Paper Adducts formed by tetrahedral anions and protonated forms of 1,4,7-triazacyclononane: competition with chloride anions Andrew C. Warden, a Mark Warren, a Andrew R. Battle, a Milton T. W. Hearn b and Leone Spiccia* a a School of Chemistry, Monash University, Victoria 3800, Australia. E-mail: [email protected]; Fax: 161 3 99054597; Tel: 161 3 99054526 b Centre for Green Chemistry, Monash University, Victoria 3800, Australia Received 22nd July 2004, Accepted 6th September 2004 First published as an Advance Article on the web 8th October 2004 Five adducts formed by 1,4,7-triazacyclononane ([9]aneN 3 , L) and four tetrahedral anions have been crystallized from aqueous solutions containing (H 3 L)Cl 3 and the appropriate acid, viz. (H 3 L)(CuCl 4 )Cl?H 2 O(1), (H 3 L)(ClO 4 )Cl 2 (2), (H 3 L)(HSO 4 )Cl 2 (3), (H 3 L)(HSO 4 ) 2 Cl (4) and (H 3 L)(H 2 PO 4 ) 3 (5). Their X-ray crystal structures have provided an indication of the stable conformations of the protonated macrocycles and its binding preferences when faced with the option of two different anions as guests. The inclusion of competitive anions (such as phosphate and sulfate) with greater hydrogen bonding abilities has the effect of excluding chloride from the lattice in favor of the formation of more highly connected networks. Also revealed are the tendencies of the anions and macrocycles to form supramolecular architectures through hydrogen bonding and electrostatic interactions, such a tripodal co-ordination pyramid formed by chloride anions and g-2 chelation by the macrocycle of a single oxygen on hydrogen sulfate and hydrogen phosphate anions. The series shows hydrogen bonded 2D sheets, 3D networks and an isolated (HSO 4 2 ) 4 cluster is found in 4. Introduction Anions play an important role in many biological processes. Approximately two thirds of proteins contain anions, 1 spark- ing efforts towards understanding the various interactions that contribute to the effective binding of these moieties and selectivity between anions of similar chemical characteristics, such as charge and geometry. The macrocycle, 1,4,7-triazacy- clononane (L, [9]aneN 3 , Fig. 1) and derivatives thereof, have been used extensively in binding metal cations, showing a great propensity for tripodal facial co-ordination to these positively charged entities, and in the development of model compounds for metal sites in many types of metalloproteins. 2–5 A less-well- explored property of these azamacrocycles is the ability of protonated forms of the macrocycle to act as cationic hosts for negatively charged ions. The binding of anions by polyaza- macrocycles has been subject of several literature reports in more recent years, 6–14 the emphasis being mainly, but not exclusively, on the determination of adduct stoichiometry and binding constants. In terms of solid state studies, our recent examination of the anion binding characteristics of [12]aneN 4 , 15 and [18]aneN 6 15–18 has provided insight into the supramolecular architectures generated by protonated forms of these macrocycles and various types of anions, that include the halides, oxoanions and organic anions. In the case of [9]aneN 3 , the structure of only one adduct, consisting of a protonated 1,4,7,-triazacyclononane moiety whose charge was counter- balanced by [IrCl 2 (H 2 O) 4 ] 1 and SO 4 22 has been reported. 19 Herein, we report the structural characterization of five anion adducts of the simplest azamacrocycle, 1,4,7-triazacyclononane (L, [9]aneN 3 ) and discuss the anion–macrocycle and anion– anion interactions present within the crystal lattices. Experimental Materials and methods All reagents were purchased from Aldrich or BDH and were used without further purification. 1,4,7-triazacyclononane (tacn) was prepared by following the classical Richman– Atkins synthesis. 20 Syntheses. (H 3 L)(CuCl 4 )Cl?H 2 O (1) To a solution containing H 3 LCl 3 (100 mg, 0.42 mmol) and copper(II) chloride dihydrate (80 mg, 47 mmol) in water (2 ml), an excess of hydrochloric acid (conc., 1 ml) was added. The yellow solution was left to slowly evaporate and after several days clear yellow crystals of 1 were obtained. (yield ~ 273 mg, 83%). Microanalysis (%) Found: C 18.0; H 6.0; N 10.5. Calc. for C 6 H 20 Cl 5 CuN 3 O: C 18.4; H 5.2; N 10.8. IR bands n (KBr disk, cm 21 ): 3500 m, 3379 s, 2997 s, 2761 s, 2677 s, 2511 m, 2446 m, 1652 m, 1607 m, 1565 w, 1542 w, 1501 m, 1481 m, 1444 s, 1410 m, 1366 m, 1325 m, 1283 m, 1227 w, 1209 w, 1179 w, 1134 w, 1102 m, 1080 w, 1051 m, 1008 m, 989 m, 947 m, 920 m, 873 m, 840 w, 791 m, 762 m, 556 m, 522 m. (H 3 L)(ClO 4 )Cl 2 (2) A solution containing H 3 LCl 3 (100 mg, 0.42 mmol) and perchloric acid (70%, 60 mg, 0.42 mmol) in water (1 ml) was prepared and left to slowly evaporate. After several days clear crystals of 2 were obtained. (yield ~ 87 mg, 68%). Micro- analysis (%) Found: C 23.6; H 6.6; N 13.7. Calc. for C 6 H 18 Cl 3 N 3 O 4 : C 23.8; H 6.0; N 13.9. IR bands n (KBr disk, cm 21 ): 3449 w, 3059 m, 2961 s, 2818 s, 2779 s, 2513 m, Fig. 1 1,4,7-Triazacyclononane ([9]aneN 3 , L). 522 CrystEngComm, 2004, 6(84), 522–530 DOI: 10.1039/b411241e This journal is # The Royal Society of Chemistry 2004 Published on 08 October 2004. Downloaded by Lomonosov Moscow State University on 29/08/2013 14:14:04. View Article Online / Journal Homepage / Table of Contents for this issue
Transcript
Paper
Adducts formed by tetrahedral anions and protonated forms of
1,4,7-triazacyclononane: competition with chloride anions
Andrew C. Warden,a Mark Warren,a Andrew R. Battle,a Milton T. W. Hearnb and
Leone Spiccia*a
aSchool of Chemistry, Monash University, Victoria 3800, Australia.
