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DOI:10.1002/ejic.201200793

Syntheses and Coordination Studies of2-(Phosphanylmethyl)pyridine Dioxide toward Silver (I)

Daniel A. Padron[a] and Kevin K. Klausmeyer*[a]

Keywords: Supramolecular chemistry / Cluster compounds / Coordination modes / Silver / N,P ligands

The coordination properties of the 2-[(diphenylphosphanyl)-methyl]pyridine N,P-dioxide ligand towards three differentsilver(I) salts are described. The molecular structures of thecoordination complexes obtained showed a strong depen-dence on the 2-[(diphenylphosphanyl)methyl]pyridine N,P-dioxide ligand and the binding ability of the counterion. Thestrongly binding trifluoroacetate ion yielded a unique planar

Introduction

The design of new metallopolymeric materials has be-come an important field of research in recent years. Muchof the current interest stems from their usefulness in a vari-ety of applications such as molecular sensing, separations,and storage, as well as catalysis and other functions.[1–8] Theligand of choice for the building of these extended struc-tures often incorporates the strongly binding carboxylatefunctionality as this provides exceptional stability. A varietyof other ligand types are also being studied for the con-struction of these materials, among them are those contain-ing phosphorus and/or nitrogen. Nitrogen ligands, particu-larly in the form of N-heterocycles, have become ubiqui-tous.[8] The oxides of tertiary phosphanes and pyridinesalso provide a possible entry into the arena of coordinationpolymers, especially if the two functionalities are combinedinto a single ligand.

The capability of AgI ions to coordinate in a wide rangeof coordination numbers and adopt different geometries isknown to give rise to materials with interesting structuralmotifs, functional properties, and potential applications.[7,9]

The solid-state packing has been shown to be strongly de-pendent on the ligand functionality, the interacting abilityof the anion, metal–metal interactions, and supramolecularforces;[7,10–18] these variables can be used to predict the mo-lecular structure of the resulting product.

There are a number of examples of pyridine N–O moie-ties complexed to Ag,[19–23] many of which form clustercompounds owing to the additional presence of bridging

[a] Department of Chemistry and Biochemistry, Baylor University,Waco, TX 76798, USAFax: +1-254-710-4272E-mail: Kevin_Klausmeyer@baylor.eduHomepage: https://bearspace.baylor.edu/Kevin_Klausmeyer/

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silver cluster complex, whereas the less strongly binding trifl-ate and BF4

– complexes yielded polymeric structures. Thesynthesized complexes were fully characterized by elemen-tal analysis and multinuclear NMR spectroscopy techniques.The crystal structures were determined by single-crystal X-ray crystallography.

carboxylate groups. There are a limited number of examplesof P=O bound to silver,[24–26] and only one previous exam-ple in which the phosphoryl oxygen atom bridges two Agcenters.[24]

The 2-[(diphenylphosphanyl)methyl]pyridine ligand hasgreat versatility for the construction of new compounds,from discrete molecules to polymeric arrays depending onits coordination mode.[27–32] The fully oxidized counterpartof this ligand, shown in Scheme 1, bears a P=O and an N–O function, and formally has five lone pairs of electronslocated on the two oxide groups, a feature that greatly en-hances its coordination ability. We have previously reportedthe coordination chemistry of the related phenylbis(pyrid-2-ylmethyl)phosphane N,N�,P-trioxide with CuII, whichshows enhanced coordination due to the extra oxygen moie-ties.[33] These features have also been exploited extensivelyfor the complexation of lanthanides and actinides for sev-eral years, in particular with 2,6-bis[(diphenylphosphanyl)-methyl]pyridine N,P,P�-trioxide.[34–42]

Scheme 1. Structure of 2-[(diphenylphosphanyl)methyl]pyridineN,P-dioxide (1).

Herein we report the synthesis and characterization ofthree new coordination complexes of silver, as a contri-bution to the understanding of the systematic control onthe coordination framework topology of these importantmaterials. These complexes take advantage of the increasednumber of available lone pairs from the oxidized ligand tocreate novel coordination structures.

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Results and Discussion

Synthesis

The ligand 1 (Figure 1) was synthesized according to apreviously reported procedure.[27,28,34] Crystals of 1 wereobtained by slow evaporation of a saturated methanol solu-tion of the ligand. Pure 1 is stable at room temperature andwhen exposed to light, and can be stored for over a yearwith no sign of decomposition. Crystals of compounds 2–4 were obtained by layering or vapor diffusion recrystalli-zation techniques with an appropriate solvent mixture, asnoted in the experimental section. Complexes 2–4 were iso-lated as crystalline products regardless of the initial reactionstoichiometries, which were attempted at 1:1, 2:1, and 3:1metal to ligand ratios. These compounds were stable undernormal conditions and showed no signs of decompositionat room temperature when exposed to light or air for shortperiods of time.

Figure 1. Thermal ellipsoid plot of 1 with atomic numberingscheme; ellipsoids are shown at the 50% level.

Figure 2. Thermal ellipsoid plot of 2 with atomic numbering scheme; ellipsoids are shown at the 50% level. Hydrogen atoms have beenremoved for clarity.

