Formation of infinite grids with chiral square compartments by self-assembly of achiral 1,1′-biphenyl-2,2′,6,6′-tetracarboxylic acids. Effect of 4,4′-substitution on the grid stacking

Article abstract of DOI:10.1135/cccc20010820

The achiral 1,1′-biphenyl-2,2′,6,6′-tetracarboxylic acid as well as its 4,4′-dibromo and 4,4′-dinitro derivative self-assemble in crystal under formation of a two-dimensional grid set up from hydrogen-bonded cyclotetrameric compartments which are individu

Full text of DOI:10.1135/cccc20010820

820
Holý, Závada, Zezula, Císařová, Podlaha:
FORMATION OF INFINITE GRIDS WITH CHIRAL SQUARE
COMPARTMENTS BY SELF-ASSEMBLY OF ACHIRAL
1,1′-BIPHENYL-2,2′,6,6′-TETRACARBOXYLIC ACIDS.+
EFFECT OF 4,4′-SUBSTITUTION ON THE GRID STACKING
a
b1
Petr HOLÝa1, Jiří ZÁVADAa2,*, Josef ZEZULA , Ivana CÍSAŘOVÁ
b
and Jaroslav PODLAHA
a
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic,
166 10Prague 6, Czech Republic; e-mail: petrholy@uochb.cas.cz, zavada@uochb.cas.cz
Charles University, Department of Inorganic Chemistry, 128 40Prague 2, Czech Republic;
1
2
b
1
e-mail: cisarova@prfdec.natur.cuni.cz
Received March 14, 2001
Accepted April 10, 2001
Th e ach iral 1,1′-biph en yl-2,2′,6,6′-tetracarboxylic acid as well as its 4,4′-dibrom o an d
4,4′-din itro derivative self-assem ble in crystal un der form ation of a two-dim en sion al grid set
up from h ydrogen -bon ded cyclotetram eric com partm en ts wh ich are in dividually ch iral (D4
sym m etry). Th e rough ly square cavities (ca 5.6 Å) of in dividual com partm en ts partly accom -
m odate th e perpen dicularly orien ted ben zen e rin gs of th e n eigh bourin g grid, in depen den ce
on th e n ature of th e 4,4′-substituen ts. As a con sequen ce, th e grids are stacked in a staggered
(n on con caten ated) m an n er.
Keyw ord s: Carboxylic acids; Crystal structure determ in ation ; Hydrogen bon ds; Crystal en gi-
n eerin g; Self assem bly; Ch iral porous solids; Biaryls; Biph en yls.
Supram olecular self-assem bly is th e spon tan eous association of m olecular
subun its (tecton s2) in to ordered aggregates, wh ich is driven by
n on -covalen t in teraction s3, e.g. by in term olecular h ydrogen bon ds. Tetra-
fun ction al m olecules with tetrah edrally arran ged substituen ts h ave been in -
vestigated in th is con text an d h ave sh own to exh ibit th e fascin atin g
capability of buildin g diam on d-like n etworks4 with m eth an etetraacetic acid
1 bein g a prototypal exam ple5.
We are in terested in th e self-assem bly of 2,2′,6,6′-tetrasubstituted biph en -
yls6,7 th at are topologically related to th e tetrasubstituted m eth an es: if we
+ Part of th e results con tain ed in th is paper h as been already com m un icated in a prelim in ary
form 1.
Collect. Czech. Chem. Commun. (Vol. 66) (2001)
doi: 10.1135/cccc20010820

Achiral 1,1′-Biphenyl-2,2′,6,6′-tetracarboxylic Acids
821
stretch th e D2d sym m etry con form er of th e tecton 1 alon g its axis, a fram e-
work of 1,1′-biph en yl-2,2′,6,6′-tetracarboxylic acid 2a can be (on furth er
syn th etic elaboration ) obtain ed (Sch em e 1).
