Crystal structure of bis-[(5-amino-1H-1,2,4-triazol-3-yl-κN (4))acetato-κO]di-aqua-nickel(II) dihydrate.

The title compound, [Ni(C4H5N4O2)2(H2O)2]·2H2O, represents the first transition metal complex of the novel chelating triazole ligand, 2-(5-amino-1H-1,2,4-triazol-3-yl)acetic acid (ATAA), to be structurally characterized. In the mol-ecule of the title complex, the nickel(II) cation is located on an inversion centre and is coordinated by two water mol-ecules in axial positions and two O and two N atoms from two trans-oriented chelating anions of the deprotonated ATAA ligand, forming a slightly distorted octa-hedron. The trans angles of the octa-hedron are all 180° due to the inversion symmetry of the mol-ecule. The cis-angles are in the range 87.25 (8)-92.75 (8)°. The six-membered chelate ring adopts a slightly twisted boat conformation with puckering parameters Q = 0.542 (2) Å, Θ = 88.5 (2) and ϕ = 15.4 (3)°. The mol-ecular conformation is stabilized by intra-molecular N-H⋯O hydrogen bonds between the amino group and the chelating carboxyl-ate O atom of two trans-oriented ligands. In the crystal, the complex mol-ecules and lattice water mol-ecules are linked into a three-dimensional framework by an extensive network of N-H⋯O, O-H⋯O and O-H⋯N hydrogen bonds.

Chemical context

C-amino-1,2,4-triazoles are employed as polydentate ligands for the synthesis of coordination compounds with various metals that demonstrate useful spectroscopic, magnetic, biological and catalytic properties (Aromí et al., 2011 ▶; Liu et al., 2011 ▶; Gao et al., 2013 ▶; Hernández-Gil et al., 2014 ▶). Generally, amino­triazoles coordinate metals by either pyridine-type endocyclic nitro­gen atoms or by the amino group (Aromí et al., 2011 ▶; Liu et al., 2011 ▶). Furthermore, amino­triazoles containing substituents with favorably oriented atoms bearing unshared electron pairs (N, S, O etc.) can act as chelating polydentate ligands (Biagini-Cingi et al., 1994 ▶; Prins et al., 1996 ▶; Ferrer et al., 2004 ▶, 2012 ▶). 5-Amino-1H-1,2,4-tri­azole-3-carb­oxy­lic acid (ATCA, Fig. 1 ▶) was found to be a promising chelating ligand for which complexes with various metal cations have been reported recently (Chen et al., 2011 ▶; Sun et al., 2011 ▶; Wang et al., 2011 ▶; Hernández-Gil et al., 2012 ▶; Tseng et al., 2014 ▶). In these complexes, metal cations are chelated by the anions of ATCA owing to the formation of coordination bonds with nitro­gen atoms of the triazole ring and the oxygen atom of the deprotonated carb­oxy­lic group.

Figure 1

Structural formulas of 5-amino-1H-1,2,4-triazole-3-carb­oxy­lic acid (ATCA) and 2-(5-amino-1H-1,2,4-triazol-3-yl)acetic acid (ATAA).

In a continuation of our work on the synthesis and reactivity of amino­triazole carb­oxy­lic acids (Chernyshev et al., 2006 ▶, 2009 ▶, 2010 ▶), we have focused our attention on another chelating ligand, namely 2-(5-amino-1H-1,2,4-triazol-3-yl)acetic acid (ATAA, Fig. 1 ▶), which can be considered as a homologue of ATCA. To the best of our knowledge, ATAA or its derivatives have not been studied previously for the synthesis of coordination compounds. Herein, we report the synthesis and crystal structure of an NiII complex of ATAA, the title compound [Ni(C4H5N4O2)2(H2O)2]·2H2O (1).

