The pentafluorophenyl group as π-acceptor for anions : a case study
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The pen a luo ophenyl g oup as π-accep o o anions : a case s udy
Giese, Michael; Alb ech , Ma kus; Valkonen, A o; Rissanen, Ka i
Giese, M., Alb ech , M., Valkonen, A., & Rissanen, K. (2015). The pen a luo ophenyl
g oup as π-accep o o anions : a case s udy. Chemical Science, 6(1), 354-359.
h ps://doi.o g/10.1039/C4SC02762K
2015
The pen afluo ophenyl g oup as p-accep o o
anions: a case s udy†‡
Michael Giese,
a
Ma kus Alb ech ,*
a
A o Valkonen
b
and Ka i Rissanen*
b
The p esen s udy gi es a comp ehensi e insigh in o anion–pin e ac ions in he solid s a e, ocusing on
pu ely o ganic and cha ge-neu al fluo ophenyl g oups bea ing a posi i e cha ge loca ed a a side chain.
The de ailed s a is ical analysis o a se ies o s uc u al da a se s shows he geome ical a iabili y o
anion–pbonding in he solid s a e. I e eals he di ec ing subs i uen s a he a ene as key elemen s o
he posi ional p e e ences o anions abo e p-sys ems. The s uc u al a ie y o he in e ac ion be ween
anions and elec on-deficien a enes is conside ed by use o he hap ici y concep . Toge he wi h new
e alua ion c i e ia, wo help ul ools o unde s and and desc ibe anion–pin e ac ions in he solid a e used.
In oduc ion
Sup amolecula chemis y is dened as he chemis y o non-
co alen in e ac ions. Due o hei b oad e sa ili y ( om weak
an de Waals in e ac ions o hyd ogen bonding and s ong
elec os a ic a ac ions) hey a y d ama ically in hei ene -
ge ics.
1
Oen non-co alen in e ac ions a e weak compa ed o
co alen bonds. Howe e , due o coope a i e and addi i e
effec s hey a e able o con ol molecula o ganiza ion and
assembly p ocesses and o m s able sup amolecula agg ega es.
Ano he impo an ea u e o non-co alen in e ac ions,
e e sibili y and sensi i i y o ex e nal s imuli p o ide he
abili y o co ec e o s in he assembly, sel -heal s uc u al
dis u bances, and c ea e new unc ional ma e ials.
2
Only ecen ly he in e ac ion be ween anions and elec on-
decien a enes has gained conside able a en ion, due o i s
po en ial applica ion in anion sensing, ecogni ion p ocesses
and ele ance in enzyme ac i i y.
3
Since 2002 his in e molec-
ula o ce is widely accep ed as an inuen ial a ac i e in e -
ac ion.
3,4
A se ies o compu a ional as well as s uc u al s udies
suppo he “exis ence”o anion–pin e ac ions based on mo e
o less a bi a y e alua ion c i e ia.
3,5
Thus, anion–pin e ac-
ions we e conside ed o be “commonplace”. In 2009 Hay and
Cus elcean epo ed an analysis o he o ien a ion o anions
owa ds p-sys ems using he Camb idge S uc u al Da abase
(CSD).
6
The s ic c i e ia o anion–pin e ac ions selec ed in
his s udy e oked a con o e sial discussion, since i did no
e eal a single example o such an in e ac ion in he CSD.
7
Since 2008, we in es iga e anion–pin e ac ions o pen a-
uo ophenyl de i a i es.
8
Due o he elec on wi hd awing
na u e o he uo ine a om his g oup shows an opposi e
cha ge dis ibu ion compa ed o co esponding phenyl
de i a i es. Only ew examples by o he g oups we e epo ed
whe e his a oma ic moie y was used o anion–ps udies
(see Fig. 1).
9
In compa ison o many p e ious in es iga ions, a se o
e ms and condi ions we e chosen o sys ema ically unde s and
he in e ac ion be ween anions and elec on decien a enes:
Fig. 1 Pen afluo ophenyl ecep o s o Reedijk (1),
9a
Ghosh (2),
9b,c
Johnson (3),
9d
Maeda (4)
9e–g
as well as Mizuse
9h,i
and Webe (5)
9j
o
“anion–pin e ac ion s udies”in he c ys al, solu ion o in he gas
phase.
a
Ins i u ¨
u O ganische Chemie, RWTH Aachen Uni e si y, Landol weg 1, 52074
Aachen, Ge many. E-mail: [email p o ec ed]w h-aachen.de
b
Depa men o Chemis y, Nanoscience Cen e , Uni e si y o Jy ¨
askyl¨
a, Su on ie 9,
40014 Jy ¨
askyl¨
a, Finland. E-mail: ka i. . issanen@jyu.; Fax: +358 14 260 2501;
Tel: +358 50 562 3721
†This manusc ip is dedica ed o P o . Jean-Ma ie Lehn on he occasion o his
75 h bi hday.