HOOC
HOOC
COOH
COOH
HOOC
HOOC
COOH
COOH
1
2a
SCHEME 1
Stereoch em ical correlation of th e tecton s 1 an d 2
All th e sam e, exam in ation of m odels suggests th at th e self-assem blin g
properties of th e two stereoch em ically akin tecton s 1 an d 2a can be en tirely
differen t. In con trast to th e establish ed propen sity of th e tetrah edral tecton
1 to form ch air-like distorted cycloh exam ers un derlyin g th e th ree-
dim en sion al diam on doid n etwork4,5, m odels of th e stretch ed tecton 2a sug-
gest a preferen tial cyclotetram erisation resultin g ultim ately in an in fin ite
“square” grid (Fig. 1).
RESULTS AND DISCUSSION
In accord with th e con sideration of m odels, X-ray crystal structure determ i-
n ation of th e paren t (un substituted) acid 2a exh ibits an approxim ately per-
pen dicular orien tation of th e ph en yls in th e in dividual m olecules with th e
FIG. 1
Sch em atic represen tation of diam on doid an d square grids
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

822
Holý, Závada, Zezula, Císařová, Podlaha:
dih edral an gle between th e least squares plan es of th e ben zen e rin gs bein g
86.26(6)° (Fig. 2). However, th e pivot atom s of th e substituen ts are dis-
placed from th e arom atic plan es by as m uch as 0.190(3) Å for th e perpen -
dicular distan ce of C(11) from th e plan e defin ed by C(1) to C(6). Th e
carboxyl groups, th e h ydrogen atom s of wh ich were located an d refin ed,
are also essen tially plan ar but adopt varyin g orien tation relatively to th eir
paren t ben zen e rin gs: th e dih edral an gles of th e carboxyl plan es relatively
to th e adjoin ed arom atic rin gs are 8.1(4)° for C(7), 35.1(3)° for C(8),
14.2(3)° for C(17) an d 44.5(2)° for C(18) carboxyl; th e steric h in dran ce im -
posed by th e crystal packin g (vide infra) is assum ed to be th e respon sible
factor. All four carboxyl groups participate in th e in term olecular h ydrogen
bon din g. Th ere are two crystallograph ically in depen den t double h ydrogen
bon ds, both n early plan ar an d with asym m etrically located h ydrogen at-
om s: on e lin ks O(1) an d O(2) with O(12′) an d O(11′) an d th e oth er is be-
tween O(3), O(4) an d O(14′′), O(13′′). Th ese results in th e form ation of
h ydrogen -bon ded cyclotetram ers (Fig. 3), set up ultim ately in to an in fin ite
quasi-plan ar “square” n etwork (grid).
FIG. 2
An ORTEP diagram of th e m olecular structure of 2a with th e crystallograph ic n um berin g
sch em e
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

Achiral 1,1′-Biphenyl-2,2′,6,6′-tetracarboxylic Acids
823
Stereoch em istry of th e cyclotetram ers (“squares”) raises a particular in ter-
est. In con trast to th e in dividual tecton s 2a th at possess D2d sym m etry an d
are accordin gly ach iral, th e self-assem bled cyclotetram ers exh ibit (in an
ideal arran gem en t) a un ique8,9 D4 sym m etry an d are th erefore ch iral.
Hom och iral cyclotetram ers are arran ged diagon ally, wh ereas altern ation of
ch irality occurs in th e h orizon tal an d vertical rows of th e grid (Fig. 4). In
con trast to th e ch irality of th e in dividual cyclotetram ers, th e in fin ite
un ilayered grid is ach iral due to th e crystal sym m etry.
Th e rough ly square cavities in side th e cyclotetram eric com partm en ts are
approxim ately 5.6 Å in size, wh ich allows to accom m odate partly th e
n early perpen dicularly orien ted ben zen e rin gs of th e n eigh bourin g grids. As
a con sequen ce, th e grids are stacked in a staggered (n on -con caten ated)
m an n er (Fig. 3).
