Syntheses and Structures of Mononuclear, Dinuclear and Polynuclear

Dec 4, 2012 - substituted 1,10-phenanthroline derivatives (L1, FL1, L2) have been synthesized and characterized by 1H and 13C NMR, IR spectroscopy ...
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Syntheses and Structures of Mononuclear, Dinuclear and Polynuclear Silver(I) Complexes of 2‑Pyrazole-Substituted 1,10-Phenanthroline Ligands Peiju Yang,† Fengjuan Cui,† Xiao-Juan Yang,† and Biao Wu*,‡,# †

State Key Laboratory for Oxo Synthesis & Selective Oxidation, Lanzhou Institute of Chemical Physics, CAS, Lanzhou 730000, China College of Chemistry and Materials Science, Northwest University, Xi’an 710069, China # State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, 730000, China ‡

S Supporting Information *

ABSTRACT: A series of mononuclear, dinuclear and polynuclear silver(I) complexes (1−6) bearing 2-pyrazolesubstituted 1,10-phenanthroline derivatives (L1, FL1, L2) have been synthesized and characterized by 1H and 13C NMR, IR spectroscopy, elemental analysis, and single crystal X-ray diffraction. Reaction of L1 (L1 = 2-(3,5-dimethylpyrazol-1-yl)1,10-phenanthroline) with AgClO4 or AgBF4 afforded two dinuclear silver(I) complexes [Ag2(L1)2(CH3CN)2](ClO4)2 (1) and [Ag2(L1)2(CH3CN)2](BF4)2 (2), in which two [AgL1(CH3CN)]+ units are linked by Ag···Ag interaction (Ag···Ag separation: 3.208(2) and 3.248(1) Å, respectively). A one-dimensional polymer {[AgL1](BF4)}∞ (3) consisting of an infinite ···Ag···Ag···Ag··· chain (Ag···Ag separation: 3.059(1) Å), as well as a dinuclear complex [Ag2(ClO4)2(L1)2] (4) in which the perchlorate anions instead of solvents are involved in the metal coordination, have also been obtained. The mononuclear complex [Ag(FL1)2](BF4) (5) was synthesized from FL1 (FL1 = 2-(3,5-bis(trifluoromethyl)pyrazol-1-yl)-1,10phenanthroline) and AgBF4, while the dinuclear [Ag2(BF4)2(L2)2] (6) was isolated from L2 (L2 = 2-[N-(3-methyl-5phenylpyrazole)]-1,10-phenanthroline). The photoluminescence properties of the ligands and complexes 1−6 have been studied both in the solid state and in solution.

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thiomethyl-2,2′:6′,2″-terpyridine.5c Such compounds are potentially useful as nanowire materials. 1,10-Phenanthroline (phen) is a classical chelating ligand for transition metal ions. Phen derivatives with pendant arms of functional group(s) are of special importance for organic, inorganic and supramolecular chemistry because they can serve as versatile building blocks for the construction of complex systems with a variety of applications. A large number of 2mono- or 2,9-disubstituted 1,10-phenanthroline derivatives have been synthesized, and their coordination chemistry toward different metal ions has been extensively studied at the solid state and in solution.6 Recently, we have designed and synthesized some 2-pyrazole-substituted 1,10-phenanthroline ligands and their nickel(II) complexes as precatalysts for ethylene oligomerization/polymerization.7 In this paper, we report the syntheses and structures of a series of silver(I) complexes (1−6) with 2-pyrazole-substituted 1,10-phenanthroline ligands, (2-(3,5-dimethylpyrazol-1-yl)-1,10-phenanthroline

INTRODUCTION Silver(I) complexes have been of constant interest not only because of their rich coordination chemistry with a wide range of coordination numbers (from two to six) and geometries (e.g., linear, trigonal, tetrahedral, and the less common trigonal pyramidal and octahedral), but also due to their extensive uses in catalysis, medicine, and luminescent materials, etc.1 Moreover, in silver(I) complexes, the main coordination bonds between Ag and X-donor ligands (X = C, N, S, O) are often supplemented by weak contacts such as Ag···Ag, Ag···π, and π···π interactions, which can result in interesting structures and potentially useful chemical and physical properties.2 By using bridging multidentate ligands, numerous silver coordination polymers have been constructed, many of which feature definite Ag···Ag interactions.3,4 However, polynuclear silver complexes with infinite metallic backbones are still rare.5 A onedimensional polymer consisting of an infinite Ag2···Ag1···Ag2···Ag1 chain has been reported, in which every two adjacent silver ions are bridged by a 2,6-bis(5-methyl-1H-pyrazol-3yl)pyridine ligand.5a Carboxylato-supported one-dimensional (1D) infinite (Ag1···Ag2···Ag2···Ag1) zigzag chains are also known,5b as well as some silver chains with the ligand 4′© 2012 American Chemical Society

Received: September 14, 2012 Revised: November 14, 2012 Published: December 4, 2012 186

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Scheme 1. Synthesis of the Silver Complexes 1−6

(L1), 2-(3,5-ditrifluoromethylpyrazol-1-yl)-1,10-phenanthroline (FL1), and 2-[N-(3-methyl-5-phenylpyrazole)]-1,10-phenanthroline (L2)) (Scheme 1). Four dinuclear complexes [Ag2(L1)2(CH3CN)2](ClO4)2 (1), [Ag2(L1)2(CH3CN)2](BF4)2 (2), [Ag2(ClO4)2(L1)2] (4), and [Ag2(BF4)2(L2)2] (6), one mononuclear species [Ag(FL1)2](BF4) (5), as well as a novel 1D polymer {[AgL1](BF4)}∞ (3) consisting of an infinite Ag···Ag···Ag chain have been obtained. The spectroscopic properties of these complexes have also been investigated.

