Copper(II) chloride and bromide complexes with 2-methyl-2H-tetra­zol-5-amine: an X-ray powder diffraction study

The complex catena-poly[[dibromidocopper(II)]-bis­([mu]-2-methyl-2H-tetra­zol-5-amine)-[kappa]²N⁴:N⁵;[kappa]²N⁵:N⁴], [CuBr₂(C₂H₅N₅)₂]_n, (I), and the isotypic chloride complex catena-poly[[dichlorido­copper(II)]-bis­([mu]-2-methyl-2H-tetra­zol-5-amine)-[kappa]²N⁴:N⁵;[kappa]²N⁵:N⁴], [CuCl₂(C₂H₅N₅)₂]_n, (II), were investigated by X-ray powder diffraction at room temperature. The crystal structure of (I) was solved by direct methods, while the Rietveld refinement of (II) started from the atomic coordinates of (I). In both structures, the Cu atoms lie on inversion centres, adopting a distorted octa­hedral coordination of two halogen atoms, two tetra­zole N atoms and two 5-amine group N atoms. Rather long Cu-N_amine bonds allow consideration of the amine group as semi-coordinated. The compounds are one-dimensional coordination polymers, formed as a result of 2-methyl-2H-tetra­zol-5-amine ligands bridging via a tetra­zole N atom and the amine N atom. In the polymeric chains, adjacent Cu atoms are connected by two such bridges.

S1. Comment

Aminotetrazoles are promising multifunctional ligands, with the amino group and the tetrazole ring N atoms able to be coordinated by metal atoms. This allows the formation of diverse coordination frameworks, resulting in coordination compounds with different structural motifs and properties.

A number of complexes of 5-aminotetrazole and its 1- and 2-substituted derivatives have been synthesized and characterized (see Voitekhovich et al., 2009, and references therein; Gaponik et al., 2006). Analysis of the structural data showed that in all compounds the 5-amine groups were not coordinated to the metal. In the case of 5-amino-1-vinyltetrazole, this fact was explained by the conjugation of the 5-amine group lone pair with the tetrazole π-ring, in accordance with quantum-chemical calculations (Lyakhov et al., 2008). In most investigated complexes with 1,5-diaminotetrazole (Qi et al., 2009; Cui, Zhang, Zhang, Yang, Hu & Zhang, 2008; Cui et al., 2008a,b; Cui, Zhang, Zhang, Yang, Zhang & Shu, 2008), the 1-amine group does not participate in metal coordination; however in the copper(II) chloride complex with this ligand (Gaponik et al., 2005) the 1-amine N atom is bonded to Cu, showing the ability of the 1-amine group to be coordinated by metal.

The present work is devoted to complexes of 2-substituted 5-aminotetrazoles. To date, only structural data for copper(II), palladium(II) and platinum(II) chloride complexes with 5-amino-2-tert-butyltetrazole (Voitekhovich et al., 2009), and also for silver complex of 5-amino-2-methyltetrazole (Karaghiosoff et al., 2009), have been available. In these compounds, the 5-amine group adopts a geometry close to planar and is not included in the coordination environment of the metal atoms. Here, we present the structures of Cu^II halogenide complexes with 5-amino-2-methyltetrazole, viz. [CuBr₂(C₂H₅N₅)₂]_n, catena-poly[dibromidocopper(II)-bis[µ- (2-methyl-2H-tetrazol-5-yl)amine-κ²N⁴:N⁵;κ²N⁵:N⁴]], (I), and the isotypic chloride complex, (II). Because it was impossible to obtain single crystals suitable for X-ray analysis, both structures were determined by laboratory X-ray powder diffraction.

Complexes (I) and (II) crystallize in the triclinic space group P1 and are isotypic. The asymmetric units contain a half a Cu atom, one Cl/Br atom and one molecule of 5-amino-2-methyltetrazole (Fig. 1). The Cu atoms lie on inversion centres, whereas all others are in general positions.