In order to assess a broader scope of th is n ovel supram olecular arch itec-
ture, we h ave exam in ed th e effect of substitution of th e paren t tecton 2a
on th e crystal structure. To th is en d, th ree 4,4′-disubstituted derivatives,
2b–2d , h ave been prepared. Brom in ation of 2a in th e presen ce of Ag+ ion s
afforded th e 4,4′-dibrom o-substituted tetraacid 2b. Sim ilarly, n itration of
2a yielded th e 4,4′-din itro-substituted tetraacid 2c. Th e Ullm an n couplin g
FIG. 3
Self-assem bly of 2a in to un ilayered h ydrogen -bon ded n etworks an d stackin g of th e n eigh -
bourin g layers in th e crystal (th e m olecules in th e secon d layer are distin guish ed by th in n er
lin es)
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

824
Holý, Závada, Zezula, Císařová, Podlaha:
of trim eth yl 2-brom oben zen e-1,3,5-tricarboxylate 3 with activated copper
bron ze followed by alkalin e h ydrolysis led to 1,1′-biph en yl-2,2′,4,4′,6,6′-
h exacarboxylic acid 2d (Sch em e 2).
X
COOCH3
HOOC
HOOC
COOH
COOH
(iii), (iv)
(i) or (ii)
2a
H3COOC
COOCH3
Br
3
X
(i) Br2, Ag2SO4, H2SO4
(ii) HNO3, H2SO4
(iii) Cu/DMF
2a, X = H
2b, X = Br
2c, X = NO2
2d, X = COOH
(iv) NaOH/aq. EtOH
SCHEME 2
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
FIG. 4
Sch em atic represen tation of th e distribution of cyclotetram ers of opposite ch irality (in di-
cated by em pty an d filled squares) in th e un ilayered h ydrogen -bon ded n etwork in th e crys-
tal of 2a
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Achiral 1,1′-Biphenyl-2,2′,6,6′-tetracarboxylic Acids
825
Th e m olecular structure of th e dibrom o-substituted tetraacid 2b is given
in Fig. 5. Th e m olecule resides on a crystallograph ic two-fold axis passin g
th rough th e m idpoin t between th e Br atom s. Th e ben zen e rin gs are plan ar
with in ±0.010 Å an d are arran ged alm ost perpen dicularly to th e dih edral
an gle of th e least-squares plan es of 85.6(1)°. In con trast to th e paren t
tetraacid 2a, th e pivot atom s of th e substituen ts are displaced on ly very
sligh tly from th e ben zen e plan e, th e greatest deviation bein g 0.023(7) Å for
C(7). Th e tiltin g of th e carboxyl groups relatively to th e ben zen e plan e is
17.8(7)° an d 13.3(9)° for C(7)–O(1)–O(2) an d C(8)–O(3)–O(4), respectively.
In th e un substituted tetraacid 2a, th e an alogous dih edral an gles of th e four
in depen den t carboxyl groups span th e m uch broader ran ge of 8.1–44.5°.
Th e carboxyl groups in 2b are lin ked by sh ort (O···O 2.601–2.616 Å),
sligh tly ben t (an gles at h ydrogen atom s bein g 163(7)° an d 164(6)°) an d
m arkedly asym m etric in term olecular double h ydrogen bon ds, givin g rise to
th e already kn own (vide supra) two-dim en sion al “square” layers propagat-
in g diagon ally th rough th e un it cell (Fig. 6). Th e staggered stackin g of th ese
layers allows to partly in terpen etrate each oth er, h owever, less effectively
th an in th e un substituted com poun d 2a. Assum edly, th e van der Waals
con tacts of brom in e atom s belon gin g to m olecules two layers apart are th e
respon sible factor th at preven ts th e adjacen t layers to becom e closer th an
8.2 Å; th e correspon din g distan ce in th e un substituted derivative is 5.28 Å.
