complex, but they

are found in all six remaining complexes, reﬂecting a range of

interactions between the same type of molecule (e.g. brom-

anilic acid to bromanilic acid) or between bromanilic acid and

the co-molecule (2-picoline, 2,5-lutidine or 3-bromo-4-

methylpyridine). The bromanilic acid–2-picoline complex

stacks in pairs of hydrogen-bonded 2-picoline–bromanilic acid

coplanar units in a head-to-tail manner. 2,5-Lutidine–broma-

nilic acid forms stacks of four molecules within the PBBP

synthon and the ꢆ-stacking in the 4-picoline complex is limited

to pairs of bromanilic acid molecules.

The methyl groups play both a steric and a connectivity role

in the crystal packing through weak hydrogen bonds. The

primary interactions formed by the methyl groups are weak C—

Hꢀ ꢀ ꢀO hydrogen bonds, with ﬁve of the nine complexes showing

a weak C—Hꢀ ꢀ ꢀBr hydrogen bond and three showing C—Hꢀ ꢀ ꢀꢆ

hydrogen bonds. None of the complexes shows a saturation of

hydrogen bonding involving the methyl group, rather showing

one or two weak hydrogen bonds per methyl group.

In general, C—Hꢀ ꢀ ꢀO interactions are found in all nine

complexes, except the 2,5- and 3,5-lutidine complexes where

ꢂ

Acta Cryst. (2013). C69, 1279–1288

Thomas et al.

Bromoanilate salts of picoline and lutidine 1287

pharmaceuticals and natural products

Hꢀ ꢀ ꢀBr hydrogen bonds and Oꢀ ꢀ ꢀBr halogen interactions.

Only one Brꢀ ꢀ ꢀBr interaction is found, in the 2,4-lutidine

molecular complex.

Despite the signiﬁcantly different interactions and the

overall packing of the supramolecular synthons into the

crystal structures, there is a clear recurrence of layers of

bromanilic acid and co-molecules. These take different forms,

with some linear and some wave-like, and some show inter-

penetration.

Proton transfer to generate charge-assisted hydrogen

bonding can clearly be used as a tool in crystal engineering for

reliably producing predictable supramolecular synthons, and

reinforces the utility of controlled introduction of proton

transfer into this design, allowing the production of ionic

molecular complexes or molecular salts. The use of molecules

which have multiple protonation or deprotonation states can

also lead to a more diverse range of synthons with potentially

different physical properties.

4. Conclusions

Nine new bromanilic acid methylpyridine molecular com-

plexes have been reported. Proton transfer from the broma-

nilic acid molecule to the N heteroatom of the pyridine

molecule is a common feature, occurring in all but one of the

molecular complexes. The different possible protonation

states of the bromanilic acid molecule (the two acidic OH

groups) allow the formation of different supramolecular

synthons. 2:1 stoichiometries (i.e. double deprotonation) give

rise to a PBP unit and 1:1 stoichiometries (i.e. single depro-

tonation) give a PBBP unit, including a hydrogen-bonded

dimer of bromanilic acid molecules. All complexes where

proton transfer has occurred form charge-assisted bifurcated

hydrogen bonds between the deprotonated bromanilic acid

molecule and the protonated N heteroatom of the pyridine

ring. This shows the predictability of this interaction in these

systems and demonstrates that such a synthon can be reliably

designed into a crystal structure.

While it is possible to predict the formation of this synthon,

it does not appear to be possible to predict the relative

orientations of the bromanilic acid molecule and the co-mol-

ecule. The presence of a methyl group on the 2-position does

tend to result in a coplanar arrangement of the molecules, due

to the formation of a weak intra-synthon C—Hꢀ ꢀ ꢀO hydrogen

bond between the methyl group and one of the O atoms of the

bromanilic acid molecule. The 2-picoline complex is unusual

as a PBP synthon, as the unit is not centrosymmetric and only

one weak intra-synthon C—Hꢀ ꢀ ꢀO hydrogen bond is formed

on one side of the bromanilic acid molecule. Where the mol-

ecules of the supramolecular synthon are not coplanar, the

bifurcated hydrogen bond tends to be asymmetric, with one

hydrogen bond dominating over the other. Where they are

approximately coplanar, the two hydrogen-bond lengths are

more similar.

There are two exceptions to the PBP and PBBP synthons.