complexes 1 and 2 were isolated. Moreover, for the same ligand L1 and silver salts, when the solvent system was changed to CH3OH/CH2Cl2 (v/v 1:1), the polynuclear complex {[AgL1](BF4)}∞ (3) and dinuclear complex [Ag2(ClO4)2(L1)2] (4) were obtained. When the ligands FL1 and L2 were used, a mononuclear complex [Ag(FL1)2](BF4) (5) and a dinuclear species [Ag2(BF4)2(L2)2] (6) were synthesized. These compounds were identified by IR, 1H and 13C NMR spectroscopy and elemental analysis. Crystal Structures. [Ag2(L1)2(CH3CN)2](ClO4)2 (1) and [Ag2(L1)2(CH3CN)2](BF4)2 (2). The two complexes are isomorphous (space group C2/c), containing a C2-related dicationic Ag···Ag dimeric motif with Ag−Ag distance of 3.208(2) Å in 1 and 3.248(1) Å in 2. These values are between that (2.88 Å) assigned for an Ag−Ag bond8 and the sum of their van-der-Waals radii (3.44 Å), indicating that there is some metal−metal interaction.9 The structure is similar to the disilver(I) bathophenanthroline2d (Ag···Ag distance: 3.386 Å) and dipalladium(II) phenanthroline10 complexes. The Ag atoms adopt a distorted tetragonal-pyramidal geometry (Figures 1, 2 and Figure S1, Supporting Information). The coordination environment comprises two nitrogen atoms N(1) and N(2) from the phen backbone, one nitrogen atom N(4) from the pyrazole moiety, one nitrogen atom N(5) from CH3CN, and the other Ag atom. The Ag−Npyrazole (1, 2.346(8) Å; 2, 2.374(5) Å) and Ag−Nphen (1, 2.484(6) and 2.362(7) Å; 2, 2.499(5) and 2.368(4) Å) bond lengths are comparable to the Ag−N bonds in the silver(I) complex [Ag(tsac)(phen)]n, (2.324(3) and 2.364(3) Å; tsac = thiosaccharinate anion),11 but are obviously longer than in other complexes such as Ag2(bp)2(OTf)2, bp = bathophenanthroline (2.248(3)− 2.352(3) Å)2d and [Ag2{μ-Ph2PN(Pri)PPh2}(1,10-phen)2](NO3)2 (2.271(6) and 2.314(2) Å).12 The Ag−N(CH3CN) bond distances of 2.163(1) Å (in 1) and 2.198(7) Å (in 2) are obviously shorter than in some CH3CN-coordinating complexes.13,14 In the complexes, the ligand shows a tridentate chelating fashion, and the phen and pyrazole planes are nearly coplanar (dihedral angles 17.8° in 1 and 17.3° in 2). The three N donors

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RESULTS AND DISCUSSION Synthesis. The ligands L1 and L2 were prepared by the reaction of acetylacetone or benzoylacetone with 2-hydrazine1,10-phenanthroline or 2-hydrazine-9-phenyl-1,10-phenanthroline, respectively, in dry methanol in the presence of a few drops of glacial acetic acid under reflux.7 However, under the same conditions, the reaction of 2-hydrazine-1,10-phenanthroline and 1,1,1,5,5,5-hexafluoro-pentan-2,4-dione did not proceed, and the desired trifluoromethyl-substituted product, 2(3,5-bis(trifluoromethyl)pyrazol-1-yl)-1,10-phenanthroline (FL1), was synthesized by addition of a few drops of concentrated sulfuric acid. The silver(I) complexes (1−6) were prepared by treatment of equimolar AgBF4 or AgClO4 with the ligands in CH3CN/ CH2Cl2 or CH3OH/CH2Cl2 (v/v 1:1) as pale yellow block crystals, which are unstable on exposure to light in both solution and the solid state and should be stored in the dark. During the reactions, a precipitate formed quickly by mixing the CH2Cl2 solution of ligand and the CH3CN or CH3OH solution of silver salt. Thus the single crystals were grown by slow diffusion of the two solutions. In the dinuclear complexes [Ag2(L1)2(CH3CN)2](ClO4)2 (1) and [Ag2(L1)2(CH3CN)2](BF4)2 (2), the five-coordinate arrangement around the silver atom is completed by a tridentate ligand, a CH3CN molecule, and the other silver atom. We have attempted to replace the coordinating CH3CN molecule by imidazole or triphenylphosphine, but no new compounds were obtained and only the 187

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dimeric structure are nearly antiparallel, forming a pair of symmetry-related π···π stacking interactions between the pyrazole group and the phen plane. The antiparallel (instead of parallel) arrangement is probably adopted to avoid the steric repulsion of the methyl groups on the pyrazole ring. Notably, the two coordinated CH3CN molecules are oriented in a nearly overlapping way (with an angle of 9.8° in 1 and 10.4° in 2), which is required by the π−π stacking interactions of the aromatic rings. The two stacking phen and pyrazole planes are almost parallel (dihedral angle 1.5° in complex 1 and 2.8° in complex 2), with centroid−centroid distances of 3.53 and 3.53 Å, respectively.15 The ClO4− and BF4− ions function as counteranions and do not coordinate to the silver(I) ion. Additionally, each [Ag2(L1)2(CH3CN)2]2+ unit links two adjacent dimeric molecules by weak intermolecular π-stacking interactions between the pyrazole and the phenanthroline moieties (dihedral angle 16.5° (1) and 15.4° (2), centroid− centroid distance 4.05 Å (1) and 4.03 Å (2), and vertical displacements between ring centroids 2.20 and 2.22 Å (1) and 2.08 and 2.14 Å (2), respectively),15 resulting in a linear chain along the a axis (Figures S2 and S3). The π-stacking interactions are weaker than those between the phenyl and the phen planes in the analogous complex [Ag2{l-iPrN(PPh2)2}(1,10-phen)2](NO3)2 (centroid−centroid distance 3.64 Å).12 Moreover, in complex 1, each [Ag2(L1)2(CH3CN)2]2+ unit further links six neighbors by weak C−H···O hydrogen bonds between the ClO4− counterion and the ligand (Figure S4). {[AgL1](BF4)}∞ (3). Compound 3 was prepared through slow diffusion of a solution of ligand L1 in CH2Cl2 and a solution of AgBF4 in CH3OH. It shows a novel polymeric structure, wherein the repeating unit consists of one AgI ion, one L1 ligand and one BF4− counteranion (Figure 3a). In contrast to the tridentate chelating manner in 1 and 2, the ligand in 3 uses the two phenanthroline N atoms to coordinate with one Ag atom, while the pyrazole N atom is coordinated to another Ag atom. Thus the ligand serves as a bridge to link two silver centers. The phen plane and pyrazole ring within a ligand are slightly twisted, with a larger dihedral angle of 21.0° than in 1 and 2. Each Ag atom is six-coordinated by two N atoms of a phen moiety, one pyrazole N atom and one phen N atom of another ligand, as well as two neighboring Ag atoms. The

