Exceptional Structural Compliance of the B12F122– Superweak Anion

Mar 23, 2017 - Of greatest significance are the three lines of evidence that demonstrate the exceptional structural compliance of B12F122–: (i) the ...
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Exceptional Structural Compliance of the B12F122− Superweak Anion Dmitry V. Peryshkov*,†,‡ and Steven H. Strauss*,† †

Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States

‡

S Supporting Information *

ABSTRACT: The single-crystal X-ray structures, thermogravimetric analyses, and/or FTIR spectra of a series of salts of the B12F122− anion and homoleptic Ag(L)n+ cations are reported (L = CH2Cl2, n = 2; L = PhCH3, n = 3; L = CH3CN; n = 2−4; L = CO, n = 1, 2). The superweak-anion nature of B12F122− (Y2−) was demonstrated by the rapid reaction of microcrystalline Ag2(Y) with 1 atm of CO to form a nonclassical silver(I) carbonyl compound with an FTIR ν(CO) band at 2198 cm−1 (and with the proposed formula [Ag(CO)n]2[Y]). In contrast, microcrystalline Ag2(B12Cl12) did not exhibit ν(CO) bands and therefore did not form Ag(CO)+ species, even after 32 h under 24 atm of CO. When Ag2(Y) was treated with carbon monoxide pressures higher than 1 atm, a new ν(CO) band at 2190 cm−1 appeared, which is characteristic of a Ag(CO)2+ dicarbonyl cation. Both Ag2(CH3CN)8(Y) and Ag2(CH3CN)5(Y) rapidly lost coordinated CH3CN at 25 °C to form Ag2(CH3CN)4(Y), which formed solvent-free Ag2(Y) only after heating above 100 °C. Similarly, Ag2(PhCH3)6(Y) rapidly lost coordinated PhCH3 at 25 °C to form Ag2(PhCH3)2(Y), which formed Ag2(Y) after heating above 150 °C, and Ag2(CH2Cl2)4(Y) rapidly lost three of the four coordinated CH2Cl2 ligands between 25 and 100 °C and formed Ag2(Y) when it was heated above 200 °C. Solvent-free Ag2(Y) was stable until it was heated above 380 °C. The rapid evaporative loss of coordinated ligands at 25 °C from nonporous crystalline solids requires equally rapid structural reorganization of the lattice and is one of three manifestations of the structural compliance of the Y2− anion reported in this work. The second, more quantitative, manifestation is that Ag+ bond-valence sums for Ag2(CH3CN)n(Y) are virtually constant, 1.20 ± 0.03, for n = 8, 5, 4, because the Y2− anion precisely compensated for the lost CH3CN ligands by readily forming the necessary number of weak Ag−F(B) bonds. The third, and most exceptional, manifestation is that the idealized structural reorganization accompanying the conceptual transformations Ag2(CH3CN)8(Y) → Ag2(CH3CN)5(Y) → Ag2(CH3CN)4(Y) involve close-packed layers of Y2− anions that sandwich the Ag(CH3CN)4+ complexes splitting into staggered flat ribbons of interconnected (Y2−)3 triangles that surround the Ag2(CH3CN)52+ complexes on four sides, conceptually re-forming close-packed layers of anions that sandwich the Ag(CH3CN)2+ complexes. The interconnected (Y2−)3 triangle lattice of anions in Ag2(CH3CN)5(Y) may be the first example of this structure type.

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INTRODUCTION In previous publications we reported the structures of hydrated, solvated, and ligated silver(I) salts of the icosahedral B12F122− sup erweak anion, including Ag 2 (H 2 O ) 4 (B 1 2 F 1 2 ), 1 Ag2(SO2)6(B12F12),1 and Ag2(1-NH2-1,2,3-triazole)4(B12F12).2 Such structures can serve as models for the solvation of Ag+ and other metal ions in solvents such as H2O3,4 and SO25 and for the solvation of Ag+ in extended framework solids such as MOFs and zeolites.6−8 They can also be used to measure the Lewis basicity, or coordinating ability, of different solvent molecules and ligands for particular metal ions in the presence of a common weakly coordinating anion (WCA) in the solid state. Conceptually, and in practice, this is a very different measure than the commonly used comparison, Gutmann’s solvent donor number,9−11 a measurement of the Lewis basicity of solvent molecules (and some ligands) toward the nonmetal Lewis acid SbCl5 in the weakly coordinating solvent 1,2C2H4Cl2 (note that this solvent can no longer be considered noncoordinating, at least not for Ag+ and Tl+ 12,13). In addition, structures of M(solv)n(WCA) can also be used to compare the © 2017 American Chemical Society

coordinating ability of different WCAs to a particular metal ion/solvent combination in solid-state structures. In a recent paper we quantitatively determined for the first time the coordinating strength of H2O versus SO2 toward Ag+ in the solid state when the counterion is B12F122−.1 We found that the average Ag−OH2 bond valence14,15 is 75% higher than the average Ag−OSO bond valence.1 The structure of Ag2(H2O)4(B12F12),1 which crystallized from aqueous solution, also demonstrated that B12F122− is more weakly coordinating toward Ag+ in the solid state than the important and more readily accessible WCA B12Cl122−,16−18 because Ag2(B12Cl12) crystallizes from aqueous solution with no coordinated H2O molecules (i.e., as anhydrous Ag2(B12Cl12)).19 We herein report single-crystal X-ray structures and thermogravimetric analyses for Ag2(L)n(B12F12) compounds with L = CH3CN (n = 4, 5, 8), PhCH3 (n = 6), and CH2Cl2 (n = 4). The results demonstrate that in the solid state the WCA Received: January 7, 2017 Published: March 23, 2017 4072

DOI: 10.1021/acs.inorgchem.7b00051 Inorg. Chem. 2017, 56, 4072−4083

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Inorganic Chemistry Table 1. Crystallographic and Data Collection Parameters for Ag2(L)nB12F12 Salts empirical formula formula wt habit, color cryst size (mm) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z T (K) ρcalc (g cm−3) R(F) (I > 2σ(I))a Rw(F2) (all data)a GOF empirical formula formula wt habit, color cryst size (mm) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z T (K) ρcalc (g cm−3) R(F) (I > 2σ(I))a Rw(F2) (all data)a GOF a

Ag2(CH3CN)4B12F12

Ag2(CH3CN)5B12F12

Ag2(CH3CN)8B12F12

C8H12B12F12Ag2N4 737.68 prism, colorless 0.07 × 0.07 × 0.30 orthorhombic Cccm 11.4426(7) 13.6213(7) 15.6534(8) 90 90 90 2439.8(2) 4 120(2) 2.008 0.0264 0.0766 1.037 Ag2(CH2Cl2)4B12F12

C10H15Ag2B12F12N5 778.73 prism, colorless 0.17 × 0.19 × 0.37 monoclinic C2/c 10.2588(5) 27.6109(13) 9.0019(4) 90 92.487(2) 104.958(2) 2547.4(2) 4 120(2) 2.030 0.0244 0.0618 0.971

