Bis([mu]-2-cyano­pyridine-N:N')­bis­[(2-cyano­pyridine-N)silver(I)] bis­(tetra­fluoro­borate): an anion-linked molecular ladder

In the title compound, [Ag₂(C₆H₄N₂)₄](BF₄)₂, the Ag^I cations adopt distorted trigonal-planar coordination geometries. The Ag^I centres are linked via two bridging 2-cyano­pyridine ligands to give a centrosymmetric dinuclear complex in which the Ag^I coordination environment is completed by monodentate non-bridging 2-cyano­pyridine ligands. Bridging Ag...F(BF₂)F...Ag interactions link the dinuclear cations into molecular ladders.

S1. Comment

The title compound, (I), isolated during studies into the formation of Ag^I coordination polymers using pyridine and nitrile donors, exists as an air-stable colourless solid. An X-ray study confirmed the stoichiometry of the compound (Fig. 1). The Ag^I centres of the dinuclear [Ag₂(NCC₅H₄N)₄]²⁺ cation are related by an inversion centre, with each Ag^I atom occupying a distorted trigonal-planar environment involving one terminal and two bridging 2-cyanopyridine ligands. Thus, each Ag^I atom is coordinated by two pyridyl and one nitrile donor and sits 0.15 Å above the N₃ plane. The BF₄^- anions sit both above and below the AgN₃ plane, displaying Ag···F interactions of 2.7029 (15) and 2.8443 (16) Å. Taking these long-range interactions into account, the Ag^I cation adopts a trigonal-bipyramidal arrangement, with the F atoms of the anion assuming apical positions, F···Ag···F = 170.95 (4)° (Fig. 2). Thus, each BF₄^- anion bridges Ag^I centres to give a molecular ladder motif, which has been widely observed in coordination polymer chemistry (Withersby et al., 1999), although not using anion bridging as observed here. Such Ag···FBF₃^- interactions are within the sum of the van der Waals radii for Ag and F, and have previously been shown to be structurally determining in Ag^I coordination polymers of 1,4-dithiane (Blake et al., 2000).

As a result of the Ag···FBF₃^- interactions, two nitrile donors per cation remain uncoordinated, which is surprising considering the preference of Ag^I for two- or four-coordinate environments and for N-donor ligands (Blake et al., 1999). However, the absence of coordinate bonds formed between Ag^I and these pendant nitrile donors reinforces the significance of the Ag···FBF₃^- interactions. The pendant nitrile groups are directed toward an aromatic H atom of a pyridyl ring of an adjacent cation. However, the distances and angles associated with this interaction (Table 2) are at the limit of what can be considered a CN···H(C) interaction (Desiraju & Steiner, 1999; Dhurjati et al., 1991; Reddy et al., 1993) [C4—H4···N8ⁱⁱⁱ = 2.56 Å, C4···N8ⁱⁱⁱ = 3.184 (3) Å and C4—H4···N8ⁱⁱⁱ = 124°; symmetry code: (iii) x - 1, 1/2 - y, z - 1/2]. An elongated π–π-stacking interaction between pendant 2-cyanopyridine ligands on adjacent complexes is also observed, with a centroid–centroid separation of 4.080 Å and a plane–centroid separation of 3.6968 Å (Janiak, 2000).

Related literature

For related literature, see: Blake et al. (1999, 2000); Desiraju & Steiner (1999); Dhurjati et al. (1991); Janiak (2000); Reddy et al. (1993); Withersby et al. (1999).

S2. Experimental

The title compound was prepared by adding a solution of AgBF₄ (0.01 mg, 0.05 mmol) in MeNO₂ (5 ml) to a solution of 2-cyanopyridine (0.011 mg, 0.1 mmol) in MeNO₂ (5 ml). Vapour diffusion of diethyl ether into the reaction solution afforded colourless sphenoidal crystals after ca 3 d.