Figure 1. Molecular structure of 1. Selected bond distances (Å) and angles (°): Ag−Aga 3.208(2), Ag−N1 2.484(6), Ag−N2 2.362(7), Ag−N4 2.346(8), Ag−N5 2.163(11), N5−Ag−N4 122.9(3), N5− Ag−N2 167.7(3), N4−Ag−N2 67.8(3), N5−Ag−N1 101.0(3), N4− Ag−N1 134.9(3), N2−Ag−N1 67.5(2), N5−Ag−Aga 92.7(2), N4− Ag−Aga 117.11(18), N2−Ag−Aga 86.66(13), N1−Ag−Aga 65.68(14). Symmetry code: a1 − x, y, 0.5 − z.

Figure 2. Molecular structure of 2. Selected bond distances (Å) and angles (°): Ag−Aga 3.248(1), Ag−N1 2.499(5), Ag−N2 2.368(4), Ag−N4 2.374(5), Ag−N5 2.198(7), N5−Ag−N4 121.5(2), N5−Ag− N2 168.7(1), N4−Ag−N2 68.2(2), N5−Ag−N1 101.6(2), N4−Ag− N1 135.8(2), N2−Ag−N1 68.0(1), N5−Ag−Aga 93.3(1), N4−Ag− Aga 116.9(1), N2−Ag−Aga 86.4(1), N1−Ag−Aga 65.6(1). Symmetry code: a1 − x, y, 0.5 − z.

and the CH3CN molecule define the basal plane of the tetragonal−pyramidal coordination sphere, while the other Ag atom occupies the apical position. The two ligands in the

Figure 3. Crystal structure of 3. (a) The coordination sphere of the Ag atom; (b) part of the infinite silver wire in a homochiral helix in 3. Selected bond distances (Å) and angles (°): Ag−Aga 3.059(1), Ag−Agb 3.059(1), Ag−N1 2.302(6), Ag−N2 2.560(6), Ag−N4a 2.422(6), Ag−N2a 2.869(1), N4−Ag−N1 163.6(2), N2−Ag−N1 67.1(2), N4a−Ag−N2 127.3(2), N1−Ag−Aga 80.9(2), N4a−Ag−Aga 99.2(2), N2−Ag−Aga 111.3(2), N1−Ag− Aga 100.3(2), N2a−Ag−Aga 60.7(1), N4a−Ag−Aga 82.3(2), N4−Ag1−Ag1 82.27(15), Aga−Ag−Agb 170.9(0), N2a−Ag−N4a 69.47, N2−Ag−Agb 60.7(2). Symmetry codes: ay, −x + y, 0.16667 + z; bx − y, x, −0.16667 + z. 188

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It should be pointed out that the dihedral angle between the two phen planes within one dimer is quite small (15.6°), but no strong π···π stacking interactions were formed in compound 4 due to the slipperiness of the planes, which is different from the head-to-tail stacking in the complexes 1 and 2. The two pyrazole rings are not stacking either. The Ag−O bond length (2.64 Å) to the ClO4− ion in complex 4 is shorter than that in the compound [Ag2(1,2-bImb)2](ClO4)2 (1,2-bImb = 1,2bis(imidazolylmethyl)benzene, 2.992 Å)17 and is similar to the complex [Ag2(napy)2](ClO4) (2.64 Å).18 However, in the dinuclear complex [Ag2(LmTol)2][ClO4] (LmTol = N,N-bidentate chelating pyrazolyl-pyridine unit), the ClO4− anions do not coordinate to the Ag atom.19 Each Ag2(ClO4)2(L1)2 unit links two adjacent molecules by C−H···O hydrogen bonding between the oxygen atom of ClO4− and a CH of the phen moiety, resulting in a zigzag chain along the a axis (Figure S6).

coordination geometry is a severely distorted octahedron with two very acute bond angles of 51.1 and 60.6°, which may be caused by the formation of the spiral silver wire. Unlike 1 and 2, there are no coordinated solvents in this complex. The most interesting structural feature of 3 is that it crystallizes in a chiral space group P6(5) with spontaneous resolution of chiral helices. This homochirality may result from the solid-state packing in which the infinite helical motifs of the stoichiometry [AgL]n were assembled by molecules of the same configuration (P-helices, Figure 3b and Figure S5). Similar crystallization of homochiral helices from a racemate was also discussed in the literature.16 In complex 3, a nearly linear silver wire can be identified with Ag···Ag···Ag angles of 170.9(0)° (Figure 3b). All of the (symmetry-related) Ag atoms are equivalent with identical Ag···Ag distances (3.059(1) Å), which is similar to the compound [AgL]n(PF6)n (L = 4′-thiomethyl2,2′:6′,2″-terpyridine).5c However, some other silver chains are composed of different AgL units and different Ag···Ag distances. For example, two kinds of Ag···Ag interactions (2.889(1) and 2.893(1) Å) were observed in the compound {[Ag2(H2L)2](NO3)2·H2O}n (L = 2,6-bis(5-methyl-1H-pyrazol-3-yl)pyridine),5a and there are three kinds of Ag···Ag interactions in [Ag3(BTC)(APYM)2]n (BTC = benzene-1,3,5tricarboxylate, APYM = 2-aminopyrimidine), with Ag···Ag distances of 2.786(2), 2.809(2), and 3.176(2) Å.5b In the extended structure of 3, every [AgL] unit also interacts with two neighbors through weak intermolecular π-stacking interactions between the pyrazole and phen planes (dihedral angle 15.6°, centroid−centroid distance 3.70 Å, and vertical displacements between ring centroids 1.29 and 1.49 Å).15 [Ag2(ClO4)2(L1)2] (4). The dinuclear complex 4 was obtained in CH3OH/CH2Cl2 when altering the anion from BF4− (for 3) to ClO4−. Instead of including two coordinated CH3CN molecules and free counteranions in 1 and 2, complex 4 contains two coordinated ClO4− anions in the coordination sphere of Ag atom. The structure also distinguishes from the polynuclear complex 3 via interrupting the infinite silver chain by the coordinated ClO4− anions. Moreover, the Ag−Ag distance of 2.994(1) Å in 4 is significantly shorter than those in complexes 1−3 (3.208(2), 3.248(1), and 3.059(1) Å, respectively). Each Ag atom resides in a five-coordinate, distorted trigonal bipyramidal geometry completed by the other silver atom, three nitrogen atoms from two ligands and one oxygen atom of ClO4−. These results clearly demonstrate the rich coordination chemistry (such as the coordination number and geometry, and the aggregation mode) of silver upon slight tuning of the solvent and anion. More interestingly, although they are all AgI···AgI dimeric structures, the coordination mode of the ligand in 4 is significantly different from that in 1 and 2. As mentioned above, in 1 and 2 the ligand assumes a nearly planar conformation with the three N donor atoms chelating one Ag atom, which sits in a tetragonal pyramidal geometry. However, in the case of 4, the silver(I) ion is in a trigonal bipyramidal environment and is coordinated by the phenanthroline moiety of one ligand and the pyrazole nitrogen atom of the other ligand. To facilitate such a coordination mode, the pyrazole ring is greatly twisted away from the phen plane with a dihedral angle of 56.1°, which is much larger than that in complex 3, although in both cases the pyrazole group coordinates to another silver atom. Therefore, the two ligands are arranged in a cross-linking fashion, and the two AgI ions are pulled closer (2.994(1) Å).