C16H24Ag2B12F12N4 901.90 prism, colorless 0.13 × 0.18 × 0.20 monoclinic P21/c 10.1859(5) 11.6479(7) 14.1573(7) 90 91.609(3) 90 1679.02(15) 2 120(2) 1.784 0.0465 0.1041 1.051 Ag2(PhCH3)6B12F12

C4H8Ag2B12Cl8F12 913.16 g mol−1 prism, colorless 0.20 × 0.29 × 0.32 monoclinic P21/n 10.6082(4) 10.3304(4) 11.6143(5) 90 97.762(2) 90 1261.11(9) 2 120(2) 2.405 0.0171 0.0441 1.177

C42H48Ag2B12F12 1126.26 g mol−1 prism, colorless 0.086 × 0.089 × 0.200 monoclinic P21/c 11.0173(6) 11.1634(6) 19.8355(9) 90 105.492(2) 90 2350.9(2) 2 120(2) 1.591 0.0414 0.1044 1.075

R(F) = ∑||Fo| − |Fc||/∑|Fo|; wR(F2) = (∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2])1/2. as previously described.1,20 Anhydrous Ag2(B12Cl12) was prepared and recrystallized from water as previously described.21 Carbon monoxide (Matheson, 99.00%) was used as received. The solvents dichloromethane, toluene, pentane, and acetonitrile (Sigma-Aldrich) were dried and distilled by standard techniques and were stored in a purified-dinitrogen-atmosphere glovebox. 22 All samples of Ag2(B12F12), Ag2(B12Cl12), and Ag2(L)n(B12F12) were stored in the glovebox with minimal exposure to light unless otherwise indicated below. Isolation and Handling of Crystalline Ag2(L)n(B12F12) Compounds. An equal volume of 1,2-C2H4Cl2 was added to Ag2(B12F12) dissolved in CH3CN. Cooling the solution to −20 °C resulted in the formation of colorless diffraction-quality crystals of Ag2(CH3CN)8(B12F12), which were isolated by filtration. A suitable crystal was quickly chosen, attached to a goniometer pin, and cooled to −120 °C in a cold stream of nitrogen on the X-ray diffractometer (vide infra) to avoid the loss of coordinated CH3CN and the concomitant loss of crystallinity. When a solution of Ag2(B12F12) dissolved in 50/50 CH3CN/1,2-C2H4Cl2 was allowed to evaporate slowly at 25 °C, colorless diffraction-quality crystals of Ag2(CH3CN)5(B12F12) were formed and isolated by filtration. As above, a suitable crystal was

B12F122− coordinates to Ag+ more weakly than B12Cl122−, Pd(OTeF5)42−, SbF6−, and BF4−, slightly more strongly than 1Me-CB11F11−, B(C6F5)4−, and Li(Al2F5(C(SiMe3)3)2)2−, and significantly more strongly than B(C6H3(CF3)2)4−. The results also indicate that PhCH3 coordinates to Ag+ more strongly than CH2Cl2 or H2O and about equally as strongly as CH3CN. In addition, FTIR spectra of [Ag(CO)n]2[B12F12], formed by treating Ag2(B12F12) with CO, are consistent with the “superweak anion” nature of B12F122−. Most importantly, three sets of observations demonstrate the exceptional structural compliance of B12F122− in facilitating rapid solidstate transformations in salts of metal complex cations.

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EXPERIMENTAL METHODS

Reagents and General Procedures. Distilled water was deionized with a Barnstead Nanopure system. The deionized distilled water (dd-H2O) had a resistivity greater than or equal to 18 MΩ. The anhydrous, solvent-free salt Ag 2 (B 12 F12 ) was prepared from Ag2(CH3CN)4(B12F12) by heating under vacuum at 270 °C for 2 h 4073

DOI: 10.1021/acs.inorgchem.7b00051 Inorg. Chem. 2017, 56, 4072−4083

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Inorganic Chemistry Table 2. Selected Interatomic Distances (Å) and Angles (deg)a Ag2(CH3CN)4(B12F12) Ag−F Ag−X ∑(Ag−F bond valences) ∑(Ag−X bond valences) ∑(Ag bond valences) closest Ag···⊙ ⊙···⊙e av ⊙···⊙e ⊥ ⊙6···⊙6f ⊙···⊙···⊙e closest Ag···Ag B−F B−B

2.797(8) × 2, 2.992(8) × 2 2.101(2)b × 2

Ag2(CH3CN)5(B12F12)

Ag2(CH3CN)8(B12F12)

2.920(2), 3.041(2)

Ag2(CH2Cl2)4(B12F12)

Ag2(PhCH3)6(B12F12)

2.225(3)−2.419(6)b

0.22

2.139(2), 2.160(2), 2.453(2)b 0.08

2.634(1), 2.649(1), 2.679(1) 2.6586(3)−2.8837(4)c

2.991(4)

0.00

0.30

0.04

1.01b

1.09b

1.21b

0.66c

0.90d

1.23 5.029 8.895, 9.695, 10.375 9.655 7.645 52.5−67.7 3.131 1.380(2)−1.387(3) 1.787(2)−1.799(4)

1.17 5.503−5.886 8.689, 9.002 8.846 10.249 58.8−62.4 3.548 1.380(2)−1.387(2) 1.786(2)−1.801(2)

1.21 6.345, 6.875 9.617 × 2, 11.648 10.294 10.182 58.6−78.9 4.084 1.382(4)−1.388(4) 1.786(5)−1.796(5)

0.96 4.766, 5.234 9.842 × 2, 10.330 10.005 7.286 58.3−66.3 6.327 1.380(1)−1.389(1) 1.794(2)−1.803(2)

0.94 5.789, 6.997 11.107, 11.381, 13.875 12.121 9.640 50.6−76.5 8.057 1.376(4)−1.387(3) 1.782(4)−1.801(5)

2.408(3)−2.899(4)d

a

All results from this work. bX = N. cX = Cl. dX = C. eThese distances and angles are within the close-packed hexagonal planes or triangular ribbons of B12 centroids (⊙s). fPerpendicular distance between hexagonal planes or triangular ribbons of ⊙s.

