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Syntheses, structures and photoluminescent properties of silver(I) complexes with in situ generated hexahydropyrimidine derivatives
Inorganica Chimica Acta 357 (2004) 443–450 www.elsevier.com/locate/ica
Syntheses, structures and photoluminescent properties of silver(I) complexes with in situ generated hexahydropyrimidine derivatives Chun-Xia Ren, Bao-Hui Ye *, Hai-Liang Zhu, Jian-Xin Shi, Xiao-Ming Chen
*
School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, PR China Received 21 March 2003; accepted 10 June 2003
Abstract Two new linear and V-shaped tetradentate ligands, namely 1,4-bis(2-hexahydropyrimidyl)benzene (L) and 1,3-bis(2-hexahydropyrimidyl)benzene (L0 ), and their silver(I) complexes, [Ag2 L(l-ONO2 )](NO3 ) 2H2 O (1), [Ag2 L(l-pn)](NO3 )2 (2), [Ag2 L(lpn)](ClO4 )2 (3) and [Ag4 L0 2 (H2 O)](NO3 )4 5H2 O (4) (pn ¼ 1,3-diaminopropane) have been synthesized in situ and structurally characterized by single-crystal X-ray diffraction. 1 and 2 were obtained from the same reaction solution but different crystallization conditions. 1 is an one-dimensional chain featuring cuboid tetranuclear silver(I) units interconnected through monoatomic nitrate bridges. Both 2 and 3 are ribbon-like helical compounds in which each L ligand acts in a tetradentate bridging mode to interconnect four metal atoms, and each pn ligand functions in a bidentate bridging mode to link a pair of metal atoms. 4 shows a truncated assisted by square-pyramidal tetranuclear motif arose by the V-shaped L0 ligand. Close Ag Ag separations (2.901–2.939 A) bis(hexahydropyrimidine) bridges were observed in 1 and 4, indicating metal–metal interactions. Photoluminescence of 1–4 has also been observed in the solid state and solution at room temperature and low temperature, respectively. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Coordination polymers; Silver; Hexahydropyrimidine; N ligands
1. Introduction Although repulsion was expected between silver(I)– silver(I) metal centers, a number of species with shorter Ag Ag separations have been structurally characterized. The principal interest has been the possibility of a metal–metal bonding interaction between the silver metal involving s- or p-orbitals [1]. The powerfully positive evidences would come from silver(I) complexes with shorter Ag Ag separations comparable to that in metallic silver [2]. Importantly, Che et al. [3] have recently (2.889 A) employed resonance Raman spectra to verify this weak Ag Ag interaction. Many examples with short Ag Ag distances are associated with the presence of bridging or capping ligands that can dictate the metal ions in a short * Corresponding authors. Tel.: +86-20-84113986; fax: +86-2084112245. E-mail addresses: [email protected] (B.-H. Ye), [email protected]. cn (X.-M. Chen).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2003.06.003
metal–metal separation (Scheme 1). One of these ligands is bis(phosphino)methane (Scheme 1 (I)) which is widely used to assemble dimeric and trimeric species [4]. Silver(I) carboxylate complexes have also been extensively investigated over the last 20 years. The coordination configurations are most commonly observed as bis(carboxylato-O,O0 )-bridged dimers (Scheme 1 (II)), bis(carboxylato)disilver(I) [5]. In contrast, polynuclear silver(I) complexes with bidentate bridging nitrogen ligands have less been well documented, although amidinates, being isoelectronic with carboxylates, have been shown to bridge silver(I) ions and have very short Ag Ag sepa [1,6,7]. So far the factors controlrations (2.65–2.805 A) ling the formation of such amidinate-bridged dimeric or tetrameric structures are not very clear. In previous studies on synthesis and structural characterization of the silver complexes either without ligand supported Ag Ag interactions [2a,8] or with bridging bis(carboxylate) groups [9], we and others found that many factors, such as the nature of the ligands, solvent,
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Scheme 1. Some typical silver(I) coordination fashions.
steric requirements of counter anions and condition of crystallization, appear to modulate the stereochemistry of the silver complexes, and that the metal coordination geometry is usually linear, T-shape, trigonal, tetrahedral or even octahedral. More interestingly, we also found that the neutral Schiff-base ligands containing imidazole groups (Scheme 1 (IV)) can act as a bridge ligand to generate polymeric complexes [10]. Cotton and coworkers [11] have reported that a formamidine ligand can coordinate to a silver ion in a monodentate fashion (Scheme 1 (V)). Therefore, it would be of interest to design and prepare dimeric or tetrameric silver hexahydropyrimidine complexes containing a close Ag Ag separation (Scheme 1 (VI)). We then design and synthesize two new hexahydropyrimidine derivatives, 1,4-bis(2-hexahydropyrimidyl)benzene and 1,3-bis(2-hexahydropyrimidyl)benzene, in which the former is linear but the latter is V-shaped, and report herewith the syntheses, crystal structures and photoluminescent properties of four new silver(I) complexes with hexahydropyrimidine derivatives, namely [Ag2 L(l-ONO2 )](NO3 ) 2H2 O (1), [Ag2 L(l-pn)](NO3 )2 (2), [Ag2 L(l-pn)](ClO4 )2 (3) and [Ag4 L0 2 (H2 O)](NO3 )2 5H2 O (4), where L ¼ 1,4-bis(2-hexahydropyrimidyl)benzene, L0 ¼ 1,3-bis(2-hexahydropyrimidyl)benzene and pn ¼ 1,3-diaminopropane. To the best of our knowledge, this is the first example of Ag Ag interactions assisted by neutral formamidine bridges. Photoluminescence of 1–4 has also been observed in the solid state and solution at room temperature and low temperature.
2. Experimental 2.1. Measurements and materials All chemicals were purchased from commercial sources, and used without further purification. The C, H, N microanalyses were carried out with a Perkin–Elmer 240 elemental analyzer. 1 H NMR spectra were recorded on a Varian INOVA 500 MHz spectrometer at
25 °C. The FT-IR spectra were recorded from KBr pellets in the range 4000–400 cm1 on a Nicolet 5DX spectrometer. For variable temperature photoluminescence measurement, samples were mounted in a closedcycle cryostat in which the temperature can be adjusted. The 325 nm line of the He–Cd laser was used as an excitation source. The emission light was collected and dispersed by a double monochromator with a watercooled photomultiplier tube and processed with a lockin amplifier. For the lifetime measurements, the third harmonics, 355 nm line of a Q-switched Nd:YAG laser, was used as the excitation light source. The emission was recorded by using a Peltier-cooled photomultiplier tube (Hamamatsu R636-10) and a HP54522A 500 MHz oscilloscope. Caution: Although no problems were encountered in the preparation of the perchlorate salt, care should be taken when handling such a potentially explosive compound. 2.2. Preparation of [Ag2 L(l-ONO2 )](NO3 ) 2H2 O (1) An acetonitrile solution (2 ml) of terephthalaldehyde (134 mg, 1 mmol) was added dropwise to a stirred acetonitrile (2 ml) solution containing 1,3-diaminopropane (148 mg, 2 mmol) at room temperature. After stirring for 4.5 h, an aqueous (5 ml) solution of AgNO3 (340 mg, 2 mmol) was added dropwise to the mixture solution. The colorless solution was allowed to stand at room temperature in air avoiding illumination for 48 h. Large colorless prismatic crystals of 1 were obtained, which were collected by filtration, washed with aqueous MeCN and dried in a vacuum desiccator over silica gel. The final yield was 217 mg (35%). 1 H NMR (500 MHz, D2 O): d 1.90 (br., 4H, C–CH2 –C), 2.84 (t, 8H, N–CH2 ), 4.98 (s, 2H, N–CH), 7.37 (s, 4H, Ar–H). Main IR bands (KBr, m, cm1 ): 3381(m, br.), 3209(m), 2922(m), 2866(m), 1764(w), 1641(m), 1381(s), 1080(m), 1051(m), 914(w), 883(w), 820(m), 641(w), 544(w), 490(w). Calc. for C14 H26 Ag2 N6 O8 : C, 27.03; H, 4.21; N, 13.51. Found: C, 27.16; H, 4.24; N, 13.59%. 2.3. Preparation of [Ag2 L(l-pn)](NO3 )2 (2) 2.3.1. Method A 2 was obtained by a similar procedure of 1, but diffusion of diethyl ether into the reaction solution was performed instead of evaporation of the solvent. Large colorless prismatic crystals of 2 were obtained, which were collected by filtration, washed with aqueous MeCN and dried in a vacuum desiccator over silica gel. The final yield was 231 mg (35%). 1 H NMR (500 MHz, DMSO): d 1.60 (t, 4H, C–CH2 –C), 1.90 (t, 2H, NH2 – CH2 )–CH2 –CH2 –NH2 ), 2.63 (t, 4H, NH2 –CH2 –CH2 ) 2.99 (t, 8H, NH–CH2 –CH2 ), 4.54 (s, 2H, NH–CH–NH), 7.59 (s, 4H, Ar–H). Main IR bands (KBr, m, cm1 ):
C.-X. Ren et al. / Inorganica Chimica Acta 357 (2004) 443–450
3258(m, br.), 2934(m), 1762(m), 1641(m), 1576(m), 1392(s), 1097(w), 1006(w), 970(w), 897(w), 824(m), 608(w). Calc. for C17 H32 Ag2 N8 O6 : C, 30.93; H, 4.89; N, 16.97. Found: C, 30.89; H, 4.93; N, 16.89%.
