A two-dimensional silver-iodide organic network constructed from a unique [Ag₆I₆] hexa­gonal prism-based one-dimensional column motif

A novel two-dimensional coordination polymer, poly[[[mu]₂-1,3-bis­(2-methyl-1H-imidazol-1-yl)propane]di-[mu]₄-iodido-di-[mu]₃-iodido-silver(I)], [Ag₄I₄(C₁₁H₁₆N₄)]_n, (I), has been synthesized by solvothermal reaction of AgNO₃, KI and 1,3-bis­(2-methyl-1H-imidazol-1-yl)propane (bmimp). In (I), the two unique Ag^I cations have AgNI₃ and AgI₄ four-coordinated tetra­hedral geometries. The bmimp ligand has imposed twofold symmetry. The Ag^I cations and iodide anions form a unique one-dimensional polymeric column motif incorporating [Ag₆I₆] hexa­gonal prisms, which are then connected by bmimp ligands to form two-dimensional organic-inorganic layers. The layers are arranged in parallel in an ABAB fashion and are packed into the resultant three-dimensional supra­molecular framework by van der Waals inter­actions.

S1. Comment

The construction of Ag^I coordination compounds has become a fruitful field because of their fascinating and diverse structures, including discrete clusters (Anson et al., 2008; Jia & Wang, 2009; Wu et al., 2010; Sun et al., 2011) and infinite coordination polymers (Sun et al., 2010; Mak et al., 2007; Khlobystov et al., 2001; Young & Hanton 2008). Among the Ag^I coordination architectures, subgroups incorporating Ag^I halides as inorganic functional modules have attracted particular attention because of their rich structural motifs and outstanding photophysical properties (Cheng et al., 2004). Various Ag^I–iodide aggregates, including discrete Ag₂I₂, Ag₃I₃ and Ag₄I₄ clusters (Di Nicola et al., 2005; Bowen et al., 1994; Effendy et al., 1991) and infinite looped-chain motifs (Peters et al., 1984), a staircase double chain (Healy et al., 1983), and wave-like quadruple-chain chains (Chen et al., 2012) have been documented. Of the reported silver(I)–iodide aggregates, those constructed by one-dimensional silver(I)–iodide motifs are quite limited and the architectures are mostly based on rigid ligands. Flexible N-heterocyclic bidentate ligands, on the other hand, have variable configurations according to the torsion angles of the flexible carbon chain (Moss, 1996). Hence, we chose a flexible N-heterocyclic ligand, 1,3-bis(2-methyl-1H-imidazol-1-yl)propane (bmimp), and carried out reactions under solvothermal conditions which gave rise to a two-dimensional Ag^I–iodide network containing a unique [Ag₆I₆] hexagonal prism-based one-dimensional column motif, the title compound, (I).

As shown in Fig. 1, the asymmetric unit of (I) contains two crystallographically independent Ag^I cations, two I^- anions and half of a bmimp ligand. A crystallographic twofold axis passes through atom C6 of the bmimp ligand. The coordination environments of the two Ag^I cations can be described as distorted tetrahedra with different ligating atoms. Atom Ag1 is in a distorted tetrahedral environment defined by three I^- anions and one N atom from a bmimp ligand, while atom Ag2 displays a tetrahedral AgI₄ geometry. The Ag—N and average Ag—I bond lengths are 2.228 (8) and 2.8608 (16) Å, respectively, which are in the normal ranges observed in related Ag^I–iodide compounds (Ansell, 1976; Powell et al., 1996). The distortion of the tetrahedron can be indicated by the value of the τ₄ parameter (Yang et al., 2007) which describes the geometry of a four-coordinate metal system; in (I), τ₄ = 0.88 and 0.96 for atoms Ag1 and Ag2, respectively (cf τ₄ = 1 for a perfect tetrahedral geometry). The distances between adjacent Ag^I cations in the Ag^I–iodide aggregate range from 3.0780 (17) to 3.2777 (18) Å, which are shorter than twice the van der Waals radius of Ag^I (3.44 Å; Bondi, 1964), indicating appreciable argentophilicity (Tong et al., 1999).