quickly chosen and mounted on the diffractometer at −120 °C. Placing a sample of crystalline Ag 2 (CH 3 CN) 5 (B 12 F 12 ) or Ag2(CH3CN)8(B12F12) under vacuum resulted in a white powder. Cooling a CH2Cl2 solution of the powder to −20 °C resulted in the f o r m a t i o n o f c o l o r l e s s d i ff r a c ti o n - q u a l i t y c r y s t a l s o f Ag2(CH3CN)4(B12F12), which, after filtration, could be handled in air briefly without loss of CH3CN. A mixture of Ag2(B12F12) (77 mg) and PhCH3 (15 mL) was heated at 50 °C for 18 h and slowly cooled to room temperature. Colorless diffraction-quality crystals of Ag2(PhCH3)6(B12F12) were isolated by filtration. A suitable crystal was handled as above to avoid loss of coordinated PhCH3. Finally, pentane vapor was allowed to slowly diffuse into a dichloromethane solution of Ag2(B12F12), resulting in colorless diffraction-quality crystals of Ag2(CH2Cl2)4(B12F12). After filtration, a suitable crystal was handled as above to avoid loss of coordinated CH2Cl2. Thermogravimetric Analysis. Platinum pans were loaded with 10−20 mg samples of microcrystalline Ag2(L)n(B12F12) compounds and placed in the sample chamber of a TA Instruments Series 2950 thermogravimetric analyzer with minimal exposure to air to minimize coordinated solvent loss before beginning the analysis. The heating rate was 3 °C/min−1. The sample chamber was continuously purged with 635 ± 10 Torr of dry helium at 60 mL min−1 (this is the typical range of atmospheric pressures in Fort Collins, CO). FTIR Spectroscopy. Spectra were recorded with a Nicolet Magna760 FTIR spectrometer at 1 cm−1 resolution. A sample of solvent-free Ag2(B12F12) in an evacuated flask was exposed to 500 Torr of CO for several minutes. After the sample flask was briefly evacuated to remove CO, the resulting sample was brought into the glovebox and quickly mulled in Nujol. The FTIR spectrum of the mull sandwiched between AgCl windows was then recorded as quickly as possible (several minutes). Spectra under a high pressure of CO were recorded using a high-pressure gas IR cell of local design.23 In this cell, a thick Nujol mull of each compound was sandwiched between two sapphire windows held 0.1 mm apart. Under these conditions, high-pressure CO slowly diffuses through the thick mull and can react with the compound without the presence of CO gas in the beam path, allowing transmission FTIR spectra of labile metal carbonyl compounds with ν(CO) bands near 2143 cm−1 (the value for CO gas) to be observed in spite of the high pressure of CO gas in the cell.23 In previous work it was shown that 1 day or more is necessary before equilibrium is established between the compound and the high pressure of CO gas.23 For Ag2(B12F12), P(CO) was 1000 psia (ca. 68 atm) and spectra were recorded after 4, 22, and 108 h. For Ag2(B12Cl12), P(CO) was 350 psia (ca. 24 atm) and spectra were recorded after 32 and 96 h.

X-ray Diffraction. Single-crystal X-ray diffraction data were collected using a Bruker Kappa APEX II CCD diffractometer employing Mo Kα radiation. Unit cell parameters were obtained from least-squares fits to the angular coordinates of all reflections, and intensities were integrated from a series of frames (ω and φ rotations) covering more than a hemisphere of reciprocal space. Absorption and other corrections were applied using SADABS. The structures were solved using direct methods and refined (on F2, using all data) by a full-matrix, weighted least-squares process. Standard Bruker control and integration software (APEX II) was employed, and Bruker SHELXTL software was used for structure solution, refinement, and molecular graphics. Other information can be found in the Supporting Information.

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RESULTS AND DISCUSSION Crystallographic and data collection parameters for the five Ag2(L)n(B12F12) structures are given in Table 1 (L = CH3CN, PhCH3, CH2Cl2). Selected distances and angles, including distances and angles involving the B12 centroids of the B12F122− anions (⊙s), are given in Table 2. Ranges of Ag−L and Ag− anion interatomic distances and sums of bond valences are given in Table 3, which also includes results for selected compounds from the literature with the same coordinated solvent molecules but with different weakly coordinating anions (WCAs). Table S1 in the Supporting Information gives the bond valence parameters14,15 used in this work.12,24−32 Individual Ag−L and Ag−anion distances and bond valence values are given in Tables S2−S22 in the Supporting Information. Drawings of the Ag2(CH3CN)22+, Ag2(CH3CN)52+, Ag(CH3CN)4+, Ag(PhCH3)3+, and Ag(CH2Cl2)2+ complexes, along with their weak bonds with one or more F atoms from proximate B12F122− anions, are shown in Figures 1−5. A thermal ellipsoid plot of the B12F122− anion in Ag2(CH3CN)5(B12F12) is also shown in Figure 2. As expected, distances and angles within the icosahedral B12F122− anions are virtually the same as those reported previously1,33 and will not be discussed further. The crystal-packing patterns of the cations and B12F122− anions will be discussed later in this section. Thermogravimetric analysis (TGA) mass and temperature vs time plots for a sample of Ag2(PhCH3)6(B12F12) are shown in Figure 6. These show that the compound was transformed into Ag2(PhCH3)2(B12F12) at 25 °C over ca. 1 h. This compound 4074

DOI: 10.1021/acs.inorgchem.7b00051 Inorg. Chem. 2017, 56, 4072−4083

4 @ 2.225(3)−2.419(6) 4 @ 2.248(6)−2.313(5) 2.139(2), 2.160(2), 2.453(1) 2.101(2) × 2 2.097(2) × 2 6 @ 2.408(3)−2.899(3) 6 @ 2.396(3)−2.790(4) 4 @ 2.363(6)−2.647(6) 6 @ 2.407(6)−2.692(7) 6 @ 2.391(6)−2.737(8) 6 @ 2.48(1)−2.89(1) 4@ 2.6586(3)−2.8837(4) 4 @ 2.775(2)−2.882(2) 4 @ 2.657(2)−3.128(3) 6 @ 2.702(3)−3.049(4) 2.613(2), 2.874(4) 4 @ 2.376(5)−2.511(5) 6 @ 2.526(5)−2.791(5)

Ag−L, Åb

3 @ 2.634(1)−2.679(1) 3.030(4) 3 @ 2.524(3)−2.601(3) 3.029(8), 3.033(6) 4 @ 2.85(1)−2.93(1) 2.742(5), 2.751(5) 2.541(3), 2.558(4)

2.920(1), 3.041(1) 4 @ 2.797(2)−2.992(2) 3.132(2) × 2 2.991(3)

Ag−F, Åc

2.377(5), 2.386(4)

2.405(5), 2.532(4)

2.596(2), 2.599(2)

Ag−O, Åc 1.21 1.26 1.17 1.23 1.08 0.94 0.95 0.96 1.01 1.01 0.96 0.96 0.92 0.97 0.94 1.00 0.88 0.93

∑(bv)d 100 100 93 82 95 96 100 77 100 100 84 69 59 59 92 36 85 72

% ∑(bv) for Ag−L bondse 0 0 7 18 5 4 0 23 0 0 16 31 41 41 8 64 15 28

% ∑(bv) for Ag−F/O bondsf

All results from this work unless otherwise specified. Bond valence parameters and the individual bond distances and bond valences for each compound are given in Tables S1−S22 in the Supporting Information. bBond distances between the Ag+ ion and the coordinated solvent-molecule atom (L). cBond distances between the Ag+ ion and coordinated F or O atoms of the counteranion. dThe sum of all Ag−L, Ag−F, and Ag−O bond valences (∑(bv)). eThe percentage of the ∑(bv) attributed to Ag−L bonds. fThe percentage of the ∑(bv) attributed to bonds between the Ag+ ion and the counteranion (i.e., to all Ag−F and Ag−O bonds). gAg−L = Ag−NCCH3. hReference 24. iReference 25. jAg−L = Ag−C(sp2). kReference 26; Z− = Li(Al2F5(C(SiMe3)3)2)2−. lReference 27; HFIP = OCH(CF3)2. mReference 28. nReference 29. oReference 30. pAg−L = Ag−ClCH2Cl. qReference 12. rReference 31. sReference 32. tReference 27; HFTB = OC(CH3) (CF3)2. uReference 1. vAg−L = Ag− OH2. wAg−L = Ag−OSO.

