Poly[([mu]₂-2,2-dimethyl­propane-1,3-diyl diisocyanide)-[mu]₂-nitrato-silver(I)]: a powder study

In order to investigate the effect of counter-anions on the polymeric structure of (2,2-dimethyl­propane-1,3-diyl diiso­cyanide)silver(I) complexes, the novel title polymeric compound, [Ag(NO₃)(C₇H₁₀N₂)]_n, has been synthesized. The crystal structure was determined by simulated annealing from X-ray powder diffraction data collected at room temperature. The current structure is similar to the recently reported structure of the analogue with chloride replacing nitrate. This study illustrates that both the chloride and nitrate complexes crystallize in the orthorhombic system in the Pbca space group with one monomer in the asymmetric unit, and also gives a strong indication that the counter-anion does not have a considerable effect on the polymeric structure of the complex. The Ag centre lies in a distorted tetra­hedral environment and is bonded to two 2,2-dimethyl­propane-1,3-diyl diiso­cyanide ligands to form chains. The nitrate anions crosslink the Ag centres of the chains to form a two-dimensional polymeric network structure.

S1. Comment

Diisocyanides are of considerable current interest as bidentate ligands in coordination chemistry (Harvey, 2001; Sakata et al., 2003; Espinet et al., 2000; Moigno et al., 2002). Some diisocyanides have been used in the synthesis of bi-, tri- and tetranuclear complexes and organometallic polymers, which have potential practical applications as new materials in the areas of hydrogen gas production (Mann et al., 1977; Sigal et al.,1980), and semi- and photoconductivity (Fortin et al., 2000). Very recently, we reported the synthesis and solid-state structure of the organometallic polymer {[AgCNCH₂C(CH₃)₂CH₂NC]Cl}_n (Al-Ktaifani et al., 2008), which was prepared by treatment of CNCH₂C(CH₃)₂CH₂NC with AgCl. Since we are currently interested in the synthesis of new metal complexes using the bidentate CNCH₂C(CH₃)₂CH₂NC ligand, it would be interesting to examine how changing the counteranion might affect the structure and properties of the product obtained. Therefore, the title compound, (I), which is a highly insoluble light-yellow powder, was prepared by treatment of CNCH₂C(CH₃)₂CH₂NC with AgNO₃. In the present work, we employed laboratory X-ray powder diffraction to solve and refine the crystal structure of this polymeric compound.

The present study reveals a polymeric structure, in which the Ag centres are bridged to each of the two adjacent Ag neighbours by bidentate CNCH₂C(CH₃)₂CH₂NC ligands via the NC groups, at distances of 2.092 (8) and 2.104 (8) Å, to form {Ag(CNCH₂C(CH₃)₂CH₂NC)}_n chains. The NO₃ counteranions crosslink the Ag centres of the chains, each via two O atoms at distances of 2.597 (4) and 2.538 (5) Å, to form a polymeric two-dimensional {[Ag(CNCH₂C(CH₃)₂CH₂NC)]NO₃}_n network (Fig. 1). The distances between the Ag centre and the C atom (C≡ N–) of the ligand and the O atom of NO₃ were restrained in the Rietveld refinement. The polymeric structure of (I) shows that the CNCH₂C(CH₃)₂CH₂NC ligand in the complex behaves only in a bis-monodentate manner, while chelate behaviour is completely absent. This is undoubtedly expected for steric reasons, as the distance between the two isocyanide groups in the CNCH₂C(CH₃)₂CH₂NC molecule are too short to allow chelate complexing (Chemin et al., 1996) (Fig. 2).

In the title complex, the C—C bond distances are 1.566 (11), 1.496 (12), 1.487 (11) and 1.574 (11) Å (average 1.531 Å). The C≡N [1.136 (11) and 1.134 (10) Å] and N—C [1.452 (10) and 1.457 (10) Å] bond lengths are in their normal ranges [Reference?] and comparable with their counterparts in the reported polymeric structures of {[AgCNCH₂C(CH₃)₂CH₂NC]Cl}_n (Al-Ktaifani et al., 2008) and {[Ag(dmb)₂]NO₃·0.7H₂O}_n (dmb is 1,8-diisocyano-p-menthan; Fortin et al., 1997), and the dinuclear complexes Ag(dmb)₂X₂ (X = Cl, Br or I; Perreault et al., 1993). These distances were restrained to their normal values in the Rietveld refinement. In each Ag(CNCH₂C(CH₃)₂CH₂NC)Ag unit of the polymer, the two Ag—C≡N angles are almost linear [169.3 (7) and 174.6 (7)°]. Excluding H···H contacts, four short contacts (less than the sum of the van der Waals radii) exist. These are: C4···N3 [2.913 (12) Å], C5···N3 [2.960 (2) Å], C5···N2 [3.000 (14) Å] and C6···N2 [2.928 (10) Å]. Two short contacts are also observed between neighbouring monomers for C1···O2(x, 1/2 - y, 1/2 + z) [2.988 (6) Å] and Ag1···O1(x, 1/2 - y, 1/2 + z) [3.047 (10) Å].