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1318(m), 1087(s), 898(w), 824(w), 630(m). Calc. for C17 H32 Ag2 Cl2 N6 O8 : C, 27.78; H, 4.39; N, 11.43. Found: C, 27.84; H, 4.42; N, 11.40%. 2.5. Preparation of [Ag4 L0 2 (H2 O)](NO3 )4 5H2 O (4)
2.3.2. Method B An acetonitrile (2 ml) solution of terephthalaldehyde (134 mg, 1 mmol) was added dropwise to a stirred acetonitrile (2 ml) solution containing 1,3-diaminopropane (222 mg, 3 mmol) at room temperature. After stirring for 4.5 h, an aqueous (5 ml) solution of AgNO3 (340 mg, 2 mmol) was added dropwise to the mixture. The colorless solution was allowed to stand at room temperature in air avoiding illumination for 48 h. Large colorless prismatic crystals of 2 were obtained, which were collected by filtration, washed with aqueous MeCN and dried in a vacuum desiccator over silica gel. Yield: 198 mg, 35%.
Complex 4 was prepared in the similar procedure described above for 1 using isophthalaldehyde in place of terephthaladehyde. Colorless crystals of 4 were obtained in 42% yield (514 mg). 1 H NMR (500 MHz, DMSO): d 1.81 (br., 4H, C–CH2 –C), 2.94 (t, 8H, N– CH2 ), 4.52 (s, 2H, NH–CH), 7.18–7.21 (m, 3H, Ar– H2 and Ar–H4 ), 7.34 (s, 1H, Ar–H5 ). Main IR bands (KBr, m, cm1 ): 3250(m, br.), 2936(m), 1797(w), 1644(m), 1391(s), 1157(m), 1091(m), 1053(m), 878(m), 698(w). Calc. for C28 H56 Ag4 N12 O18 : C, 26.27; H, 4.41; N, 13.13. Found: C, 26.24; H, 4.37; N, 13.12%. 2.6. X-ray data collection and structure refinement
2.4. Preparation of [Ag2 L(l-pn)](ClO4 )2 (3) Diffraction intensities for the complex were collected at 21 °C on a Siemens R3m diffractometer with graphite usmonochromated Mo Ka radiation (k ¼ 0:71073 A) ing the x-scan technique to maximum 2h values of 56°, 58°, 58° and 52° for 1, 2, 3 and 4, respectively. Lorentzpolarization and absorption corrections were applied [12]. The structure was solved with direct methods and refined with full-matrix least-squares technique using the S H E L X S -97 and S H E L X L -97 programs, respectively [13, 14]. Non-hydrogen atoms were refined anisotropically.
Complex 3 was prepared in the similar procedure described above for 2 (Section 2.3.1) using AgClO4 instead of AgNO3 . Colorless crystals of 3 were obtained in 33% yield (242 mg). 1 H NMR (500 MHz, DMSO): d 1.59 (t, 4H, C–CH2 –C), 1.76 (t, 2H, NH2 –CH2 –CH2 – CH2 –NH2 ), 2.73 (t, 4H, NH2 –CH2 –CH2 ) 2.96 (t, 8H, NH–CH2 –CH2 ), 4.54 (s, 2H, NH–CH–NH), 7.57 (s, 4H, Ar–H). Main IR bands (KBr, m, cm1 ): 3271 (m, br.), 2935(m), 1795(w), 1641(m), 1575(m), 1467(m), Table 1 Crystal and refinement data for 1–4 Complex Empirical formula Formula weight Crystal size (mm) T (K) Wavelength (A)
1
C14 H26 Ag2 N6 O8 622.15 0.37 0.36 0.28 293(2) 0.71073 Crystal system monoclinic Space group P 21 =c a (A) 7.346(3) b (A) 23.415(10) c (A) 7.346(3) b (°) 104.77(3) 3 ) V (A 2118(2) Z 4 Dcalc (mg m3 ) 1.951 l (Mo Ka) (mm1 ) 1.902 F ð0 0 0Þ 1240 Absorption correction empirical Number of measured reflections 5171 Number of observations ðI > 2rðIÞÞ 4800 Parameters 267 R1 ðI > 2rðIÞÞa 0.0399 0.1079 wR2 a Goodness-of-fit on F 2 1.040 3 ) (max., min.) D (e A 0.907, )0.501 hP 2 . P 2 2 i1=2 P P a R1 ¼ jjFo j jFc jj= jFo j, wR2 ¼ w Fo2 Fc2 . w Fo
2
3
4
C17 H32 Ag2 N8 O6 660.25 0.42 0.32 0.28 293(2) 0.71073 orthorhombic Pna21 9.563(4) 23.531(9) 10.977(3)
C17 H32 Ag2 Cl2 N6 O8 735.12 0.42 0.32 0.28 293(2) 0.71073 orthorhombic P 21 21 21 9.272(4) 11.154(2) 24.981(10)
2470(2) 4 1.775 1.633 1328 empirical 3298 3146 299 0.0557 0.1540 1.031 0.808, )0.635
2584(2) 4 1.890 1.776 1472 empirical 2501 2479 317 0.0511 0.1215 1.036 0.491, )0.546
C28 H56 Ag4 N12 O18 1280.30 0.52 0.44 0.32 293(2) 0.71073 monoclinic P 21 =m 9.816(5) 17.821(10) 13.209(8) 104.65(2) 2236(2) 2 1.902 1.809 1280 empirical 4373 4103 299 0.0696 0.1896 0.979 1.110, )1.118
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Table 2 and angles (°) for 1–4 Selected bond lengths (A) 1 Ag(1)–N(5a) Ag(1)–O(2) Ag(2)–N(4) N(5a)–Ag(1)–N(3) N(3)–Ag(1)–O(2) N(6a)–Ag(2)–O(2b) 2 Ag(1)–N(5) Ag(1)–N(1) Ag(2)–N(2a) N(5)–Ag(1)–N(3a) N(3a)–Ag(1)–N(1) N(6)–Ag(2)–N(4) 3 Ag(1)–N(5) Ag(1)–N(4a) Ag(2)–N(3) N(5)–Ag(1)–N(1) N(1)–Ag(1)–N(4a) N(6)–Ag(2)–N(2a) 4 Ag(1)–N(3) Ag(1)–O(4W) Ag(2)–N(1) Ag(3)–N(2) Ag(4)–N(4) N(3a)–Ag(1)–N(3) N(3)–Ag(1)–O(4W) N(2a)–Ag(3)–N(2)
2.236(3) 2.598(4) 2.285(4) 168.4(1) 90.2(1) 105.1(2) 2.17(1) 2.57(1) 2.28(1) 158.2(5) 106.9(4) 127.3(6) 2.21(1) 2.456(8) 2.23(1) 144.5(4) 109.1(4) 107.0(4) 2.231(7) 2.59(1) 2.241(7) 2.313(7) 2.257(7) 167.2(3) 92.6(2) 165.7(4)
Ag(1)–N(3) Ag(2)–N(6a) Ag(2)–O(2b) N(5a)–Ag(1)–O(2) N(6a)–Ag(2)–N(4) N(4)–Ag(2)–O(2b) Ag(1)–N(3a) Ag(2)–N(6) Ag(2)–N(4) N(5)–Ag(1)–N(1) N(6)–Ag(2)–N(2a) N(2a)–Ag(2)–N(4) Ag(1)–N(1) Ag(2)–N(6) Ag(2)–N(2a) N(5)–Ag(1)–N(4a) N(6)–Ag(2)–N(3) N(3)–Ag(2)–N(2a) Ag(1)–N(3a) Ag(2)–N(1a) Ag(3)–N(2a) Ag(4)–N(4a) N(3a)–Ag(1)–O(4W) N(1a)–Ag(2)–N(1) N(4a)–Ag(4)–N(4)
2.242(3) 2.240(4) 2.578(4) 98.42(1) 165.0(1) 86.2(1) 2.235(9) 2.17(1) 2.37(1) 93.7(5) 128.7(6) 102.0(4) 2.28(1) 2.21(2) 2.466(9) 105.6(5) 142.1(4) 108.2(4) 2.230(7) 2.241(7) 2.313(7) 2.257(7) 92.7(2) 165.5(4) 164.1(4)
Symmetry codes for 1: (a) x þ 1, y, z þ 1; (b) x, y, z þ 1; for 2: (a) x, y, z 1=2; for 3: (a) x, y 1=2, z þ 1=2; for 4: (a) x, y þ 1=2, z.