Figure 4. Molecular structure of 4. Selected bond distances (Å) and angles (°): Ag−Aga 2.994(1), Ag−N1 2.308(2), Ag−N2 2.411(2), Ag−N4a 2.203(2), N4a−Ag−N1 139.3(1), N2−Ag−N1 71.4(1), N4a−Ag−N2 136.3(1), N1−Ag−Aga 95.8(1), N4a−Ag−Aga 78.9(1), N2−Ag−Aga 65.2(1). Symmetry code: a2−x, y, 0.5−z.

[Ag(FL1)2](BF4) (5). Silver is particularly versatile in its coordination number and geometry when varying the metal-toligand ratio, counteranion, and reaction conditions, which has been well documented in a number of reviews.20 Here, by finetuning the ligand substituents, significantly different structures were obtained. When the ligand FL1, in which the two methyl groups on the pyrazole ring in L1 were replaced by trifluoromethyl (CF3) groups, was reacted with AgBF4 in mixed solvent system CH3OH/CH2Cl2, the mononuclear complex [Ag(FL1)2](BF4) (5) was obtained (Figure 5). Complex 5 has a metal-to-ligand ratio of 1:2, which is different from the 1:1 complexes of 1−4. There are two independent halves of the [Ag(FL1)2](BF4) molecule in an asymmetric unit, and their corresponding bond parameters are very close (Figure S7). The Ag atom is four-coordinated by two phen moieties in a seesaw geometry, with a τ4 value of 0.54 (the value of τ4 ranges from 1.00 for a perfect tetrahedral geometry to 0 for a perfect square planar geometry, while intermediate structures, including trigonal-pyramidal and seesaw, fall within the range of 0−1.00).21 Hanton et al.22 summarized a series of square planar Ag(I) complexes. This four-coordinate mode is typical for bipy or phen silver complexes, such as bis(5,5′-dicyano-2,2′bipyridine)silver(I) tetrafluoroborate, 23 [Ag(tmbp) 2 ]BF 4 (tmbp = 4,4′,6,6′-tetramethyl-2,2′-bipyridine),24 and [AgL2]BF4 (L = phendione).25 Notably, in contrast to the compounds 189

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chelate one silver(I) ion and the pyrazole nitrogen to the other silver(I) ion, as in the case of complex 4. In both complexes, the anions (ClO4− or BF4−) coordinate weakly to the Ag atoms, which is similar to the complex {[Ag2(μ3-tp)2](PF6)2·6H2O}n (tp = 1,2,4-triazolo[1,5-a]pyrimidine) with a weak Ag···F contact to a PF6− anion.2k In contrast, it is different from complexes 1−3 and 5, wherein the anions serve as charge balancing counterions. The dihedral angles between phen and pyrazole planes in the two ligands are slightly different (61.2° and 56.0°), and both are comparable to those in complex 4 (56.1°). The Ag···Ag interaction of 3.009(1) Å is slightly longer than in 4 (2.994(1) Å) but is shorter than in 1 (3.208(2) Å) and 2 (3.248(1) Å). The slightly longer AgI···AgI distance in 6 compared to 4 could be attributed to the steric effects of the bulkier ligand substituents in L2 than L1. The dihedral angles between phen and the 9-phenyl planes are 35.9° and 32.7°. The two phen planes in the dimer are nearly parallel (dihedral angle 11.2°), which is similar to compounds 1 and 2. There is a significant intramolecular π-stacking interaction between the aromatic rings of phen moieties (Figure 6, dihedral angle 7.2°, centroid− centroid distance 3.60 Å, and vertical displacements between ring centroids 0.19 and 0.27 Å).15 In this work, we have obtained six remarkably different (mononuclear, dinuclear and polynuclear) silver complexes (1−6) under various conditions, such as different solvent systems CH3CN/CH2Cl2 or CH3OH/CH2Cl2, different counteranion BF4− or ClO4−, or ligand substituents. The coordination modes of the ligands are significantly different in the complexes. In the dinuclear complexes 1 and 2 the ligand functions as a tridentate chelating ligand, and the Ag atoms adopt a distorted square-pyramidal coordination geometry. In contrast, the ligand in 3 employs the two phenanthroline N atoms to coordinate with one Ag atom, while the pyrazole N atom coordinates to another Ag atom. Thus the ligand serves as a bridge to link two silver centers and an infinite homochiral spiral chain motif was formed. In complex 4, the silver(I) ion is coordinated by the phen moiety of one ligand and the pyrazole nitrogen atom of the other ligand, and a perchlorate ion is also coordinated. When the two methyl groups on the pyrazole ring in L1 were replaced by CF3 groups, the mononuclear complex [Ag(FL1)2](BF4) (5) was obtained, which shows a metal-toligand ratio of 1:2 different from the 1:1 complexes 1−4. Finally, when the 2,9-positions of 1,10-phenanthroline were substituted by a phenyl and a 3-methyl-5-phenylpyrazole group, respectively, the reaction with AgBF4 in CH3OH/CH2Cl2 (1:1 v:v) gave the dinuclear complex Ag2(BF4)2(L2)2, which shows a similar structure to complex 4 (with the ligand L1). Spectroscopic Properties. The UV−vis spectra of the ligands and Ag complexes were measured in DMSO. The ligands display typical ligand-centered π−π* transitions at 215 and 300 nm for L1 and L2, and at 215 and 270 nm for FL1, respectively (Figure 7). Upon coordination with the silver(I) ion, there is a slight increase of the absorption intensity with a minor bathochromic shift (Δλ = 0.5−2 nm). The solid-state emission spectra of the ligands and complexes 1−6 have been studied both in the solid state and in solution at room temperature. In the solid-state spectra (Figure S8), L1 shows two emission bands at 460 and 487 nm with nearly the same intensity, as well as a less intensive shoulder at 520 nm and a very weak emission at 642 nm upon excitation at 420 nm. F 1 L shows emission bands at 438 and 460 nm, with less intensive shoulders and a very weak emission band at 625 nm