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X-ray Crystallography

The crystallographic data and refinement details for theligand 1 and the complexes 2, 3, and 4 reported herein wereprovided by X-ray diffraction studies. Figures 1, 2, 7, and 9display the molecular structures of all four compounds.Crystal data are presented in Table 1, and a summary ofselected angles and interatomic distances is given inTables 2 and 3.

Description of the Crystal Structures

The crystal structure of ligand 1 displays a nearly tetra-hedral geometry about the phosphorus atom. The C–P–Cangles are slightly smaller than 109.5°, and the C–P–Oangles are slightly greater than 109.5°. The P=O distance is1.4843(12) Å, and the N–O distance is 1.3152(18) Å. Thedistance between the oxygen atoms is 5.189 Å.

Complex 2 was obtained by the reaction of 1 equiv. of1 and 3 equiv. of Ag trifluoractetate (Tfa–). The structureconsists of a polynuclear silver complex in a 1:3 ligand-to-metal ratio. The unique portion of the molecule is formedby the three silver atoms Ag1, Ag2, and Ag3, three Tfa–

counteranions, and one 1 ligand unit. The complete struc-ture, shown in Figure 2, displays a hexanuclear metal coresupported by two ligands and six Tfa– counteranions. Thiscomplex possesses an inversion center which passes throughthe Ag2–Ag2A axis.

The metal core displays a perfectly planar framework ofinteracting silver centers in a parallelogram form and con-tains four nearly ideal equilateral triangles, as illustrated inFigure 3. All the Ag···Ag distances are in the range 2.871–3.074 Å, which is much shorter than the sum of the van derWaals radii for silver (3.44 Å) and puts them in the rangeof strong argentophilic interactions but they are not shortenough to be considered bonds. The Ag–Ag interactions

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Table 1. Crystallographic data and refinement details for 1, 2, 3, and 4.

1 2 3 4

Empirical formula C18H16NO2P C48H32Ag6F18N2O16P2 C21H18Ag2Cl2F6NO8PS2 C38H36Ag2B2Cl4F8N2O4P2

Formula mass 309.29 1943.92 908.09 1177.79a [Å] 10.6764(4) 10.4423(9) 26.8758(13) 11.5012(7)b [Å] 7.8602(3) 11.7176(9) 9.6622(5) 12.6965(8)c [Å] 35.7789(12) 13.0240(11) 23.8190(12) 15.0632(10)α [°] 90 84.704(4) 90 85.727(4)β [°] 90 66.423(3) 114.924(2) 81.373(4)γ [°] 90 81.360(4) 90 77.937(3)V [Å3] 3002.52(19) 1443.1(2) 5609.2(5) 2124.6(2)Z 8 1 8 2Crystal system orthorhombic triclinic monoclinic triclinicSpace group Pbca P1 C2/c P1T [K] 110(2) 110(2) 110(2) 110(2)Dcalcd. [g/cm–3] 1.368 2.237 2.151 1.841μ [mm–1] 0.190 2.179 1.881 1.3282θmax [°] 26.72 25.35 26.36 26.66Reflections measured 26503 30768 39988 27334Reflections used 3173 5218 5703 8748Data/restraints/parameters 3173/0/199 5218/0/415 5703/0/390 8748/0/562R1 [I�2σ(I)] 0.0383 0.0238 0.0531 0.0370wR2 [I�2σ(I)] 0.0835 0.0526 0.1560 0.0723R [Fo

2] (all data) 0.0523 0.0360 0.0685 0.0598Rw (Fo

2) (all data) 0.0901 0.0579 0.1692 0.0816GOF on F2 1.054 1.021 1.071 1.016

Figure 3. Geometric arrangement of the metal core of 2.

are likely favored because of the hard ligand environmentprovided by the oxygen donor atoms. In the absence of anysoft donor atoms, the Ag ions may prefer to interact witheach other than be solely bound by hard donor atoms.

The triangle generated by the silver atoms Ag1, Ag2, andAg3A presents a Ag···Ag contact distance range of 2.949–3.064 Å [average: (3.015 �0.059) Å], and a Ag–Ag–Ag an-gle range of 57.8–61.6° [average: (60.0�1.9)°]. The otherthree triangles formed by the interacting metal centers Ag2,Ag3, Ag1A, Ag2A, and Ag3A are similar.

