Counterion influence on the N–I–N halogen bond

This is an elec onic ep in o he o iginal a icle. This ep in may di e om he o iginal in pagina ion and ypog aphic de ail. Au ho (s): Ti le: Yea : Ve sion: Please ci e he o iginal e sion: All ma e ial supplied ia JYX is p o ec ed by copy igh and o he in ellec ual p ope y igh s, and duplica ion o sale o all o pa o any o he eposi o y collec ions is no pe mi ed, excep ha ma e ial may be duplica ed by you o you esea ch use o educa ional pu poses in elec onic o p in o m. You mus ob ain pe mission o any o he use. Elec onic o p in copies may no be o e ed, whe he o sale o o he wise o anyone who is no an au ho ised use . Coun e ion in luence on he N–I–N halogen bond Bedin, Michele; Ka im, Ala i; Rei i, Ma cus; Ca lsson, Anna-Ca in C.; Topic, Filip; Ce ina, Ma io; Pan, Fang ang; Ha el, Vacla ; Al-Ame i, Fa ima; Sindela , Vladimi ; Rissanen, Ka i; G ä ens ein, Jü gen; E dély, Má é Bedin, M., Ka im, A., Rei i, M., Ca lsson, A.-C. C., Topic, F., Ce ina, M., Pan, F., Ha el, V., Al-Ame i, F., Sindela , V., Rissanen, K., G ä ens ein, J., & E dély, M. (2015). Coun e ion in luence on he N–I–N halogen bond. Chemical Science, 6(7), 3746-3756. h ps://doi.o g/10.1039/C5SC01053E 2015 Coun e ion influence on he N–I–N halogen bond† Michele Bedin,‡ a Ala i Ka im,‡ a Ma cus Rei i, a Anna-Ca in C. Ca lsson, a Filip Topi´ c, b Ma io Ce ina, be Fang ang Pan, b Vacla Ha el, c Fa ima Al-Ame i, a Vladimi Sindela , c Ka i Rissanen, b J¨ u gen G ¨ a ens ein a and M´ a ´ e E d´ elyi* ad A de ailed in es iga ion o he influence o coun e ions on he [N–I–N] + halogen bond in solu ion, in he solid s a e and in silico is p esen ed. T ansla ional diffusion coefficien s indica e close a achmen o coun e ions o he ca ionic, h ee-cen e halogen bond in dichlo ome hane solu ion. Iso opic pe u ba ion o equilib ium NMR s udies pe o med on iso opologue mix u es o egioselec i ely deu e a ed and nondeu e a ed analogues o he model sys em showed ha he coun e ion is incapable o al e ing he symme y o he [N–I–N] + halogen bond. This symme y emains e en in he p esence o an un a o able geome ic es ain . A high p e e ence o he symme ic geome y was ound also in he solid s a e by single c ys al X- ay c ys allog aphy. Molecula sys ems encompassing weakly coo dina ing coun e ions beha e simila ly o he co esponding sil e (I) cen e ed coo dina ion complexes. In con as , sys ems possessing mode a ely o s ongly coo dina ing anions show a dis inc ly diffe en beha io . Such sil e (I) complexes a e con e ed in o mul i-coo dina e geome ies wi h s ong Ag–O bonds, whe eas he iodine cen e ed sys ems emain linea and lack di ec cha ge ans e in e ac ion wi h he coun e ion, as e ified by 15 N NMR and DFT compu a ion. This sugges s ha he [N–I–N] + halogen bond may no be sa is ac o ily desc ibed in e ms o a pu e coo dina ion bond ypical o ansi ion me al complexes, bu as a seconda y bond wi h a subs an ial cha ge- ans e cha ac e . In oduc ion Coun e ions play impo an oles in chemis y, o example in he modula ion o o ganoca alysis, 1,2 chemical eac ions' ene gy p oles, 3,4 me al clus e a oma ici y, 5 spec oscopic p ope ies o o ganic compounds, 6 su ac an micelliza ion, 7 memb ane pe mea ion, 8 gela ion, 9 sup amolecula assemblies, 10–12 c ys al s uc u e, 13 and ch oma og aphic sepa a ion. 14 A concei able inuence o coun e ions on he s eng h and geome y o halogen bonding has, howe e , so a ba ely ecei ed any a en ion. 15–17 Halogen bonding has ecen ly been dened, 18 and has a ac ed as in e es due o i s immense po en ial o p o ide a no el ool o sup amolecula chemis y, 19,20 c ys al enginee ing, 21,22 anion ecogni ion, 23,24 o ganic syn hesis, 25 s uc u al biology, 26 medicinal chemis y and chemical biology, 27 o ins ance. Th ee-cen e halogen bonds, 15 some imes also e med coo - dina i e halogen bonds, 28,29 a e o med by he simul aneous in e ac ion o an elec ophilic halogen (X) wi h wo elec on dono unc ionali ies (D). The h ee in e ac ing a oms may be a anged in an asymme ic [D–X/D] + , o in a symme ic [D/ X/D] + geome y. O hese, he o me is bes desc ibed by a double well, whe eas he la e by a single well ene gy po en- ial. 30 The asymme ic a angemen ha encompasses a sho e and s onge co alen bond (D d+ –X), and a weake and longe halogen bond (D d /X) is mo e pola han he one possessing a symme ic geome y and, acco dingly, a symme ic cha ge dis ibu ion (D d /X d+ / d D). S ong, asymme ic coo dina ion o a coun e ion may a o he o ma ion o he asymme ic, mo e pola geome y o e he symme ic, less pola one. The asymme y o he analogous h ee-cen e [N–H–N] + hyd ogen bond 31 has been pa ly a ibu ed o he pola izing effec o he coun e ion. 32 Limbach e al. epo ed he size and cha ge delocaliza ion dependen effec o coun e ions on he symme y o low ba ie hyd ogen bonds. 