E-mail: [email protected]; Fax: 161 3 99054597; Tel: 161 3 99054526bCentre for Green Chemistry, Monash University, Victoria 3800, Australia
Received 22nd July 2004, Accepted 6th September 2004
First published as an Advance Article on the web 8th October 2004
Five adducts formed by 1,4,7-triazacyclononane ([9]aneN3, L) and four tetrahedral anions have been
crystallized from aqueous solutions containing (H3L)Cl3 and the appropriate acid, viz. (H3L)(CuCl4)Cl?H2O (1),
(H3L)(ClO4)Cl2 (2), (H3L)(HSO4)Cl2 (3), (H3L)(HSO4)2Cl (4) and (H3L)(H2PO4)3 (5). Their X-ray crystal
structures have provided an indication of the stable conformations of the protonated macrocycles and its
binding preferences when faced with the option of two different anions as guests. The inclusion of competitive
anions (such as phosphate and sulfate) with greater hydrogen bonding abilities has the effect of excluding
chloride from the lattice in favor of the formation of more highly connected networks. Also revealed are the
tendencies of the anions and macrocycles to form supramolecular architectures through hydrogen bonding and
electrostatic interactions, such a tripodal co-ordination pyramid formed by chloride anions and g-2 chelation
by the macrocycle of a single oxygen on hydrogen sulfate and hydrogen phosphate anions. The series shows
hydrogen bonded 2D sheets, 3D networks and an isolated (HSO42)4 cluster is found in 4.
Introduction
Anions play an important role in many biological processes.Approximately two thirds of proteins contain anions,1 spark-ing efforts towards understanding the various interactions thatcontribute to the effective binding of these moieties andselectivity between anions of similar chemical characteristics,such as charge and geometry. The macrocycle, 1,4,7-triazacy-clononane (L, [9]aneN3, Fig. 1) and derivatives thereof, havebeen used extensively in binding metal cations, showing a greatpropensity for tripodal facial co-ordination to these positivelycharged entities, and in the development of model compoundsfor metal sites in many types of metalloproteins.2–5 A less-well-explored property of these azamacrocycles is the ability ofprotonated forms of the macrocycle to act as cationic hosts fornegatively charged ions. The binding of anions by polyaza-macrocycles has been subject of several literature reports inmore recent years,6–14 the emphasis being mainly, but notexclusively, on the determination of adduct stoichiometry andbinding constants. In terms of solid state studies, our recentexamination of the anion binding characteristics of[12]aneN4,15 and [18]aneN6
15–18 has provided insight into thesupramolecular architectures generated by protonated forms ofthese macrocycles and various types of anions, that include thehalides, oxoanions and organic anions. In the case of [9]aneN3,the structure of only one adduct, consisting of a protonated1,4,7,-triazacyclononane moiety whose charge was counter-balanced by [IrCl2(H2O)4]1 and SO4
22 has been reported.19
Herein, we report the structural characterization of five anionadducts of the simplest azamacrocycle, 1,4,7-triazacyclononane(L, [9]aneN3) and discuss the anion–macrocycle and anion–anion interactions present within the crystal lattices.