a

g

Ag2(CH3CN)8(B12F12) Ag(CH3CN)4(SO3F)g,h Ag2(CH3CN)5(B12F12)g Ag2(CH3CN)4(B12F12)g Ag(CH3CN)2(B(C6H3(CF3)2)4)g,i Ag2(PhCH3)6(B12F12)j Ag(PhCH3)3(Z)j,k Ag(PhCH3)2(Al(HFIP)4)j,l Ag(CHPh3)(1-Me-CB11F11)j,m Ag(C6H6)3(B(C6F5)4)j,n Ag(C6D6)3(BF4)j,o Ag2(CH2Cl2)4(B12F12)p Ag2(CH2Cl2)4(Pd(OTeF5)4)p,q Ag(CH2Cl2)2(SbF6)p,r Ag2(CH2Cl2)6(Ti(OTeF5)6)p,s Ag(CH2Cl2) (Al(HFTB)4)p,t Ag2(H2O)4(B12F12)u,v Ag2(SO2)6(B12F12)u,w

compd

Table 3. Bond Distances and Bond Valence (bv) Sums and Percentages for Structurally Characterized Compounds Containing Weakly Coordinating Anions and Homoleptic Ag(L)n+ Cations (L = CH3CN, PhCH3, C6H6, C6D6, H2O, SO2, CH2Cl2)a

Inorganic Chemistry Article

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Figure 3. Ag(CH 3 CN) 4 + complex in the structure of Ag2(CH3CN)8(B12F12) (50% probability ellipsoids except for H atoms). The coordination geometry is that of a slightly flattened tetrahedron. The longer “vertical” Ag−N distance is 2.419(6) Å; the three shorter Ag−N distances are 2.225(3), 2.263(8), and 2.295(4) Å. The closest Ag···Ag distance between the tetrahedral Ag(CH3CN)4+ cations is 4.084(1) Å and is not considered to be attractive.

Figure 1. D2-symmetric Ag2F8(CH3CN)42+ dimers in the structure of Ag2(CH3CN)4(B12F12) (50% probability ellipsoids except for H atoms). The Ag···Ag vector is a crystallographic C2 axis; the Ag···Ag distance is 3.131(1) Å. The next shortest Ag···Ag distance is 4.696(1) Å. For each of the two monomeric Ag(CH3CN)2+ complex cations, the two Ag−N distances are 2.101(2) Å and the N−Ag−N angle is 172.4(1)°. The four Ag−F distances for each Ag(CH3CN)2+ complex are 2.797(2) (×2) and 2.992(2) (×2) Å.

Figure 4. Ag(PhCH 3 ) 3 + complex in the structure of Ag2(PhCH3)6(B12F12) (50% probability ellipsoids except for H atoms). The PhCH3 ligands are coordinated in a hybrid of η1 and η2 fashion. The Ag−C1, Ag−C2, Ag−C8, Ag−C9, Ag−C15, and Ag− C20 distances are 2.427(3), 2.652(3), 2.408(3), 2.600(3), 2.512(3), and 2.899(3) Å, respectively. The C9−C8−Ag, C2−C1−Ag, and C20−C15−Ag angles are 81.6(1), 83.4(4), and 91.3(1)°. The very long Ag···F(B) interaction of 2.991(3) Å has a nearly insignificant bond-valence value of 0.04.

Figure 2. Drawing of the structure of Ag2(CH3CN)5(B12F12) showing one entire B12F122− anion (50% probability ellipsoids except for H atoms). A different view of the [(CH3CN)2Ag(μ-CH3CN-κ1,κ2N)Ag(CH3CN)2]2+ dinuclear complex and the four F atoms bonded to it is shown in Figure S4 in the Supporting Information. The Ag···Ag distance is 3.548(1) Å and is not considered to be attractive. The ranges of B−B and B−F bond distances are 1.786(2)−1.801(2) and 1.380(2)−1.387(2) Å, respectively.

was stable until ca. 120 °C and upon an increase in the temperature was transformed first into Ag2(PhCH3)(B12F12) at ca. 200 °C and ultimately into solvent-free Ag2(B12F12), which was stable until ca. 380 °C. Similar TGA plots for samples of Ag2(CH2Cl2)4(B12F12) and Ag2(CH3CN)4(B12F12), which confirmed the thermal stability of Ag2(B12F12) up to 380 °C, are shown in Figure S1 in the Supporting Information. FTIR spectra of Ag2(CO)2(B12F12) and of Ag2(CO)n>2(B12F12) over time under a constant 1000 psia pressure of CO gas are shown in Figure 7. A comparison of FTIR spectra of Ag2(B12F12) and Ag2(B12Cl12) under high pressures of CO is shown in Figure S2 in the Supporting Information. An FTIR spectrum of Ag2(CH3CN)4(B12F12) is shown in Figure S3 in the Supporting Information.

Figure 5. Ag(CH 2 Cl 2 ) 2 + cations in the structure of Ag2(CH2Cl2)4(B12F12), also showing the three Ag−F bonds to proximate B12F122− anions (50% probability ellipsoids except for H atoms). The four Ag−Cl distances are 2.6586(3), 2.6913(3), 2.8341(4), and 2.8837(4) Å and the three Ag−F(B) distances are 2.634(1), 2.639(1), and 2.679(1) Å.

Superweak-Anion Nature of B12F122−. In 1998 we defined a superweak anion as the conjugate base of a superacid, whether or not that superacid exists or is only a theoretically 4076

DOI: 10.1021/acs.inorgchem.7b00051 Inorg. Chem. 2017, 56, 4072−4083

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Table 4. Solid-State FTIR ν(CO) Values for Silver(I) Carbonylsa,b compd

FTIR ν(CO), cm−1

Monocarbonyl Complexes [Ag(CO)][Nb(OTeF5)6] 2208 [Ag(CO)]2[Ti(OTeF5)6] 2207 [Ag(CO)][B(CF3)4] 2205 [Ag(CO)][B(OTeF5)4] 2204 [Ag(CO)]2[B12F12] 2198 [Ag(CO)][ZSM-5] 2192 [Ag(CO)][Al(OC(CH3)(CF3)2)4] 2190 [Ag(CO)][OTeF5] 2189 [Ag(CO)][SbF6] 2185 [Ag(CO)][HB(C3N2(CF3)3)3]c 2177 [Ag(CO)][Nafion] 2173 Dicarbonyl Complexes [Ag(CO)2][Nb(OTeF5)6] 2198 (2200 Raman) [Ag(CO)2]2[Ti(OTeF5)6] 2197d [Ag(CO)2][B(OTeF5)4] 2198d [Ag(CO)2][B(CF3)4] e (2216 Raman) [Ag(CO)2]2[B12F12] 2190d

