Poly[μ₄-sulfido-tris­(thio­cyanato-κN)tris­(μ₃-1,2,4-triazolato-κ³N¹:N²:N⁴)tetra­zinc(II)]: a three-dimensional zinc sulfide coordination polymer

The title compound, [Zn₄(C₂H₂N₃)₃(NCS)₃S]_n, is a three-dimensional coordination polymer consisting of tetra­hedral SZn₄ clusters bridged by triazole ligands. In the tetra­hedral unit, three Zn atoms are connected to six bridging triazolate ligands, whereas the fourth Zn atom (site symmetry 3m) is bonded to three terminal thio­cyanate anions that protrude into the void space created by the Zn–triazolate network. The network prototype is simple cubic, but a strong distortion along a body diagonal and the imposition of a polar direction by the arrangement of the mol­ecular constituents lead to the trigonal space group R3m. This study demonstrates the use of the 3-mercapto-1,2,4-triazole ligand as an effective source for sulfide ions in the synthesis of sulfide-based coordination polymers.

S1. Comment

Research into organic–inorganic hybrid solids has resulted in a tremendous number of new and interesting structures in recent years (Cheetham et al., 2006; Férey, 2008; Suh et al., 2008). Many of these have been investigated for potential applications in gas storage, catalysis, magnetism, luminescence etc. (Maspoch et al. 2007; Morris & Wheatley, 2008). While a wide variety of organic ligands are available for the construction of coordination polymers, polyazaheterocyclic compounds, such as pyrazole, imidazole and triazole, have been extensively applied as organic linkers due to their ability to form multi-dimensional frameworks through multiple metal-binding sites. For example, a new class of zeolitic imidazolate frameworks (ZIFs) have recently been found to have exceptional stability and structrual similarities to traditional zeolites (Huang et al., 2006; Park et al., 2006; Hayashi et al., 2007). There are also a number of compounds containing triazole-type ligands (Haasnoot, 2000; Zhang & Chen, 2006; Park et al., 2007; Ouellette et al., 2006, 2007). The ZnF(AmTAZ) (AmTAZ = 3-amino-1,2,4-triazole) coordination polymer forms an especially interesting hollow tubular architecture (Su et al., 2004).

In addition to their fascinating framework architectures, polyazaheterocycle-based compounds are of interest as functional materials, since they can possess interesting photoluminescence properties when d¹⁰ metal ions such as Cu⁺, Zn²⁺ and Cd²⁺ are present (Ouellette et al., 2007; Zhao et al., 2008). Although there are many known sulfide-based inorganic frameworks, coordination polymers based on metal–sulfur linkages are still quite uncommon. Recent developments by Feng and co-workers have resulted in a number of transition metal–sulfide clusters linked by organic ligands (Xie et al., 2005; Zhang, Lin et al., 2008; Zhang, Liu et al., 2008). These materials contain tetrahedral M₄S (M = Zn or Cd) units which are connected to each other via substituted phenylthiolates in order to create a three-dimensional open framework. The single-crystal growth of these materials depends on the slow release of sulfide from the decomposition of thiourea. There is only one example of a sulfide-based metal–triazolate complex known in the literature to date (Schlueter et al., 2006). In that case, the sulfide is generated by the slow thermal decomposition of thiocyanate. The basic building block for the [Zn₆(AmTAZ)₆S₂](NO₃)₃(H₃O)(H₂O)_x structure is a sulfide-centered triangle of Zn atoms. The assembly of eight of these building units results in the formation of a three-dimensional cage structure. In this report, we describe a new zinc triazole–thiolate coordination polymer, the title compound, (I). To our knowledge, the crystallization of (I) is the first example whereby 3-mercapto-1,2,4-trizole undergoes a gradual in situ dethiolation process to generate both the triazolate ligand and the sulfide anion during the solvothermal reaction.

The atom-numbering scheme of (I) is shown in Fig. 1. The structure is based on the [SZn₃(triazole)₃]⁺ secondary building unit (SBU) which has a Zn₃S core. The central S2 sulfide ion of the [SZn₃(triazole)₃]⁺ SBU is bonded to three Zn1 atoms and Zn2 of the [Zn(NCS)₃]^- anion. Atom Zn1 is further bound to one N2 atom and two N3 atoms of three triazolate ligands. Atom N2 is at the 4-position of the triazole ring, while the N3 atoms are at the 1,2-positions. The Zn1—N3 bonds complete the trimeric [SZn₃(triazole)₃]⁺ SBU. A three-dimensional cage structure is formed by linking eight [SZn₃(triazole)₃]⁺ SBUs through Zn1—N2 bonds. The Zn1—N bond lengths are in the range 1.995 (2)–2.0310 (13) Å, which is consistent with the values reported for similar tetrahedral Zn²⁺ coordination polymers (Park et al., 2007; Ouellette et al., 2007). The resulting environment around Zn1 is a distorted tetrahedron, with N—Zn—N and N—Zn—S bond angles varying from 107.45 (5) to 125.05 (7)°. Distorted tetrahedral coordination about the S2 sulfide center is completed by coordination to the Zn2 atom of the [Zn(NCS)₃]^- anion [Zn2—S2 = 2.3580 (11) Å]. Atom Zn2 is also coordinated to the N atoms of three [NCS]^- anions, with Zn2—N distances of 1.952 (3) Å, resulting in a stretched tetrahedral coordination.