33 Whe he a coun e ion is capable o desymme izing he [N–I–N] + halogen bond depends on he in insic ene ge ic p e e ence o he halogen bond o he symme ic geome y 30 as well as on he p ope ies o he coun e ion. a Depa men o Chemis y and Molecula Biology, Uni e si y o Go henbu g, SE-412 96 Go henbu g, Sweden. E-mail: [email p o ec ed]; Tel: +46-31-786 9033 b Uni e si y o Jy askyla, Depa men o Chemis y, Nanoscience Cen e , P.O. Box. 35, FI-40014 Uni e si y o Jy askyla, Finland c Depa men o Chemis y and RECETOX, Masa yk Uni e si y, Kamenice 5, 625 00 B no, Czech Republic d The Swedish NMR Cen e, Medicina ega an 5, SE-413 90 Go henbu g, Sweden e Depa men o Applied Chemis y, Facul y o Tex ile Technology, Uni e si y o Zag eb, P ilaz ba una Filipo i´ ca 28a, HR-10000 Zag eb, C oa ia †Elec onic supplemen a y in o ma ion (ESI) a ailable: Expe imen al de ails o syn hesis, compound cha ac e isa ion, IPE NMR measu emen s, compu a ional and c ys allog aphic p ocedu es, and c ys al da a o 1-Ag/I o 7-Ag/I,and12-Ag. CCDC 1045981–1045995. Fo ESI and c ys allog aphic da a in CIF o o he elec onic o ma see DOI: 10.1039/c5sc01053e ‡These au ho s con ibu ed equally o his wo k. Ci e his: Chem. Sci.,2015,6,3746 Recei ed 23 d Ma ch 2015 Accep ed 20 h Ap il 2015 DOI: 10.1039/c5sc01053e www. sc.o g/chemicalscience 3746 |Chem. Sci.,2015,6,3746–3756 This jou nal is © The Royal Socie y o Chemis y 2015 Chemical Science EDGE ARTICLE Open Access A icle. Published on 20 Ap il 2015. Downloaded on 29/06/2015 13:02:52. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online View Jou nal | View Issue Ea ly solid s a e 14 N nuclea quad upole esonance (NQR) and in a ed s udies sugges ed 34 ha he N–B bonds o [bis(py idine)b omine] + a e equi alen o i s hexauo ophospha e sal , bu nonequi alen o i s pe chlo a e and ib omide sal s. The loss o cen osymme y in he la e wo may be in e p e ed as a consequence o c ys al packing o ces in combina ion wi h he diffe en coo dina ion s eng h o a ious coun e ions. Al e na- i ely, i may be explained by he highly compa able ene gies o he symme ic and he asymme ic geome ies. Howe e , bo h in e - p e a ions a e deba able. Diffe en N–B bond leng hs, 2.120(3) ˚ A and 2.156(3) ˚ A, we e epo ed o he analogous [bis(quinuclidine) b omine] + e auo obo a e complex in he solid s a e. 35 Fo he analogous iodine cen e ed py idine sal s no analogous coun- e ion effec s ha e ye been epo ed. Such [N–X–N] + complexes a e common syn he ic eagen s, 36–41 whose eac i i y is ema k- ably sensi i e o minu e s uc u al 42 and en i onmen al changes. 41 In con as o he de ailed knowledge collec ed on he inuence o en i onmen al ac o s on he closely ela ed h ee- cen e hyd ogen bonds, 32 simila effec s on halogen bonds ha e so a been assessed o a much lesse ex en . As pa o ou ongoing in es iga ion o he h ee-cen e halogen bond, 30,43 he inuence o he coun e ion on he s eng h and geome y o he in e ac ion in solu ion and in he solid s a e is add essed he ein. Resul s and discussion [Bis(py idine)iodine] + complexes 44 and hei s uc u ally closely ela ed, geome ically es ained 1,2-bis(py idin-2-yle hynyl) benzene analogues p o ide e sa ile models o he in es iga- ion o he s uc u e and p ope ies o h ee-cen e halogen bonds, 15,30,38,39,43,45,46 and we e he e o e u ilized in his s udy. In o de o e alua e he coun e ion's abili y o modula e he geome y o he iodine cen e ed, h ee-cen e halogen bond, a se ies o anions o a ying size, cha ge dis ibu ion and coo - dina ion s eng h we e explo ed. Besides he sphe ical, weakly coo dina ing anions 12 BF 4  , ClO 4  , and PF 6  ha ha e p e i- ously been sugges ed 34,35 o inuence he geome y o he ela ed [bis(py idine)b omine] + complex, he weakly coo di- na ing SbF 6  , he mode a ely coo dina ing T O  and TsO  , and he small and s ongly coo dina ing 10,12 NO 3  and CF 3 CO 2  we e assessed (Fig. 1). To ensu e igh coo dina ion, 45 dichlo ome hane was chosen as sol en o he solu ion s udies. By sca enging he coun e ion wi h he bambusu il Bn 12 BU[6], 47,48 he “coun e ion- ee”[N–I–N] + complex was also in es iga ed. As he h ee-cen e halogen bond was p oposed o be essen ially analogous o he coo dina ion bond o sil e (I) complexes, 28,29 and as iodine(I) esembles sil e (I) in i s ionic adius (I + : 1.33 ˚ A, Ag + : 1.29 ˚ A) and in he linea geome y o i s bis-coo dina ion complex, we discuss he p ope ies o he [N–I–N] + complexes 1- I o 8-I in compa ison o he co esponding [N–Ag–N] + species 1- Ag o 8-Ag (Fig. 1). Syn hesis [Bis(py idine)iodine] + e auo obo a e (1-I), pe chlo a e (2-I), hexauo ophospha e (3-I), hexauo oan imona e (4-I), ia e (5-I), osyla e (6-I), ni a e (7-I), and iuo oace a e (8-I) complexes (Fig. 1), as well as hei selec i ely deu e a ed analogues (1-I-d o 8-I-d), we e syn hesized ollowing a p e i- ously published p ocedu e 30,46 om he co esponding sil e (I) complexes (1-Ag o 8-Ag,1-Ag-d o 8-Ag-d). Complex 9was p epa ed by addi ion o 1.8 equi alen s o he anion sca enge 47,48 dodecabenzylbambus[6]u il (Bn 12 BU[6]) o he dichlo ome hane solu ion o 1-I, o p oduce a “naked” [bis(py idine)iodine] + complex by apping he BF 4  coun e ion. Fo he p epa a ion o [(1,2-bis(py idin-2-yle hynyl)benzene) iodine] + e auo obo a e (10), ia e (11), and ni a e (12) and hei mono-deu e a ed analogues (10-d o 12-d), published syn he ic ou es 30 we e ollowed. See ESI† o de ails. Coun e ion coo dina ion in solu ion Ion coo dina ion in solu ion was e alua ed by acqui ing he ansla ional diffusion coefficien o he posi i ely and nega- i ely cha ged species o complexes 1–9(Table 1), using 1 H and 19 F NMR. Tigh