Experimental
Materials and methods
All reagents were purchased from Aldrich or BDH and wereused without further purification. 1,4,7-triazacyclononane(tacn) was prepared by following the classical Richman–Atkins synthesis.20
Syntheses. (H3L)(CuCl4)Cl?H2O (1)
To a solution containing H3LCl3 (100 mg, 0.42 mmol) andcopper(II) chloride dihydrate (80 mg, 47 mmol) in water (2 ml),an excess of hydrochloric acid (conc., 1 ml) was added. Theyellow solution was left to slowly evaporate and after severaldays clear yellow crystals of 1 were obtained. (yield ~ 273 mg,83%). Microanalysis (%) Found: C 18.0; H 6.0; N 10.5. Calc.for C6H20Cl5CuN3O: C 18.4; H 5.2; N 10.8. IR bands n (KBrdisk, cm21): 3500 m, 3379 s, 2997 s, 2761 s, 2677 s, 2511 m,2446 m, 1652 m, 1607 m, 1565 w, 1542 w, 1501 m, 1481 m,1444 s, 1410 m, 1366 m, 1325 m, 1283 m, 1227 w, 1209 w,1179 w, 1134 w, 1102 m, 1080 w, 1051 m, 1008 m, 989 m, 947 m,920 m, 873 m, 840 w, 791 m, 762 m, 556 m, 522 m.
(H3L)(ClO4)Cl2 (2)
A solution containing H3LCl3 (100 mg, 0.42 mmol) andperchloric acid (70%, 60 mg, 0.42 mmol) in water (1 ml) wasprepared and left to slowly evaporate. After several days clearcrystals of 2 were obtained. (yield ~ 87 mg, 68%). Micro-analysis (%) Found: C 23.6; H 6.6; N 13.7. Calc. forC6H18Cl3N3O4: C 23.8; H 6.0; N 13.9. IR bands n (KBrdisk, cm21): 3449 w, 3059 m, 2961 s, 2818 s, 2779 s, 2513 m,Fig. 1 1,4,7-Triazacyclononane ([9]aneN3, L).
2131 w, 2098 w, 2017 w, 1627 m, 1590 m, 1496 m, 1423 m,1384 m, 1354 m, 1269 w, 1241 w, 1094 s, 1029 m, 983 m, 932 m,850 m, 802 w, 763 w, 623 s, 506 m.
(H3L)(HSO4)Cl2 (3)
A solution containing H3LCl3 (100 mg, 0.42 mmol) and sulfuricacid (conc. 41 mg, 0.42 mmol) in water (1 ml) was prepared andleft to slowly evaporate. After several days clear crystals of 3were obtained. (yield ~ 101 mg, 80%). Microanalysis (%)Found: C 24.5; H 6.2; N 14.3. Calc. for C6H19Cl2N3O4S: C24.0; H 6.4; N 14.0. IR bands n (KBr disk, cm21): 3569 w,3050 s, 2944 s, 2766 s, 2622 m, 2450 m, 1605 m, 1583 m, 1460 m,1438 m, 1422 m, 1225 s, 1183 s, 1043 s, 981 s, 938 m, 867 s,783 m, 576 s.
(H3L)(HSO4)2Cl (4)
A solution containing H3LCl3 (100 mg, 0.42 mmol) and sulfuricacid (conc. 82 mg, 0.82 mmol) in water (1 ml) was prepared andleft to slowly evaporate, yielding clear crystals of 4 after severaldays. (yield ~ 112 mg, 74%). Microanalysis (%) Found: C 20.1;H 6.4; N 11.9. Calc. for C6H20ClN3O8S2: C 19.9; H 5.6; N 11.6.IR bands n (KBr disk, cm21): 3422 m, 3000 s, 2945 s, 2767 s,2447 m, 2370 m, 2344 m, 1584 m, 1460 m, 1439 m, 1378 m,1224 s, 1182 s, 1114 m, 1097 s, 1046 s, 981 m, 936 m, 882 s,782 m, 580 s.
(H3L)(H2PO4)3 (5)
A solution containing H3LCl3 (100 mg, 0.42 mmol) andphosphoric acid (85%, 145 mg, 1.26 mmol) in water (1 ml) wasprepared and left to slowly evaporate, yielding clear crystals of5 after several days. (yield ~ 86 mg, 48%). Microanalysis (%)Found: C 16.5; H 6.1; N 10.0. Calc. for C6H24N3O12P3: C 17.0;H 5.7; N 9.9. IR bands n (KBr disk, cm21): 3061 s, 2900 s,2799 s, 1654 m, 1618 m, 1544 w, 1525 w, 1478 m, 1448 m,1379 m, 1352 w, 1236 m, 1133 m, 1036 s, 955 s, 922 s, 856 m,756 m, 513 s.
