A novel dimeric zinc(II) complex: bis­[μ-1,2-bis­(1H-1,2,4-triazol-1-yl)­ethane-κ²N⁴:N^4′]­bis­[diisothio­cyanato­zinc(II)]

The coordination geometry of the Zn^II atom in the title complex, [Zn₂(NCS)₄(C₆H₈N₆)₂], is that of a distorted tetra­hedron, in which the Zn^II atom is coordinated by four N atoms from the triazole rings of two symmetry-related 1,2-bis­(1,2,4-triazol-1-yl)ethane ligands and two thio­cyanate ligands. Two Zn^II atoms are bridged by two organic ligands to form a dimer. The dimer lies about an inversion center.

S1. Comment

1,2,4-Triazole and its derivatives are very interesting ligands, because they combine the coordination geometry of both pyrazole and imidazole with regard to the arrangement of their three heteroatoms. A large number of mononuclear, oligonuclear and polynuclear transition metal complexes of 1,2,4-triazole derivatives have been synthesized and characterized because of their magnetic properties and novel topologies (Haasnoot, 2000). However, the complexes of the flexible bis(triazole) ligands have not been well explored (Haasnoot, 2000; Albada et al., 2000; Zhao et al., 2002; Meng et al., 2004; Li et al., 2005).

In our previous studies, we synthesized several coordination polymers with the flexible ligand 1,2-bis(1,2,4-triazol-1-yl)ethane (bte; Li et al., 1999, 2003; Zhu et al., 2004; Wang et al., 2005). In order to extend our work, in the present paper, we report the preparation and crystal structure of a novel dimeric Zn^II complex [Zn(bte)(NCS)₂]₂, (I).

The crystal structure of (I) is made of a neutral dimeric metallocycle. The dimer is centrosymmetric. As shown in Fig. 1, in each dimer, two zinc(II) centers are connected by two bte ligands, resulting in a discrete Zn₂(bte)₂ 18-membered binuclear metallocycle. Wilke (1978) reported many binuclear complexes containing 3-, 4-, 5-, 7-, 9-, 11-, 12-, 13- and 14-membered binuclear metallocycles. Previously, we synthesized a dimeric copper(II) complex {[Cu(TTA)₂]₂(bte)} in which bte acts as a bridge, linking two [Cu(TTA)₂] units and forming a dimer structure (TTA is1,1,1-trifluoro-3-(2-thenoyl)acetone; Li et al., 1999). Complex (I) is the second dimer complex constructed from bte.

Each zinc(II) center is four-coordinated by two N atoms of bte ligands and two N atoms of two thiocyanate ligands (Table 1), forming a distorted tetrahedral geometry. The Zn—N (triazole) bond lengths in (I) are shorter than those in the similar compounds [Zn(bte)(N₃)₂]_n (Zhu et al., 2004) and [Zn(bte)₂(dca)₂]_n (dca is dicyanamide; Li et al., 2003). The N—Zn—N bond angles are in the range 102.35 (11)–116.53 (9)°. The monodentate N-bound NCS^- ligands are almost linear (Table 1).

However, the zinc(II) centers have different coordination geometry in the previously reported bte complexes. For example, the coordination environment of the zinc(II) center is distorted octahedral in [Zn(bte)₂(dca)₂]_n, which has a one-dimensional double chain containing a Zn₂(bte)₂ 18-membered metallocycle (Li et al., 2003). The coordination environment of the zinc(II) center is a distorted trigonal bipyramid in [Zn(bte)(N₃)₂]_n, which forms an infinite one-dimensional chain containing both 18-membered Zn₂(bte)₂ and four-membered Zn₂(µ-1,1-N₃)₂ rings (Zhu et al., 2004).

Each bte ligand exhibits the gauche conformation in (I) and the above two cited compounds, in contrast to the anti conformation of the free bte molecule (Li et al., 2004). The N1—C5—C6—N4 torsion angles are 69.1 (3)° in (I), 58.1 (2)° in [Zn(bte)₂(dca)₂]_n (Li et al., 2003) and 62.6 (2)° in [Zn(bte)(N₃)₂]_n (Zhu et al., 2004). The dihedral angles between two triazole rings are 60.03 (10)° in (I), 58.05 (6)° in [Zn(bte)₂(dca)₂]_n and 51.65 (6)° in [Zn(bte)(N₃)₂]_n. The Zn···Zn separation via the bridging bte ligand is 7.268 (2) Å in (I), compared with the corresponding values 8.369 (4) Å in [Zn(bte)₂(dca)₂]_n and 6.722 (2) Å in [Zn(bte)(N₃)₂]_n.