In both structures, the 5-amino-2-methyltetrazole molecules reveal similar geometry (Tables 1 and 3). The formally single tetrazole ring bond N2—N3 is rather short, reflecting a tendency to be the shortest in the ring, as follows from previous structural investigations of 2-substituted tetrazoles and their complexes (Voitekhovich et al., 2009; Karaghiosoff et al., 2009; Lyakhov, Degtyarik et al., 2005; Lyakhov, Gaponik et al., 2005, and references therein).

In complexes (I) and (II), the Cu atoms are surrounded by four ligand molecules and two halogen atoms. Two of the four molecules are bonded to the metal through the tetrazole ring N4 atoms, occupying together with two halogen atoms equatorial sites of a distorted coordination octahedron. Two other molecules of the Cu environment are coordinated via the amine N7 atoms, which are distant from the metal by 2.783 (10) Å in complex (I) and 2.683 (6) Å in complex (II) and can be considered as semi-coordinated. Two 5-amino-2-methyltetrazole molecules play the role of bridges between two adjacent Cu atoms in polymeric chains, running along the a axis (Figs. 1 and 2). Halogen atoms do not participate in building the coordination polymer.

In both structures, the amine group H atoms are involved in hydrogen bonds (N7—H7···Br/Cl; Tables 2 and 4). Two H atoms of the amine group are connected with two halogen atoms belonging to different polymeric chains (Fig. 3), to form polymeric layers parallel to the ab plane.

Thus, complexes (I) and (II) are the first examples of coordination of tetrazole ligands via the 5-amine group. Among complexes of 5-aminotetrazole and its 1-substituted derivatives, no such coordination has been observed. Probably, the amine group of 2-substituted 5-aminotetrazoles is conjugated with the tetrazole π-ring to a lesser extent than the 5-amine group of 1-substituted analogues.

Related literature

For related literature, see: Altomare et al. (1999); Bérar & Baldinozzi (1993); Cui et al. (2008, 2008a, 2008b, 2008c); Dollase (1986); Gaponik et al. (2005, 2006); Karaghiosoff et al. (2009); Lyakhov et al. (2008); Lyakhov, Degtyarik, Ivashkevich & Gaponik (2005); Lyakhov, Gaponik, Degtyarik & Ivashkevich (2005); March (1932); Qi et al. (2009); Rodrigues-Carvajal (2001); Sheldrick (2008); Voitekhovich et al. (2009); Werner et al. (1985).

S2. Experimental

For the synthesis of (I), CuBr₂ (0.44 g, 0.002 mol) was added with intensive stirring to a solution containing 5-amino-2-methyltetrazole (0.4 g, 0.004 mol) in 15 ml of methanol–hexane mixture (1:3 v/v). The resulting green precipitate, obtained simultaneously with the dissolution of copper(II) bromide, was filtered off, washed with diethyl ether (3 × 5 ml) and dried in air [0.68 g, yield 81%; m.p. 473 K (decomposition)]. Analyis calculated: Cu 15.1, Br 38.0%; found: Cu 15.4, Br 38.1%. IR (cm^-1): 3328 (s), 3262 (s), 3042 (s), 1600 (sh), 1524 (s), 1464 (w), 1436 (s), 1371 (s), 1351 (w), 1324 (s), 1199 (s), 107 (s), 1070 (s), 1020 (s), 818 (s), 765 (s), 706 (s), 638 (s), 520 (s), 467 (s).

For the synthesis of (II), a solution containing 5-amino-2-methyl-tetrazole (0.4 g, 0.004 mol) in a mixture of methanol and diethyl ether (1:3 v/v, 15 ml) was added to a solution of CuCl₂^.2H₂O (0.34 g, 0.002 mol) in 10 ml of the same solvent mixture. After stirring the reaction mixture for 0.5 h, the resulting blue–green precipitate was filtered off, washed with diethyl ether (3 × 5 ml) and dried in air [0.53 g, yield 80%; m.p. 483 K (decomposition)]. Analysis calculated: Cu 19.1, Cl 21.4%; found: Cu 19.4, Cl 21.6%. IR (cm^-1): 3338 (s), 3267 (s), 3047 (s), 1600 (sh), 1524 (s), 1468 (w), 1436 (s), 1371 (s), 1351 (sh), 1323 (s), 1203 (s), 1109 (w), 1070 (s), 1017 (s), 818 (s), 765 (m), 709 (s), 640 (s), 540 (m), 481 (s).

