Diaqua­bis­(4-hy­droxy-5-nitro­pyridine-2-carboxyl­ato-κ²N¹,O²)copper(II)

In the title compound, [Cu(C₆H₃N₂O₅)₂(H₂O)₂], the Cu^II ion, lying on an inversion center, is coordinated by two pyridine N atoms and two carboxyl­ate O atoms from symmetry-related two 4-hy­droxy-5-nitro­pyridine-2-carboxyl­ate ligands, and two water mol­ecules, forming a distorted octa­hedral geometry. In the crystal, O—H...O hydrogen bonds link the complex mol­ecules. One of the H atoms of the water mol­ecule is disordered over two sites of equal occupancy.

Key indicators

• Single-crystal X-ray study
• T = 113 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.029
• wR factor = 0.077
• Data-to-parameter ratio = 12.3

checkCIF/PLATON results

No syntax errors found





Alert level A
PLAT900_ALERT_1_A No Matching Reflection File Found ..............          !
PLAT900_ALERT_1_A No Matching Reflection File Found ..............          !
PLAT902_ALERT_1_A No (Interpretable) Reflections found in FCF ....          !

Alert level C
PLAT222_ALERT_3_C Large Non-Solvent    H    Uiso(max)/Uiso(min) ..        6.9 Ratio
PLAT230_ALERT_2_C Hirshfeld Test Diff for    O2     --  C1      ..        6.1 su

Alert level G
PLAT002_ALERT_2_G Number of Distance or Angle Restraints on AtSite          4
PLAT005_ALERT_5_G No _iucr_refine_instructions_details in CIF ....          ?
PLAT128_ALERT_4_G Alternate Setting of Space-group P21/c   .......      P21/n
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          6

   3 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   2 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   4 ALERT level G = General information/check it is not something unexpected

   3 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

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S1. Comment

Carboxylate ligands play an important role in constructing novel metal-organic frameworks (MOFs) in coordination chemistry. Especially, a large number of MOFs based on pyridyl dicarboxylic acid ligands containing N- and O-donors with multi-connecting ability have been constructed. 4-Hydroxyl-pyridine-2,6-dicarboxylic acid has been widely used in the construction of high-dimensional structures with large pores. It usually adopts diverse coordination binding modes such as chelating to one metal center, bridging bidentate in syn–syn or syn–anti configuration to two or three metal centers. A systematic study of 3d–4f, 4d–4f and 3d–4d–4f complexes based on 4-hydroxyl-pyridine-2,6-dicarboxylic acid ligand has been undertaken (Zhao et al., 2006, 2009, 2011). However, to the best of our knowledge, no reports on the synthesis of the title compound have been seen in literature. In this paper, we report the synthesis and crystal structure of the title compound using a hydrothermal method with 4-hydroxyl-pyridine-2,6-dicarboxylic acid as ligand.

The title compound features a 3-nitro-4-hydroxyl-pyridine-6-carboxylate ligand, which was in situ generated by decarboxylation and nitration of 4-hydroxyl-pyridine-2,6-dicarboxylic acid under the hydrothermal conditions. A similar reaction has been reported (Xu et al., 2011). Structure analysis shows that the Cu^II ion is centrosymmetrically coordinated by two N atoms [Cu—N = 1.9685 (16) Å] and two carboxylate O atoms [Cu—O = 1.9667 (15) Å] from two 3-nitro-4-hydroxyl-pyridine-6-carboxylate ligands and two water molecules [Cu—O = 2.479 (2) Å], forming a distorted octahedral geometry, as shown in Fig. 1. O—H···O hydrogen bonds link the complex molecules (Table 1).

Related literature

For complexes based on the 4-hydroxylpyridine-2,6-dicarboxylic acid ligand, see: Zhao et al. (2006, 2009, 2011). For a similar reaction to the formation of the ligand, see: Xu et al. (2011).

S2. Experimental

A mixture of 4-hydroxyl-pyridine-2,6-dicarboxylic acid (366 mg, 2.0 mmol), copper nitrate trihydrate (242 mg, 1.0 mmol), lanthanide nitrate hexahydrate (Ln = Eu, Sm, Pr, Tb) (1.0 mmol) and deionized water (10 ml) was placed in a 25 ml Teflon-lined steel autoclave, which was kept at 433 K for 3 days. The resuling blue prismatic crystals suitable for X-ray diffraction experiment were collected after washing with deionized water and diethyl ether (yield: 43% based on the mass of copper nitrate trihydrate).