The π–π stacking interactions and weak hydrogen bonding play an important role in formation of the crystal structure. The dimers superpose together along [010] and form the channels with the dimensions 6.4 × 5.5 Å. The S atoms of adjacent dimers along [100] insert into the channels. The N4–N6/C3/C4 triazole ring and its symmetry-related (2 - x, -y, -z) triazole ring are absolutely parallel, with the centroid-to-centroid distance 4.048 Å and the perpendicular distance 3.723 Å, exhibiting obvious π–π stacking interactions (Fig. 2). There are weak C—H···S hydrogen-bonding interactions between the H atoms of the bte molecules and S atoms of the thiocyanate groups of adjacent dimers (Table 2).

Related literature

For related literature, see: Albada et al. (2000); Haasnoot (2000); Li et al. (1999, 2003, 2004, 2005); Meng et al. (2004); Wang et al. (2005); Wilke (1978); Zhao et al. (2002); Zhu et al. (2004).

S2. Experimental

A 25 ml water/MeOH solution (1:1 v/v) of Zn(NO₃)₂^.6H₂O (0.5 mmol) was added to one leg of an H-shaped tube, and a 25 ml water/MeOH (1:1 v/v) solution of 1,2-bis(1,2,4-triazol-1-yl)ethane (bte) (0.5 mmol) and KSCN (1.0 mmol) was added to another leg of the tube. Colourless crystals were obtained after about two months. Analysis calculated for C₁₆H₁₆N₁₆S₄Zn₂: C 27.79, H 2.33, N 32.42%; found: C 27.75, H 2.31, N 32.36%.

S3. Refinement

H atoms were placed in idealized positions and refined as riding, with C—H distances of 0.95 (triazole) and 0.99 Å (ethane), and with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: CrystalClear (Rigaku, 2000); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1998); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The dimeric structure of (I), with displacement ellipsoids drawn at 30% probability level. H atoms have been omitted for clarity. [Symmetry code: (i) -x + 1, -y, -z + 1.]
	Fig. 2. The cell packing of (I) along [010], showing π–π stacking interactions as dashed lines.

bis[µ-1,2-bis(1H-1,2,4-triazol-1-yl)ethane- κ²N⁴:N^4']bis[diisothiocyanatozinc(II)]

Crystal data

[Zn2(NCS)4(C6H8N6)2]	Z = 1
Mr = 691.51	F(000) = 348
Triclinic, P1	Dx = 1.697 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 8.3859 (14) Å	Cell parameters from 2682 reflections
b = 8.7715 (19) Å	θ = 3.4–25.4°
c = 10.0402 (10) Å	µ = 2.12 mm^−1
α = 80.784 (13)°	T = 193 K
β = 68.195 (11)°	Block, colorless
γ = 87.373 (14)°	0.30 × 0.24 × 0.14 mm
V = 676.8 (2) Å^3

Data collection

Rigaku Mercury CCD diffractometer	2462 independent reflections
Radiation source: fine-focus sealed tube	2192 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.025
ω scans	θmax = 25.3°, θmin = 3.4°
Absorption correction: multi-scan (Jacobson, 1998)	h = −10→9
Tmin = 0.546, Tmax = 0.748	k = −10→10
6769 measured reflections	l = −12→11