Interestingly, a hexanuclear [Ag₆I₆] core (Fig. 2a) is observed in (I). The structure of the hexanuclear [Ag₆I₆] core is similar to that of the double six-membered rings (D6R, hexagonal prisms) found in zeolite (Baerlocher et al., 2001). The [Ag₆I₆] hexagonal prism can also be described as two face-to-face six-membered Ag₃I₃ rings with a chair conformation, arranged alternately and connected by six pairs of perpendicular alternating Ag—I bonds. It is noteworthy that this infinite Ag^I–iodide column has not been reported previously, according to a survey of the 2012 version of the Cambridge Structural Database (CSD; Version 5.33, August 2012 update; Allen, 2002), although a two-dimensional Ag^I–iodide double sheet built from the fused arrangement of this kind of one-dimensional column has been reported (Niu et al., 2006). The hexanuclear [Ag₆I₆] cores in (I) are connected to each other by sharing of the rhombic [Ag₂I₂] four-membered faces to form an infinite one-dimensional column (Fig. 2b). These columns are connected by bmimp ligands to form two-dimensional layers (Fig. 2c), which are packed in an ABAB fashion to form the resultant three-dimensional supramolecular framework by van der Waals interactions.

Diimidazole-based silver(I)–iodide compounds have not been widely studied. A related structure constructed from AgI and the semi-rigid diimidazole ligand 1,4-bis[(imidazol-1-yl)methyl]benzene (bix), viz. [Ag₄I₄(bix)]_n, (II), has been reported (Chen et al., 2012). In (II), the Ag^I cations and I^- anions form an inorganic wave-like chain which is bridged by bidentate bix ligands, giving a two-dimensional network. Compound (II) has a similar two-dimensional network to that in (I) but with different Ag^I–iodide cores, which indicates that differences in the diimidazole ligand and the reactant ratio play important roles in the formation of the different structural motifs.

Related literature

For related literature, see: Allen (2002); Ansell (1976); Anson et al. (2008); Baerlocher et al. (2001); Bondi (1964); Bowen et al. (1994); Chen et al. (2012); Cheng et al. (2004); Di Nicola, Effendy, Fazaroh, Pettinari, Skelton, Somers & White (2005); Effendy, Engelhardt, Healy, Skelton & White (1991); Healy et al. (1983); Jia & Wang (2009); Khlobystov et al. (2001); Mak et al. (2007); Moss (1996); Niu et al. (2006); Peters et al. (1984); Powell et al. (1996); Sun et al. (2010, 2011); Tong et al. (1999); Wu et al. (2010); Yang et al. (2007); Young & Hanton (2008).

S2. Experimental

A mixture of AgNO₃ (8.4 mg, 0.05 mmol), KI (50 mg, 0.3 mmol), bmimp (4.1 mg, 0.02 mmol) and dimethylformamide–CH₃CN (1.5 ml) mixed solvent was sealed in a glass tube and heated to 393 K over a period of 10 h, kept at 393 K for 50 h and then cooled slowly to 303 K over a period of 13 h. Colourless needle-shaped crystals of (I) were collected and washed with ethanol and finally dried in the air (yield 80%). [Any recrystallization?]

S3. Refinement

All H atoms were generated geometrically and allowed to ride on their parent atoms in a riding-model approximation, with aromatic C—H = 0.93 Å and methyl C—H = 0.96 Å, and with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: APEX2 (Bruker ,2005); cell refinement: APEX2 (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2008); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. The structure of (I), showing the atom-numbering scheme and the coordination environment around the Ag^I centres. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) x, y - 1, z; (ii) -x + 3/2, y, -z + 3/2; (iii) x, y + 1, z; (iv) -x + 3/2, y, -z + 1/2.]
	Fig. 2. (a) A ball-and-stick view of the [Ag6I6] hexagonal prism. (b) A ball-and-stick view of the one-dimensional silver(I)–iodide column. (c) The two-dimensional sheet, viewed along the a axis. (Colour key for the electronic version of the paper: Ag purple, C grey, I yellow and N blue.)

Poly[[µ₂-1,3-bis(2-methylimidazol-1-yl)propane]di-µ₄-iodido-di-µ₃-iodido-silver(I)]

Crystal data

[Ag4I4(C11H16N4)]	F(000) = 1020
Mr = 1143.36	Dx = 3.506 Mg m^−3
Monoclinic, P2/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yac	Cell parameters from 1399 reflections
a = 12.809 (6) Å	θ = 3.5–26.3°
b = 4.541 (2) Å	µ = 9.27 mm^−1
c = 18.788 (9) Å	T = 298 K
β = 97.621 (7)°	Needle, colourless
V = 1083.1 (9) Å^3	0.15 × 0.10 × 0.10 mm
Z = 2