anion coo dina ion o [bis(py idine)iodine] + was indica ed by he compa able ansla ional diffusion a es o he wo ions in he same solu ion, o each s udied sys em. A signican diffe ence be ween he diffusion coefficien s o he anionic and ca ionic species was de ec ed o 9-I. This indica es ha [bis(py idine)iodine] + and BF 4  o 9-I do no o m a igh ion pai . In line wi h ou expec a ions, he diffusion a e o he apped BF 4  o 9-I is lowe han ha o 1-I, and ma ches he diffusion a e o he anion sca enging agen Bn 12 BU[6] (D¼ 5.8 10 10 m 2 s 1 ) ha was added o he solu ion. The slowe diffusion a e o [bis(py idine)iodine] + o 9-I han ha o 1-I is well explained by he inc eased sol a ion o cha ged species as compa ed o neu al ones in apola sol en s, 49 and by an inc eased iscosi y o he solu ion upon addi ion o Bn 12 BU[6]. Diffusion NMR e eals s ong coo dina ion o he coun e ions o he sil e cen e ed complexes 1-Ag o 8-Ag as well. Fig. 1 The s uc u e o he model sys ems assessed o elucida ion o he coun e ion (Y  )effec on he [N–I–N] + halogen bond (X ¼I): [bis(py idine)iodine] + BF 4  (1-I), ClO 4  (2-I), PF 6  (3-I), SbF 6  (4-I), T O  (5-I), TsO  (6-I), NO 3  (7-I), and CF 3 CO 2  (8-I), and hei geome ically es ained [(1,2-bis(py idin-2-yle hynyl)benzene) iodine] + BF 4  (10-I), T O  (11-I) and NO 3  (12-I) analogues. The BF 4  o 9-I was sca enged wi h dodecabenzylbambus[6]u il (Bn 12 BU[6]). 47 The spec oscopic da a o 1-I o 8-I we e compa ed o hose o he co esponding sil e (I) complexes (X ¼Ag) 1-Ag o 8-Ag. This jou nal is © The Royal Socie y o Chemis y 2015 Chem. Sci.,2015,6,3746–3756 | 3747 Edge A icle Chemical Science Open Access A icle. Published on 20 Ap il 2015. Downloaded on 29/06/2015 13:02:52. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online 15 N NMR is a sensi i e ool o in es iga ion o halogen bond o ma ion, 30,43,45,50 and is commonly used o he assessmen o sol en effec s, p o ona ion and me al coo dina ion o ni oge- nous Lewis bases. 51–53 The 15 N NMR chemical shiso compounds 1–9we e de ec ed using 1 H, 15 N-HMBC expe i- men s, 54 p o iding a single signal o each compound (Table 1). Fo ma ion o he [N–I–N] + complex is accompanied by a compa able, la ge han 100 ppm chemical shichange (py idine, d 15N ¼67 ppm ( e . 30)) o 1-I o 9-I. The a ia ion o he 15 N NMR chemical shiso 1-Ag o 8-Ag indica es ha , in con as o iodine(I), sil e (I) in e ac s wi h anions in a coo di- na ion-s eng h dependen manne . Sol en and coun e ion coo dina ion o sil e (I) complexes has p e iously been epo - ed 52 o ha e a majo inuence on py idine 15 N NMR coo dina ion shis(d coo d ¼d complex d ligand ). S ongly coo - dina ing coun e ions may con e he linea , bis- coo dina e [bis(py idine)sil e ] + o is-coo dina e, neu al [bis(py idine)(coun e ion)sil e ] complexes. 52,55 The complex 8-Ag shows he mos deshielded 15 N NMR chemical shiamong he sil e (I) complexes, which is in line wi h CF 3 CO 2  being he s onges coo dina ing anion o he se ies. A smalle absolu e coo dina ion shi,41–45 ppm, o he sil e (I) complexes pos- sessing s ongly coo dina ing coun e ions, such as TsO  , CF 3 CO 2  and NO 3  , is explained by an efficien cha ge ans e om he anion o sil e (I) h ough o bi al o e lap. This dec eases he posi i e cha ge o sil e (I) and consequen ly he cha ge ans e om he py idine ni ogens o sil e (I), yielding smalle 15 N NMR coo dina ion shis. The small, #1 ppm, 15 N chemical shi a ia ion o 1-I o 9-I indica es he absence o an analogous di ec cha ge ans e in e ac ion o he coun e ion o he iodine(I) o [bis(py idine)iodine] + . Hence, s ong di ec coo dina ion o a coun e ion o iodine(I) by o bi al o e lap does no ake place; a he , his in e ac ion emains elec os a ic. Sligh ly lowe 15 N NMR chemical shis we e obse ed o 10-I (165.5 ppm), 11-I (165.0 ppm) and 12-I (163.3 ppm), eec ing weakened N–I bonds, as a consequence o he s e ic es ain in oduced by he 1,2-die hynylbenzene backbone. 28 The p opensi y o he coun e ions o 1-I o 9-I o compe e wi h py idine o coo dina ion o he emp y p-o bi al o I + was e alua ed by analyses o he 15 N NMR chemical shis o he [bis(py idine)iodine] + coun e ion and o he al e na i e [(py idine)(coun e ion)iodine] py idine geome ies, p edic ed a he B3LYP le el using he dichlo ome hane con inuum sol en model (Table 2, see ESI† o de ails). The 15 N chemical shiso he [bis(py idine)iodine] + coun e ion geome ies o 1-I o 8-I (N B , Table 2) a e p edic ed o be i ually coun e ion indepen- den , and compa able in magni ude o hose expe imen ally obse ed (Table 1). In con as , conside ably coun e ion depen- den shis a e p edic ed o he [(py idine)(coun e ion)iodine] complexes (N A , Table 2), wi h highe shielding o he ni ogen o hose encompassing weake coo dina ing anions. This sugges s ha py idine e sus anion exchange does no ake place. Compu a ional he mochemical analysis p edic s ha o ma ion o a [(py idine)(coun e ion)iodine] complex is endo he mic o complexes ha possess weakly and mode a ely coo dina ing anions, ye somewha exo he mic o TsO  ,NO 3  ,andCF 3 CO 2  (Table 2). I should be unde lined ha he applied he mochemical calcula ion does no ake in o accoun he elec os a ic a ac ion ha a ises in he elec oly e o