Poly[tetra­chlorido­{μ₄-tetra­kis­[(imidazol-1-yl)methyl]methane-κ⁴N³:N^3′:N^3′′:N^3′′′}dizinc(II)] exhibiting a three-dimensional diamond topology

The title novel noncentrosymmetric metal–organic framework, [Zn₂Cl₄(C₁₇H₂₀N₈)]_n, was prepared solvothermally using the tetra­dentate tetra­kis­[(imidazol-1-yl)methyl]methane (tiym) linker in the presence of zinc nitrate under acidic conditions. The asymmetric unit contains one Zn^II cation, two Cl⁻ anions and a quarter of each of two symmetry-independent tiym ligands. Each Zn^II cation is four-coordinated by two Cl⁻ anions and two imidazole N atoms from two tiym ligands, forming a distorted tetra­hedral coordination geometry. The tetra­hedral tetra­dentate tiym linker has a quaternary C atom located on a crystallographic axis. With its four peripheral imidazole N atoms, the linkers are bridged by four [ZnCl₂] subunits to generate a three-dimensional diamond topological framework, which is represented by the Schläfli symbol {6⁶}. To the best of our knowledge, the title compound is the first example of a non-inter­penetrating diamond net based on the tiym ligand.

S1. Introduction

Metal–organic frameworks (MOFs) have long been a subject of intense research because of their exceptionally beautiful structures and unquestionably enormous potential applications in hydrogen storage, in luminescent or nonlinear optical materials etc. (Allendorf et al., 2009; Evans & Lin, 2002; Lin et al., 2000; Suh et al., 2011). Considering the relationship between the nature and structure of organic linkers and the properties of the products, the physical and chemical properties of the linkers play a decisive role in the properties of the functional MOFs (Paz et al., 2012). N- and O-donor bridging linkers, such as pyridine derivatives and carb­oxy­lic acids, have been widely reported in the construction of MOFs (Robin & Fromm, 2006). Among the N-donor bridging ligands, flexible multidentate ligands with imidazole groups have attracted great inter­est. Tetra­kis[(imidazol-1-yl)methyl]­methane (tiym) is the first reported alkyl-substituted tetra­kis(imidazole) ligand (Bai, Ma, Yang, Liu, Wu & Ma, 2010).

In previous research, Bai and co-workers (Bai, Ma, Yang, Zhang et al., 2010; Bai et al., 2011) systematically investigated the coordination modes of the tetra­kis(imidazole) ligand in the presence of a variety of metal cations, and a variety of organic and inorganic anions. Several three-dimensional frameworks containing tiym and Zn^II cations have been previously reported (Bai, Ma, Yang, Zhang et al., 2010; Bai, Ma, Yang, Liu, Zhang et al., 2010; Bai et al., 2011). To better understand the coordination chemistry of tiym, we have employed it in a reaction with Zn(NO₃)₂.6H₂O in di­methyl­formamide (DMF) and obtained the title three-dimensional coordination complex [Zn₂Cl₄(tiym)]_n, (I).

S2. Experimental

S2.1. Synthesis and crystallization

Tetra­kis[(imidazol-1-yl)methyl]­methane (tiym) was prepared according to the method of Bai, Ma, Yang, Liu, Wu & Ma (2010). To a solution of Zn(NO₃)₂.6H₂O (0.060 g, 0.20 mmol) in di­methyl­formamide (DMF; 5 ml) was added a solution of tiym (0.033 g, 0.098 mmol) in DMF (5 ml). A white precipitate appeared, which disappeared after adding two drops of aqueous HCl (1:1 v/v) (pH ~5). The mixture was transferred to a vial, which was then sealed and heated to 373 K for 3 d. The vial was then allowed to cool to room temperature. Colourless block crystals of (I) (0.036 g) were obtained by filtration and washed with DMF and CH₂Cl₂ three times, respectively (yield 60.3%, based on tiym). Spectroscopic analysis: FT–IR (KBr, ν, cm^-1): 3412 (m), 3173 (m), 3101 (m), 2959 (w), 2494 (w), 1657 (m), 1596 (w), 1522 (vs), 1462 (s), 1366 (m), 1291 (m), 1245 (s), 1117 (vs), 1094 (vs), 1023 (m), 948 (m), 885 (m), 847 (m), 808 (m), 739 (m), 719 (m), 652 (s), 624 (m), 530 (w), 444 (w).