The silver center Ag1 is pentacoordinate and interactswith the oxygen atom from the pyridyl group of one ligand(Ag1–O2 2.377 Å) and two oxygen atoms from two dif-ferent anions (Ag1–O3 and Ag1–O4 2.246 and 2.252 Å,respectively). The coordination number of five is completedby the argentophilic interaction of Ag1 with two other Agatoms (average Ag–Ag distance: 2.945 Å). Ag2 is eight co-ordinate. The Ag ion interacts with two oxygen donoratoms from two different anions (Ag2–O5 and Ag2–O6Adistances: 2.194 and 2.202 Å, respectively) and the two oxy-gen atoms from the P=O and N–O groups of one ligand(Ag2–O1 2.457 and Ag1–O2 2.462 Å). The coordinationsphere is completed by the argentophilic interaction of Ag2with Ag1, Ag3, Ag2A, and Ag3A with an average Ag···Agcontact of (3.01� 0.09) Å (Ag2···Ag1 3.064, Ag2···Ag3

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3.073, Ag2···Ag2A2.871, Ag2···Ag3A3.034 Å). A searchbased on the Cambridge Structural Database (CSD) re-ported that from 3319 crystal structures containing silverions coordinated to nonmetal atoms, only 0.3% are eight-coordinate, which makes it the least common coordinationnumber for this metal ion.[43] There are a number of Agclusters reported in the literature with a variety of ligands.In particular, Mak and coworkers have successfully usedvarious forms of acetylide and other ligands to constructnumerous clusters, however so far none of the producedclusters have been planar.[44–51] Ag3 coordinates to two oxy-gen donor atoms from two different Tfa– anions (Ag–O72.187, Ag–O8 2.195 Å), the oxygen atom from the ligandP=O function (Ag3–O1 2.406 Å), and three other silveratoms [average Ag···Ag distance: (3.018� 0.063) Å] to givea coordination number of six. The very slight elongation ofthe N–O or P=O bonds upon complexation compared tothose of the free ligand 1 is common.[19–26]

The P1–O1–Ag2 and P1–O1–Ag3 angles are nearly equal(140.6 and 139.7°, respectively), and the N1–O2–Ag1 andN1–O2–Ag2 angles are 126.1 and 109.1°, respectively. Thiscrystal structure shows the enhanced coordination versatil-ity of the oxidized ligand through the two extra electronlone pairs compared to the nitrogen donor atom in the non-oxidized counterpart. In this case, each oxygen atom brid-

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Table 2. Selected bond lengths [Å] and angles [°] for 1 and 2.[a]

1

P(1)–O(1) 1.4843(12) O(1)–P(1)–C(7) 113.15(7)P(1)–C(13) 1.8005(17) O(1)–P(1)–C(1) 113.59(7)P(1)–C(7) 1.8043(17) C(13)–P(1)–C(1) 108.68(8)P(1)–C(1) 1.8148(17) C(7)–P(1)–C(1) 101.46(8)O(2)–N(1) 1.3152(18) O(2)–N(1)–C(6) 118.99(14)N(1)–C(6) 1.360(2) O(2)–N(1)–C(2) 120.79(14)N(1)–C(2) 1.369(2) C(6)–N(1)–C(2) 120.21(14)C(16)–C(17) 1.383(3) C(2)–C(1)–P(1) 115.43(12)C(17)–C(18) 1.389(3) N(1)–C(2)–C(3) 119.02(15)

N(1)–C(2)–C(1) 117.69(14)

2

Ag(1)–O(3) 2.246(2) Ag(2)–O(2) 2.467(2)Ag(1)–O(4) 2.252(2) Ag(2)–Ag(2)#1 2.8715(5)Ag(1)–O(2) 2.377(2) Ag(2)–Ag(3)#1 3.0337(4)Ag(1)–Ag(3)#1 2.9492(4) Ag(2)–Ag(3) 3.0734(4)Ag(1)–Ag(2) 3.0641(4) Ag(3)–O(7) 2.187(2)Ag(2)–O(5) 2.194(2) Ag(3)–O(8) 2.195(2)Ag(2)–O(6)#1 2.202(2) Ag(3)–O(1) 2.406(2)Ag(2)–O(1) 2.457(2) N(1)–O(2) 1.335(3)P(1)–O(1) 1.496(2)O(3)–Ag(1)–O(4) 138.19(8) O(6)#1-Ag(2)–Ag(1) 91.76(6)O(3)–Ag(1)–O(2) 113.86(7) O(1)–Ag(2)–Ag(1) 128.16(5)O(4)–Ag(1)–O(2) 105.83(8) O(2)–Ag(2)–Ag(1) 49.46(5)O(3)–Ag(1)–Ag(3)# 77.99(5) Ag(2)#1-Ag(2)–Ag(1) 120.488(13)O(4)–Ag(1)–Ag(3)#1 75.46(6) Ag(3)#1-Ag(2)–Ag(1) 57.846(9)O(2)–Ag(1)–Ag(3)#1 111.98(5) O(5)–Ag(2)–Ag(3) 86.91(6)O(3)–Ag(1)–Ag(2) 94.78(6) O(6)#1-Ag(2)–Ag(3) 89.67(6)O(4)–Ag(1)–Ag(2) 99.51(6) O(1)–Ag(2)–Ag(3) 50.07(5)O(2)–Ag(1)–Ag(2) 52.07(5) O(2)–Ag(2)–Ag(3) 128.98(5)Ag(3)#1–Ag(1)–Ag(2) 60.561(9) Ag(2)#1–Ag(2)–Ag(3) 61.257(10)O(5)–Ag(2)–O(6)#1 163.03(8) Ag(3)#1–Ag(2)–Ag(3) 123.912(10)O(5)–Ag(2)–O(1) 92.14(8) Ag(1)–Ag(2)–Ag(3) 177.923(10)O(6)#1–Ag(2)–O(1) 98.38(8) O(7)–Ag(3)–O(8) 150.87(9)O(5)–Ag(2)–O(2) 102.74(8) O(7)–Ag(3)–O(1) 97.61(8)O(6)#1–Ag(2)–O(2) 92.32(8) O(8)–Ag(3)–O(1) 96.63(7)O(1)–Ag(2)–O(2) 79.29(7) O(7)–Ag(3)–Ag(1)#1 86.63(6)O(5)–Ag(2)–Ag(2)#1 83.49(6) O(8)–Ag(3)–Ag(1)#1 84.04(6)O(6)#1–Ag(2)–Ag(2)#1 80.30(6) O(1)–Ag(3)–Ag(1)#1 169.18(5)O(1)–Ag(2)–Ag(2)#1 111.33(5) O(7)–Ag(3)–Ag(2)#1 104.23(6)O(2)–Ag(2)–Ag(2)#1 167.73(5) O(8)–Ag(3)–Ag(2)#1 95.41(6)O(5)–Ag(2)–Ag(3)#1 86.98(6) O(1)–Ag(3)–Ag(2)#1 107.63(5)O(6)#1–Ag(2)–Ag(3)#1 81.16(6) Ag(1)#1–Ag(3)–Ag(2)#1 61.593(9)O(1)–Ag(2)–Ag(3)#1 173.98(5) O(7)–Ag(3)–Ag(2) 108.73(7)O(2)–Ag(2)–Ag(3)#1 106.72(5) O(8)–Ag(3)–Ag(2) 100.03(6)Ag(2)#1–Ag(2)–Ag(3)#1 62.655(10) O(1)–Ag(3)–Ag(2) 51.54(5)O(5)–Ag(2)–Ag(1) 92.15(6) Ag(1)#1–Ag(3)–Ag(2) 117.669(11)

