metal-organic compounds
(2-Amino-7-methyl-4-oxidopteridine-6-carboxylato-κ3O4,N5,O6)aqua(ethane-1,2-diamine-κ2N,N′)nickel(II) dihydrate
aDepartment of Chemistry, University of North Bengal, Siliguri 734 013, India
*Correspondence e-mail: psrnbu@gmail.com
The NiII atom in the title complex, [Ni(C8H5N5O3)(C2H8N2)(H2O)]·2H2O, is six-coordinated in a distorted octahedral geometry by a tridentate 2-amino-7-methyl-4-oxidopteridine-6-carboxylate (pterin) ligand, a bidentate ancillary ethane-1,2-diamine (en) ligand and a water molecule. The pterin ligand forms two chelate rings. The en and pterin ligands are arranged nearly orthogonally [dihedral angle between the mean plane of the en molecule and the pterin ring = 77.1 (1)°]. N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonds link the complex molecules and lattice water molecules into a three-dimensional network. π–π interactions are observed between the pyrazine and pyrimidine rings [centroid–centroid distance = 3.437 (2) Å].
Related literature
For the importance of pterin in metalloenzymes, see: Basu & Burgmayer (2011); Burgmayer (1998); Fitzpatrick (2003); Fukuzumi & Kojima (2008); Kaim et al. (1999). For the structure of a related nickel complex, see: Crispini et al. (2005). For structures of related copper complexes, see: Odani et al. (1992). For the electron-shuffling ability of the pterin unit as well as its donor groups and the effect on the geometric parameters of related complexes, see: Beddoes et al. (1993); Kohzuma et al. (1988); Russell et al. (1992). For the synthesis of the pterin ligand, see: Wittle et al. (1947). For of H atoms, see: Cooper et al. (2010).
Experimental
Crystal data
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Refinement
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Data collection: APEX2 (Bruker, 2007); cell SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS.
Supporting information
10.1107/S160053681300069X/hy2612sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S160053681300069X/hy2612Isup2.hkl
2-Amino-4-hydroxy-7-methylpteridine-6-carboxylic acid sesquihydrate (C8H7N5O3.1.5H2O) was obtained by published procedure (Wittle et al., 1947). The title complex was prepared by the slow addition of an aqueous alkaline solution (NaOH: 44 mg, 1.1 mmol) of the pterin ligand (124 mg, 0.5 mmol) to a well stirred warm (323 K; paraffin oil bath) aqueous reaction mixture containing NiSO4.7H2O (140 mg, 0.5 mmol) and 1,2-ethanediamine (36 mg, 0.6 mmol) under subdued light; final volume was 35 ml. The pH value was adjusted to 9.2 and the stirring was continued for 3 h. Upon standing, the reaction medium deposited yellow-brown crystals after 2 days, which were suitable for single-crystal X-ray diffraction (yield: 30%). Analytically pure compound could be obtained by filtration, repeated washing with small quantities of water and drying in vacuo over silica gel. Analysis, calculated for C10H19N7NiO6: C 30.70, H 4.89, N 25.06%; found: C 30.51, H 5.11, N 24.55%.
H atoms were all located in a difference map, but those attached to C atoms were repositioned geometrically. The H atoms were initially refined with soft restraints on bond lengths and angles to regularize their geometry (C—H = 0.93–0.98, N—H = 0.86–0.89, O—H = 0.82 Å) and with Uiso(H) = 1.2–1.5Ueq(parent atom), after which the positions were refined with riding constraints (Cooper et al., 2010).