X-ray crystallography. General procedures
A summary of the crystal data and structure refinement for 1–5is given in Table 1. Single crystal X-ray data were collected onan Nonius Kappa CCD diffractometer with monochromatedMo Ka radiation (l ~ 0.71073 A) at 123(2) K using Q and/or vscans. Data were corrected for Lorentz and polarizationeffects. The structures were solved by the direct methods andrefined using the full matrix least-squares method of theprograms SHELXS-9721 and SHELXL-97,22 respectively. The
program X-Seed23 was used as an interface to the SHELXprograms, and to prepare the figures. In each case all non-hydrogen atoms were refined anisotropically. In the figures,dashed lines represent hydrogen bonds and, where ORTEPrepresentation has been used, ellipsoids have been drawn at the50% probability level unless otherwise indicated. Whereapplicable, * indicates symmetry generated atoms. Specificcomments (H3L)(CuCl4)Cl?H2O (1), (H3L)(ClO4)Cl2 (2).Nearly all hydrogen atoms (with the exception of a few CHhydrogens) were located on Fourier difference maps andrefined isotropically. (H3L)(HSO4)Cl2 (3) and (H3L)(HSO4)2Cl(4). All hydrogen atoms were located on Fourier difference mapsand refined isotropically without restraint. (H3L)(H2PO4)3 (5).All hydrogen atoms were placed in idealized geometries withthe exception of H(6)P which was located on Fourier differencemaps and restrained to 0.9 A from its parent oxygen atom(O(12)). Refinement in several centrosymmetric space groupsresulted in some atoms going non-positive definite, or anunreasonable amount of apparent disorder among some phos-phate groups. The crystal was refined with the TWIN matrix[1 0 0 0 21 0 0 0 21] (monoclinic emulating orthorhombic withb ~ 90.016(9)) with BASF parameter indicating approximatelya 25% twinned component. The flack parameter value of20.11(17) was also indicative of a non-centric structure.
CCDC reference numbers 245595–245599. See http://www.rsc.org/suppdata/ce/b4/b411241e/ for crystallographic data inCIF or other electronic format.
Results and discussion
Synthesis and characterization
Compounds 2–5 initially crystallized from slowly evaporatingaqueous solutions containing tacn?3HCl and an excess of theappropriate oxoanions as their acids. Cleaner and higheryielding reactions were then developed which used stoichio-metric equivalents of the acids. These subsequent reactions arereported herein. In the case of 1, the [CuCl4]22 anion wasformed in situ from cupric chloride. The IR spectra exhibitedabsorptions corresponding to the macrocycle (C–H stretches at2800–3100 cm21 and N–H stretches at 3300–3500 cm21), O–Hstretches from HSO4
2 and H2PO422 at 3200–3400 cm21 and
other characteristic bands from oxoanions, in particular thestrong absorbances at 950–1200 cm21.
Crystal structure determinations
For the purposes of this discussion we have adopted thehydrogen bonding distance criterion proposed in previous
Table 1 Crystal and refinement data for 1–5
1 2 3 4 5
Empirical formula C6H20Cl5CuN3O C6H18Cl3N3O4 C6H19Cl2N3O4S C6H20ClN3O8S2 C6H24N3O12P3
work by Ilioudis et al,24 which requires that the D–H…Adistance (from H to A) is less than the sum of the van der Waalsradii, (ca. 1.20 A for H, 1.40 A for O, 1.50 A for N and 1.80 Afor Cl.25,26 Although there is no specific definition of whatconstitutes a ‘strong’ or ‘weak’ hydrogen bond for a particularhydrogen bond type, it is expected that the shorter D…Adistances with D–H–A angles of w110u (say, low end of3.1–3.3 A range for D…Cl interactions) are reasonably strongcompared to those in the upper end of this range. The rangeover which D…Cl interatomic distances may be considered toconstitute hydrogen bonds is greater for chloride than for thesmaller elements such as nitrogen and oxygen. The function-ality of both donor and acceptor are also important, withtypical O…O hydrogen bond distances between water mole-cules being between 2.7 and 2.9 A, but O…O distances forhydrogen bonded phosphate anions, for example, are between2.4 and 2.7 A. N–H…O hydrogen bonds usually involveslightly longer distances, ranging from 2.8 to 3.0 A. It should beemphasized that these ranges do not represent rigid cutoffs foreach H-bond types, and real interactions may exist beyondthese limits. The existence of weaker C–H…A hydrogen bondshas recently been established and examples of this continue toarise in the literature.27 We have focused on the stronger ofthese interactions in our discussion.
(H3L)(CuCl4)Cl?H2O (1)
The structure of 1 comprises a triprotonated macrocycle, onechloride anion, one [CuCl4]22 anion in distorted tetrahedralgeometry and a water molecule (Fig. 2). All of the six ammo-nium protons are involved in hydrogen bonding interactionswith either the chlorides or the water molecule. Only one of thechlorine atoms (Cl(5)) of the [CuCl4]22 anion is involved in twohydrogen bonding interactions, accepting one H–bond fromthe water molecule and one from an ammonium group (N(1)).Cl(2) and Cl(4) are accepting weaker hydrogen bonds fromN(2). The water molecule accepts a hydrogen bond from anammonium group (N(3)) and donates two hydrogen bonds,one to the chloride anion and one to Cl(5) of the [CuCl4]22
anion. The nitrogen atoms are all on the same side of themacrocyclic plane, a conformation most likely induced by theinteraction with the chloride anion (Cl(1)), which forms atrigonal pyramid with the three ammonium groups, sitting3.0434(9) A from the mean plane of the macrocycle defined byall C and N atoms (Fig. 3). The average N…Cl(1) distance isslightly longer in 1 than in the analogous motif in 2 most likelyowing to the fact that there is an additional hydrogen bondfrom a water molecule to the apical chloride in the presentstructure. This last interaction generates a distorted tetrahedralgeometry around Cl(1).