med by [bis(py idine)iodine] + and i s coun e ion in he solu ion. This a ac ion, which is also supposed o accoun o he a ia ion in he expe imen al 15 N shis o 1-I o 8-I,ises ima ed obe20–30 kJ mol 1 (see ESI† o de ails). Wi h his co ec ion, he DFT esul s a e compa ible wi h he [bis(py idine)iodine] + complex, being s able o 1-I o Table 1 T ansla ional diffusion coefficien s, measu ed by 1 H and 19 F NMR de ec ion, and 15 N NMR chemical shi s Anion S uc u e D(ca ion) a 10 10 (m 2 s 1 )D(anion) 10 10 (m 2 s 1 )d( 15 N) (ppm) BF 4  1-I 16.8 16.4 175.1 ClO 4  2-I 9.5 — c 175.0 PF 6  3-I 10.3 10.5 175.8 SbF 6  4-I 9.8 — d 175.1 T O  5-I 14.0 15.0 175.1 TsO  6-I 16.3 16.2 174.8 NO 3  7-I 10.8 — c 174.8 CF 3 CO 2  8-I 18.7 15.7 175.2 [BF 4  ] b 9-I 9.4 6.0 175.5 BF 4  1-Ag 9.3 9.9 126.5 ClO 4  2-Ag 10.7 — c 124.0 PF 6  3-Ag 9.5 9.4 128.4 SbF 6  4-Ag 15.1 — d 129.3 T O  5-Ag 13.1 13.0 122.0 TsO  6-Ag 9.4 8.5 111.8 NO 3  7-Ag 10.4 — c 113.1 CF 3 CO 2  8-Ag 15.2 12.9 109.5 a [Bis(py idine)iodine] + . b BF 4  was sca enged wi h Bn 12 BU[6] in his solu ion p o iding a naked [bis(py idine)iodine] + . c This anion lacks an NMR ac i e nucleus p e en ing he acquisi ion o i s diffusion coefficien . d The 19 F NMR signal o his coun e ion is ex ensi ely spli and b oadened due o 1 J Sb,F . 3748 |Chem. Sci.,2015,6,3746–3756 This jou nal is © The Royal Socie y o Chemis y 2015 Chemical Science Edge A icle Open Access A icle. Published on 20 Ap il 2015. Downloaded on 29/06/2015 13:02:52. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online 8-I. S ong ion pai ing is suppo ed by he diffusion NMR da a. This conclusion is u he suppo ed by de ec ion o he [bis(py idine)iodine] + complex by HR(ESI)MS o all s udied sys ems (see ESI o de ails†), u he co obo a ing ha py idine e sus anion exchange does no ake place in solu ion. The 15 N NMR shio 9-I is compa able o ha o 1-I, sug- ges ing ha he p esence o absence o a weakly coo dina ing coun e ion does no inuence he elec on dis ibu ion o he [N–I–N] + halogen bond. The BF 4  o 9-I was sca enged by addi ion o an excess (1.8 eq.) o Bn 12 BU[6] o he solu ion o 1-I wi h he efficien apping o he coun e ion being con med by cha ac e is ic changes (a) in he 1 H NMR chemical shiso bambusu il 47 (Fig. 2), (b) o he ansla ional diffusion coeffi- cien s o BF 4  (Table 1), (c) o he 15 N NMR shis al e a ion o Bn 12 BU[6] (Dd 15N ¼2.1 ppm o N–CH 3 ,and2.4ppm o N–CH 2 , Fig. S1†), and (d) by obse a ion o in e molecula 1 H, 19 Fhe e - onuclea O e hause effec s be ween BF 4  and Bn 12 BU[6] (Fig. S2†) whe eas he e is no 1 H, 1 H NOESY c osspeak be ween [bis(py idine)iodine] + and Bn 12 BU[6]. The use o an excess o Bn 12 BU[6] in he s udies o 9-I ensu ed he absence o ee BF 4  in solu ion, and hence ha a coun e ion- ee [bis(py idine)iodine] + complex was in es iga ed. EXSY c osspeaks be ween he signals o he ee and BF 4  -bound Bn 12 BU[6] (Fig. S3†) indica ed anion mig a ion be ween he Bn 12 BU[6] uni s. Upon addi ion o Bn 12 BU [6] o 8-I, he 15 N NMR chemical shi emained unal e ed, suppo ing he abo e conclusions, and in addi ion u he con med ha CF 3 CO 2  is incapable o compe ing wi h py idine o iodine(I) coo dina ion. Halogen bond symme y in solu ion Iso opic pe u ba ion o equilib ium (IPE) NMR 56 is a echnique capable o dis inguishing be ween a s a ic, symme ic geome y and a apidly in e con e ing pai o asymme ic geome ies in solu ion. I has been used success ully, o example, in he symme y elucida ion o [N–H/N] + hyd ogen bonded 57,58 and [N/X/N] + halogen bonded 30,46 molecula sys ems, as well as o ca boca ions 59 and me al chela ing complexes. 60 The main ad an age o IPE is ha i succeeds e en when he apidly in e con e ing species canno be “ ozen ou ”due o a shallow ene gy ba ie be ween hem. I equi es he analysis o an iso opologue mix u e o a compound, which is oen a mix u e o i s selec i ely deu e a ed and nondeu e a ed analogues. In such solu ions, wo se s o NMR signals a e obse ed due o he seconda y iso ope effec on he ib a ional equencies. 61 The chemical shidiffe ence o he signal o igina ing om he deu e a ed and ha o he nondeu e a ed molecule, mos commonly de ec ed a 13 C NMR equency, is he seconda y iso ope effec (IE) (eqn (1)), n D obs ¼dC (D) dC (H) (1) whe e nis he numbe o bonds be ween he deu e ium and he obse ed nucleus, whils C (D) and C (H) a e he 13 C NMR chem- ical shis o he deu e a ed and nondeu e a ed iso opologues. Al hough he magni ude o he iso ope effec is dependen on he dis ance o he de ec ed nucleus om he posi ion o Table 2 Compu a ionally p edic ed 15 N NMR chemical shi s o he (A) [(py idine)(coun e ion)iodine] py idine and o he al e na i e (B) [bis(py idine)iodine(coun e ion)] geome ies o 1-I o 8-I, and he es ima ed ene gies o (1) he hypo he ical eac ion o a py idine- coun e ion exchange, and (2) he o ma ion o he [bis(py idine)iodi- ne(coun e ion)] ion pai a Anion S uc u e d( 15 N) ppm DGkJ mol 1 N A N B (1) (2) BF 4  1-I 222.6 173.7 28.9 5.4 ClO 4  2-I 201.5 173.9 18.5 6.2 PF 6  3-I 233.6 174.3 44.2 19.7 SbF 6  4-I 233.9 174.6 39.7 3.9 T O  5-I 198.7 173.6 12.6 9.4 TsO  6-I 182.2 175.2 6.1 37.7 NO 3  7-I 180.3 172.7 16.4 4.9 CF 3 CO 2  8-I 176.1 173.2 25.7 40.4 a The