S2.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. All H atoms were placed in geometrically idealized positions and treated as riding, with C—H = 0.96 (methyl), 0.97 (methyl­ene) or 0.93 Å (imdazole), and with U_iso(H) = 1.5U_eq(C) for methyl H atoms or 1.2U_eq(C) otherwise.

S3. Comment

Compound (I) crystallizes in the noncentrosymmetric tetra­gonal space group I4, which is associated with the point group S₄. The asymmetric unit contains half a Zn^II cation, one Cl^- anion and a quarter of a tiym ligand. As shown in Fig.1, the Zn atom occupies the centre of a distorted tetra­hedron defined by two Cl atoms and two N atoms from two tiym ligands (Table 2). The Zn—Cl and Zn—N bond lengths are comparable with those reported in other Zn^II complexes (Bai, Ma, Yang, Zhang et al., 2010; Wang et al., 2013). The L—Zn—L angles (L = basal N or Cl atom) range from 103.53 (1) to 114.04 (6)° and the edge lengths range from 3.1672 (4) to 3.7401 (2) Å. The spatial geometry of the tiym ligand is also a distorted tetra­hedron [the centre is atom C2 and the four vertices are occupied by atoms N2, N2^iv, N2^v and N2^vi; symmetry codes: (iv) -y + 1/2, x - 1/2, -z - 1/2; (v) -x + 1, -y, z; (vi) y + 1/2, -x + 1/2, -z - 1/2]. The N—C2—N angles range from 89.7 to 120.2° and the edge lengths range from 6.404 (4) to 7.870 (4) Å. Generally, each tiym ligand is linked by four Zn^II-centred distorted tetra­hedra which are linked by two tiym ligands, thereby forming a three-dimensional framework. The structure is further stabilized by two types of weak hydrogen bond (C—H···Cl and C—H···N; Table 3).

A better insight into the structure of (I) can be achieved by the application of a topological approach, that is, reducing the multidimensional structure to a simple node-and-linker net (Batten & Robson, 1998). According to the simplification principle, the tetra­dentate tiym ligand is considered as a 4-connecting node, while the neutral [ZnCl₂] subunits serve as linear linkers. Therefore, the structure of (I) can be reduced to the topology of a uninodal 4-connected diamond net (see Fig. 2), with the Schläfli symbol {6⁶}, as calculated by the TOPOS software (Blatov, 2006).

It is well known that the voids of diamond topological networks tend to be occupied by either inter­penetration or guest molecules. It is of particular inter­est, and the most striking feature of (I), that there is no structure inter­penetration, nor even guest molecules in the structure (see Fig. 3), a phenomenon which is relatively rarely reported (Cheng et al., 2005; Qu et al., 2004; Wang et al., 2010). This feature is probably a result of the V-shaped [ZnCl₂] linker unit, which adopts a bent geometry, and the hydrogen bonds in the diamond structure, which together reduce the size of the void and prevent the entrance of guest molecules.

Related literature

For related literature, see: Allendorf et al. (2009); Bai et al. (2011); Bai, Ma, Yang, Liu, Wu & Ma (2010); Bai, Ma, Yang, Liu, Zhang, Ma & Liu (2010); Bai, Ma, Yang, Zhang, Ma & Liu (2010); Batten & Robson (1998); Blatov (2006); Cheng et al. (2005); Evans & Lin (2002); Lin et al. (2000); Paz et al. (2012); Qu et al. (2004); Robin & Fromm (2006); Suh et al. (2011); Wang et al. (2010, 2013).

Computing details

Data collection: SMART (Bruker, 2005); cell refinement: SMART (Bruker, 2005); data reduction: SAINT (Bruker, 2001); 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 (Sheldrick, 2008).

Figures

Fig. 1. The coordination environment of the Zn^II cation of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been omitted for clarity. [Symmetry codes: (i) -y + 1, x, -z; (ii) y, -x + 1, -z; (iii) -x + 1, -y + 1, z; (iv) -y + 1/2, x - 1/2, -z - 1/2; (v) -x + 1, -y, z; (vi) y + 1/2, -x + 1/2, -z - 1/2.] [Only (iv), (v) and (vi) are used here - can the others be removed?]