S3. Refinement

Powder diffraction patterns of complexes (I) and (II) were indexed using the program TREOR90 (Werner et al., 1985). As a result, triclinic unit cells were found for both compounds, with a = 5.224 Å, b = 6.512 Å, c = 9.120 Å, α = 99.02°, β = 102.45°, γ = 90.29° [F₂₀ = 118, M₂₀ = 60, F₃₀ = 111, M₃₀ = 45] for complex (I), and a = 5.164 Å, b = 6.332 Å, c = 9.002 Å, α = 100.09°, β = 101.47°, γ = 90.41° [F₂₀ = 45, M₂₀ = 26, F₃₀ = 42, M₃₀ = 20] for complex (II). Similarity of the obtained unit cells as well as of powder patterns of (I) and (II) allowed the assumption to be made that the compounds were isotypic. This prediction was supported later by the obtained results.

Structure solution was performed only for complex (I) using the program EXPO (Altomare et al., 1999). Both possible space groups, P1 and P1, were tested, but P1 was found to be appropriate, allowing a reasonable solution to be obtained. All non-H atoms were located by stucture solution, with R(F) = 0.124. The solved structure of (I) was refined with the FULLPROF package (Rodrigues-Carvajal, 2001). The refined atomic positions in complex (I) was used as starting coordinates for complex (II).

Both structures were refined in the same way. The background was adjusted iteratively at each cycle by using a Fourier filtering technique as implemented in the FULLPROF program. The pseudo-Voigt profile function was used to fit the patterns. An asymmetry correction was applied according to the Bérar–Baldinozzi function (Bérar & Baldinozzi, 1993). A March–Dollase correction of intensities for the (001) preferred orientation of plate-like grains (March, 1932; Dollase, 1986) was used in the Rietveld refinement. The preferred orientation parameter G₁ was refined to 0.7801 (13) for complex (I) and 0.9096 (18) for complex (II). For both compounds, the G₂ parameters were found to be practically equal to 0 and were not included in the final refinement. The displacement parameters of all non-H atoms were refined isotropically and were constrained to be the same. The H atoms were placed in calculated positions (Sheldrick, 2008), with C—H distances of 0.96 Å for the methyl group, N—H distances of 0.90 Å for the amine group and U_iso(H) = 1.5U_iso(C,N). Pyramidal geometry was assigned to the amine group in view of its coordination to the Cu atom. A set of suitable soft restraints on the bond lengths of the ligand molecule was introduced into the refinement. They were obtained as a result of analysis of bond lengths in copper(II), palladium(II) and platinum(II) chloride complexes with 5-amino-2-tert-buthyltetrazole (Voitekhovich et al., 2009), and a silver complex of 5-amino-2-methyltetrazole (Karaghiosoff et al., 2009). The bonds were restrained to 1.32 (1) Å (N1—N2), 1.32 (1) Å (N1—C5), 1.30 (1) Å (N2—N3), 1.32 (1) Å (N3—N4), 1.33 (1) Å (N4—C5), 1.50 (1) Å (N2—C6) and 1.35 (1) Å (C5—N7). The final Rietveld refinement plots are shown in Fig. 4.

Computing details

For both compounds, data collection: Local program; cell refinement: FULLPROF (Rodrigues-Carvajal, 2001); data reduction: Local program. Program(s) used to solve structure: EXPO (Altomare et al., 1999) for (I). For both compounds, program(s) used to refine structure: FULLPROF (Rodrigues-Carvajal, 2001); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: FULLPROF (Rodrigues-Carvajal, 2001), PLATON (Spek, 2009).