[a] Symmetry transformations used to generate equivalent atoms.For 2: #1 –x, –y + 2, –z + 1.

ges two Ag ions, which allows a weak interaction betweenthese metal centers. The supramolecular interactions are re-inforced by F···H–C bonding with H···F distances in therange 2.609–2.979 Å and F···H–C angles in the range145.1–153.2°. Interactions of this kind are illustrated in Fig-ure 4 between F4B and H3, which has a H···F distance of2.609 Å and a F···H–C angle of 153.2°.

The reaction of two equiv. of 1 with 3 equiv. of AgOTfyields the polymeric compound 3. The 1D polymeric chainshown in Figure 5 consists of consecutive triads of silveratoms interconnected by a bridging Ag(OTf)2

– unit. TheAg···Ag contact distance within a triad is 3.252 Å and theAg–Ag–Ag angle is 180.0°. The argentophilic interactions

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Table 3. Selected bond lengths [Å] and angles [°] for 3 and 4.[a]

3

Ag(1)–O(2) 2.346(4) Ag(2)–O(2) 2.558(4)Ag(1)–O(4)#1 2.416(6) Ag(2)–Ag(1)#1 3.2523(5)Ag(1)–O(1) 2.427(4) Ag(3)–O(7) 2.392(5)Ag(1)–O(6) 2.542(5) Ag(3)–C(17)#3 2.459(6)Ag(1)–Ag(2) 3.2523(5) Ag(3)–C(16)#3 2.513(8)Ag(2)–O(1) 2.345(5) Ag(2)–O(3) 2.498(6)P(1)–O(2) 1.492(4) N(1)–O(1) 1.343(7)O(2)–Ag(1)–O(4)#1 104.52(18) O(3)#1–Ag(2)–Ag(1) 73.04(13)O(2)–Ag(1)–O(1) 95.76(15) O(3)–Ag(2)–Ag(1) 106.96(13)O(4)#1–Ag(1)–O(1) 78.73(18) O(2)–Ag(2)–Ag(1) 45.71(9)O(2)–Ag(1)–O(6) 111.53(16) O(2)#1–Ag(2)–Ag(1) 134.29(9)O(4)#1–Ag(1)–O(6) 142.96(18) O(1)–Ag(2)–Ag(1)#1 131.89(10)O(1)–Ag(1)–O(6) 89.30(15) O(1)#1–Ag(2)–Ag(1)#1 48.11(11)O(2)–Ag(1)–Ag(2) 51.32(10) O(2)–Ag(2)–Ag(1)#1 134.29(9)O(4)#1–Ag(1)–Ag(2) 82.12(13) Ag(1)–Ag(2)–Ag(1)#1 180.000(1)O(1)–Ag(1)–Ag(2) 45.98(11) O(7)–Ag(3)–O(7)#2 88.3(2)O(6)–Ag(1)–Ag(2) 114.06(11) O(7)–Ag(3)–C(17)#3 103.0(2)O(1)–Ag(2)–O(1)#1 180.0(2) O(7)#2–Ag(3)–C(17)#3 91.77(19)O(1)–Ag(2)–O(3)#1 91.18(16) O(7)#2–Ag(3)–C(17)#4 103.0(2)O(1)–Ag(2)–O(3) 88.82(16) C(17)#3–Ag(3)–C(17)#4 159.4(3)O(3)#1–Ag(2)–O(3) 180.00(14) O(7)–Ag(3)–C(16)#3 135.3(2)O(1)–Ag(2)–O(2) 92.37(14) O(7)#2–Ag(3)–C(16)#3 88.6(2)O(1)#1–Ag(2)–O(2) 87.63(14) C(17)#3–Ag(3)–C(16)#3 32.6(2)O(3)–Ag(2)–O(2) 101.68(18) C(17)#4–Ag(3)–C(16)#3 132.2(2)O(3)–Ag(2)–O(2)#1 78.32(18) O(1)–Ag(2)–Ag(1) 48.11(11)O(2)–Ag(2)–O(2)#1 180.00(13)

