A novel three-dimensional copper(II) coordination polymer with 1,4-bis(1,2,4-triazol-1-ylmeth­yl)benzene and thio­cyanate

In the title complex, poly[copper(II)-di-μ₂-thio­cyanato-μ₂-1,4-bis­(1,2,4-triazol-1-ylmeth­yl)benzene], [Cu(NCS)₂(C₁₂H₁₂N₆)]_n, the Cu^II atom lies on an inversion centre in a tetra­gonally distorted octa­hedral environment. Four N atoms from thio­cyanate and 1,4-bis­(1,2,4-triazol-1-ylmeth­yl)benzene (bbtz) ligands fill the equatorial positions, and S atoms from symmetry-related thio­cyanate ligands fill the axial positions. The benzene ring of the bbtz ligand lies about an inversion centre. Single thio­cyanate bridges link the Cu^II atoms into two-dimensional sheets containing an unprecedented 16-membered [Cu₄(μ-NCS-N:S)₄] ring. The bbtz ligands further link the two-dimensional sheets into a three-dimensional network.

S1. Comment

The design and construction of coordination polymers is of great interest because of their intriguing structural topologies and potential applications as functional materials (Yaghi et al., 1998; Batten & Robson 1998; Moulton & Zaworotko 2001). The design of coordination polymers requires appropriate components, such as suitable bridging ligands, to link metal centres. The pseudohalide thiocyanate has been demonstrated to be an extremely versatile ligand, which can provide µ-NCS⁻(N,S), µ-NCS⁻(N,N), terminal N-bonded NCS⁻ or terminal S-bonded NCS⁻ modes (Zhang et al., 1999). Many double thiocyanate-bridged copper(II) complexes have been characterized (Zhang et al., 1999; Bie et al., 2003). However, single thiocyanate-bridged copper(II) compounds are relatively rare (Ribas, et al., 1995; Karan et al., 2002).

The most widely used ligands for construction of coordination polymers are rigid rod-like N-donor organic ligands, and a variety of topological architectures have been synthesized (Fujita et al., 1994; Li et al., 2001). However, flexible ligands containing triazole or imidazole have not been well studied to date (Effendy et al., 2004; Van Albada et al., 2000; Shen et al., 1999). In our previous studies, we synthesized several coordination polymers with the flexible ligands 1,2-bis(1,2,4-triazol-1-yl)ethane (bte; Li et al., 1999, 2003; Zhu et al., 2004; Zhou et al., 2004), 1,2-bis(imidazol-1-yl)ethane (bim; B.-L. Li et al., 2004) and 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene (bbtz; Peng et al., 2004; B.-Z. Li et al., 2004). In the present paper, we report the preparation and crystal structure of a three-dimensional coordination polymer [Cu(bbtz)(NCS)₂]_n, (I), which contains novel 16-membered [Cu₄(µ-SCN-N,S)₄] rings.