The organic hydrogen atoms were generated geometri the aqua hydrogen atoms were locally (C–H 0.96 A); cated from difference maps and refined with isotropic temperature factors. The absolute structures have been refined with Flack parameters [15] of 0.09(8) and 0.00(9) for 2 and 3, respectively. Analytical expressions of neutral-atom scattering factors were employed, and anomalous dispersion corrections were incorporated [16]. The crystallographic data for all the four complexes and bond are listed in Table 1, selected bond lengths (A) angle (°) are given in Table 2. Drawings were produced with S H E L X T L [17].
3. Results and discussion 3.1. Synthesis The reaction of diamine and dialdahyde depends greatly on the reaction condition, such as the ratio of the reactants, solvent, concentration and temperature. In a 2 + 2 condensation, the major product is usually mac-
rocyclic Schiff-base [18]. In our case, L and L0 (Scheme 2) have been synthesized in situ by the condensation of 1,3diaminopropane with terephthaladehyde and isophthalaldehyde in the ratio of 2:1 in acetonitrile solution at room temperature, respectively, instead of the common cyclic imine [19]. Formation of the amine rings is likely to be the driving force for this unusual reaction, therefore, high dilution condition is unnecessary. The similar reaction of 1,3-propanediamine or its derivatives with monoaldehydes to give cyclic hexahydropyrimidine or its derivatives has been reported [20]. Practically, in the presence of AgNO3 , two silver(I) compounds, 1 and 2, were obtained under different crystallization conditions. 1 crystallized from the mixture solution by slow evaporation in air, while 2 was obtained by diffusion of diethyl ether into the reaction mixture, indicating that the formation of compounds is very sensitive to crystallization condition. This fact also suggests that the reaction of cyclic condensation was incomplete, which may be responsible for the low yield of this reaction. When additional one equivalent pn was added to the solution, the major product obtained under
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above-mentioned different crystallization conditions was uniquely 2, being confirmed by elemental analyses and IR spectra, as well as crystal cell parameters. This observation may be attributed to the presence of the strong ligating pn ligand can alter the coordination environment of the metal atom, as shown in Scheme 3. In order to investigate the anion effect, we have used bulk tetrahedral anion ClO 4 in place of the trigonal planar anion NO 3 in the synthesis of 3. Unfortunately, we can see from the fact that the coordination and polymeric structure of 3 with ClO 4 anions are very similar to those of 2 with NO 3 anions. This fact may be also attributed to the presence of a much more strong ligating ligand pn. 3.2. Crystal structures The crystal structure of 1 consists of [Ag2 L(l-ONO2 )]þ 2 cations, NO 3 counter anions and lattice water molecules in the solid. As shown in Fig. 1, the tetranuclear cation has a crystallographic C2 symmetry. The two L ligands in a cis, cis conformation are in a face-to-face orientation and are joined together by four silver ions through coordination bonds to give a cuboid motif with the distances of Ag(1) Ag(2a), Ag(1) Ag(2) and Ag(1) Ag(1a) at respectively, and the face2.901(1), 7.033 and 7.597 A, In to-face distance between the two phenyl rings at 5.45 A. this Ag4 unit, a pair of non-equivalent silver ions are bridged by two hexahydropyrimidine groups, leading to the short Ag(1) Ag(2a) distance. Such short Ag Ag distance is well below the sum of the van der Waals radii of [19] and is virtually identical to two silver atoms (3.44 A) indicating a that of metallic Ag–Ag distance (2.89 A), significant Ag Ag interaction. To the best of our knowledge, this is the first example of Ag Ag interac-
Scheme 2. The route of ligands synthesis.
Scheme 3. Proposed structural conversion from 1 to 2.
Fig. 1. A perspective view (a) and a schematic presentation (b) of the tetranuclear [Ag2 L(NO3 )]2þ 2 structural unit in 1.
tions assisted by neutral formamidine bridges. The intramolecular Ag Ag separation in 1 is slightly shorter than those observed in [Ag2 (R2 PCH2 PR2 )2 ]2þ (2.943– and [Ag2 (RCO2 )2 ] (2.90–2.967 A) frameworks 3.099 A) [4,5], but markedly longer than those found in [Ag2 [6,7], [Ag2 (PhNNNPh)2 ] (RNHCHNHR)2 ] (2.65–2.805 A) [21] and [Ag2 (o-(Me3 Si)2 CC5 H4 N)2 ] [2.654 [2.669(1) A] [22] cores. Each Ag(I) ion is three-coordinated by (1) A] two nitrogen atoms from two L ligands and one nitrate oxygen atom, resulting in an approximately T-shaped coordination geometry when neglecting the Ag–Ag interactions. The nitrogen atoms of L ligand coordinate to silver ion in an axial–axial fashion with the distances of which are Ag–N in the range of 2.236(3)–2.285(4) A, slightly shorter than those found for the four silver com but plexes of piperazine in the axial fashion (2.316 A), markedly shorter than those in the equatorial fashion [23]. The Ag–O distances [2.598(4) (2.438 and 2.439 A) being markedly longer than the Ag–N and 2.578(4) A], docubonds, are compatible to those (2.354–2.689 A) mented previously [24,25]. The bond angles around the silver ion [N–Ag–N 165.0(1)° or 168.4(1)°, N–Ag–O 86.2(1)°–105.2(1)°] indicate typical T-shaped coordination geometries for both crystallographically independent silver(I) ions. Interestingly, the cuboid Ag4 units are further interlinked by two NO 3 anions via monoatomic bridges to form a hexagonal motif, with resulting one-dimensional chains running along the b-axis direction, as shown in Fig. 2. Nitrate anion can coordinate to metal ion in a monodentate, chelate or bridge fashion. In 1, nitrate anion adopts a monoatomic bridging fashion with the angle
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Fig. 2. A perspective view (a) and a schematic presentation (b) of the monoatomic nitrate-bridged ribbon in 1.