S3. Refinement

H atoms bound to C atoms were positioned geometrically and refined as riding atoms, with C—H = 0.95 Å and with U_iso(H) = 1.2U_eq(C). H atoms bound to O atoms were located from a difference Fourier map and refined isotropically. One of H atoms of the water molecule is disordered over two sites with equal occupancy factors.

Computing details

Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear (Rigaku, 2005); data reduction: CrystalClear (Rigaku, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

Fig. 1. Molecular structure of the title compound. Displacement ellipsoids are drawn at the 30% probability level. One of the disordered H atom sites on water molecule is not shown. [Symmetry code: (A) -x, 1-y, 1-z.]

Diaquabis(4-hydroxy-5-nitropyridine-2-carboxylato- κ²N¹,O²)copper(II)

Crystal data

[Cu(C6H3N2O5)2(H2O)2]	F(000) = 470
Mr = 465.79	Dx = 2.023 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 3085 reflections
a = 6.5327 (7) Å	θ = 2.1–27.9°
b = 9.7963 (10) Å	µ = 1.52 mm^−1
c = 12.2562 (12) Å	T = 113 K
β = 102.86 (2)°	Prism, colorless
V = 764.68 (15) Å^3	0.20 × 0.18 × 0.10 mm
Z = 2

Data collection

Rigaku Saturn 724 CCD diffractometer	1829 independent reflections
Radiation source: rotating anode	1466 reflections with I > 2σ(I)
Multilayer monochromator	Rint = 0.053
Detector resolution: 14.22 pixels mm^-1	θmax = 27.9°, θmin = 2.7°
ω scans	h = −8→7
Absorption correction: multi-scan (CrystalClear; Rigaku, 2005)	k = −12→12
Tmin = 0.752, Tmax = 0.863	l = −15→16
9563 measured reflections

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)] = 0.029	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.077	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.036P)^2] where P = (Fo^2 + 2Fc^2)/3
1829 reflections	(Δ/σ)max < 0.001
149 parameters	Δρmax = 0.39 e Å^−3
6 restraints	Δρmin = −0.49 e Å^−3

Special details

Experimental. Rigaku CrystalClear-SM Expert 2.0 r2

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	Occ. (<1)
Cu1	0.0000	0.5000	0.5000	0.01573 (13)
O1	0.0540 (2)	0.53885 (14)	0.66132 (12)	0.0145 (3)
O2	0.1475 (2)	0.70789 (14)	0.78407 (11)	0.0150 (3)
O3	0.3093 (2)	1.08681 (14)	0.52856 (13)	0.0144 (3)
H3	0.331 (5)	1.107 (3)	0.592 (2)	0.058 (11)*
O4	0.2830 (3)	1.07679 (17)	0.31323 (14)	0.0291 (4)
O5	0.0819 (3)	0.9216 (2)	0.22215 (13)	0.0408 (5)
O6	0.3578 (3)	0.40247 (18)	0.52615 (15)	0.0253 (4)
H6A	0.371 (5)	0.381 (3)	0.5936 (10)	0.060 (11)*
H6B	0.454 (7)	0.455 (5)	0.516 (3)	0.06 (2)*	0.50
H6C	0.348 (10)	0.332 (3)	0.484 (3)	0.09 (3)*	0.50
N1	0.1030 (3)	0.68775 (16)	0.49202 (13)	0.0113 (4)
C1	0.1142 (3)	0.6591 (2)	0.68823 (16)	0.0121 (4)
C2	0.1493 (3)	0.7498 (2)	0.59364 (16)	0.0108 (4)
C3	0.2222 (3)	0.8799 (2)	0.61022 (16)	0.0109 (4)
H3A	0.2576	0.9169	0.6837	0.013*
C4	0.2450 (3)	0.9596 (2)	0.51800 (17)	0.0106 (4)
C5	0.1881 (3)	0.8957 (2)	0.41301 (16)	0.0114 (4)
C6	0.1219 (3)	0.7610 (2)	0.40323 (16)	0.0119 (4)
H6	0.0891	0.7197	0.3313	0.014*
N2	0.1874 (3)	0.97025 (17)	0.30795 (15)	0.0150 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0276 (2)	0.00876 (18)	0.0110 (2)	−0.00692 (15)	0.00460 (15)	−0.00212 (14)
O1	0.0212 (8)	0.0095 (7)	0.0123 (8)	−0.0040 (6)	0.0028 (6)	0.0002 (5)
O2	0.0251 (8)	0.0103 (7)	0.0088 (7)	−0.0004 (6)	0.0021 (6)	−0.0006 (6)
O3	0.0201 (8)	0.0090 (7)	0.0146 (8)	−0.0040 (6)	0.0052 (7)	−0.0001 (6)
O4	0.0442 (11)	0.0199 (9)	0.0253 (9)	−0.0091 (8)	0.0124 (8)	0.0029 (7)
O5	0.0523 (13)	0.0497 (12)	0.0151 (9)	−0.0240 (10)	−0.0036 (9)	0.0070 (8)
O6	0.0271 (10)	0.0238 (9)	0.0234 (10)	−0.0057 (8)	0.0019 (8)	0.0029 (8)
N1	0.0125 (9)	0.0104 (8)	0.0100 (8)	−0.0010 (7)	0.0004 (7)	−0.0013 (6)
C1	0.0107 (10)	0.0107 (10)	0.0149 (11)	0.0005 (8)	0.0027 (8)	0.0031 (8)
C2	0.0123 (10)	0.0102 (9)	0.0091 (10)	0.0006 (8)	0.0006 (8)	0.0012 (7)
C3	0.0109 (10)	0.0116 (10)	0.0093 (10)	0.0000 (8)	0.0007 (8)	−0.0011 (7)
C4	0.0077 (9)	0.0100 (9)	0.0145 (10)	0.0007 (7)	0.0030 (8)	−0.0003 (7)
C5	0.0104 (10)	0.0139 (10)	0.0105 (10)	−0.0004 (8)	0.0034 (8)	0.0030 (8)
C6	0.0117 (11)	0.0149 (10)	0.0099 (10)	−0.0002 (8)	0.0036 (8)	−0.0028 (8)
N2	0.0150 (9)	0.0165 (9)	0.0136 (9)	−0.0015 (7)	0.0033 (8)	0.0011 (7)