The supramolecular structure of 1 can be described as layersof macrocycles, chlorides and [CuCl4]22 anions connected by
water molecules. The layers lie parallel to the b–0–c plane andare comprised of subunits of 1D chains connected through thewater molecules (involving all of the ionic components)running parallel to each other in a top-to-tail fashion(Fig. 4). The macrocycles within the chains are most directlyconnected by dichloride bridges formed by two symmetryrelated chlorine atoms (Cl(4)) on the [CuCl4]22 anion (seeFig. 2). Longer intermacrocycle bridges are formed viaN(1)…Cl(5)–Cu(1)–Cl(4)…N(2) interactions. A complete listof hydrogen bonds in 1–4 is given in Table 2.
(H3L)(ClO4)Cl2 (2)
The crystal structure of 2 consists of a macrocycle, two chlorideanions (Cl(1) and Cl(2)) and a perchlorate anion (Fig. 5).Triprotonated [9]aneN3 has all ammonium protons involved inhydrogen bonds with chloride anions. The nitrogen atomsdeviate in the same direction from the mean plane of themacrocycle (defined by C and N atoms) by nearly the samedegree (0.475–0.495 A) as seen in 1. Cl(1) sits on top of atripodal co-ordination pyramid defined by the three macro-cyclic nitrogen atoms while Cl(2) sits on a tripodal co-ordination pyramid generated by three different macrocycles(Fig. 6a). The Cl(1) co-ordination pyramid is significantlysteeper than that for Cl(2) owing to the tightly restrainedammonium groups of the macrocycle, with Cl(1) sitting
Fig. 2 ORTEP plot showing the 1D chains of 1.
Fig. 3 ORTEP plot of the tripodal co-ordination pyramid formed bythe macrocyclic ammonium groups and the chloride anion in 1. N…Cldistances are given in A with esd’s in parentheses.
Fig. 4 Packing of the structure in 1 viewed down the b-axis. Chlorineatoms are shown in ORTEP representation with all other atoms shownin stick representation. Click here to access a 3D image of Fig. 4.
2.550(2) A from the mean plane of its nitrogen donor whereasCl(2) is only 1.058(2) A from the mean plane of its donors(Fig. 6a). The flatter pyramid is likely to be more representativeof the natural geometry that chloride would prefer in acompletely unrestricted ammonium co-ordination environmentgiven absence of any other strongly interfering lattice inter-actions. The only competitive influences in the structure are thevan der Waals and electrostatic components provided by theweakly interacting perchlorate anions. The tripodal co-ordination pyramids formed by the chlorides and theirrespective donors have been seen in previous work.15 Giventhe frequency of this mode of co-ordination it is possible that it
Fig. 5 ORTEP plot of the hydrogen bonding environment around themacrocycle in 2.
Fig. 6 (a) Two adjacent co-ordination pyramids formed by thechloride anions and macrocyclic ammonium groups in 2. N…Cldistances are given in A with esd’s in parentheses. Fig. 6b. Coordina-tion pyramids formed by the chloride anions and groups from acyclicpolyammonium moieties (from ref. 24). N…Cl distances are given in Awith esd’s in parentheses. Fig. 6c. Co-ordination pyramids formed bythe chloride anions and different donor groups (from ref. 15 (top) andref. 17 (bottom)). N…Cl distances are given in A with esd’s inparentheses.
represents a preferred co-ordination mode for the chlorideanion. Figs. 6a–c depict the co-ordination pyramids formed byCl2 in the present work and the two aforementioned publica-tions that describe the interactions of chloride with acyclicpolyammonium moieties.
The flattest co-ordination pyramid occurs in the one casewhere the pyramid has a square base. The steepest pyramidoccurs in the present structure where the restrictions of themacrocycle force the chloride further away from the basalplane. The remaining pyramids whose bases are comprised ofnitrogen donors have very similar geometries with the primarydifferences between them being the distances between the basalpoints, rather than the steepness of the pyramids (Fig. 6b). It isdifficult to discuss the geometries strictly in terms of theD…Cl…D angles as these and the steepness of the pyramid areinterrelated. The pyramids utilizing other donors such as OHor CH groups to interact with the halides, however, aregenerally flatter (Fig. 6c).
The pyramids in 2 link up to form 2D sheets that areseparated by layers of perchlorate anions (Fig. 7) that lieslightly offset from one another rather than 180u out-of-phase.The perchlorate anions do not participate in any hydrogenbonding interactions, instead occupying interstitial channelsformed between the macrocycle–chloride layers (Fig. 8).