Data collection: APEX2 (Bruker, 2007); cell
SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS (Betteridge et al., 2003).Fig. 1. The molecular structure of the title compound. Displacement ellipsoids are drawn at the 40% probability level. Lattice water molecules are omitted for clarity. | |
Fig. 2. The crystal packing diagram of the title compound, viewed along the c axis. Dotted lines indicate hydrogen bonds. |
[Ni(C8H5N5O3)(C2H8N2)(H2O)]·2H2O | F(000) = 816 |
Mr = 392.01 | Dx = 1.675 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 8393 reflections |
a = 10.406 (4) Å | θ = 2.0–28.2° |
b = 14.323 (5) Å | µ = 1.29 mm−1 |
c = 10.450 (4) Å | T = 293 K |
β = 93.294 (6)° | Plate, brown |
V = 1554.9 (10) Å3 | 0.49 × 0.38 × 0.28 mm |
Z = 4 |
Bruker Kappa APEXII CCD diffractometer | 2760 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.035 |
ϕ & ω scans | θmax = 28.2°, θmin = 2.0° |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | h = −13→13 |
Tmin = 0.56, Tmax = 0.70 | k = −18→15 |
8393 measured reflections | l = −11→13 |
3488 independent reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Hydrogen site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.050 | H-atom parameters constrained |
wR(F2) = 0.135 | Method = Modified Sheldrick w = 1/[σ2(F2) + (0.09P)2 + 1.95P], where P = (max(Fo2,0) + 2Fc2)/3 |
S = 0.92 | (Δ/σ)max = 0.001 |
3488 reflections | Δρmax = 1.12 e Å−3 |
217 parameters | Δρmin = −0.84 e Å−3 |
0 restraints |
[Ni(C8H5N5O3)(C2H8N2)(H2O)]·2H2O | V = 1554.9 (10) Å3 |
Mr = 392.01 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 10.406 (4) Å | µ = 1.29 mm−1 |
b = 14.323 (5) Å | T = 293 K |
c = 10.450 (4) Å | 0.49 × 0.38 × 0.28 mm |
β = 93.294 (6)° |
Bruker Kappa APEXII CCD diffractometer | 3488 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | 2760 reflections with I > 2σ(I) |
Tmin = 0.56, Tmax = 0.70 | Rint = 0.035 |
8393 measured reflections |
R[F2 > 2σ(F2)] = 0.050 | 0 restraints |
wR(F2) = 0.135 | H-atom parameters constrained |
S = 0.92 | Δρmax = 1.12 e Å−3 |
3488 reflections | Δρmin = −0.84 e Å−3 |
217 parameters |
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems open-flow nitrogen cryostat (Cosier, J. & Glazer, A.M., 1986. J. Appl. Cryst. 105–107) with a nominal stability of 0.1 K. |
x | y | z | Uiso*/Ueq | ||
Ni1 | 0.33168 (3) | 0.37414 (3) | 0.40998 (3) | 0.0270 | |
O1 | 0.2677 (2) | 0.35342 (17) | 0.2158 (2) | 0.0355 | |