Figure 5. Molecular structure of 5. Selected bond distances (Å) and angles (°): Ag1−N1 2.303(3), Ag1−N2 2.434(3), Ag1−N5 2.298(3), Ag1−N6 2.436(3), N5−Ag1−N1 128.16(12), N5−Ag1−N2 138.88(11), N1−Ag1−N2 71.68(12), N5−Ag1−N6 71.39(11), N1− Ag1−N6 145.22(11), N2−Ag1−N6 114.42(10).

1−4, the FL1 molecule acts only as a bidentate chelating ligand by using the phen N donors, while the pyrazole nitrogen atom is not involved in the coordination to the metal ion in complex 5. The dihedral angles of pyrazole rings and the phen plane are 34.4° and 43.2°, which are much larger than that in 1 (17.8°), 2 (17.3°), and 3 (21.0°) but are smaller than that (56.1°) in complex 4. [Ag2(BF4)2(L2)2] (6). The ligand L2 was also used to examine the effect of the substituents on the structure of the silver complexes. In L2, the 2,9-positions of 1,10-phenanthroline are substituted by a phenyl and 3-methyl-5-phenylpyrazole group, respectively. Treatment of L2 with AgBF4 in CH3OH/CH2Cl2 (1:1 v:v) gave the dinuclear complex [Ag2(BF4)2(L2)2]. In the complex (Figure 6), the silver center adopts a five-coordinate, trigonal bipyramidal geometry completed by the other Ag atom, three nitrogen atoms from two different ligands, and one F atom of a BF4− ion. The ligand uses the phen moiety to

Figure 6. Molecular structure of 6. Selected bond distances (Å) and angles (°): Ag1−Ag2 3.009(1), Ag1−N4 2.209(4), Ag1−N6 2.367(4), Ag1−N5 2.374(4), Ag2−N8 2.196(4), Ag2−N2 2.341 (4), Ag2−N1 2.365(4), N6−Ag1−Ag2 65.77(10), N5−Ag1−Ag2 98.16(10), N8− Ag2−Ag1 75.53(12), N2−Ag2−Ag1 66.54(9), N1−Ag2−Ag1 99.10(10). 190

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Figure 7. Absorption spectra of ligands L1, FL1 and L2 and complexes 1−6 in DMSO (5 × 10−5 mol/L) at room temperature.

Figure 8. (a−c) Fluorescence emission spectra of ligands L1, FL1 and L2 (in CH2Cl2) and complexes 1−6 (in CH3CN for 1, 2 and CH3OH for 3− 6), [M] = 4 × 10−6 mol/L.

upon excitation at 400 nm. The ligand L2 emits at 434 and 459 nm and shows a very weak emission band at 620 nm upon excitation at 404 nm. These emission peaks are assignable to the intraligand π−π* transitions. For the complexes, multiple emission bands were observed at 470, 510, 537, and 644 nm (λex = 420 nm) for 1−4, at 439, 468, 494, 516, and 625 nm (λex = 400 nm) for 5, and at 494, 520, 629 nm (λex = 404 nm) for compound 6. The emission bands are significantly red-shifted (Δλ = 10−20 nm) and largely quenched compared to the corresponding ligands, which can be attributed to the heavy atom effect of Ag.26 The solution photoluminescent properties of the complexes 1−6 were also studied in CH3CN (for 1, 2) or CH3OH (for 3− 6) at room temperature (Figure 8). The fluorescence lifetimes (3.83, 3.82, 3.63, 3.68, and 3.73 ns, respectively) of the complexes 1−4 and 6 that contain Ag···Ag interactions are significantly longer than the mononuclear complex 5 (1.10 ns). The λmax and the shapes of emission bands of complexes 1−4 are almost the same (λmax = 376, 362 nm) upon excitation at 300 nm, while complex 5 (λmax = 343, 366, 383 nm) is blueshifted by ∼20 nm compared to complexes 1−4 upon excitation at 275 nm. Complex 6 (λmax = 364, 386 nm) is red-shifted by ∼10 nm under excitation at 300 nm. These emission peaks are attributable to the intraligand π−π* transitions.

significant quenching of the emission of the corresponding ligands (450−600 nm), and the fluorescence lifetimes of the dinuclear (or polynuclear) 1−4 and 6 (3.63−3.73 ns, respectively) are significantly longer than the mononuclear complex 5 (1.10 ns).