(H3L)(HSO4)Cl2 (3) and (H3L)(HSO4)2Cl (4)
The triprotonated macrocycle in 3 has its charge balanced bytwo chloride anions and a hydrogen sulfate anion (Fig. 9). Allof the macrocyclic ammonium protons are involved inhydrogen bonding interactions (see Table 2). N(2) is the onlygroup to donate three hydrogen bonds: one to Cl(2) throughH(7) and two to O(3) and O(3)* through H(8). The macrocycliccavity is bridged by a N…O–S–O…N interaction with ahydrogen sulfate anion. In contrast to the previous structures,the chloride closest to the cavity (Cl(1)) is held by only onehydrogen bond from an ammonium group (N(1)). The othertwo macrocyclic nitrogen atoms are pointing in the oppositedirection with respect to the plane of the macrocycle. As a
result, this chloride is significantly further away from the meanplane of the macrocycle (3.631(1) A) than those participating intripodal pyramid formations in 1 and 2. Each of the twochlorides accept just two hydrogen bonds. Cl(1) accommodatesthe abovementioned ammonium hydrogen bond and anadditional bond from the OH group of the hydrogen sulfateanion. Cl(2) bridges between adjacent macrocycles, acceptinghydrogen bonds from N(3) on one [9]aneN3 and N(2) onanother. The macrocycles are also bridged by another pair ofinteractions involving symmetry related oxygen atoms (O(3)and O(3)*) on hydrogen sulfate anions (Fig. 9). Expansion ofthe structure reveals that this interaction is also holdingtogether the 2D sheets formed by the macrocycles, chloride andsulfate anions (Fig. 10).
Compound 4 contains one [9]aneN3 moiety with twohydrogen sulfate anions and one chloride anion. In thestructure, the macrocycle is triprotonated and used all sixammonium protons in hydrogen bonding (Fig. 11 andTable 2). Two of these protons bind to chloride anions, therest are involved in hydrogen bonding to oxygen atoms ofHSO4
2 anions. One of the oxygen atoms on a HSO42 anion
bridges the macrocyclic cavity (N(1)…O(3)…N(2)) and theremaining two ammonium protons bind externally to twosymmetry related sulfate oxygen atoms (N(1)–H(2)…O(5)2.811(3) A, 157(3)u and N(3)–H(8)…O(5) 2.804(3) A,162(2)u). In contrast to the cases in 1 and 2, two of themacrocyclic nitrogen atoms point upwards from the plane of
Fig. 7 ORTEP plot of the 2D sheets formed by [9]aneN3 and chlorideanions in 2.
Fig. 8 Stacking of the 2D sheets in 2 with chloride anions shown inORTEP representation. Click here to access a 3D image of Fig. 8.
Fig. 9 ORTEP plot of the hydrogen bonding environment around themacrocycle in 3. The asterisk indicates symmetry generated atoms.
Fig. 10 Stacking of the 2D sheets in 3 viewed down the a-axis, withchloride anions shown in ORTEP representation and all other atomsshown in stick representation. Click here to access a 3D image ofFig. 10.
the macrocycle and one points downwards. The nitrogen atomsdeviate less significantly overall from the plane of themacrocycle (N(1) 0.333(2), N(2) 0.605(2), N(3) 0.458(2)). Thechloride anion bridges two symmetry related macrocyclesthrough N(3)…Cl(1)…N(2). The N…Cl…N angle for thisinteraction is 103u, similar to the chelate bite angles in 1 forCl(2) (109, 115 and 102u). Notably, the oxygen atom (O(4))chelated by two of the macrocyclic ammonium groups has achelate bite angle of 67u similar to that of the internallychelated chloride in 2 (Cl(2)) which has chelate bite angles of59, 60 and 60u.
The HSO42 anions in 4 link up through strong O–H…O
interactions (O(4)–H(1)S…O(6) 2.603(3) A, 173(3)u, O(8)–H(2)S…O(2) 2.616(3) A, 173(5)u) to form a tetramer thatbridges six macrocycles through N–H…O hydrogen bonds(Fig. 12). The tetramers do not interact with the chlorideanions, and instead lie isolated by the macrocycles in the crystallattice. The two crystallographically unique sulfates share thesame hydrogen bonding mode, with one oxygen atom hostingtwo N–H…O hydrogen bonds, another hosting an O–H…Ohydrogen bond from the other unique HSO4
2 anion and thelast oxygen (with the shortest S–O bond) being free of anyhydrogen bonding interactions. The packing of the structure in4 reveals 2D sheet formations that lie parallel to the a–0–b
plane (Fig. 13). Chloride anions occupy the spaces between thesheets but are well separated from the sheet adjacent to that towhich they are hydrogen bonded. The closest point of contactfor the sheets is between Cl(1) and C(1) (3.55 A). Each sheet canbe described as a three-layered construct in which the middlelayer of hydrogensulfate tetramers is sandwiched between twolayers of macrocycle-chloride moieties, with the chloridesoccupying the extreme faces of the constructs.
Fig. 14a shows the interaction modes of the chloride anionsfound in 3 and 4. There is a great deal of similarity between theexamples shown, each having similar chelate bite angles andD…Cl distances. For comparison, Fig. 14b shows the similarconstructs found in ref. 24. These g-2 types of interactions,whilst being fairly common in these polyammonium-chloridestructures, are not as prevalent as the tripodal pyramidsdiscussed above.