Data collection

Bruker SMART APEXII CCD area-detector diffractometer	1870 independent reflections
Radiation source: fine-focus sealed tube	1350 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.037
ω and ϕ scans	θmax = 25.0°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Bruker, 2005)	h = −15→8
Tmin = 0.337, Tmax = 0.458	k = −5→4
4420 measured reflections	l = −22→22

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.056	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.141	H-atom parameters constrained
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0789P)^2 + 4.0792P] where P = (Fo^2 + 2Fc^2)/3
1870 reflections	(Δ/σ)max = 0.001
106 parameters	Δρmax = 1.50 e Å^−3
0 restraints	Δρmin = −1.06 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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	0.75421 (8)	0.9855 (2)	0.60049 (5)	0.0574 (3)
Ag2	0.85289 (9)	1.4548 (2)	0.70705 (6)	0.0664 (3)
I1	0.63534 (6)	1.47674 (16)	0.64143 (4)	0.0464 (3)
I2	0.96478 (6)	0.95382 (17)	0.66561 (4)	0.0499 (3)
C1	0.8601 (10)	0.586 (3)	0.4589 (6)	0.064 (3)
H1A	0.8950	0.6544	0.5043	0.097*
H1B	0.9058	0.6107	0.4228	0.097*
H1C	0.8427	0.3814	0.4626	0.097*
C2	0.7609 (8)	0.761 (3)	0.4386 (5)	0.050 (3)
C3	0.6278 (9)	1.050 (3)	0.4420 (6)	0.053 (3)
H3	0.5815	1.1834	0.4588	0.064*
C4	0.6185 (10)	0.943 (3)	0.3761 (6)	0.059 (3)
H4	0.5652	0.9847	0.3389	0.071*
C5	0.7218 (13)	0.581 (3)	0.3114 (6)	0.075 (4)
H5A	0.6590	0.4682	0.2949	0.090*
H5B	0.7788	0.4433	0.3254	0.090*
C6	0.7500	0.775 (3)	0.2500	0.042 (3)
H6A	0.6907	0.9001	0.2327	0.050*
N1	0.7162 (7)	0.936 (2)	0.4819 (4)	0.050 (2)
N2	0.7037 (7)	0.754 (2)	0.3730 (4)	0.051 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.0645 (6)	0.0700 (6)	0.0364 (5)	0.0015 (5)	0.0013 (4)	−0.0080 (4)
Ag2	0.0675 (7)	0.0709 (7)	0.0610 (6)	−0.0054 (5)	0.0089 (5)	−0.0070 (5)
I1	0.0477 (5)	0.0462 (4)	0.0458 (4)	−0.0001 (3)	0.0083 (3)	0.0001 (3)
I2	0.0431 (4)	0.0543 (5)	0.0516 (5)	−0.0032 (4)	0.0040 (3)	−0.0034 (3)
C1	0.075 (8)	0.077 (8)	0.046 (7)	0.010 (8)	0.027 (6)	0.000 (6)
C2	0.066 (7)	0.057 (7)	0.026 (5)	−0.010 (7)	0.006 (5)	0.008 (5)
C3	0.050 (6)	0.072 (8)	0.038 (6)	0.001 (6)	0.007 (5)	0.004 (5)
C4	0.057 (7)	0.074 (8)	0.042 (7)	−0.022 (7)	−0.009 (5)	0.005 (6)
C5	0.141 (13)	0.050 (7)	0.037 (6)	−0.008 (8)	0.015 (7)	−0.003 (5)
C6	0.048 (8)	0.047 (8)	0.033 (7)	0.000	0.013 (6)	0.000
N1	0.050 (5)	0.073 (6)	0.029 (4)	−0.017 (5)	0.015 (4)	−0.011 (4)
N2	0.078 (6)	0.046 (5)	0.030 (4)	−0.014 (6)	0.008 (4)	−0.003 (4)

Geometric parameters (Å, º)