C9 | 0.1450 (3) | 0.3461 (2) | 0.1944 (3) | 0.0297 | |
O2 | 0.0914 (2) | 0.3290 (2) | 0.0880 (2) | 0.0430 | |
C3 | 0.0659 (3) | 0.3591 (2) | 0.3117 (3) | 0.0255 | |
N3 | 0.1423 (2) | 0.37361 (17) | 0.4173 (2) | 0.0245 | |
C8 | 0.0909 (3) | 0.3850 (2) | 0.5295 (3) | 0.0236 | |
C5 | −0.0427 (3) | 0.3859 (2) | 0.5402 (3) | 0.0248 | |
N4 | −0.1228 (2) | 0.37363 (19) | 0.4340 (2) | 0.0282 | |
C4 | −0.0692 (3) | 0.3588 (2) | 0.3213 (3) | 0.0279 | |
C10 | −0.1616 (3) | 0.3442 (3) | 0.2074 (3) | 0.0400 | |
H111 | −0.1653 | 0.2810 | 0.1853 | 0.0637* | |
H113 | −0.1353 | 0.3768 | 0.1326 | 0.0631* | |
H112 | −0.2477 | 0.3644 | 0.2257 | 0.0629* | |
N5 | −0.0930 (2) | 0.39909 (19) | 0.6560 (2) | 0.0285 | |
C6 | −0.0042 (3) | 0.4045 (2) | 0.7565 (3) | 0.0290 | |
N6 | 0.1283 (2) | 0.4046 (2) | 0.7564 (2) | 0.0310 | |
C7 | 0.1792 (3) | 0.3970 (2) | 0.6422 (3) | 0.0268 | |
O3 | 0.2995 (2) | 0.39847 (18) | 0.6257 (2) | 0.0369 | |
N7 | −0.0522 (3) | 0.4136 (3) | 0.8732 (3) | 0.0489 | |
O6 | 0.3383 (2) | 0.51989 (16) | 0.3730 (2) | 0.0341 | |
H182 | 0.2833 | 0.5626 | 0.3735 | 0.0551* | |
H181 | 0.3889 | 0.5230 | 0.3156 | 0.0554* | |
N1 | 0.3513 (3) | 0.2334 (2) | 0.4537 (3) | 0.0343 | |
C1 | 0.4854 (4) | 0.2201 (3) | 0.5050 (4) | 0.0463 | |
C2 | 0.5735 (3) | 0.2713 (3) | 0.4201 (4) | 0.0475 | |
N2 | 0.5298 (3) | 0.36927 (19) | 0.4057 (3) | 0.0343 | |
H221 | 0.5559 | 0.3888 | 0.3326 | 0.0516* | |
H222 | 0.5630 | 0.3994 | 0.4691 | 0.0520* | |
H211 | 0.6626 | 0.2705 | 0.4560 | 0.0603* | |
H212 | 0.5706 | 0.2394 | 0.3383 | 0.0606* | |
H202 | 0.5096 | 0.1546 | 0.5123 | 0.0585* | |
H201 | 0.4910 | 0.2482 | 0.5908 | 0.0590* | |
H192 | 0.2966 | 0.2195 | 0.5135 | 0.0560* | |
H191 | 0.3371 | 0.2006 | 0.3817 | 0.0561* | |
O4 | 0.5313 (3) | 0.5259 (3) | 0.2007 (3) | 0.0699 | |
H231 | 0.5947 | 0.5499 | 0.2395 | 0.1050* | |
H232 | 0.5749 | 0.5189 | 0.1384 | 0.1048* | |
O5 | 0.2936 (3) | 0.4894 (2) | −0.0008 (3) | 0.0646 | |
H241 | 0.3113 | 0.5370 | 0.0413 | 0.1023* | |
H242 | 0.3059 | 0.4542 | 0.0622 | 0.1021* | |
H171 | 0.0041 | 0.4206 | 0.9433 | 0.0500* | |
H172 | −0.1306 | 0.4416 | 0.8977 | 0.0500* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Ni1 | 0.0198 (2) | 0.0344 (2) | 0.0270 (2) | −0.00059 (15) | 0.00148 (14) | −0.00027 (15) |
O1 | 0.0291 (12) | 0.0516 (15) | 0.0262 (11) | −0.0017 (10) | 0.0057 (9) | −0.0032 (10) |
C9 | 0.0317 (16) | 0.0329 (16) | 0.0248 (14) | 0.0026 (12) | 0.0035 (12) | 0.0003 (12) |