Structural commentary

In the mol­ecule of the title complex (1), the NiII cation is six-coordinated by two bidentate chelating ligands, anions of ATAA, and by two water mol­ecules, forming a slightly distorted octa­hedron (Fig. 2 ▶). The trans-angles of the octa­hedron are all 180° due to the inversion symmetry of the complete mol­ecule. The cis-angles are in the range 87.25 (8)–92.75 (8)°. The third water mol­ecule is not involved in coordination. The anions of ATAA coordinate the NiII cation through the nitro­gen atom N1 of the triazole ring and the oxygen atom O53 of the carboxyl­ate group (Fig. 2 ▶), similarly to the complexes of ATCA with various metal cations (Chen et al., 2011 ▶; Sun et al., 2011 ▶; Wang et al., 2011 ▶; Hernández-Gil et al., 2012 ▶). The six-membered chelate ring adopts a slightly twisted boat conformation with puckering parameters of Q = 0.542 (2) Å, Θ = 88.5 (2), ϕ = 15.4 (3)°. The Ni—N1 bond length is 2.051 (2) Å, and the Ni—O1 and Ni—O53 bond lengths are 2.083 (2) and 2.059 (2) Å, respectively, within the normal ranges for other reported NiII complexes (Lenstra et al., 1989 ▶; Virovets et al., 2000 ▶; Bushuev et al., 2002 ▶; Drozdzewski et al., 2003 ▶; Fan et al., 2010 ▶; Zheng et al., 2011 ▶; Jin et al., 2011 ▶). The amino­triazole fragment N1/C2/N3/N4/C5/N21 is planar (maximum deviation = 0.021 (3) Å for C2), its bond lengths and angles being analogous to complexes of C-amino-1,2,4-triazoles with transition metals (Ferrer et al., 2004 ▶; Siddiqui et al., 2011 ▶; Tabatabaee et al., 2011 ▶). The bonds C2—N3 [1.330 (4) Å] and C5—N4 [1.304 (3) Å] are shorter than the bonds C2—N1 [1.342 (3) Å] and C5—N1 [1.365 (3) Å]. The mol­ecular conformation is stabilized by intra­molecular N21—H21B⋯O53 hydrogen bonds (Fig. 2 ▶, Table 1 ▶).

Figure 2

The mol­ecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. Intra­molecular N—H⋯O hydrogen bonds are shown as dashed lines. Equivalent atoms are generated by symmetry code −x, −y, −z.

Table 1

Hydrogen-bond geometry (, )

DHA	DH	HA	D A	DHA
N21H21AO2i	0.83(2)	2.04(2)	2.876(3)	176(3)
N21H21BO53ii	0.83(2)	2.19(2)	2.941(3)	151(3)
N3H3O54iii	0.83(3)	2.10(3)	2.885(3)	156(3)
O1H1AO2iv	0.82(2)	1.92(2)	2.739(3)	176(3)
O1H1BO54v	0.82(2)	1.96(2)	2.780(3)	173(4)
O2H2AN4vi	0.83(2)	2.09(2)	2.903(3)	164(3)
O2H2BO53vii	0.83(2)	1.98(2)	2.811(3)	176(3)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) ; (vii) .

Supra­molecular features

In the crystal, mol­ecules of the complex and lattice water mol­ecules are linked into a three–dimensional framework by extensive N—H⋯O, O—H⋯O and O—H⋯N hydrogen bonds (Table 1 ▶, Fig. 3 ▶).

Figure 3

The crystal packing of the title compound viewed along the a axis. Hydrogen bonds are shown as dashed lines.

Database survey

More than twenty structures of chelate complexes of 3-substituted 5-amino-1,2,4-triazoles, in which N, O or S atoms of the substituent in the position 3 of the triazole ring play the role of a donor atom, were found in the Cambridge Structural Database (Version 5.35, November 2013 with 2 updates; Thomas et al., 2010 ▶). The database reveals a total of seven structures of coordination compounds of 5-amino-1H-1,2,4-triazole-3-carb­oxy­lic acid (ATCA) with various metals (Chen et al., 2011 ▶; Sun et al., 2011 ▶; Wang et al., 2011 ▶; Hernández-Gil et al., 2012 ▶; Tseng et al., 2014 ▶; Siddiqui et al., 2011 ▶), six of which are chelate complexes. Coordination compounds of metals with the ATAA ligands or its derivatives were not found in the literature.

