catena-Poly[di-μ₃-bromido-bis­[(1-ethyl-1H-imidazole-κN ³)disilver(I)]]

Abstract

The asymmetric unit of the title coordination complex, [Ag₂Br₂(C₅H₈N₂)₂]_n, comprises a monodentate 1-ethyl­imida­zole ligand, an Ag⁺ cation and a μ₃-bridging Br⁻ anion, giving a distorted tetra­hedral AgNBr₃ stereochemistry about the Ag⁺ cation [Ag—N = 2.247 (2) Å and Ag—Br = 2.7372 (4)–2.7523 (4) Å]. Two bridging bromide anions generate the dimeric [Ag₂Br₂(C₅H₈N)₂] repeat unit [Ag⋯Ag = 3.0028 (5) Å], while a third Br⁻ anion links the units through corner sharing in an inversion-related Ag₂Br₂ association [Ag⋯Ag = 3.0407 (4) Å], generating a one-dimensional ribbon step-polymer structure, extending along the c axis.

Related literature  

For general background to N-heterocyclic carbenes, see: Arnold (2002 ▶); Lin & Vasam (2004 ▶). For related structures, see: Wang & Lin (1998 ▶); Liu et al. (2003 ▶); Helgesson & Jagner (1990 ▶, 1991 ▶); Chen & Liu (2003 ▶).

Experimental  

Crystal data  

• [Ag₂Br₂(C₅H₈N₂)₂]

• M _r = 567.80

• Monoclinic,

• a = 15.2489 (15) Å

• b = 13.9888 (13) Å

• c = 7.7198 (7) Å

• β = 109.809 (1)°

• V = 1549.3 (3) ų

• Z = 4

• Mo Kα radiation

• μ = 7.67 mm⁻¹

• T = 173 K

• 0.17 × 0.16 × 0.15 mm

Data collection  

• Bruker APEXII CCD diffractometer

• Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▶) T _min = 0.355, T _max = 0.392

• 3840 measured reflections

• 1362 independent reflections

• 1315 reflections with I > 2σ(I)

• R _int = 0.024

Refinement  

• R[F ² > 2σ(F ²)] = 0.019

• wR(F ²) = 0.048

• S = 1.05

• 1362 reflections

• 83 parameters

• H-atom parameters constrained

• Δρ_max = 0.38 e Å⁻³

• Δρ_min = −0.68 e Å⁻³

Data collection: APEX2 (Bruker, 2006 ▶); cell refinement: SAINT (Bruker, 2006 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: SHELXTL (Sheldrick, 2008 ▶); software used to prepare material for publication: SHELXTL.

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Comment

Silver and other transition metal N-heterocyclic carbene complexes have played an important role in development of metal-carbene systems for transmetalation reactions. Recent reviews dealing with silver N-heterocyclic carbenes were published by Arnold (2002) and Lin & Vasam (2004). The products differ depending upon reaction conditions and the imidazolium salt used. Deprotonation by use of Ag₂O has been the most widely used method in the syntheses of N-heterocyclic carbene complexes of silver. The procedure can be accomplished using the reaction of Ag₂O with the imidazolium salt in CH₂Cl₂ solution. The 3-diethylbenzole N-heterocyclic carbene complexes of silver have been successfully synthesized by the reaction of the 1,3-diethylbenzolium salt with Ag₂O in CH₂Cl₂ (Wang & Lin, 1998). In an attempt to prepare similar N-heterocyclic carbene complexes of silver by the reaction of Ag₂O with 1,2-dibromocyclohexane and 1-ethylimidazole in DMSO solution, we obtained the title compound, [(C₅H₈N)₂Ag₂Br₂]_n, instead and the synthesis and crystal structure are reported herein. Although the stair polymers of [(C₅H₅N)₄Ag₄I₄]_n (Liu et al., 2003) and 1-allyl-3-methylimidazole carbine silver iodide (Chen & Liu, 2003) have recently been reported, their structural features are different from that of the title complex being formed through triple and quadruple halide bridges with Ag···Ag interactions.