O2 | 0.0388 (13) | 0.0651 (17) | 0.0246 (11) | 0.0035 (12) | −0.0024 (9) | −0.0070 (11) |
C3 | 0.0270 (15) | 0.0261 (15) | 0.0230 (13) | 0.0008 (11) | −0.0010 (11) | −0.0025 (11) |
N3 | 0.0232 (12) | 0.0270 (12) | 0.0234 (12) | −0.0004 (9) | 0.0012 (9) | −0.0012 (9) |
C8 | 0.0213 (13) | 0.0270 (15) | 0.0225 (13) | 0.0001 (11) | 0.0002 (10) | 0.0002 (11) |
C5 | 0.0243 (14) | 0.0264 (15) | 0.0236 (13) | 0.0007 (11) | 0.0010 (11) | 0.0007 (11) |
N4 | 0.0210 (12) | 0.0360 (14) | 0.0273 (12) | −0.0003 (10) | −0.0011 (9) | 0.0011 (10) |
C4 | 0.0254 (14) | 0.0316 (16) | 0.0261 (14) | −0.0005 (11) | −0.0026 (11) | 0.0014 (12) |
C10 | 0.0275 (16) | 0.062 (2) | 0.0293 (16) | 0.0013 (15) | −0.0087 (13) | −0.0057 (15) |
N5 | 0.0222 (12) | 0.0391 (15) | 0.0242 (12) | 0.0033 (10) | 0.0026 (9) | −0.0006 (10) |
C6 | 0.0281 (15) | 0.0344 (16) | 0.0245 (14) | 0.0061 (12) | 0.0006 (11) | 0.0019 (12) |
N6 | 0.0258 (13) | 0.0416 (15) | 0.0252 (12) | 0.0018 (11) | −0.0016 (10) | −0.0017 (11) |
C7 | 0.0233 (14) | 0.0311 (16) | 0.0255 (14) | 0.0000 (11) | −0.0018 (11) | −0.0014 (12) |
O3 | 0.0213 (11) | 0.0557 (15) | 0.0332 (12) | −0.0005 (10) | −0.0013 (9) | −0.0076 (10) |
N7 | 0.0346 (16) | 0.090 (3) | 0.0223 (13) | 0.0139 (16) | 0.0031 (11) | −0.0031 (15) |
O6 | 0.0233 (10) | 0.0379 (13) | 0.0413 (12) | 0.0031 (9) | 0.0028 (9) | 0.0008 (10) |
N1 | 0.0297 (14) | 0.0376 (15) | 0.0361 (14) | −0.0018 (11) | 0.0058 (11) | 0.0034 (12) |
C1 | 0.042 (2) | 0.047 (2) | 0.049 (2) | 0.0061 (16) | −0.0049 (16) | 0.0111 (17) |
C2 | 0.0299 (18) | 0.047 (2) | 0.065 (2) | 0.0032 (15) | −0.0009 (17) | 0.0042 (19) |
N2 | 0.0263 (13) | 0.0369 (15) | 0.0396 (15) | −0.0014 (11) | 0.0009 (11) | 0.0022 (12) |
O4 | 0.0535 (18) | 0.117 (3) | 0.0386 (15) | −0.0370 (18) | −0.0034 (13) | 0.0002 (16) |
O5 | 0.065 (2) | 0.0592 (19) | 0.071 (2) | 0.0075 (15) | 0.0150 (16) | 0.0168 (16) |
Ni1—O1 | 2.120 (2) | C6—N7 | 1.350 (4) |
Ni1—N3 | 1.977 (3) | N6—C7 | 1.338 (4) |
Ni1—O3 | 2.324 (2) | C7—O3 | 1.273 (4) |
Ni1—O6 | 2.125 (2) | N7—H171 | 0.917 |
Ni1—N1 | 2.075 (3) | N7—H172 | 0.958 |
Ni1—N2 | 2.066 (3) | O6—H182 | 0.838 |
O1—C9 | 1.288 (4) | O6—H181 | 0.821 |
C9—O2 | 1.239 (4) | N1—C1 | 1.478 (5) |
C9—C3 | 1.527 (4) | N1—H192 | 0.892 |
C3—N3 | 1.339 (4) | N1—H191 | 0.892 |
C3—C4 | 1.416 (4) | C1—C2 | 1.503 (5) |
N3—C8 | 1.326 (4) | C1—H202 | 0.974 |
C8—C5 | 1.401 (4) | C1—H201 | 0.981 |
C8—C7 | 1.461 (4) | C2—N2 | 1.479 (5) |
