- Email: [email protected]
Coordination polymers derived from silver salts and an aliphatic N,O ligand
Inorganica Chimica Acta 348 (2003) 107 /114 www.elsevier.com/locate/ica
Coordination polymers derived from silver salts and an aliphatic N,O ligand Andrea Erxleben * Fachbereich Chemie, Universita¨t Dortmund, 44221 Dortmund, Germany Received 6 August 2002; accepted 6 November 2002
Abstract Cocrystallization of silver salts with the polyfunctional, conformationally flexible ligand N -(2-cyanoethyl)-b-alanine (cea) yielded three different coordination polymers, namely a rare example of a compound containing helical chains assembled into an infinite 2D array, [Ag4(cea )2(NO3)]BF4 (1), a 3D channel structure, [Ag4(cea)2(H2O)(CF3SO3)4] (2), and an unprecedented structure comprising 1D polymeric anions sandwiched between the loops of a cationic pleated sheet, [Ag3(cea)2(NO3)][Ag2(NO3)3]NO3 (3). In 2 and 3 the central amino nitrogen of cea is protonated and non-coordinating so that the ligand has two metal binding sites separated by a five-membered aliphatic linker and a central hydrogen bond donating site. In the case of 2 this gives rise to 44membered macrometallacyclic subunits that generate large rhombic channels hosting the counterions. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Silver; Coordination polymers; Crystal structures
1. Introduction A large number of coordination polymers with various topologies like infinite chains, ladders, helices, sheets, honeycomb structures or 3D networks have been reported to date [1 /5]. Reasons for the ongoing interest in this field are potential applications of coordination polymers as functional materials as well as the continuing discovery of ever new topological types of networks. As for the latter, Ag(I) ions that easily adopt various coordination geometries are particularly suited to explore the network-forming abilities of polydentate ligands and to generate novel coordination polymers. We are interested in the use of polyfunctional, conformationally flexible ligands with hydrogen bond donating functionality [6]. In principle, bidentate ligands with the donor sites being separated by long, organic linkers are capable of generating polymers with channels or pores that are particularly attractive with regard to possible applications in host-guest chemistry [5a,f,7].
* Fax: /49-231-755-3797. E-mail address: [email protected] Erxleben).
(A.
However, since nature tends to avoid vacuum, large void volumes are often prevented by interpenetration of identical nets [1 /4]. The influence of hydrogen bonding on network architectures is well recognized and several examples have shown that the introduction of functional groups capable of hydrogen bonding interactions can be exploited in the synthesis of coordination polymers [8]. In the present study we report three Ag coordination polymers derived from N -(2-cyanoethyl)-b-alanine (cea). Under neutral conditions silver ions bind to the carboxylate group, the nitrile nitrogen and the amine nitrogen to give a rare example of a 2D polymeric structure of infinite helices. Under more acidic conditions silver cannot compete with the ammonium protons and the zwitterionic cea molecule represents a ligand with a central hydrogen bond donor functionality and two metal binding sites separated by a five-membered aliphatic chain. It is shown that cocrystallization of cea with AgCF3SO3 at pH 4 leads to the formation of a 3D channel structure built up by large macrometallacycles and stabilized by the triflate ions that form coordination bonds with silver and acceptor hydrogen bonds with the ammonium nitrogen, while AgNO3 affords an unprecedented structure consisting of 2D polymeric cations and 1D polymeric anions.
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0020-1693(02)01484-6
108
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114
2. Experimental 2.1. Starting materials Cea was prepared according to Ref. [9]. All chemicals and solvents were reagent grade and used without further purification. 2.2. Preparations [Ag4(cea )2(NO3)]BF4 (1) was obtained by treating cea (1.00 mmol) with AgBF4 (1.00 mmol) and AgNO3 (1.00 mmol) in ethanol/water (2:1, 12 ml) at pH 6. Colorless plates crystallized at 4 8C in 43% yield. Anal . Calc. for C12H18Ag4BF4N5O7: C, 16.7; H, 2.1; N, 8.1. Found: C, 16.3; H, 2.2; N, 8.1%. Selected IR data (KBr, n (cm1)): 3404 s vbr, 2251 w (C /N), 1573 s (C/O), 1468 m, 1384 s (NO3), 1318 m, 1084 s (BF4), 1035 s, 821 w (NO3), 533 w, 522 w. Colorless needles of [Ag4(cea)2(H2O)(CF3SO3)4] (2) suitable for X-ray analysis resulted from crystallization of cea (1.00 mmol) with AgCF3SO3 (2.00 mmol) from ethanol/water (2:1, 12 ml, pH 4) at 4 8C. Yield: 34%. Anal . Calc. for C16H22Ag4F12N4O17S4: C, 14.5; H, 1.7; N, 4.2. Found: C, 14.3; H, 1.8; N, 4.4%. Selected IR data (KBr, n(cm 1)): 3494 m br, 2269 w (C/N), 1597 s (C /O), 1544 m, 1260 s, 1171 s, 1035 s, 826 m, 765 w, 641 m, 579 w, 520 m, 229 w. X-ray suitable crystals of [Ag3(cea)2(NO3)][Ag2(NO3)3]NO3 (3) were obtained in 36% yield by mixing AgNO3 (2.00 mmol) and cea (1.00 mmol) in ethanol/ water (2:1, 12 ml, pH 4) followed by slow evaporation of the solution at 4 8C. Anal . Calc for C12H20Ag5N9O19: C, 12.7; H, 1.8; N, 11.1. Found: C, 13.2; H, 1.7; N, 11.2%. Selected IR data (KBr, n(cm 1)): 3038 m, 2780 m, 2651 m, 2271 w (C /N), 1655 m, 1567 s, 1383 vs (NO3), 1104 m, 1056 m, 1014 m, 825 m, 816 m, 790 m, 700 m, 615 m, 589 m, 428 m. 2.3. Instrumentation and methods 1
H NMR spectra were recorded on a Varian mercury spectrometer at 200.13 MHz. using sodium 3-trimethylsilyl-propanesulfonate as internal reference. The pKa value for cea was obtained by pH-dependent 1H NMR spectroscopy from graphs of chemical shifts versus uncorrected pH (pH*) values [10]. Infrared spectra were taken on a Bruker IFS 28 FT-spectrometer. 2.4. Crystallography Crystal data for compounds 1/3 were collected at room temperature (1, 2) and 153 K (3) on an Enraf / Nonius-kCCD diffractometer [11] using graphite-mono˚ ). For data chromated Mo Ka radiation (l/0.71069 A reduction and cell refinement the programs DENZO and
SCALEPACK were used [12]. The structures were solved by conventional Patterson methods and subsequent Fourier syntheses and refined by full-matrix leastsquares on F2 using the SHELXTL PLUS, SHELXL-93 and SHELXL-97 programs [13]. Graphics were produced with SHELXTL PLUS and ORTEP-3 [14]. Hydrogen atoms were generated geometrically and given fixed isotropic thermal parameters (1, 2) or isotropic thermal parameters equivalent to 1.2 times those of the atom to which they were attached (3). In compound 1, one nitrate oxygen (O(12)) is located on a twofold axis while the nitrate nitrogen and the other two oxygens (O(10) and O(11)) have site occupancy factors of 0.5 and are disordered over the two positions generated by the symmetry operator. Crystallographic data and details of refinement are reported in Table 1.