In the title complex the asymmetric unit comprises one monodentate 1-ethylimidazole ligand, an Ag⁺ cation and a doubly bridging Br^- anion, giving a distorted tetrahedral AgNBr₃stereochemistry about silver [Ag—N, 2.247 (2) Å; Ag—Br, 2.7372 (4)–2.7752 (3) Å and bond angle range about Ag of 106.78 (6)–113.55 (5)°] (Fig. 1). These Ag—Br bond distances are considerably longer than those found in the [Ag₂Br₄]^2- complex anion [2.518 (2) Å] (Helgesson & Jagner, 1990). The Ag1—N1 bond [2.247 (2) Å] is somewhat shorter than 2.335 Å found in the pyridine silver iodide polymer [(C₅H₅N)₄Ag₄I₄]_n (Liu et al., 2003). The dimeric Ag₂Br₂ repeating core unit in the title complex is generated through a double Br bridge, giving an Ag···Agⁱ separation of 3.0028(r) Å [for symmetry code (i): -x + 1, y, -z) + 1/2]. The four-membered core ring so formed is very similar to that in the complex anion [Ag₄Br₈]^4-(Helgesson & Jagner, 1991).

The basic coomplex is extended into a one-dimensional step-polymer ribbon structure through centrosymmetric Ag—Br and Br—Ag bonds along the c axial direction (Fig. 2). Within these cyclic Ag₂Br₂ linkages, the Ag···Agⁱⁱⁱ separation is 3.0407 (4) Å [for symmetry code (iii): -x + 1, -y + 1, -z].

Experimental

1,2-Dibromocyclohexane (2.42 g, 10 mmol) was added to a solution of 1-ethylimidazole (1.92 g, 20 mmol) in DMSO (100 ml) at room temperature and stirred for 2 h, after which Ag₂O (2.32 g, 10 mmol) was added and the mixture was refluxed for 3 h with stirring. The volume of the solution was reduced to 50 ml under vacuum, the residue was removed by filtration and the filtrate was kept at room temperature for a few days. Colorless crystals of the title compound were obtained after slow evaporation (1.74 g, 30% yield). (mp: 335 K). ¹H NMR(CDCl₃): 9.42(m,1H), 6.88(s, 1H, CH), 6.84 (s, 1H, CH), 4.54(s, 2H, CH₂), 3.65 (s, 3H, CH₃)p.p.m. Anal. calcd.: C, 21.12; H, 2.82; N, 9.86%; found: C, 21.05; H, 2.76; N, 9.75%.

Refinement

The H atoms attached to C atoms of the imidazole ring were positioned geometrically and allowed to ride on their parent atoms, with C—H = 0.95 Å and U_iso(H) = 1.2U_eq(C). Methylene and methyl H atoms were likewise positioned geometrically (C—H = 0.99 and 0.98 Å, respectively) and also refined as riding atoms, and U_iso(H) = 1.2U_eq(C)

Figures

Fig. 1.

The atom numbering scheme for the contents of the asymmetric unit in the title complex. Displacement ellipsoids are drawn at the 30% probability level. For symmetry codes: (i) -x + 1, y, -z) - 1/2]; (ii) x, -y, z) + 1/2.

Fig. 2.

The step-polymeric structure of the title complex, extending along the c axial direction.

Crystal data

[Ag2Br2(C5H8N2)2]	F(000) = 1072
Mr = 567.80	Dx = 2.434 Mg m−3
Monoclinic, C2/c	Melting point: 335 K
Hall symbol: -C 2yc	Mo Kα radiation, λ = 0.71073 Å
a = 15.2489 (15) Å	Cell parameters from 3344 reflections
b = 13.9888 (13) Å	θ = 2.8–28.4°
c = 7.7198 (7) Å	µ = 7.67 mm−1
β = 109.809 (1)°	T = 173 K
V = 1549.3 (3) Å3	Block, colourless
Z = 4	0.17 × 0.16 × 0.15 mm

Data collection

Bruker APEXII CCD diffractometer	1362 independent reflections
Radiation source: fine-focus sealed tube	1315 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.024
φ and ω scans	θmax = 25.0°, θmin = 2.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −16→18
Tmin = 0.355, Tmax = 0.392	k = −16→14
3840 measured reflections	l = −6→9