The 2,3-lutidine molecular complex does show the bifurcated

charge-assisted hydrogen bond between the N heteroatom of

the pyridine ring and the O atoms of the singly deprotonated

bromanilic acid molecule, but the bromanilic acid dimer does

not form. In contrast, there is no proton transfer in the 2-

bromo-3-methylpyridine molecular complex and therefore the

bifurcated N—Hꢀ ꢀ ꢀO hydrogen bonds do not form. Despite

this, a PBP unit is formed, with an intramolecular O—Hꢀ ꢀ ꢀN

hydrogen bond to the 2-bromo-3-methylpyrdine molecule

which competes with an intramolecular O—Hꢀ ꢀ ꢀO hydrogen

bond. However, the stoichiometry of the complex is 1:1, not

2:1, and the second bromanilic acid molecule connects the

PBP units into an extended structure through O—Hꢀ ꢀ ꢀO

hydrogen bonds, creating a bromanilic acid chain.

MSA and AON were funded by the University of Glasgow.

Supplementary data for this paper are available from the IUCr electronic

archives (Reference: FM3015). Services for accessing these data are

described at the back of the journal.

References

Adam, M. S., Parkin, A., Thomas, L. H. & Wilson, C. C. (2010). CrystEng-

Comm , 12 , 917–924.

Akhtaruzzaman, M., T o mura, M., Nishida, J. & Yamashita, Y . (2004). J. Org.

Chem. 69 , 2953–2958.

Allen, F . H . (2002). Acta Cryst. B 58 , 380–388.

Blessing, R. H. (1995). Acta Cryst. A 51 , 33–38.

Bojdys, M. J., Briggs, M. E., Jones, J. T. A., Adams, D. J., Chong, S. Y.,

Schmidtmann, M. & Cooper, A. I. (2011). J. Am. Chem. Soc. 133 , 16566–

16571.

Bondi, A. (1964). J. Phys. Chem. 68 , 441–451.

Bruker (2009). APEX . Bruker AXS Inc., Madison, Wisconsin, USA.

Childs, S. L., Stahly, G. P . & P ark, A. (2007). Mol. Pharm. 4 , 323–338.

Hakim Al-arique, Q. N. M., Jasinski, J. P ., Butcher, R. J., Yathirajan, H. S. &

Narayana, B. (2010). Acta Cryst. E 66 , o1507–o1508.

Horiuchi, S., Kumai, R., Tokunaga, Y . & T o kura, Y . (2008). J. Am. Chem. Soc.

130 , 13382–13391.

Horiuchi, S., Kumai, R. & T o kura, Y . (2005). J. Am. Chem. Soc. 127 , 5010–

5011.

Horiuchi, S., Kumai, R. & Tokura, Y . (2009). J. Mater. Chem. 19 , 4421–4434.

Ishida, H. (2004). Acta Cryst. E 60 , o974–o976.

Ishida, H. & Kashino, S. (2002). Z. Naturforsch. Teil A , 57 , 829–836.

Kumai, R., Horiuchi, S., Sagayama, H., Arima, T.-H., Watanabe, M., Noda, Y .

& T o kura, Y . (2007). J. Am. Chem. Soc. 129 , 12920–12921.

ˇ

´

Molcanov, K. & Kojic-Prodic, B. (2010). CrystEngComm , 12 , 925–939.

Nauha, E., Kolehmainen, E. & Nissinen, M. (2011). CrystEngComm , 13 , 6531–

6537.

Priimagi, A., Cavallo, G., Metrangolo, P . & R esnati, G. (2013). Acc. Chem. Res.

30 , doi:10.1021/ar400103r.

Robl, C. (1987). Z. Kristallogr. 180 , 249–253.

Schultheiss, N. & Newman, A. (2009). Cryst. Growth Des. 9 , 2950–2967.

Sheldrick, G. M. (2008). Acta Cryst. A 64 , 112–122.

Thomas, L. H. et al. (2009). Acta Cryst. E 65 , o1218.

T o mura, M. & Yamashita, Y . (2000). CrystEngComm , 2 , 92–95.

Ward, M. D. (2005). Chem. Commun. pp. 5838–5842.

Zaman, M. B., Tomura, M. & Yamashita, Y . (2001). J. Org. Chem. 66 , 5987–

5995.

Introducing additional Br atoms into the complexes by

using brominated co-molecules does not, in the two cases

reported here, induce the introduction of Brꢀ ꢀ ꢀBr interactions.