Ag1—N1	2.228 (8)	C1—H1A	0.9600
Ag1—I2	2.8139 (16)	C1—H1B	0.9600
Ag1—I1	2.8628 (15)	C1—H1C	0.9600
Ag1—I1^i	2.9255 (15)	C2—N1	1.323 (14)
Ag1—Ag2	3.0780 (17)	C2—N2	1.348 (12)
Ag1—Ag2^i	3.2777 (18)	C3—C4	1.321 (16)
Ag2—I1^ii	2.832 (2)	C3—N1	1.375 (14)
Ag2—I2^iii	2.8447 (16)	C3—H3	0.9300
Ag2—I2	2.8514 (16)	C4—N2	1.395 (15)
Ag2—I1	2.8956 (17)	C4—H4	0.9300
Ag2—Ag2^ii	3.268 (3)	C5—N2	1.443 (14)
Ag2—Ag1^iii	3.2777 (18)	C5—C6	1.532 (15)
I1—Ag2^ii	2.832 (2)	C5—H5A	0.9700
I1—Ag1^iii	2.9255 (15)	C5—H5B	0.9700
I2—Ag2^i	2.8447 (16)	C6—C5^iv	1.532 (15)
C1—C2	1.502 (16)	C6—H6A	0.9700
N1—Ag1—I2	120.0 (2)	Ag1—I1—Ag2	64.62 (4)
N1—Ag1—I1	107.1 (3)	Ag2^ii—I1—Ag1^iii	109.38 (4)
I2—Ag1—I1	115.87 (4)	Ag1—I1—Ag1^iii	103.34 (5)
N1—Ag1—I1^i	97.6 (2)	Ag2—I1—Ag1^iii	68.54 (4)
I2—Ag1—I1^i	110.34 (4)	Ag1—I2—Ag2^i	70.79 (4)
I1—Ag1—I1^i	103.34 (5)	Ag1—I2—Ag2	65.81 (4)
N1—Ag1—Ag2	137.4 (2)	Ag2^i—I2—Ag2	105.72 (5)
I2—Ag1—Ag2	57.68 (3)	C2—C1—H1A	109.5
I1—Ag1—Ag2	58.21 (4)	C2—C1—H1B	109.5
I1^i—Ag1—Ag2	123.97 (5)	H1A—C1—H1B	109.5
N1—Ag1—Ag2^i	123.5 (3)	C2—C1—H1C	109.5
I2—Ag1—Ag2^i	55.04 (3)	H1A—C1—H1C	109.5
I1—Ag1—Ag2^i	125.77 (5)	H1B—C1—H1C	109.5
I1^i—Ag1—Ag2^i	55.30 (4)	N1—C2—N2	110.3 (10)
Ag2—Ag1—Ag2^i	91.14 (5)	N1—C2—C1	125.6 (9)
I1^ii—Ag2—I2^iii	106.58 (4)	N2—C2—C1	124.1 (11)
I1^ii—Ag2—I2	109.93 (4)	C4—C3—N1	109.7 (11)
I2^iii—Ag2—I2	105.72 (5)	C4—C3—H3	125.1
I1^ii—Ag2—I1	110.28 (4)	N1—C3—H3	125.1
I2^iii—Ag2—I1	110.33 (4)	C3—C4—N2	107.0 (10)
I2—Ag2—I1	113.67 (4)	C3—C4—H4	126.5
I1^ii—Ag2—Ag1	129.84 (5)	N2—C4—H4	126.5
I2^iii—Ag2—Ag1	123.49 (5)	N2—C5—C6	111.7 (10)
I2—Ag2—Ag1	56.51 (4)	N2—C5—H5A	109.3
I1—Ag2—Ag1	57.17 (3)	C6—C5—H5A	109.3
I1^ii—Ag2—Ag2^ii	56.13 (4)	N2—C5—H5B	109.3
I2^iii—Ag2—Ag2^ii	127.14 (3)	C6—C5—H5B	109.3
I2—Ag2—Ag2^ii	127.04 (3)	H5A—C5—H5B	107.9
I1—Ag2—Ag2^ii	54.30 (5)	C5^iv—C6—C5	109.9 (13)
Ag1—Ag2—Ag2^ii	91.87 (5)	C5^iv—C6—H6A	109.7
I1^ii—Ag2—Ag1^iii	123.56 (5)	C5—C6—H6A	109.7
I2^iii—Ag2—Ag1^iii	54.16 (4)	C2—N1—C3	106.5 (9)
I2—Ag2—Ag1^iii	125.94 (5)	C2—N1—Ag1	128.4 (7)
I1—Ag2—Ag1^iii	56.16 (3)	C3—N1—Ag1	124.3 (7)
Ag1—Ag2—Ag1^iii	91.14 (5)	C2—N2—C4	106.4 (9)
Ag2^ii—Ag2—Ag1^iii	91.76 (5)	C2—N2—C5	128.2 (11)
Ag2^ii—I1—Ag1	106.45 (4)	C4—N2—C5	125.3 (10)
Ag2^ii—I1—Ag2	69.57 (4)

Symmetry codes: (i) x, y−1, z; (ii) −x+3/2, y, −z+3/2; (iii) x, y+1, z; (iv) −x+3/2, y, −z+1/2.