3. Results and discussion 3.1. Silver complex formation with anionic cea In neutral or slightly acidic (pH 6) solution cea whose pKa value for the deprotonation of the ammonium nitrogen was determined by pH-dependent 1H NMR spectroscopy to be 7.9 behaves as a tridentate ligand for silver ions. The cocrystallization of cea with AgBF4 in the presence of NO3 from ethanol/water afforded Xray suitable crystals of composition [Ag4(cea)2(NO3)]BF4 (1). 3.1.1. Crystal structure of {[Ag4(cea )2(NO3)]BF4}n (1) Single-crystal X-ray analysis of 1 revealed infinite, single-stranded helices that assembled into a 2D network. As illustrated in Fig. 1(a) the polymer is built up by bicyclic subunits having C2 symmetry. Within the subunits three silver ions and two negatively charged cea ligands constitute two fused 14-membered rings. Each ligand binds the three Ag ions through the nitrile nitrogen and the carboxylate group with the latter one coordinating in a m2-bridging fashion. The Ag /O bond lengths are normal, while the Ag /N bond distance of ˚ is at the low end of the usual range (2.18/ 2.172(9) A ˚ 2.33 A) [15a]. The Ag /N /C bond angle is close to linear (174.1(9)8) as expected. The valence angles of the N ,O and O ,O coordinated silver ions are 161.2(3) and 178.3(3)8. The nitrate ion that is statistically distributed on two close positions is weakly bound to Ag(3) thus extending the linear coordination environment of the metal ion to a distorted T-shaped O2N coordination sphere. The {Ag3(cea )2(NO3)} entities are connected through a fourth silver ion that binds to one amine nitrogen of each moiety. This results in an infinite 21helix of trinuclear subunits linked together by linear N / Ag /N-bridges. The pitch height of the helix that extends
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114
109
Table 1 Crystallographic data for 1 /3
Formula Mr Crystal color and habit Crystal size (mm3) Crystal system Space group Unit cell dimensions ˚) a (A ˚) b (A ˚) c (A a (8) b (8) g (8) ˚ 3) V (A Z Dcalc (g cm 3) m (Mo Ka) (mm 1) F (000) 2u Range (8) No. of measured reflections No. of independent reflections (Rint) No. of observed reflections No. of parameters Final R1, wR2 (observed reflections) a Final R1, wR2 (all reflections) a Goodness-of-fit (observed reflections) Goodness-of-fit (all reflections)
1
2
3
C6H9Ag2B0.5F2N2.5O3.5 431.30 colorless needle 0.20/0.15/0.06 orthorhombic Pcca
C16H22Ag4F12N4O17S4 1330.10 colorless block 0.40 /0.24 /0.12 triclinic P 1¯
C6H10Ag2.5N4.5O9.5 566.86 colorless needle 0.50/0.10/0.06 monoclinic P 21/m
8.726(1) 14.883(1) 16.566(1)
5.748(1) 17.794(1) 18.339(1) 95.83(1) 98.89(1) 95.49(1) 1831.7(3) 2 2.412 2.469 1284 6.8 /53.4 36184 7774 (7.3%) 3241 489 R1 /5.7%, wR2 /14.8% R1 /14.2%, wR2 /19.4% 1.282 0.859
5.557(1) 11.652(1) 21.260(1)
2151.4(3) 8 2.663 2.288 1640 6.8 /53.4 13842 2286 (4.9%) 1346 (I /2s (I )) 160 R1 /5.4%, wR2 /16.4% R1 /9.1%, wR2 /18.2% 1.238 0.986
96.03(1) 1369.0(3) 4 2.750 3.615 1084 5.2 /54.2 17022 3149 (7.6%) 1808 218 R1 /4.6%, wR2 /9.8% R1 /9.5%, wR2 /16.9% 1.216 0.977
a R1 /SjjFoj/jFcjj/SjFoj; wR2 /[S w (Fo2/Fc2)2/S w (Fo2)2]1/2; w 1 /s2(Fo2)/(aP )2; P/(Fo2/2Fc2)/3; a /0.1107 for 1, 0.0866 for 2 and 0.0457 for 3.
˚ . The in the crystallographic a direction is 8.726(1) A carboxylate group that bridges two silver ions of the bicyclic units forms a weak bond to a third silver ion belonging to an adjacent helix (Ag(2) O(2) 2.700(7) ˚ ). This connects helices of opposite helicity into a 2D A network as shown in Fig. 1(bc). In the crystal packing layers of helical chains linked through weak silver/ carboxylate interactions are stacked parallel to the ac plane. The BF4 ions are located between the layers, while the disordered NO3 anions lie inside the helices ˚ (Table that have inner diameters of approximately 8.5 A 2). The formation of infinite metallohelices receives much current attention due to potential applications in materials science and the fundamental role of helicity in biology [2,16]. There are an increasing number of examples where */ like in 1 */ a 1D coordination polymer spontaneously assumes a helical conformation [17], although these are less numerous than discrete oligonuclear helicates [18]. However, examples, where single-stranded silver helices are assembled by (weak) coordination bonds into a polydimensional network are rather rare [5h,15b,16b,19,20].
3.2. Silver complexes with neutral (zwitterionic) cea Protonation of the amino nitrogen under acidic conditions converts cea into a bifunctional ligand that combines coordination bond forming and hydrogen bond forming capabilities. Depending on the counterion two different coordination polymers, [Ag4(cea)2(H2O)(CF3SO3)4] (2) and [Ag3(cea)2(NO3)][Ag2(NO3)3]NO3 (3), were obtained at pH 4. Single crystals of 2 and 3 suitable for X-ray crystallography were grown from aqueous ethanol solutions at 4 8C. Views of the structures of 2 and 3 are displayed in Figs. 2 and 3, relevant bond lengths, angles and hydrogen-bonding interactions are summarized in Tables 3 and 4. 3.2.1. Crystal structure of [Ag4(cea)2(H2O)(CF3SO3)4]n (2) The asymmetric unit of 2 consists of four nonequivalent silver ions, two neutral cea ligands in their zwitterionic forms, one coordinated water molecule and four triflate anions. The basic structural motif is a 44membered macrocycle containing four ligand molecules and eight silver ions (Fig. 2(a)). Within the ring the silver ions are connected alternately through a monatomic
110
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114 Table 2 ˚ ) and bond angles (8) in 1 Bond lengths (A Bond lengths Ag(1) /N(1) Ag(3) /N(2) Ag(3) O(11)
2.209(6) 2.172(9) 2.58(2)
Ag(2) /O(1) Ag(3) /O(2) b
2.210(6) 2.176(6)
Bond angles N(1) /Ag(1) /N(1) a N(2) /Ag(3) /O(2) b
176.6(3) 161.2(3)
O(1) /Ag(2) /O(1) b N(2) /Ag(3) O(11)
178.3(3) 111.3(5)
a b
/x , y , 0.5/z . 0.5/x , 1/y , z .
carboxylate bridge and cea binding via the cyano nitrogen and the carboxylate group. All silver ions have distinct coordination spheres: Ag(1) adopts a distorted trigonal bipyramidal coordination geometry with an NO4 (2 /carboxylate, 2 /triflate) donor set, Ag(3) is distorted tetrahedrally coordinated by a cyano nitrogen, a triflate and a carboxylate oxygen as well as a water ligand, while Ag(2) and Ag(4) have Y-shaped O3 coordination environments (Ag(2): 2/carboxylate, 1/ triflate and Ag(4): 3 /carboxylate). The Ag /N/C bond angles are 151.8(8) and 162.6(8)8 and are more acute than they are usually in silver nitrile compounds (166 / 1768) [15a]. The formation of the large macrometallacycles is supported by the triflate anions that are hosted in the macrocycles thus filling the void volume and preventing an interpenetrated structure. The incorporation of the counterions is stabilized by direct coordina˚ ) and tion of triflate oxygen to silver ions (2.419/2.583 A hydrogen bonding interactions with the ammonium nitrogen of the ligands (Table 3). The carboxylate group of each ligand coordinates four silver ions so that overall a cationic 3D polymeric network is generated. The 3D structure is constituted of parallel layers of fused macrocycles that stack along the crystallographic a axis and that are interconnected through Ag /carboxylate bonds. This gives rise to a rhombic channel architecture as shown in Fig. 2(b) and (c). The channels that are filled by the anions make up 46% of the cell volume [21]. The effective cavity size as measured by the shortest distance between the van der Waals surfaces of ˚. opposing sides is approximately 8.6 /8.9 A
Fig. 1. (a) Bicyclic [Ag3(cea )2(NO3)] subunits in 1. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms are omitted for clarity. (b) Linkage of the [Ag3(cea )2(NO3)] entities through Ag into an infinite 21-helical chain. (c) Assembly of 21-helical chains into an infinite 2D polymeric structure. Ag: cross-hatched circles; N, O: hatched circles; and C: empty circles.
3.2.2. Crystal structure of {[Ag3(cea)2(NO3)][Ag2(NO3)3]NO3}n (3) Single-crystal X-ray analysis of 3 showed an assembly of 2D polymeric cations of composition [Ag3(cea)2(NO3)]n2n, 1D polymeric anions of composition [Ag2(NO3)3]nn and nitrate ions. A section of the anionic polymer is depicted in Fig. 3(a). Silver ions and nitrate anions form an infinite, straight chain of fused unsymmetric rings each of which contains three metal ions and three nitrates. Different coordination modes */ m3-bridging, m2-bridging and chelating */ are adopted by the nitrates. The silver ions have a distorted trigonal-
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114
Fig. 2. (a) Macrocyclic ring in 2 formed by Ag and cea with H bonding interactions between N(1) /H and CF3SO3 indicated. Thermal ellipsoids are drawn at 30% probability level. Hydrogen atoms except for those of the ammonium nitrogens are omitted for clarity. (b,c) 3D network structure with rhombic channels running along the a -axis. Counterions and hydrogen atoms are omitted for clarity.