Fig. 2. An illustration of the topological structure of (I). Spheres (which are positioned at the core of the tiym ligand) represent 4-connected nodes and lines represent tiym ligands.

Fig. 3. A perspective view of the three-dimensional framework of (I). H atoms have been omitted for clarity.

Poly[tetrachlorido{µ₄-tetrakis[(imidazol-1-yl)methyl]methane-κ⁴N³:N^3':N^3'':N^3'''}dizinc(II)]

Crystal data

[Zn2Cl4(C17H20N8)]	Dx = 1.707 Mg m^−3
Mr = 608.95	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4	Cell parameters from 1539 reflections
Hall symbol: I -4	θ = 2.4–21.0°
a = 15.119 (3) Å	µ = 2.50 mm^−1
c = 10.368 (4) Å	T = 291 K
V = 2369.9 (13) Å^3	Block, colourless
Z = 4	0.18 × 0.17 × 0.16 mm
F(000) = 1224

Data collection

Bruker SMART APEX CCD area-detector diffractometer	2209 independent reflections
Radiation source: fine-focus sealed tube	1791 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.040
φ and ω scans	θmax = 25.5°, θmin = 1.9°
Absorption correction: multi-scan (SADABS; Bruker, 2000)	h = −15→18
Tmin = 0.662, Tmax = 0.691	k = −18→15
6257 measured reflections	l = −10→12

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.034	H-atom parameters constrained
wR(F^2) = 0.045	w = 1/[σ^2(Fo^2) + (0.0011P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.94	(Δ/σ)max = 0.001
2209 reflections	Δρmax = 0.40 e Å^−3
140 parameters	Δρmin = −0.34 e Å^−3
0 restraints	Absolute structure: Flack (1983), with 1037 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.015 (14)

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 > 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
C1	0.5000	0.5000	0.0000	0.024 (2)
C2	0.5858 (3)	0.4868 (2)	0.0804 (4)	0.0306 (11)
H2A	0.6359	0.4872	0.0219	0.037*
H2B	0.5924	0.5368	0.1381	0.037*
C3	0.5454 (2)	0.3844 (3)	0.2683 (5)	0.0407 (11)
H3	0.5030	0.4186	0.3100	0.049*
C4	0.5755 (3)	0.3039 (3)	0.3059 (4)	0.0377 (12)
H4	0.5564	0.2730	0.3783	0.045*
C5	0.6442 (3)	0.3383 (3)	0.1329 (4)	0.0391 (12)
H5	0.6822	0.3359	0.0624	0.047*
C6	0.5000	0.0000	−0.2500	0.0201 (17)
C7	0.5744 (2)	−0.0396 (3)	−0.1672 (3)	0.0288 (11)
H7A	0.5480	−0.0804	−0.1061	0.035*
H7B	0.6128	−0.0738	−0.2231	0.035*
C8	0.7067 (3)	0.0575 (3)	−0.1377 (4)	0.0511 (14)
H8	0.7319	0.0486	−0.2184	0.061*
C9	0.7397 (3)	0.1059 (3)	−0.0433 (4)	0.0479 (13)
H9	0.7927	0.1370	−0.0473	0.057*
C10	0.6201 (3)	0.0526 (3)	0.0247 (4)	0.0344 (12)
H10	0.5725	0.0383	0.0776	0.041*
Cl1	0.67905 (10)	0.08136 (9)	0.39701 (13)	0.0631 (4)
Cl2	0.85512 (7)	0.20402 (7)	0.21752 (15)	0.0668 (5)
N1	0.6380 (2)	0.2757 (2)	0.2207 (4)	0.0380 (9)
N2	0.5895 (2)	0.4057 (2)	0.1570 (3)	0.0306 (9)
N3	0.6847 (2)	0.1036 (2)	0.0604 (3)	0.0334 (9)
N4	0.6290 (2)	0.0228 (2)	−0.0954 (3)	0.0291 (8)
Zn1	0.71261 (3)	0.16455 (3)	0.22744 (5)	0.03761 (14)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.024 (3)	0.024 (3)	0.024 (5)	0.000	0.000	0.000
C2	0.030 (3)	0.027 (3)	0.036 (3)	0.001 (2)	0.002 (2)	0.003 (2)
C3	0.031 (3)	0.044 (3)	0.047 (3)	0.006 (2)	0.001 (3)	0.006 (3)
C4	0.037 (3)	0.042 (3)	0.034 (3)	−0.004 (2)	−0.004 (2)	0.005 (2)
C5	0.038 (3)	0.045 (3)	0.035 (3)	0.007 (2)	0.000 (2)	−0.001 (2)
C6	0.022 (2)	0.022 (2)	0.015 (5)	0.000	0.000	0.000
C7	0.031 (3)	0.031 (3)	0.024 (2)	−0.0009 (19)	−0.0025 (19)	0.0021 (19)
C8	0.036 (3)	0.084 (4)	0.033 (3)	−0.014 (3)	0.006 (2)	−0.006 (3)
C9	0.036 (3)	0.062 (4)	0.046 (3)	−0.022 (3)	0.004 (3)	0.002 (3)
C10	0.026 (3)	0.044 (3)	0.033 (3)	−0.004 (2)	0.001 (2)	0.003 (2)
Cl1	0.0763 (11)	0.0667 (10)	0.0463 (9)	0.0060 (8)	0.0163 (8)	0.0135 (7)
Cl2	0.0413 (7)	0.0502 (8)	0.1089 (13)	−0.0093 (6)	−0.0221 (8)	0.0108 (9)
N1	0.035 (2)	0.037 (2)	0.043 (3)	−0.0018 (17)	−0.010 (2)	−0.001 (2)
N2	0.024 (2)	0.030 (2)	0.038 (2)	0.0018 (17)	−0.0076 (18)	−0.0017 (18)
N3	0.027 (2)	0.044 (3)	0.030 (2)	−0.0063 (19)	−0.0019 (18)	0.0025 (18)
N4	0.027 (2)	0.037 (2)	0.023 (2)	−0.0044 (17)	−0.0007 (17)	0.0015 (17)
Zn1	0.0388 (3)	0.0330 (3)	0.0410 (3)	0.0000 (3)	−0.0095 (3)	0.0000 (3)

