(2-Amino-7-methyl-4-oxido­pteridine-6-carboxyl­ato-κ3 O 4,N 5,O 6)aqua(1,10-phen­an­thro­line-κ2 N,N′)cobalt(II) trihydrate

Siddhartha S Baisya; Samir Sen; Parag S Roy

doi:10.1107/S1600536812051185

. 2012 Dec 22;69(Pt 1):m70–m71. doi: 10.1107/S1600536812051185

(2-Amino-7-methyl-4-oxidopteridine-6-carboxylato-κ³ O ⁴,N ⁵,O ⁶)aqua(1,10-phenanthroline-κ² N,N′)cobalt(II) trihydrate

Siddhartha S Baisya ^a, Samir Sen ^a, Parag S Roy ^a,^*

PMCID: PMC3588366 PMID: 23476360

Abstract

In the title compound, [Co(C₈H₅N₅O₃)(C₁₂H₈N₂)(H₂O)]·3H₂O, a tridentate 2-amino-7-methyl-4-oxidopteridine-6-carboxylate ligand, a bidentate ancillary 1,10-phenanthroline (phen) ligand and a water molecule complete a distorted octahedral geometry around the Co^II atom. The pterin ligand forms two chelate rings. The phen and pterin ring systems are nearly perpendicular [dihedral angle = 85.15 (8)°]. N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonds link the complex molecules and lattice water molecules into a layer parallel to (001). π–π stacking contacts (involving phen–phen and pteridine–pteridine) are also observed [centroid–centroid distances = 3.670 (2), 3.547 (2), 3.698 (2) and 3.349 (2) Å].

Related literature

For background to the chemistry of pterins in metalloenzymes, see: Basu & Burgmayer (2011 ▶); Burgmayer (1998 ▶); Fitzpatrick (2003 ▶); Fukuzumi & Kojima (2008 ▶). For structures of related cobalt complexes, see: Acuña-Cueva et al. (2003 ▶); Beddoes et al. (1997 ▶); Burgmayer & Stiefel (1988 ▶); Funahashi et al. (1997 ▶). 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 ▶).

Experimental

Crystal data

[Co(C₈H₅N₅O₃)(C₁₂H₈N₂)(H₂O)]·3H₂O
M _r = 530.36
Triclinic,
a = 8.454 (2) Å
b = 9.934 (3) Å
c = 13.778 (4) Å
α = 97.534 (4)°
β = 95.281 (4)°
γ = 110.603 (4)°
V = 1061.8 (5) Å³
Z = 2
Mo Kα radiation
μ = 0.87 mm⁻¹
T = 110 K
0.23 × 0.11 × 0.04 mm

Data collection

Bruker Kappa APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▶) T _min = 0.82, T _max = 0.97
8945 measured reflections
4726 independent reflections
4360 reflections with I > 2σ(I)
R _int = 0.030

Refinement

R[F ² > 2σ(F ²)] = 0.057
wR(F ²) = 0.129
S = 1.03
4726 reflections
316 parameters
H-atom parameters constrained
Δρ_max = 0.99 e Å⁻³
Δρ_min = −0.88 e Å⁻³

Data collection: APEX2 (Bruker, 2007 ▶); cell refinement: 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.

Supplementary Material

Click here for additional data file.^{(27.8KB, cif)}

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536812051185/hy2609sup1.cif

e-69-00m70-sup1.cif^{(27.8KB, cif)}

Click here for additional data file.^{(297.3KB, hkl)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812051185/hy2609Isup2.hkl

e-69-00m70-Isup2.hkl^{(297.3KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N7—H141⋯O2ⁱ	0.85	2.12	2.942 (4)	163
N7—H142⋯O6ⁱⁱ	0.84	2.15	2.970 (4)	165
O4—H181⋯O6	0.81	1.93	2.717 (3)	164
O4—H182⋯N5ⁱⁱ	0.80	2.25	3.051 (4)	176
O5—H341⋯O1	0.82	2.34	3.079 (4)	151
O5—H341⋯O2	0.82	2.23	2.896 (4)	139
O5—H342⋯N4ⁱⁱⁱ	0.82	2.04	2.844 (4)	166
O6—H351⋯O5	0.83	1.92	2.740 (4)	174
O6—H352⋯N5^iv	0.82	2.05	2.871 (4)	176
O7—H331⋯O5ⁱ	0.80	2.25	2.941 (4)	145
O7—H332⋯O3	0.81	2.23	2.962 (5)	151

Open in a new tab

Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) .