111
planar O3- (Ag(3)) and four-coordinate O4- (Ag(4)) coordination sphere. The polymeric cation contains 24-membered metallamacrocycles. Each macrocycle consists of three silver ions, two cea molecules in their zwitterionic forms and one nitrate anion (Fig. 3(b)). Within the rings one silver binds to one carboxylate oxygen of each ligand. The other two silver ions (Ag(1) and Ag(1a)) coordinate to the two nitrile nitrogens. These silver ions are connected through a nitrate ligand that binds in a monodentate manner to one silver and in a chelating mode to the ˚ ) and C /N (1.142(9) other one. The Ag /N (2.230(7) A ˚ A) bond lengths fall in the normal range (2.18/2.33 and ˚ ) [15a], while the Ag /N/C bond angles of 1.07 /1.15 A 149.8(7)8 are relatively acute as already observed for compound 2. The carboxylate groups serve as m3bridging ligands and link the macrocycles into an 1D array as shown in Fig. 3(c). The carboxylate /silver coordination shows the usual geometric features: The Ag /O bond lengths (Table 4) compare well with those observed in related Ag /carboxylate compounds, where Ag /O(axial) and Ag /O(equatorial) bond distances ˚ , respectively typically range from 2.2 /2.3 and 2.4 /2.5 A ˚ [22]. The carboxylate-bridged silver ions are 2.774(1) A ˚ (Ag(2) Ag(2a) at /1/x , 1/y, 1/z ) and 3.637(9) A (Ag(2) Ag(2b) at /1/x , y, z ) apart with the Ag(2) Ag(2a) separation being at the low end of the range observed in anti /anti {Ag2(m2-RCOO)2} units ˚ ) [23]. The chain of carboxylate-bridged (2.78/3.00 A silver ions and fused macrocycles extends along the crystallographic a direction. In the overall structure of the cation these chains are arranged in parallel along the b direction. The nitrile bound Ag(1) ions and nitrate ligands are shared by macrocycles of neighboring layers so that a 2D polymer is generated. Consequently, the Ag(1) ions have five-coordinate N2O3 environments in contrast to the Y-shaped O3 geometries of the Ag(2) ions. As evident from Fig. 3(c) the cationic polymer assumes a highly undulate sheet conformation. The view of the structure depicted in Fig. 3(d) suggests that the folding of the sheet is brought about by the nitrate ions each of which forms two acceptor hydrogen bonds with the ammonium nitrogens of opposite sides at the tops of the troughs. The anionic [Ag2(NO3)3]nn chains are ˚ depth. This encapsulated by the troughs of 5.557 A packing of anionic and cationic entities that is to the best of our knowledge unprecedented is stabilized by hydrogen bond interactions between nitrate oxygens of the polymeric anion and the ammonium nitrogens of cea ˚) (Table 4) as well as by short contacts (2.778(5) A between carboxylate groups of the cationic sheet and silver ions of the anionic chain. Unfortunately, attempts to prepare Ag complexes of cea with other anions (ClO4, PF6) at pH 4 and 6 gave only glassy, non-crystalline materials whose structures could not be elucidated. Likewise, attempts to crystallize
112
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114
Fig. 3. (a) 1D polymeric structure of the anion of 3, [Ag2(NO3)3]nn . Thermal ellipsoids are drawn at 50% probability level. (b) Macrocyclic subunits of the polymeric cation of 3. Hydrogen atoms are omitted for clarity. (c) Section of the polymeric structure of the cation of 3, [Ag3(cea)2(NO3)]n2n , showing the chain of fused macrocycles. Ag: cross-hatched circles; N, O: hatched circles; and C: empty circles. (d) ORTEP drawing of the packing of 2D cationic sheets and 1D anionic chains. Ag: light gray; C, N, O: dark gray.
cea with AgBF4 in the absence of NO3 were unsuccessful. 3.3. Spectroscopic characterisation of 1 /3 1
H NMR spectra in D2O indicate complete dissociation of the silver complexes into Ag and the ‘free’ ligand in solution. In the infrared spectrum of 2 and 3 the n(C /N) stretching vibration is shifted by about 20 cm 1 to higher wavenumbers compared with the ‘free’ ligand as expected upon metal coordination to the cyano nitrogen (n (C/N) /2269 (2), 2271 (3) and 2252 cm 1 (‘free’ ligand)). By contrast, the n(C /N) stretching vibration frequency in 1 is essentially unchanged (n(C /N) /2251 cm 1). This may indicate p-backbonding, since s-donation shifts n (C /N) bands to
higher wavenumbers, while p-back-bonding has the reverse effect. Reinforcement of the s-bond by p-backbonding in the case of 1 is in accordance with the Ag / ˚ ) being at the low end N(nitrile) bond length (2.172(9) A of the range typically found for silver nitrile complexes ˚ ) [15]. (2.18/2.33 A
4. Conclusions In conclusion we have structurally characterised three different Ag coordination polymers with the conformationally flexible ligand cea. When the central nitrogen is protonated and non-bonding, cea connects silver ions into macrometallacycles. Depending on the counterion, these are 24-membered or larger 44-membered rings. In
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114 Table 3 ˚ ), bond angles (8) and hydrogen-bonding interactions Bond lengths (A ˚ ) in 2 (A Bond lengths Ag(1) /N(2?) a Ag(1) /O(1) Ag(1) /O(2) b Ag(1) O(10) c Ag(1) /O(30) Ag(2) /O(1) Ag(2) /O(2) d Ag(2) /O(10)
2.415(9) 2.450(5) 2.381(5) 2.571(5) 2.478(6) 2.291(5) 2.341(5) 2.419(5)
Hydrogen-bonding interactions N(1) O(1) 2.835(8) N(1) O(22) e 2.869(8) N(1?) O(40) 3.08(1) O(1w) O(20) e 3.15(1) O(1w) O(21) f 2.80(1) Bond angles N(2?) a /Ag(1) /O(1) O(1) /Ag(1) /O(2) b O(1) /Ag(2) /O(2) d N(2) /Ag(3) /O(1?) O(2?) e /Ag(4) /O(2?) b a b c d e f g h
90.9(2) 104.1(2) 130.0(2) 141.9(3) 77.1(2)
Ag(3) /N(2) Ag(3) /O(1?) Ag(3) /O(1w) Ag(3) O(40) Ag(4) /O(1?) Ag(4) /O(2’) e Ag(4) /O(2’) b
2.134(8) 2.386(6) 2.392(9) 2.583(9) 2.308(6) 2.268(6) 2.475(6)
N(1) O(12) N(1?) O(31) g N(1?) O(42) h O(1w) O(2’) b
2.938(8) 2.933(9) 2.84(1) 2.94(1)
N(2?) a /Ag(1) /O(2) b O(2) b /Ag(1) /O(30) O(1) /Ag(2) /O(10) N(2) /Ag(3) /O(1w) O(1?) /Ag(4) /O(2?) b
161.4(2) 87.1(2) 106.8(2) 117.3(3) 110.7(2)
1/x , 1/y , z . /1/x , y , z . /x , 1/y , 1/z . 1/x , 1/y , 1/z . /1/x , /y , /z . /2/x , /y , /z . x , /1/y , z . 1/x , y , z .
Bond lengths Ag(1) /N(2) Ag(1) /O(50) Ag(1) O(51) a Ag(2) /O(1) Ag(2) /O(2) a Ag(2) /O(2) b
2.230(7) 2.486(8) 2.597(7) 2.189(4) 2.433(4) 2.249(4)
Ag(3) O(12) Ag(3) /O(21) Ag(3) O(22) c Ag(4) /O(11) Ag(4) /O(10) c Ag(4) O(41)
2.550(6) 2.434(8) 2.560(8) 2.398(6) 2.461(6) 2.578(5)
Bond angles N(2) /Ag(1) /N(2) d N(2) /Ag(1) /O(50) d N(2) /Ag(1) /O(51) a O(21) /Ag(3) /O(22) c O(12) /Ag(3) /O(22) c O(11) /Ag(4) /O(41) d
112.6(4) 146.1(3) 88.2(2) 130.9(2) 125.1(2) 108.4(2)
N(2) /Ag(1) /O(50) O(50) /Ag(1) /O(50) d O(1) /Ag(2) /O(2) a O(12) /Ag(3) /O(21) O(11) /Ag(4) /O(10) c O(41) /Ag(4) /O(10) c
98.9(3) 47.9(4) 119.4(2) 104.1(2) 131.6(2) 115.2(2)
N(1) O(31) b N(1) O(41)
2.996(6) 2.928(6)
Hydrogen-bonding interactions N(1) O(30) e 2.809(5) N(1) O(40) 3.164(5) b c d e
the latter case incorporation of the anions by coordination to Ag and hydrogen bonding interaction with the ammonium nitrogens prevents interpenetration and favors the formation of a channel structure.
5. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. 189694 (1), 189695 (2) and 189696 (3). Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: /44-1223-336033; e-mail: [email protected] or www: http:// www.ccdc.cam.ac.uk).