4

Ag(1)–O(1) 2.265(2) Ag(2)–O(4) 2.237(2)Ag(1)–O(3) 2.270(2) Ag(3)–O(2) 2.199(2)Ag(1)–O(4) 2.499(3) Ag(1)–Ag(2) 3.2244(3)Ag(1)–O(2) 2.512(3) P(1)–O(1) 1.503(3)Ag(1)–Ag(3) 3.1990(3) P(2)–O(3) 1.498(3)O(2)–N(2) 1.348(4) O(4)–N(2) 1.348(4)O(1)–Ag(1)–O(3) 166.68(9) O(2)–Ag(1)–Ag(2) 137.79(6)O(1)–Ag(1)–O(4) 91.46(8) Ag(3)–Ag(1)–Ag(2) 162.463(10)O(3)–Ag(1)–O(4) 85.67(8) O(4)–Ag(2)–O(4)#1 180.000(1)O(1)–Ag(1)–O(2) 85.39(8) O(4)–Ag(2)–Ag(1)#1 129.39(6)O(3)–Ag(1)–O(2) 94.72(8) O(4)–Ag(2)–Ag(1) 50.61(6)O(4)–Ag(1)–O(2) 167.87(8) O(4)#1–Ag(2)–Ag(1) 129.39(6)O(1)–Ag(1)–Ag(3) 127.81(6) Ag(1)#1–Ag(2)–Ag(1) 180.0O(3)–Ag(1)–Ag(3) 55.60(6) O(2)#2–Ag(3)–O(2) 180.00(10)O(4)–Ag(1)–Ag(3) 140.65(6) O(2)#2–Ag(3)–Ag(1) 128.50(7)O(2)–Ag(1)–Ag(3) 43.24(5) O(2)–Ag(3)–Ag(1) 51.50(7)O(1)–Ag(1)–Ag(2) 54.15(6) Ag(1)–Ag(3)–Ag(1)#2 180.0O(3)–Ag(1)–Ag(2) 127.46(6)O(4)–Ag(1)–Ag(2) 43.77(5)

[a] Symmetry transformations used to generate equivalent atoms.For: 3: #1 –x + 2, –y + 2, –z + 1; #2 –x + 2, y, –z + 1/2; #3 –x +2, y + 1, –z + 1/2; #4 x, y + 1, z; #5 x, y – 1, z. For 4: #1 –x +2, –y, –z + 1; #2 –x + 2, –y + 1, –z + 1.

are assisted by two ligand units coordinated on either sideof the trinuclear axis and by two bidentate OTf– anionscoordinated on each side of this same axis.

The central silver atom, Ag2, is octacoordinate and lieson a crystallographic inversion center (Figure 6).

The uncommon eight-coordinate inner sphere environ-ment around this metal center includes two oxygen donoratoms, O3 and O3A, from two different OTf– anions, (Ag–O 2.502 Å), four oxygen donor atoms from the bridgingP=O and N–O functions of two bidentate ligand units(Ag2–OP=O 2.569, Ag2–ON–O 2.356 Å), and two silveratoms, Ag1 and Ag1A, on each side (Ag···Ag 3.252 Å). The

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Figure 4. Intermolecular hydrogen bonding (F···H–C) in 2.

Figure 5. Perspective view of the 1D polymeric structure of 3.

Figure 6. Perspective view of the octacoordinate silver center Ag2in 3.

silver center Ag1 is five-coordinate and is bonded to twoOTf– anions through the oxygen atoms O6 and O4A (Ag1–O6 2.546, Ag1–O4A 2.411 Å), and the two oxygen atomsof the P1=O2 and N1–O1 functions from two different li-

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gand units (Ag–OP1=O2 2.353, Ag–ON1–O1 2.431 Å). TheAg1···Ag2 interaction completes the pentacoordinatesphere of Ag1. As in 2, the N–O and P=O bond lengths arevery similar to those in the free ligand. The average Ag–Obond length for 3 [(2.412�0.192) Å] is similar to that foundfor 2 [(2.426�0.042) Å].