Comparing the average C—C (1.531 Å), Ag—C (2.098 Å), N≡C (1.135 Å) and N—C (1.455 Å) bond distances and average Ag—C—N (172.0°) and C—Ag—C (159.9°) bond angles of {Ag(I)[CNCH₂C(CH₃)₂CH₂NC]NO₃}_n with their analogous bond distances [average C—C (1.548 Å), Ag—C (2.116 Å), N≡C (1.160 Å), N—C (1.480 Å)] and angles [average Ag—C—N (164.0°) and C—Ag—C (159.9°)] in {Ag(I)[CNCH₂C(CH₃)₂CH₂NC]Cl}_n, although the conformations of the bidentate CNCH₂C(CH₃)₂CH₂NC ligand in both polymeric strucures are almost alike, it can be concluded that both molecular structures are very similar. Thus, the counteranion (NO₃ or Cl) plays no effective role in changing the polymeric structure of the complex.

Related literature

For related literature, see: Al-Ktaifani, Rukiah & Shaaban (2008); Boultif & Louër (2004); Chemin et al. (1996); Espinet et al. (2000); Favre-Nicolin & Černý (2002); Finger et al. (1994); Fortin et al. (1997, 2000); Harvey (2001); Laugier & Bochu (2001); Mann et al. (1977); Moigno et al. (2002); Perreault et al. (1993); Petříček et al. (2000); Sakata et al. (2003); Sigal et al. (1980).

S2. Experimental

All reactions and manipulations were carried out under an inert atmosphere using a twofold vacuum line and Schlenk techniques. Solvents were dried and distilled over sodium wire. Glassware was dried and flamed before use. AgNO₃ was a commercial sample [Company?] and was used as received. To a suspension of AgNO₃ (0.12 g, 0.71 mmol) in dry EtOH (15 ml) was added dropwise a solution of CNCH₂C(CH₃)₂CH₂NC (0.17 g, 1.39 mmol) in EtOH (Volume?) with rapid stirring at room temperature. The resulting solution was stirred for 1 h, filtered, and volatiles were removed in vacuo. The resulting product was washed with ether to afford a light-yellow powder [0.24 g, yield 90%, m.p. 441 K (starts to decompose)]. Analytical data for AgC₇H₁₀N₃O₃: found: C 28.60, H 3.77, N 14.62%; required: C 28.78, H 3.45, N 14.38%. IR (KBr) ν cm^-1: 2200.3 (N≡C).

S3. Refinement

The powder sample was ground lightly in a mortar, loaded between two Mylar foils and fixed in the sample holder with a mask of suitable internal diameter. Data were collected at room temperature and pressure in transmission geometry employing Cu Kα₁ radiation. The pattern was indexed using the program DICVOL04 (Boultif & Louër, 2004). An orthorhombic unit cell of reasonable volume (assuming Z = 8) gave indexing figures of merit M₂₀ = 30.9 and F₂₀ = 79.0 (0.0054, 47). The best estimated space group in the orthorhombic system was Pbca, which was determined with the help of the program CHEKCELL (Laugier & Bochu, 2001). The program FOX (Favre-Nicolin & Černý, 2002) was employed for structure solution. The powder pattern was truncated to 35.3° in 2θ (Cu Kα₁), corresponding to a real-space resolution of 2.54 Å. Monte Carlo simulated annealing (parallel tempering algorithm) was used to solve the crystal structure of (I) from the powder pattern in direct space. One molecule of the CNCH₂C(CH₃)₂CH₂NC ligand, one molecule of the nitrate anion and one free Ag atom were introduced randomly in the orthorhombic cell calculated by Le Bail refinement. The H atoms can be ignored during the structure solution process because they do not contribute significantly to the powder diffraction pattern, due to their low X-ray scattering power. During the parallel tempering calculations, the ligand was allowed to translate, to rotate around its centre of mass and to modify its torsion angles, the nitrate anion was only allowed to translate, and the atom Ag was allowed to modify its position in the unit cell. The model found by FOX was introduced into the program JANA2000 (Petříček et al., 2000) for Rietveld refinement. The effect of the asymmetry of some low-order peaks was corrected using a pseudo-Voigt description of the peak shape which allows for angle-dependent asymmetry with axial divergence (Finger et al., 1994), restricted by the equation H/L = S/L [variables need defining]. Geometric soft restraints were applied to the Ag—C, Ag—O, C≡N, N—C and C—C distances and to O—N—O angles to their normal values. H atoms were introduced in their theoretical positions, with CH₂ and CH₃ distances constrained to be 0.97 Å for CH₃ and 0.98 Å for CH₂. They were refined as riding on their carrier atoms. The atomic displacement parameters for C and N atoms were assigned isotropic. The final refinement cycles were performed using anisotropic displacement parameters for Ag and O atoms. H atoms were assigned constant isotropic displacement parameters of 1.2 times those of their carrier atoms. No preferred orientation was applied to the final refinement. The observed and calculated diffraction patterns for the refined crystal structure are shown in Fig. 3 (χ²= 1.61, R_exp = 0.029, R_p = 0.028 and R_wp = 0.036).