In fact, the frequency of formation of halogen interactions of

any kind does not appear to be increased. The prevalent

bromine interactions in this series of complexes are weak C—

Zaman, M. B., Udachin, K. A. & Ripmeester, J. A. (2004). Cryst. Growth Des.

4 , 585–589.

ꢂ

1288 Thomas et al. Bromoanilate salts of picoline and lutidine

Acta Cryst. (2013). C69, 1279–1288

supplementary materials

Acta Cryst. (2013). C69, 1279-1288 [doi:10.1107/S0108270113029533]

Utilizing proton transfer to produce molecular salts in bromanilic acid

substituted-pyridine molecular complexes – predictable synthons?

Lynne H. Thomas, Martin S. Adam, Andrew O′Neill and Chick C. Wilson

Computing details

For all compounds, data collection: APEX2 (Bruker, 2009); cell refinement: APEX2 (Bruker, 2009); data reduction:

APEX2 (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008). Program(s) used to refine

structure: SHELXL2013 (Sheldrick, 2008) for ba2pic_100k_1-1, ba24lut, ba_3br4mepyr; SHELXL97 (Sheldrick, 2008)

for ba3pic100k1121apr_0m, br3p14jan_0m, ba25lut_100k_11aug_0m, ba_35lut, ba23lut, ba_2br3mepyr.

(ba2pic_100k_1-1) Bis(2-picolinium) bromanilate

Crystal data

2C₆H₈N⁺·C₆Br₂O₄²⁻

M_r= 484.15

Z = 4

F(000) = 960

D_x= 1.799 Mg m⁻³

Mo Kα radiation, λ = 0.71073 Å

µ = 4.56 mm⁻¹

T = 100 K

Block, purple

0.3 × 0.25 × 0.15 mm

Monoclinic, P2₁/c

Hall symbol: -P 2ybc

a = 16.3604 (13) Å

b = 7.7452 (6) Å

c = 14.3658 (9) Å

β = 100.911 (3)°

V = 1787.4 (2) Å³

Data collection

Bruker APEXII CCD area-detector

diffractometer

CCD; rotation images scans

Absorption correction: multi-scan

(SADABS; Blessing, 1995)

4883 independent reflections

3506 reflections with I > 2σ(I)

R_int= 0.056

θ

_max= 29.4°, θ_min= 1.3°

h = −22→22

k = −10→10

l = −19→17

T

_min= 0.567, T_max= 1.000

20956 measured reflections

Refinement

Refinement on F²

Least-squares matrix: full

R[F²> 2σ(F²)] = 0.033

wR(F²) = 0.080

S = 1.00

4883 reflections

245 parameters

0 restraints

Hydrogen site location: mixed

H atoms treated by a mixture of independent

and constrained refinement

w = 1/[σ²(F_o²) + (0.0356P)²]

where P = (F_o²+ 2F_c²)/3

(Δ/σ)_max= 0.001

Δρ_max= 0.64 e Å⁻³

Δρ_min= −0.45 e Å⁻³

Acta Cryst. (2013). C69, 1279-1288

sup-1

supplementary materials

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance

matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles;

correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate

(isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²)

x

y

z

U_iso*/U_eq

C14

H14

N2

0.37734 (17)

0.3549

0.6533 (4)

0.6463

0.6404 (2)

0.6951

0.0225 (6)

0.027*

0.47738 (15)

0.5221 (18)

0.44575 (17)

0.37626 (17)

0.353

0.7632 (3)

0.819 (3)

0.7605 (3)

0.5683 (3)

0.5058

0.55824 (16)

0.555 (2)

0.0154 (5)

0.014 (8)*

0.0182 (6)

0.0198 (6)

0.024*

H2

C13

C16

H16

C17

H17

C15

H15

C18

H18A

H18B

H18C

Br1

Br2

O3

0.6381 (2)

0.4798 (2)

0.426

0.44378 (18)

0.467

0.6720 (3)

0.6799

0.4803 (2)

0.4261

0.0190 (6)

0.023*

0.34340 (18)

0.298

0.5586 (4)

0.4873

0.5619 (2)

0.5637

0.0228 (6)

0.027*

0.48453 (18)

0.518

0.8700 (4)

0.7995

0.7190 (2)

0.7665

0.0233 (6)

0.035*

0.4418

0.9256

0.7457

0.035*

0.5189

0.956

0.6974

0.035*

0.77406 (2)

0.69958 (2)

0.59107 (12)