The resulting linear macromolecule is propagated in a2D network (Figure 7) through the coordination of the dis-torted tetrahedral silver center Ag3 through a bis-η2 inter-action with two phenyl moieties in the adjacent polymericchain.

The tetrahedral geometry around Ag3 (Figure 8) is com-pleted by the interaction of this silver center with oxygenatoms from two bridging triflate groups (Ag3–O7 2.398 Å)with an O7–Ag3–O7A angle of 88.4°. The Ag3–C16 andAg3–C17 distances are 2.532 and 2.472 Å, respectively, witha C16–Ag3–C17 angle of 32.4°. The distance from the Ag3ion to the center of the C16=C17 bond, CC1, is 2.402 Åwith a CC1–Ag3–CC2 angle of 140.1°, where CC2 representsthe center of the C16A=C17A bond. The angles O7A–Ag3–CC1 and O7A–Ag3–CC2 are 89.8 and 119.5°, respectively.The C16=C17 bond length (1.399 Å) shows a slight elong-ation compared to the same C=C bond in the free ligand(1.382 Å). This observation suggests that the interaction be-

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Figure 7. Perspective view of the 2D silver(I) polymer sheet of 3.

Figure 8. Perspective view of the pseudo-tetrahedral geometry around Ag3 in 3.

tween the silver center Ag3 and the π faces of the phenylmoieties is mainly electrostatic (charge-induced dipole) innature, with small back-donation of electronic density fromthe 4d orbitals of the silver ion into the π* 2p orbitals ofthe C16=C17 bond. Also, this C16=C17 bond length isshorter than that found by other research groups (1.405 Å)and those predicted by different computational approachessuch as B3LYP DFT (1.430 Å) and Hartree–Fock calcula-tions (1.403 Å) reported in other work.[52,53]

The distance between Ag3 and the main plane of thecoordinated phenyl group, d, is 2.47 Å with a deviationfrom the centroid axis, Δ, of 1.33 Å. The angular parameterβ is 30.9° (Scheme 2), and the angle between the planes of

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the coordinated phenyl groups, α, is 100.8°. The structuralparameters d, Δ, and β found for Ag3 in 3 are consistentwith those reported by Kochi as optimal (bonding) values[d = (2.41 �0.05) Å; Δ = (1.53�0.2) Å; β = 32�3)°].[54]

Scheme 2. Structural features of Ag3–arene in 3.

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The reaction between AgBF4 and 1 yields the 1D poly-meric compound 4 with a 1:2 ligand-to-metal ratio. Similarto 3, consecutive Ag–Ag–Ag triads are observed in 4, whichresults in a zigzag chainlike arrangement of silver atomsextended along the x axis (Figure 9). Within a triad, theAg–Ag–Ag angle is 180°, and the Ag···Ag contact distanceis 3.199 Å, whereas between triads, the Ag–Ag–Ag angle is162.5°, and the Ag···Ag distance is 3.224 Å. The metallo-philic interactions are supported by the bridging P=O andN–O ligand functions and by two fluorine donor atomsfrom one dual bridging BF4

– unit, which generates the lossof linearity along the polymeric structure (Figure 10, right).The BF4

– anion also acts in a chelating fashion on Ag1through F1 and F2 and presents the shortest Ag···F dis-tances (Ag1···F1 2.807, Ag1···F2 2.798 Å) in this complex.The Ag···F interactions range from 2.807 to 3.071 Å withan average distance of (2.902 �0.128) Å. A search in theCambridge Structural Database (CSD, version 5.32)showed four different crystal structures with interactions

Figure 9. Perspective view of the 1D polymeric structure of 4.

Figure 10. Coordination environment around the silver center Ag1 in 4 (left). Perspective view of the dual bridging mode of the BF4–

anion in 4 (right).

Eur. J. Inorg. Chem. 2013, 299–308 © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim305

between silver ions and BF4– anions. The BF4

– anions in allthese structures were reported to act in a chelating fashiontowards the silver centers.[55–58] To the best of our knowl-edge, 4 is the first reported solid-state coordination com-pound in which the BF4

– anion simultaneously acts in achelating and a dual-bridging mode. The Ag–OP=O dis-tances range from 2.270 (Ag1–O3) to 2.680 Å (Ag3–O3)with an average Ag–OP=O distance of (2.530� 0.226) Å,and the Ag–ON–O distances range from 2.199 (Ag3–O2) to2.512 Å (Ag1–O2) with an average Ag–ON–O distance of(2.316�0.170) Å. As in 2 and 3, the N–O and P=O bondlengths in 4 present a small elongation when compared tothose in the free ligand. Nevertheless, these differences inbond lengths fall within the experimental error. The averageAg–O bond length for 4 [(2.423� 0.214) Å] is also similarto those obtained for 2 [(2.426 �0.042) Å] and 3[(2.412 �0.192) Å].

