A Silver(I) Difluorophosphate(V)-tetramethylhexathiaadamantane Coordination Polymer with a 3-D Rutile (TiO2) Framework Construction
CRYSTAL GROWTH & DESIGN 2001 VOL. 1, NO. 5 395-399
Neil R. Brooks, Alexander J. Blake, Neil R. Champness,* John W. Cunningham, Peter Hubberstey,* and Martin Schro¨der* School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD, U.K. Received June 11, 2001
ABSTRACT: Hydrolysis of the PF6- anion during the reaction of AgPF6 with tetramethylhexathiaadamantane (hta) in MeOH leads to the crystallization of a coordination polymer, {[Ag3(hta)(PO2F2)3]}∞, in which hexanuclear [Ag(PO2F2)]6 cages are linked by tetramethylhexathiaadamantane molecules in a three-dimensional architecture. The unprecedented [Ag(PO2F2)]6 cages act as six-connecting units with approximately octahedral geometry, and the tetramethylhexathiaadamantane molecules form three-connecting units with approximately trigonal planar geometry to give a rare example of a metal-organic material with a rutile-like framework construction. Introduction A wide variety of N-donor organic linkers have been used to bridge metal ions to generate a plethora of metal-organic multi-dimensional materials with diverse properties.1 Usually based on pyridyl2 or nitrile3 derivatives, the major attraction of these ligands is their rigidity that results in bridges with highly predictable coordination properties and connectivities that are simply determined by the number of N-donors.2,3 Additionally, the structural chemistry of coordination polymers based on bridging S-donor ligands has been probed.4-14 The attraction of these bridging ligands, relative to N-donors, is their potential for increased connectivity, which results from replacement of a nitrogen atom, which has just one σ-donating lone pair, with a sulfur atom, which has potentially two σ-donating lone pairs. Cyclic thioethers have been shown to be very effective ligands for soft Lewis acids such as Ag(I).4-16 Thus, we and others have generated a variety of polymeric constructions by linking Ag(I) centers into 1-D chains and 2-D sheets using dithiacyclohexanes (1,3-dithiane4,5 and 1,4-dithiane6-9) and 1,3,5-trithiacyclohexane (trithiane8,10-13), which have four and six σ-donating lone pairs, respectively (Scheme 1). 1,3-Dithiane (Scheme 1b)4,5 and 1,4-dithiane (Scheme 1a)6-9 normally use just two of their four σ-donor orbitals to bridge two silver(I) centers, 1,3-dithiane in an ax-eq fashion and 1,4dithiane in an eq-eq or ax-ax fashion. There are, however, examples of coordination polymers in which 1,3-dithiane {[Ag2(µ4-1,3-dithiane)][SO4]‚3H2O}∞4 and 1,4-dithiane {[Ag2(µ4-1,4-dithiane)][SO4]‚H2O}∞6 use all four σ-based lone pairs to bridge four silver(I) centers. Trithiane (Scheme 1c)8,11-13,15 coordinates metal centers in a variety of ways, the maximum number of lone pairs used being three. It can bridge metal centers in * To whom correspondence should be addressed. E-mail:
[email protected];
[email protected];
[email protected].