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EXPERIMENTAL SECTION

General Procedures. 1,10-Phenanthroline, bromobenzene, acetylacetone, 1,1,1,5,5,5-hexafluoro-pentan-2,4-dione, the silver(I) salts, and other common chemicals were commercially available and were used without further purification. Benzoylacetone27 was synthesized according to literature procedures. 2-Phenyl-1,10-phenanthroline, 2hydrazine-1,10-phenanthroline, 2-[N-(3,5-dimethylpyrazole)]-1,10phenanthroline (L1), and 2-[N-(3-methyl-5-phenylpyrazole)]-1,10phenanthroline (L2) were prepared as described previously.7 The 2(3,5-bis(trifluoromethyl)pyrazol-1-yl)-1,10-phenanthroline (FL1) was synthesized using modified literature procedures reported for L1. 1H and 13C NMR spectra were obtained in DMSO-d6 on a Mercury plus400 spectrometer with TMS as the internal standard. IR spectra were recorded as KBr pellets with an HP5890 II GC/NEXUS-870 spectrometer. ESI-MS spectra were measured on a Waters ZQ 4000 instrument. Element analyses were performed with an Elementar VarioEL instrument. Fluorescence spectra were recorded at room temperature (Hitachi F-7000 spectrophotometer). Fluorescence lifetimes were measured on a Horiba Jobin-Yvon FluoroMax-4 spectrophotometer. Synthesis of the Ligand FL1. The new ligand FL1 was prepared by slightly modified procedures. A mixture of 2-hydrazine-1,10-phenanthroline (0.63 g, 3.0 mmol) and 1,1,1,5,5,5-hexafluoro-pentan-2,4dione (0.75 g, 3.6 mmol) was refluxed in dry methanol (15 mL) containing a few drops of conc. H2SO4 for 3 h. The solvent was removed and the residue was recrystallized from chloroform/activated charcoal to give the product FL1.

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CONCLUSION The synthesis and structures of a series of silver(I) complexes with 2-pyrazole-substituted 1,10-phenanthroline (L1, FL1, L2) ligands are reported. The coordination number and geometry of the silver(I) complexes vary significantly upon changing the counteranion, solvent and ligand substituents, by which a novel polynuclear ···Ag···Ag···Ag··· chain and several dinuclear complexes with Ag···Ag interactions have been obtained. The results clearly demonstrate the rich coordination chemistry of Ag, which often includes the coordination of solvents and anions, as well as formation of weak contacts such as Ag···Ag and π−π interactions. The fluorescence properties of these complexes have been investigated. Complexes 1−6 show 191

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Article

Table 1. Crystallographic Data for Complexes 1−6 formula fw crystal system space group a /Å b /Å c /Å α /° β /° γ /° V /Å3 Z Dcalc /g cm−3 F(000) μ /mm−1 θ range /° reflns collected (Rint) independent reflns observed reflns [I > 2σ(I)] R1, wR2 [I > 2σ(I)] R1, wR2 (all data) GOF (F2) Flack parameter30

1

2

3

4

5

6

C19N5H17AgClO4 522.70 monoclinic C2/c 23.368(14) 13.206(6) 14.201(7) 90 114.663(15) 90 3983(4) 8 1.743 2096 1.184 1.82−25.05 9012 (0.1151) 3461 1420 0.0660, 0.1719 0.1231, 0.1909 0.837

C19N5H17AgBF4 510.06 monoclinic C2/c 23.121(5) 13.145(3) 14.197(3) 90 113.583(3) 90 3954.5(15) 8 1.713 2032 1.072 1.82−25.65 13414 (0.0425) 3719 2117 0.0456, 0.1304 0.0930, 0.1652 0.977

C17N4H14AgBF4 469.00 hexagonal P6(5) 12.8394(19) 12.8394(19) 18.121(6) 90 90 120 2587.0(10) 6 1.806 1392 1.219 1.83−25.98 18791 (0.0635) 2990 2701 0.0428, 0.1135 0.0471, 0.1150 1.052 0.01(5)

C17N4H14AgClO4 481.64 monoclinic C2/c 20.0242(18) 15.1045(14) 15.580(2) 90 125.389(1) 90 3841.7(8) 8 1.665 1920 1.218 1.90−29.85 12761 (0.0253) 5091 4100 0.0324, 0.0915 0.0431, 0.0982 1.017

C68N16H31Ag2B2F32 1917.45 monoclinic P2(1)/n 12.8452(8) 42.980(3) 13.2162(8) 90 107.040(1) 90 6976.2(7) 4 1.826 3772 0.705 1.68−28.29 44373 (0.0309) 17025 10739 0.0591, 0.1642 0.1017, 0.1847 1.145

C56N8H40Ag2B2F8 1214.32 orthorhombic Pbcn 31.980(5) 15.107(2) 23.655(3) 90 90 90 11428(3) 8 1.412 4864 0.754 1.72−24.93 71539 (0.0478) 9904 6933 0.0541, 0.1410 0.0790, 0.1495 1.156