Acknowledgements This work was supported by the Fonds der Chemischen Industrie (FCI) and a fellowship granted by the Deutsche Forschungsgemeinschaft. We thank Prof. Bernhard Lippert for the continuous support of our work.
References
Table 4 ˚ ), bond angles (8) and hydrogen-bonding interactions Bond lengths (A ˚ ) in 3 (A
a
113
/1/x , y , z . /1/x , 1/y , 1/z . 1/x , y , z . x , 1/1/2/y , z . /1/x , 1/2/y , 1/z .
[1] S.R. Batten, R. Robson, Angew. Chem., Int. Ed. Engl. 37 (1998) 1460 (and references therein). [2] M. Munakata, L.P. Wu, T. Kuroda-Sowa, Adv. Inorg. Chem. 46 (1999) 173 (and references therein). [3] R. Robson, J. Chem. Soc., Dalton Trans. (2000) 3735 and references therein. [4] M.J. Zaworotko, Chem. Commun. (2001) 1 and references therein. [5] (a) For Ag coordination polymers with aliphatic nitriles or amines see, e.g.: M.-L. Tong, X.-M. Chen, B.-H. Ye, L.N. Ji, Angew. Chem., Int. Ed. Engl. 38 (1999) 2237; (b) C.-X. Ren, H.-L. Zhu, G. Yang, X.-M. Chen, J. Chem. Soc., Dalton Trans. (2001) 85.; (c) K.A. Hirsch, S.R. Wilson, J.S. Moore, Inorg. Chem. 36 (1997) 2960; (d) N.J. Melcer, G.D. Enright, J.A. Ripmeester, G.K.H. Shimizu, Inorg. Chem. 40 (2001) 4641; (e) H.J. Choi, M.P. Suh, J. Am. Chem. Soc. 120 (1998) 10622; (f) K.S. Min, M.P. Suh, J. Am. Chem. Soc. 122 (2000) 6834; (g) K.A. Hirsch, S.R. Wilson, J.S. Moore, Chem. Commun. (1998) 13.; (h) Y. Kang, S.S. Lee, K.-M. Park, S.O. Kang, J. Ko, Inorg. Chem. 40 (2001) 7027; (i) L. Carlucci, G. Ciani, P. Macchi, D.M. Proserpio, S. Rizzato, Chem. Eur. J. 5 (1999) 237; (j) M.-L. Tong, S.-L. Zheng, X.-M. Chen, Chem. Eur. J. 6 (2000) 3729. [6] A. Erxleben, Cryst. Eng. Commun. 4 (2002) 472. [7] (a) For silver complexes see, e.g.: X.-H. Bu, S.-L. Chen, R.-H. Zhang, D.-Z. Liao, W.-M. Bu, M. Shionoya, F. Brisse, J. Ribas, Angew. Chem., Int. Ed. Engl. 40 (2001) 3201; (b) S. Ferlay, S. Koenig, M.W. Hosseini, J. Pansanel, A. De Cian,
114
[8]
[9] [10]
[11] [12] [13]
[14] [15]
[16]
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114 N. Kyritsakas, Chem. Commun. (2002) 218.; (c) S.K. Ma¨kinen, N.J. Melcer, M. Parvez, G.K.H. Shimizu, Chem. Eur. J. 7 (2001) 5176; (d) M.-C. Brandys, R.J. Puddephatt, Chem. Commun. (2001) 1508. (a) G. Smith, G.A. Cloutt, D.E. Lynch, K.A. Byriel, C.H.L. Kennard, Inorg. Chem. 37 (1998) 3236; (b) M. Mitsumi, J. Toyoda, K. Nakasuji, Inorg. Chem. 34 (1995) 3367; (c) L.P. Wu, M. Munakata, T. Kuroda-Sowa, M. Maekawa, Y. Suenaga, Inorg. Chim. Acta 249 (1996) 183; (d) A.D. Burrows, D.M.P. Mingos, A.J.P. White, D.J. Williams, Chem. Commun. (1996) 97. Y. Kim, F. Zeng, S.C. Zimmerman, Chem. Eur. J. 5 (1999) 2133. (a) R.B. Martin, Science 139 (1963) 1198; (b) K.H. Scheller, V. Scheller-Krattinger, R.B. Martin, J. Am. Chem. Soc. 103 (1981) 6833; (c) R. Lumry, E.L. Smitz, R.R. Glantz, J. Am. Chem. Soc. 73 (1951) 4335. KappaCCD package, Nonius, Delft, The Netherlands, 1997. Z. Otwinowsky, W. Minor, Methods Enzymol. 276 (1997) 307. (a) G.M. Sheldrick, SHELXTL-PLUS (VMS), Siemens Analytical Xray Instruments Inc., Madison, WI, 1990.; (b) G.M. Sheldrick, SHELXL-93, Program for Crystal Structure Refinement, University of Go¨ttingen, Go¨ttingen, Germany, 1993.; (c) G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany, 1997. L. Farrugia, J. Appl. Cryst. 30 (1997) 565. (a) K. Nilsson, A. Oskarsson, Acta Chem. Scand. A 38 (1984) 79; (b) H.P. Wu, C. Janiak, G. Rheinwald, H.J. Lang, Chem. Soc., Dalton Trans. (1999) 183. (a) O.J. Gelling, F. van Bolhuis, B.L. Feringer, Chem. Soc., Chem. Commun. (1991) 917.; (b) M.A. Withersby, A.J. Blake, N.R. Champness, P. Hubberstey, W.-S. Li, M. Schro¨der, Angew. Chem., Int. Ed. Engl. 36 (1997) 2327; (c) S.R. Batten, B.F. Hoskins, R. Robson, Angew. Chem., Int. Ed. Engl. 36 (1997) 636; (d) R.W. Saalfrank, M. Decker, F. Hampel, K. Peters, H.G. von Schnering, Chem. Ber. 130 (1997) 1309;
[17]
[18] [19] [20] [21] [22] [23]
(e) E. Psillakis, J.C. Jeffery, J.A. McCleverty, M.D. Ward, J. Chem. Soc., Dalton Trans. (1997) 1645.; (f) L. Carlucci, G. Ciani, D.M. Proserpio, A. Sironi, Inorg. Chem. 37 (1998) 5941; (g) C. Kaes, M.W. Hosseini, C.E.F. Rickard, B.W. Skelton, H. White, Angew. Chem., Int. Ed. Engl. 37 (1998) 920; (h) K. Biradha, C. Seward, M.J. Zaworotko, Angew. Chem., Int. Ed. Engl. 38 (1999) 492; (i) T. Ezuhara, K. Endo, Y. Aoyama, J. Am. Chem. Soc. 121 (1999) 3279; (j) K. Nomiya, S. Takahashi, R. Noguchi, J. Chem. Soc., Dalton Trans. (2000) 1343. (a) For infinite silver helices see, e.g.: A. Erxleben, Inorg. Chem. 40 (2001) 2928; (b) T. Suzuki, H. Kotsuki, K. Isobe, N. Moriya, Y. Nakagawa, M. Ochi, Inorg. Chem. 34 (1995) 530; (c) B. Wu, W.-J. Zhang, S.-Y. Yu, X.-T. Wu, J. Chem. Soc., Dalton Trans. (1997) 1795.; (d) M.-L. Tong, X.-M. Chen, B.-H. Ye, S.W. Ng, Inorg. Chem. 37 (1998) 5278; (e) P.K. Bowyer, K.A. Porter, A.D. Rae, A.C. Willis, S.B. Wild, Chem. Commun. (1998) 1153.; (f) S.-P. Yang, X.-M. Chen, L.-N. Ji, J. Chem. Soc., Dalton Trans. (2000) 2337.; (g) K. Nomiya, S. Takahashi, R. Noguchi, S. Nemoto, T. Takayama, M. Oda, Inorg. Chem. 39 (2000) 3301; (h) E. Psillakis, J.C. Jeffery, J.A. McCleverty, M.D. Ward, J. Chem. Soc., Dalton Trans. (1997) 1645. C. Piguet, G. Bernardinelli, G. Hopfgartner, Chem. Rev. 97 (1997) 2005 (and references therein). M.-L. Tong, X.-M. Chen, B.-H. Ye, Inorg. Chem. 37 (1998) 5278. C. Janiak, L. Uehlin, H.-P. Wu, P. Klu¨fers, H. Piotrowski, T.G. Scharmann, J. Chem. Soc., Dalton Trans. (1999) 3121. A.-L. Spek, PLATON, A Multipurpose Crystallographic Tool, Utrecht University, Utrecht, 1999. T.C.W. Mak, W.-H. Yip, C.H.L. Kennard, G. Smith, E.J. O’Reilly, Aust. J. Chem. A39 (1986) 541. G. Smith, A.N. Reddy, K.A. Byriel, C.H.L. Kennard, Polyhedron 13 (1994) 2425.
