Bis­[1,3-bis(2-methyl­tetrazol-5-yl-κN⁴)­triazenido-κN²]­nickel(II)

The title compound, [Ni(BMTT)₂], where BMTT is 1,3-bis(2-methyl­tetrazol-5-yl)­triazenide (C₄H₆N₁₁), presents a molecular complex with tridentate ligands. The tridentate mode of the ligand is realised through the central N atom of the triazene group and two N atoms of the two tetrazole rings. The [Ni(BMTT)₂] mol­ecule is the meridional isomer, with crystallographic symmetry in space group P4₂/n. The nickel centre has a distorted octahedral environment, with two axial Ni—N bonds of 2.041 (2) Å and four equatorial Ni—N bonds of 2.0739 (14) Å. The mol­ecules are linked together by van der Waals interactions only.

S1. Comment

During the past two decades, the coordination properties of the triazene ligands R—NH—N=N—R, where R is an aryl or heterocyclic group, have been intensively studied due to their versatility in coordination (Hanot et al., 1999). The introduction of two N-substituted 5-tetrazolyl groups as the R substituents leads to polynitrogen binuclear heterocyclic compounds. These, similar to other bis(tetrazoles), are attractive as chelating agents (Voitekhovich et al., 2002), and act as ligands for the synthesis of coordination polymers in one, two and three dimensions (Grunert et al., 2004; Bronisz, 2004). However, complexes of bis(tetrazolyl)triazenes have not been described previously. Here, we report the crystal structure of a complex obtained by the reaction of 1,3-bis(2-methyltetrazol-5-yl)triazene (BMTT) with nickel(II) chloride in ethanol. In this reaction, 1,3-bis(2-methyltetrazol-5-yl)triazene undergoes deprotonation to form the thermally stable title bis(chelate) complex [Ni(BMTT)₂], (I), (Fig. 1). \sch

The complex molecule of (I) contains an Ni^II cation and two deprotonated BMTT⁻ ligands. The ligand shows tridentate chelating properties and is coordinated to the metallic centre through the N4 atoms of the two tetrazole rings and the central N8 atom of the triazene group. The molecule has crystallographic 4 symmetry and the reference Ni^II cation was selected as that lying at (1/4, 1/4, 3/4). Except for atom N8, which lies on the twofold rotation axis along (1/4, 1/4, z), all remaining atoms occupy general positions.

The six N atoms around the Ni^II cation form a distorted octahedron, with two axial Ni—N8 bonds of 2.041 (2) Å and four longer equatorial Ni—N4 bonds of 2.0739 (14) Å. The complex is the meridional isomer, with a normalized bite b of 1.24 [b = 2sin(α/2) (Kepert, 1982), where α is the angle N4—Ni—N8 in the case of (I)] and a tridentate bite angle N4—N8—N4ⁱⁱ of ca 104.6° [symmetry code (ii) as in Fig. 1]. The observed meridional configuration of the ligands in (I) is in agreement with the predicted stabilization of the meridional isomer, rather than the symmetrical-facial and unsymmetrical-facial isomers, for ligands with a small normalized bite, b < 1.3, and/or for relatively rigid tridentate ligands with a tridentate angle higher than ca 100° (Kepert, 1982).

As a result of the formation of two adjacent five-membered Ni—N8—N7—C5—N4 rings for each ligand, the nitrogen octahedron is somewhat distorted. Thus, the axial-equatorial N8—Ni—N4 angles, with both N atoms belonging to the same ligand, are 76.58 (4)°, while the diequatorial angles, involving N atoms from two different ligands, are 93.086 (19)°. The coordination geometry in (I) is very similar to that found previously in [Ni(BATT)₂]·4H₂O, where BATT is 1,3-bis[3-(5-amino-1,2,4-triazolyl)]triazene (Hanot et al., 1999).

The entire BMTT ligand in (I), with twofold rotation symmetry, is nearly planar: the mean deviation of the ligand atoms from the best least-squares plane is 0.0542 (17) Å. Each half of the ligand is planar to within 0.0132 (14) Å. The tetrazole ring bond lengths are shown in Table 1. The formal single bond N2—N3 is the shortest in the ring, whereas the N4—C5 bond is the longest. The remaining bonds have values lying in the range 1.326 (2)–1.339 (2) Å. The tetrazole ring is planar to within 0.0006 (10) Å. The geometry of the tetrazole ring in (I) is similar to that observed previously in copper(II) complexes of 2-substituted tetrazoles (van den Heuvel et al., 1983; Bronisz, 2002; Lyakhov Gaponik Degtyarik & Ivashkevich, 2003a,b; Lyakhov Gaponik Degtyarik et al., 2003). The deprotonated triazene bridge N7—N8—N7ⁱⁱ is symmetrical. The bond lengths and angles at N7 and N8 indicate hybridization rather close to sp³ and sp³, respectively.