expe imen al 15 N NMR chemical shio 9-I was used as seconda y e e ence. Fig. 2 The alipha ic egion o he 1 H NMR o dodecabenzylbambus[6] u il (Bn 12 BU[6]) in he absence and p esence o complex 1/1-d.Top ow ( ed): he spec um o ee Bn 12 BU[6]. Middle ow (g een): he spec um ollowing addi ion o 1 eq. [bis(py idine)iodine] + e afluo obo a e o he solu ion. The coun e ion is apped as [(Bn 12 BU[6])(BF 4  )]. Bo om ow (blue): he spec um o Bn 12 BU[6] wi h 0.55 eq. [bis(py idine)iodine] + e afluo obo a e. Signals belonging o he BF 4  complexed and he ee Bn 12 BU[6] a e obse ed simul aneously, indica ing s ong BF 4  binding. Hence, he use o an excess o Bn 12 BU[6] ensu es he comple e apping o he anion om he dichlo ome hane solu ion. This jou nal is © The Royal Socie y o Chemis y 2015 Chem. Sci.,2015,6,3746–3756 | 3749 Edge A icle Chemical Science Open Access A icle. Published on 20 Ap il 2015. Downloaded on 29/06/2015 13:02:52. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online iso opic subs i u ion, a sizeable n D eq. need no be es ic ed o a small n. The obse ed iso ope effec , n D obs , consis s o in insic, n D 0 , and equilib ium, n D eq. , iso ope effec s (eqn (2)). n D obs ¼ n D 0 + n D eq. (2) The  s componen , n D 0 , is he di ec consequence o iso ope subs i u ion, and is essen ially empe a u e indepen- den . The second componen , n D eq. , mani es s only in sys ems ha a e in ol ed in a dynamic exchange p ocess. Due o i s dependence on he equilib ium cons an o an exchange p ocess (eqn (3)), n D eq. is empe a u e dependen . n D eq. ¼D(K1)/[2(K+ 1)] (3) whe e Kis he equilib ium cons an and Dis he chemical shi diffe ence o he exchanging species, in his s udy he chemical shidiffe ence o a selec ed nucleus in he N d+ –I, and he N d /I d+ o ms o py idine. Acco dingly, s a ic ([N/I/N] + ) and dynamic ([N–I/N] + %[N/I–N] + ) halogen bonding geome ies a e dis inguishable in solu ion by obse a ion o he empe a- u e dependence o hei 2 H-induced 13 C NMR iso ope effec s. 30,56 We applied IPE o e alua e whe he he geome y o he h ee- cen e [N–I–N] + halogen bond o [bis(py idine)iodine] + 14,30,46 could be inuenced in solu ion by coun e ion coo dina ion. P e iously his bond was demons a ed o be s a ic and symme ic in solu ion in a complex encompassing T O  as coun e ion. 30 By acquisi ion o 13 C{ 1 H, 2 H} NMR spec a o iso opologue mix u es o 1-I o 9-I dissol ed in CD 2 Cl 2 a a ious empe a u es, he empe a u e dependence o he iso ope shis was de e mined. 62 Simila o p e ious s udies, 30,45,46,63 he C3 posi ion o he py idine o 1-I o 9-I showed he la ges empe a u e dependence and p o ided da a wi h he highes squa ed co ela ion coefficien s (Fig. 3). The o e all smalle empe a u e dependence o he IEs o he s udied [bis(py idine) iodine] + complexes (Table 3) as compa ed o ha o py idine py idinium ia e (5-H), which was p e iously shown o exis as a apidly in e con e ing au ome ic mix u e, 30,45,46 indica es ha 1-I o 9-I a e p esen as s a ic, symme ic species in solu ion. He e i should be no ed ha he nonze o empe a u e depen- dence o he in insic iso ope effec s is due o he empe a u e dependence o he pola i y o he sol en , 64 he pola i y-al e - a ion o he sol en modula es he cha ge dis ibu ion o py i- dine. 65 An efficien elec on densi y ans e be ween he ni ogen lone pai and adjacen bonds, inuencing he magni- ude o he obse ed iso ope effec s as well as he amine basici y, has been p e iously desc ibed. 66 Th ough-space pola iza ion ia dipola in e ac ion has also been epo ed p e iously o e he s, o example. 67 The s a ic symme ic [N/I/N] + geome y o 1-I o 9-I is co obo a ed by he p ima y dependency o he magni ude o hei IEs on he dis ance o he obse ed ca bon om he posi ion o 1 H- o- 2 H subs i u ion, in con as o hose o [bis(py idine)hyd ogen] + ia e 5-H (Table 3) being p edominan ly dependen on he numbe o in e ening bonds be ween he obse ed nucleus and he ni ogen in ol ed in o he [N–H/N] + %[N/H–N] + au ome iza ion p ocess. 31,68 Simila o 1-I,9-I has a s a ic, symme ic [N/I/N] + halogen bond in solu ion, con ming ha a weakly coo dina ing anion does no inuence he symme y o he iodine cen e ed halogen bond. The abo e obse a ions ag ee wi h he p e iously epo - ed 15,30,43,46 high ene ge ic gain upon o ma ion o a symme ic [N/I/N] + halogen bond. Simila o o he s, 13 we ha e obse ed a lowe s abili y o 5-I, mani es ed in i s sho e li e ime in solu ion as compa ed o [bis(py idine)iodine] + complexes ha encompass o he coun e ions. This diffe ence is likely due o he hyg oscopici y o iic acid and no due o any specic in e - ac ion o T O  wi h he [N/I/N] + halogen bond. Coun e ion dependen s abili y and eac i i y o [bis(py idine)halogen] + Fig. 3 The simila empe a u e dependence o he wo-bond iso ope effec ( 2 D obs ) measu ed on C-3 o 1-I o 8-I indica es ha he [N–I–N] + halogen bond is s a ic and symme ic in solu ion, ega dless o he coun e ion. BBF 4  ,;ClO 4  ,-PF 6  ,,SbF 6  ,CT O  ,ATsO  ,O NO 3  ,:CF 3 CO 2  , and >BF 4  . Table 3 Tempe a u e coefficien s (ppm K) o he iso ope shi s o 1–9, obse ed o CD 2 Cl 2 solu ions Anion S uc u e C2 1 D obs C3 2 D obs C4 3 D obs C5 4 D obs C6 3 D obs BF 4  1-I 6.6 8.4 0.3 0 2.9 ClO 4  2-I 5.6 8.3 0.3 0 3.6 PF 6  3-I 6.3 8.9 0.4 0 3.4 SbF 6  4-I 6.2 9.0 0.8 0 3.4 T O  5-I 5.9 8.5 0.2 0 3.8 T O  5-H b 6.1 9.8 4.5 5.8 6.5 TsO  6-I 2.6 8.1 0.3 0 3.2 NO 3  7-I 5.8 8.0 0.9 0 2.5 CF 3 CO 2  8-I 6.3 8.8 0.9 0 4.6 [BF 4  ]9-I a 6.5 9.4 0.6 0 3.5 BF 4  10-I 6.5 9.4 n.d. c 0 n.d. c T O  11-I b 7.4 6.5 2.4 0 2.7 T O  11-H b 10.0 10.6 3.5 0 +15.0 NO 3  12-I n.d. c 9.8 2.5 0 4.2 a The coun e ion o 9-I was sca enged using Bn 12 BU[6] p o iding a naked [bis(py idine)iodine] + . 