Figure 6. Thermogravimetric analysis plot for Ag2(PhCH3)6(B12F12).

ref 44 44 45 42, 44 this work 50 46 44 47 48 49 44 44 43, 44 45 this work

a The ν(CO) value for CO gas is 2143 cm−1. bSamples were recorded as Nujol mulls exposed to CO gas. cHB(C3N2(CF3)3)3− = 3,4,5tris(pyrazolyl)borate(1−). dThe Raman spectrum was not recorded. e The FTIR ν(CO) band for [Ag(CO)2][B(CF3)4] was “not observed”. The structure of [Ag(CO)2][B(OTeF5)4] was shown to contain linear Ag(CO)2+ dicarbonyl cations.43

containing WCAs, and [Ag(CO)][HB(C3N2(CF3)3)3].42−50 The X-ray structures of [Ag(CO)][B(OTeF 5 ) 4 ], [Ag(CO)]2[B(OTeF5)4], [Ag(CO)][Al(OC(CH3) (CF3)2)4], and [Ag(CO)][HB(C3N2(CF3)3)3], all of which contain Ag−CO bonds, provide the justification for formulating all of the complexes given in Table 4 as silver(I) carbonyls (i.e., they exhibit FTIR spectra characteristic of compounds with Ag−CO bonds). We also report that Ag2(B12Cl12) did not react with CO gas, even at a pressure of nearly 24 atm, demonstrating that B12Cl122− coordinates more strongly to Ag+ in the solid state than does B12F122−. This is significant because B12Cl122−,16 the conjugate base of the superacid H2B12Cl12,51 has recently been shown to coordinate slightly more weakly than B12F122− to K+ in the solid state.1 The FTIR ν(CO) values in Table 4 indicate that B12F122− coordinates more weakly to Ag+ in the solid state than Al(OC(CH3)(CF3)2)4−, OTeF5−, SbF6−, and HB(C3N2(CF3)3)3− since their Ag(CO)+ salts have ν(CO) values lower than the 2198 cm−1 value for Ag2(CO)2(B12F12). Furthermore, the FTIR ν(CO) values in Table 4 indicate that B12F122− coordinates more strongly to Ag+ in the solid state than B(CF3)4−, Ti(OTeF5)62−, B(OTeF5)6−, or Nb(OTeF5)6−. In addition to being a superweak anion, B12F122− is also chemically, electrochemically, and thermally robust. It was unchanged after 24 h on dissolution in 98% H2SO4 and in 70% HNO3 as well as after 10 days on dissolution in 3 M KOH.52 In addition, the B12F12−/2− E1/2 value is 4.9 V vs Li in EC/DMC solution52 and the one-electron-oxidized radical B12F12− is stable at 25 °C (as crystalline [CoCp2][B12F12]).53 Both K2(B12F12) and Cs2(B12F12) were unchanged after heating to 500 and 600 °C, respectively.54 We now report that Ag2(B12F12) is stable to 380 °C, as shown in the TGA plots in Figure 6 and Figure S1 in the Supporting Information (the heated sample completely dissolved in CD3CN and exhibited

Figure 7. Nujol-mull FTIR spectra of Ag2(B12F12) after treatment with 1 atm of CO and brief evacuation (top) and over time after treatment with 1,000 psi CO in a high-pressure transmission IR cell of local design (bottom) (see Experimental Methods for details).

predicted or hypothetical compound.34 The concept was introduced to draw attention to the growing number of extremely weakly coordinating anions (WCAs) that result in metal cations with gas-phase-like reactivity in condensed phases,35−37 allowing the isolation of compounds such as [Cu(CO)4][1-Et-CB11F11],38 [Ag(CH2Cl2)3]2[Ti(OTeF5)6],32 and hexane- and toluene-soluble, catalytically active lithium “salts” such as LiAl(OC(Ph)(CF3)2)4.39 In addition to the crystallographic evidence presented in this paper, we report that Ag2(B12F12) reacted with 1 atm of CO gas in the solid state to form Ag(CO)+ species (hereinafter referred to as [Ag(CO)]2[B12F12]), as shown in Figure 7. This figure also shows that Ag(CO)2+ species were formed under higher pressure of CO gas. The hallmark of nonclassical behavior is a ν(CO) value greater than 2143 cm−1.40−43 Table 4 gives the FTIR ν(CO) values for [Ag(CO)]2[B12F12], [Ag(CO)2][B12F12], other examples of silver(I) carbonyl compounds 4077

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Inorganic Chemistry the same single-resonance 11B{19F} and 19F{11B} NMR spectra characteristic of the icosahedral B anion,20,54 indicating that, in addition to no mass loss, no rearrangement of the anion had occurred upon heating). In contrast, the silver(I) WCA salts Ag(B(3,5-C6H3(CF3)2)4),25,55 Ag(BF4),56 and Ag(B(CF3)4)45 decompose at 120−140, 230, and 260 °C, respectively. Structures of Ag2(CH3CN)n(B12F12). These three structures, with n = 4, 5, 8, are shown in Figures 1−3, respectively (an alternate view of the [(CH3CN)2F2Ag(μ-CH3CN-κ1,κ2N)AgF2(CH3CN)2]2+ dinuclear dication in Ag2(CH3CN)5(B12F12) is shown in Figure S4 in the Supporting Information). Setting aside for a moment the weak Ag−F(B) interactions, these compounds are related, conceptually, by progressive loss of CH3CN from (i) discrete four-coordinate flattened-tetrahedral Ag(CH3CN)4+ cations, to (ii) dinuclear [(CH3CN)2Ag(μ-CH3CN-κ1,κ2N)Ag(CH3CN)2]2+ dications with two three-coordinate T-shaped Ag(CH3CN)3+ complexes joined by the bridging CH3CN ligand, to (iii) linear twocoordinate Ag(CH3CN)2+ complexes. (It is not known, and we are not suggesting, that crystalline Ag2(CH3CN)8(B12F12) is transformed into crystalline Ag2(CH3CN)5(B12F12) by evaporation of CH3CN or that crystalline Ag2(CH3CN)5(B12F12) is transformed into crystalline Ag2(CH3CN)4(B12F12) by evaporation of CH3CN.) The sums of Ag−N and Ag−F bond valence (bv) values (i.e., ∑(bv)) are 1.20 ± 0.03 for all three compounds, which can be attributed to the precise compensation by the B12F122− anion for the lost CH3CN ligands by forming the necessary number of weak Ag−F(B) bonds. This is a manifestation of the structural compliance of B12F122− as a counterion for forming lattices with metal complexes with relatively weak solvent molecules as ligands. The percentages of the ∑(bv) sums due to Ag−F interactions are 0, 7, and 18% for the n = 8, 5, 4 structures, respectively. As the conceptual transformations Ag(CH3 CN) 4 + → Ag(CH3CN)3+ → Ag(CH3CN)2+ occur, the largest N−Ag−N angle changes from 131° (flattened tetrahedron) to 159° (distorted T-shaped) to 172° (essentially linear). An FTIR spectrum of Ag2(CH3CN)4(B(C6F5)4) in the ν(CN) region is shown in Figure S3 in the Supporting Information. The nearly linear [CH3CN−Ag−NCCH3]+ cations should exhibit only one infrared-active ν(CN) band. The presence of two bands indicates that pairs of [CH3CN−Ag−NCCH3]+ complexes, with an Ag···Ag separation of 3.131 Å, are acting as a vibrationally coupled unit, giving rise to two equal-intensity ν(CN) bands in the FTIR spectrum. Structure of Ag2(PhCH3)6(B12F12). The Ag(PhCH3)3+ complex and its one long Ag−F interaction of 2.991(3) Å is shown in Figure 4. The C15 toluene molecule is coordinated in an η1 fashion (the triangle formed by C15, C20, and Ag is essentially a 30−60−90° right triangle, with angles of 28.7(1), 60.0(1), and 91.3(1)°). The other two PhCH3 ligands are approximately halfway between η1 and η2. Both types of coordination are common in silver(I)−arene complexes (see refs 26 and 28−30 and references therein). Not counting the extremely weak Ag−F interaction, the coordination is approximately trigonal planar (the Ag+ ion is only 0.05 Å out of the mean least-squares plane formed by C1, C2, C8, C9, and C15. Very similar Ag(arene)3+ trigonal-planar coordination was observed in the structures of Ag(PhCH3)3(Li(Al2F5(C(SiMe3)3)2)2),26 Ag(CHPh3)(1-MeCB11F11),28 Ag(C6H6)3(B(C6F5)4),29 and Ag(C6D6)3(BF4)30 (see Table 3). Structure of Ag2(CH2Cl2)4(B12F12). The Ag+ ion in this compound is coordinated to two bidentate CH2Cl2 molecules