0.87359 (12)

0.84955 (12)

0.62485 (11)

0.65969 (16)

0.67803 (17)

0.71999 (16)

0.80862 (16)

0.75152 (17)

0.79362 (16)

0.96988 (16)

0.934 (3)

1.20048 (3)

0.79178 (3)

0.8222 (2)

1.1929 (2)

1.0180 (3)

0.9647 (2)

0.8970 (3)

0.9850 (3)

0.9081 (3)

1.1020 (3)

1.0828 (3)

1.0039 (3)

1.2838 (3)

1.254 (5)

1.2292 (4)

1.1531

0.68748 (2)

0.26985 (2)

0.42497 (13)

0.52699 (13)

0.36536 (13)

0.59632 (13)

0.44594 (18)

0.54532 (18)

0.38883 (18)

0.50893 (18)

0.56894 (18)

0.41342 (18)

0.40231 (18)

0.426 (3)

0.01821 (8)

0.01666 (8)

0.0183 (4)

0.0204 (4)

0.0235 (5)

0.0184 (4)

0.0136 (5)

0.0143 (5)

0.0147 (5)

0.0154 (5)

0.0151 (5)

0.0191 (5)

0.058 (14)*

0.0225 (6)

0.027*

O1

O2

O4

C5

C6

C4

C2

C1

C3

N1

H1

C10

H10

C9

1.09443 (19)

1.1357

0.3478 (2)

0.3371

1.09745 (17)

1.1408

1.4029 (4)

1.4444

0.32392 (18)

0.2966

0.0206 (6)

0.025*

H9

C8

1.03543 (17)

1.0379

1.5140 (3)

1.6305

0.34108 (18)

0.3262

0.0191 (6)

0.023*

H8

C7

0.97025 (17)

1.02907 (18)

1.0258

1.4529 (3)

1.1726 (3)

1.057

0.37997 (18)

0.3874 (2)

0.4039

0.0166 (5)

0.0202 (6)

0.024*

C11

H11

C12

H12A

0.89918 (18)

0.8514

1.5601 (4)

1.5385

0.3976 (2)

0.3489

0.0241 (6)

0.036*

Acta Cryst. (2013). C69, 1279-1288

sup-2

supplementary materials

H12B

H12C

0.9139

0.8865

1.6801

1.531

0.397

0.036*

0.4582

Atomic displacement parameters (Å²)

U¹¹

U²²

U³³

U¹²

U¹³

U²³

C14

N2

0.0175 (15)

0.0142 (12)

0.0193 (15)

0.0147 (14)

0.0188 (15)

0.0176 (15)

0.0213 (16)

0.02134 (16)

0.01661 (15)

0.0170 (10)

0.0224 (11)

0.0206 (11)

0.0168 (10)

0.0127 (13)

0.0184 (15)

0.0160 (14)

0.0169 (14)

0.0206 (15)

0.0159 (14)

0.0160 (13)

0.0236 (16)

0.0181 (15)

0.0224 (15)

0.0177 (14)

0.0210 (15)

0.0243 (16)

0.0271 (15)

0.0156 (11)

0.0181 (13)

0.0196 (13)

0.0183 (13)

0.0217 (14)

0.0280 (15)

0.02129 (14)

0.01926 (13)

0.0197 (10)

0.0223 (10)

0.0298 (11)

0.0237 (10)

0.0112 (11)

0.0126 (11)

0.0172 (12)

0.0139 (12)

0.0148 (12)

0.0157 (12)

0.0221 (12)

0.0272 (15)

0.0298 (15)

0.0179 (13)

0.0198 (13)

0.0169 (13)

0.0285 (15)

0.0244 (16)

0.0167 (12)

0.0176 (14)

0.0248 (15)

0.0201 (15)

0.0305 (17)

0.0206 (15)

0.01274 (14)

0.01452 (14)

0.0187 (10)

0.0176 (10)

0.0226 (11)

0.0166 (10)

0.0170 (13)

0.0127 (13)

0.0108 (13)

0.0155 (13)

0.0111 (13)

0.0145 (13)

0.0198 (13)

0.0156 (14)

0.0141 (14)

0.0152 (14)

0.0109 (13)

0.0217 (15)

0.0177 (15)

0.0084 (12)

0.0021 (9)

0.0076 (12)

0.0037 (9)

0.0078 (13)

0.0031 (9)

C13

C16

C17

C15

C18

Br1

Br2

O3

0.0080 (10)