47 b The da a o 5-H,11-I and 11-H a e om e . 30 and 46. c Due o limi ed solubili y and mino empe a u e dependence, his coefficien could no be eliably de e mined. 3750 |Chem. Sci.,2015,6,3746–3756 This jou nal is © The Royal Socie y o Chemis y 2015 Chemical Science Edge A icle Open Access A icle. Published on 20 Ap il 2015. Downloaded on 29/06/2015 13:02:52. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online complexes may inuence hei syn he ic applicabili y, 36,41,69 encou aging o u he s udies. The h ee-cen e halogen bond is sligh ly des abilized by he in oduc ion o a geome ical es ain en o cing a somewha longe han op imal ni ogen–ni ogen dis ance o he [N/I/N] + bond, he eby dec easing he o e lap o he lled nonbonding o bi al o he py idine ni ogens wi h he emp y p-o bi al o iodi- ne(I). 30,45 Consequen ly, op imal N–I bond leng hs a e ob ainable o such a sys em only upon an ene ge ically penalized adjus men o i s co alen backbone. To e alua e whe he he coun e ion is capable o inuencing a weakened h ee-cen e halogen bond, [(1,2-bis(py idin-2-yle hynyl)benzene)iodine] + complexes (Fig. 1) encompassing he weakly coo dina ing e auo obo a e (10-I), he mode a ely coo dina ing ia e (11-I), and he s ongly coo - dina ing ni a e (12-I) we e assessed using IPE NMR. The o e all lowe empe a u e dependence o he IEs o 10-I o 12-I as compa ed o 11-H (Table 3), and he p ima y dependence o he empe a u e coefficien s o hei IEs on he posi ion o he 1 H- o- 2 H subs i u ion indica e ha he [N/I/N] + halogen bond o hesesys emsisalsos a icandsymme ic.Hence,coun e ion coo dina ion is incapable o in oducing asymme y in o e en a sligh ly weakened h ee-cen e halogen bond in solu ion. Coun e ion coo dina ion in silico Fo heo e ical con ma ion o he expe imen al ndings, he equilib ium geome ies o 1-I o 9-I we e calcula ed using densi y unc ional heo y (DFT) employing he B3LYP exchange and co ela ion unc ional. 70–73 In he he mochemical calcula- ions, he LANL08d and LANL08 74 basis se s, in conjunc ion wi h he LANL2DZ 75,76 effec i e co e po en ial, we e used o I and Sb, espec i ely; he LANL2DZ 75,76 basis se was used o Ag; Pople's 6-311+G(d,p) 77–79 basis se was used o B, O, N, F and Cl; and Pople's 6-311G(d,p) basis se was used o he emaining a oms. Fo he es ima ion o chemical shieldings, single-poin calcula ions a he geome ies ob ained we e pe o med using he 6-311+G(d,p) basis se 80 o I, and Ku zelnigg's IGLO-III basis se 81 o he emaining a oms. Sol en effec s we e accoun ed o by he Pola izable Con inuum Model (PCM), 82,83 wi h CH 2 Cl 2 as he sol en . All calcula ions we e pe o med using he Gaussian09 p og am package. 84 The po en ial ene gy su aces (PES) o all he complexes con aining coun e ions a e complica ed and likely o show a numbe o local minima o he placemen and o ien a ion o he coun e ion. Ca e was aken o nd he mos a ou able congu a ion o each coun- e ion; howe e , i can ne e be ully excluded ha he e a e local minima wi h sligh ly lowe ene gies han hose p esen ed. The PESs a e shallow in he egion o in e es , so e en i a sligh ly lowe minimum geome y was missed his would no affec he conclusions o he he mochemical analysis, shown in Table 2. In good ag eemen wi h he spec oscopic da a, DFT calcula ions p edic symme ic [bis(py idine)iodine] + geome y o complexes 1-I o 9-I. The mino , <0.2%, diffe ence in he N–I bond leng hs o 8-I (Table 4), o example, is likely insigni- can . 85 The N–I bond leng h is i ually unaffec ed by he coun e ion, whe eas he N–I–N angle shows some mino a i- a ion, ye emains o e all linea . The la e de ia ion om comple e linea i y is likely due o weak hyd ogen bonding o some o he coun e ions o he H-2 o he py idines. This in e ac ion has p e iously been no iced o s uc u ally closely ela ed complexes. 52,86,87 Mos o he analogous sil e complexes a e also linea and symme ic; howe e , a sligh asymme y along wi h a signican dis o ion om linea i y o he N–Ag–N angle is p edic ed o 5-Ag,7-Ag and 8-Ag. These complexes encompass small, mode a ely o s ongly coo dina ing coun- e ions (T O  ,NO 3  and CF 3 CO 2  ), and hei geome y is likely al e ed due o he s e ic equi emen s o igh coun e ion coo dina ion ha yields neu al, T-shaped and sligh ly asym- me ic species (Fig. 4). Nei he small symme ic (BF 4  , ClO 4  , PF 6  , SbF 6  ) no la ge s e ically hinde ed anions (TsO  ) a e capable o di ec coo dina ion o sil e (I) in hese complexes. I should be no ed ha he co esponding iodine(I) cen e ed complexes 7-I and 8-I do no o m a compa able s ong iodine– oxygen bond, and hus emain linea and bis-coo dina e. Coun e ion coo dina ion in he solid-s a e Single c ys als we e ob ained ia slow diffusion o hexane in o he dichlo oe hane solu ion o