Synthesis and crystallization

All attempts to prepare crystals of complex (1) suitable for X-ray investigation by mixing solutions of ATAA or its sodium salt with solutions of NiII salts were unsuccessful and only microcrystalline precipitates of the sparingly soluble complex were obtained. Crystals of acceptable quality were prepared by slow hydrolysis of ethyl 2-(5-amino-1H-1,2,4-triazol-3-yl)acetate (2) in an aqueous solution of nickel nitrate (Fig. 4 ▶). A solution of 0.65 g (3.8 mmol) of compound (2) in water (10 ml) was added to a solution of 0.55 g, (1.9 mmol) of Ni(NO3)2·6H2O in water (5 ml). After standing at room temperature for two weeks, the formed crystals were collected by filtration yielding the target compound (1).

Figure 4

Reaction scheme showing the synthesis of the title compound (1).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▶. C-bound H atoms were placed in calculated positions with C—H = 0.97 Å for the CH2 group and refined as riding, with U iso(H) = 1.2U eq(C). The N,O-bound H atoms that are involved in hydrogen bonds were found from difference Fourier maps. Their distances to the parent atoms were refined to be equal, with a common U iso(H) value for pairs of related H atoms.

Table 2

Experimental details

Crystal data
Chemical formula
M r	412.99
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	295
a, b, c ()	7.6270(17), 7.2603(16), 13.580(3)
()	91.91(2)
V (3)	751.6(3)
Z	2
Radiation type	Ag K, = 0.56085
(mm1)	0.72
Crystal size (mm)	0.20 0.20 0.20
Data collection
Diffractometer	EnrafNonius CAD-4
Absorption correction	scan (North et al., 1968 ▶)
T min, T max	0.945, 0.958
No. of measured, independent and observed [I > 2(I)] reflections	1706, 1640, 1215
R int	0.021
(sin /)max (1)	0.638
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.035, 0.077, 1.02
No. of reflections	1640
No. of parameters	140
No. of restraints	3
max, min (e 3)	0.34, 0.31

Computer programs: CAD-4 EXPRESS (EnrafNonius, 1994 ▶), XCAD4 (Harms Wocadlo, 1995 ▶), SHELXS97 and SHELXL2013 (Sheldrick, 2008 ▶), ORTEP-3 for Windows and WinGX (Farrugia, 2012 ▶).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S1600536814021436/wm5066sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536814021436/wm5066Isup2.hkl

CCDC reference: 1026535

Additional supporting information: crystallographic information; 3D view; checkCIF report

	F(000) = 428
Mr = 412.99	Dx = 1.825 Mg m−3
Monoclinic, P21/n	Ag Kα radiation, λ = 0.56085 Å
Hall symbol: -P 2yn	Cell parameters from 25 reflections
a = 7.6270 (17) Å	θ = 10.8–12.9°
b = 7.2603 (16) Å	µ = 0.72 mm−1
c = 13.580 (3) Å	T = 295 K
β = 91.91 (2)°	Prism, light green
V = 751.6 (3) Å3	0.20 × 0.20 × 0.20 mm
Z = 2

Enraf–Nonius CAD-4 diffractometer	1215 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.021
Graphite monochromator	θmax = 21.0°, θmin = 2.4°
non–profiled ω–scans	h = −9→9
Absorption correction: ψ scan (North et al., 1968)	k = 0→9
Tmin = 0.945, Tmax = 0.958	l = 0→17
1706 measured reflections	1 standard reflections every 60 min
1640 independent reflections	intensity decay: 1%

Refinement on F2	3 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.035	Secondary atom site location: difference Fourier map
wR(F2) = 0.077	w = 1/[σ2(Fo2) + (0.0282P)2 + 0.467P] where P = (Fo2 + 2Fc2)/3
S = 1.02	(Δ/σ)max < 0.001
1640 reflections	Δρmax = 0.34 e Å−3
140 parameters	Δρmin = −0.31 e Å−3

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.