S3. Refinement

All H atoms were included at geometrically calculated positions and constrained to ride at a distance of 0.95 Å from their parent C atoms, with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT and SHELXTL (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1997); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2001).

Figures

	Fig. 1. View of (I) showing atom-numbering scheme and displacement ellipsoids drawn at the 50% probability level. [Symmetry code: (i) -x, -y, -z.]
	Fig. 2. View of the molecular ladder formed by Ag···F interactions, which are represented by open lines. Ag atoms are represented by left-hatched circles, N atoms are represented by right-hatched circles, B atoms are represented by dotted circles and F atoms are represented by cross-hatched circles.

Bis(µ-2-cyanopyridine-N:N')bis[(2-cyanopyridine-N)silver(I)] bis(tetrafluoroborate)

Crystal data

[Ag2(C6H4N2)4](BF4)2	Dx = 1.949 Mg m^−3
Mr = 805.80	Melting point: not recorded K
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.3265 (7) Å	Cell parameters from 4803 reflections
b = 25.364 (2) Å	θ = 2.4–28.6°
c = 7.0865 (6) Å	µ = 1.51 mm^−1
β = 113.427 (1)°	T = 150 K
V = 1373.3 (2) Å^3	Sphenoid, colourless
Z = 2	0.33 × 0.22 × 0.14 mm
F(000) = 784

Data collection

Bruker SMART1000 CCD area-detector diffractometer	3224 independent reflections
Radiation source: fine-focus sealed tube	3035 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.026
ω scans	θmax = 29.0°, θmin = 1.6°
Absorption correction: multi-scan (SADABS; Siemens, 1996)	h = −11→11
Tmin = 0.641, Tmax = 0.717	k = −32→32
13628 measured reflections	l = −9→9

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.027	H-atom parameters constrained
wR(F^2) = 0.058	w = 1/[σ^2(Fo^2) + (0.014P)^2 + 1.214P] where P = (Fo^2 + 2Fc^2)/3
S = 1.30	(Δ/σ)max = 0.001
3224 reflections	Δρmax = 0.52 e Å^−3
199 parameters	Δρmin = −0.43 e Å^−3
0 restraints