2-(3,5-Bis(trifluoromethyl)pyrazol-1-yl)-1,10-phenanthroline (FL1). White solid (0.85 g, 68%). m.p.: 132−134 °C. ESI-MS: m/z 383, [M + H]+. 1H NMR (400 MHz, CDCl3, δ/ppm): 9.21 (dd, J = 2.0, 2.4 Hz, 1H, H-9), 8.49 (d, J = 8.4 Hz, 1H, H-7), 8.28 (dd, J = 1.6, 2.0 Hz, 1H, H-8), 8.08 (d, J = 8.8 Hz, 1H, H-4), 7.90 (dd, J = 8.8, 4.4 Hz, 2H, H-5, H-6), 7.67 (dd, J = 4.4, 3.6 Hz, 1H, H-3), 7.20 (s, 1H, pyrazoleH); 13C NMR (100 MHz, CDCl3, δ/ppm): 151.0 (C-2), 149.3 (C12), 145.7 (C-9), 144.9 (C-5′), 139.5 (C-3′), 136.0 (C-4, C-7), 129.3 (C-13, C-14), 128.8 (C-11), 128.2 (C-5, C-6), 125.7 (C-8), 123.7 (CF3), 117.7 (C-3), 108.9 (C-4′); IR (KBr, ν/cm−1): 2919 (w, C−H), 1594 (w, CN), 1559 (m, CC), 1506 (m, CC), 1451(w, C C), 1299, 1239, 1134 (s, C−F), 1093, 847 (m, C−H), 736 (m, C−F); Anal. Calcd for C17H8N4F6 (382): C, 74.43; H, 5.14; N, 20.42. Found: C, 74.31; H, 5.19; N, 20.48%. Synthesis of the Complexes [Ag2(L1)2(CH3CN)2](ClO4)2 (1) and [Ag2(L1)2(CH3CN)2](BF4)2 (2). A solution of ligand L1 (0.055 g, 0.2 mmol) in CH2Cl2 was added to a stirred solution of AgClO4 (0.041 g, 0.2 mmol) or AgBF4 (0.039 g, 0.2 mmol) in CH3CN (2 mL). The pale yellow solution thus formed was evaporated to 2 mL, and a pale yellow solid was obtained. The solid was collected, washed with CH3CN, CH2Cl2 and diethyl ether, and dried in a vacuum. Both complexes 1 and 2 were prepared in high yield in this manner. [Ag2(L1)2(CH3CN)2](ClO4)2 (1). (0.093 g, 89%), m.p.: > 300 °C; 1H NMR (400 MHz, DMSO-d6, δ/ppm): 8.93 (d, J = 8.4 Hz, 1H, H-9), 8.63 (dd, J = 1.2, 6.8 Hz, 1H, H-7), 8.53 (d, J = 3.2 Hz, 1H, H-4), 8.30 (d, J = 8.8 Hz, 1H, H-8), 8.19 (d, J = 8.8 Hz, 1H, H-6), 8.13 (d, J = 8.8 Hz, 1H, H-5), 7.76 (dd, J = 3.6, 4.4 Hz, 1H, H-3), 6.11 (s, 1H, pyrazole-H), 2.53 (s, 3H, CH3), 2.08 (s, 3H, CH3), 1.59 (s, 3H, CH3); 13 C NMR (100 MHz, DMSO-d6, δ/ppm): 150.0 (C-2), 149.9 (C-12), 147.1 (C-9), 141.5 (C-5′), 140.1 (C-3′), 139.7 (C-4), 139.6 (C-7), 137.1 (C-11), 127.9, 126.8 (C-5), 126.4, (C-6), 125.3, 123.7 (C-8), 119.2 (C-3), 116.9 (CN), 107.9 (C-4′), 11.8 (CH3), 11.3 (CH3); IR (KBr, ν/cm−1): 3059, 2965, 2920 (w, C−H), 1609 (m, CN), 1577 (m, CC), 1504 (s, CC), 1453 (m, CC), 1354 (s, C−H), 1085 (s, ClO4), 847 (m, C−H), 626 (m, C−H); Anal. Calcd for C19N5H17AgClO4 (522.37): C, 43.66; H, 3.28; N, 13.40. Found: C, 43.76; H, 3.11; N, 12.53%. [Ag2(L1)2(CH3CN)2](BF4)2 (2). (0.090 g, 88%), m.p.: > 300 °C; 1H NMR (400 MHz, DMSO-d6, δ/ppm): 8.93 (d, J = 8.8 Hz, 1H, H-9),

8.61 (dd, J = 1.2, 7.2 Hz, 1H, H-7), 8.47 (d, J = 3.6 Hz, 1H, H-4), 8.31 (d, J = 8.4 Hz, 1H, H-8), 8.17 (d, J = 8.8 Hz, 1H, H-6), 8.12 (d, J = 8.8 Hz, 1H, H-5), 7.76 (dd, J = 4.4, 4.8 Hz, 1H, H-3), 6.12 (s, 1H, pyrazole-H), 2.51 (s, 3H, CH3), 2.08 (s, 3H, CH3), 1.55 (s, 3H, CH3); 13 C NMR (100 MHz, DMSO-d6, δ/ppm): 150.0 (C-2), 149.9 (C-12), 147.1 (C-9), 141.6 (C-5′), 140.2 (C-3′), 139.7 (C-4), 139.4 (C-7), 137.2 (C-11), 127.8, 126.9 (C-5), 126.5, (C-6), 125.3, 123.7 (C-8), 119.7 (C-3), 117.0 (CN), 107.7 (C-4′), 11.7 (CH3), 11.1 (CH3); IR (KBr, ν/cm−1): 3068, 2921 (w, C−H), 1613 (w, CN), 1581 (m, CC), 1560 (m, CC), 1506 (s, CC), 1454 (m, CC), 1354 (s, C−H), 1056, 857, 736 (m, C−H); Anal. Calcd for C19N5H17AgBF4 (509.68): C, 44.74; H, 3.36; N, 13.73. Found: C, 44.44; H, 3.15; N, 13.58%. Synthesis of the Complexes 3−6. A solution of ligand (L1 0.055 g, L2 0.082 g, 0.2 mmol, FL1 0.153 g, 0.4 mmol) in CH2Cl2 was added to a stirred solution of AgClO4 (0.041 g, 0.2 mmol) or AgBF4 (0.039 g, 0.2 mmol) in CH3OH (2 mL). A pale yellow solution was formed, the volume was reduced to 2 mL and pale yellow solid was isolated. {[AgL1](BF4)}∞ (3). (0.083 g, 88%), m.p.: > 300 °C; 1H NMR (400 MHz, DMSO-d6, δ/ppm): 8.93 (d, J = 8.4 Hz, 1H, H-9), 8.63 (dd, J = 1.2, 6.8 Hz, 1H, H-7), 8.48 (d, J = 3.6 Hz, 1H, H-4), 8.31 (d, J = 8.4 Hz, 1H, H-8), 8.18 (d, J = 8.8 Hz, 1H, H-6), 8.12 (d, J = 8.8 Hz, 1H, H-5), 7.77 (dd, J = 4.4, 4.8 Hz, 1H, H-3), 6.11 (s, 1H, pyrazole-H), 2.51 (s, 3H, CH3), 1.55 (s, 3H, CH3); 13C NMR (100 MHz, DMSOd6, δ/ppm): 151.1 (C-2), 151.0 (C-12), 148.2 (C-9), 142.6 (C-5′), 141.2 (C-3′), 140.8 (C-4), 140.6 (C-7), 138.3 (C-11), 129.0, 128.0 (C-5), 127.6 (C-6), 126.4, 124.8 (C-8), 120.7 (C-3), 107.7 (C-4′), 12.8 (CH3), 12.3 (CH3); IR (KBr, ν/cm−1): 3069, 2922 (w, C−H), 1616 (m, CN), 1581 (m, CC), 1559 (m, CC), 1508 (s, C C), 1453 (s, CC), 1354, 1054 (s, C−H), 859, 736 (m, C−H). Anal. Calcd for C17N4H14AgBF4 (468.68): C, 43.54; H, 3.01; N, 11.95. Found C, 43.79; H, 2.63; N, 12.06%. [Ag2(ClO4)2(L1)2](4). (0.086 g, 90%), m.p.: > 300 °C; 1H NMR (400 MHz, DMSO-d6, δ/ppm): 8.95 (d, J = 8.8 Hz, 1H, H-9), 8.61 (t, J = 7.2 Hz, 1H, H-7), 8.44 (d, J = 3.2 Hz, 1H, H-4), 8.34 (d, J = 8.8 Hz, 1H, H-8), 8.18 (d, J = 8.8 Hz, 1H, H-6), 8.12 (d, J = 8.8 Hz, 1H, H-5), 7.75 (dd, J = 4.4, 4.8 Hz, 1H, H-3), 6.15 (s, 1H, pyrazole-H), 2.53 (s, 3H, CH3), 1.55 (s, 3H, CH3); 13C NMR (100 MHz, DMSO-d6, δ/ ppm): 151.2 (C-2), 151.0 (C-12), 148.2 (C-9), 142.8 (C-5′), 142.8 192