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)] = 0.032	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.083	H-atom parameters constrained
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0453P)^2 + 0.3766P] where P = (Fo^2 + 2Fc^2)/3
2462 reflections	(Δ/σ)max = 0.001
172 parameters	Δρmax = 0.55 e Å^−3
0 restraints	Δρmin = −0.39 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
Zn1	0.13787 (4)	0.25826 (4)	0.60212 (3)	0.03123 (13)
S1	−0.35612 (10)	0.15645 (10)	0.52657 (9)	0.0405 (2)
S2	−0.10257 (10)	0.65350 (10)	0.86288 (9)	0.0411 (2)
N1	0.4950 (3)	0.3109 (3)	0.1842 (2)	0.0257 (5)
N2	0.5188 (3)	0.4511 (3)	0.2172 (2)	0.0332 (6)
N3	0.3254 (3)	0.3067 (3)	0.4078 (2)	0.0285 (5)
N4	0.7652 (3)	0.0662 (3)	0.0910 (2)	0.0264 (5)
N5	0.6985 (3)	−0.0600 (3)	0.0645 (3)	0.0349 (6)
N6	0.8002 (3)	−0.1243 (3)	0.2427 (2)	0.0272 (5)
N7	−0.0638 (4)	0.1722 (3)	0.5900 (3)	0.0451 (7)
N8	0.0852 (4)	0.4535 (3)	0.6766 (3)	0.0474 (7)
C1	0.4128 (4)	0.4427 (3)	0.3526 (3)	0.0336 (7)
H1	0.3986	0.5248	0.4071	0.040*
C2	0.3803 (4)	0.2279 (3)	0.2972 (3)	0.0302 (6)
H2	0.3424	0.1268	0.2993	0.036*
C3	0.7233 (4)	−0.1712 (3)	0.1583 (3)	0.0324 (6)
H3	0.6904	−0.2756	0.1666	0.039*
C4	0.8238 (3)	0.0256 (3)	0.1965 (3)	0.0279 (6)
H4	0.8753	0.0940	0.2338	0.034*
C5	0.5807 (4)	0.2739 (3)	0.0379 (3)	0.0313 (6)
H5A	0.5830	0.3670	−0.0331	0.038*
H5B	0.5131	0.1928	0.0234	0.038*
C6	0.7627 (4)	0.2185 (3)	0.0076 (3)	0.0311 (6)
H6A	0.8203	0.2134	−0.0973	0.037*
H6B	0.8274	0.2933	0.0332	0.037*
C7	−0.1837 (4)	0.1664 (3)	0.5632 (3)	0.0316 (6)
C8	0.0083 (4)	0.5370 (3)	0.7532 (3)	0.0307 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0315 (2)	0.0317 (2)	0.0273 (2)	0.00030 (14)	−0.00921 (14)	0.00043 (13)
S1	0.0343 (4)	0.0414 (5)	0.0491 (5)	−0.0014 (3)	−0.0194 (4)	−0.0060 (4)
S2	0.0343 (4)	0.0438 (5)	0.0470 (5)	0.0038 (3)	−0.0139 (4)	−0.0152 (4)
N1	0.0277 (12)	0.0249 (12)	0.0244 (11)	0.0036 (9)	−0.0111 (10)	−0.0009 (9)
N2	0.0420 (15)	0.0260 (13)	0.0288 (12)	−0.0059 (11)	−0.0103 (11)	−0.0016 (10)
N3	0.0309 (12)	0.0265 (13)	0.0275 (12)	0.0009 (10)	−0.0123 (10)	0.0007 (9)
N4	0.0268 (12)	0.0240 (12)	0.0250 (11)	0.0036 (9)	−0.0067 (9)	−0.0023 (9)
N5	0.0434 (15)	0.0294 (14)	0.0369 (13)	0.0015 (11)	−0.0205 (12)	−0.0059 (11)
N6	0.0263 (12)	0.0276 (13)	0.0245 (11)	0.0005 (10)	−0.0064 (9)	−0.0023 (9)
N7	0.0403 (16)	0.0459 (17)	0.0499 (16)	−0.0019 (13)	−0.0200 (13)	−0.0008 (13)
N8	0.0597 (18)	0.0341 (15)	0.0416 (15)	0.0012 (13)	−0.0117 (14)	−0.0044 (12)
C1	0.0411 (17)	0.0276 (16)	0.0316 (15)	−0.0013 (13)	−0.0138 (13)	−0.0022 (12)
C2	0.0346 (16)	0.0234 (15)	0.0322 (14)	0.0024 (12)	−0.0135 (12)	−0.0008 (11)
C3	0.0384 (16)	0.0267 (15)	0.0323 (15)	−0.0008 (12)	−0.0131 (13)	−0.0051 (12)
C4	0.0256 (14)	0.0287 (15)	0.0277 (14)	−0.0012 (11)	−0.0073 (11)	−0.0050 (11)
C5	0.0382 (16)	0.0295 (16)	0.0263 (14)	0.0075 (13)	−0.0133 (12)	−0.0030 (11)
C6	0.0343 (15)	0.0265 (15)	0.0261 (14)	0.0017 (12)	−0.0060 (12)	0.0014 (11)
C7	0.0323 (16)	0.0253 (15)	0.0317 (14)	−0.0055 (12)	−0.0058 (13)	−0.0024 (11)
C8	0.0360 (16)	0.0246 (15)	0.0331 (15)	−0.0069 (13)	−0.0173 (13)	0.0043 (12)

Geometric parameters (Å, º)