Coordination polymers derived from silver salts and an aliphatic N,O ligand Andrea Erxleben * Fachbereich Chemie, Universita¨t Dortmund, 44221 Dortmund, Germany Received 6 August 2002; accepted 6 November 2002
Abstract Cocrystallization of silver salts with the polyfunctional, conformationally flexible ligand N -(2-cyanoethyl)-b-alanine (cea) yielded three different coordination polymers, namely a rare example of a compound containing helical chains assembled into an infinite 2D array, [Ag4(cea )2(NO3)]BF4 (1), a 3D channel structure, [Ag4(cea)2(H2O)(CF3SO3)4] (2), and an unprecedented structure comprising 1D polymeric anions sandwiched between the loops of a cationic pleated sheet, [Ag3(cea)2(NO3)][Ag2(NO3)3]NO3 (3). In 2 and 3 the central amino nitrogen of cea is protonated and non-coordinating so that the ligand has two metal binding sites separated by a five-membered aliphatic linker and a central hydrogen bond donating site. In the case of 2 this gives rise to 44membered macrometallacyclic subunits that generate large rhombic channels hosting the counterions. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Silver; Coordination polymers; Crystal structures
1. Introduction A large number of coordination polymers with various topologies like infinite chains, ladders, helices, sheets, honeycomb structures or 3D networks have been reported to date [1 /5]. Reasons for the ongoing interest in this field are potential applications of coordination polymers as functional materials as well as the continuing discovery of ever new topological types of networks. As for the latter, Ag(I) ions that easily adopt various coordination geometries are particularly suited to explore the network-forming abilities of polydentate ligands and to generate novel coordination polymers. We are interested in the use of polyfunctional, conformationally flexible ligands with hydrogen bond donating functionality [6]. In principle, bidentate ligands with the donor sites being separated by long, organic linkers are capable of generating polymers with channels or pores that are particularly attractive with regard to possible applications in host-guest chemistry [5a,f,7].
* Fax: /49-231-755-3797. E-mail address: [email protected] Erxleben).
(A.
However, since nature tends to avoid vacuum, large void volumes are often prevented by interpenetration of identical nets [1 /4]. The influence of hydrogen bonding on network architectures is well recognized and several examples have shown that the introduction of functional groups capable of hydrogen bonding interactions can be exploited in the synthesis of coordination polymers [8]. In the present study we report three Ag coordination polymers derived from N -(2-cyanoethyl)-b-alanine (cea). Under neutral conditions silver ions bind to the carboxylate group, the nitrile nitrogen and the amine nitrogen to give a rare example of a 2D polymeric structure of infinite helices. Under more acidic conditions silver cannot compete with the ammonium protons and the zwitterionic cea molecule represents a ligand with a central hydrogen bond donor functionality and two metal binding sites separated by a five-membered aliphatic chain. It is shown that cocrystallization of cea with AgCF3SO3 at pH 4 leads to the formation of a 3D channel structure built up by large macrometallacycles and stabilized by the triflate ions that form coordination bonds with silver and acceptor hydrogen bonds with the ammonium nitrogen, while AgNO3 affords an unprecedented structure consisting of 2D polymeric cations and 1D polymeric anions.
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0020-1693(02)01484-6
108
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114
2. Experimental 2.1. Starting materials Cea was prepared according to Ref. [9]. All chemicals and solvents were reagent grade and used without further purification. 2.2. Preparations [Ag4(cea )2(NO3)]BF4 (1) was obtained by treating cea (1.00 mmol) with AgBF4 (1.00 mmol) and AgNO3 (1.00 mmol) in ethanol/water (2:1, 12 ml) at pH 6. Colorless plates crystallized at 4 8C in 43% yield. Anal . Calc. for C12H18Ag4BF4N5O7: C, 16.7; H, 2.1; N, 8.1. Found: C, 16.3; H, 2.2; N, 8.1%. Selected IR data (KBr, n (cm1)): 3404 s vbr, 2251 w (C /N), 1573 s (C/O), 1468 m, 1384 s (NO3), 1318 m, 1084 s (BF4), 1035 s, 821 w (NO3), 533 w, 522 w. Colorless needles of [Ag4(cea)2(H2O)(CF3SO3)4] (2) suitable for X-ray analysis resulted from crystallization of cea (1.00 mmol) with AgCF3SO3 (2.00 mmol) from ethanol/water (2:1, 12 ml, pH 4) at 4 8C. Yield: 34%. Anal . Calc. for C16H22Ag4F12N4O17S4: C, 14.5; H, 1.7; N, 4.2. Found: C, 14.3; H, 1.8; N, 4.4%. Selected IR data (KBr, n(cm 1)): 3494 m br, 2269 w (C/N), 1597 s (C /O), 1544 m, 1260 s, 1171 s, 1035 s, 826 m, 765 w, 641 m, 579 w, 520 m, 229 w. X-ray suitable crystals of [Ag3(cea)2(NO3)][Ag2(NO3)3]NO3 (3) were obtained in 36% yield by mixing AgNO3 (2.00 mmol) and cea (1.00 mmol) in ethanol/ water (2:1, 12 ml, pH 4) followed by slow evaporation of the solution at 4 8C. Anal . Calc for C12H20Ag5N9O19: C, 12.7; H, 1.8; N, 11.1. Found: C, 13.2; H, 1.7; N, 11.2%. Selected IR data (KBr, n(cm 1)): 3038 m, 2780 m, 2651 m, 2271 w (C /N), 1655 m, 1567 s, 1383 vs (NO3), 1104 m, 1056 m, 1014 m, 825 m, 816 m, 790 m, 700 m, 615 m, 589 m, 428 m. 2.3. Instrumentation and methods 1
H NMR spectra were recorded on a Varian mercury spectrometer at 200.13 MHz. using sodium 3-trimethylsilyl-propanesulfonate as internal reference. The pKa value for cea was obtained by pH-dependent 1H NMR spectroscopy from graphs of chemical shifts versus uncorrected pH (pH*) values [10]. Infrared spectra were taken on a Bruker IFS 28 FT-spectrometer. 2.4. Crystallography Crystal data for compounds 1/3 were collected at room temperature (1, 2) and 153 K (3) on an Enraf / Nonius-kCCD diffractometer [11] using graphite-mono˚ ). For data chromated Mo Ka radiation (l/0.71069 A reduction and cell refinement the programs DENZO and
SCALEPACK were used [12]. The structures were solved by conventional Patterson methods and subsequent Fourier syntheses and refined by full-matrix leastsquares on F2 using the SHELXTL PLUS, SHELXL-93 and SHELXL-97 programs [13]. Graphics were produced with SHELXTL PLUS and ORTEP-3 [14]. Hydrogen atoms were generated geometrically and given fixed isotropic thermal parameters (1, 2) or isotropic thermal parameters equivalent to 1.2 times those of the atom to which they were attached (3). In compound 1, one nitrate oxygen (O(12)) is located on a twofold axis while the nitrate nitrogen and the other two oxygens (O(10) and O(11)) have site occupancy factors of 0.5 and are disordered over the two positions generated by the symmetry operator. Crystallographic data and details of refinement are reported in Table 1.