he s udied complexes unde s epwise cooling om 25 C o20 C. X- ay c ys allog aphic analyses e ied ha he iodine cen e ed complexes 1-I o 7-I p e e a symme ic, linea , bis-coo dina ed N–I–N s uc u e in he solid s a e (Table 4). The coun e ion has only a mino , <2%, inuence on he N–I bond leng hs. A weak coo dina ion o he anions and hei consequen negligible effec on he geome y o he h ee- cen e ed halogen bond in he solid s a e is in good ag eemen wi h he DFT p edic ed s able, symme ic [bis(py idine)iodine] + solu ion geome ies. The N–I bond leng hs o hese complexes a e signican ly sho e han he sum o he an de Waals adii o he pa icipa ing a oms (R XB ¼0.64, whe e R XB ¼d NI /(I dW + N dW ) 88 ), well eec ing he unusual s eng h o he halogen bond 29 o 1-I o 7-I. Impo an ly, he asymme ic coo dina ion o he coun e ion (Fig. 5) o hese complexes is unable o induce asymme y in he h ee-cen e halogen bond. Whe eas he [N/I/N] + in e ac ion has a signican co alen cha ac e , 15,28,30,43,45 he coo dina ion o he coun e ions o [bis(py idine)iodine] + is p edominan ly Coulombic and is weak. Un o una ely, single c ys als o complex 8-I we e no ob ained, despi e epea ed a emp s. Sil e (I) cen e ed complexes 1-Ag o 4-Ag ha encompass weakly coo dina ing anions p e e linea , bis-coo dina e N–Ag– N geome ies in he solid s a e (Table 4). The in e ac ion o [bis(py idine)sil e ] + wi h hese coun e ions is o ionic cha - ac e , simila o ha o he co esponding [bis(py idine) iodine] + . In con as , pseudo- e acoo dina e (3 + 1) dime s we e obse ed o 5-Ag and 6-Ag ha possess he mode a ely coo - dina ing coun e ions T O  and TsO  (Fig. 5). X- ay analyses o [bis(py idine)sil e ] + ni a e showed a pseudo-squa e plana N– Ag(NO 3  ) 2 –N geome y (Fig. 6a, Table 4, 7-Ag), and a e ame (dime o dime s) wi h an ex ao dina y combina ion o a pseudo- e ahed al (2 + 2) N–(Ag)Ag(NO 3  )–N coo dina ion and an excep ional pseudo-oc ahed al (5 + 1) N–(Ag)Ag(NO 3  ) 2 –N coo dina ion (Fig. 6b, Table 4, 7-Ag-2). Despi e epea ed a emp s, single c ys als o he [bis(py idine)sil e ] + complex This jou nal is © The Royal Socie y o Chemis y 2015 Chem. Sci.,2015,6,3746–3756 | 3751 Edge A icle Chemical Science Open Access A icle. Published on 20 Ap il 2015. Downloaded on 29/06/2015 13:02:52. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online wi h he s ongly coo dina ing coun e ion CF 3 CO 2  (8-Ag) we e no ob ained. X- ay analyses o 7-Ag and 8-Ag we e a emp ed ea lie by Whi e e al., 90 who epo ed he o ma ion o binuclea species con aining sil e ni a e and py idine in a 1 : 3, and sil e iuo oace a e and py idine in a 3 : 2, a io. DFT p edic s he is-coo dina e complexes o 7-Ag and 8-Ag o be ene ge i- cally mo e a o able han hei bis-coo dina e analogues. The s ong in e ac ion o he coun e ion o complexes 5-Ag o 8-Ag wi h sil e (I) mani es s in specic, close in e a omic con ac s, i.e. d Ag–O ¼2.705 ˚ A(5-Ag, XRD), 2.545 ˚ A(6-Ag, XRD), 2.690 ˚ A(7- Ag, DFT), and 2.749 ˚ A(8-Ag, DFT). The coun e ion coo dina ion o sil e (I) in hese species is s ong (R coo d ¼0.79–0.85, whe e Table 4 Compu a ionally p edic ed and X- ay c ys allog aphically de e mined N–X bond dis ances and N–X–N bond angles o he complexes 1-I o 9-I and 1-Ag o 8-Ag Anion S uc u e Compu a ionally p edic ed dis ances and angles X- ay c ys allog aphic dis ances and angles (N–X) 1 (˚ A) (N–X) 2 (˚ A) s(N–X–N) () (N–X) 1 (˚ A) (N–X) 2 (˚ A) s(N–X–N) () BF 4  1-I a 2.301 2.301 178.0 2.260(3) 2 c 180.0 2.261(3) 2 c 180.0 2.255(3) 2.261(3) 177.7(1) ClO 4  2-I 2.301 2.301 175.8 2.257(2) 2 c 180.0 2.260(2) 2 c 180.0 2.256(2) 2.256(2) 177.72(9) PF 6  3-I 2.303 2.301 178.8 2.268(2) 2.268(2) 180.0 SbF 6  4-I 2.302 2.302 179.2 2.252(3) 2.252(3) 180.0 T O  5-I 2.301 2.300 178.0 2.246(8) 2.261(7) 178.0(3) TsO  6-I 2.301 2.300 177.8 2.241(3) 2.268(3) 178.75(8) NO 3  7-I 2.303 2.303 179.0 2.250(4) 2 c 180.0 2.265(3) 2 c 180.0 CF 3 CO 2  8-I 2.302 2.298 177.4 ——— [BF 4  ]9-I b 2.301 2.301 180.0 ——— BF 4  1-Ag 2.198 2.197 175.7 2.137(3) 2.138(3) 176.0(1) ClO 4  2-Ag 2.190 2.189 179.1 2.131(3) 2.132(3) 177.0(1) PF 6  3-Ag 2.193 2.192 176.9 2.128(4) 2.133(4) 176.9(1) SbF 6  4-Ag 2.193 2.192 178.0 2.130(2) 2.143(2) 174.84(8) T O  5-Ag 2.225 2.222 166.8 2.153(4) 2.158(3) 167.4(1) TsO  6-Ag 2.191 2.188 176.8 2.177(2) 2.192(2) 155.01(7) NO 3  7-Ag 2.251 2.251 162.5 2.176(2) 2.176(2) 173.85(8) NO 3  7-Ag-2 2.152(2) 2.152(2) 173.2(1) 2.255(3) d —— CF 3 CO 2  8-Ag 2.274 2.250 164.5 ——— a C ys allog aphic da a is om e . 89. b Compu a ional da a is om e . 30. c Complex lies on a symme y elemen wi h wo equal N–I dis ances wi h an exac 180angle. d Only one Ag–N bond in a pseudo-oc ahed al complex. Fig. 4 The DFT-p edic ed equilib ium geome ies o complexes 8-Ag and 8-I a e shown on he le and igh , espec i ely. Whe eas sil e (I)is p edic ed o o m T-shaped, is-coo dina e species wi h a s ongly bound coun e ion, sho iodine–oxygen con ac is no seen o he co esponding iodine(I) complex, which p e e s a linea , bis-coo di- na e N–I–N geome y. Fig. 5 The solid s a e geome ies o complexes (a) 5-Ag, (b) 6-Ag, (c) 5-I and (d) 6-I ob ained by X- ay c ys allog aphy e eal ha he bis(py idine) complexes o sil e (I) o m pseudo- e acoo dina ed dime s, whe eas hose o iodine(I) o m ionic, linea , bis-coo dina ed N–I–N complexes in he p esence o mode a ely coo dina ing coun e ions, such as T O  and TsO  . 