The thiocyanate anion shows a typical linear geometry, with an N—C—S angle of 178.8 (3)°. The C≡N bond length is 1.151 (5) Å, and the C—S bond distance is 1.624 (4) Å. The resulting structure (Fig. 2) is a three-dimensional distorted (6,4) simple cubic net with pore dimensions of approximately 3.5 × 3.5 Ų, taking the van der Waals radii into account. However, the porosity of the structure is removed as the bulky thiocyanate ligands protrude into the void space.

In conclusion, a new sulfide-based three-dimensional Zn–triazolate coordination polymer has been prepared. This work demonstrates that the slow decomposition of 3-mercapto-1,2,4-triazole provides an effective source of sulfide ions for the crystallization of novel sulfide-based coordination complexes and framework materials. In contrast with the crystallization of [Zn₆(AmTAZ)₆S₂](NO₃)₃(H₃O)(H₂O)_x, where the sulfide is formed from the slow thermal decomposition of thiocyanate, in the case of (I), the sulfide is formed from the thermal decompositon of 3-mercapto-1,2,4-triazole, while the thiocyanate is incorporated into the crystal structure.

Related literature

For related literature, see: Cheetham et al. (2006); Férey (2008); Flack (1983); Haasnoot (2000); Hayashi et al. (2007); Huang et al. (2006); Maspoch et al. (2007); Morris & Wheatley (2008); Ouellette et al. (2006, 2007); Park et al. (2006, 2007); Schlueter et al. (2006); Su et al. (2004); Suh et al. (2008); Xie et al. (2005); Zhang & Chen (2006); Zhang, Lin, Bu, Wu & Feng (2008); Zhang, Liu, Bu, Wu & Feng (2008); Zhao et al. (2008).

S2. Experimental

Zn₄S(SCN)₃(triazolate)₃ was prepared under mild solvothermal conditions. Zinc nitrate hexahydrate (Zn(NO₃)₂.6H₂O, 0.594 g, 2 mmol), 3-mercapto-1,2,4-triazole (C₂H₃N₃S, 0.202 g, 2 mmol) and potassium thiocyanate (KSCN, 0.194 g, 2 mmol) were added to a solvent mixture of water (6.0 ml) and ethanol (4.0 ml) in a 23 ml Teflon-lined stainless steel autoclave. The sealed reaction vessel was heated at 423 K for 3 d. After cooling to room temperature, the product was filtered, washed with deionized water and dried in air. Colorless block-shaped crystals of (I) were recovered.

S3. Refinement

H atoms were positioned geometrically and treated as riding, with C—H = 0.93 Å, and with U_iso(H) = 1.2U_eq(C) [Please check added text]. The correct orientation of the structure with respect to the polar axis direction was established by means of the Flack x parameter (Flack, 1983).

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2003).

Figures

	Fig. 1. The structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) -x + y, y, z; (ii) 2/3 - y, 1/3 - x, 1/3 + z; (iii) 2/3 - y, 1/3 + x - y, 1/3 + z; (iv) -x + y, -x, z; (v) -y, x - y, z]
	Fig. 2. Ball-and-stick representation of the distorted (6,4) nets formed by [SZn3(triazole)3]^+ secondary building units. The [Zn(NCS)3]^- groups occupy the void space.

Poly[µ₄-sulfido-tris(thiocyanato-κN)tris(µ₃-1,2,4-triazolato- κ³N¹:N²:N⁴)tetrazinc(II)]

Crystal data

[Zn4(C2H2N3)3(NCS)3S]	Dx = 2.343 Mg m^−3
Mr = 672.10	Mo Kα radiation, λ = 0.71073 Å
Hexagonal, R3m	Cell parameters from 2038 reflections
Hall symbol: R 3 -2"	θ = 2.9–28.2°
a = 13.9947 (4) Å	µ = 5.44 mm^−1
c = 8.4249 (3) Å	T = 298 K
V = 1428.97 (8) Å^3	Block, colorless
Z = 3	0.30 × 0.22 × 0.22 mm
F(000) = 984