Acknowledgments

The authors express their gratitude 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 the University of North Bengal for infrastructure.

supplementary crystallographic information

Comment

The primary motivation for pursuing coordination chemistry of pterins is the ubiquitous presence of this heterocyclic system in nature including a substantial number of metalloenzymes (Basu & Burgmayer, 2011; Burgmayer, 1998; Fitzpatrick, 2003; Fukuzumi & Kojima, 2008). Literature survey reveals the existence of only a few X-ray structurally characterized cobalt-pterin/pteridine/lumazine complexes as well as one containing an organocobalt moiety (Acuña-Cueva et al., 2003; Beddoes et al., 1997; Burgmayer & Stiefel, 1988; Funahashi et al., 1997). The concerned ligands usually act as bidentate O,N-donors and none of the above complexes possesses a typical π-acceptor ancillary ligand like 1,10-phenanthroline (phen). In this crystallographic study on the title cobalt(II) complex, possessing both a tridentate pterin ligand and a π-acidic ligand like phen, different aspects are considered, e.g. crystal, molecular and electronic structures.

In the title compound (Fig. 1), the stereochemistry around the Co^II atom is essentially distorted octahedral with two N atoms of phen, a pyrazine ring N atom (N3) of the pterin ligand and an aqua O atom forming the equatorial plane; two pterin O atoms (O1 and O3) define the longer axial positions, with the phenolate O3 forming the longest axial bond [2.270 (2) Å]. Extent of distortion of this coordination octahedron is much more pronounced as compared to that of the Co(II)-pteridine complexes reported earlier (Acuña-Cueva et al., 2003; Burgmayer & Stiefel, 1988; Funahashi et al., 1997). A major cause of this departure from regular geometry is that the pterin ligand forms two five-membered chelate rings having small bite angles [75.10 (10) and 76.26 (9)°], instead of only one per pteridine ligand for the earlier cases. Location of the short Co1—N3 bond [2.016 (3) Å] in the equatorial plane is consistent with the literature, which suggests a strong cobalt-pterin interaction (Odani et al., 1992). The pterin ligand is coordinated here as a binegative tridentate ONO donor, as evident from the charge balance of this complex. The phen and pterin rings are nearly perpendicular to each other for minimizing the steric repulsion. The Co1—N1 [2.079 (3) Å] and Co1—N2 [2.123 (3) Å] bond lengths are at par with that of the Co1—N3 bond [2.016 (3) Å] and indicate receipt of π-back donation to both phen and pterin rings from the Co(II) centre (d⁷) through dπ–pπ interactions. This process is further strengthened by the presence of π-donating phenolate and carboxylate O atoms around the metal centre (Kohzuma et al., 1988).

For rationalizing the near double bond nature of the O3—C18 [1.265 (4) Å] bond, a hypothesis of Joule (Beddoes et al., 1993; Russell et al., 1992) may be invoked, which suggests withdrawl of electron density from the pyrazine ring N6 by the pyrimidine ring C18-carbonyl group through mesomeric interaction. Formation of the O3—Co1 bond accentuates this electron withdrawal towards O3. The electron-rich N7—C17 [1.337 (4) Å] bond may also participate in this electron transfer. The pyrimidine ring is fairly planer and deviations of the C16/N5/C17 and C17/N4/C18 segments with respect to the N7—C17 multiple bonds are 2.6 and 0.7°, respectively.

In the crystal, intermolecular N—H···O, O—H···N and O—H···O hydrogen bonds (Table 1) link the complex molecules and lattice water molecules into a layer parallel to (001) (Fig. 2). The lattice water molecules are decisive for the crystal packing. Fig. 3 reveals π–π stacking interactions involving two parallel, inversion-related pterin rings within the same unit cell and showing face-to-face distance of 3.283 (4) and 3.366 (4) Å. Again the phen rings display two types of π–π stacking on either side of the unit cell. In one case, the adjacent phen rings are essentially parallel to each other with an average interplanar distance of 3.496 (4) Å; on the other side of the unit cell, the face-to-face seperations between parallel phen rings are 3.578 (4) and 3.629 (5) Å.

Experimental

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 dropwise addition of an aqueous alkaline solution (NaOH: 11 mg, 0.275 mmol) of the pterin ligand (31 mg, 0.125 mmol) to a warm (311 K) aqueous reaction medium containing CoSO₄.7H₂O (35 mg, 0.125 mmol) and 1,10-phenanthroline monohydrate (25 mg, 0.125 mmol) in a total volume of 60 ml. The pH value was adjusted to 10.8 using aqueous NaOH solution and dioxygen was bubbled in for 48 h; final pH was 10.3. Initially a small amount of yellow-white precipitate came out and the reaction mixture ultimately assumed a reddish-pink tinge. It was transferred to a 100 ml beaker, requisite quantity of water was added to make up for the evaporation loss and allowed to stand at room temperature. Pink crystals suitable for single-crystal X-ray diffraction appeared after 15 days (yield: 30%).