The silver center Ag1 (Figure 10) possesses an octacoor-dinate environment and interacts with two silver centers(Ag–Ag–Ag 162.5°, Ag1···Ag2 3.224, Ag1···Ag3 3.199 Å),two fluorine donor atoms from one BF4

– unit (F1–Ag1–F247.8°, Ag1–F1 2.807, Ag1–F2 2.798 Å), and four oxygenatoms from the P=O and N–O functions of two ligandunits. The Ag1–OP1=O1 and Ag1–OP2=O3 distances (2.265and 2.270 Å, respectively) are shorter than the correspond-ing Ag1–ON1–O2 and Ag1–ON2–O4 distances (2.512 and2.499 Å, respectively).

The angles formed by the interaction of Ag1 with twooxygen atoms in the same ligand unit (O1–Ag1–O2 85.4,O3–Ag1–O4 85.7°) are smaller than those formed by thissame silver center and two oxygen atoms from two differentligand units (O2–Ag1–O3 94.7, O4–Ag1–O1 91.5°). Theseangle differences can be attributed to the steric hindrancebetween the two ligand units that is generated by the bulkyphenyl substituents. A molecule of CH2Cl2 solvent is in thepocket formed by the phenyl groups with the chlorideatoms oriented toward the electron deficient Ag1 ion. Themetal center Ag2 (Figure 11) displays a heavily distortedoctahedral geometry defined by the angles F2A–Ag2–O4

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(104.6°), F2A–Ag2–O4A (75.4°), and the symmetry-forcedstraight angles Ag1A–Ag2–Ag1, O4–Ag2–O4A, and F2B–Ag2–F2A (180°).

Figure 11. Coordination environment around the silver center Ag2in 4.

The hexacoordinate environment around Ag2 is formedby the interaction of this silver ion with the two silver ionsAg1 and Ag1A (Ag···Ag 3.224 Å), two fluorine donoratoms from two BF4

– anion units (Ag2–F2 2.807 Å), andthe N–O groups of two ligand units (Ag2–ON2–O4 2.237 Å).The bond length Ag2–ON2–O4 is significantly shorter thanthe Ag–ON–O distances in 2 and 3, in which the Ag–ON–O

distance range is 2.35–2.43 Å. This contraction is also ob-served in the Ag–OP=O bond lengths. In 3, the Ag–OP=O

distance is 2.265 Å, whereas in 3 and 4 it is in the range2.35–2.57 Å. This suggests that the silver centers in 4 are

Figure 12. Coordination environment around the silver center Ag3 in 4.

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more deficient in electron density than those in 2 and 3,probably because of the poorer coordinating ability of theBF4

– anion (Ag–F range: 2.935–3.071 Å) compared to thatof the Tfa– and OTf– anions, which can partially neutralizethe charge on the silver ions more efficiently (Ag–OTfa andAg–OOTf ranges: 2.187–2.252 and 2.398–2.546 Å, respec-tively). As a result of this, and in addition to the steric ef-fects imposed by the bulky ligands, coulombic repulsionsbetween interchain AgI centers contribute to the separationof adjacent macromolecules in 4 with chain–chain distancesof 10.784 Å.

The silver center Ag3 presents an octacoordinate envi-ronment (Figure 12) formed by its interaction with the twosilver ions Ag1 and Ag1A (Ag···Ag 3.199 Å), two fluorinedonor atoms from two BF4

– anion units (Ag2–F2 3.071 Å)and the N–O groups of two ligand units (Ag2–ON1–O2

2.199 Å). The angles F1–Ag3–F1A, Ag1–Ag3–Ag1B, andO2–Ag3–O2B are forced to 180° by symmetry, and theangles F1–Ag3–Ag1, F1–Ag3–O2, and Ag1–Ag3–O2 are53.1, 71.1, and 51.5°, respectively.

ConclusionsThree novel silver(I) 2-[(diphenylphosphanyl)methyl]pyr-

idine N,P-dioxide complexes have been synthesized andcharacterized by elemental analysis, multinuclear NMRspectroscopy and single-crystal X-ray crystallography. Themolecular structure of the complexes showed a strong de-pendence on the coordination properties of thecounteranion, steric hindrance imposed by the bulkiness ofthe ligand substituents, and weak supramolecular forcessuch as π–metal interactions and coulombic interactions be-tween the silver centers. In comparison to structures ob-tained with the unoxidized version of this ligand, which are

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considerably simpler, the harder oxo moiety appears to notbe as good a fit for the softer silver(I) ion and results inmore complex structures, both as a result of the increasednumber of available electron pairs and the need for a softligand environment for stability, which results in higher co-ordination numbers. The better match between the softerphosphorus and nitrogen atoms compared to the oxygenatoms plays a role in the lower coordination number for thecompounds containing the unoxidized ligand. The abilityof the counteranions and ligand to act in a polydentatemanner gave support to the molecular structures to yieldthe hexanuclear AgI cluster 2 and the polymeric complexes3 and 4. The linearity of 3 was severely affected by the inter-action of the OTf– counteranions with the metal centers. Onthe other hand, 4 showed a zigzag chainlike arrangement ofsilver atoms extended along the polymeric backbone, whichis a product of the weak interactions of the BF4

–

counteranions with the silver ions. The structural param-eters d, Δ, and β found for the Ag–arene interactions in 3showed consistency with those previously reported in otherwork as optimal bonding values.