3. Results and discussion 3.1. Silver complex formation with anionic cea In neutral or slightly acidic (pH 6) solution cea whose pKa value for the deprotonation of the ammonium nitrogen was determined by pH-dependent 1H NMR spectroscopy to be 7.9 behaves as a tridentate ligand for silver ions. The cocrystallization of cea with AgBF4 in the presence of NO3 from ethanol/water afforded Xray suitable crystals of composition [Ag4(cea)2(NO3)]BF4 (1). 3.1.1. Crystal structure of {[Ag4(cea )2(NO3)]BF4}n (1) Single-crystal X-ray analysis of 1 revealed infinite, single-stranded helices that assembled into a 2D network. As illustrated in Fig. 1(a) the polymer is built up by bicyclic subunits having C2 symmetry. Within the subunits three silver ions and two negatively charged cea ligands constitute two fused 14-membered rings. Each ligand binds the three Ag ions through the nitrile nitrogen and the carboxylate group with the latter one coordinating in a m2-bridging fashion. The Ag /O bond lengths are normal, while the Ag /N bond distance of ˚ is at the low end of the usual range (2.18/ 2.172(9) A ˚ 2.33 A) [15a]. The Ag /N /C bond angle is close to linear (174.1(9)8) as expected. The valence angles of the N ,O and O ,O coordinated silver ions are 161.2(3) and 178.3(3)8. The nitrate ion that is statistically distributed on two close positions is weakly bound to Ag(3) thus extending the linear coordination environment of the metal ion to a distorted T-shaped O2N coordination sphere. The {Ag3(cea )2(NO3)} entities are connected through a fourth silver ion that binds to one amine nitrogen of each moiety. This results in an infinite 21helix of trinuclear subunits linked together by linear N / Ag /N-bridges. The pitch height of the helix that extends
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114
109
Table 1 Crystallographic data for 1 /3
Formula Mr Crystal color and habit Crystal size (mm3) Crystal system Space group Unit cell dimensions ˚) a (A ˚) b (A ˚) c (A a (8) b (8) g (8) ˚ 3) V (A Z Dcalc (g cm 3) m (Mo Ka) (mm 1) F (000) 2u Range (8) No. of measured reflections No. of independent reflections (Rint) No. of observed reflections No. of parameters Final R1, wR2 (observed reflections) a Final R1, wR2 (all reflections) a Goodness-of-fit (observed reflections) Goodness-of-fit (all reflections)
1
2
3
C6H9Ag2B0.5F2N2.5O3.5 431.30 colorless needle 0.20/0.15/0.06 orthorhombic Pcca
C16H22Ag4F12N4O17S4 1330.10 colorless block 0.40 /0.24 /0.12 triclinic P 1¯
C6H10Ag2.5N4.5O9.5 566.86 colorless needle 0.50/0.10/0.06 monoclinic P 21/m
8.726(1) 14.883(1) 16.566(1)
5.748(1) 17.794(1) 18.339(1) 95.83(1) 98.89(1) 95.49(1) 1831.7(3) 2 2.412 2.469 1284 6.8 /53.4 36184 7774 (7.3%) 3241 489 R1 /5.7%, wR2 /14.8% R1 /14.2%, wR2 /19.4% 1.282 0.859
5.557(1) 11.652(1) 21.260(1)
2151.4(3) 8 2.663 2.288 1640 6.8 /53.4 13842 2286 (4.9%) 1346 (I /2s (I )) 160 R1 /5.4%, wR2 /16.4% R1 /9.1%, wR2 /18.2% 1.238 0.986
96.03(1) 1369.0(3) 4 2.750 3.615 1084 5.2 /54.2 17022 3149 (7.6%) 1808 218 R1 /4.6%, wR2 /9.8% R1 /9.5%, wR2 /16.9% 1.216 0.977
a R1 /SjjFoj/jFcjj/SjFoj; wR2 /[S w (Fo2/Fc2)2/S w (Fo2)2]1/2; w 1 /s2(Fo2)/(aP )2; P/(Fo2/2Fc2)/3; a /0.1107 for 1, 0.0866 for 2 and 0.0457 for 3.
˚ . The in the crystallographic a direction is 8.726(1) A carboxylate group that bridges two silver ions of the bicyclic units forms a weak bond to a third silver ion belonging to an adjacent helix (Ag(2) O(2) 2.700(7) ˚ ). This connects helices of opposite helicity into a 2D A network as shown in Fig. 1(bc). In the crystal packing layers of helical chains linked through weak silver/ carboxylate interactions are stacked parallel to the ac plane. The BF4 ions are located between the layers, while the disordered NO3 anions lie inside the helices ˚ (Table that have inner diameters of approximately 8.5 A 2). The formation of infinite metallohelices receives much current attention due to potential applications in materials science and the fundamental role of helicity in biology [2,16]. There are an increasing number of examples where */ like in 1 */ a 1D coordination polymer spontaneously assumes a helical conformation [17], although these are less numerous than discrete oligonuclear helicates [18]. However, examples, where single-stranded silver helices are assembled by (weak) coordination bonds into a polydimensional network are rather rare [5h,15b,16b,19,20].
3.2. Silver complexes with neutral (zwitterionic) cea Protonation of the amino nitrogen under acidic conditions converts cea into a bifunctional ligand that combines coordination bond forming and hydrogen bond forming capabilities. Depending on the counterion two different coordination polymers, [Ag4(cea)2(H2O)(CF3SO3)4] (2) and [Ag3(cea)2(NO3)][Ag2(NO3)3]NO3 (3), were obtained at pH 4. Single crystals of 2 and 3 suitable for X-ray crystallography were grown from aqueous ethanol solutions at 4 8C. Views of the structures of 2 and 3 are displayed in Figs. 2 and 3, relevant bond lengths, angles and hydrogen-bonding interactions are summarized in Tables 3 and 4. 3.2.1. Crystal structure of [Ag4(cea)2(H2O)(CF3SO3)4]n (2) The asymmetric unit of 2 consists of four nonequivalent silver ions, two neutral cea ligands in their zwitterionic forms, one coordinated water molecule and four triflate anions. The basic structural motif is a 44membered macrocycle containing four ligand molecules and eight silver ions (Fig. 2(a)). Within the ring the silver ions are connected alternately through a monatomic
110
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114 Table 2 ˚ ) and bond angles (8) in 1 Bond lengths (A Bond lengths Ag(1) /N(1) Ag(3) /N(2) Ag(3) O(11)
2.209(6) 2.172(9) 2.58(2)
Ag(2) /O(1) Ag(3) /O(2) b
2.210(6) 2.176(6)
Bond angles N(1) /Ag(1) /N(1) a N(2) /Ag(3) /O(2) b
176.6(3) 161.2(3)
O(1) /Ag(2) /O(1) b N(2) /Ag(3) O(11)
178.3(3) 111.3(5)
a b
/x , y , 0.5/z . 0.5/x , 1/y , z .
carboxylate bridge and cea binding via the cyano nitrogen and the carboxylate group. All silver ions have distinct coordination spheres: Ag(1) adopts a distorted trigonal bipyramidal coordination geometry with an NO4 (2 /carboxylate, 2 /triflate) donor set, Ag(3) is distorted tetrahedrally coordinated by a cyano nitrogen, a triflate and a carboxylate oxygen as well as a water ligand, while Ag(2) and Ag(4) have Y-shaped O3 coordination environments (Ag(2): 2/carboxylate, 1/ triflate and Ag(4): 3 /carboxylate). The Ag /N/C bond angles are 151.8(8) and 162.6(8)8 and are more acute than they are usually in silver nitrile compounds (166 / 1768) [15a]. The formation of the large macrometallacycles is supported by the triflate anions that are hosted in the macrocycles thus filling the void volume and preventing an interpenetrated structure. The incorporation of the counterions is stabilized by direct coordina˚ ) and tion of triflate oxygen to silver ions (2.419/2.583 A hydrogen bonding interactions with the ammonium nitrogen of the ligands (Table 3). The carboxylate group of each ligand coordinates four silver ions so that overall a cationic 3D polymeric network is generated. The 3D structure is constituted of parallel layers of fused macrocycles that stack along the crystallographic a axis and that are interconnected through Ag /carboxylate bonds. This gives rise to a rhombic channel architecture as shown in Fig. 2(b) and (c). The channels that are filled by the anions make up 46% of the cell volume [21]. The effective cavity size as measured by the shortest distance between the van der Waals surfaces of ˚. opposing sides is approximately 8.6 /8.9 A
Fig. 1. (a) Bicyclic [Ag3(cea )2(NO3)] subunits in 1. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms are omitted for clarity. (b) Linkage of the [Ag3(cea )2(NO3)] entities through Ag into an infinite 21-helical chain. (c) Assembly of 21-helical chains into an infinite 2D polymeric structure. Ag: cross-hatched circles; N, O: hatched circles; and C: empty circles.
3.2.2. Crystal structure of {[Ag3(cea)2(NO3)][Ag2(NO3)3]NO3}n (3) Single-crystal X-ray analysis of 3 showed an assembly of 2D polymeric cations of composition [Ag3(cea)2(NO3)]n2n, 1D polymeric anions of composition [Ag2(NO3)3]nn and nitrate ions. A section of the anionic polymer is depicted in Fig. 3(a). Silver ions and nitrate anions form an infinite, straight chain of fused unsymmetric rings each of which contains three metal ions and three nitrates. Different coordination modes */ m3-bridging, m2-bridging and chelating */ are adopted by the nitrates. The silver ions have a distorted trigonal-
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114
Fig. 2. (a) Macrocyclic ring in 2 formed by Ag and cea with H bonding interactions between N(1) /H and CF3SO3 indicated. Thermal ellipsoids are drawn at 30% probability level. Hydrogen atoms except for those of the ammonium nitrogens are omitted for clarity. (b,c) 3D network structure with rhombic channels running along the a -axis. Counterions and hydrogen atoms are omitted for clarity.