0.0022 (11)

0.0065 (11)

0.0022 (11)

0.0060 (12)

−0.00143 (11)

−0.00167 (11)

−0.0032 (8)

−0.0088 (8)

−0.0077 (9)

−0.0008 (8)

0.0037 (10)

0.0040 (10)

−0.0002 (10)

0.0023 (10)

0.0009 (10)

−0.0005 (10)

−0.0042 (10)

0.0044 (12)

−0.0074 (12)

−0.0029 (11)

−0.0004 (11)

−0.0009 (11)

0.0033 (12)

0.0046 (11)

0.0028 (11)

0.0038 (11)

0.0081 (12)

0.0036 (11)

0.00508 (10)

0.00401 (10)

0.0046 (8)

0.0043 (11)

0.0003 (11)

0.0032 (11)

0.0073 (12)

0.0019 (13)

−0.00220 (11)

−0.00316 (11)

−0.0016 (8)

−0.0054 (8)

−0.0060 (9)

0.0018 (8)

O1

0.0069 (8)

O2

0.0103 (8)

O4

0.0078 (8)

C5

0.0028 (10)

0.0043 (10)

0.0024 (10)

0.0030 (10)

0.0057 (10)

0.0046 (10)

0.0050 (10)

0.0011 (11)

0.0036 (10)

−0.0005 (11)

−0.0010 (10)

0.0021 (11)

−0.0005 (12)

0.0028 (10)

0.0039 (10)

−0.0006 (10)

0.0011 (10)

−0.0010 (10)

0.0004 (10)

0.0015 (10)

−0.0013 (12)

0.0014 (12)

−0.0002 (11)

−0.0002 (10)

0.0015 (11)

−0.0033 (12)

C6

C4

C2

C1

C3

N1

C10

C9

C8

C7

C11

C12

Geometric parameters (Å, º)

C14—C15

C14—C13

C14—H14

N2—C13

1.371 (4)

C5—C4

1.400 (4)

1.399 (4)

0.93

C5—C6

C6—C1

C4—C3

C2—C1

C2—C3

N1—C11

N1—C7

N1—H1

C10—C11

C10—C9

C10—H10

C9—C8

C9—H9

C8—C7

1.559 (4)

1.407 (4)

1.402 (4)

1.394 (4)

1.547 (4)

1.343 (4)

1.349 (3)

0.77 (4)

1.375 (4)

1.392 (4)

0.93

1.346 (3)

1.350 (4)

0.86 (3)

1.481 (4)

1.365 (4)

1.388 (4)

0.93

N2—C17

N2—H2

C13—C18

C16—C17

C16—C15

C16—H16

C17—H17

C15—H15

C18—H18A

C18—H18B

C18—H18C

0.93

0.96

1.387 (4)

0.93

0.96

1.378 (4)

Acta Cryst. (2013). C69, 1279-1288

sup-3

supplementary materials

Br1—C1

Br2—C4

O3—C5

O1—C2

O2—C3

O4—C6

1.905 (2)

1.905 (3)

1.249 (3)

1.260 (3)

1.251 (3)

1.249 (3)

C8—H8

0.93

C7—C12

1.489 (4)

0.93

C11—H11

C12—H12A

C12—H12B

C12—H12C

0.96

C15—C14—C13

C15—C14—H14

C13—C14—H14

C13—N2—C17

C13—N2—H2

C17—N2—H2

N2—C13—C14

N2—C13—C18

C14—C13—C18

C17—C16—C15

C17—C16—H16

C15—C16—H16

N2—C17—C16

N2—C17—H17

C16—C17—H17

C14—C15—C16

C14—C15—H15

C16—C15—H15

C13—C18—H18A

C13—C18—H18B

H18A—C18—H18B

C13—C18—H18C

H18A—C18—H18C

H18B—C18—H18C

O3—C5—C4

120.0 (3)

120

O1—C2—C1

O1—C2—C3

C1—C2—C3

C2—C1—C6

C2—C1—Br1

C6—C1—Br1

O2—C3—C4

O2—C3—C2

C4—C3—C2

C11—N1—C7

C11—N1—H1

C7—N1—H1

C11—C10—C9

C11—C10—H10

C9—C10—H10

C8—C9—C10

C8—C9—H9

C10—C9—H9

C7—C8—C9

C7—C8—H8

C9—C8—H8

N1—C7—C8

N1—C7—C12

C8—C7—C12

N1—C11—C10

N1—C11—H11

C10—C11—H11

C7—C12—H12A

C7—C12—H12B

124.8 (2)