C5—N4 | 1.361 (4) | C2—H211 | 0.980 |
C5—N5 | 1.359 (4) | C2—H212 | 0.969 |
N4—C4 | 1.349 (4) | N2—H221 | 0.872 |
C4—C10 | 1.501 (4) | N2—H222 | 0.847 |
C10—H111 | 0.934 | O4—H231 | 0.828 |
C10—H113 | 0.965 | O4—H232 | 0.821 |
C10—H112 | 0.970 | O5—H241 | 0.827 |
N5—C6 | 1.361 (4) | O5—H242 | 0.833 |
C6—N6 | 1.378 (4) | ||
O1—Ni1—N3 | 77.16 (10) | C5—N5—C6 | 114.6 (2) |
O1—Ni1—O3 | 153.46 (8) | N5—C6—N6 | 129.4 (3) |
N3—Ni1—O3 | 76.30 (9) | N5—C6—N7 | 115.6 (3) |
O1—Ni1—O6 | 88.57 (10) | N6—C6—N7 | 115.0 (3) |
N3—Ni1—O6 | 93.08 (9) | C6—N6—C7 | 116.6 (2) |
O3—Ni1—O6 | 92.13 (9) | C8—C7—N6 | 117.7 (3) |
O1—Ni1—N1 | 95.53 (11) | C8—C7—O3 | 118.1 (3) |
N3—Ni1—N1 | 94.21 (11) | N6—C7—O3 | 124.2 (3) |
O3—Ni1—N1 | 87.12 (10) | Ni1—O3—C7 | 109.05 (19) |
O6—Ni1—N1 | 172.28 (9) | C6—N7—H171 | 118.7 |
O1—Ni1—N2 | 103.50 (11) | C6—N7—H172 | 130.3 |
N3—Ni1—N2 | 177.63 (11) | H171—N7—H172 | 104.8 |
O3—Ni1—N2 | 103.04 (10) | Ni1—O6—H182 | 133.3 |
O6—Ni1—N2 | 89.22 (10) | Ni1—O6—H181 | 102.4 |
N1—Ni1—N2 | 83.47 (11) | H182—O6—H181 | 115.6 |
Ni1—O1—C9 | 115.57 (18) | Ni1—N1—C1 | 106.5 (2) |
O1—C9—O2 | 124.2 (3) | Ni1—N1—H192 | 108.2 |
O1—C9—C3 | 115.1 (3) | C1—N1—H192 | 110.2 |
O2—C9—C3 | 120.6 (3) | Ni1—N1—H191 | 108.4 |
C9—C3—N3 | 111.1 (3) | C1—N1—H191 | 110.2 |
C9—C3—C4 | 129.8 (3) | H192—N1—H191 | 113.2 |
N3—C3—C4 | 119.1 (3) | N1—C1—C2 | 108.6 (3) |
C3—N3—Ni1 | 120.9 (2) | N1—C1—H202 | 112.7 |
C3—N3—C8 | 119.9 (3) | C2—C1—H202 | 110.7 |
Ni1—N3—C8 | 119.15 (19) | N1—C1—H201 | 106.5 |
N3—C8—C5 | 121.6 (3) | C2—C1—H201 | 109.5 |
N3—C8—C7 | 117.4 (3) | H202—C1—H201 | 108.8 |
C5—C8—C7 | 121.0 (3) | C1—C2—N2 | 109.2 (3) |
C8—C5—N4 | 119.9 (3) | C1—C2—H211 | 111.3 |
C8—C5—N5 | 120.5 (3) | N2—C2—H211 | 109.2 |
N4—C5—N5 | 119.6 (3) | C1—C2—H212 | 107.6 |
C5—N4—C4 | 117.9 (3) | N2—C2—H212 | 111.4 |
C3—C4—N4 | 121.6 (3) | H211—C2—H212 | 108.2 |
C3—C4—C10 | 122.6 (3) | C2—N2—Ni1 | 109.3 (2) |
N4—C4—C10 | 115.9 (3) | C2—N2—H221 | 106.5 |
C4—C10—H111 | 110.4 | Ni1—N2—H221 | 111.7 |
C4—C10—H113 | 112.1 | C2—N2—H222 | 107.1 |
H111—C10—H113 | 106.2 | Ni1—N2—H222 | 109.2 |
C4—C10—H112 | 111.0 | H221—N2—H222 | 112.9 |
H111—C10—H112 | 108.2 | H231—O4—H232 | 88.8 |
H113—C10—H112 | 108.8 | H241—O5—H242 | 93.4 |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H192···O1i | 0.89 | 2.39 | 3.175 (4) | 147 |
N1—H192···O2i | 0.89 | 2.42 | 3.243 (4) | 154 |
N2—H221···O4 | 0.87 | 2.40 | 3.103 (5) | 137 |
N2—H222···O6ii | 0.85 | 2.22 | 3.064 (4) | 176 |