Computing details

Data collection: WinXpow (Stoe & Cie, 1999); cell refinement: JANA2000 (Petříček et al., 2000); data reduction: WinXpow (Stoe & Cie, 1999); program(s) used to solve structure: FOX (Favre-Nicolin & Černý, 2002); program(s) used to refine structure: JANA2000 (Petříček et al., 2000); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: JANA2000 (Petříček et al., 2000).

Figures

	Fig. 1. The crystal structure of polymer (I), viewed parallel to the a axis. H atoms have been omitted
	Fig. 2. The asymmetric unit of (I), showing the atom-labelling scheme.
	Fig. 3. Final observed (points), calculated (line) and difference profiles for the Rietveld refinement of (I).

Poly[(µ₂-2,2-dimethylpropane-1,3-diyl diisocyanide)-µ₂-nitrato-silver(I)]

Crystal data

[Ag(NO3)(C7H10N2)]	F(000) = 1152
Mr = 292	Dx = 1.853 Mg m^−3
Orthorhombic, Pbca	Cu Kα1 radiation, λ = 1.54060 Å
Hall symbol: -P 2ac 2ab	µ = 15.39 mm^−1
a = 16.8649 (8) Å	T = 295 K
b = 16.5864 (9) Å	Particle morphology: fine powder (visual estimate)
c = 7.4838 (4) Å	light-yellow
V = 2093.43 (19) Å^3	flat sheet, 7.00 × 7.00 mm
Z = 8	Specimen preparation: Prepared at 295 K and 101.3 kPa

Data collection

Stoe STADI P transmission diffractometer	Scan method: step
Radiation source: sealed X-ray tube	Absorption correction: for a cylinder mounted on the φ axis (JANA2000; Petříček et al., 2000)
Curved Ge 111 monochromator	Tmin = 0.370, Tmax = 0.400
Specimen mounting: drifted powder between two Mylar foils	2θmin = 8.00°, 2θmax = 88.99°, 2θstep = 0.01°
Data collection mode: transmission