and three F atoms from two different anions, as shown in Figure 5. The Ag−Cl distances, which range from 2.6586(3) to 2.8837(3) Å, are similar to those in the Ag(CH2Cl2)2+ cations in the structures of Ag2(CH2Cl2)4(Pd(OTeF5)4)12 and Ag(CH2Cl2)2(SbF6).31 Two other Ag(CH2Cl2)n+ cations isolated in salts of WCAs are Ag(CH2Cl2)2(Al(OC(CH3)(CF3)2)4)27 and Ag2(CH2Cl2)6(Ti(OTeF5)6)32 (see Table 3). The crystal packing of cations and anions in the structures of Ag 2 (CH 2 Cl 2 ) 4 (B 1 2 F 1 2 ), Ag 2 (PhCH 3 ) 6 (B 1 2 F 1 2 ), and Ag2(H2O)4(B12F12)1 are compared side by side in Figure S5 in the Supporting Information). The icosahedral B12F122− anions pack into idealized close-packed layers in which the B12 centroids (⊙s) are rigorously coplanar. The anions are not close-packed in the third dimension. Instead, they are offset (i) by ca. one-half of the ⊙···⊙ distance along one of their respective ⊙···⊙···⊙ vectors and (ii) by a much smaller displacement perpendicular to the aforementioned ⊙···⊙···⊙ vector. This can also be visualized as a pseudo-BCC stacking of anions, as shown in Figure S5 for Ag2(CH2Cl2)4(B12F12), and the pseudo-BCC anion lattice possesses distorted (flattened) octahedral interstices. In the structures of both Ag2(CH2Cl2)4(B12F12) and Ag2(PhCH3)6(B12F12), pairs of Ag(L)n+ complexes reside in these octahedral holes (the centroids of the holes are highlighted as black dots in Figure S5). The packings of cations and anions in the Ag2(CH2CN)n(B12F12) structures are discussed in detail in the last part of the Results and Discussion. Relative Affinities of Solvent Ligands for Ag(I) in the Solid State. There are several ways that Lewis base ligands, including solvent molecules, can be ordered according to their affinities for specific metal ions. Each way has its uses and limitations. One way is to compare gas-phase affinities, the experimentally or theoretically determined M−L bond dissociation energies (BDEs) or ΔH values for M+(g) + L(g) → M(L)+(g) reactions. For example, the experimental gasphase Ag+−L BDEs for L = H2O, CH3CN, C6H6, CO are 131(8), 57 162(6), 58 156(7), 59 and 89(5) kJ mol −1 60 , respectively. Other selected M−L BDEs are given in Table S23 in the Supporting Information. Another way is to compare qualitative or quantitative affinities of a set of ligands for a specific metal ion in a specific solvent. Two examples are Gutmann’s complilation of ligand donor numbers (Lewis acid, SbCl5; solvent, 1,2-C2H4Cl2)10,11 and Martell’s complilation of stability constants (solvent, H2O).61,62 Of course, such comparisons depend on the choice of the reference solvent. For example, CH3CN is a stronger ligand than H2O for the UO22+ cation in the gas phase but is a weaker ligand than H2O for UO22+ in acetonitrile, in which the concentration ratio [H2O]/[UO22+] is only 6.63,64 Furthermore, Gutmann’s donor number scale assigns a donor number of 0 to 1,2-C2H4Cl2, but it is now well-known that solvents such as 1,2-C2H4Cl2 and CH 2 Cl 2 coordinate relatively strongly to some metal ions.12,13,27,31,65,66 A third way, which is the one we use in this paper, is to compare M−L distances, and their derived bond valence (bv) values, in solid-state X-ray structures of M(L)n(WCA) compounds. Such compounds consist of homoleptic M(L)nm+ cations for a the set of ligands L to be compared with the same metal ion and the same weakly coordinating anion (WCA). This approach has been used recently to show that SO2 is a weaker ligand than either CH2Cl231 or H2O1 toward Ag+ in the solid state. Obtaining M(L)n(WCA) crystals depends not only on the cation and the ligand but also on the anion. A soluble 4078

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(C6H3(CF3)2)4) are 82 and 95%, respectively, indicating that B12F122− is significantly more strongly coordinating to Ag+ in the solid state than B(C6H3(CF3)2)4−. Finally, the % ∑(bv) values for the two coordinated CH2Cl2 ligands in Ag2(CH2Cl2)4(B12F12), Ag2(CH2Cl2)4(Pd(OTeF5)4), and Ag(CH2Cl2)2(SbF6) are 69, 59, and 59%, respectively, indicating that B12F122− is significantly more weakly coordinating to Ag+ in the solid state than either Pd(OTeF5)42− or SbF6−. Exceptional Structural Compliance of B12F122−. The three Ag2(CH3CN)n(B12F12) structures, with n = 4, 5, 8 (Figures 1−3), provide a unique opportunity to illustrate the progressive desolvation of a series of homoleptic cationic or cation-like metal complexes paired with the same WCA (the closest analogy is a paper by Kühn et al. reporting the structures of Ag(CH 3 CN) 4 (B(C 6 F 5 ) 4 ) and Ag(CH 3 CN) 2 (B(3,5C6H3(CF3)2)4)25). The lattice “transformations” discussed below are intended to show how the B12F122− anion can readily accommodate different numbers of ligands. The points we are making do not depend on whether these transformations actually occur from one crystalline phase to another, which was not investigated in this study. Drawings of the conceptual desolvation of Ag 2 (CH 3 CN) 8 (B 12 F 12 ) to Ag2(CH3CN)5(B12F12) emphasizing the structural changes of the cations and of the three-dimensional arrays of anions are shown in Figures 8 and 9, respectively. Similar drawings of the desolvation of Ag2(CH3CN)5(B12F12) to Ag2(CH3CN)4(B12F12) are shown in Figures 10 and 11.