Because of the lack of hydrogen bonds in the structure of (I), the crystal packing is determined by van der Waals interactions only.

S2. Experimental

1,3-Bis(2-methyltetrazol-5-yl)triazene was prepared by treating 2-methyl-5-aminotetrazole with nitric acid and sodium nitrite, according to the method of Hattori et al. (1956). Complex (I) was synthesized by slow evaporation (20 d) of a solution composed of nickel(II) chloride hexahydrate (0.24 g, 1 mmol) and 1,3-bis(2-methyltetrazol-5-yl)triazene (0.21 g, 1 mmol) in ethanol (30 ml) at room temperature. The resulting dark-red prismatic crystals of (I) were found to be thermally stable and to decompose at temperatures higher than 520 K.

S3. Refinement

The H atoms of the methyl groups were placed in geometrically calculated positions, with C—H distances of 0.96 Å, and refined using a riding model, with U_iso(H) = 1.5U_eq(C).

Computing details

Data collection: R3m Software (Nicolet, 1980); cell refinement: R3m Software; data reduction: R3m Software; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. The structure of the complex molecule of (I), with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) 1/2 − y, x, 3/2 − z; (ii) 1/2 − x, 1/2 − y, z; (iii) y, 1/2 − x, 3/2 − z.]

Bis[1,3-bis(2-methyltetrazol-5-yl-κ²N⁴)triazenido-κN²]nickel(II)

Crystal data

[Ni(C4H6N11)2]	Dx = 1.770 Mg m^−3
Mr = 475.09	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P42/n	Cell parameters from 25 reflections
Hall symbol: -P 4bc	θ = 19.6–22.3°
a = 9.5785 (15) Å	µ = 1.15 mm^−1
c = 9.713 (2) Å	T = 293 K
V = 891.2 (3) Å^3	Prism, dark red
Z = 2	0.38 × 0.36 × 0.20 mm
F(000) = 484

Data collection

Nicolet R3m four-circle diffractometer	1139 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.032
Graphite monochromator	θmax = 30.1°, θmin = 3.0°
ω/2θ scans	h = −13→13
Absorption correction: multi-scan (Blessing, 1995)	k = −4→13
Tmin = 0.670, Tmax = 0.803	l = −6→13
3195 measured reflections	3 standard reflections every 100 reflections
1315 independent reflections	intensity decay: none

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)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.121	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.077P)^2 + 0.1594P] where P = (Fo^2 + 2Fc^2)/3
1315 reflections	(Δ/σ)max < 0.001
72 parameters	Δρmax = 0.61 e Å^−3
0 restraints	Δρmin = −0.45 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
Ni	0.2500	0.2500	0.7500	0.03140 (17)
N1	0.59152 (15)	0.13348 (15)	0.97344 (15)	0.0386 (3)
N2	0.64701 (15)	0.10387 (15)	0.85037 (15)	0.0381 (3)
N3	0.56367 (19)	0.12509 (18)	0.74526 (14)	0.0395 (4)
N4	0.44541 (14)	0.17144 (14)	0.79955 (15)	0.0361 (3)
C5	0.46349 (16)	0.17588 (15)	0.93773 (17)	0.0342 (3)
C6	0.78857 (18)	0.0501 (2)	0.8336 (2)	0.0457 (4)
H6A	0.7847	−0.0472	0.8100	0.068*
H6B	0.8391	0.0613	0.9183	0.068*
H6C	0.8350	0.1006	0.7617	0.068*
N7	0.36081 (14)	0.21488 (15)	1.03002 (14)	0.0386 (3)
N8	0.2500	0.2500	0.9601 (2)	0.0326 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ni	0.0320 (2)	0.0320 (2)	0.0301 (3)	0.000	0.000	0.000
N1	0.0359 (7)	0.0393 (7)	0.0407 (7)	0.0031 (5)	−0.0014 (5)	0.0003 (5)
N2	0.0344 (7)	0.0348 (7)	0.0452 (8)	0.0014 (5)	0.0010 (6)	−0.0008 (5)
N3	0.0367 (8)	0.0399 (8)	0.0419 (8)	0.0019 (6)	0.0015 (5)	−0.0019 (5)
N4	0.0347 (7)	0.0374 (7)	0.0361 (7)	0.0014 (5)	0.0008 (5)	0.0001 (5)
C5	0.0337 (7)	0.0310 (7)	0.0380 (8)	0.0005 (5)	−0.0020 (6)	0.0022 (6)
C6	0.0348 (8)	0.0437 (9)	0.0585 (10)	0.0050 (7)	0.0028 (7)	−0.0010 (8)
N7	0.0353 (7)	0.0458 (8)	0.0347 (6)	0.0035 (6)	−0.0022 (5)	0.0006 (6)
N8	0.0324 (8)	0.0335 (8)	0.0317 (9)	−0.0011 (6)	0.000	0.000