‡Elec onic supplemen a y in o ma ion (ESI) a ailable. CCDC 967089, 967097,
1005267–1005289. Fo ESI and c ys allog aphic da a in CIF o o he elec onic
o ma see DOI: 10.1039/c4sc02762k
Ci e his: Chem. Sci.,2015,6,354
Recei ed 9 h Sep embe 2014
Accep ed 3 d Oc obe 2014
DOI: 10.1039/c4sc02762k
www. sc.o g/chemicalscience
354 |Chem. Sci.,2015,6, 354–359 This jou nal is © The Royal Socie y o Chemis y 2015
Chemical
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(1) The cha ge neu al pen auo ophenyl uni (C
6
F
5
) was
chosen as elec on decien moie y in o de o ule ou ha he
in e ac ion be ween he p-sys em and he anion is mainly based
on elec os a ic a ac ion which o e ules a possible weak
epulsion be ween he a oma ic uni and he anion.
(2) A posi i e cha ge was es ablished a he subs i uen o he
C
6
F
5
g oup ei he di ec ly bound o he ing o sepa a ed by a
space . This gua an ees he p esence o an anion in he icini y
o he elec on decien moie y.
Resul s
Ou p esen s udy is in he way unique, as i analyses a huge
da a se o expe imen ally ob ained s uc u es o pu ely o ganic
p-accep o complexes o uo oa enes (pe uo ina ed o pa ly
uo ina ed) wi h a ious anions. In con as o p e ious epo s,
he ocus is on he in e ac ion o anions wi h uncha ged
p-sys ems. The ole o he anion as well as o di ec ing
subs i uen s in he pe iphe y o he elec on decien a ene is
in es iga ed. In his wo k, he posi ions o 101 anions ob ained
a e sys ema ically compa ed om 80 c ys al s uc u es de e -
mined by us, 25 in his wo k (see ESI‡), he emaining 55 being
published ea lie ,
8
wi h he aim o ge a comp ehensi e pic u e
o he e sa ili y o anion–pcon ac s in he solid s a e (see
Fig. 2).
C i e ia o desc ibe in e ac ions be ween anions and p-
sys ems
In o de o ge an o e iew o he in es iga ed s uc u es, he
posi ions o 101 anions (8 chlo ide, 58 b omide, 17 iodide and
17 s uc u es wi h o he anions such as e auo obo a e, hex-
auo ophospha e o ni a e) we e plo ed in a no malized
coo dina e sys em. The eby, he uo ina ed phenyl g oup is
loca ed in he xz-plane wi h i s cen e in he ze o poin .
The g aphical analysis (Fig. 3) shows ha he majo i y o he
anions (91, 89%) a e loca ed abo e (o below) he plane o he
a ene (on- op posi ion). Only 11 anions a e ound in he ou e
pe iphe y o he a ene (side-on posi ion). In hose examples,
ei he coc ys allized sol en molecules o ce he anions away
om he op o he p-sys em o hey a e bound o o ho-
hyd ogen a oms o pa ially uo ina ed a enes ( ew examples o
C
6
HF
4
,C
6
H
2
F
3
,C
6
H
3
F
2
de i a i es a e included in he e).
8e
Anions loca ed on- op o he p-sys em show a b oad posi ional
dis ibu ion abo e he plane o he a ene wi h a ocus o he
densi y o he anions nea he cen e o he a oma ic uni .
As men ioned in he in oduc ion, anion–pin e ac ions in
he solid s a e a e ega ded as ei he “commonplace o
ex ao dina y”depending on he selec ed e alua ion c i e ia. In
he e diffe en epo ed c i e ia we e applied on he collec ed
s uc u al da a se . The ea ly c i e ia o Dey`
ae al. (2002:
dis ance be ween a ene-ca bon a oms and anion <P dW + 1.0
˚
A)
5b
and Reedijk and cowo ke s (2008: dis ance be ween cen e
o a ene, any o he a ene a oms and he anion <P4.0 ˚
A)
10
lead
o 54 o 40 hi s, espec i ely, o halide con aining anion–p
agg ega es. Mo e es ic ed e alua ion c i e ia by Hay and
Cus elcean (2009: dis ance be ween each a ene-ca bon a om
and anion <P dW + 0.2 ˚
A)
6
do no lead o any anion–pcon ac
in he analysis o he pen auo ophenyl sys em. In 2011 Dey`
a
and cowo ke s epo ed modied c i e ia o anion–pin e ac-
ions conside ing he s uc u al a iabili y o he ela i e posi-
ion o he anion abo e he p-sys em (dis ance be ween a ene-
ca bon a oms and anion <P dW + 0.8 ˚
A).