FIG. 5
An ORTEP diagram of th e m olecular structure of 2b with th e crystallograph ic n um berin g
sch em e. Sym m etry code: i, 1 – x, y, 0.5 – z
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

826
Holý, Závada, Zezula, Císařová, Podlaha:
Th e crystal structure of th e din itro-substituted tetraacid 2c in volves two
crystallograph ically in depen den t m olecules A an d B differin g in th eir con -
form ation , in particular in th e degree of ben din g of th e ben zen e rin gs away
from th e idealised two-fold axis. In all oth er aspects, th e m olecules A an d B
are very sim ilar. Th e perspective view of m olecule A is given in Fig. 7; for
FIG. 6
Self-assem bly of 2b in to un ilayered h ydrogen -bon ded n etworks an d stackin g of th e n eigh -
bourin g layers in th e crystal (th e m olecules in th e secon d layer are distin guish ed by th in n er
lin es)
FIG. 7
An ORTEP diagram of on e crystallograph ically in depen den t m olecule of 2c with th e n um -
berin g sch em e. For th e secon d m olecule, add 2 to th e first digit of th e atom labels
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

Achiral 1,1′-Biphenyl-2,2′,6,6′-tetracarboxylic Acids
827
m olecule B, add 2 to th e first digit of th e atom labels. Th e ben zen e rin gs in
each m olecule are arran ged alm ost perpen dicularly, th e appropriate least
squares plan es subten din g th e dih edral an gle of 89.70(9)° an d 89.17(9)° for
m olecules A an d B, respectively. Com pared to th e un substituted tetraacid
2a, th e m ost con spicuous differen ce is th e alm ost coplan ar arran gem en t of
th e carboxyl groups with th e adjacen t ben zen e plan es; th e largest deviation
from coplan arity is 16.4(1)°, in a close an alogy with th e situation foun d for
th e dibrom o-substituted tecton 2b.
In th e crystal of th e com poun d 2c, th ere are two kin ds of in term olecular
in teraction . Th e first is com m on for th e tecton s 2a–2c: sh ort, double h ydro-
gen bon d bridges between th e carboxyl groups lin k th e m olecules in to
two-dim en sion al “square” grids stacked in a staggered m an n er, allowin g
th e in dividual layers to partly pen etrate (Fig. 8). Con siderin g th e two in de-
pen den t m olecules A an d B, th e grids defin ed by th e cen troids of th e m ole-
cules are arran ged in to ABAB rows an d in altern atin g AAA an d BBB
colum n s. In con trast to th e crystal structure of 2a an d 2b, in wh ich th e
cen troids with in each layer are coplan ar due to crystal sym m etry, th e grid
in th e din itro derivative 2c is puckered: th e an gles of th e in tercen troid lin ks
are 166.9(2)° alon g th e ABAB direction , 178.7(2)° alon g AAA an d 175.8(2)°
alon g BBB. Th is appears to be th e con sequen ce of th e secon d type of th e
FIG. 8
View of th e staggered grids in 2c resultin g by h ydrogen bon din g. Secon dary ch ain s form ed
by stackin g of th e n itro groups run approxim ately parallel to th e grids
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

828
Holý, Závada, Zezula, Císařová, Podlaha:
in term olecular in teraction , wh ich in th e in vestigated series is specific for
th e n itro substituen t. Because of th e zig-zag arran gem en t of th e ABAB rows,
th eir periph eral n itro groups com e in to close con tacts with th e n itro groups
of th e m olecules wh ich are two layers apart. Due to th e presen ce of two in -
depen den t m olecules, th ere are two such in teraction s between th e
tran slation ally related n itro substituen ts of A an d B: N(11) to N(41) (x – 1,
y, z), distan ce of th e cen troids of th e n itro groups 3.141(3) Å, dih edral an gle
of th e NO2 plan es 1.0(1)°; N(21) to N(31) (x, y, 1 – z), 3.085 Å, 3.19(9)°. Th is
NO2-stackin g lin ks th e m olecules in to secon dary ch ain s wh ich are approxi-
m ately perpen dicular to th e layers form ed by th e h ydrogen bon din g. Th e
assum ption th at th is stackin g accoun ts for th e deform ation of th e grid from
plan arity is supported by th e fact th at th e lin ks of th e cen troids are alm ost
lin ear with in th e colum n s of th e AAA an d BBB type, wh ich lack an y sec-
on dary NO2 in teraction perpen dicular to th e direction of th e colum n .