	x	y	z	Uiso*/Ueq
Ni	0.0000	0.0000	0.0000	0.01840 (14)
N1	−0.0590 (3)	0.0113 (4)	−0.14834 (14)	0.0215 (5)
C2	0.0459 (3)	0.0087 (5)	−0.22579 (18)	0.0237 (5)
N21	0.2095 (3)	−0.0555 (4)	−0.22436 (19)	0.0380 (8)
H21A	0.278 (3)	−0.036 (5)	−0.2696 (17)	0.040 (7)*
H21B	0.248 (4)	−0.090 (5)	−0.1692 (15)	0.040 (7)*
N3	−0.0433 (3)	0.0713 (4)	−0.30469 (18)	0.0307 (6)
H3	−0.010 (4)	0.083 (4)	−0.362 (2)	0.029 (9)*
N4	−0.2124 (3)	0.1187 (4)	−0.28023 (17)	0.0289 (6)
C5	−0.2135 (4)	0.0798 (4)	−0.18651 (19)	0.0218 (6)
C51	−0.3727 (3)	0.1003 (4)	−0.12754 (19)	0.0242 (6)
H51A	−0.4200	−0.0215	−0.1160	0.029*
H51B	−0.4597	0.1678	−0.1668	0.029*
C52	−0.3496 (3)	0.1962 (4)	−0.02933 (19)	0.0206 (6)
O53	−0.2044 (2)	0.1806 (3)	0.01848 (14)	0.0248 (5)
O54	−0.4765 (3)	0.2802 (3)	0.00309 (17)	0.0335 (5)
O1	−0.1634 (3)	−0.2263 (3)	0.01911 (18)	0.0327 (5)
H1A	−0.129 (4)	−0.313 (3)	0.053 (2)	0.048 (8)*
H1B	−0.271 (2)	−0.238 (5)	0.017 (3)	0.048 (8)*
O2	0.4528 (3)	0.0268 (3)	0.62437 (15)	0.0320 (5)
H2A	0.556 (3)	0.054 (5)	0.641 (2)	0.039 (7)*
H2B	0.404 (4)	0.110 (4)	0.591 (2)	0.039 (7)*

	U11	U22	U33	U12	U13	U23
Ni	0.0162 (2)	0.0239 (3)	0.0150 (2)	0.0020 (2)	−0.00011 (16)	0.0011 (3)
N1	0.0180 (10)	0.0313 (13)	0.0150 (9)	0.0003 (12)	−0.0003 (8)	0.0021 (12)
C2	0.0253 (13)	0.0265 (14)	0.0193 (12)	−0.0005 (14)	0.0020 (10)	0.0020 (15)
N21	0.0282 (14)	0.063 (2)	0.0236 (13)	0.0098 (13)	0.0102 (10)	0.0131 (13)
N3	0.0322 (14)	0.0449 (16)	0.0152 (12)	0.0033 (12)	0.0051 (10)	0.0053 (11)
N4	0.0275 (13)	0.0400 (16)	0.0190 (12)	0.0058 (12)	−0.0017 (9)	0.0048 (11)
C5	0.0225 (13)	0.0246 (14)	0.0181 (13)	−0.0026 (12)	−0.0009 (11)	0.0006 (11)
C51	0.0161 (13)	0.0340 (17)	0.0224 (14)	0.0006 (12)	−0.0015 (11)	0.0017 (13)
C52	0.0202 (13)	0.0221 (14)	0.0196 (13)	0.0002 (11)	0.0032 (10)	0.0040 (11)
O53	0.0208 (10)	0.0322 (11)	0.0210 (10)	0.0049 (9)	−0.0042 (8)	−0.0041 (9)
O54	0.0238 (11)	0.0486 (13)	0.0282 (10)	0.0106 (10)	0.0032 (9)	−0.0058 (12)
O1	0.0202 (10)	0.0327 (13)	0.0448 (14)	−0.0046 (10)	−0.0041 (10)	0.0108 (11)
O2	0.0309 (11)	0.0371 (14)	0.0280 (11)	−0.0022 (11)	0.0007 (9)	0.0026 (11)