Scheme 1. Potential Connectivities for (a) 1,4-Dithiane, (b) 1,3-Dithiane, and (c) Trithiane
an eq-eq-eq fashion to generate a two-dimensional sheet structure as in {[Ag(µ3-trithiane)][NO3]}∞ (Scheme 2a)11 or it can adopt an ax-ax-ax mode to cap a cluster of three metal centers as in [{Ru(CO)2}3(µ2-CO)3(µ3trithiane)] (Scheme 2b).15 Other coordination modes observed for trithiane include ax-eq µ2-trithiane as in {[{Ag(trithiane)}(µ2-trithiane)][NO3]}∞ (Scheme 3a)10, eq-eq µ2-trithiane as in [(MCl2)(µ2-trithiane)]∞ (Scheme 3b),12 and terminal monodentate trithiane as in {[{Ag(trithiane)}(µ2-trithiane)][NO3]}∞ (Scheme 3a).10 To extend this work, we have initiated a study of the crystal engineering of Ag(I) salts with the potentially twelve-fold connecting ligand, tetramethylhexathiaadamantane (hta; Scheme 4), which can be considered to comprise four fused trithiane rings. Hta offers a diverse range of bridging modes and the potential for a rich coordination polymer chemistry. Thus far, the only structurally characterized coordination compound containing hta is the discrete mononuclear Pd(II) complex, [Pd(hta)Cl2],17 in which a square planar Pd(II) center is coordinated by two chlorine anions and a bidentate chelating hta ligand. We describe herein the unprecedented extended architecture of the 3:1 adduct of AgPO2F2 and hta.
10.1021/cg010015o CCC: $20.00 © 2001 American Chemical Society Published on Web 08/17/2001
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Scheme 2. Schematic Representations of Trithiane in (a) eq-eq-eq and (b) ax-ax-ax Fashion in (a) the {[Ag(µ3-trithiane)]+}∞ 2-D Sheet Polymer and (b) the {[Ru(CO)2]3(µ2-CO)3(µ3-trithiane)] Molecular Cluster
Scheme 3. Schematic Representations of (a) Bidentate Bridging (ax-eq) and Monodentate Binding in the {[{Ag(trithiane)}(µ2-trithiane)]+}∞ 1-D Cation and of (b) Bidentate Bridging (eq-eq) in the [(MCl2) (µ2-trithiane)]∞ (M ) Cu, Hg) 1-D Polymers
Results and Discussion Treatment of AgPF6 dissolved in MeOH with hta dissolved in CH2Cl2 in a 3:1 molar ratio gave a white powder in low yield, following addition of Et2O. IR spectroscopic analysis of the product revealed the presence of the [PO2F2]- anion [νas(P-O) 1314 (1311) cm-1; νs(P-O) 1152 (1145) cm-1; νas(P-F) 853 (857) cm-1; νs(P-F) 513 (517) cm-1; the values in parentheses are those for KPO2F218] as well as hta. Elemental analysis (C H N) suggested the formulation 3Ag(PO2F2)‚hta. Crystals, of a single morphology, were grown by layered diffusion of a MeOH solution of AgPF6 and a CH2Cl2 solution of hta. X-ray diffraction studies of these crystals
Brooks et al. Scheme 4. Schematic Representation of Tetramethylhexathiaadamantane (hta)
revealed the structure of the product, confirming the above formulation. The formation of the [PO2F2-] anion, although unexpected, is not surprising as the hydrolysis of the [PF6-] anion in wet solvents is a well-characterized process.19 The structure of the product comprises [Ag(PO2F2)]6 cages linked by hta molecules to give a 3-D polymeric network of formula {[Ag3(hta)(PO2F2)3]}∞. The centrosymmetric [Ag(PO2F2)]6 cages (Figure 1a) are unprecedented. The three crystallographically independent [PO2F2]- anions behave similarly, each bridging the three crystallographically independent Ag(I) centers in an µ2-O-, µ1-O′- fashion. Selected Ag-O interatomic distances and O-Ag-O angles are collated in Table 1. Hence, the cage comprises three types of rings: a fourmembered AgOAgO, six-membered AgOPOAgO, and