Experimental SectionGeneral Remarks: All experiments were performed under a nitrogenatmosphere by using Schlenk techniques. All air and light sensitivecompounds were stored and handled in an inert atmosphereglovebox and used as received. All solvents were reagent grade andwere distilled under an inert atmosphere from the appropriate dry-ing agent immediately before use. 1H and 31P NMR spectra wererecorded at 499.78 and 202.31 MHz, respectively at 25.0 °C with aVarian VNMRS 500 MHz Spectrometer. Elemental analyses wereperformed by Atlantic Microlabs Inc. in Norcross, Georgia, yieldsfor compounds 2–4 were calculated with respect to 1.

Synthesis of AgTfa(1) (2): A solution of 1 (0.061 g, 0.200 mmol) inCH2Cl2 (5 mL) was added to a solution of AgTfa (0.132 g,0.600 mmol) in CH2Cl2 (5 mL). The resulting solution was allowedto stir for 5 min and then dried under vacuum to leave an off-whitepowder. This was then dissolved in a small amount of CH2Cl2 andprecipitated with diethyl ether (30 mL). Colorless blocks were ob-tained by slow diffusion of diethyl ether into a CH2Cl2 solution of2 at 5 °C, yield 68.5% (0.133 g). 1H NMR (CD3OD, 298.1 K): δ =4.42 (d, 2 H), 7.54 (m, 13 H), 8.28 (d, 1 H) ppm. 31P NMR(CD3OD, 298.1 K): δ = 34.59, (s) ppm. C24H16Ag3F9NO8P·2CH2Cl2 (1141.82): calcd. C 27.35, H 1.77, N 1.23; found C 27.04,H 1.34, N 1.20.

Synthesis of AgOTf(1) (3): A solution of 1 (0.0635 g, 0.205 mmol)in CH2Cl2 (5 mL) was added to a solution of AgOTf (0.112 g,0.410 mmol) in CH2Cl2 (5 mL). The resulting solution was allowedto stir for 10 min and then dried under vacuum to leave an off-white powder. This was then dissolved in a small amount ofCH2Cl2 and precipitated with diethyl ether (30 mL). Colorlessblocks were obtained by layering of diethyl ether into a CH2Cl2solution of 3 at 5 °C, yield 84.1% (0.142 g). 1H NMR (CD3CN,298.1 K): δ = 4.24 (d, 2 H), 7.49 (m, 13 H), 8.07 (d, 1 H) ppm.31P NMR (CD3CN, 298.1 K): δ = 29.82, (s) ppm.C20H16Ag2F6NO8PS2·2CH2Cl2 (993.04): calcd. C 26.61, H 2.03, N1.41; found C 26.20, H 1.92, N 1.54.

Synthesis of AgBF4(1) (4): A solution of 1 (0.068 g, 0.220 mmol) inCH2Cl2 (5 mL) was added to a solution of AgBF4 (0.086 g,

Eur. J. Inorg. Chem. 2013, 299–308 © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim307

0.440 mmol) in CH2Cl2 (5 mL). The resulting solution was allowedto stir for 10 min and then dried under vacuum to leave an off-white powder. This was then dissolved in a small amount ofCH2Cl2 and precipitated with diethyl ether (30 mL). Colorlessblocks were obtained by layering diethyl ether into a CH2Cl2 solu-tion of 4 at 5 °C, yield 74.5% (0.163 g). 1H NMR (CD2Cl2,298.1 K): δ = 4.22 (d, 2 H), 7.48 (m, 13 H), 8.06 (d, 1 H) ppm.31P NMR (CD2Cl2, 298.1 K): δ = 41.99, (s) ppm.C36H32Ag2B2F8N2O4P2·CH2Cl2·H2O (1110.90): calcd. C 40.00, H3.27, N 2.52; found C 39.79, H 3.37, N 2.53.

X-ray Crystallographic Analysis: Crystallographic data was col-lected on crystals with dimensions 0.297�0.130 �0.118 mm for 1,0.243�0.083�0.081 mm for 2, 0.067�0.193�0.100 mm for 3,and 0.050�0136� 0.140 mm for 4. Data was collected at 110 Kon a Bruker X8 Apex diffractometer using Mo-K radiation (λ =0.71073 Å). All structures were solved by direct methods after cor-rection of the data using SADABS.[59,60] All the data were pro-cessed using the Bruker AXS SHELXTL software, version 6.10.[61]

Unless otherwise noted, all non-hydrogen atoms were refined an-isotropically and hydrogen atoms were placed in calculated posi-tions.

CCDC-891860 (for 1), -891857 (for 2), -891858 (for 3), and -891859(for 4) contain the supplementary crystallographic data for thispaper. These data can be obtained free of charge from The Cam-bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Acknowledgments

This research was supported by funds provided by the Departmentof Chemistry & Biochemistry at Baylor University and the RobertA. Welch Foundation (AA-1508). This study was supported in partby funds from the University Research Committee and the ViceProvost for Research at Baylor University.

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Received: July 13, 2012Published Online: November 26, 2012