7
This leads o 36 hi s
o anion–pcomplexes wi hin he p esen s udy.
Since c ys al s uc u es a e he esul o a complex in e play
o non-co alen in e ac ions as packing effec s anions migh be
o ced in un a ou able posi ions in he c ys al la ice. Based on
his, he ini ial 2002 c i e ia o Dey`
a seem o be oo loosely
selec ed. On he o he hand, anion–pin e ac ions easily can be
inuenced by o he non-co alen in e ac ions. Due o di ec ing
effec s o he subs i uen s a he uo oa ene he posi ion abo e
he cen e o he p-sys em does no ha e o be he mos
a ou able one o he anion. The e o e, Hay's 2009 c i e ia
would be co ec , i he in e ac ion would ha e a high co alen
con ibu ion. Howe e , anion–pin e ac ions a e mainly based
Fig. 2 Rep esen a i e s uc u es o pen afluo ophenyl ecep o s 6–10
in he c ys al discussed in he p esen s udy showing he e sa ili y o
anion–pcomplexes as obse ed in he solid s a e (C: g ey, F: yellow,
Cl: g een, B : ed, I: pink; co-c ys allized sol en molecules and
coun e ca ions a e omi ed o cla i y).
8b,e, ,i
Fig. 3 G aphical analysis o 101 anion posi ions in espec o a
no malized (pen a)fluo oa ene. (A) Top iew; (B) side iew (C: g ey, F:
yellow, Cl: g een, B : ed, I: pink, o he anions (e.g. BF
4
,PF
6
,NO
3
,
I
3
, B IB
,I
42
): ligh g een).
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on non-di ec ed elec os a ic a ac ion. Consequen ly, he
in e ac ion o molecula species wi h a p-sys em should no be
es ic ed o he posi ion di ec ly abo e he cen e o an a ene
and he exac sum o an de Waals adii is no a sufficien
c i e ion o e alua e anion–pcon ac s. Fo example, ca ion–p
in e ac ions o phenyl g oups can span he whole ange om h
1
o h
6
. Based on his, a deni ion o anion–pin e ac ions using
he “hap ici y concep ”in combina ion wi h newly adjus ed
c i e ia a e ecommended in he e:
(1) The anion has o be loca ed abo e he p-sys em. The e-
o e, any cen oid- ing a om–anion angle should no be highe
han 90(+10% o ole ance).
(2) The dis ance be ween he anion and he plane o he
p-sys em has o be sho e han P dW + 0.4 ˚
A ( he p oblem o a
xed numbe o he dW adii o halogen anions is discussed
in e . 7).
(3) The hap ici y o he anion–pin e ac ions is gi en by he
numbe o con ac s o ing a oms which a e <P dW + 0.4 ˚
A.
The main ex o he a icle should go he e wi h headings as
app op ia e.
An al e na i e o epo he hap ici y would be o lis he
“offse ”o he anion om he cen e o he a oma ic uni in
o de o desc ibe he ela i e posi ion o he anion o he
a oma ic ing, which is easy o quan i y. Howe e , o us he
simple hap ici y seems o be mo e desc ip i e and easie
compa able.
The e alua ion c i e ia p oposed in he e a e based on ou
expe ience wi h solid s a e anion–pin e ac ions. Fo an
a ac i e in e ac ion be ween an anion and an elec on-
decien a ene he anion has o be loca ed on op o he
a ene (c i e ion 1) in close p oximi y o he a ene plane
(c i e ion 2). The 0.4 ˚
A which a e added o he dW adii a e
due o a ecen adjus men o he abula ed dW adii o
halide anions as epo ed by Dey`
a and cowo ke s in 2011.
7
The nal c i e ion in oduces a ool o desc ibe he
e sa ili y o anion–pin e ac ions in he solid s a e by a
simple conside a ion o he gi en a ene a om/anion
dis ances.