N7—H171···O2iii | 0.92 | 2.16 | 2.890 (4) | 136 |
N7—H172···O5iv | 0.96 | 2.29 | 3.225 (5) | 167 |
O4—H231···O3ii | 0.83 | 1.89 | 2.683 (4) | 160 |
O4—H232···O5v | 0.82 | 2.04 | 2.858 (5) | 171 |
O5—H242···O1 | 0.83 | 2.21 | 3.010 (4) | 160 |
O6—H181···O4 | 0.82 | 1.96 | 2.774 (4) | 171 |
O6—H182···N5iv | 0.84 | 2.06 | 2.805 (3) | 148 |
Symmetry codes: (i) x, −y+1/2, z+1/2; (ii) −x+1, −y+1, −z+1; (iii) x, y, z+1; (iv) −x, −y+1, −z+1; (v) −x+1, −y+1, −z. |
Experimental details
Crystal data | |
Chemical formula | [Ni(C8H5N5O3)(C2H8N2)(H2O)]·2H2O |
Mr | 392.01 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 293 |
a, b, c (Å) | 10.406 (4), 14.323 (5), 10.450 (4) |
β (°) | 93.294 (6) |
V (Å3) | 1554.9 (10) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 1.29 |
Crystal size (mm) | 0.49 × 0.38 × 0.28 |
Data collection | |
Diffractometer | Bruker Kappa APEXII CCD diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 1996) |
Tmin, Tmax | 0.56, 0.70 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 8393, 3488, 2760 |
Rint | 0.035 |
(sin θ/λ)max (Å−1) | 0.665 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.050, 0.135, 0.92 |
No. of reflections | 3488 |
No. of parameters | 217 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 1.12, −0.84 |
Computer programs: APEX2 (Bruker, 2007), SAINT (Bruker, 2007), SHELXS97 (Sheldrick, 2008), CRYSTALS (Betteridge et al., 2003), CAMERON (Watkin et al., 1996).
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H192···O1i | 0.89 | 2.39 | 3.175 (4) | 147 |
N1—H192···O2i | 0.89 | 2.42 | 3.243 (4) | 154 |
N2—H221···O4 | 0.87 | 2.40 | 3.103 (5) | 137 |
N2—H222···O6ii | 0.85 | 2.22 | 3.064 (4) | 176 |
N7—H171···O2iii | 0.92 | 2.16 | 2.890 (4) | 136 |
N7—H172···O5iv | 0.96 | 2.29 | 3.225 (5) | 167 |
O4—H231···O3ii | 0.83 | 1.89 | 2.683 (4) | 160 |
O4—H232···O5v | 0.82 | 2.04 | 2.858 (5) | 171 |
O5—H242···O1 | 0.83 | 2.21 | 3.010 (4) | 160 |
O6—H181···O4 | 0.82 | 1.96 | 2.774 (4) | 171 |
O6—H182···N5iv | 0.84 | 2.06 | 2.805 (3) | 148 |
Symmetry codes: (i) x, −y+1/2, z+1/2; (ii) −x+1, −y+1, −z+1; (iii) x, y, z+1; (iv) −x, −y+1, −z+1; (v) −x+1, −y+1, −z. |
Acknowledgements
The authors are grateful to the UGC, New Delhi, for financial assistance (SAP–DRS program). Thanks are due to the CSMCRI, Bhavnagar, Gujrat, India, for the X-ray structural data and elemental analysis data, and the University of North Bengal for infrastructure.