eight-membered AgOPOAgOPO (Figure 1a; Scheme 5). The Ag(I) centers have similar coordination geometries, each being surrounded by an approximately tetrahedral arrangement of three oxygens from different [PO2F2]anions and a sulfur atom of a hta ligand. They differ in the type of coordinating oxygen, Ag(1) being surrounded by three µ2-oxygens, Ag(2) by two µ2-oxygens and a µ1oxygen and Ag(3) by one µ2-oxygen and two µ1-oxygens. They also differ in their binding of the hta ligand. Whereas, Ag(1) and Ag(2) are bound to the hta molecule by single, relatively short, Ag‚‚‚S contacts, [Ag(1) ‚‚‚S 2.5572(11) Å; Ag(2) ‚‚‚S 2.5183(11) Å], Ag(3) is bound by one somewhat longer Ag‚‚‚S contact [Ag(3)‚‚‚S 2.7341(11),] supported by two even longer Ag‚‚‚S contacts [Ag(3)‚‚‚S 3.0252(11), 3.0871(12) Å] (Figure 1b), the hta acting as a weakly binding facially capping tridentate ligand. To aid clarity, only the shortest Ag‚‚‚S contacts are shown in Figure 1. The [Ag(PO2F2)]6 cage (Figure 1a) and the hta ligand (Figure 1b) act as six- and three-connecting units, respectively, to generate the extended 3-D structure (Figure 2a and 2b). A detailed examination of the structure reveals a trigonal planar connectivity for the hta molecule and a distorted octahedral connectivity for the [Ag(PO2F2)]6 cage (Figure 3). The elongation along one of the C3 axes and the angles subtended by the Ag(I) centers at the center of the hta molecule and at the inversion center of the [Ag(PO2F2)]6 cage (Table 2) confirm the near perfect trigonal planar geometry of the hta connectivity and the distorted octahedral geometry of the [Ag(PO2F2)]6 cage connectivity. Comparison of this structure with that of the rutile form of TiO2, a (6‚3) coordinated structure (Figure 2c),20 shows them to have the same framework. The correspondence between the two structures can be seen by comparing (Figure 2) the views along the a and b axes of {[Ag3(hta)(PO2F2)3]}∞ with the view along the a axis of rutile (for rutile, which has a tetragonal unit cell, the a and b axes are
Silver(I) Difluorophosphate(V)-tetramethylhexathiaadamantane
Crystal Growth & Design, Vol. 1, No. 5, 2001 397
Figure 1. Views of (a) the [Ag(PO2F2)]6 cage and (b) the tetramethylhexathiaadamantane molecule in {[Ag3(hta)(PO2F2)3]}∞ showing the 6-fold connectivity of the former and 3-fold connectivity of the latter. Displacement ellipsoids shown at the 50% probability level. Symmetry codes: i 2 - x, 3 - y, 1 - z; ii 1.5 - x, 0.5 + y, 0.5 - z; iii 2.5 - x, 0.5 + y, 0.5 - z; iv 2.5 - x, -0.5 + y, 0.5 z; v 1.5 - x, -0.5 + y, 0.5 - z. Table 1. Selected Interatomic Distances and Angles for {[Ag3(hta)(PO2F2)3]}∞ distances (Å) Ag1-O1a Ag1-O12 Ag1-O22 Ag1-S4b
O12-Ag1-O22 O1a-Ag1-O12 O1a-Ag1-O22 O22-Ag1-S4b O12-Ag1-S4b O1a-Ag1-S4b a
- z.
2.276(3) 2.413(3) 2.451(3) 2.5572(11)
80.82(11) 105.1(2) 110.6(2) 92.95(9) 109.60(9) 140.60(10)
Ag2-O12 Ag2-O22 Ag2-O2 Ag2-S5
2.354(3) 2.423(3) 2.339(3) 2.5183(11)
angles (deg) O12-Ag2-O22 82.61(11) O2-Ag2-O12 95.36(12) O2-Ag2-O22 116.54(11) O22-Ag2-S5 105.67(9) O2-Ag2-S5 108.84(9) O12-Ag2-S5 146.37(9)
Ag3-O1 Ag3-O11 Ag3-O21a Ag3-S2c Ag3d-S(3) Ag3d-S(1) O1-Ag3-O11 O1-Ag3-O21a O11-Ag3-O21a O21a-Ag3-S2c O1-Ag3-S2c O11-Ag3-S2c
2.418(3) 2.283(4) 2.354(4) 2.7341(11) 3.0252(11) 3.0871(12) 100.7(2) 101.1(2) 111.2(2) 95.27(1) 101.83(10) 140.91(11)
Symmetry transformations used to generate equivalent atoms: 2 - x, 3 - y, 1 - z. b 1.5 - x, 0.5 + y, 0.5 - z. c 2.5 - x, 0.5 + y, 0.5 d 2.5 - x, -0.5 + y, 0.5 - z.