Figures

	Fig. 1. A polymeric chain in the crystal structure of complex (II); the atomic numbering for the asymmetric unit is the same for complex (I).
	Fig. 2. The crystal structure of complex (II), viewed along the a axis.
	Fig. 3. Coordination polymeric chains in (II), connected by hydrogen bonds to polymeric layers, parellel with the ab plane. The methyl groups have been omitted for clarity.
	Fig. 4. Experimental, calculated and difference powder patterns for complexes (I) (top) and (II) (bottom) in the range 2θ = 5–65°. The positions of the Bragg reflections are marked by ticks.

(I) catena-poly[[dibromidocopper(II)]-bis(µ-2-methyl-2H-tetrazol- 5-amine)-κ²N⁴:N⁵;κ²N⁵:N⁴]

Crystal data

[CuBr2(C2H5N5)2]	V = 298.56 (2) Å^3
Mr = 421.57	Z = 1
Triclinic, P1	F(000) = 203.0
Hall symbol: -P 1	Dx = 2.345 Mg m^−3
a = 5.22187 (19) Å	Cu Kα radiation, λ = 1.5418 Å
b = 6.5081 (2) Å	T = 295 K
c = 9.1165 (3) Å	Particle morphology: finely ground powder
α = 99.0064 (15)°	green
β = 102.4480 (15)°	flat sheet, 30 × 30 mm
γ = 90.2997 (18)°	Specimen preparation: Prepared at 295 K and 100 kPa

Data collection

HZG-4A (Carl Zeiss, Jena) diffractometer	Data collection mode: reflection
Radiation source: fine-focus sealed X-ray tube, BSV-29	Scan method: step
Ni filtered monochromator	2θmin = 8.00°, 2θmax = 110.00°, 2θstep = 0.02°
Specimen mounting: packed powder pellet

Refinement

Refinement on Inet	Profile function: pseudo-Voigt
Least-squares matrix: full with fixed elements per cycle	40 parameters
Rp = 0.037	7 restraints
Rwp = 0.050	0 constraints
Rexp = 0.029	H-atom parameters constrained
RBragg = 0.043	Weighting scheme based on measured s.u.'s
χ^2 = 3.028	(Δ/σ)max = 0.002
5101 data points	Background function: Fourier filtering
Excluded region(s): none	Preferred orientation correction: March-Dollase function (March, 1932; Dollase, 1986)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cu1	1.00000	0.00000	1.00000	0.0288 (4)*
Br1	1.0113 (4)	−0.3259 (3)	0.82721 (17)	0.0288 (4)*
N1	0.4701 (18)	0.2743 (17)	0.6853 (8)	0.0288 (4)*
N2	0.6671 (15)	0.2061 (17)	0.6214 (8)	0.0288 (4)*
N3	0.8551 (17)	0.1126 (17)	0.7019 (8)	0.0288 (4)*
N4	0.7747 (17)	0.1165 (16)	0.8276 (8)	0.0288 (4)*
C5	0.550 (2)	0.215 (3)	0.8202 (11)	0.0288 (4)*
N7	0.3877 (18)	0.2256 (17)	0.9193 (9)	0.0288 (4)*
C6	0.690 (2)	0.2569 (19)	0.4729 (10)	0.0288 (4)*
H7A	0.30700	0.34482	0.90462	0.0432*
H7B	0.50276	0.25817	1.00926	0.0432*
H6A	0.53613	0.32483	0.42971	0.0432*
H6B	0.70900	0.13140	0.40589	0.0432*
H6C	0.84193	0.34817	0.48653	0.0432*

Geometric parameters (Å, º)