116.3 (2)

118.9 (2)

123.4 (2)

117.56 (19)

119.02 (19)

126.2 (2)

115.9 (2)

117.9 (2)

123.3 (3)

121 (3)

116 (3)

120

122.5 (3)

121.9 (19)

115.5 (19)

117.9 (3)

118.9 (3)

123.2 (3)

118.1 (3)

121

121.0 (3)

119.5

118.5 (3)

120.8

119.5

120.8

120.6 (3)

119.7

119.6 (3)

120.2

119.7

120.2

109.5

120.5 (3)

119.7

109.5

119.7

109.5

117.9 (3)

117.5 (3)

124.5 (3)

120.2 (3)

119.9

109.5

126.0 (2)

115.6 (2)

118.4 (2)

125.8 (2)

116.6 (2)

117.6 (2)

123.5 (2)

118.27 (19)

118.22 (19)

O3—C5—C6

C4—C5—C6

119.9

O4—C6—C1

109.5

O4—C6—C5

109.5

C1—C6—C5

H12A—C12—H12B

C7—C12—H12C

109.5

C5—C4—C3

C5—C4—Br2

H12A—C12—H12C

H12B—C12—H12C

C3—C4—Br2

Hydrogen-bond geometry (Å, º)

D—H···A

D—H

H···A

D···A

D—H···A

N2—H2···O4

N2—H2···O3

N1—H1···O1

N1—H1···O2

0.86 (3)

0.77 (4)

2.02 (3)

2.36 (3)

1.96 (4)

2.36 (4)

2.838 (3)

2.946 (3)

2.693 (3)

2.828 (3)

159 (3)

126 (2)

160 (4)

121 (4)

Acta Cryst. (2013). C69, 1279-1288

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supplementary materials

(ba3pic100k1121apr_0m) Bis(3-picolinium) bromanilate

Crystal data

2C₆H₈N⁺·C₆Br₂O₄²⁻

M_r= 484.15

Z = 2

F(000) = 480

D_x= 1.846 Mg m⁻³

Mo Kα radiation, λ = 0.71073 Å

µ = 4.68 mm⁻¹

T = 100 K

Block, purple

Monoclinic, P2₁/c

a = 8.9526 (7) Å

b = 9.6149 (8) Å

c = 10.4275 (8) Å

β = 103.935 (4)°

V = 871.17 (12) Å³

0.3 × 0.25 × 0.15 mm

Data collection

Bruker APEXII CCD area-detector

diffractometer

Graphite monochromator

CCD; rotation images scans

Absorption correction: multi-scan

(SADABS; Blessing, 1995)

2280 independent reflections

2018 reflections with I > 2σ(I)

R_int= 0.033

θ

_max= 28.9°, θ_min= 2.3°

h = −12→12

k = −13→11

l = −11→14

T

_min= 0.671, T_max= 1.000

9784 measured reflections

Refinement

Refinement on F²

Least-squares matrix: full

R[F²> 2σ(F²)] = 0.023

wR(F²) = 0.061

S = 1.08

2280 reflections

Secondary atom site location: difference Fourier

map

Hydrogen site location: mixed

H atoms treated by a mixture of independent

and constrained refinement

w = 1/[σ²(F_o²) + (0.0286P)²+ 0.5432P]

where P = (F_o²+ 2F_c²)/3

123 parameters

0 restraints

(Δ/σ)_max< 0.001

Primary atom site location: structure-invariant

direct methods

Δρ_max= 0.45 e Å⁻³

Δρ_min= −0.63 e Å⁻³

Special details

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance

matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles;

correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate

(isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes.