Ag(1)–O(2)–Ag(2b) at 118.5(1)°, which is rare in nitrate coordination chemistry [26]. The closest Ag Ag sepa and the ration of the hexagon is Ag(1) Ag(2b) at 4.449 A longest one is Ag(1) Ag(1b) at 8.456 A. The lattice water molecules form hydrogen bonds with the coordinated and uncoordinated nitrate oxygen atoms, and the nitrogen atom from L ligand [O(1w) O(3) 2.800(5); O(1w) O(4) 2.859(6); O(2w) O(6e) 2.828(6); O(2w) O(6f) 2.907(5); O(1we) N(5) 2.943(5) A]. Due to the presence of another ligand pn, the crystal structures of 2 and 3 are significantly different from that of 1. In the solid state, both 2 and 3 consist of onedimensional polymeric [Ag2 L(l-pn)]2nþ cations, as well n as NO and ClO counter anions in the solid state, 3 4 respectively. As shown in Fig. 3, a pair of non-equivalent silver(I) ions bound to the two L ligands are further linked with bridging pn ligands to generate ribbon
Fig. 3. A perspective view of the coordination environments in 2.
structures running along the c-axis and b-axis directions in 2 and 3, respectively. Although they crystallize in two different orthorhombic space groups, the ribbons in 2 and 3 are very similar. Each ribbon in 2 or 3 possesses a crystallographic 21 -screw axis in the c- or b-axis direction, thus is in fact helical with the pitch of 10.977(3) or respectively. Each Ag(I) atom in 2 or 3 is 11.154(2) A, three-coordinated by two nitrogen atoms from two L ligands in an axial-equatorial fashion and one pn nitrogen atom, resulting in an approximately trigonal P planar geometry [ (\N–Ag–N) ¼ 358.9° and 358.2° for 2, and 359.2° and 357.3° for 3]. The Ag–N lengths as in 2, and sociated with L ligands [2.235(9) and 2.28(1) A 2.23(1) and 2.28(1) A in 3] in the axial fashion are significantly shorter than those in the equatorial fashion in 2, and 2.456(8) and 2.466(9) A [2.37(1) and 2.57(1) A in 3]. The separations of Ag(1) Ag(2) are at 5.649 and for 2 and 3, respectively, indicating no metal– 5.694 A metal interaction in 2 and 3. The pn ligand displays a trans–gauche conformation. Based on the structures of 2 and 3, the counter anions, as the only difference between them, should be responsible for the different molecular packing fashions in the solid state. On the other hand, compared with 1, it is also obvious that the presence of a much stronger ligating pn ligand dictates the polymeric ribbon structures. As illustrated in Fig. 4, the crystal structure of 4 is composed of [Ag4 L0 2 (H2 O)]4þ cations, NO 3 counter anions and lattice water molecules in the solid. The two L0 ligands, acting in a cis, cis mode, are orientated in a face-to-face fashion and joined together by four silver
Fig. 4. A perspective view (a) and a schematic presentation (b) of the tetranuclear [Ag4 L0 2 (H2 O)]4þ cation in 4.
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ions through coordination bonds to give a truncated square-pyramidal motif (Fig. 4(b)). It can be seen that 4 is structurally very different from 1, though both of them have tetranuclear cuboid motifs. These may be attributed to the different shapes of the ligands, since L is linear while L0 is V-shaped. All the four silver(I) atoms are crystallographically independent of the tetranuclear core of 4. There is a mirror symmetry passing through the plane defined by the four silver ions. One nitrate anion [N(5), O(1), O(2), O(3)], the N(6)– O(5) bond, O(3w) and O(4w) atoms are also located on this mirror plane. The Ag(2), Ag(3) and Ag(4) ions are each two-coordinated in a virtually linear geometry by two nitrogen atoms from two different L0 ligands in an axial–axial fashion with the N–Ag–N bond angles in the range of 164.1(4)°–167.2(3)°. Besides the coordination of two nitrogen atoms from two different L0 ligands, the Ag(1) ion further binds with a water molecule [O(4w)] resulting in a T-shaped geometry with N(3)–Ag(1)–N(3a) at 167.2(3)° and N(3)–Ag(1)–O(4w) are at 92.7(2)°. The Ag–N distances (2.231–2.313 A) agreement with those observed in 1, 2 and 3 in the axial fashion, but shorter than those in the equatorial is fashion. The Ag(1)–O(4w) length being 2.59(1) A significantly longer than those of Ag–N. The metal– and metal separations of Ag(1) Ag(4) [2.937(3) A] Ag(2) Ag(3) [2.939(3) A] are also well below the sum of van der Waals radii of two silver atoms [19] and slightly longer than that found in metallic silver (2.89 indicating significant Ag–Ag interactions. The A), while the Ag(1) Ag(2) distance is 4.635 A, to suit Ag(3) Ag(4) distance is elongated to 7.720 A the conformation of the ligands. The distance and di hedral angle between the two phenyl plane are 4.434 A and 42.8°, respectively. The nitrate anion is un-coordinated in 4 and the This is different from closest Ag O distance is 2.828 A. 1, in which the nitrate anion bridge two silver ions in the monoatomic fashion. The lattice water molecules also form hydrogen bonds with each other [O(1w) O(2w) and with the uncoordinate nitrate anion 2.844 A] [O(1w) O(4a) 2.849 A]. 3.3. Photoluminescent properties At room temperature, compounds 1–4 exhibit photoluminescence in the solid state at 538, 528, 530 and 484 nm, respectively (Fig. 5). Lowing the temperature leads to an increase of the emission intensity. Exponential decays were observed at both room temperature and 77 K, giving lifetimes of 0.6 and 1.5 ls for 1, 0.2 and 1.9 ls for 2, 0.5 and 1.7 ls for 3 and 0.2 and 2.2 ls for 4, respectively. The transitions associated with the emissions of the silver(I) clusters 1–4 originate probably from a ligand-to-metal charge-transfer (LMCT) excited state, with mixing of a metal-centered (d–s/d–p) silver(I) state, according to
449
Fig. 5. Emission spectra of 1–4 and L in the solid state at room temperature.
similar assignments suggested for other luminescent polynuclear Ag(I) systems [27]. In DMF solution, 1–4 display very weak emission at 298 K. While at 77 K, 1 exhibits a band at 495 nm with two shoulders at 464 and 536 nm, 2 and 3 only display a weak band at about 540 nm, and 4 displays a band at 498 nm. The bands at 536 nm for 1, and 540 nm for 2 and 3 may also be assigned to LMCT transitions, with mixing of a metal-centered state. The bands at 495 nm for 1 and 498 nm for 4 can be assigned to a metal-centered state analogous to that of [Ag4 (P2 bpy)2 ](BF4 )4 (P2 -bpy ¼ 6,6-bis(diphenylphosphanyl)2,20 -bipyridyl) [28]. 4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. CCDC 198619–198622 for 1– 4, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223336-033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk). Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 20131020) and the Ministry of Education of China (No. 01134). References [1] F.A. Cotton, X.-J. Feng, M. Matusz, R. Poli, J. Am. Chem. Soc. 110 (1988) 7077. [2] (a) M.-L. Tong, X.-M. Chen, B.-H. Ye, L.-N. Ji, Angew. Chem., Int. Ed. Engl. 38 (1999) 2237; (b) R. Villanneau, A. Proust, F. Robert, P. Gouzerh, Chem. Commun. (1998) 1491. [3] C.-M. Che, M.-C. Tse, M.C.W. Chan, K.-K. Cheung, D.L. Phillips, K.-H. Leung, J. Am. Chem. Soc. 122 (2000) 2464.