Some interesting comparisons can be made between anionbinding preferences of [9]aneN3 in 3 and 4 and those exhibitedby [18]aneN6.15 In the latter, the macrocycle retains thechloride co-ordinated within the macrocyclic cavity whenconcurrently presented with the option of hosting a hydrogensulfate anion. In the present structures (3 and 4), the tripodalpyramid is not stable enough to compete with lattice forcesproduced by packing of the HSO4
2 anions, with the chlorideanions instead being shunted to positions external to the cavity.This is corroborated by the fact that in the present work(structures 1 and 2), when presented with weak hydrogen
Fig. 11 ORTEP plot of the hydrogen bonding environment aroundthe macrocycle in 4.
Fig. 12 ORTEP plot of the isolated HSO42 tetramers stabilized by
N–H…O interactions in 4. Chloride anions are not shown for clarity.
Fig. 13 Two views of the 2D sheets in 4 looking down the a-axis (left) and the b-axis (right). Chloride anions are shown in ORTEP representation.Click here to access a 3D image of Fig. 13.
bonding competitors such as perchlorate and copper tetra-chloride, the tripodal interaction of the macrocyclic ammo-nium groups with chloride remains, with the competitorshaving to arrange themselves around it using fewer inter-actions. The hydrogen bonding modes of the HSO4
2 anions in3, 4 and those reported in ref. 17 are shown in Fig. 15a and b.One feature that is immediately apparent is that the HSO4
2
anions can participate in as few as two and as many as fourhydrogen bonding interactions. There is always a chargebalancing interaction with an ammonium group, and where theO–H group donates to a negatively charged moiety such aschloride, there is an additional ammonium group donor to oneof the hydrogen sulfate oxygen atoms. Donors from neutralamine N–H groups are not observed, with preference forproton transfer from the oxoacid to the amines reflecting theincreased stability provided by hydrogen bonding interactions.In Fig. 15b, the first and last anions appear to have the samemodes of interaction (accepting two N–H and one O–Hinteraction and donating an O–H hydrogen bond to an oxygenatom), however they are oriented in the same way (i.e. with thehorizontal O–S–O section having the oxygen atoms directedoutward from the plane of the page) imparting ‘chirality’ to theanions.
(H3L)(H2PO4)3 (5)
The structure of 5 consists of the triprotonated macrocycle andthree dihydrogen phosphate anions (Fig. 16). Interestingly,there are no chloride anions in the structure, possibly owing tothe very tight and stable hydrogen bonding network set up bythe strongly interacting H2PO4
2 anions. Table 3 lists thehydrogen bonds found in 5. Similar types of complexH-bonded phosphate lattices have been seen before in recentlyreported structures containing the [18]aneN6 azamacrocycle.16
The [9]aneN3 macrocycle in the present structure has a similarconformation to those seen in 3 and 4, with two of themacrocyclic amines directed upwards from the plane of themacrocycle and the third facing downwards. As in 2 and 4, allammonium protons are involved in hydrogen bonding
interactions. The g-2 chelate motif of the macrocyclic cavitywith an anionic oxygen atom is also present in 5 (see interactionof O(6) with the macrocycle) and is of a very similar geometryto that found in 4 (Fig. 17). The N–H…O hydrogen bonddistances are much shorter for the phosphate oxygen thanfor the sulfate oxygen and the chelate bite angle is,
2 anions in 3 (left) and 4 (right). (b) ORTEP plots showing thehydrogen bonding modes of the HSO4
2 anions in ref. 17.
Fig. 16 ORTEP plot of the hydrogen bonding environment aroundthe macrocycle in 5.
Fig. 14 (a) ORTEP plot of the macrocyclic chelate motifs in 3 (top)and 4 (bottom) showing the chelate bite angles. N…Cl and O…Cldistances are given in A with esd’s in parentheses. (b) ORTEP plot ofmacrocyclic g-2 chelate motifs from ref. 24 showing the chelate biteangles. N…Cl distances are given in A with esd’s in parentheses.
correspondingly, slightly larger. This is in line with thetendency of dihydrogen phosphate anions to form shorterhydrogen bonds than hydrogen sulfate, even though the twoanions have the same charge and both exhibit a tetrahedralgeometry.