cation with a full complement of coordinated solvent-molecule ligands can lose some, or all, of these ligands upon crystallization. For example, both KBF4 and K2(B12F12) are soluble in anhydrous HF, and K(HF)n+ species are undoubtedly present in both solutions. However, crystallization produces solvent-free KBF4 but solvated K2(HF)3(B12F12) containing discrete K2(μ-HF)32+ cations.67 Another example is that both Ag2(B12Cl12) and Ag2(B12F12) are soluble in water, but crystallization results in anhydrous Ag2(B12Cl12)19 but hydrated Ag2(H2O)4(B12F12) containing Ag(H2O)4+ cations (each H2O ligand bridges two Ag+ ions).1 Let us now consider the Ag2(L)n(B12F12) compounds. Three PhCH3 ligands satisfy 96% of the valence of Ag+. This can be compared with 93% for three CH3CN ligands, 85% for four H2O ligands, and 69% for four Ag−Cl bonds from two CH2Cl2 ligands. Therefore, PhCH3 coordinates about as strongly as CH3CN to Ag+ in the solid state and significantly more strongly than either H2O or CH2Cl2. Note that four CH3CN ligands satisfy 100% of the valence of Ag+. However, this is also true when the counteranion is SO3F− (see Table 3), B(C6F5)4− (see Table S20 in the Supporting Information),25 ClO4− (see Table S21 in the Supporting Information),68 or Co(C2B9H11)2− (see Table S22 in the Supporting Information).69 In addition to the compounds with Ag(CH2Cl2)n+ moieties given in Table 3, there are two other structurally characterized compounds with CH2Cl2 coordinated to Ag+. One is a poorly resolved twinned structure of Ag(CH2Cl2)OTeF5, in which a bidentate CH2Cl2 ligand coordinates to Ag+.12 The other is [Ag(CH2Cl2)]2[(HFTB)3AlOAl(HFTB)3], in which a monodentate CH2Cl2 ligand coordinates to Ag+.27 Coordination of B12F122− vs Other Weakly Coordinating Anions to Ag+ in the Solid State. Earlier crystallographic evidence indicated that B12F122− is more weakly ion paired than BF4− with triarylcarbenium(1+) cations in the solid state (e.g., (B)F···C(Ar3) distances were 3.087(2) Å for [CPh3]2[B12F12]52 and 2.58−2.68 Å for two [CAr3][BF4] salts).70 It was recently reported that (i) B12F122− is marginally more strongly coordinated to K+ in the solid state than B12Cl122− (SO2 complexes) and (ii) B12F122− is significantly more strongly coordinated to Na+ in the solid state than B12Cl122− (H2O complexes). In contrast, as discussed above, B12F122− is significantly more weakly coordinated to Ag+ in the solid state than B12Cl122−.1 It is becoming clear that the relative coordinating strength of B12F122− versus B12Cl122− may depend in large part on the polarizability of the cation: B12F122− is the more weakly coordinating of the two anions to soft metal cations such as Ag+, and B12Cl122− is more weakly coordinating to hard metal ions such as Na+ and K+. The results reported in this work allow the coordinating strength of B12F122− to Ag+ in the solid state to be compared to a variety of other WCAs (see Table 3). First, note that the % ∑(bv) values for the three coordinated π-arene ligands in Ag2(PhCH3)6(B12F12) and Ag(C6D6)(BF4) are 96 and 84%, respectively. By this criterion, B12F122− is more weakly coordinating than BF4−. However, the corresponding % ∑(bv) values are 100% for Ag(PhCH 3 ) 3 (Li(Al 2 F 5 (C(SiMe3)3)2)2), Ag(CHPh3)(1-Me-CB11F11), and Ag(C6H6)(B(C6F5)4), indicating that B12F122− is marginally more strongly coordinating to Ag+ in the solid state than Li(Al2F5(C(SiMe3)3)2)2−, 1-Me-CB11F11−, or B(C6F5)4−, all of which have only a single negative charge. The % ∑(bv) values for the two coordinated CH3CN ligands in Ag2 (CH 3CN) 4 (B12 F12) and Ag(CH3CN) 2(B-

Figure 8. Conceptual transformation of Ag2(CH3CN)8(B12F12) into Ag2(CH3CN)5(B12F12) (50% probability ellipsoids except for H atoms). For Ag2(CH3CN)8(B12F12): the Ag−N1, Ag′−N1, and Ag··· Ag′ distances are 2.23, 3.77, and 4.08 Å, respectively, and the Ag−N1− Ag′ angle is 81.5°. For Ag2(CH3CN)5(B12F12): the Ag−N1, Ag′−N1, and Ag···Ag′ distances are 2.45, 2.45, and 3.55 Å, respectively, and the Ag−N1−Ag′ angle is 92.6°. 4079

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Figure 9. Rearrangement of the B12F122− anion lattices during the conceptual transformation of Ag 2 (CH 3 CN) 8 (B 1 2 F 1 2 ) to Ag2(CH3CN)5(B12F12) (only the B12 centroids are shown). The expanded close-packed layers of anions in Ag2(CH3CN)8(B12F12) are split into flat ribbons of interconnected (B12F122−)3 triangles.

Figure 11. Rearrangement of the B12F122− anion lattices during the conceptual transformation of Ag 2 (CH 3 CN) 5 (B 1 2 F 1 2 ) to Ag2(CH3CN)4(B12F12) (B and F atoms omitted for clarity; only the B12 centroids of the anions are shown). The flat ribbons of interconnected (B12F122−)3 triangles in Ag2(CH3CN)5(B12F12) are reassembled into expanded close-packed layers of anions in Ag2(CH3CN)4(B12F12).