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[13] G.M. Sheldrick, S H E L X S -97, Program for Crystal Structure Solution, University of G€ ottingen, Germany, 1997. [14] G.M. Sheldrick, S H E L X S -97, Program for Crystal Structure Refinement, University of G€ ottingen, Germany, 1997. [15] D. Flack, D. Schwarzenbach, Acta Crystallogr., Sect. A 44 (1988) 499. [16] International Tables for X-ray Crystallography, vol. C, Tables 4.2.6.8 and 6.1.1.4. Kluwer Academic Publisher, Dordrecht, 1992. [17] G.M. Sheldrick, S H E L X T L Version 5, Siemens Industrial Automation Inc, Madison, WI, 1995. [18] (a) D.A. Nation, A.E. Martell, R.I. Carroll, A. Clearfield, Inorg. Chem. 35 (1996) 7246; (b) G.-Q. Shangguan, A.E. Martell, Z.-R. Zhang, J.H. Reibenspies, Inorg. Chim. Acta 299 (2000) 47. [19] A. Bondi, J. Phys. Chem. 68 (1964) 441. [20] (a) R.F. Evans, Aust. J. Chem. 20 (1967) 1643; (b) B.T. Golding, I.K. Nassereddin, J. Chem. Soc., Perkin Trans. I (1985) 2011; (c) H.-Y. Luo, J.-M. Lo, P.E. Fanwick, J.G. Stowell, M.A. Green, Inorg. Chem. 38 (1999) 2071. [21] J. Beck, J. Strahle, Z. Naturforsch. B 41B (1986) 4. [22] R.I. Papasergio, C.L. Raston, A.H. White, J. Chem. Soc., Dalton Trans. (1987) 3085. [23] L. Carlucci, G. Ciani, D.M. Proserpio, A. Sironi, Inorg. Chem. 34 (1995) 5698. [24] (a) M.A. Withersby, A.J. Blake, N.R. Champness, P. Hubberstey, W.-S. Li, M. Schr€ oder, Angew. Chem., Int. Ed. Engl. 36 (1997) 2327; (b) E. Benedetti, A. Bavoso, B.D. Blasio, V. Pavone, C. Pedone, Inorg. Chim. Acta 116 (1986) 31. [25] (a) F. Robinson, M.J. Zaworotko, Chem. Commun. (1995) 2413; (b) D.M. Ho, R. Bau, Inorg. Chem. 22 (1983) 4073; (c) N.R. Brooks, A.J. Blake, N.R. Champness, J.W. Cunningham, P. Hubberstey, S.J. Teat, C. Wilson, M. Schr€ oder, J. Chem. Soc., Dalton Trans. (2001) 2530. [26] M.R. Rosenthal, J. Chem. Edu. 50 (1973) 331. [27] C.R. Wang, K.K.-W. Lo, V.W.-W. Yam, J. Chem. Soc., Dalton Trans. (1997) 227. [28] V.J. Catalano, H.M. Kar, J. Garnas, Angew. Chem., Int. Ed. Engl. 38 (1999) 1979.
Syntheses, structures and photoluminescent properties of silver(I) complexes with in situ generated hexahydropyrimidine derivatives Chun-Xia Ren, Bao-Hui Ye *, Hai-Liang Zhu, Jian-Xin Shi, Xiao-Ming Chen
*
School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, PR China Received 21 March 2003; accepted 10 June 2003
Abstract Two new linear and V-shaped tetradentate ligands, namely 1,4-bis(2-hexahydropyrimidyl)benzene (L) and 1,3-bis(2-hexahydropyrimidyl)benzene (L0 ), and their silver(I) complexes, [Ag2 L(l-ONO2 )](NO3 ) 2H2 O (1), [Ag2 L(l-pn)](NO3 )2 (2), [Ag2 L(lpn)](ClO4 )2 (3) and [Ag4 L0 2 (H2 O)](NO3 )4 5H2 O (4) (pn ¼ 1,3-diaminopropane) have been synthesized in situ and structurally characterized by single-crystal X-ray diffraction. 1 and 2 were obtained from the same reaction solution but different crystallization conditions. 1 is an one-dimensional chain featuring cuboid tetranuclear silver(I) units interconnected through monoatomic nitrate bridges. Both 2 and 3 are ribbon-like helical compounds in which each L ligand acts in a tetradentate bridging mode to interconnect four metal atoms, and each pn ligand functions in a bidentate bridging mode to link a pair of metal atoms. 4 shows a truncated assisted by square-pyramidal tetranuclear motif arose by the V-shaped L0 ligand. Close Ag Ag separations (2.901–2.939 A) bis(hexahydropyrimidine) bridges were observed in 1 and 4, indicating metal–metal interactions. Photoluminescence of 1–4 has also been observed in the solid state and solution at room temperature and low temperature, respectively. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Coordination polymers; Silver; Hexahydropyrimidine; N ligands
1. Introduction Although repulsion was expected between silver(I)– silver(I) metal centers, a number of species with shorter Ag Ag separations have been structurally characterized. The principal interest has been the possibility of a metal–metal bonding interaction between the silver metal involving s- or p-orbitals [1]. The powerfully positive evidences would come from silver(I) complexes with shorter Ag Ag separations comparable to that in metallic silver [2]. Importantly, Che et al. [3] have recently (2.889 A) employed resonance Raman spectra to verify this weak Ag Ag interaction. Many examples with short Ag Ag distances are associated with the presence of bridging or capping ligands that can dictate the metal ions in a short * Corresponding authors. Tel.: +86-20-84113986; fax: +86-2084112245. E-mail addresses: [email protected] (B.-H. Ye), [email protected]. cn (X.-M. Chen).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2003.06.003
metal–metal separation (Scheme 1). One of these ligands is bis(phosphino)methane (Scheme 1 (I)) which is widely used to assemble dimeric and trimeric species [4]. Silver(I) carboxylate complexes have also been extensively investigated over the last 20 years. The coordination configurations are most commonly observed as bis(carboxylato-O,O0 )-bridged dimers (Scheme 1 (II)), bis(carboxylato)disilver(I) [5]. In contrast, polynuclear silver(I) complexes with bidentate bridging nitrogen ligands have less been well documented, although amidinates, being isoelectronic with carboxylates, have been shown to bridge silver(I) ions and have very short Ag Ag sepa [1,6,7]. So far the factors controlrations (2.65–2.805 A) ling the formation of such amidinate-bridged dimeric or tetrameric structures are not very clear. In previous studies on synthesis and structural characterization of the silver complexes either without ligand supported Ag Ag interactions [2a,8] or with bridging bis(carboxylate) groups [9], we and others found that many factors, such as the nature of the ligands, solvent,
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Scheme 1. Some typical silver(I) coordination fashions.
steric requirements of counter anions and condition of crystallization, appear to modulate the stereochemistry of the silver complexes, and that the metal coordination geometry is usually linear, T-shape, trigonal, tetrahedral or even octahedral. More interestingly, we also found that the neutral Schiff-base ligands containing imidazole groups (Scheme 1 (IV)) can act as a bridge ligand to generate polymeric complexes [10]. Cotton and coworkers [11] have reported that a formamidine ligand can coordinate to a silver ion in a monodentate fashion (Scheme 1 (V)). Therefore, it would be of interest to design and prepare dimeric or tetrameric silver hexahydropyrimidine complexes containing a close Ag Ag separation (Scheme 1 (VI)). We then design and synthesize two new hexahydropyrimidine derivatives, 1,4-bis(2-hexahydropyrimidyl)benzene and 1,3-bis(2-hexahydropyrimidyl)benzene, in which the former is linear but the latter is V-shaped, and report herewith the syntheses, crystal structures and photoluminescent properties of four new silver(I) complexes with hexahydropyrimidine derivatives, namely [Ag2 L(l-ONO2 )](NO3 ) 2H2 O (1), [Ag2 L(l-pn)](NO3 )2 (2), [Ag2 L(l-pn)](ClO4 )2 (3) and [Ag4 L0 2 (H2 O)](NO3 )2 5H2 O (4), where L ¼ 1,4-bis(2-hexahydropyrimidyl)benzene, L0 ¼ 1,3-bis(2-hexahydropyrimidyl)benzene and pn ¼ 1,3-diaminopropane. To the best of our knowledge, this is the first example of Ag Ag interactions assisted by neutral formamidine bridges. Photoluminescence of 1–4 has also been observed in the solid state and solution at room temperature and low temperature.