In term olecular stackin g of arom atic n itro groups is, of course, a com m on
ph en om en on an d alm ost th ousan d cases h as been retrieved from th e Cam -
bridge Structural Database for th e absolute value of th e dih edral an gle lim -
ited to 10° an d th e in tercen troid distan ce up to 4.5 Å. However, th e m ean
of th e (n on -Gaussian ) distribution of th e distan ces reach es 3.586 Å an d th e
values sh orter th an 3.2 Å represen t less th an 7% of th e total. In th e presen t
structure, th e stron g in teraction of th e n itro groups allows th e layers to
in terpen etrate m ore effectively th an in th e dibrom o derivative 2b, in spite
of th e form al van der Waals diam eter of th e n itro group (assum in g its free
rotation ) wh ich is larger th an th at of th e brom o substituen t.
Irrespective of th e specific (relatively m in or) substituen t effect, un iform
pattern in th e solid-state self-assem bly of th e biph en yl tecton s 2a–2c h as
been in th is way establish ed. Structure tun in g of th e n ovel supram olecular
arch itecture rem ain s n everth eless on th e agen da. First, th e effective size of
th e in dividual “square” com partm en ts sh ould be expan ded, em ployin g ap-
propriate spacers. Next, ch irality of th e in dividual “squares” sh ould be ex-
ten ded to th e overall n etwork (grid) by th e use of appropriate ch iral
tecton s10. Lastly, stackin g of th e in dividual grids sh ould be exam in ed in a
m ore detail. Alth ough th e staggered stackin g h as n ow been sh own in th e
tecton s 2a–2c to be a “n orm al” outcom e of th e self-assem bly, en forcem en t
of th e altern ative, eclipsed stackin g stan ds as a ch allen gin g task. In troduc-
tion of appropriate “stickin g” substituen ts in to th e 4,4′-position s of th e
biph en yl tecton m igh t be in strum en tal11 in th is respect, allowin g form a-
tion of an addition al (perpen dicular) n etwork of in term olecular n on -
covalen t bon ds. We h ave th erefore in troduced “stickin g” 4,4′-carboxyl
groups in to th e tecton 2d as th e first probe; un fortun ately, we h ave failed
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

Achiral 1,1′-Biphenyl-2,2′,6,6′-tetracarboxylic Acids
829
to grow a suitable crystal. Furth er studies alon g th ese lin es wh ich ultim ately
could lead to th e design of ch iral porous solids12 are in progress.
EXPERIMENTAL
Meltin g poin ts were determ in ed on a Kofler apparatus an d are un corrected. 1H NMR spectra
were m easured on
a Varian Un ity XL-200 spectrom eter (200 MHz, FT m ode) usin g
tetram eth ylsilan e as an in tern al stan dard. Mass spectra were recorded on a ZAB-EQ (VG An a-
lytical) in strum en t, for FAB tech n ique th ioglycerol/glycerol m atrices were used. Ch em ical
sh ifts are given in ppm (δ-scale).