111
planar O3- (Ag(3)) and four-coordinate O4- (Ag(4)) coordination sphere. The polymeric cation contains 24-membered metallamacrocycles. Each macrocycle consists of three silver ions, two cea molecules in their zwitterionic forms and one nitrate anion (Fig. 3(b)). Within the rings one silver binds to one carboxylate oxygen of each ligand. The other two silver ions (Ag(1) and Ag(1a)) coordinate to the two nitrile nitrogens. These silver ions are connected through a nitrate ligand that binds in a monodentate manner to one silver and in a chelating mode to the ˚ ) and C /N (1.142(9) other one. The Ag /N (2.230(7) A ˚ A) bond lengths fall in the normal range (2.18/2.33 and ˚ ) [15a], while the Ag /N/C bond angles of 1.07 /1.15 A 149.8(7)8 are relatively acute as already observed for compound 2. The carboxylate groups serve as m3bridging ligands and link the macrocycles into an 1D array as shown in Fig. 3(c). The carboxylate /silver coordination shows the usual geometric features: The Ag /O bond lengths (Table 4) compare well with those observed in related Ag /carboxylate compounds, where Ag /O(axial) and Ag /O(equatorial) bond distances ˚ , respectively typically range from 2.2 /2.3 and 2.4 /2.5 A ˚ [22]. The carboxylate-bridged silver ions are 2.774(1) A ˚ (Ag(2) Ag(2a) at /1/x , 1/y, 1/z ) and 3.637(9) A (Ag(2) Ag(2b) at /1/x , y, z ) apart with the Ag(2) Ag(2a) separation being at the low end of the range observed in anti /anti {Ag2(m2-RCOO)2} units ˚ ) [23]. The chain of carboxylate-bridged (2.78/3.00 A silver ions and fused macrocycles extends along the crystallographic a direction. In the overall structure of the cation these chains are arranged in parallel along the b direction. The nitrile bound Ag(1) ions and nitrate ligands are shared by macrocycles of neighboring layers so that a 2D polymer is generated. Consequently, the Ag(1) ions have five-coordinate N2O3 environments in contrast to the Y-shaped O3 geometries of the Ag(2) ions. As evident from Fig. 3(c) the cationic polymer assumes a highly undulate sheet conformation. The view of the structure depicted in Fig. 3(d) suggests that the folding of the sheet is brought about by the nitrate ions each of which forms two acceptor hydrogen bonds with the ammonium nitrogens of opposite sides at the tops of the troughs. The anionic [Ag2(NO3)3]nn chains are ˚ depth. This encapsulated by the troughs of 5.557 A packing of anionic and cationic entities that is to the best of our knowledge unprecedented is stabilized by hydrogen bond interactions between nitrate oxygens of the polymeric anion and the ammonium nitrogens of cea ˚) (Table 4) as well as by short contacts (2.778(5) A between carboxylate groups of the cationic sheet and silver ions of the anionic chain. Unfortunately, attempts to prepare Ag complexes of cea with other anions (ClO4, PF6) at pH 4 and 6 gave only glassy, non-crystalline materials whose structures could not be elucidated. Likewise, attempts to crystallize
112
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114
Fig. 3. (a) 1D polymeric structure of the anion of 3, [Ag2(NO3)3]nn . Thermal ellipsoids are drawn at 50% probability level. (b) Macrocyclic subunits of the polymeric cation of 3. Hydrogen atoms are omitted for clarity. (c) Section of the polymeric structure of the cation of 3, [Ag3(cea)2(NO3)]n2n , showing the chain of fused macrocycles. Ag: cross-hatched circles; N, O: hatched circles; and C: empty circles. (d) ORTEP drawing of the packing of 2D cationic sheets and 1D anionic chains. Ag: light gray; C, N, O: dark gray.
cea with AgBF4 in the absence of NO3 were unsuccessful. 3.3. Spectroscopic characterisation of 1 /3 1
H NMR spectra in D2O indicate complete dissociation of the silver complexes into Ag and the ‘free’ ligand in solution. In the infrared spectrum of 2 and 3 the n(C /N) stretching vibration is shifted by about 20 cm 1 to higher wavenumbers compared with the ‘free’ ligand as expected upon metal coordination to the cyano nitrogen (n (C/N) /2269 (2), 2271 (3) and 2252 cm 1 (‘free’ ligand)). By contrast, the n(C /N) stretching vibration frequency in 1 is essentially unchanged (n(C /N) /2251 cm 1). This may indicate p-backbonding, since s-donation shifts n (C /N) bands to
higher wavenumbers, while p-back-bonding has the reverse effect. Reinforcement of the s-bond by p-backbonding in the case of 1 is in accordance with the Ag / ˚ ) being at the low end N(nitrile) bond length (2.172(9) A of the range typically found for silver nitrile complexes ˚ ) [15]. (2.18/2.33 A
4. Conclusions In conclusion we have structurally characterised three different Ag coordination polymers with the conformationally flexible ligand cea. When the central nitrogen is protonated and non-bonding, cea connects silver ions into macrometallacycles. Depending on the counterion, these are 24-membered or larger 44-membered rings. In
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114 Table 3 ˚ ), bond angles (8) and hydrogen-bonding interactions Bond lengths (A ˚ ) in 2 (A Bond lengths Ag(1) /N(2?) a Ag(1) /O(1) Ag(1) /O(2) b Ag(1) O(10) c Ag(1) /O(30) Ag(2) /O(1) Ag(2) /O(2) d Ag(2) /O(10)
2.415(9) 2.450(5) 2.381(5) 2.571(5) 2.478(6) 2.291(5) 2.341(5) 2.419(5)
Hydrogen-bonding interactions N(1) O(1) 2.835(8) N(1) O(22) e 2.869(8) N(1?) O(40) 3.08(1) O(1w) O(20) e 3.15(1) O(1w) O(21) f 2.80(1) Bond angles N(2?) a /Ag(1) /O(1) O(1) /Ag(1) /O(2) b O(1) /Ag(2) /O(2) d N(2) /Ag(3) /O(1?) O(2?) e /Ag(4) /O(2?) b a b c d e f g h
90.9(2) 104.1(2) 130.0(2) 141.9(3) 77.1(2)
Ag(3) /N(2) Ag(3) /O(1?) Ag(3) /O(1w) Ag(3) O(40) Ag(4) /O(1?) Ag(4) /O(2’) e Ag(4) /O(2’) b
2.134(8) 2.386(6) 2.392(9) 2.583(9) 2.308(6) 2.268(6) 2.475(6)
N(1) O(12) N(1?) O(31) g N(1?) O(42) h O(1w) O(2’) b
2.938(8) 2.933(9) 2.84(1) 2.94(1)
N(2?) a /Ag(1) /O(2) b O(2) b /Ag(1) /O(30) O(1) /Ag(2) /O(10) N(2) /Ag(3) /O(1w) O(1?) /Ag(4) /O(2?) b
161.4(2) 87.1(2) 106.8(2) 117.3(3) 110.7(2)
1/x , 1/y , z . /1/x , y , z . /x , 1/y , 1/z . 1/x , 1/y , 1/z . /1/x , /y , /z . /2/x , /y , /z . x , /1/y , z . 1/x , y , z .
Bond lengths Ag(1) /N(2) Ag(1) /O(50) Ag(1) O(51) a Ag(2) /O(1) Ag(2) /O(2) a Ag(2) /O(2) b
2.230(7) 2.486(8) 2.597(7) 2.189(4) 2.433(4) 2.249(4)
Ag(3) O(12) Ag(3) /O(21) Ag(3) O(22) c Ag(4) /O(11) Ag(4) /O(10) c Ag(4) O(41)
2.550(6) 2.434(8) 2.560(8) 2.398(6) 2.461(6) 2.578(5)
Bond angles N(2) /Ag(1) /N(2) d N(2) /Ag(1) /O(50) d N(2) /Ag(1) /O(51) a O(21) /Ag(3) /O(22) c O(12) /Ag(3) /O(22) c O(11) /Ag(4) /O(41) d
112.6(4) 146.1(3) 88.2(2) 130.9(2) 125.1(2) 108.4(2)
N(2) /Ag(1) /O(50) O(50) /Ag(1) /O(50) d O(1) /Ag(2) /O(2) a O(12) /Ag(3) /O(21) O(11) /Ag(4) /O(10) c O(41) /Ag(4) /O(10) c
98.9(3) 47.9(4) 119.4(2) 104.1(2) 131.6(2) 115.2(2)
N(1) O(31) b N(1) O(41)
2.996(6) 2.928(6)
Hydrogen-bonding interactions N(1) O(30) e 2.809(5) N(1) O(40) 3.164(5) b c d e
the latter case incorporation of the anions by coordination to Ag and hydrogen bonding interaction with the ammonium nitrogens prevents interpenetration and favors the formation of a channel structure.
5. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. 189694 (1), 189695 (2) and 189696 (3). Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: /44-1223-336033; e-mail: [email protected] or www: http:// www.ccdc.cam.ac.uk).
Acknowledgements This work was supported by the Fonds der Chemischen Industrie (FCI) and a fellowship granted by the Deutsche Forschungsgemeinschaft. We thank Prof. Bernhard Lippert for the continuous support of our work.