Selec ed c ys al s uc u es
The dened c i e ia will be illus a ed by he c ys al s uc u es
o he chlo ide 11, he iodide 12 as well as he b omide sal s 13–
15 ep esen ed in Fig. 4. The de i a i es bea diffe en ca ionic
uni s (ammonium e sus imidazolium e sus aminopy idinium)
in he side chain. In he discussion o he c ys al s uc u es only
ele an dis ances and in e ac ions will be desc ibed al hough
he e a e many mo e p esen .
The c ys al s uc u e o 11 ep esen s he ideal case o anion–
pcon ac s (see Fig. 5). The chlo ide is xed di ec ly on op o he
cen e o he pen auo ophenyl uni by wo non-classical
hyd ogen bonds o he wo me hyl g oups (CH/Cl ¼2.92, 2.94
˚
A). All six ca bon/anion dis ances ma ch ou c i e ia (C1–C6 ¼
3.50–3.83 ˚
A) esul ing in he “h
6
”- ype in e ac ion. Howe e , he
sho es non-co alen con ac s in he solid s a e s uc u e o 11
a e obse ed be ween he anion and he coc ys allized wa e
(HOH/Cl ¼2.43 ˚
A).
The closely ela ed s uc u e o compound 12 is shown in
Fig. 6. Iodide is loca ed close o he ca ionic ammonium g oup
as well as o he pen auo ophenyl p-accep o . In e ac ion wi h
he e ae hylammonium uni akes place by non-classical
hyd ogen bonds be ween iodide and a-CH o wo e hyl g oups
(CH/I¼3.17, 3.22 ˚
A). The iodide is loca ed close o he cen e
o he pen auo ophenyl uni wi h dis ances o ca bon a oms o
4.10 (C1), 4.07/4.05 (C2/C6), 3.98/3.99 (C3/C5) and 3.94 ˚
A (C4).
The dis ance be ween iodide and C1 sligh ly exceeds ou limi
esul ing in a “h
5
” ype a angemen . Howe e , due o he
Fig. 4 Selec ed examples o pen afluo ophenyl de i a i es wi h
diffe en ca ionic side chains.
Fig. 5 S uc u e o 11 in he c ys al exhibi ing he h
6
in e ac ion
be ween he pen afluo ophenyl g oup and chlo ide. The co-c ys al-
lized wa e was omi ed o cla i y.
Fig. 6 S uc u e o 12 in he c ys al exhibi ing he h
5
in e ac ion
be ween he pen afluo ophenyl g oup and iodide.
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bulkiness o he ammonium subs i uen , he anion is some-
wha shied om he cen e owa ds C4 p ohibi ing “h
6
”.
The ele an anion ca ion pai o 13 as ound in he c ys al is
depic ed in Fig. 7. The imidazoline plane is somewha il ed
agains he C1–C4 axis o he uo ina ed phenyl g oup wi h he
CH]CH uni poin ing owa ds he elec on decien ing.
Imidazoline-CH in 5-posi ion binds o he b omide anion (H/
B ¼2.77 ˚
A). Dis ances be ween b omide and he ing ca bon
a oms a e 4.04 (C1), 3.91 (C2), 3.65 (C3), 3.46 (C4), 3.59 (C5) and
3.87 ˚
A (C6). The in e ac ion o C1 clea ly exceeds ou limi and
he s uc u e again can be desc ibed o be h
5
.
In o de o show he e sa ili y o obse ed anion–pcon ac s
in he p esen solid s a e s udy we depic in addi ion he c ys al
s uc u e o 14 (Fig. 8). Simila o he s uc u es o 11 and 12 he
b omide is xed by non-classical hyd ogen bonds o he alkyl
g oups close o he pen auo ophenyl sys em (CH/B ¼3.41,
3.71 ˚
A). Howe e , in con as o he s uc u es desc ibed abo e,
he anion is shied owa ds he im o he p-sys em leading o
ou C/B dis ances wi hin he applied e alua ion c i e ia
(C3–C6 ¼3.92, 3.54, 3.43 and 3.70 ˚
A) esul ing in a “h
4
”- ype
a angemen o he anion ela i e o he elec on-decien
a ene.