in Ag2(CH3CN)5(B12F12), with ⊙···⊙ distances of 8.69 (×2) and 9.00 Å. Remarkably, the 10.25 Å perpendicular distance between the ribbons of interconnected (B12F122−)3 triangles is nearly the same as the aforementioned 10.18 Å distance between the close-packed anion planes in Ag2(CH3CN)8(B12F12). Instead of 2D galleries between the planes of anions in Ag2(CH3CN)8(B12F12), in which the Ag(CH3CN)4+ cations are located, there are 1D channels in Ag2(CH3CN)5(B12F12), formed by four triangle ribbons, that contain the Ag2(CH3CN)52+ cations. Interestingly, a significant portion of the 32% change in formula unit volume on going from Ag2(CH3CN)8(B12F12) to Ag2(CH3CN)5(B12F12) is due to the 23% change in the area of the (B12F122−)3 isosceles triangles in the two structures (41.2 and 33.5 Å2 in Ag2(CH3CN)8(B12F12) and Ag2(CH3CN)5(B12F12), respectively). The loss of one CH3CN ligand per formula unit from Ag 2 (CH 3 CN) 5 (B 12 F 12 ), resulting in the formation of Ag2(CH3CN)4(B12F12), causes a formula-unit volume change of 26.9 Å3, less than half of the 67.6 Å3 change in volume per CH3CN lost on going from Ag2(CH3CN)8(B12F12) to Ag2(CH3CN)5(B12F12). This is because the Ag2(CH3CN)52+ and Ag2(CH3CN)42+ cores in Ag2(CH3CN)5(B12F12) and Ag2(CH3CN)4(B12F12) are similar in size and shape, as shown in Figure 10. The terminal Ag−N distances are 2.14− 2.16 and 2.10 Å, respectively, the N−Ag···Ag′−N′ torsion angles involving the terminal CH3CN ligands are 72.7 and 58.7°, respectively, and the Ag···Ag distances are 3.55 and 3.13 Å, respectively, for Ag2(CH3CN)5(B12F12) and Ag2(CH3CN)4(B12F12). Figure 11 shows that the flat ribbons of interconnected (B 12 F 12 2− ) 3 isosceles triangles in Ag2(CH3CN)5(B12F12) are conceptually re-formed into closepacked layers of anions in Ag2(CH3CN)5(B12F12), exactly the opposite of the anion lattice transformation for the hypothetical Ag2(CH3CN)8(B12F12) → Ag2(CH3CN)5(B12F12) desolvation described in the previous paragraph. (Interestingly, the 38% decrease in formula-unit volume due to the loss of four CH3CN ligands on going from Ag 2 (CH 3 CN) 8 (B 1 2 F 1 2 ) to Ag2(CH3CN)4(B12F12) is almost entirely due to the 34%

Figure 10. Conceptual transformation of Ag2(CH3CN)5(B12F12) into Ag2(CH3CN)4(B12F12) (50% probability ellipsoids except for H atoms). In both drawings the view is looking down the Ag···Ag vector. The Ag···Ag distances are 3.55 and 3.13 Å, respectively, in Ag2(CH3CN)5(B12F12) and Ag2(CH3CN)4(B12F12). The N−Ag··· Ag′−N′ torsion angles involving the terminal CH3CN ligands are 72.7 and 58.7°, respectively, for Ag 2 (CH 3CN) 5 (B 12F 12 ) and Ag2(CH3CN)4(B12F12).

The formula units of Ag 2 (CH 3 CN) 8 (B 12 F 12 ) and Ag2(CH3CN)5(B12F12) differ by three CH3CN ligands, and the respective formula unit volumes differ by 202.7 Å3, or 67.6 Å3 per CH3CN. Figure 8 shows that the Ag2(μ-CH3CN) core in Ag2(CH3CN)5(B12F12), with Ag−N1, Ag′−N1, and Ag···Ag′ distances of 2.45, 2.45, and 3.55 Å, respectively, and an Ag− N1−Ag′ angle of 92.6°, can be conceptually formed by relatively minor movements of the Ag atoms and the incipient bridging CH3CN ligand in Ag2(CH3CN)8(B12F12), which has Ag−N1, Ag′···N1, and Ag···Ag′ distances of 2.23, 3.77, and 4.08 Å, respectively, and an Ag−N1−Ag′ angle of 81.5°. The conceptual rearrangement of the anions during the loss of three CH3CN ligands is shown in Figure 9. The B12F122− anions in Ag2(CH3CN)8(B12F12) are in rigorously planar, expanded close-packed layers, with ⊙···⊙ distances of 9.17 (×2) and 11.65 Å, which are stacked so that the perpendicular distance between the layers is 10.18 Å. The close-packed layers are split into infinite flat ribbons of interconnected (B12F122−)3 triangles 4080

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Inorganic Chemistry decrease in the perpendicular distance between their respective close-packed layers of anions (i.e., 10.18 and 7.65 Å) because the areas of the (B12F122−) triangles in these two structures are almost equal, 41.2 Å2 in Ag2(CH3CN)8(B12F12) and 40.8 Å2 in Ag2(CH3CN)4(B12F12).)

SUMMARY AND CONCLUSIONS The results presented in this paper further demonstrate the “superweak-anion” nature of B12F122− through the generation of nonclassical Ag(CO)n+ carbonyls with ν(CO) values ≥2190 cm−1 and the isolation of a new Ag(CH2Cl2)2+ complex with bidentate CH2Cl2 ligands. The results also show that PhCH3 coordinates to Ag+ in the solid state more strongly than either H2O or CH2Cl2 and about as strongly as CH3CN. Of greatest significance are the three lines of evidence that demonstrate the exceptional structural compliance of B12F122−: (i) the rapid evaporative loss of coordinated ligands at 25 °C from nonporous, crystalline Ag2(L)n(B12F12) solids implies facile, equally rapid reorganization of the lattice, which is dominated by the large B12F122− anions, whether or not the facile losses of ligands are crystal to crystal transformations, (ii) the Ag+ bondvalence sums for the Ag2(CH3CN)n(B12F12) compounds are virtually constant, 1.20 ± 0.03, for n = 8, 5, 4, because the B12F122− anions precisely compensated for the lost CH3CN ligands by forming the necessary network of weak Ag−F(B) bonds, and (iii) the structural reorganization accompanying the conceptual transformations Ag 2 (CH 3 CN) 8 (B 12 F 12 ) → Ag2(CH3CN)5(B12F12) → Ag2(CH3CN)4(B12F12) involve close-packed layers of B12F122− anions that sandwich the Ag(CH3CN)4+ complexes, rapidly splitting into staggered flat ribbons of interconnected (B12F122−)3 triangles that form channels around the Ag2(CH3CN)52+ complexes, and just as rapidly re-forming close-packed layers of anions that sandwich the Ag(CH3CN)2+ complexes in Ag2(CH3CN)4(B12F12). The interconnected (B12F122−)3 triangle lattice of anions in Ag2(CH3CN)5(B12F122−) may be the first example of this structure type.

ACKNOWLEDGMENTS

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REFERENCES

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00051 Crystallographic data are also available from the CCDC as file numbers 1521911−1521915. Additional figures and tables as mentioned in the text (PDF) Crystallographic data (CIF) Crystallographic data (CIF) Crystallographic data (CIF) Crystallographic data (CIF) Crystallographic data (CIF)

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We thank Professor Oren P. Anderson and Susie M. Miller for assistance with some of the X-ray structures reported in this paper. This work was supported by the Colorado State University Foundation and the U.S. National Science Foundation (Grant CHE-1362302).

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AUTHOR INFORMATION

Corresponding Authors

*E-mail for D.V.P.: [email protected]. *E-mail for S.H.S.: [email protected]. ORCID

Steven H. Strauss: 0000-0001-7636-2671 Notes

The authors declare no competing financial interest. 4081

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Inorganic Chemistry

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