Figure 2. Projections of the structures of {[Ag3(hta)(PO2F2)3]}∞ onto (a) the (1 0 0) and (b) the (0 1 0) planes showing the correspondence to the projection of the TiO2 (rutile) structure onto the (1 0 0) plane. For clarity, bonds within the [Ag(PO2F2)]6 cages are shown as blue dashed lines and those within the tetramethylhexathiaadamantane molecules are shown as solid red lines.
equivalent). Metal-organic coordination polymers with the rutile structure are extremely rare and have only been seen previously in the structures of the tricyanomethanides, {M[C(CN)3]2}∞ (M ) Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, or Hg).21
Conclusions The metal-organic coordination polymer produced in this work is one of a small number that adopts classical inorganic structures, such as β-crystobalite (diamond),22
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Brooks et al. Table 3. Crystallographic Data Summary for {[Ag3(hta)(PO2F2)3]}∞
Figure 3. Structural connectivity in the extended structure of {[Ag3(hta)(PO2F2)3]}∞ showing the disposition of the hta molecules [centroid represented by point B (dotted spheres)] around the [Ag(PO2F2)]6 cage [inversion center of the cage represented by point A (crosshatched spheres)] linked via Ag(I) centers (open spheres) showing the trigonal planar connectivity of the hta molecule and the distorted octahedral connectivity of the [Ag(PO2F2)]6 cage.
Scheme 5. Schematic Representation of the Connectivities in the [Ag(PO2F2)]6 Cluster
Table 2. Geometrical Data (distances/Å; Angles/°) for the Connectivities of the Hta Molecule and of the [Ag(PO2F2)]6 Cage in {[Ag3(hta)(PO2F2)3]}∞ distances (Å) A‚‚‚Ag1 A‚‚‚Ag2 A‚‚‚Ag3 B‚‚‚Ag1 B‚‚‚Ag2 B‚‚‚Ag3
angles (deg) 3.518 3.584 3.696 3.544 3.993 3.828
Ag1‚‚‚A‚‚‚Ag2 Ag1‚‚‚A‚‚‚Ag3 Ag2‚‚‚A‚‚‚Ag3 Ag1‚‚‚B‚‚‚Ag2 Ag1‚‚‚B‚‚‚Ag3 Ag2‚‚‚B‚‚‚Ag3
117.3 120.5 122.2 57.4 119.4 81.9
CdSO4,6,23 ReO3 (R-Po),24 and PtS.25 In this case, the (6‚ 3) coordination structure of the rutile phase of TiO2 is adopted, the distorted octahedral Ti(IV) centers being replaced by [Ag(PO2F2)]6 cages and the distorted trigonal planar oxide anions by hta bridging ligands. The cages arise following hydrolysis of [PF6-] in the wet solvent according to the equilibria: + H2O
+ H2O
[PF6-] y\ z [POF4-] y\ z [PO2F2-] - 2HF - 2HF which are driven to the right by the crystallization of {[Ag3(hta)(PO2F2)3]}∞. The connectivity exhibited by the
formula M crystal system space group a (Å)
C8H12Ag3F6O6P3S6 927.06 monoclinic
U/Å3 Z T/K
2348.41(11) 4 150(2)
P21/n
3.288
b (Å)
10.1883(3)
c (Å)
19.2059(5)
m(Mo - Ka) (mm-1) reflections collected unique reflections, Rint R1
b (deg)
92.790(2)
wR2 (all data)
12.0158(3)
15661 5316, 0.043 0.0380 [4611 > 2s(I)] 0.0780