Refinement

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.019	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.048	H-atom parameters constrained
S = 1.05	w = 1/[σ2(Fo2) + (0.025P)2 + 1.7996P] where P = (Fo2 + 2Fc2)/3
1362 reflections	(Δ/σ)max < 0.001
83 parameters	Δρmax = 0.38 e Å−3
0 restraints	Δρmin = −0.68 e Å−3

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	0.445475 (14)	0.080848 (14)	−0.12049 (3)	0.02369 (10)
Br1	0.363999 (18)	0.066857 (18)	−0.49464 (4)	0.01975 (10)
N1	0.39450 (15)	0.21798 (15)	−0.0362 (3)	0.0183 (5)
N2	0.34342 (14)	0.31681 (15)	0.1304 (3)	0.0204 (5)
C1	0.38660 (17)	0.23374 (18)	0.1262 (4)	0.0182 (5)
H1	0.4088	0.1914	0.2280	0.022*
C2	0.32148 (18)	0.35730 (18)	−0.0411 (4)	0.0236 (6)
H2	0.2903	0.4163	−0.0808	0.028*
C3	0.35336 (18)	0.29593 (19)	−0.1426 (4)	0.0216 (6)
H3	0.3482	0.3052	−0.2676	0.026*
C4	0.3277 (2)	0.3578 (2)	0.2924 (4)	0.0307 (7)
H4A	0.3101	0.3061	0.3618	0.037*
H4B	0.2751	0.4036	0.2514	0.037*
C5	0.4122 (2)	0.4081 (2)	0.4169 (4)	0.0295 (7)
H5A	0.4648	0.3635	0.4555	0.044*
H5B	0.3996	0.4318	0.5256	0.044*
H5C	0.4275	0.4620	0.3512	0.044*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Ag1	0.02308 (14)	0.02533 (14)	0.02428 (15)	0.00355 (7)	0.01013 (10)	−0.00298 (8)
Br1	0.01675 (15)	0.02566 (16)	0.01700 (17)	0.00117 (9)	0.00595 (12)	0.00022 (10)
N1	0.0171 (11)	0.0193 (10)	0.0203 (12)	−0.0016 (9)	0.0089 (9)	−0.0010 (9)
N2	0.0145 (10)	0.0223 (11)	0.0242 (12)	−0.0017 (9)	0.0064 (9)	−0.0064 (9)
C1	0.0148 (12)	0.0213 (13)	0.0179 (13)	−0.0015 (10)	0.0046 (10)	−0.0001 (10)
C2	0.0193 (13)	0.0171 (13)	0.0312 (15)	−0.0016 (10)	0.0043 (11)	0.0014 (11)
C3	0.0201 (13)	0.0219 (13)	0.0215 (14)	−0.0036 (10)	0.0053 (11)	0.0047 (11)
C4	0.0247 (15)	0.0373 (17)	0.0332 (17)	−0.0033 (12)	0.0138 (13)	−0.0189 (13)
C5	0.0228 (15)	0.0343 (15)	0.0287 (17)	0.0016 (12)	0.0050 (13)	−0.0108 (13)

Geometric parameters (Å, º)