2. Experimental 2.1. Measurements and materials All chemicals were purchased from commercial sources, and used without further purification. The C, H, N microanalyses were carried out with a Perkin–Elmer 240 elemental analyzer. 1 H NMR spectra were recorded on a Varian INOVA 500 MHz spectrometer at
25 °C. The FT-IR spectra were recorded from KBr pellets in the range 4000–400 cm1 on a Nicolet 5DX spectrometer. For variable temperature photoluminescence measurement, samples were mounted in a closedcycle cryostat in which the temperature can be adjusted. The 325 nm line of the He–Cd laser was used as an excitation source. The emission light was collected and dispersed by a double monochromator with a watercooled photomultiplier tube and processed with a lockin amplifier. For the lifetime measurements, the third harmonics, 355 nm line of a Q-switched Nd:YAG laser, was used as the excitation light source. The emission was recorded by using a Peltier-cooled photomultiplier tube (Hamamatsu R636-10) and a HP54522A 500 MHz oscilloscope. Caution: Although no problems were encountered in the preparation of the perchlorate salt, care should be taken when handling such a potentially explosive compound. 2.2. Preparation of [Ag2 L(l-ONO2 )](NO3 ) 2H2 O (1) An acetonitrile solution (2 ml) of terephthalaldehyde (134 mg, 1 mmol) was added dropwise to a stirred acetonitrile (2 ml) solution containing 1,3-diaminopropane (148 mg, 2 mmol) at room temperature. After stirring for 4.5 h, an aqueous (5 ml) solution of AgNO3 (340 mg, 2 mmol) was added dropwise to the mixture solution. The colorless solution was allowed to stand at room temperature in air avoiding illumination for 48 h. Large colorless prismatic crystals of 1 were obtained, which were collected by filtration, washed with aqueous MeCN and dried in a vacuum desiccator over silica gel. The final yield was 217 mg (35%). 1 H NMR (500 MHz, D2 O): d 1.90 (br., 4H, C–CH2 –C), 2.84 (t, 8H, N–CH2 ), 4.98 (s, 2H, N–CH), 7.37 (s, 4H, Ar–H). Main IR bands (KBr, m, cm1 ): 3381(m, br.), 3209(m), 2922(m), 2866(m), 1764(w), 1641(m), 1381(s), 1080(m), 1051(m), 914(w), 883(w), 820(m), 641(w), 544(w), 490(w). Calc. for C14 H26 Ag2 N6 O8 : C, 27.03; H, 4.21; N, 13.51. Found: C, 27.16; H, 4.24; N, 13.59%. 2.3. Preparation of [Ag2 L(l-pn)](NO3 )2 (2) 2.3.1. Method A 2 was obtained by a similar procedure of 1, but diffusion of diethyl ether into the reaction solution was performed instead of evaporation of the solvent. Large colorless prismatic crystals of 2 were obtained, which were collected by filtration, washed with aqueous MeCN and dried in a vacuum desiccator over silica gel. The final yield was 231 mg (35%). 1 H NMR (500 MHz, DMSO): d 1.60 (t, 4H, C–CH2 –C), 1.90 (t, 2H, NH2 – CH2 )–CH2 –CH2 –NH2 ), 2.63 (t, 4H, NH2 –CH2 –CH2 ) 2.99 (t, 8H, NH–CH2 –CH2 ), 4.54 (s, 2H, NH–CH–NH), 7.59 (s, 4H, Ar–H). Main IR bands (KBr, m, cm1 ):
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3258(m, br.), 2934(m), 1762(m), 1641(m), 1576(m), 1392(s), 1097(w), 1006(w), 970(w), 897(w), 824(m), 608(w). Calc. for C17 H32 Ag2 N8 O6 : C, 30.93; H, 4.89; N, 16.97. Found: C, 30.89; H, 4.93; N, 16.89%.
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1318(m), 1087(s), 898(w), 824(w), 630(m). Calc. for C17 H32 Ag2 Cl2 N6 O8 : C, 27.78; H, 4.39; N, 11.43. Found: C, 27.84; H, 4.42; N, 11.40%. 2.5. Preparation of [Ag4 L0 2 (H2 O)](NO3 )4 5H2 O (4)
2.3.2. Method B An acetonitrile (2 ml) solution of terephthalaldehyde (134 mg, 1 mmol) was added dropwise to a stirred acetonitrile (2 ml) solution containing 1,3-diaminopropane (222 mg, 3 mmol) at room temperature. After stirring for 4.5 h, an aqueous (5 ml) solution of AgNO3 (340 mg, 2 mmol) was added dropwise to the mixture. The colorless solution was allowed to stand at room temperature in air avoiding illumination for 48 h. Large colorless prismatic crystals of 2 were obtained, which were collected by filtration, washed with aqueous MeCN and dried in a vacuum desiccator over silica gel. Yield: 198 mg, 35%.
Complex 4 was prepared in the similar procedure described above for 1 using isophthalaldehyde in place of terephthaladehyde. Colorless crystals of 4 were obtained in 42% yield (514 mg). 1 H NMR (500 MHz, DMSO): d 1.81 (br., 4H, C–CH2 –C), 2.94 (t, 8H, N– CH2 ), 4.52 (s, 2H, NH–CH), 7.18–7.21 (m, 3H, Ar– H2 and Ar–H4 ), 7.34 (s, 1H, Ar–H5 ). Main IR bands (KBr, m, cm1 ): 3250(m, br.), 2936(m), 1797(w), 1644(m), 1391(s), 1157(m), 1091(m), 1053(m), 878(m), 698(w). Calc. for C28 H56 Ag4 N12 O18 : C, 26.27; H, 4.41; N, 13.13. Found: C, 26.24; H, 4.37; N, 13.12%. 2.6. X-ray data collection and structure refinement
2.4. Preparation of [Ag2 L(l-pn)](ClO4 )2 (3) Diffraction intensities for the complex were collected at 21 °C on a Siemens R3m diffractometer with graphite usmonochromated Mo Ka radiation (k ¼ 0:71073 A) ing the x-scan technique to maximum 2h values of 56°, 58°, 58° and 52° for 1, 2, 3 and 4, respectively. Lorentzpolarization and absorption corrections were applied [12]. The structure was solved with direct methods and refined with full-matrix least-squares technique using the S H E L X S -97 and S H E L X L -97 programs, respectively [13, 14]. Non-hydrogen atoms were refined anisotropically.
Complex 3 was prepared in the similar procedure described above for 2 (Section 2.3.1) using AgClO4 instead of AgNO3 . Colorless crystals of 3 were obtained in 33% yield (242 mg). 1 H NMR (500 MHz, DMSO): d 1.59 (t, 4H, C–CH2 –C), 1.76 (t, 2H, NH2 –CH2 –CH2 – CH2 –NH2 ), 2.73 (t, 4H, NH2 –CH2 –CH2 ) 2.96 (t, 8H, NH–CH2 –CH2 ), 4.54 (s, 2H, NH–CH–NH), 7.57 (s, 4H, Ar–H). Main IR bands (KBr, m, cm1 ): 3271 (m, br.), 2935(m), 1795(w), 1641(m), 1575(m), 1467(m), Table 1 Crystal and refinement data for 1–4 Complex Empirical formula Formula weight Crystal size (mm) T (K) Wavelength (A)
1
C14 H26 Ag2 N6 O8 622.15 0.37 0.36 0.28 293(2) 0.71073 Crystal system monoclinic Space group P 21 =c a (A) 7.346(3) b (A) 23.415(10) c (A) 7.346(3) b (°) 104.77(3) 3 ) V (A 2118(2) Z 4 Dcalc (mg m3 ) 1.951 l (Mo Ka) (mm1 ) 1.902 F ð0 0 0Þ 1240 Absorption correction empirical Number of measured reflections 5171 Number of observations ðI > 2rðIÞÞ 4800 Parameters 267 R1 ðI > 2rðIÞÞa 0.0399 0.1079 wR2 a Goodness-of-fit on F 2 1.040 3 ) (max., min.) D (e A 0.907, )0.501 hP 2 . P 2 2 i1=2 P P a R1 ¼ jjFo j jFc jj= jFo j, wR2 ¼ w Fo2 Fc2 . w Fo
2
3
4
C17 H32 Ag2 N8 O6 660.25 0.42 0.32 0.28 293(2) 0.71073 orthorhombic Pna21 9.563(4) 23.531(9) 10.977(3)
C17 H32 Ag2 Cl2 N6 O8 735.12 0.42 0.32 0.28 293(2) 0.71073 orthorhombic P 21 21 21 9.272(4) 11.154(2) 24.981(10)
2470(2) 4 1.775 1.633 1328 empirical 3298 3146 299 0.0557 0.1540 1.031 0.808, )0.635
2584(2) 4 1.890 1.776 1472 empirical 2501 2479 317 0.0511 0.1215 1.036 0.491, )0.546
C28 H56 Ag4 N12 O18 1280.30 0.52 0.44 0.32 293(2) 0.71073 monoclinic P 21 =m 9.816(5) 17.821(10) 13.209(8) 104.65(2) 2236(2) 2 1.902 1.809 1280 empirical 4373 4103 299 0.0696 0.1896 0.979 1.110, )1.118