References
Table 4 ˚ ), bond angles (8) and hydrogen-bonding interactions Bond lengths (A ˚ ) in 3 (A
a
113
/1/x , y , z . /1/x , 1/y , 1/z . 1/x , y , z . x , 1/1/2/y , z . /1/x , 1/2/y , 1/z .
[1] S.R. Batten, R. Robson, Angew. Chem., Int. Ed. Engl. 37 (1998) 1460 (and references therein). [2] M. Munakata, L.P. Wu, T. Kuroda-Sowa, Adv. Inorg. Chem. 46 (1999) 173 (and references therein). [3] R. Robson, J. Chem. Soc., Dalton Trans. (2000) 3735 and references therein. [4] M.J. Zaworotko, Chem. Commun. (2001) 1 and references therein. [5] (a) For Ag coordination polymers with aliphatic nitriles or amines see, e.g.: M.-L. Tong, X.-M. Chen, B.-H. Ye, L.N. Ji, Angew. Chem., Int. Ed. Engl. 38 (1999) 2237; (b) C.-X. Ren, H.-L. Zhu, G. Yang, X.-M. Chen, J. Chem. Soc., Dalton Trans. (2001) 85.; (c) K.A. Hirsch, S.R. Wilson, J.S. Moore, Inorg. Chem. 36 (1997) 2960; (d) N.J. Melcer, G.D. Enright, J.A. Ripmeester, G.K.H. Shimizu, Inorg. Chem. 40 (2001) 4641; (e) H.J. Choi, M.P. Suh, J. Am. Chem. Soc. 120 (1998) 10622; (f) K.S. Min, M.P. Suh, J. Am. Chem. Soc. 122 (2000) 6834; (g) K.A. Hirsch, S.R. Wilson, J.S. Moore, Chem. Commun. (1998) 13.; (h) Y. Kang, S.S. Lee, K.-M. Park, S.O. Kang, J. Ko, Inorg. Chem. 40 (2001) 7027; (i) L. Carlucci, G. Ciani, P. Macchi, D.M. Proserpio, S. Rizzato, Chem. Eur. J. 5 (1999) 237; (j) M.-L. Tong, S.-L. Zheng, X.-M. Chen, Chem. Eur. J. 6 (2000) 3729. [6] A. Erxleben, Cryst. Eng. Commun. 4 (2002) 472. [7] (a) For silver complexes see, e.g.: X.-H. Bu, S.-L. Chen, R.-H. Zhang, D.-Z. Liao, W.-M. Bu, M. Shionoya, F. Brisse, J. Ribas, Angew. Chem., Int. Ed. Engl. 40 (2001) 3201; (b) S. Ferlay, S. Koenig, M.W. Hosseini, J. Pansanel, A. De Cian,
114
[8]
[9] [10]
[11] [12] [13]
[14] [15]
[16]
A. Erxleben / Inorganica Chimica Acta 348 (2003) 107 /114 N. Kyritsakas, Chem. Commun. (2002) 218.; (c) S.K. Ma¨kinen, N.J. Melcer, M. Parvez, G.K.H. Shimizu, Chem. Eur. J. 7 (2001) 5176; (d) M.-C. Brandys, R.J. Puddephatt, Chem. Commun. (2001) 1508. (a) G. Smith, G.A. Cloutt, D.E. Lynch, K.A. Byriel, C.H.L. Kennard, Inorg. Chem. 37 (1998) 3236; (b) M. Mitsumi, J. Toyoda, K. Nakasuji, Inorg. Chem. 34 (1995) 3367; (c) L.P. Wu, M. Munakata, T. Kuroda-Sowa, M. Maekawa, Y. Suenaga, Inorg. Chim. Acta 249 (1996) 183; (d) A.D. Burrows, D.M.P. Mingos, A.J.P. White, D.J. Williams, Chem. Commun. (1996) 97. Y. Kim, F. Zeng, S.C. Zimmerman, Chem. Eur. J. 5 (1999) 2133. (a) R.B. Martin, Science 139 (1963) 1198; (b) K.H. Scheller, V. Scheller-Krattinger, R.B. Martin, J. Am. Chem. Soc. 103 (1981) 6833; (c) R. Lumry, E.L. Smitz, R.R. Glantz, J. Am. Chem. Soc. 73 (1951) 4335. KappaCCD package, Nonius, Delft, The Netherlands, 1997. Z. Otwinowsky, W. Minor, Methods Enzymol. 276 (1997) 307. (a) G.M. Sheldrick, SHELXTL-PLUS (VMS), Siemens Analytical Xray Instruments Inc., Madison, WI, 1990.; (b) G.M. Sheldrick, SHELXL-93, Program for Crystal Structure Refinement, University of Go¨ttingen, Go¨ttingen, Germany, 1993.; (c) G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany, 1997. L. Farrugia, J. Appl. Cryst. 30 (1997) 565. (a) K. Nilsson, A. Oskarsson, Acta Chem. Scand. A 38 (1984) 79; (b) H.P. Wu, C. Janiak, G. Rheinwald, H.J. Lang, Chem. Soc., Dalton Trans. (1999) 183. (a) O.J. Gelling, F. van Bolhuis, B.L. Feringer, Chem. Soc., Chem. Commun. (1991) 917.; (b) M.A. Withersby, A.J. Blake, N.R. Champness, P. Hubberstey, W.-S. Li, M. Schro¨der, Angew. Chem., Int. Ed. Engl. 36 (1997) 2327; (c) S.R. Batten, B.F. Hoskins, R. Robson, Angew. Chem., Int. Ed. Engl. 36 (1997) 636; (d) R.W. Saalfrank, M. Decker, F. Hampel, K. Peters, H.G. von Schnering, Chem. Ber. 130 (1997) 1309;
[17]
[18] [19] [20] [21] [22] [23]
(e) E. Psillakis, J.C. Jeffery, J.A. McCleverty, M.D. Ward, J. Chem. Soc., Dalton Trans. (1997) 1645.; (f) L. Carlucci, G. Ciani, D.M. Proserpio, A. Sironi, Inorg. Chem. 37 (1998) 5941; (g) C. Kaes, M.W. Hosseini, C.E.F. Rickard, B.W. Skelton, H. White, Angew. Chem., Int. Ed. Engl. 37 (1998) 920; (h) K. Biradha, C. Seward, M.J. Zaworotko, Angew. Chem., Int. Ed. Engl. 38 (1999) 492; (i) T. Ezuhara, K. Endo, Y. Aoyama, J. Am. Chem. Soc. 121 (1999) 3279; (j) K. Nomiya, S. Takahashi, R. Noguchi, J. Chem. Soc., Dalton Trans. (2000) 1343. (a) For infinite silver helices see, e.g.: A. Erxleben, Inorg. Chem. 40 (2001) 2928; (b) T. Suzuki, H. Kotsuki, K. Isobe, N. Moriya, Y. Nakagawa, M. Ochi, Inorg. Chem. 34 (1995) 530; (c) B. Wu, W.-J. Zhang, S.-Y. Yu, X.-T. Wu, J. Chem. Soc., Dalton Trans. (1997) 1795.; (d) M.-L. Tong, X.-M. Chen, B.-H. Ye, S.W. Ng, Inorg. Chem. 37 (1998) 5278; (e) P.K. Bowyer, K.A. Porter, A.D. Rae, A.C. Willis, S.B. Wild, Chem. Commun. (1998) 1153.; (f) S.-P. Yang, X.-M. Chen, L.-N. Ji, J. Chem. Soc., Dalton Trans. (2000) 2337.; (g) K. Nomiya, S. Takahashi, R. Noguchi, S. Nemoto, T. Takayama, M. Oda, Inorg. Chem. 39 (2000) 3301; (h) E. Psillakis, J.C. Jeffery, J.A. McCleverty, M.D. Ward, J. Chem. Soc., Dalton Trans. (1997) 1645. C. Piguet, G. Bernardinelli, G. Hopfgartner, Chem. Rev. 97 (1997) 2005 (and references therein). M.-L. Tong, X.-M. Chen, B.-H. Ye, Inorg. Chem. 37 (1998) 5278. C. Janiak, L. Uehlin, H.-P. Wu, P. Klu¨fers, H. Piotrowski, T.G. Scharmann, J. Chem. Soc., Dalton Trans. (1999) 3121. A.-L. Spek, PLATON, A Multipurpose Crystallographic Tool, Utrecht University, Utrecht, 1999. T.C.W. Mak, W.-H. Yip, C.H.L. Kennard, G. Smith, E.J. O’Reilly, Aust. J. Chem. A39 (1986) 541. G. Smith, A.N. Reddy, K.A. Byriel, C.H.L. Kennard, Polyhedron 13 (1994) 2425.