Ag1—N1	2.247 (2)	N2—C4	1.467 (3)
Ag1—Br1	2.7372 (4)	C1—H1	0.9500
Ag1—Br1i	2.7420 (4)	C2—C3	1.358 (4)
Ag1—Br1ii	2.7523 (4)	C2—H2	0.9500
Ag1—Ag1i	3.0028 (5)	C3—H3	0.9500
Ag1—Ag1iii	3.0407 (4)	C4—C5	1.497 (4)
Br1—Ag1i	2.7420 (4)	C4—H4A	0.9900
Br1—Ag1iv	2.7522 (4)	C4—H4B	0.9900
N1—C1	1.318 (3)	C5—H5A	0.9800
N1—C3	1.381 (3)	C5—H5B	0.9800
N2—C1	1.342 (3)	C5—H5C	0.9800
N2—C2	1.374 (4)
N1—Ag1—Br1	106.78 (6)	C2—N2—C4	127.2 (2)
N1—Ag1—Br1i	113.55 (5)	N1—C1—N2	111.8 (2)
Br1—Ag1—Br1i	112.899 (9)	N1—C1—H1	124.1
N1—Ag1—Br1ii	107.26 (5)	N2—C1—H1	124.1
Br1—Ag1—Br1ii	102.771 (10)	C3—C2—N2	106.1 (2)
Br1i—Ag1—Br1ii	112.797 (10)	C3—C2—H2	126.9
N1—Ag1—Ag1i	121.11 (5)	N2—C2—H2	126.9
Br1—Ag1—Ag1i	56.845 (11)	C2—C3—N1	109.6 (2)
Br1i—Ag1—Ag1i	56.690 (10)	C2—C3—H3	125.2
Br1ii—Ag1—Ag1i	130.781 (8)	N1—C3—H3	125.2
N1—Ag1—Ag1iii	128.97 (6)	N2—C4—C5	112.2 (2)
Br1—Ag1—Ag1iii	123.435 (12)	N2—C4—H4A	109.2
Br1i—Ag1—Ag1iii	56.559 (9)	C5—C4—H4A	109.2
Br1ii—Ag1—Ag1iii	56.238 (11)	N2—C4—H4B	109.2
Ag1i—Ag1—Ag1iii	95.508 (11)	C5—C4—H4B	109.2
Ag1—Br1—Ag1i	66.464 (9)	H4A—C4—H4B	107.9
Ag1—Br1—Ag1iv	109.172 (11)	C4—C5—H5A	109.5
Ag1i—Br1—Ag1iv	67.204 (10)	C4—C5—H5B	109.5
C1—N1—C3	105.3 (2)	H5A—C5—H5B	109.5
C1—N1—Ag1	124.76 (17)	C4—C5—H5C	109.5
C3—N1—Ag1	129.32 (18)	H5A—C5—H5C	109.5
C1—N2—C2	107.1 (2)	H5B—C5—H5C	109.5
C1—N2—C4	125.6 (2)
N1—Ag1—Br1—Ag1i	116.60 (6)	Br1i—Ag1—N1—C3	107.5 (2)
Br1i—Ag1—Br1—Ag1i	−8.881 (15)	Br1ii—Ag1—N1—C3	−127.1 (2)
Br1ii—Ag1—Br1—Ag1i	−130.686 (9)	Ag1i—Ag1—N1—C3	43.4 (2)
Ag1iii—Ag1—Br1—Ag1i	−72.907 (15)	Ag1iii—Ag1—N1—C3	172.66 (18)
N1—Ag1—Br1—Ag1iv	169.81 (6)	C3—N1—C1—N2	−0.2 (3)
Br1i—Ag1—Br1—Ag1iv	44.330 (16)	Ag1—N1—C1—N2	−172.05 (16)
Br1ii—Ag1—Br1—Ag1iv	−77.474 (18)	C2—N2—C1—N1	0.3 (3)
Ag1i—Ag1—Br1—Ag1iv	53.212 (9)	C4—N2—C1—N1	−176.8 (2)
Ag1iii—Ag1—Br1—Ag1iv	−19.696 (19)	C1—N2—C2—C3	−0.3 (3)
Br1—Ag1—N1—C1	152.24 (18)	C4—N2—C2—C3	176.8 (2)
Br1i—Ag1—N1—C1	−82.7 (2)	N2—C2—C3—N1	0.1 (3)
Br1ii—Ag1—N1—C1	42.6 (2)	C1—N1—C3—C2	0.0 (3)
Ag1i—Ag1—N1—C1	−146.79 (17)	Ag1—N1—C3—C2	171.36 (17)
Ag1iii—Ag1—N1—C1	−17.6 (2)	C1—N2—C4—C5	80.9 (3)
Br1—Ag1—N1—C3	−17.5 (2)	C2—N2—C4—C5	−95.7 (3)

Symmetry codes: (i) −x+1, y, −z−1/2; (ii) x, −y, z+1/2; (iii) −x+1, −y, −z; (iv) x, −y, z−1/2.