4,4′-Dibrom o-1,1′-biph en yl-2,2′,6,6′-tetracarboxylic Acid (2b)
To a stirred m ixture of th e un substituted1 tetraacid 2a (3.30 g, 10 m m ol) an d silver(I) sul-
fate13 (3.43 g, 11 m m ol) in con cen trated sulfuric acid (98%, 40 m l), brom in e (3.52 g,
22 m m ol) was added dropwise at 120 °C (0.5 h ). After addition al 4 h h eatin g, th e cooled
m ixture was poured on to crush ed ice (200 g). Th e yellow precipitate was filtered off, wash ed
with cold water an d suspen ded in a saturated aqueous solution of NaHCO3 (2 × 50 m l). Th e
in soluble silver salt was filtered off an d th e filtrate was acidified to pH 1 with con cen trated
HCl. Th e precipitated product was collected an d recrystallised from h ot water. Yield 3.55 g
(73 %), m .p. >370 °C. 1H NMR (DMSO-d6): 8.13 s, 4 H (H-3,3′,5,5′); 12.95 br s, 4 H (4 ×
COOH). FAB MS, m/z (rel.%): 491 (MH+, 10), 489 (MH+, 20), 487 (MH+, 10), 473 (13), 471
(26), 469 (13), 201 (33), 181 (21), 149 (15), 115 (25), 110 (36), 91 (100), 75 (73), 73 (70), 57
(73). For C16H8Br2O8 (488.0) calculated: 39.38% C, 1.65% H, 32.74% Br; foun d: 39.56% C,
1.60% H, 32.76% Br.
4,4′-Din itro-1,1′-biph en yl-2,2′,6,6′-tetracarboxylic Acid (2c)
A m ixture of th e un substituted1 tetraacid 2a (3.30 g, 10 m m ol), n itric acid (65%, 20 m l) an d
con cen trated sulfuric acid (98%, 20 m l) was h eated at 120 °C un der stirrin g for 4 h . After
coolin g, th e m ixture was poured on to crush ed ice (200 g). Th e precipitated product was fil-
tered off an d recrystallised from h ot water. Yield 3.05 g (73%), m .p. >370 °C. 1H NMR
(DMSO-d6): 8.79 s, 4 H (H-3,3′,5,5′); 13.43 br s, 4 H (4 × COOH). EI MS, m/z (rel.%): 420
(M+, 20), 331 (31), 313 (14), 288 (20), 287 (100), 250 (21), 126 (15), 69 (14), 57 (18), 55 (16),
44 (21), 43(20). For C16H8N2O12 (420.3) calculated: 45.73% C, 1.92% H, 6.67% N; foun d:
46.09% C, 1.86% H, 6.38% N.
1,1′-Biph en yl-2,2′,4,4′,6,6′-h exacarboxylic Acid (2d )
A stirred m ixture of th e triester 3 (3.31 g, 10 m m ol) an d activated copper bron ze14 (2.5 g) in
dim eth ylform am ide (15 m l) was h eated at 150 °C un der argon for 1 h , th en poured in to wa-
ter (100 m l) an d extracted with eth yl acetate (3 × 20 m l). Th e com bin ed extracts were dried
with an h ydrous MgSO4, filtered an d evaporated to dryn ess. Th e solid residue was dissolved
in of h ot m eth an ol (100 m l). After coolin g th e crystals of th e resultin g h exam eth yl ester
were collected, wash ed by m eth an ol an d dried. Yield 1.85 g (73.6%), m .p. 212–214 °C.
1H NMR (CDCl3): 8.85 s, 4 H (H-3,3′,5,5′); 3.99 s, 12 H (CH3-2,2′,6,6′); 3.65 s, 6 H (CH3-4,4′).
EI MS, m/z (rel.%): 502 (M+, 100), 471 (73), 443 (32), 427 (38), 381 (28), 369 (12), 220 (19),
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

830
Holý, Závada, Zezula, Císařová, Podlaha:
7 (16), 57 (21). For C24H22O12 (502.4) calculated: 57.37% C, 4.41% H; foun d: 57.18% C,
4.36% H.