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Ag1	0.06053 (2)	0.091493 (7)	−0.12561 (3)	0.02405 (6)
N1	−0.1132 (2)	0.16448 (8)	−0.2064 (3)	0.0224 (4)
C2	−0.0425 (3)	0.21204 (9)	−0.1404 (4)	0.0230 (5)
C3	−0.1366 (3)	0.25867 (10)	−0.1851 (4)	0.0294 (5)
H3	−0.0806	0.2916	−0.1390	0.035*
C4	−0.3146 (3)	0.25561 (11)	−0.2990 (4)	0.0344 (6)
H4	−0.3841	0.2867	−0.3303	0.041*
C5	−0.3911 (3)	0.20711 (10)	−0.3672 (4)	0.0312 (5)
H5	−0.5135	0.2043	−0.4458	0.037*
C6	−0.2858 (3)	0.16283 (10)	−0.3185 (4)	0.0258 (5)
H6	−0.3385	0.1296	−0.3671	0.031*
C7	0.1430 (3)	0.21251 (10)	−0.0137 (4)	0.0287 (5)
N8	0.2881 (3)	0.21275 (10)	0.0900 (4)	0.0424 (6)
N11	0.3457 (2)	0.07206 (7)	0.0396 (3)	0.0200 (4)
C12	0.3997 (3)	0.03059 (9)	0.1673 (3)	0.0198 (4)
C13	0.5736 (3)	0.01732 (9)	0.2783 (3)	0.0231 (5)
H13	0.6048	−0.0128	0.3653	0.028*
C14	0.6999 (3)	0.04944 (10)	0.2578 (4)	0.0264 (5)
H14	0.8207	0.0421	0.3320	0.032*
C15	0.6477 (3)	0.09221 (9)	0.1281 (4)	0.0267 (5)
H15	0.7324	0.1148	0.1119	0.032*
C16	0.4702 (3)	0.10224 (9)	0.0210 (4)	0.0235 (5)
H16	0.4360	0.1317	−0.0690	0.028*
C17	0.2632 (3)	−0.00218 (9)	0.1827 (3)	0.0220 (5)
N18	0.1588 (3)	−0.02897 (8)	0.1965 (3)	0.0282 (4)
B1	0.1744 (3)	0.11034 (11)	0.4646 (4)	0.0235 (5)
F1	0.1764 (2)	0.15297 (6)	0.5873 (2)	0.0374 (4)
F2	0.11561 (19)	0.06582 (6)	0.5347 (2)	0.0316 (3)
F3	0.0608 (2)	0.12056 (7)	0.2622 (2)	0.0377 (4)
F4	0.34222 (19)	0.10065 (6)	0.4762 (2)	0.0335 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.01680 (9)	0.02494 (10)	0.02804 (10)	0.00221 (6)	0.00640 (7)	0.00364 (7)
N1	0.0178 (9)	0.0231 (9)	0.0242 (9)	0.0000 (7)	0.0063 (8)	0.0018 (8)
C2	0.0173 (10)	0.0247 (11)	0.0262 (11)	−0.0018 (8)	0.0079 (9)	0.0009 (9)
C3	0.0246 (12)	0.0215 (11)	0.0404 (14)	−0.0015 (9)	0.0112 (11)	−0.0001 (10)
C4	0.0253 (13)	0.0265 (12)	0.0477 (16)	0.0057 (10)	0.0106 (12)	0.0039 (11)
C5	0.0166 (11)	0.0307 (13)	0.0392 (14)	0.0017 (9)	0.0036 (10)	0.0030 (11)
C6	0.0190 (11)	0.0238 (11)	0.0307 (12)	−0.0023 (9)	0.0055 (9)	0.0009 (9)
C7	0.0225 (12)	0.0230 (11)	0.0364 (13)	−0.0026 (9)	0.0073 (10)	−0.0024 (10)
N8	0.0230 (12)	0.0351 (13)	0.0581 (16)	−0.0054 (9)	0.0043 (11)	−0.0014 (12)
N11	0.0178 (9)	0.0199 (9)	0.0206 (9)	0.0001 (7)	0.0059 (7)	−0.0010 (7)
C12	0.0179 (10)	0.0207 (10)	0.0190 (10)	−0.0014 (8)	0.0053 (8)	−0.0038 (8)
C13	0.0204 (11)	0.0230 (11)	0.0218 (11)	0.0033 (8)	0.0041 (9)	−0.0008 (9)
C14	0.0162 (11)	0.0323 (13)	0.0263 (12)	0.0012 (9)	0.0037 (9)	−0.0038 (10)
C15	0.0211 (11)	0.0268 (12)	0.0320 (12)	−0.0051 (9)	0.0104 (10)	−0.0057 (10)
C16	0.0220 (11)	0.0213 (11)	0.0260 (11)	−0.0008 (8)	0.0084 (9)	0.0002 (9)
C17	0.0203 (11)	0.0228 (11)	0.0191 (10)	0.0020 (9)	0.0037 (9)	0.0008 (8)
N18	0.0248 (10)	0.0276 (10)	0.0294 (11)	−0.0029 (8)	0.0076 (9)	0.0011 (8)
B1	0.0197 (12)	0.0267 (13)	0.0226 (12)	0.0029 (10)	0.0067 (10)	0.0016 (10)
F1	0.0419 (9)	0.0315 (8)	0.0373 (8)	0.0081 (7)	0.0142 (7)	−0.0045 (7)
F2	0.0270 (7)	0.0324 (8)	0.0352 (8)	−0.0025 (6)	0.0122 (6)	0.0048 (6)
F3	0.0276 (8)	0.0560 (10)	0.0233 (7)	0.0016 (7)	0.0036 (6)	0.0083 (7)
F4	0.0207 (7)	0.0372 (8)	0.0436 (9)	−0.0001 (6)	0.0139 (7)	−0.0011 (7)