As shown in Fig. 1, the Cu^II atom lies on an inversion centre. The Cu^II atom is in a tetragonally distorted octahedral environment, coordinated by four N atoms from the symmetry-related thiocyanate ligands and the symmetry-related bis-monodentate bbtz ligands in the equatorial positions, and two S atoms from symmetry-related thiocyanate ligands in the axial positions. This coordination environment is similar to that in [Cu(4-picoline)₂(NCS)₂]_n (Cambridge Structural Database (Allen, 2002) refcode DUPFOJ10; Koziskova et al., 1990), [Cu(imidazole)₂(NCS)₂]_n (Bie et al., 2003) and [Cu(4-cyano-pyridine)₂(NCS)₂]_n (Li et al., 2002). The Cu—N (bbtz) bond lengths are 2.0074 (15) Å, longer than the Cu—N (NCS⁻) bond lengths [1.9700 (15) Å] and similar to those in the three cited compounds. The NCS⁻ ion acts as bridging ligand in a µ-(N,S) mode in (I), as in the three cited compounds. In (I), however, single thiocyanate bridges link two Cu^II atoms, while double thiocyanate bridges connect two Cu^II atoms in the cited compounds. The Cu—S bond length is 2.9163 (6) Å, shorter than the sum of the van der Waals radii of the Cu and S atoms (3.4 Å) and similar to the values 2.968 (4)–3.258 (4) Å in [Cu(4-picoline)₂(NCS)₂]_n (CSD refcode DUPFOJ10), 3.135 (52) Å in [Cu(imidazole)₂(NCS)₂]_n (Bie et al., 2003), 2.950 (4) and 2.996 (4) Å in [Cu(4-cyano-pyridine)₂(NCS)₂]_n (Li et al., 2002), and 3.021 (3) and 3.038 (3) Å in [Cu(2,2'-bipyridine)(NCS)₂] (FAZQOM; Ferlay et al., 1999), in which the S atoms adopt the axial positions in a similarly distorted octahedron around the Cu^II atom. In the Cu^II complexes, N-bonded thiocyanate groups mostly appear in the equatorial positions, while the S-bonded groups are observed in the axial directions. The Cu—N—C (NCS) bond angle is 166.68 (16)°, in good agreement with the values in singly thiocyanate-bridged copper(II) complexes, viz. 163.6 (8) and 169.0 (7)° in [Cu(2,2'-bipyridine)(NCS)₂] (FAZQOM), 167.4 (14) and 169.1 (13)° in [Cu(dach)(NCS)₂]_n (dach is 1,4-diazacycloheptane; Karan et al., 2002), and 155.6 (5)° in [{Cu₂(tmen)₂NCS(µ-Cu(pba))}(µ-SCN)]_n.(3H₂O)_n {Cu(pba) is [1,3-propanediylbis(oxamato)]cuprate(II) and tmen is N,N,N^',N^'-tetramethylenediamine; Ribas et al., 1995). The Cu—S—C (SCN) bond angle is 100.67 (6)°, comparable to the values 97.9 (3), 90.3 (5) and 112.31 (7)° in the latter three cited compounds The thiocyanate ligand is normal.

Each NCS⁻ anion in (I) coordinates to two Cu^II atoms in a µ-NCS-(N,S) mode and single thiocyanate bridges link the Cu^II centres into a two-dimensional sheet, resulting in an `hourglass-shaped' 16-membered [Cu₄(µ-NCS-N,S)₄] metallocycle (Fig. 2). To the best of our knowledge, such a [Cu₄(µ-NCS-N,S)₄] arrangement of the metallocycle is unprecedented in copper–thiocyanate systems. Three similar structures with the [M₄(µ-NCS-N,S)₄] subunit have been reported for three transition metal complexes, viz. [Mn₄(µ-NCS-N,S)₄] in [Mn(EtOH)₂(NCS)₂] (McElearney et al., 1979), and [Cd₄(µ-NCS-N,S)₄] in [Cd(NCS)₂(nicotinamide)₂]·H₂O and [Cd(SCN)₂(isonicotinamide)₂] (Yang et al., 2001). The Cu···Cu separation through the NCS⁻ ligand is 6.0783 (6) Å, compared with values ranging from 5.27 (2) Å in [Cu(dach)(NCS)₂]_n singly thiocyanate-bridged copper(II) complexes (dach is 1,4-diazacycloheptane; Karan et al., 2002) to 6.113 Å in the doubly thiocyanate-bridged copper(II) complex [Cu(2,2'-bipyridine)(NCS)₂] (Diaz et al., 1999).

Because the methyl C atoms of bbtz can rotate freely to adjust to the coordination environment, bbtz can exhibit trans–gauche and gauche--gauche conformations, similar to the ligand 1,4-bis(imidazol-1-ylmethyl)benzene (bix), as shown in the polyrotaxane [Ag₂(bix)₃](NO₃)₂ (Hoskins et al., 1997b). The bbtz ligands exhibit the trans–gauche conformation in (I), similar to the free bbtz molecule (Peng et al., 2004) and the bridging bbtz ligand in [Co(N₃)₂(bbtz)₂]_n, (II) (B.-Z. Li et al., 2004). The three rings (two triazole rings and one benzene ring) of one bbtz ligand are not coplanar in (I), (II) or the free bbtz molecule. However, the dihedral angle between the two triazole planes is 0° by imposed crystallographic symmetry in (I) and in the free bbtz molecule (Peng et al., 2004), compared with 61.94 (19)° in (II). The dihedral angles between the benzene and triazole planes in (I) are 70.51 (7)°, similar to the values in the free bbtz molecule [77.81 (9)°] and those in (II) [67.26 (9) and 66.96 (7)°].