The H2PO42 anions all differ greatly in their hydrogen
bonding modes when compared with the HSO42 anions in 3
and 4. The O–H groups of all the phosphate anions donatehydrogen bonds to oxygen atoms of other phosphate anionsand all of the oxygen atoms act as hydrogen bond acceptors.Interestingly, the only oxygen atom in the structure to acceptonly one hydrogen bond is O(4), the rest being involved in twohydrogen bonds. This is in direct contrast to the sulfate caseswhere only one oxygen atom accepts more than one hydrogenbond (see Fig. 15a). The P(1) anion bridges three separatemacrocycles and also provides the only instance of an O–Hoxygen atom accepting a hydrogen bond. The P(2) anion is theonly one to have an oxygen chelated by the macrocycle, whilstthe P(3) anion in completely isolated from the macrocycles,participating in hydrogen bonds with other phosphate moietiesonly. All three crystallographically unique H2PO4
2 anionsparticipate in six hydrogen bonding interactions. Fig. 18adepicts the various H-bond donors and acceptors to the threedihydrogen phosphate anions in 5 and Fig. 18b shows thehydrogen bonding modes of H2PO4
22 anions reported recentlyby our group.16 It is immediately apparent that the dihydrogenphosphates exhibit a much wider range of hydrogen bondingmodes than the analogous hydrogen sulfate, to the totalexclusion of chloride from the structure. A comparison ofFig. 18a and b reveals that the P(2) anion in 5 has the same
hydrogen bond distribution as 3, P(1) from the [18]aneN6
structures, and P(3) is the same as 2, P(2). Notably, thehydrogen bonding mode exhibited by P(1) in 5 is uniqueamongst the structures of adducts formed by dihydrogenphosphate and polyammonium macrocycles reported to date.16
Hydrogen bonding involving tetrahedral oxoanions has beenexplored by Hay and co-workers in an analysis of H…O–Aangles found in published crystal structures.28 A strong biaswas found in that these angles clustered around 120u. Thestructures reported herein are in keeping with these findings,although there is significant variation in the H…O–A angles,viz. the largest angle is found in 4 (H(1)…O(3)–S(1) 144u) andthe smallest in 5 (H(1)…O(1)–P(1) 102u).
Expansion of the structure reveals a 2D layered formation,with sheets comprised of dihydrogen phosphate anions beingconnected to each other through hydrogen bonding inter-actions with the macrocycle. Fig. 19 shows the highly inter-connected 2D sheets formed by the phosphate anions alone andFig. 20 shows the packing of the structure with the macrocyclesseparating the anionic layers.
Fig. 17 ORTEP plot of the macrocyclic chelate motif in 4 (left) and 5(right) showing the chelate bite angle. N…O distances are given in Awith esd’s in parentheses.
Fig. 18 (a) ORTEP plots of the hydrogen bonding modes for theH2PO4
2 anions in 5. Fig. 18b. Hydrogen bonding modes for thedihydrogen phosphate anions taken from ref. 16. All OH groups aredonating hydrogen bonds to oxygen atoms (not shown for clarity).
Table 3 Hydrogen bonds in 5a
D–H…Ab d(D–H) d(H…A) d(D…A) /(DHA)O(1)–H(1P)…O(9)#1 0.84 1.92 2.584(6) 135N(1)–H(1)…O(1)#2 0.92 1.93 2.811(6) 160N(1)–H(2)…O(6) 0.92 1.75 2.638(7) 161O(2)–H(2P)…O(10) 0.84 1.95 2.624(6) 137N(2)–H(7)…O(4) 0.92 1.79 2.674(6) 161N(2)–H(8)…O(5)#3 0.92 1.76 2.677(6) 171N(3)–H(13)…O(6) 0.92 1.80 2.720(7) 177N(3)–H(14)…O(3)#4 0.92 1.84 2.741(6) 167O(7)–H(3P)…O(10)#4 0.84 1.87 2.630(5) 149O(8)–H(4P)…O(9)#5 0.84 1.83 2.586(5) 150O(11)–H(5P)…O(5)#3 0.84 1.72 2.548(6) 170O(12)–H(6P)…O(3)#6 0.90 (1) 1.80(6) 2.575(5) 142(8)a Distances (A) and angles (u) are listed (esd’s in parentheses whereapplicable). b Symmetry transformations used to generate equivalentatoms: #1 x 2 1, y, z; #2 x 1 1/2, 2y 1 3/2, z 2 1/2; #3 x, 2y 1
2, z 1 1/2; #4 x 2 1/2, 2y 1 3/2, z 2 1/2; #5 x 2 1, 2y 1 2, z 21/2; #6 x 1 1/2, y 1 1/2, z.
The crystal structures of adducts of [9]aneN3 and thetetrahedral oxoanions, ClO4
2, HSO42 and H2PO4
2, revealthat stronger hydrogen bonding networks are established byoxoanions with stronger hydrogen bonding ability. Theperchlorate anions exhibited no hydrogen bonding tendenciesin the solid state, as opposed to the sulfate anions, which wereintermediate in the range of hydrogen bonding modes and thephosphates, which show considerable variability in theirinteractions. The chloride anions display trigonal pyramidalmotifs seen in previous work24 that show a considerable degreeof flexibility in the ‘steepness’ of the co-ordination pyramid.
Acknowledgements
This work was supported by the Australian Research Council.ACW was the recipient of a Research and Teaching Fellowship
and a Departmental Scholarship from Monash University. Theauthors thank Dr Stuart Batten and Dr Peter Junk for theirassistance with X-ray crystallography.
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Fig. 19 ORTEP plot showing one of the 2D sheets formed by theH2PO4
2 anions in 5, viewed down the c-axis.
Fig. 20 Packing diagram highlighting the separation of the anionicsheets by layers of [9]aneN3 in 5, viewed down the a-axis. Click here toaccess a 3D image of Fig. 20.