Refinement. Refinement of F²against 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> 2σ(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 F²are 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 (Å²)

x

y

z

U_iso*/U_eq

H5

Br1

O1

O2

C1

C3

0.893 (4)

0.515 (3)

0.285 (3)

0.057 (10)*

0.01678 (7)

0.0185 (3)

0.0182 (3)

0.0137 (3)

0.0136 (3)

0.43444 (2)

0.71755 (15)

0.23321 (14)

0.4732 (2)

0.3575 (2)

0.23608 (2)

0.42622 (14)

0.35789 (14)

0.38635 (18)

0.41949 (18)

0.18610 (2)

0.21943 (13)

−0.07254 (14)

0.07990 (18)

−0.03428 (18)

Acta Cryst. (2013). C69, 1279-1288

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supplementary materials

C6

1.2623 (2)

1.3581

0.61801 (19)

0.6454

0.47325 (18)

0.5237

0.0158 (4)

0.019*

H6

C2

0.6123 (2)

0.98369 (19)

0.9917 (2)

0.9021

0.45631 (18)

0.53679 (17)

0.64850 (19)

0.6963

0.11904 (18)

0.32431 (16)

0.40243 (19)

0.4047

0.0135 (3)

0.0179 (3)

0.0160 (4)

0.019*

N1

C4

H4

C5

1.1315 (2)

1.2510 (2)

1.3384

0.69418 (19)

0.5025 (2)

0.4521

0.47996 (18)

0.39267 (19)

0.3886

0.0141 (3)

0.0181 (4)

0.022*

C7

H7

C9

1.1387 (2)

1.1519

0.8178 (2)

0.9007

0.5686 (2)

0.5213

0.0210 (4)

0.031*

H9A

H9B

H9C

C8

1.2239

0.8077

0.6441

0.031*

1.0448

0.8242

0.5974

0.031*

1.1086 (2)

1.0992

0.4633 (2)

0.3854

0.31852 (19)

0.2642

0.0195 (4)

0.023*

H8

Atomic displacement parameters (Å²)

U¹¹

U²²

U³³

U¹²

U¹³

U²³

Br1

O1

O2

C1

C3

C6

C2

N1

C4

C5

C7

C9

C8

0.01435 (10)

0.0149 (6)

0.0133 (6)

0.0145 (8)

0.0129 (8)

0.0113 (8)

0.0136 (8)

0.0150 (8)

0.0127 (8)

0.0151 (8)

0.0175 (9)

0.0212 (9)

0.0258 (10)

0.01840 (11)

0.0217 (7)

0.0184 (7)

0.0134 (8)

0.0138 (8)

0.0192 (9)

0.0142 (8)

0.0223 (8)

0.0177 (9)

0.0138 (8)

0.0182 (9)

0.0177 (9)

0.0172 (9)

0.01676 (11)

0.0159 (7)

0.0207 (7)

0.0136 (9)

0.0138 (9)

0.0159 (9)

0.0127 (8)

0.0138 (8)

0.0168 (9)

0.0140 (9)

0.0190 (9)

0.0259 (11)

0.0151 (9)

−0.00363 (7)

0.00212 (7)

−0.0021 (5)

−0.0004 (5)

0.0042 (7)

0.0027 (6)

0.0011 (7)

0.0034 (7)

−0.0016 (6)

0.0023 (7)

0.0044 (7)

0.0055 (7)

0.0091 (8)

0.0044 (8)

0.00366 (7)

0.0023 (5)

0.0005 (5)

0.0001 (7)

−0.0032 (7)

0.0013 (7)

−0.0025 (7)

0.0051 (6)

0.0072 (7)

0.0035 (7)

0.0016 (7)

−0.0029 (8)

−0.0009 (7)

−0.0044 (5)

−0.0043 (5)

−0.0027 (6)

−0.0005 (6)

−0.0013 (7)

−0.0006 (6)

−0.0055 (6)

0.0015 (7)

−0.0009 (7)

0.0034 (7)

0.0002 (7)

−0.0035 (7)

Geometric parameters (Å, º)

Br1—C1

O1—C2

O2—C3

C1—C2

C1—C3

C3—C2ⁱ

C6—C7

C6—C5

C6—H6

C2—C3ⁱ

N1—C8

1.9025 (18)

N1—C4

1.339 (3)

1.262 (2)

1.238 (2)

1.387 (2)

1.414 (2)

1.548 (3)

1.381 (3)

1.397 (3)

0.9300

N1—H5

C4—C5

C4—H4

C5—C9

C7—C8

C7—H7

C9—H9A

C9—H9B

C9—H9C

C8—H8

0.85 (3)

1.387 (3)

0.9300

1.498 (3)

1.375 (3)

0.9300

0.9600

1.548 (3)

1.336 (3)

0.9600

0.9300

C2—C1—C3

C2—C1—Br1

C3—C1—Br1

124.22 (16)

118.27 (13)

117.51 (13)

C5—C4—H4

C4—C5—C6

C4—C5—C9

119.4

117.00 (17)

120.62 (17)