Refinement

Refinement on Inet	Profile function: pseudo-Voigt
Rp = 0.028	92 parameters
Rwp = 0.036	18 restraints
Rexp = 0.029	H-atom parameters constrained
RBragg = 0.025	Weighting scheme based on measured s.u.'s Mesur
R(F) = 0.025	(Δ/σ)max = 0.048
8200 data points	Background function: 15 Legendre polynoms
Excluded region(s): none	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq
Ag1	0.09520 (7)	0.18220 (5)	0.44903 (12)	0.0617 (4)
C1	0.1759 (5)	0.1075 (5)	0.5817 (13)	0.051 (3)*
C2	0.2987 (4)	0.0472 (6)	0.7379 (13)	0.064 (3)*
C3	0.3761 (5)	0.0873 (5)	0.6642 (11)	0.071 (5)*
C4	0.4442 (5)	0.0569 (6)	0.7734 (11)	0.074 (3)*
C5	0.3881 (8)	0.0751 (4)	0.4685 (11)	0.074 (3)*
C6	0.3634 (4)	0.1790 (4)	0.7096 (12)	0.064 (3)*
C7	0.4880 (4)	0.2599 (6)	0.6156 (14)	0.051 (3)*
N1	0.2023 (2)	0.1719 (4)	0.0604 (9)	0.066 (5)*
N2	0.2283 (4)	0.0752 (5)	0.6449 (10)	0.042 (3)*
N3	0.4337 (4)	0.2246 (4)	0.6586 (10)	0.042 (3)*
O1	0.1327 (3)	0.1588 (4)	0.1165 (5)	0.086 (5)
O2	0.2140 (3)	0.2239 (3)	−0.0552 (10)	0.083 (4)
O3	0.2594 (3)	0.1347 (4)	0.1265 (9)	0.071 (4)
H2a	0.293579	0.058888	0.865773	0.0769*
H2b	0.302691	−0.01149	0.726593	0.0769*
H4a	0.493665	0.071062	0.715105	0.0888*
H4b	0.442494	0.081313	0.891131	0.0888*
H4c	0.440567	−0.001195	0.784637	0.0888*
H5a	0.367111	0.121072	0.403919	0.0888*
H5b	0.360617	0.026578	0.430855	0.0888*
H5c	0.444262	0.069634	0.443597	0.0888*
H6a	0.317359	0.199359	0.643755	0.0769*
H6b	0.35413	0.185028	0.838188	0.0769*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.0343 (6)	0.0663 (7)	0.0844 (8)	0.0038 (10)	−0.0031 (10)	0.0031 (9)
O1	0.041 (7)	0.158 (10)	0.060 (7)	0.004 (7)	0.013 (5)	0.026 (6)
O3	0.071 (7)	0.067 (7)	0.076 (8)	0.028 (6)	0.014 (6)	0.009 (6)
O2	0.132 (8)	0.045 (7)	0.073 (8)	0.009 (6)	0.032 (8)	0.004 (7)

Geometric parameters (Å, º)

Ag1—C1	2.092 (8)	C4—H4b	0.973
Ag1—C7^i	2.104 (8)	C4—H4c	0.970
Ag1—O1	2.597 (4)	C5—H5a	0.972
Ag1—O2^ii	2.538 (5)	C5—H5b	0.972
C1—N2	1.136 (11)	C5—H5c	0.970
N2—C2	1.452 (10)	C6—N3	1.457 (10)
C2—C3	1.566 (11)	C6—H6a	0.981
C2—H2a	0.979	C6—H6b	0.977
C2—H2b	0.979	N3—C7	1.134 (10)
C3—C4	1.496 (12)	N1—O1	1.265 (6)
C3—C5	1.487 (11)	N1—O3	1.246 (8)
C3—C6	1.574 (11)	N1—O2	1.236 (9)
C4—H4a	0.969
C1—Ag1—C7^i	159.9 (3)	C5—C3—C6	111.4 (6)
C1—Ag1—O1	102.1 (2)	H4a—C4—H4b	109.3
C1—Ag1—O2^ii	81.7 (3)	H4a—C4—H4c	109.6
C7^i—Ag1—O1	93.2 (2)	H4b—C4—H4c	109.3
C7^i—Ag1—O2^ii	113.3 (3)	C3—C6—N3	109.5 (6)
O1—Ag1—O2^ii	83.6 (2)	C3—C6—H6a	109.3
Ag1—C1—N2	169.3 (7)	C3—C6—H6b	109.6
C1—N2—C2	170.3 (9)	N3—C6—H6a	109.4
N2—C2—C3	112.1 (7)	N3—C6—H6b	109.5
N2—C2—H2a	109.4	H6a—C6—H6b	109.5
N2—C2—H2b	109.4	C6—N3—C7	178.7 (8)
H2a—C2—H2b	106.7	Ag1^iii—C7—N3	174.6 (7)
C2—C3—C4	107.7 (6)	O1—N1—O3	120.0 (6)
C2—C3—C5	113.7 (7)	O1—N1—O2	120.0 (5)
C2—C3—C6	102.7 (6)	O3—N1—O2	120.0 (5)
C4—C3—C5	112.6 (8)	Ag1—O1—N1	121.2 (4)
C4—C3—C6	108.1 (7)	Ag1^iv—O2—N1	107.1 (4)
N2—C2—C3—C4	177.8 (7)	C2—C3—C6—N3	176.5 (6)
N2—C2—C3—C5	−56.5 (10)	C4—C3—C6—N3	62.7 (8)
N2—C2—C3—C6	63.7 (8)	C5—C3—C6—N3	−61.6 (9)

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