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The importance of pterins in several classes of metalloenzymes has catalysed symbiotic developments of their coordination chemistry (Basu & Burgmayer, 2011; Burgmayer, 1998; Fitzpatrick, 2003; Fukuzumi & Kojima, 2008; Kaim et al., 1999). A SciFinder search reveals the existence of only one structurally characterized nickel(II)–pterin complex (Crispini et al., 2005), thereby highlighting the urgency of development in this direction. The present endeavour is concerned with the title complex, possessing both a tridentate pterin ligand and a σ-donor ligand like en. The six-coordinated NiII atom shows departure from a regular octahedral geometry with respect to both bond lengths and angles (Fig. 1). The equatorial plane is formed by the two N atoms (N1, N2) of en, the pyrazine ring N atom (N3) of the pterin ligand and the aqua O atom (O6). The axial positions are occupied by the two pterin O atoms (O1 and O3), with the latter one forming the longest axial bond [2.327 (2) Å]. One important factor causing distortion from regular octahedral geometry is that this pterin ligand forms two five-membered chelate rings with small bite angles [76.31 (9) and 77.20 (10)°], instead of only one per pterin ligand for the earlier case (Crispini et al., 2005). A perusal of the charge balance of this complex indicates that this pterin ligand acts as a binegative tridentate ONO-donor. A near orthogonal disposition of the en ligand and pterin chelate ring is observed, which helps to minimize the steric repulsion. Of the three axes, least deviation from linearity is observed in the N3—Ni1—N2 direction [177.56 (11)°], where the highest electron density is concentrated [Ni1—N3 = 1.976 (2), Ni1—N2 = 2.065 (3) Å]. It represents the unique combination of a σ-donor atom N2 (en) and the N3 atom of the redox noninnocent pterin ligand from the opposite directions of the NiII centre (d8), with possible assistance from the π-donating phenolate and carboxylate O atoms (Kohzuma et al., 1988). Again, location of the pyrazine ring N atom (N3) in the equatorial plane is consistent with the earlier observations on related copper complexes (Odani et al., 1992).
Although the exocyclic bond length data of the pyrazine ring, e.g. C3—C9 [1.527 (4) Å] and C4—C10 [1.503 (4) Å] reflect only limited conjugation with the pyrazine ring π system, the corresponding bond length data of the pyrimidine ring, C7—O3 [1.267 (3) Å] and C6—N7 [1.349 (4) Å] merit attention. Small deviations, e.g. 2.02° and 1.37° of the C7/N6/C6 and C5/N5/C6 segments respectively, with respect to the C6—N7 multiple bond, indicate near planarity for the pyrimidine ring. So it can participate in the electron-shuffling process by the pterin unit from the pyrazine ring N4 to the C7-carbonyl group, as per literature suggestion (Beddoes et al., 1993; Russell et al., 1992). Formation of the Ni1—O3 bond assists this process.
In the crystal, the complex molecules and lattice water molecules are linked by intermolecular N—H···O, O—H···N and O—H···O hydrogen bonds (Table 1) into a three-dimensional network. The lattice water molecules are decisive for the crystal packing (Figure 2).