Acta Cryst. (2013). C69, 1279-1288

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supplementary materials

O2—C3—C1

O2—C3—C2ⁱ

C1—C3—C2ⁱ

C7—C6—C5

C7—C6—H6

C5—C6—H6

O1—C2—C1

O1—C2—C3ⁱ

C1—C2—C3ⁱ

C8—N1—C4

C8—N1—H5

C4—N1—H5

N1—C4—C5

N1—C4—H4

125.66 (17)

116.88 (16)

117.47 (15)

120.83 (17)

119.6

C6—C5—C9

C8—C7—C6

C8—C7—H7

C6—C7—H7

C5—C9—H9A

C5—C9—H9B

H9A—C9—H9B

C5—C9—H9C

H9A—C9—H9C

H9B—C9—H9C

N1—C8—C7

N1—C8—H8

C7—C8—H8

122.36 (16)

118.99 (18)

120.5

109.5

119.6

109.5

124.82 (17)

116.88 (15)

118.30 (15)

121.90 (16)

124 (2)

109.5

120.14 (18)

119.9

114 (2)

121.13 (17)

119.4

119.9

C2—C1—C3—O2

Br1—C1—C3—O2

C2—C1—C3—C2ⁱ

Br1—C1—C3—C2ⁱ

C3—C1—C2—O1

Br1—C1—C2—O1

C3—C1—C2—C3ⁱ

Br1—C1—C2—C3ⁱ

179.04 (18)

−1.0 (3)

C8—N1—C4—C5

N1—C4—C5—C6

N1—C4—C5—C9

C7—C6—C5—C4

C7—C6—C5—C9

C5—C6—C7—C8

C4—N1—C8—C7

C6—C7—C8—N1

0.9 (3)

−0.4 (3)

−178.95 (17)

−0.1 (3)

178.45 (18)

0.1 (3)

−1.2 (3)

178.77 (12)

−178.72 (18)

1.4 (3)

1.2 (3)

−0.9 (3)

0.4 (3)

−178.76 (12)

Symmetry code: (i) −x+1, −y+1, −z.

Hydrogen-bond geometry (Å, º)

D—H···A

D—H

H···A

D···A

D—H···A

N1—H5···O1

N1—H5···O2ⁱ

C4—H4···Br1ⁱⁱ

0.84 (3)

0.93

1.78 (3)

2.54 (3)

2.96

2.598 (2)

3.039 (2)

3.7977 (18)

165 (3)

119 (3)

151

Symmetry codes: (i) −x+1, −y+1, −z; (ii) −x+1, y+1/2, −z+1/2.

(br3p14jan_0m) Bis(4-picolinium) bromanilate

Crystal data

2C₆H₈N⁺·C₆Br₂O₄²⁻

M_r= 484.15

Z = 2

F(000) = 480

D_x= 1.817 Mg m⁻³

Mo Kα radiation, λ = 0.71073 Å

µ = 4.61 mm⁻¹

T = 100 K

Block, purple

0.35 × 0.25 × 0.2 mm

Monoclinic, P2₁/c

a = 8.1345 (8) Å

b = 6.1517 (6) Å

c = 17.7868 (17) Å

β = 96.177 (7)°

V = 884.90 (15) Å³

Data collection

Bruker APEXII CCD area-detector

diffractometer

Absorption correction: multi-scan

(SADABS; Blessing, 1995)

Graphite monochromator

CCD; rotation images scans

T_min= 0.576, T_max= 1.000

14105 measured reflections

3234 independent reflections

Acta Cryst. (2013). C69, 1279-1288

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supplementary materials

2464 reflections with I > 2σ(I)

R_int= 0.047

h = −11→12

k = −9→8

θ

_max= 32.8°, θ_min= 2.3°

l = −26→25

Refinement

Refinement on F²

Least-squares matrix: full

R[F²> 2σ(F²)] = 0.034

wR(F²) = 0.087

S = 1.06

3234 reflections

Secondary atom site location: difference Fourier

map

Hydrogen site location: mixed

H atoms treated by a mixture of independent

and constrained refinement

w = 1/[σ²(F_o²) + (0.040P)²+ 0.2356P]

where P = (F_o²+ 2F_c²)/3

123 parameters

0 restraints

(Δ/σ)_max< 0.001

Primary atom site location: structure-invariant

direct methods

Δρ_max= 0.82 e Å⁻³

Δρ_min= −0.54 e Å⁻³