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(C-3′), 141.4 (C-4), 140.8 (C-7), 140.4 (C-11), 138.3, 128.9 (C-5), 128.1, (C-6), 126.4, 124.8 (C-8), 121.1 (C-3), 108.9 (C-4′), 12.9 (CH3), 12.2 (CH3); IR (KBr, ν/cm−1): 3070, 2922 (w, C−H), 1617 (m, CN), 1581 (m, CC), 1557 (m, CC), 1508 (s, CC), 1454 (m, CC), 1354 (s, C−H), 1088 (s, ClO4), 859 (s, C−H), 621 (s, C−H); Anal. Calcd for C17N4H14AgClO4 (481.37): C, 42.39; H, 2.93; N, 11.63. Found C, 42.46; H, 3.19; N, 11.91%. [Ag(FL1)2](BF4) (5). (0.161 g, 84%), m.p.: > 300 °C; 1H NMR (400 MHz, DMSO-d6, δ/ppm): 9.07 (m, 4H, H-9, H-7), 8.85 (t, J = 8.0 Hz, 2H, H-8), 8.36 (m, 4H, H-5, H-6), 8.26 (d, J = 8.4 Hz, 2H, H-4), 8.05 (m, 2H, H-3), 7.44 (s, 1H, pyrazole-H), 7.36 (s, 1H, pyrazole-H); 13C NMR (100 MHz, DMSO-d6, δ/ppm): 152.1, 151.9 (C-2), 147.4, 147.3 (C-12), 142.2, 142.0 (C-9), 141.5 (C-5′), 138.8, 138.6 (C-3′), 133.9, 133.5 (C-4, C-7), 129.7, 129.6 (C-13, C-14), 129.0 (C-11), 126.5 (C5, C-6), 125.5, 125.3 (C-8), 121.3 (CF3), 110.9 (C-3), 108.4 (C-4′); IR (KBr, ν/cm−1): 3168, 2919, 2852 (w, C−H), 1621 (m, CN), 1594 (m, CC), 1561 (m, CC), 1508 (m, CC), 1451 (w, C C), 1240, 1136, 1080 (s, C−F), 847 (m, C−H); Anal. Calcd for C34N8H16AgBF16 (958.66): C, 42.57; H, 1.68; N, 11.68. Found C, 42.50; H, 1.78; N, 11.77%. [Ag2(BF4)2(L2)2] (6). (0.098 g, 81%), m.p.: > 300 °C; 1H NMR (400 MHz, DMSO-d6, δ/ppm): 8.55 (d, J = 8.4 Hz, 1H, H-4), 8.24 (s, 1H, H-7), 7.99 (d, J = 8.0 Hz, 2H, H-8, H-3), 7.80 (s, 3H, H-5, H-6, PhH), 7.42 (m, 4H, Ph-H), 7.19 (d, J = 6.0 Hz, 3H, Ph-H), 6.84 (s, 2H, Ph-H), 6.57 (s, 1H, H-4′), 2.21 (s, 3H, CH3); 13C NMR (100 MHz, DMSO-d6, δ/ppm): 157.0 (C-2), 147.3 (C-9), 144.9 (C-12), 140.3 (C-5′), 140.0 (C-3′), 138.9 (Ph−C), 138.6 (C-7), 129.6 (C-4), 129.1 (C-11), 128.4 (Ph−C), 128.2, 127.6, 127.4, 127.3 (C-5, 6), 126.0, 123.6 (C-8), 120.2 (C-3), 109.9 (C-4′), 13.7 (CH3); IR (KBr, ν/ cm−1): 3059 (w, C−H), 1621 (m, CN), 1587 (m, CC), 1558 (m, CC), 1499 (s, CC), 1452 (m, CC), 1363 (s, C−H), 1059, 861 (s, C−H), 770 (s, C−H), 702 (s, C−H). Anal. Calcd for C28N4H20AgBF4 (606.68): C, 55.39; H, 3.32; N, 9.23. Found C, 55.19; H, 3.57; N, 8.90%. X-ray Crystal Structure Determination. Diffraction data for the complexes were collected with a Bruker SMART CCD area detector at room temperature (293 K) with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). An empirical absorption correction using SADABS28 was applied for all data. The structure was solved by direct methods using the SHELXS program. All non-hydrogen atoms were refined anisotropically by full-matrix least-squares on F2 by the use of the program SHELXL.29 Crystallographic data for the complexes are listed in Table 1.

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ASSOCIATED CONTENT

S Supporting Information *

Extended structures in the crystal packing, solid-state fluorescence spectra, and detailed information of the X-ray crystal structure analysis of compounds 1−6 (CIF files). This information is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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