Th e h exaester (1.17 g, 2.33 m m ol) was sapon ified by sodium h ydroxide (0.836 g,
21 m m ol) in 70% aqueous eth an ol (25 m l). After 6 h reflux, th e m ixture was acidified to
pH 1 with 2 M HCl an d solven ts were evaporated. Th e residue was crystallised from h ot
water (100 m l). Yield 0.82 g (84.2%), m .p. >370 °C. 1H NMR (DMSO-d6): 8.55 s, 4 H
(H-3,3′,5,5′); 10.95 br s, 6 H (6 × COOH). FAB MS, m/z (rel.%): 419 (MH+, 16), 401 (29), 307
(20), 232 (17), 215 (100), 214 (62), 197 (75), 181 (45), 165 (23), 149 (33), 133 (30), 123 (48),
110 (68). For C18H10O12 (418.3) calculated: 51.69% C, 2.41% H; foun d: 51.56% C, 2.44% H.
Trim eth yl 2-Brom oben zen e-1,3,5-tricarboxylate (3)
To a stirred m ixture of 2-brom om esitylen e (21.2 g, 0.106 m ol) an d aqueous NaOH (5.5 g,
0.1375 m ol, 500 m l H2O) un der reflux solid KMn O4 (112g, 0.709 m ol) was added
portion swise durin g 4 h . After addition al 4 h h eatin g, th e excess of KMn O4 was rem oved by
several drops of form alin e, th e m ixture was filtered an d th e separated Mn O2 was wash ed
with h ot water. Th e filtrate an d wash in gs were com bin ed, con cen trated to 100 m l an d acidi-
fied to pH 1 with con cen trated HCl. Th e deposited triacid was isolated by filtration , wash ed
with little water an d dried. Yield 19.3 g (63.0%), m .p. 291–294 °C; ref.15 260–275 °C.
Th e crude acid was suspen ded in m eth an ol (700 m l), con cen trated sulfuric acid (20 m l)
was added an d th e m ixture was h eated to reflux for 20 h . Th e volum e was reduced to
200 m l an d cooled in a refrigerator. Th e resultin g triester was filtered off, wash ed with a
sm all volum e of m eth an ol an d dried. Yield 18.7 g (84.6%), m .p. 93–95 °C. 1H NMR
(DMSO-d6): 8.35 s, 2 H (H-3,5); 3.98 s, 6 H (CH3-2,6); 3.96 s, 3 H (CH3-4). EI MS, m/z (rel.%):
332 (M+, 42), 330 (M+, 43), 301 (98), 299 (100), 258 (8), 256 (8), 227 (8), 225 (8), 177 (11),
115 (25), 74 (15), 59 (7). For C12H11BrO6 (331.1) calculated: 43.53% C, 3.35% H, 24.13% Br;
foun d: 43.80% C, 3.36% H, 24.29% Br.
Sin gle-Crystal X-Ray Diffraction
All m easurem en ts h ave been perform ed on a CAD4 diffractom eter at 293(2) K (MoKα radia-
tion , λ = 0.710073 Å).
2a: C16H10O8, M = 330.24, orth orh om bic, space group Pbca (No. 61), a = 11.862(2) Å, b =
12.098(1) Å, c = 21.0333(2) Å, V = 3018.4(6) Å3, F(000) = 1 360, Dc = 1.453 g cm –3 for Z = 8.
A colourless plate of th e dim en sion s 0.30 × 0.19 × 0.11 m m was grown from h ot water by
slow coolin g. From a total of 2 361 reflection s m easured in th e ran ge h = 0 to 13, k = 0 to
13, l = 0 to 24, 1 642 were regarded as observed accordin g to th e I > 2σ(I) criterion . Absorp-
tion was n eglected (µ = 0.119 m m –1). Th e structure was solved by direct m eth ods
(SHELXS86)16 an d refin ed by full-m atrix least squares based on F2 (SHELXL93)17. Th e
O-bon ded h ydrogen atom s were refin ed isotropically, th e C-bon ded h ydrogen s were fixed in
calculated position s an d assign ed th e tem perature param eters am oun tin g to 1.2-m ultiples
of th ose of th eir bon din g partn ers. Th e refin em en t con verged to R = 0.0383, wR = 0.0874,
GOF = 1.042 for 233 param eters. Th e fin al differen ce m ap displayed n o peaks of ch em ical
sign ifican ce.