As illustrated in Fig. 3, each bbtz ligand in (I) coordinates to Cu^II atoms through its two triazole N atoms, thus acting as a bridging bidentate ligand to further link the [Cu(µ-NCS-N,S)₂]_n sheets into a three-dimensional network. A 34-membered ring is formed through four Cu atoms linked by two single µ-NCS⁻(N,S) bridges and two bbtz ligands. The Cu···Cu distance is 13.2178 (13) Å through the bridging bbtz ligand, similar to the corresponding metal–metal separations in (II) [14.4156 (18) Å; B.-Z. Li et al., 2004) and the related bix complexes [Zn(bix)₂(NO₃)₂]·4.5H₂O [15.037 (2) Å; Hoskins et al., 1997a], [Ag₂(bix)₃(NO₃)₂] [14.626 (2) Å; Hoskins et al., 1997b] and [Mn(bix)₃(NO₂)₂·4H₂O] (12.659 Å; Shen et al., 1999). By way of comparison, two-dimensional sheets of [Mn₄(µ-NCS-N,S)₄]_n are separated by ethanol groups in [Mn(EtOH)₂(NCS)₂] (McElearney et al., 1979), and N—H···O amide hydrogen bonds between two-dimensional [Cd₄(µ-NCS-N,S)₄]_n sheets extend the two-dimensional networks to three-dimensional structures in [Cd(NCS)₂(nicotinamide)₂]·H₂O and [Cd(NCS)₂(isonicotinamide)₂] (Yang et al., 2001).

S2. Experimental

A water–methanol solution (20 ml, 1:1, v/v) of bbtz (0.120 g, 0.50 mmol) and KNCS (0.194 g, 2.0 mmol) was added to one leg of an H-shaped tube, and a water–methanol solution (20 ml, 1:1, v/v) of CuSO₄·5H₂O (0.150 g, 0.6 mmol) was added to the other leg of the tube. Well shaped green crystals suitable for X-ray analysis were obtained after about two months. The product is stable in ambient atmosphere and insoluble in most common inorganic and organic solvents. Analysis found: C 39.92, H 2.83, N 26.57%; calculated for C₁₄H₁₂CuN₈S₂: C 40.04, H 2.88, N 26.69%.

S3. Refinement

H atoms were placed in idealized positions and refined as riding, with C—H distances of 0.95 (triazole and benzene) and 0.99 Å (methane), and with U_iso(H) = 1.2U_eq(C). Two reflections (−602 and −402) were excluded by the image processing software.

Computing details

Data collection: CrystalClear (Rigaku Corporation, 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. A view of the local coordination of the Cu^II atom in (I), with displacement ellipsoids drawn at the 50% probability level. Only the atoms of the asymmetric unit have been labelled.
	Fig. 2. A perspective view of the two-dimensional sheet in (I). Only the Cu and thiocyanate atoms are shown for clarity (see text).
	Fig. 3. The three-dimensional network in (I). S, N and Cu atoms are fully hatched, partially hatched and not hatched, respectively. H atoms have been omitted for clarity (see text).

poly[copper(II)-di-µ₂-thiocyanato-µ₂-1,4-bis(1,2,4-triazol-1- ylmethyl)benzene]

Crystal data

[Cu(NCS)2(C12H12N6)]	F(000) = 852
Mr = 420.01	Dx = 1.705 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 3412 reflections
a = 23.005 (3) Å	θ = 3.4–27.5°
b = 9.2208 (12) Å	µ = 1.61 mm^−1
c = 7.9222 (11) Å	T = 193 K
β = 103.200 (3)°	Block, green
V = 1636.1 (4) Å^3	0.40 × 0.32 × 0.09 mm
Z = 4

Data collection

Rigaku Mercury CCD diffractometer	1870 independent reflections
Radiation source: fine-focus sealed tube	1784 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
ω scans	θmax = 27.5°, θmin = 3.4°
Absorption correction: multi-scan (North et al., 1968)	h = −29→27
Tmin = 0.566, Tmax = 0.869	k = −11→11
8843 measured reflections	l = −10→10