Geometric parameters (Å, º)

Ag1—N1	2.2778 (19)	C13—C14	1.383 (3)
Ag1—N11	2.2455 (19)	C14—C15	1.376 (4)
Ag1—N18^i	2.318 (2)	C15—C16	1.391 (3)
Ag1—F2^ii	2.7029 (15)	C17—N18	1.138 (3)
Ag1—F3	2.8443 (16)	N18—Ag1^i	2.318 (2)
N1—C6	1.338 (3)	B1—F1	1.384 (3)
N1—C2	1.342 (3)	B1—F4	1.388 (3)
C2—C3	1.384 (3)	B1—F3	1.393 (3)
C2—C7	1.446 (3)	B1—F2	1.398 (3)
C3—C4	1.379 (4)	C3—H3	0.9500
C4—C5	1.381 (4)	C4—H4	0.9500
C5—C6	1.382 (3)	C5—H5	0.9500
C7—N8	1.137 (3)	C6—H6	0.9500
N11—C16	1.336 (3)	C13—H13	0.9500
N11—C12	1.343 (3)	C14—H14	0.9500
C12—C13	1.387 (3)	C15—H15	0.9500
C12—C17	1.447 (3)	C16—H16	0.9500
N1—Ag1—N11	138.04 (7)	C15—C14—C13	118.9 (2)
N1—Ag1—N18^i	97.74 (7)	C14—C15—C16	119.6 (2)
N1—Ag1—F2^ii	106.71 (6)	N11—C16—C15	122.6 (2)
N1—Ag1—F3	77.80 (6)	N18—C17—C12	178.3 (3)
N11—Ag1—N18^i	122.80 (7)	C17—N18—Ag1^i	162.4 (2)
N11—Ag1—F2^ii	83.84 (6)	F1—B1—F4	109.9 (2)
N11—Ag1—F3	87.63 (6)	F1—B1—F3	109.6 (2)
N18^i—Ag1—F2^ii	92.30 (6)	F4—B1—F3	110.4 (2)
N18^i—Ag1—F3	94.86 (6)	F1—B1—F2	109.0 (2)
F2^ii—Ag1—F3	170.95 (4)	F4—B1—F2	108.8 (2)
C6—N1—C2	117.0 (2)	F3—B1—F2	109.0 (2)
C6—N1—Ag1	123.27 (16)	B1—F3—Ag1	133.31 (15)
C2—N1—Ag1	119.76 (15)	C4—C3—H3	121.2
N1—C2—C3	124.0 (2)	C2—C3—H3	121.2
N1—C2—C7	115.8 (2)	C3—C4—H4	120.2
C3—C2—C7	120.2 (2)	C5—C4—H4	120.2
C4—C3—C2	117.7 (2)	C4—C5—H5	120.7
C3—C4—C5	119.6 (2)	C6—C5—H5	120.7
C4—C5—C6	118.5 (2)	N1—C6—H6	118.4
N1—C6—C5	123.2 (2)	C5—C6—H6	118.4
N8—C7—C2	178.3 (3)	C14—C13—H13	121.2
C16—N11—C12	116.77 (19)	C12—C13—H13	121.2
C16—N11—Ag1	121.58 (15)	C15—C14—H14	120.6
C12—N11—Ag1	121.61 (15)	C13—C14—H14	120.6
N11—C12—C13	124.5 (2)	C14—C15—H15	120.2
N11—C12—C17	116.01 (19)	C16—C15—H15	120.2
C13—C12—C17	119.5 (2)	N11—C16—H16	118.7
C14—C13—C12	117.6 (2)	C15—C16—H16	118.7

Symmetry codes: (i) −x, −y, −z; (ii) x, y, z−1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C4—H4···N8^iii	0.95	2.56	3.184 (3)	124

Symmetry code: (iii) x−1, −y+1/2, z−1/2.