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Table 2 and angles (°) for 1–4 Selected bond lengths (A) 1 Ag(1)–N(5a) Ag(1)–O(2) Ag(2)–N(4) N(5a)–Ag(1)–N(3) N(3)–Ag(1)–O(2) N(6a)–Ag(2)–O(2b) 2 Ag(1)–N(5) Ag(1)–N(1) Ag(2)–N(2a) N(5)–Ag(1)–N(3a) N(3a)–Ag(1)–N(1) N(6)–Ag(2)–N(4) 3 Ag(1)–N(5) Ag(1)–N(4a) Ag(2)–N(3) N(5)–Ag(1)–N(1) N(1)–Ag(1)–N(4a) N(6)–Ag(2)–N(2a) 4 Ag(1)–N(3) Ag(1)–O(4W) Ag(2)–N(1) Ag(3)–N(2) Ag(4)–N(4) N(3a)–Ag(1)–N(3) N(3)–Ag(1)–O(4W) N(2a)–Ag(3)–N(2)
2.236(3) 2.598(4) 2.285(4) 168.4(1) 90.2(1) 105.1(2) 2.17(1) 2.57(1) 2.28(1) 158.2(5) 106.9(4) 127.3(6) 2.21(1) 2.456(8) 2.23(1) 144.5(4) 109.1(4) 107.0(4) 2.231(7) 2.59(1) 2.241(7) 2.313(7) 2.257(7) 167.2(3) 92.6(2) 165.7(4)
Ag(1)–N(3) Ag(2)–N(6a) Ag(2)–O(2b) N(5a)–Ag(1)–O(2) N(6a)–Ag(2)–N(4) N(4)–Ag(2)–O(2b) Ag(1)–N(3a) Ag(2)–N(6) Ag(2)–N(4) N(5)–Ag(1)–N(1) N(6)–Ag(2)–N(2a) N(2a)–Ag(2)–N(4) Ag(1)–N(1) Ag(2)–N(6) Ag(2)–N(2a) N(5)–Ag(1)–N(4a) N(6)–Ag(2)–N(3) N(3)–Ag(2)–N(2a) Ag(1)–N(3a) Ag(2)–N(1a) Ag(3)–N(2a) Ag(4)–N(4a) N(3a)–Ag(1)–O(4W) N(1a)–Ag(2)–N(1) N(4a)–Ag(4)–N(4)
2.242(3) 2.240(4) 2.578(4) 98.42(1) 165.0(1) 86.2(1) 2.235(9) 2.17(1) 2.37(1) 93.7(5) 128.7(6) 102.0(4) 2.28(1) 2.21(2) 2.466(9) 105.6(5) 142.1(4) 108.2(4) 2.230(7) 2.241(7) 2.313(7) 2.257(7) 92.7(2) 165.5(4) 164.1(4)
Symmetry codes for 1: (a) x þ 1, y, z þ 1; (b) x, y, z þ 1; for 2: (a) x, y, z 1=2; for 3: (a) x, y 1=2, z þ 1=2; for 4: (a) x, y þ 1=2, z.
The organic hydrogen atoms were generated geometri the aqua hydrogen atoms were locally (C–H 0.96 A); cated from difference maps and refined with isotropic temperature factors. The absolute structures have been refined with Flack parameters [15] of 0.09(8) and 0.00(9) for 2 and 3, respectively. Analytical expressions of neutral-atom scattering factors were employed, and anomalous dispersion corrections were incorporated [16]. The crystallographic data for all the four complexes and bond are listed in Table 1, selected bond lengths (A) angle (°) are given in Table 2. Drawings were produced with S H E L X T L [17].
3. Results and discussion 3.1. Synthesis The reaction of diamine and dialdahyde depends greatly on the reaction condition, such as the ratio of the reactants, solvent, concentration and temperature. In a 2 + 2 condensation, the major product is usually mac-
rocyclic Schiff-base [18]. In our case, L and L0 (Scheme 2) have been synthesized in situ by the condensation of 1,3diaminopropane with terephthaladehyde and isophthalaldehyde in the ratio of 2:1 in acetonitrile solution at room temperature, respectively, instead of the common cyclic imine [19]. Formation of the amine rings is likely to be the driving force for this unusual reaction, therefore, high dilution condition is unnecessary. The similar reaction of 1,3-propanediamine or its derivatives with monoaldehydes to give cyclic hexahydropyrimidine or its derivatives has been reported [20]. Practically, in the presence of AgNO3 , two silver(I) compounds, 1 and 2, were obtained under different crystallization conditions. 1 crystallized from the mixture solution by slow evaporation in air, while 2 was obtained by diffusion of diethyl ether into the reaction mixture, indicating that the formation of compounds is very sensitive to crystallization condition. This fact also suggests that the reaction of cyclic condensation was incomplete, which may be responsible for the low yield of this reaction. When additional one equivalent pn was added to the solution, the major product obtained under
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above-mentioned different crystallization conditions was uniquely 2, being confirmed by elemental analyses and IR spectra, as well as crystal cell parameters. This observation may be attributed to the presence of the strong ligating pn ligand can alter the coordination environment of the metal atom, as shown in Scheme 3. In order to investigate the anion effect, we have used bulk tetrahedral anion ClO 4 in place of the trigonal planar anion NO 3 in the synthesis of 3. Unfortunately, we can see from the fact that the coordination and polymeric structure of 3 with ClO 4 anions are very similar to those of 2 with NO 3 anions. This fact may be also attributed to the presence of a much more strong ligating ligand pn. 3.2. Crystal structures The crystal structure of 1 consists of [Ag2 L(l-ONO2 )]þ 2 cations, NO 3 counter anions and lattice water molecules in the solid. As shown in Fig. 1, the tetranuclear cation has a crystallographic C2 symmetry. The two L ligands in a cis, cis conformation are in a face-to-face orientation and are joined together by four silver ions through coordination bonds to give a cuboid motif with the distances of Ag(1) Ag(2a), Ag(1) Ag(2) and Ag(1) Ag(1a) at respectively, and the face2.901(1), 7.033 and 7.597 A, In to-face distance between the two phenyl rings at 5.45 A. this Ag4 unit, a pair of non-equivalent silver ions are bridged by two hexahydropyrimidine groups, leading to the short Ag(1) Ag(2a) distance. Such short Ag Ag distance is well below the sum of the van der Waals radii of [19] and is virtually identical to two silver atoms (3.44 A) indicating a that of metallic Ag–Ag distance (2.89 A), significant Ag Ag interaction. To the best of our knowledge, this is the first example of Ag Ag interac-
Scheme 2. The route of ligands synthesis.
Scheme 3. Proposed structural conversion from 1 to 2.
Fig. 1. A perspective view (a) and a schematic presentation (b) of the tetranuclear [Ag2 L(NO3 )]2þ 2 structural unit in 1.
tions assisted by neutral formamidine bridges. The intramolecular Ag Ag separation in 1 is slightly shorter than those observed in [Ag2 (R2 PCH2 PR2 )2 ]2þ (2.943– and [Ag2 (RCO2 )2 ] (2.90–2.967 A) frameworks 3.099 A) [4,5], but markedly longer than those found in [Ag2 [6,7], [Ag2 (PhNNNPh)2 ] (RNHCHNHR)2 ] (2.65–2.805 A) [21] and [Ag2 (o-(Me3 Si)2 CC5 H4 N)2 ] [2.654 [2.669(1) A] [22] cores. Each Ag(I) ion is three-coordinated by (1) A] two nitrogen atoms from two L ligands and one nitrate oxygen atom, resulting in an approximately T-shaped coordination geometry when neglecting the Ag–Ag interactions. The nitrogen atoms of L ligand coordinate to silver ion in an axial–axial fashion with the distances of which are Ag–N in the range of 2.236(3)–2.285(4) A, slightly shorter than those found for the four silver com but plexes of piperazine in the axial fashion (2.316 A), markedly shorter than those in the equatorial fashion [23]. The Ag–O distances [2.598(4) (2.438 and 2.439 A) being markedly longer than the Ag–N and 2.578(4) A], docubonds, are compatible to those (2.354–2.689 A) mented previously [24,25]. The bond angles around the silver ion [N–Ag–N 165.0(1)° or 168.4(1)°, N–Ag–O 86.2(1)°–105.2(1)°] indicate typical T-shaped coordination geometries for both crystallographically independent silver(I) ions. Interestingly, the cuboid Ag4 units are further interlinked by two NO 3 anions via monoatomic bridges to form a hexagonal motif, with resulting one-dimensional chains running along the b-axis direction, as shown in Fig. 2. Nitrate anion can coordinate to metal ion in a monodentate, chelate or bridge fashion. In 1, nitrate anion adopts a monoatomic bridging fashion with the angle
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Fig. 2. A perspective view (a) and a schematic presentation (b) of the monoatomic nitrate-bridged ribbon in 1.