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)] = 0.030	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.079	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0446P)^2 + 1.4357P] where P = (Fo^2 + 2Fc^2)/3
1870 reflections	(Δ/σ)max < 0.001
116 parameters	Δρmax = 0.39 e Å^−3
0 restraints	Δρmin = −0.38 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
Cu1	0.2500	0.2500	0.0000	0.02331 (12)
S1	0.31450 (2)	0.71159 (6)	0.22614 (7)	0.03223 (15)
N1	0.40289 (7)	0.18230 (17)	0.38129 (19)	0.0245 (3)
N2	0.40758 (8)	0.06144 (19)	0.2869 (2)	0.0374 (4)
N3	0.32549 (7)	0.18796 (16)	0.16601 (18)	0.0226 (3)
N4	0.26537 (8)	0.45199 (16)	0.0786 (2)	0.0295 (4)
C1	0.35955 (9)	0.0705 (2)	0.1599 (3)	0.0358 (5)
H1A	0.3497	−0.0004	0.0709	0.043*
C2	0.35421 (10)	0.25522 (19)	0.3087 (3)	0.0285 (4)
H2A	0.3416	0.3429	0.3522	0.034*
C3	0.44843 (9)	0.2183 (2)	0.5394 (2)	0.0298 (4)
H3A	0.4800	0.1432	0.5599	0.036*
H3B	0.4298	0.2192	0.6404	0.036*
C4	0.47586 (8)	0.3644 (2)	0.5221 (2)	0.0241 (4)
C5	0.44648 (8)	0.4907 (2)	0.5506 (2)	0.0292 (4)
H5A	0.4097	0.4845	0.5857	0.035*
C6	0.52969 (8)	0.3750 (2)	0.4716 (2)	0.0287 (4)
H6A	0.5502	0.2894	0.4523	0.034*
C7	0.28523 (8)	0.56014 (19)	0.1396 (2)	0.0228 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.02710 (19)	0.01484 (18)	0.02385 (19)	−0.00095 (11)	−0.00282 (13)	−0.00297 (10)
S1	0.0361 (3)	0.0256 (3)	0.0369 (3)	−0.0113 (2)	0.0124 (2)	−0.0119 (2)
N1	0.0256 (8)	0.0206 (7)	0.0253 (8)	−0.0039 (6)	0.0018 (6)	0.0003 (6)
N2	0.0338 (9)	0.0326 (9)	0.0409 (10)	0.0064 (7)	−0.0017 (7)	−0.0115 (7)
N3	0.0254 (8)	0.0182 (7)	0.0228 (7)	−0.0018 (6)	0.0026 (6)	−0.0013 (6)
N4	0.0369 (9)	0.0179 (7)	0.0299 (8)	−0.0017 (6)	0.0000 (7)	−0.0032 (6)
C1	0.0360 (11)	0.0292 (10)	0.0371 (10)	0.0050 (8)	−0.0022 (8)	−0.0120 (8)
C2	0.0335 (11)	0.0234 (9)	0.0247 (10)	0.0032 (7)	−0.0013 (8)	−0.0045 (7)
C3	0.0290 (10)	0.0304 (9)	0.0249 (9)	−0.0066 (8)	−0.0044 (7)	0.0034 (8)
C4	0.0234 (8)	0.0264 (9)	0.0192 (8)	−0.0047 (7)	−0.0022 (6)	−0.0012 (6)
C5	0.0223 (9)	0.0344 (10)	0.0310 (9)	−0.0052 (7)	0.0063 (7)	−0.0056 (8)
C6	0.0231 (9)	0.0275 (9)	0.0335 (10)	0.0003 (7)	0.0026 (7)	−0.0057 (7)
C7	0.0233 (8)	0.0222 (9)	0.0221 (8)	0.0018 (7)	0.0033 (6)	0.0006 (6)

Geometric parameters (Å, º)