Cu1—Br1	2.4452 (18)	N4—C5	1.334 (16)
Cu1—N4	2.004 (8)	N7—C5	1.360 (14)
Cu1—N7^i	2.783 (10)	N7—H7A	0.9000
N1—N2	1.333 (12)	N7—H7B	0.9000
N1—C5	1.328 (15)	C6—H6A	0.9600
N2—N3	1.307 (13)	C6—H6B	0.9600
N2—C6	1.472 (12)	C6—H6C	0.9600
N3—N4	1.299 (11)
Br1—Cu1—N4	89.2 (3)	N2—N3—N4	101.6 (8)
Br1—Cu1—N7^i	98.4 (2)	Cu1—N4—N3	119.1 (7)
Br1—Cu1—N7^ii	81.6 (2)	Cu1—N4—C5	130.4 (7)
Br1—Cu1—Br1^iii	180.00	N3—N4—C5	110.3 (9)
Br1—Cu1—N4^iii	90.8 (3)	Cu1^iv—N7—C5	142.5 (10)
N4—Cu1—N7^i	81.4 (3)	Cu1^iv—N7—H7B	101.00
N4—Cu1—N7^ii	98.6 (3)	C5—N7—H7B	101.00
Br1^iii—Cu1—N4	90.8 (3)	H7A—N7—H7B	105.00
N4—Cu1—N4^iii	180.00	C5—N7—H7A	101.00
N7^i—Cu1—N7^ii	180.00	Cu1^iv—N7—H7A	101.00
Br1^iii—Cu1—N7^i	81.6 (2)	N1—C5—N7	120.4 (11)
N4^iii—Cu1—N7^i	98.6 (3)	N4—C5—N7	127.6 (12)
Br1^iii—Cu1—N7^ii	98.4 (2)	N1—C5—N4	111.0 (9)
N4^iii—Cu1—N7^ii	81.4 (3)	N2—C6—H6A	110.00
Br1^iii—Cu1—N4^iii	89.2 (3)	N2—C6—H6B	110.00
N2—N1—C5	99.2 (9)	N2—C6—H6C	109.00
N1—N2—N3	117.9 (7)	H6A—C6—H6B	110.00
N1—N2—C6	121.2 (9)	H6A—C6—H6C	109.00
N3—N2—C6	120.6 (8)	H6B—C6—H6C	109.00

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N7—H7A···Br1^v	0.90	2.74	3.634 (11)	172
N7—H7B···Br1^iii	0.90	2.65	3.463 (9)	151

Symmetry codes: (iii) −x+2, −y, −z+2; (v) x−1, y+1, z.

(II) catena-poly[[dichloridocopper(II)]-bis(µ-2-methyl-2H-tetrazol- 5-amine)-κ²N⁴:N⁵;κ²N⁵:N⁴]

Crystal data

[CuCl2(C2H5N5)2]	V = 282.81 (1) Å^3
Mr = 332.67	Z = 1
Triclinic, P1	F(000) = 167.0
Hall symbol: -P 1	Dx = 1.953 Mg m^−3
a = 5.16248 (13) Å	Cu Kα radiation, λ = 1.5418 Å
b = 6.32103 (16) Å	T = 295 K
c = 8.9925 (2) Å	Particle morphology: finely ground powder
α = 100.1652 (13)°	blue-green
β = 101.4538 (12)°	flat sheet, 30 × 30 mm
γ = 90.4234 (12)°	Specimen preparation: Prepared at 295 K and 100 kPa

Data collection

HZG-4A (Carl Zeiss, Jena) diffractometer	Data collection mode: reflection
Radiation source: fine-focus sealed X-ray tube, BSV-29	Scan method: step
Ni filtered monochromator	2θmin = 8.000°, 2θmax = 120.000°, 2θstep = 0.020°
Specimen mounting: packed powder pellet