Geometric parameters (Å, º)

C1—C2^i	1.555 (4)	C6—C7	1.537 (3)
C1—C2	1.555 (4)	C6—C7^vi	1.537 (3)
C1—C2^ii	1.555 (4)	C7—N4	1.458 (5)
C1—C2^iii	1.555 (4)	C7—H7A	0.9700
C2—N2	1.461 (4)	C7—H7B	0.9700
C2—H2A	0.9700	C8—C9	1.320 (5)
C2—H2B	0.9700	C8—N4	1.359 (5)
C3—C4	1.356 (5)	C8—H8	0.9300
C3—N2	1.371 (5)	C9—N3	1.360 (5)
C3—H3	0.9300	C9—H9	0.9300
C4—N1	1.363 (5)	C10—N3	1.299 (5)
C4—H4	0.9300	C10—N4	1.330 (5)
C5—N1	1.316 (5)	C10—H10	0.9300
C5—N2	1.336 (5)	Zn1—Cl1	2.2204 (15)
C5—H5	0.9300	Zn1—Cl2	2.2381 (13)
C6—C7^iv	1.537 (3)	Zn1—N1	2.025 (3)
C6—C7^v	1.537 (3)	Zn1—N3	2.006 (3)
C2^i—C1—C2	106.69 (14)	N4—C7—H7B	108.1
C2^i—C1—C2^ii	115.2 (3)	C6—C7—H7B	108.1
C2—C1—C2^ii	106.69 (14)	H7A—C7—H7B	107.3
C2^i—C1—C2^iii	106.69 (14)	C9—C8—N4	107.6 (4)
C2—C1—C2^iii	115.2 (3)	C9—C8—H8	126.2
C2^ii—C1—C2^iii	106.69 (14)	N4—C8—H8	126.2
N2—C2—C1	115.5 (3)	C8—C9—N3	109.9 (4)
N2—C2—H2A	108.4	C8—C9—H9	125.0
C1—C2—H2A	108.4	N3—C9—H9	125.0
N2—C2—H2B	108.4	N3—C10—N4	113.1 (4)
C1—C2—H2B	108.4	N3—C10—H10	123.5
H2A—C2—H2B	107.5	N4—C10—H10	123.5
C4—C3—N2	106.8 (4)	C5—N1—C4	105.8 (3)
C4—C3—H3	126.6	C5—N1—Zn1	125.5 (3)
N2—C3—H3	126.6	C4—N1—Zn1	128.6 (3)
C3—C4—N1	109.1 (4)	C5—N2—C3	106.2 (4)
C3—C4—H4	125.4	C5—N2—C2	124.2 (4)
N1—C4—H4	125.4	C3—N2—C2	129.5 (4)
N1—C5—N2	112.1 (4)	C10—N3—C9	104.4 (4)
N1—C5—H5	124.0	C10—N3—Zn1	132.6 (3)
N2—C5—H5	124.0	C9—N3—Zn1	122.9 (3)
C7^iv—C6—C7^v	112.0 (3)	C10—N4—C8	105.0 (4)
C7^iv—C6—C7	108.20 (14)	C10—N4—C7	129.8 (4)
C7^v—C6—C7	108.20 (14)	C8—N4—C7	125.0 (4)