Cu1—N4^i	1.9700 (15)	N4—C7	1.156 (2)
Cu1—N4	1.9700 (15)	C1—H1A	0.9500
Cu1—N3^i	2.0074 (15)	C2—H2A	0.9500
Cu1—N3	2.0074 (15)	C3—C4	1.507 (3)
Cu1—S1^ii	2.9163 (6)	C3—H3A	0.9900
Cu1—S1^iii	2.9163 (6)	C3—H3B	0.9900
S1—C7	1.6317 (18)	C4—C6	1.389 (3)
N1—C2	1.320 (2)	C4—C5	1.390 (3)
N1—N2	1.360 (2)	C5—C6^iv	1.382 (3)
N1—C3	1.476 (2)	C5—H5A	0.9500
N2—C1	1.316 (3)	C6—C5^iv	1.382 (3)
N3—C2	1.326 (2)	C6—H6A	0.9500
N3—C1	1.344 (2)
N4^i—Cu1—N4	180.00 (9)	N2—C1—N3	114.70 (17)
N4^i—Cu1—N3^i	89.79 (6)	N2—C1—H1A	122.6
N4—Cu1—N3^i	90.21 (6)	N3—C1—H1A	122.6
N4^i—Cu1—N3	90.21 (6)	N1—C2—N3	109.96 (16)
N4—Cu1—N3	89.79 (6)	N1—C2—H2A	125.0
N3^i—Cu1—N3	180.00 (13)	N3—C2—H2A	125.0
N4^i—Cu1—S1^ii	87.99 (5)	N1—C3—C4	110.77 (15)
N4—Cu1—S1^ii	92.01 (5)	N1—C3—H3A	109.5
N3^i—Cu1—S1^ii	89.37 (4)	C4—C3—H3A	109.5
N3—Cu1—S1^ii	90.63 (4)	N1—C3—H3B	109.5
N4^i—Cu1—S1^iii	92.01 (5)	C4—C3—H3B	109.5
N4—Cu1—S1^iii	87.99 (5)	H3A—C3—H3B	108.1
N3^i—Cu1—S1^iii	90.63 (4)	C6—C4—C5	119.12 (18)
N3—Cu1—S1^iii	89.37 (4)	C6—C4—C3	120.57 (18)
S1^ii—Cu1—S1^iii	180.00 (3)	C5—C4—C3	120.28 (17)
C2—N1—N2	110.10 (15)	C6^iv—C5—C4	120.53 (17)
C2—N1—C3	128.49 (16)	C6^iv—C5—H5A	119.7
N2—N1—C3	121.40 (16)	C4—C5—H5A	119.7
C1—N2—N1	102.14 (16)	C5^iv—C6—C4	120.35 (18)
C2—N3—C1	103.09 (16)	C5^iv—C6—H6A	119.8
C2—N3—Cu1	127.84 (13)	C4—C6—H6A	119.8
C1—N3—Cu1	129.07 (13)	N4—C7—S1	178.95 (18)
C7—N4—Cu1	166.68 (16)
C2—N1—N2—C1	−0.1 (2)	C2—N3—C1—N2	−0.9 (3)
C3—N1—N2—C1	−179.50 (17)	Cu1—N3—C1—N2	178.45 (14)
N4^i—Cu1—N3—C2	−157.20 (17)	N2—N1—C2—N3	−0.4 (2)
N4—Cu1—N3—C2	22.80 (17)	C3—N1—C2—N3	178.90 (17)
S1^ii—Cu1—N3—C2	114.81 (17)	C1—N3—C2—N1	0.7 (2)
S1^iii—Cu1—N3—C2	−65.19 (17)	Cu1—N3—C2—N1	−178.61 (12)
N4^i—Cu1—N3—C1	23.62 (18)	C2—N1—C3—C4	−58.3 (3)
N4—Cu1—N3—C1	−156.38 (18)	N2—N1—C3—C4	120.92 (19)
S1^ii—Cu1—N3—C1	−64.37 (17)	N1—C3—C4—C6	−97.0 (2)
S1^iii—Cu1—N3—C1	115.63 (17)	N1—C3—C4—C5	80.8 (2)
N3^i—Cu1—N4—C7	−167.5 (7)	C6—C4—C5—C6^iv	0.3 (3)
N3—Cu1—N4—C7	12.5 (7)	C3—C4—C5—C6^iv	−177.50 (17)
S1^ii—Cu1—N4—C7	−78.1 (7)	C5—C4—C6—C5^iv	−0.3 (3)
S1^iii—Cu1—N4—C7	101.9 (7)	C3—C4—C6—C5^iv	177.49 (17)
N1—N2—C1—N3	0.7 (2)

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