Refinement

Refinement on Inet	Profile function: psevdo-Voigt
Least-squares matrix: full with fixed elements per cycle	40 parameters
Rp = 0.030	7 restraints
Rwp = 0.039	0 constraints
Rexp = 0.025	H-atom parameters constrained
RBragg = 0.045	Weighting scheme based on measured s.u.'s
χ^2 = 2.434	(Δ/σ)max = 0.001
5601 data points	Background function: Fourier filtering
Excluded region(s): none	Preferred orientation correction: March-Dollase function (March, 1932; Dollase, 1986)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cu1	1.00000	0.00000	1.00000	0.0227 (3)*
Cl1	1.0253 (4)	−0.3188 (4)	0.8346 (2)	0.0227 (3)*
N1	0.4609 (11)	0.2789 (10)	0.6788 (7)	0.0227 (3)*
N2	0.6653 (11)	0.2114 (12)	0.6192 (7)	0.0227 (3)*
N3	0.8589 (11)	0.1207 (10)	0.6938 (6)	0.0227 (3)*
N4	0.7562 (11)	0.1194 (10)	0.8198 (7)	0.0227 (3)*
C5	0.5317 (14)	0.2183 (15)	0.8152 (7)	0.0227 (3)*
N7	0.3871 (11)	0.2243 (12)	0.9289 (7)	0.0227 (3)*
C6	0.7091 (13)	0.2576 (12)	0.4719 (8)	0.0227 (3)*
H7A	0.32285	0.35726	0.93370	0.03405*
H7B	0.51557	0.23496	1.01409	0.03405*
H6A	0.55753	0.32454	0.42251	0.03405*
H6B	0.73579	0.12546	0.40610	0.03405*
H6C	0.86268	0.35217	0.48962	0.03405*

Geometric parameters (Å, º)

Cu1—Cl1	2.305 (2)	N2—C6	1.465 (9)
Cu1—N4	2.101 (6)	N3—N4	1.344 (8)
Cu1—N7^i	2.683 (6)	N4—C5	1.318 (10)
Cu1—N7^ii	2.683 (6)	N7—C5	1.376 (9)
Cu1—Cl1^iii	2.305 (2)	N7—H7A	0.9000
Cu1—N4^iii	2.101 (6)	N7—H7B	0.9000
N1—N2	1.317 (8)	C6—H6A	0.9600
N1—C5	1.332 (9)	C6—H6B	0.9600
N2—N3	1.287 (9)	C6—H6C	0.9600
Cl1—Cu1—N4	90.03 (18)	N2—N3—N4	96.4 (5)
Cl1—Cu1—N7^i	98.04 (16)	Cu1—N4—N3	115.4 (4)
Cl1—Cu1—N7^ii	81.96 (16)	Cu1—N4—C5	130.8 (5)
Cl1—Cu1—Cl1^iii	180.00	N3—N4—C5	113.1 (6)
Cl1—Cu1—N4^iii	89.97 (18)	Cu1^iv—N7—C5	140.2 (5)
N4—Cu1—N7^i	84.2 (2)	Cu1^iv—N7—H7B	102.00
N4—Cu1—N7^ii	95.8 (2)	C5—N7—H7B	102.00
Cl1^iii—Cu1—N4	89.97 (18)	H7A—N7—H7B	105.00
N4—Cu1—N4^iii	180.00	C5—N7—H7A	102.00
N7^i—Cu1—N7^ii	180.00	Cu1^iv—N7—H7A	102.00
Cl1^iii—Cu1—N7^i	81.96 (16)	N1—C5—N7	128.2 (7)
N4^iii—Cu1—N7^i	95.8 (2)	N4—C5—N7	122.2 (7)
Cl1^iii—Cu1—N7^ii	98.04 (16)	N1—C5—N4	109.0 (6)
N4^iii—Cu1—N7^ii	84.2 (2)	N2—C6—H6A	110.00
Cl1^iii—Cu1—N4^iii	90.03 (18)	N2—C6—H6B	109.00
N2—N1—C5	98.7 (6)	N2—C6—H6C	110.00
N1—N2—N3	122.5 (6)	H6A—C6—H6B	109.00
N1—N2—C6	123.1 (6)	H6A—C6—H6C	110.00
N3—N2—C6	114.0 (6)	H6B—C6—H6C	109.00

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N7—H7A···Cl1^v	0.90	2.74	3.587 (8)	157
N7—H7B···Cl1^iii	0.90	2.49	3.323 (6)	154

Symmetry codes: (iii) −x+2, −y, −z+2; (v) x−1, y+1, z.