C7^iv—C6—C7^vi	108.20 (14)	N1—Zn1—N3	103.53 (15)
C7^v—C6—C7^vi	108.20 (14)	N1—Zn1—Cl1	111.73 (12)
C7—C6—C7^vi	112.0 (3)	N1—Zn1—Cl2	108.26 (10)
N4—C7—C6	116.6 (3)	N3—Zn1—Cl1	112.06 (11)
N4—C7—H7A	108.1	N3—Zn1—Cl2	106.55 (11)
C6—C7—H7A	108.1	Cl1—Zn1—Cl2	114.04 (6)
C2^i—C1—C2—N2	−176.0 (3)	C8—C9—N3—C10	0.6 (5)
C2^ii—C1—C2—N2	−52.4 (2)	C8—C9—N3—Zn1	177.4 (3)
C2^iii—C1—C2—N2	65.8 (3)	N3—C10—N4—C8	0.9 (5)
N2—C3—C4—N1	0.7 (5)	N3—C10—N4—C7	175.7 (3)
C7^iv—C6—C7—N4	49.8 (2)	C9—C8—N4—C10	−0.5 (5)
C7^v—C6—C7—N4	171.4 (3)	C9—C8—N4—C7	−175.6 (4)
C7^vi—C6—C7—N4	−69.4 (3)	C6—C7—N4—C10	92.6 (4)
N4—C8—C9—N3	−0.1 (5)	C6—C7—N4—C8	−93.5 (4)
N2—C5—N1—C4	0.4 (5)	C10—N3—Zn1—N1	−82.5 (4)
N2—C5—N1—Zn1	−176.8 (3)	C9—N3—Zn1—N1	101.7 (4)
C3—C4—N1—C5	−0.7 (5)	C10—N3—Zn1—Cl1	38.1 (4)
C3—C4—N1—Zn1	176.4 (3)	C9—N3—Zn1—Cl1	−137.8 (3)
N1—C5—N2—C3	0.0 (5)	C10—N3—Zn1—Cl2	163.5 (4)
N1—C5—N2—C2	176.2 (3)	C9—N3—Zn1—Cl2	−12.4 (4)
C4—C3—N2—C5	−0.4 (4)	C5—N1—Zn1—N3	−60.6 (4)
C4—C3—N2—C2	−176.3 (4)	C4—N1—Zn1—N3	122.8 (3)
C1—C2—N2—C5	111.4 (4)	C5—N1—Zn1—Cl1	178.6 (3)
C1—C2—N2—C3	−73.4 (5)	C4—N1—Zn1—Cl1	2.0 (4)
N4—C10—N3—C9	−0.9 (5)	C5—N1—Zn1—Cl2	52.2 (4)
N4—C10—N3—Zn1	−177.3 (3)	C4—N1—Zn1—Cl2	−124.4 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2A···N2^i	0.97	2.50	2.913 (5)	106
C2—H2B···Cl2^vii	0.97	2.79	3.647 (4)	148
C7—H7A···Cl1^viii	0.97	2.68	3.507 (4)	144
C7—H7B···N4^v	0.97	2.47	2.915 (5)	108

Symmetry codes: (i) −y+1, x, −z; (v) y+1/2, −x+1/2, −z−1/2; (vii) y+1/2, −x+3/2, −z+1/2; (viii) y+1/2, −x+1/2, −z+1/2.