Ag(1)–O(2)–Ag(2b) at 118.5(1)°, which is rare in nitrate coordination chemistry [26]. The closest Ag Ag sepa and the ration of the hexagon is Ag(1) Ag(2b) at 4.449 A longest one is Ag(1) Ag(1b) at 8.456 A. The lattice water molecules form hydrogen bonds with the coordinated and uncoordinated nitrate oxygen atoms, and the nitrogen atom from L ligand [O(1w) O(3) 2.800(5); O(1w) O(4) 2.859(6); O(2w) O(6e) 2.828(6); O(2w) O(6f) 2.907(5); O(1we) N(5) 2.943(5) A]. Due to the presence of another ligand pn, the crystal structures of 2 and 3 are significantly different from that of 1. In the solid state, both 2 and 3 consist of onedimensional polymeric [Ag2 L(l-pn)]2nþ cations, as well n as NO and ClO counter anions in the solid state, 3 4 respectively. As shown in Fig. 3, a pair of non-equivalent silver(I) ions bound to the two L ligands are further linked with bridging pn ligands to generate ribbon
Fig. 3. A perspective view of the coordination environments in 2.
structures running along the c-axis and b-axis directions in 2 and 3, respectively. Although they crystallize in two different orthorhombic space groups, the ribbons in 2 and 3 are very similar. Each ribbon in 2 or 3 possesses a crystallographic 21 -screw axis in the c- or b-axis direction, thus is in fact helical with the pitch of 10.977(3) or respectively. Each Ag(I) atom in 2 or 3 is 11.154(2) A, three-coordinated by two nitrogen atoms from two L ligands in an axial-equatorial fashion and one pn nitrogen atom, resulting in an approximately trigonal P planar geometry [ (\N–Ag–N) ¼ 358.9° and 358.2° for 2, and 359.2° and 357.3° for 3]. The Ag–N lengths as in 2, and sociated with L ligands [2.235(9) and 2.28(1) A 2.23(1) and 2.28(1) A in 3] in the axial fashion are significantly shorter than those in the equatorial fashion in 2, and 2.456(8) and 2.466(9) A [2.37(1) and 2.57(1) A in 3]. The separations of Ag(1) Ag(2) are at 5.649 and for 2 and 3, respectively, indicating no metal– 5.694 A metal interaction in 2 and 3. The pn ligand displays a trans–gauche conformation. Based on the structures of 2 and 3, the counter anions, as the only difference between them, should be responsible for the different molecular packing fashions in the solid state. On the other hand, compared with 1, it is also obvious that the presence of a much stronger ligating pn ligand dictates the polymeric ribbon structures. As illustrated in Fig. 4, the crystal structure of 4 is composed of [Ag4 L0 2 (H2 O)]4þ cations, NO 3 counter anions and lattice water molecules in the solid. The two L0 ligands, acting in a cis, cis mode, are orientated in a face-to-face fashion and joined together by four silver
Fig. 4. A perspective view (a) and a schematic presentation (b) of the tetranuclear [Ag4 L0 2 (H2 O)]4þ cation in 4.
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ions through coordination bonds to give a truncated square-pyramidal motif (Fig. 4(b)). It can be seen that 4 is structurally very different from 1, though both of them have tetranuclear cuboid motifs. These may be attributed to the different shapes of the ligands, since L is linear while L0 is V-shaped. All the four silver(I) atoms are crystallographically independent of the tetranuclear core of 4. There is a mirror symmetry passing through the plane defined by the four silver ions. One nitrate anion [N(5), O(1), O(2), O(3)], the N(6)– O(5) bond, O(3w) and O(4w) atoms are also located on this mirror plane. The Ag(2), Ag(3) and Ag(4) ions are each two-coordinated in a virtually linear geometry by two nitrogen atoms from two different L0 ligands in an axial–axial fashion with the N–Ag–N bond angles in the range of 164.1(4)°–167.2(3)°. Besides the coordination of two nitrogen atoms from two different L0 ligands, the Ag(1) ion further binds with a water molecule [O(4w)] resulting in a T-shaped geometry with N(3)–Ag(1)–N(3a) at 167.2(3)° and N(3)–Ag(1)–O(4w) are at 92.7(2)°. The Ag–N distances (2.231–2.313 A) agreement with those observed in 1, 2 and 3 in the axial fashion, but shorter than those in the equatorial is fashion. The Ag(1)–O(4w) length being 2.59(1) A significantly longer than those of Ag–N. The metal– and metal separations of Ag(1) Ag(4) [2.937(3) A] Ag(2) Ag(3) [2.939(3) A] are also well below the sum of van der Waals radii of two silver atoms [19] and slightly longer than that found in metallic silver (2.89 indicating significant Ag–Ag interactions. The A), while the Ag(1) Ag(2) distance is 4.635 A, to suit Ag(3) Ag(4) distance is elongated to 7.720 A the conformation of the ligands. The distance and di hedral angle between the two phenyl plane are 4.434 A and 42.8°, respectively. The nitrate anion is un-coordinated in 4 and the This is different from closest Ag O distance is 2.828 A. 1, in which the nitrate anion bridge two silver ions in the monoatomic fashion. The lattice water molecules also form hydrogen bonds with each other [O(1w) O(2w) and with the uncoordinate nitrate anion 2.844 A] [O(1w) O(4a) 2.849 A]. 3.3. Photoluminescent properties At room temperature, compounds 1–4 exhibit photoluminescence in the solid state at 538, 528, 530 and 484 nm, respectively (Fig. 5). Lowing the temperature leads to an increase of the emission intensity. Exponential decays were observed at both room temperature and 77 K, giving lifetimes of 0.6 and 1.5 ls for 1, 0.2 and 1.9 ls for 2, 0.5 and 1.7 ls for 3 and 0.2 and 2.2 ls for 4, respectively. The transitions associated with the emissions of the silver(I) clusters 1–4 originate probably from a ligand-to-metal charge-transfer (LMCT) excited state, with mixing of a metal-centered (d–s/d–p) silver(I) state, according to
449
Fig. 5. Emission spectra of 1–4 and L in the solid state at room temperature.
similar assignments suggested for other luminescent polynuclear Ag(I) systems [27]. In DMF solution, 1–4 display very weak emission at 298 K. While at 77 K, 1 exhibits a band at 495 nm with two shoulders at 464 and 536 nm, 2 and 3 only display a weak band at about 540 nm, and 4 displays a band at 498 nm. The bands at 536 nm for 1, and 540 nm for 2 and 3 may also be assigned to LMCT transitions, with mixing of a metal-centered state. The bands at 495 nm for 1 and 498 nm for 4 can be assigned to a metal-centered state analogous to that of [Ag4 (P2 bpy)2 ](BF4 )4 (P2 -bpy ¼ 6,6-bis(diphenylphosphanyl)2,20 -bipyridyl) [28]. 4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. CCDC 198619–198622 for 1– 4, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223336-033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk). Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 20131020) and the Ministry of Education of China (No. 01134). References [1] F.A. Cotton, X.-J. Feng, M. Matusz, R. Poli, J. Am. Chem. Soc. 110 (1988) 7077. [2] (a) M.-L. Tong, X.-M. Chen, B.-H. Ye, L.-N. Ji, Angew. Chem., Int. Ed. Engl. 38 (1999) 2237; (b) R. Villanneau, A. Proust, F. Robert, P. Gouzerh, Chem. Commun. (1998) 1491. [3] C.-M. Che, M.-C. Tse, M.C.W. Chan, K.-K. Cheung, D.L. Phillips, K.-H. Leung, J. Am. Chem. Soc. 122 (2000) 2464.
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