hta ligand (three short and two longer chelating Ag-S contacts) is greater than that of the analogous ligand (two short contacts) in the only other structurally characterized hta-containing complex, [Pd(hta)Cl2].17 This variabile connectivity suggests that hta may be a highly flexible S-donor bridging ligand, a phenomenon we are presently pursuing by probing the structural chemistry of hta complexes of a variety of diverse Ag(I) salts. Experimental Section General Procedures. With the exception of hta, which was prepared following a literature procedure,26 all reagents were used as received. Elemental analysis (C H N) was performed by the Nottingham University School of Chemistry Microanalytical Service using a Perkin-Elmer 240B instrument. Infrared spectra were obtained (as KBr pressed pellets) using a Nicolet Avatar 360 FTIR spectrometer. 1H- and 13C NMR spectra were obtained using a Bruker DPX 300 spectrometer. Synthesis of hta. ZnCl2 (5 g, 36.7 mmol) was slowly added to thioacetic acid (10 cm3; 140 mmol), and the resultant mixture was stirred overnight. Addition of HCl (16 mol dm-3; 20 cm3) gave a precipitate which was removed by filtration, washed thoroughly with HCl (2 mol dm-3; 2 × 20 cm3), H2O (2 × 10 cm3), MeOH (2 × 10 cm3), and CHCl3 (2 × 25 cm3). The solid product was recrystallized twice from pyridine to give hta as a white powder. Yield 2.88 g, 9.6 mmol, 41%. Found (calc. for C8H12S6) %: C, 32.15 (31.95); H, 3.85 (4.05). IR (KBr disk) ν/cm-1: 2964 m, 2910 w, 1431 m, 1365 s, 1087 s, 1025 s, 716 s. 1H NMR (CDCl3) δ/ppm 2.16 (CH3C-). 13C NMR (CDCl3) δ/ppm 29.2 (CH3-), 58.5 (CH3C-). Synthesis of {[Ag3(hta)(PO2F2)3]}∞. To a solution of AgPF6 (195 mg; 0.78 mmol) in MeOH (10 cm3) was added a solution of hta (78 mg; 0.26 mmol) in CH2Cl2 (10 cm3). Et2O was added and the mixture was stirred at room temperature for 1 h. The resultant white precipitate was recovered by filtration, washed with CH2Cl2 and dried in a vacuum. Yield: 30 mg, 11%. Found (calc. for C8H12Ag3P3F6O6S6) %: C, 10.45 (10.25); H, 1.35 (1.30). IR (KBr disk) ν/cm-1: 2965 w, 2940 w, 1437 w, 1314 vs, 1152 s, 1087 m, 1025 w, 853 s, 836 s, 716 s, 513 m, 499 s. Single crystals suitable for X-ray diffraction studies were grown by slow layered diffusion of solutions of AgPF6 and hta in the same solvents as used for the bulk preparation and in the appropriate stoichiometry. Crystallography. Single-crystal X-ray diffraction data were collected at 150(2) K on an Enraf Nonius kappaCCD area detector diffractometer equipped with an Oxford Cryosystems open flow cryostat27 and using a rotating anode source of graphite monochromated Mo-KR radiation (λ ) 0.71073 Å). Pertinent details of crystal data, data collection, and processing are given in Table 3. The structure was solved by direct methods using SHELXS 9728 and full-matrix least squares refinement was undertaken using SHELXL 97.29 All hydrogen atoms were placed in geometrically calculated positions and thereafter refined using a riding model. All non-hydrogen atoms were refined with anisotropic displacement parameters.
Silver(I) Difluorophosphate(V)-tetramethylhexathiaadamantane The largest residual electron density features were located close to the silver atom.
Acknowledgment. We thank the EPSRC for provision of diffractometer facilities and for financial support (to N.R.B.), the EPSRC X-ray crystallographic facilities at the University of Southampton, and the University of Nottingham for financial support (to J.W.C.). Supporting Information Available: An X-ray crystallographic file in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.
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CG010015O