2b: C16H8Br2O8, M = 488.04, m on oclin ic, space group C2/c (No. 15), a = 13.633(1) Å, b =
11.160(1) Å, c = 12.7769(9) Å, β = 101.694(6)°, V = 1903.6(6) Å3, F(000) = 1 088, Dc
=
1.703 g cm –3 for Z = 4. A colourless irregular block of th e dim en sion s 0.10 × 0.12 × 0.13 m m
was grown from aqueous eth an ol. From a total of 1 738 reflection s m easured in th e ran ge
Collect. Czech. Chem. Commun. (Vol. 66) (2001)

Achiral 1,1′-Biphenyl-2,2′,6,6′-tetracarboxylic Acids
831
h = 0 to 16, k = 0 to 13, l = –15 to 14, 1 671 were in depen den t (Rin t = 0.019) an d 1 176 were
regarded as observed accordin g to th e I > 2σ(I) criterion . Th ree stan dard reflection s m on i-
tored every 1 h sh owed 2.7% total decay. Th e in ten sities were corrected for absorption (µ =
0.140 m m –1) by a n um erical m eth od18 (Tm in = 0.4249, 0.5607). Th e structure was solved by
direct m eth ods (SIR3)19 an d refin ed by full-m atrix least squares based on F2 (SHELXL93)17
.
Th e arom atic h ydrogen s were fixed in calculated position s an d assign ed th e tem perature pa-
ram eters am oun tin g to 1.2-m ultiples of th ose of th eir bon din g partn ers; th e carboxyl h ydro-
gen s were refin ed isotropically. Th e refin em en t con verged to R = 0.0456, wR = 0.1020,
GOF = 1.069 for 126 param eters. Th e fin al differen ce m ap displayed n o peaks of ch em ical
sign ifican ce.
2c: C16H8N2O12, M = 437.38, m on oclin ic, space group P21/c (No. 14), a = 14.684(2) Å, b =
16.993(1) Å, c = 15.470(2) Å, β = 111.812(9)°, V = 3583.3(7) Å3, F(000) = 1 848, Dc
=
1.621 g cm –3 for Z = 8. A colourless irregular prism of th e dim en sion s 0.35 × 0.40 ×
0.40 m m was selected from th e preparative batch . From a total of 5 852 reflection s m easured
in th e ran ge h = 0 to 16, k = 0 to 19, l = –17 to 16, 5 614 were in depen den t (Rin t = 0.013)
an d 3 647 were regarded as observed accordin g to th e I > 2σ(I) criterion . Th ree stan dard re-
flection s m on itored every 1 h sh owed 2.9% total decay. Th e structure was solved by direct
m eth ods (SIR3)19 an d refin ed by full-m atrix least squares based on F2 (SHELXL93)17. Th e ar-
om atic h ydrogen s were fixed in calculated position s an d assign ed th e tem perature param e-
ters am oun tin g to 1.2-m ultiples of th ose of th eir bon din g partn ers; th e carboxyl h ydrogen s
were refin ed isotropically. Th e refin em en t con verged to R = 0.0435, wR = 0.1154, GOF =
1.030 for 573 param eters. Th e fin al differen ce m ap displayed n o peaks of ch em ical sign ifi-
can ce.
Crystallograph ic data for th e structures reported in th is paper h ave been deposited with
th e Cam bridge Crystallograph ic Data Cen tre as supplem en tary publication n um bers
CCDC-102374 (2a), CCDC-152285 (2b) an d CCDC-152286 (2c). Copies of th e data can be
obtain ed free of ch arge on application to CCDC, e-m ail: deposit@ccdc.cam .ac.uk.
This work was performed within the framework of the research project Z4 055 905 and was sup-
ported by the Grant Agency of the Czech Republic (grant No. 203/00/0138).
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