Data collection

Siemens SMART CCD area-detector diffractometer	871 independent reflections
Radiation source: fine-focus sealed tube	865 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.026
area–detector ω scans	θmax = 28.3°, θmin = 2.9°
Absorption correction: integration (SADABS; Sheldrick, 2001)	h = −18→18
Tmin = 0.201, Tmax = 0.442	k = −18→17
4682 measured reflections	l = −10→11

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.014	w = 1/[σ^2(Fo^2) + (0.0189P)^2 + 0.264P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.034	(Δ/σ)max < 0.001
S = 1.13	Δρmax = 0.24 e Å^−3
871 reflections	Δρmin = −0.31 e Å^−3
56 parameters	Extinction correction: SHELXTL (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 0.00071 (16)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack (1983), with 421 Friedel pairs
Secondary atom site location: difference Fourier map	Absolute structure parameter: 0.032 (10)

Special details

Experimental. The data collection nominally covered over a hemisphere of reciprocal space by a combination of four sets of exposures; each set had a different φ angle for the crystal and each exposure covered 0.3° in ω. The crystal-to-detector distance was 4.975 cm. Coverage of the unique set was 100% complete to at least 27.2° in θ, 99.9% complete to at least 28.2° in θ.

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
Zn1	0.082094 (10)	0.16419 (2)	0.542210 (18)	0.01806 (9)
Zn2	0.0000	0.0000	0.12110 (7)	0.03677 (16)
S1	0.18436 (4)	0.36873 (8)	−0.06133 (12)	0.04217 (19)
N1	0.07655 (14)	0.1531 (3)	0.0492 (5)	0.0574 (8)
C1	0.12143 (15)	0.2429 (3)	0.0049 (4)	0.0365 (6)
S2	0.0000	0.0000	0.40099 (11)	0.0178 (2)
N2	0.15726 (9)	0.31451 (19)	0.4456 (3)	0.0201 (4)
N3	0.18542 (11)	0.46937 (12)	0.33373 (18)	0.0191 (3)
C2	0.11270 (14)	0.37625 (15)	0.4009 (2)	0.0219 (3)
H2	0.0390	0.3554	0.4158	0.026*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.01433 (10)	0.01439 (13)	0.02548 (14)	0.00720 (7)	0.00149 (5)	0.00298 (10)
Zn2	0.0431 (2)	0.0431 (2)	0.0241 (3)	0.02155 (12)	0.000	0.000
S1	0.0337 (3)	0.0372 (4)	0.0568 (5)	0.0186 (2)	−0.00194 (18)	−0.0039 (4)
N1	0.0680 (15)	0.058 (2)	0.0427 (15)	0.0292 (11)	0.0093 (8)	0.0185 (16)
C1	0.0352 (10)	0.0485 (18)	0.0302 (14)	0.0242 (9)	−0.0007 (6)	−0.0013 (13)
S2	0.0174 (3)	0.0174 (3)	0.0185 (4)	0.00869 (14)	0.000	0.000
N2	0.0166 (7)	0.0160 (9)	0.0276 (10)	0.0080 (4)	0.0020 (4)	0.0039 (8)
N3	0.0174 (7)	0.0163 (7)	0.0252 (7)	0.0096 (6)	−0.0015 (5)	−0.0010 (6)
C2	0.0163 (7)	0.0199 (8)	0.0295 (9)	0.0089 (6)	0.0027 (6)	0.0014 (6)

Geometric parameters (Å, º)

Zn1—N2	1.995 (2)	N1—C1	1.150 (5)
Zn1—N3^i	2.0309 (13)	N2—C2	1.348 (2)
Zn1—S2	2.3185 (6)	N3—C2	1.314 (2)
Zn2—N1	1.952 (3)	N3—N3^ii	1.379 (3)
Zn2—S2	2.3580 (11)	C2—H2	0.9300
S1—C1	1.624 (4)
N2—Zn1—N3^i	107.45 (5)	Zn1—S2—Zn2	120.88 (2)
N3^i—Zn1—N3^iii	116.40 (8)	C2—N2—C2^ii	103.1 (2)
N2—Zn1—S2	125.05 (7)	C2—N2—Zn1	128.39 (10)
N3^iii—Zn1—S2	100.51 (4)	C2—N3—N3^ii	106.17 (9)
N1^iv—Zn2—N1	110.83 (14)	C2—N3—Zn1^vi	132.18 (12)
N1—Zn2—S2	108.07 (14)	N3^ii—N3—Zn1^vi	120.60 (4)
C1—N1—Zn2	179.1 (4)	N3—C2—N2	112.27 (15)
N1—C1—S1	178.9 (4)	N3—C2—H2	123.9
Zn1^v—S2—Zn1	96.03 (3)	N2—C2—H2	123.9
C2^ii—N2—C2—N3	−0.1 (3)

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