Ni—N1	2.051 (2)	N3—H3	0.83 (3)
Ni—N1i	2.051 (2)	N4—C5	1.304 (3)
Ni—O53	2.0590 (19)	C5—C51	1.484 (4)
Ni—O53i	2.0590 (19)	C51—C52	1.509 (4)
Ni—O1	2.083 (2)	C51—H51A	0.9700
Ni—O1i	2.084 (2)	C51—H51B	0.9700
N1—C2	1.342 (3)	C52—O54	1.238 (3)
N1—C5	1.365 (3)	C52—O53	1.270 (3)
C2—N3	1.330 (4)	O1—H1A	0.822 (19)
C2—N21	1.332 (4)	O1—H1B	0.822 (19)
N21—H21A	0.834 (19)	O2—H2A	0.83 (2)
N21—H21B	0.834 (19)	O2—H2B	0.83 (2)
N3—N4	1.386 (3)
N1—Ni—N1i	180.0	H21A—N21—H21B	120 (3)
N1—Ni—O53	87.25 (8)	C2—N3—N4	110.3 (2)
N1i—Ni—O53	92.75 (8)	C2—N3—H3	129 (2)
N1—Ni—O53i	92.75 (8)	N4—N3—H3	121 (2)
N1i—Ni—O53i	87.25 (8)	C5—N4—N3	102.5 (2)
O53—Ni—O53i	180.00 (13)	N4—C5—N1	114.6 (2)
N1—Ni—O1	92.36 (9)	N4—C5—C51	122.5 (2)
N1i—Ni—O1	87.63 (9)	N1—C5—C51	122.9 (2)
O53—Ni—O1	91.63 (9)	C5—C51—C52	116.7 (2)
O53i—Ni—O1	88.37 (9)	C5—C51—H51A	108.1
N1—Ni—O1i	87.63 (9)	C52—C51—H51A	108.1
N1i—Ni—O1i	92.37 (9)	C5—C51—H51B	108.1
O53—Ni—O1i	88.37 (9)	C52—C51—H51B	108.1
O53i—Ni—O1i	91.63 (9)	H51A—C51—H51B	107.3
O1—Ni—O1i	180.0	O54—C52—O53	122.8 (3)
C2—N1—C5	103.7 (2)	O54—C52—C51	118.2 (2)
C2—N1—Ni	130.69 (17)	O53—C52—C51	119.0 (2)
C5—N1—Ni	123.09 (17)	C52—O53—Ni	130.20 (18)
N3—C2—N21	125.8 (2)	Ni—O1—H1A	120 (2)
N3—C2—N1	108.9 (2)	Ni—O1—H1B	132 (3)
N21—C2—N1	125.2 (2)	H1A—O1—H1B	104 (3)
C2—N21—H21A	123 (2)	H2A—O2—H2B	112 (3)
C2—N21—H21B	115 (2)
C5—N1—C2—N3	−0.3 (3)	Ni—N1—C5—N4	163.8 (2)
Ni—N1—C2—N3	−162.2 (2)	C2—N1—C5—C51	177.4 (3)
C5—N1—C2—N21	−177.1 (3)	Ni—N1—C5—C51	−18.9 (4)
Ni—N1—C2—N21	21.0 (5)	N4—C5—C51—C52	−133.3 (3)
N21—C2—N3—N4	177.1 (3)	N1—C5—C51—C52	49.6 (4)
N1—C2—N3—N4	0.4 (4)	C5—C51—C52—O54	151.7 (3)
C2—N3—N4—C5	−0.2 (3)	C5—C51—C52—O53	−31.5 (4)
N3—N4—C5—N1	0.0 (3)	O54—C52—O53—Ni	162.5 (2)
N3—N4—C5—C51	−177.2 (3)	C51—C52—O53—Ni	−14.2 (4)
C2—N1—C5—N4	0.2 (4)

D—H···A	D—H	H···A	D···A	D—H···A
N21—H21A···O2ii	0.83 (2)	2.04 (2)	2.876 (3)	176 (3)
N21—H21B···O53i	0.83 (2)	2.19 (2)	2.941 (3)	151 (3)
N3—H3···O54iii	0.83 (3)	2.10 (3)	2.885 (3)	156 (3)
O1—H1A···O2iv	0.82 (2)	1.92 (2)	2.739 (3)	176 (3)
O1—H1B···O54v	0.82 (2)	1.96 (2)	2.780 (3)	173 (4)
O2—H2A···N4vi	0.83 (2)	2.09 (2)	2.903 (3)	164 (3)
O2—H2B···O53vii	0.83 (2)	1.98 (2)	2.811 (3)	176 (3)