Zn1—N7	1.935 (3)	N5—C3	1.309 (4)
Zn1—N8	1.945 (3)	N6—C4	1.321 (4)
Zn1—N3	1.994 (2)	N6—C3	1.358 (4)
Zn1—N6^i	2.009 (2)	N6—Zn1^i	2.009 (2)
S1—C7	1.628 (3)	N7—C7	1.139 (4)
S2—C8	1.623 (3)	N8—C8	1.146 (4)
N1—C2	1.315 (4)	C1—H1	0.9500
N1—N2	1.365 (3)	C2—H2	0.9500
N1—C5	1.458 (3)	C3—H3	0.9500
N2—C1	1.311 (4)	C4—H4	0.9500
N3—C2	1.326 (4)	C5—C6	1.515 (4)
N3—C1	1.354 (4)	C5—H5A	0.9900
N4—C4	1.320 (4)	C5—H5B	0.9900
N4—N5	1.367 (3)	C6—H6A	0.9900
N4—C6	1.462 (3)	C6—H6B	0.9900
N7—Zn1—N8	110.66 (12)	N3—C1—H1	123.0
N7—Zn1—N3	112.05 (11)	N1—C2—N3	109.8 (3)
N8—Zn1—N3	105.54 (11)	N1—C2—H2	125.1
N7—Zn1—N6^i	109.15 (10)	N3—C2—H2	125.1
N8—Zn1—N6^i	102.35 (11)	N5—C3—N6	114.1 (3)
N3—Zn1—N6^i	116.53 (9)	N5—C3—H3	123.0
C2—N1—N2	110.2 (2)	N6—C3—H3	123.0
C2—N1—C5	128.4 (2)	N4—C4—N6	109.9 (2)
N2—N1—C5	121.2 (2)	N4—C4—H4	125.1
C1—N2—N1	102.5 (2)	N6—C4—H4	125.1
C2—N3—C1	103.5 (2)	N1—C5—C6	113.4 (2)
C2—N3—Zn1	130.4 (2)	N1—C5—H5A	108.9
C1—N3—Zn1	125.69 (19)	C6—C5—H5A	108.9
C4—N4—N5	110.1 (2)	N1—C5—H5B	108.9
C4—N4—C6	129.6 (2)	C6—C5—H5B	108.9
N5—N4—C6	120.4 (2)	H5A—C5—H5B	107.7
C3—N5—N4	102.5 (2)	N4—C6—C5	111.3 (2)
C4—N6—C3	103.5 (2)	N4—C6—H6A	109.4
C4—N6—Zn1^i	129.92 (19)	C5—C6—H6A	109.4
C3—N6—Zn1^i	126.59 (19)	N4—C6—H6B	109.4
C7—N7—Zn1	159.1 (3)	C5—C6—H6B	109.4
C8—N8—Zn1	156.4 (3)	H6A—C6—H6B	108.0
N2—C1—N3	114.1 (3)	N7—C7—S1	179.3 (3)
N2—C1—H1	123.0	N8—C8—S2	179.2 (3)
C2—N1—N2—C1	−0.1 (3)	N2—N1—C2—N3	−0.6 (3)
C5—N1—N2—C1	175.6 (2)	C5—N1—C2—N3	−175.9 (2)
N7—Zn1—N3—C2	−41.1 (3)	C1—N3—C2—N1	0.9 (3)
N8—Zn1—N3—C2	−161.6 (2)	Zn1—N3—C2—N1	173.22 (17)
N6^i—Zn1—N3—C2	85.6 (2)	N4—N5—C3—N6	0.3 (3)
N7—Zn1—N3—C1	129.6 (2)	C4—N6—C3—N5	−0.1 (3)
N8—Zn1—N3—C1	9.1 (2)	Zn1^i—N6—C3—N5	−179.51 (18)
N6^i—Zn1—N3—C1	−103.7 (2)	N5—N4—C4—N6	0.3 (3)
C4—N4—N5—C3	−0.4 (3)	C6—N4—C4—N6	179.7 (2)
C6—N4—N5—C3	−179.8 (2)	C3—N6—C4—N4	−0.1 (3)
N8—Zn1—N7—C7	48.1 (8)	Zn1^i—N6—C4—N4	179.24 (17)
N3—Zn1—N7—C7	−69.3 (8)	C2—N1—C5—C6	−102.0 (3)
N6^i—Zn1—N7—C7	160.0 (7)	N2—N1—C5—C6	83.1 (3)
N7—Zn1—N8—C8	47.0 (7)	C4—N4—C6—C5	−114.0 (3)
N3—Zn1—N8—C8	168.5 (7)	N5—N4—C6—C5	65.4 (3)
N6^i—Zn1—N8—C8	−69.2 (7)	N1—C5—C6—N4	69.1 (3)
N1—N2—C1—N3	0.7 (3)	Zn1—N7—C7—S1	−151 (25)
C2—N3—C1—N2	−1.1 (3)	Zn1—N8—C8—S2	−4 (23)
Zn1—N3—C1—N2	−173.83 (19)

Symmetry code: (i) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C1—H1···S1^ii	0.95	2.95	3.853 (3)	159
C2—H2···S1^iii	0.95	2.82	3.525 (3)	131
C4—H4···S2^iv	0.95	2.79	3.574 (3)	140
C6—H6B···S2^iv	0.99	2.95	3.819 (3)	148

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