3752 |Chem. Sci.,2015,6,3746–3756 This jou nal is © The Royal Socie y o Chemis y 2015 Chemical Science Edge A icle Open Access A icle. Published on 20 Ap il 2015. Downloaded on 29/06/2015 13:02:52. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online R coo d ¼d Ag–O /(Ag dW +O dW ) 29,88 ), ye i emains weake as compa ed o he coo dina ion o py idines (R coo d ¼0.67–0.69). [(1,2-Bis(py idin-2-yle hynyl)benzene)sil e ] + ni a e (12-Ag) c ys allized as a T-shaped complex, as shown in Fig. 7. The N–Ag bond dis ances o 2.169(3) ˚ A and 2.177(3) ˚ A, and he Ag–O bond dis ance o 2.658(4) ˚ A o his complex co espond well o hose obse ed o he s e ically un es ained 7-Ag (Table 4). The adap abili y o he (1,2-bis(py idin-2-yle hynyl)benzene) back- bone o his complex o pe mi op imal ni ogen–ni ogen dis ances o complexa ion ag ees well wi h p e ious obse a- ions made o he analogous [N/I/N] + and [N/B /N] + complexes. 30 Conclusions Coun e ions do no inuence he in insically p e e ed linea , cen osymme ic geome y o he [N/I/N] + halogen bond, ei he in solu ion o in he solid s a e. Nei he does he sca - enging o he coun e ion inuence he symme y o he h ee- cen e bond. In con as , he weakly coo dina ing coun e ions BF 4  and ClO 4  we e p oposed 34,35 o be capable o desymme- izing he [N/B /N] + halogen bond o [bis(py idine)b omine] + in he solid s a e. This obse a ion may be explained by he lowe ene gy gain upon o ma ion o he [N/B /N] + as compa ed o he [N/I/N] + halogen bond. 43 The h ee-cen e halogen bonds o 1-I o 8-I esemble he classical coo dina ion bond o he co esponding [N/Ag/N] + complexes. 28 Whe eas mode a ely and s ongly coo dina ing coun e ions, e.g. T O  , TsO  ,NO 3  and CF 3 CO 2  , do no affec he [N/I/N] + halogen bond, hey ha e a conside able inuence on he co esponding coo dina i e sil e (I) complexes. Hence, he la e a e al e ed om linea , bis-coo dina e [bis(py idine)sil e ] + coun e ion complexes o mul i-coo dina e [bis(py idine)(coun e ion)sil e ] species. These coun e ions en o ce nonlinea , and occasionally also asymme ic geome ies, o he [N/Ag/N] + coo dina ion bonds. This is mos appa en in he solid s a e (Table 4, Fig. 5 and 6), and ye i akes place in solu ion (Fig. 4) as well. O e all, he h ee-cen e [N/I/N] + and [N/Ag/N] + bonds beha e simila ly in he p esence o weakly coo dina ing anions (1-I o 4-I, and 1-Ag o 4-Ag), bu diffe en ly when mode a ely o s ongly coo dina ing coun e ions a e p esen (5-I o 8-I, and 5- Ag o 8-Ag). Ou esul s sugges ha ca e should be aken when he h ee-cen e halogen bond is discussed in e ms o coo di- na ion bonds o ansi ion me als. The [N/I/N] + bonds a e bes desc ibed as halogen bonds possessing a signican cha ge ans e cha ac e , 43 which is p esen o all ypes o halogen bonds bu ye may be o a ying impo ance. 91–93 Despi e some diffe ences, 15 he h ee-cen e [D/X/D] + halogen bond esembles a “sho -s ong”[D/H/D] + hyd ogen bond, 94 and may al e na i ely be e med a sho , s ong halogen bond. [Bis(py idine)iodine] + complexes a e common syn he ic eagen s o halogena ion and oxida ion, 95–103 wi h Ba luenga's eagen being he mos amous one. 36,41 The la e was ecen ly shown o exhibi a coun e ion dependen o de –diso de phase ansi ion in he solid s a e 13 and has ecei ed inc easing a en ion o applica ions in pa allel syn hesis 104 and p o ein chemis y, 69 o example. The unde s anding o he s uc u e and p ope ies o hese eagen s is he e o e o bo h unda- men al and p ac ical impo ance. Acknowledgemen s The esea ch leading o hese esul s has ecei ed unding om he Eu opean Union Se en h F amewo k P og amme (FP7/ 2007–2013) unde g an ag eemen no. 259638. We hank he Swedish Resea ch Council (2012:3819), he Academy o Finland (263256 and 265328), and he Czech Science Founda ion (13- 15576S) o nancial suppo . FT acknowledges he suppo om NGS-NANO h ough a Ph.D. ellowship. We hank Albe e X. Veiga (Uni e si y o Go henbu g) o help ul syn he ic ad ice. Molecula g aphics we e gene a ed wi h he UCSF Chime a package, 82 by he Resou ce o Biocompu ing, Visualiza ion, and In o ma ics a he Uni e si y o Cali o nia, San F ancisco (sup- po ed by NIGMS P41-GM103311). No es and e e ences 1 S. Gup a, D. Koley, K. Ra ikuma and B. Kundu, J. O g. Chem., 2013, 78, 8624. 2 S. L. Dabb, J. H. Ho, R. Hodgson, B. A. Messe le and J. Wagle , Dal on T ans., 2009, 634. 3 Y. Ren, X. Wang, S. Y. Chu and N. B. Wong, Theo . Chem. Acc., 2008, 119, 407. 4 A. Eb ahimi, M. Habibi and A. Ami mijani, J. Mol. S uc ., 2007, 809, 115. Fig. 6 X- ay c ys allog aphic in es iga ion o [bis(py idine)iodine] ni a e e ealed (a) pseudo-squa e plana N–Ag(NO 3  ) 2 –N(7-Ag), and (b) coexis ing pseudo- e ahed al and pseudo-oc ahed al (5 + 1) N– (Ag)Ag(NO 3  ) 2 –N(7-Ag-2) coo dina ion geome ies. Fig. 7 The X- ay s uc u e o 12-Ag. This jou nal is © The Royal Socie y o Chemis y 2015 Chem. Sci.,2015,6,3746–3756 | 3753 Edge A icle Chemical Science Open Access A icle. Published on 20 Ap il 2015. Downloaded on 29/06/2015 13:02:52. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online