S uc u e 15 is e y diffe en (Fig. 9). The 2-aminopy idin
subs i uen is o ien a ed wi h he amino g oup away om he
pen auo ophenyl moie y. The amine unde goes hyd ogen
bonds o b omide anions which a e no ele an o he p esen
discussion. The in e ac ion o H6 o he py idine o b omide
(2.77 ˚
A) is ele an . I di ec s he anion o e he a oma ic uni ,
no a he cen e bu a he im. Ca bon b omide dis ances a e
4.33 (C1), 3.69 (C2), 3.60 (C3), 4.15 (C4), 4.73 (C5), and 4.80 ˚
A
showing clea ly he h
2
mode o in e ac ion.
In e ac ions o halides wi h pen auo ophenyl de i a i es
Due o he sphe ical shape and easy de e mina ion o hei
posi ion, halides a e ideal anions o analyze anion–pin e ac-
ions. The e o e he ollowing discussion will ocus on his class
o anions.
Applying hose c i e ia o ou da a se leads o 48 anion–p
con ac s o he halide s uc u es con aining pen auo ophenyl
uni . A summa y o he s uc u al ndings depending on he
applied sea ch c i e ia is gi en in Table 1.
In o de o e alua e he posi ion o he anion in espec o he
p-sys em, he “hap ici y”( he numbe o easonable bonding
con ac s be ween an anion and ca bon a oms o he a ene) was
de e mined (Fig. 10). In eigh cases he anions a e loca ed close
o he cen e o he a ene and ma ching he c i e ia o all six
ca bon a oms, hus hey show a h
6
- ype binding mo i . Howe e ,
he majo i y o anions (40 anions) in e ac s pa ially wi h he
elec on-decien p-sys em (h
1
–h
5
binding) and, in e es ingly,
in only wo s uc u es he anion is loca ed close o only one
ca bon a om o he pen auo ophenyl uni .
The s uc u al compa ison o he c ys allog aphic da a
e eals a signican inuence o he scaffold o med by he
subs i uen o he p-accep o s. Those s uc u es whe e he side
g oup o he p-accep o (i) is igid, (ii) does no in oduce
dissymme y and (iii) any dis u bing coc ys allized sol en
molecules a e absen (see 6, Fig. 2 as a ep esen a i e example
o an example) lead o ou een hi s wi hin ou collec ion o
da a wi h anions loca ed close abo e he cen e o he elec on-
decien a ene (see Fig. 11a and b). In con as o ha ,
Fig. 8 Solid s a e s uc u e o 14 illus a ing he h
4
- ype a angemen
o he b omide ela i e o he pen afluo ophenyl uni .
Fig. 9 S uc u e o 15 in he c ys al exhibi ing he h
2
in e ac ion
be ween he pen afluo ophenyl g oup and b omide.
Table 1 Anion–pcon ac s o in es iga ed halide de i a i es in espec o he applied e alua ion c i e ia
Reedijk e al. 2008 ( e . 10) Hay e al. 2009 ( e . 6) Dey`
ae al. 2002 ( e . 5b) Dey`
ae al.2011 ( e . 7) This s udy 2014
Cl 3 0 3 3 6
B 33 0 35 25 29
I 11 0 16 8 13
P47 0 54 36 48
Fig. 7 S uc u e o 13 in he c ys al exhibi ing he h
5
in e ac ion
be ween he pen afluo ophenyl g oup and b omide.
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co esponding s uc u es wi h mo e exible and less symme ic
scaffolds (see 7, Fig. 2 as a ep esen a i e example) show a
signican ly b oade dis ibu ion o he anion posi ion abo e
he ing (see Fig. 11c and d o an example). This obse a ion
suppo s ou p e ious sugges ion ha he posi ion o he anion
in espec o he p-acidic uni s ongly depends on he
subs i uen s in he pe iphe y o he a ene and can be con olled
by hose.
8a,b
Conclusions
In conclusion, he p esen ed s a is ical app oached based on
sys ema ically ob ained expe imen al da a, in es iga es me al-
ee and cha ge-neu al uo ophenyl de i a i es in espec o
hei p-accep o abili y o anions. Posi i e cha ge is only
in oduced in he pe iphe y o he a ene side chains. The esul s
clea ly show ha anions p e e he posi ion abo e he elec on-
decien p-sys em (nea ly 90%). The high a iabili y o he
anion posi ion is caused by in e play o a ious non-co alen
in e ac ions. The eby, di ec ing subs i uen s a he uo oa ene
play a key ole. The in oduced concep o hap ici y as well as
he p oposed e alua ion c i e ia a e help ul o sufficien ly
desc ibe anion–pin e ac ions in he c ys al.
Acknowledgemen s
We hank he Fonds de Chemischen Indus ie (MA) and he
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