Geometric parameters (Å, º)

Ni—N8	2.041 (2)	N2—C6	1.460 (2)
Ni—N8^i	2.041 (2)	N3—N4	1.326 (2)
Ni—N4^ii	2.0739 (14)	N4—C5	1.354 (2)
Ni—N4^iii	2.0740 (14)	C5—N7	1.382 (2)
Ni—N4^i	2.0740 (14)	C6—H6A	0.9600
Ni—N4	2.0740 (14)	C6—H6B	0.9600
N1—C5	1.338 (2)	C6—H6C	0.9600
N1—N2	1.339 (2)	N7—N8	1.3040 (17)
N2—N3	1.312 (2)	N8—N7^iii	1.3040 (17)
N8—Ni—N8^i	180.0	N1—N2—C6	122.89 (15)
N8—Ni—N4^ii	103.42 (4)	N2—N3—N4	105.20 (13)
N8^i—Ni—N4^ii	76.58 (4)	N3—N4—C5	107.19 (13)
N8—Ni—N4^iii	76.58 (4)	N3—N4—Ni	143.14 (12)
N8^i—Ni—N4^iii	103.42 (4)	C5—N4—Ni	109.52 (11)
N4^ii—Ni—N4^iii	93.086 (19)	N1—C5—N4	111.39 (14)
N8—Ni—N4^i	103.42 (4)	N1—C5—N7	124.49 (15)
N8^i—Ni—N4^i	76.58 (4)	N4—C5—N7	124.08 (14)
N4^ii—Ni—N4^i	153.16 (8)	N2—C6—H6A	109.5
N4^iii—Ni—N4^i	93.089 (19)	N2—C6—H6B	109.5
N8—Ni—N4	76.58 (4)	H6A—C6—H6B	109.5
N8^i—Ni—N4	103.42 (4)	N2—C6—H6C	109.5
N4^ii—Ni—N4	93.088 (19)	H6A—C6—H6C	109.5
N4^iii—Ni—N4	153.16 (8)	H6B—C6—H6C	109.5
N4^i—Ni—N4	93.086 (19)	N8—N7—C5	108.13 (14)
C5—N1—N2	101.35 (13)	N7^iii—N8—N7	117.3 (2)
N3—N2—N1	114.87 (14)	N7^iii—N8—Ni	121.37 (10)
N3—N2—C6	122.24 (16)	N7—N8—Ni	121.37 (10)
C5—N1—N2—N3	0.11 (19)	N2—N1—C5—N7	177.82 (14)
C5—N1—N2—C6	−179.00 (15)	N3—N4—C5—N1	0.15 (19)
N1—N2—N3—N4	0.0 (2)	Ni—N4—C5—N1	−176.45 (10)
C6—N2—N3—N4	179.09 (15)	N3—N4—C5—N7	−177.83 (15)
N2—N3—N4—C5	−0.07 (19)	Ni—N4—C5—N7	5.57 (19)
N2—N3—N4—Ni	174.57 (14)	N1—C5—N7—N8	179.99 (13)
N8—Ni—N4—N3	−179.2 (2)	N4—C5—N7—N8	−2.3 (2)
N8^i—Ni—N4—N3	0.8 (2)	C5—N7—N8—N7^iii	177.43 (14)
N4^ii—Ni—N4—N3	−76.2 (2)	C5—N7—N8—Ni	−2.57 (14)
N4^iii—Ni—N4—N3	−179.2 (2)	N4^ii—Ni—N8—N7^iii	94.31 (9)
N4^i—Ni—N4—N3	77.7 (2)	N4^iii—Ni—N8—N7^iii	4.31 (9)
N8—Ni—N4—C5	−4.68 (10)	N4^i—Ni—N8—N7^iii	−85.69 (9)
N8^i—Ni—N4—C5	175.33 (10)	N4—Ni—N8—N7^iii	−175.69 (9)
N4^ii—Ni—N4—C5	98.39 (10)	N4^ii—Ni—N8—N7	−85.69 (9)
N4^iii—Ni—N4—C5	−4.67 (10)	N4^iii—Ni—N8—N7	−175.69 (9)
N4^i—Ni—N4—C5	−107.74 (11)	N4^i—Ni—N8—N7	94.31 (9)
N2—N1—C5—N4	−0.15 (17)	N4—Ni—N8—N7	4.31 (9)

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