Geometric parameters (Å, º)

Cu1—N1	1.9685 (16)	O6—H6C	0.85 (1)
Cu1—O1	1.9667 (15)	N1—C6	1.332 (2)
Cu1—O6	2.479 (2)	N1—C2	1.358 (2)
O1—C1	1.263 (2)	C1—C2	1.518 (3)
O2—C1	1.242 (2)	C2—C3	1.360 (3)
O3—C4	1.312 (2)	C3—C4	1.409 (3)
O3—H3	0.79 (3)	C3—H3A	0.9500
O4—N2	1.211 (2)	C4—C5	1.405 (3)
O5—N2	1.219 (2)	C5—C6	1.385 (3)
O6—H6A	0.84 (1)	C5—N2	1.480 (2)
O6—H6B	0.85 (1)	C6—H6	0.9500
O1—Cu1—O1^i	180.0	O2—C1—C2	118.24 (17)
O1—Cu1—N1	83.24 (6)	O1—C1—C2	115.97 (17)
O1^i—Cu1—N1	96.76 (6)	N1—C2—C3	123.75 (18)
O1—Cu1—N1^i	96.76 (6)	N1—C2—C1	113.45 (17)
O1^i—Cu1—N1^i	83.24 (6)	C3—C2—C1	122.80 (18)
N1—Cu1—N1^i	180.0	C2—C3—C4	119.73 (18)
O1—Cu1—O6	89.52 (6)	C2—C3—H3A	120.1
O1—Cu1—O6^i	90.48 (6)	C4—C3—H3A	120.1
N1—Cu1—O6^i	87.50 (7)	O3—C4—C5	121.85 (18)
O6—Cu1—N1	92.50 (7)	O3—C4—C3	122.42 (18)
O6—Cu1—O6^i	180.00	C5—C4—C3	115.70 (18)
C1—O1—Cu1	114.76 (13)	C6—C5—C4	121.20 (18)
C4—O3—H3	109 (2)	C6—C5—N2	117.04 (17)
H6A—O6—H6B	112.7 (17)	C4—C5—N2	121.71 (17)
H6A—O6—H6C	111.5 (17)	N1—C6—C5	121.74 (18)
H6B—O6—H6C	111.2 (17)	N1—C6—H6	119.1
C6—N1—C2	117.79 (17)	C5—C6—H6	119.1
C6—N1—Cu1	129.69 (14)	O4—N2—O5	124.71 (18)
C2—N1—Cu1	112.42 (13)	O4—N2—C5	118.54 (17)
O2—C1—O1	125.79 (19)	O5—N2—C5	116.68 (17)
N1—Cu1—O1—C1	3.72 (14)	N1—C2—C3—C4	2.6 (3)
N1^i—Cu1—O1—C1	−176.28 (14)	C1—C2—C3—C4	−178.09 (18)
O1—Cu1—N1—C6	−178.60 (18)	C2—C3—C4—O3	178.19 (18)
O1^i—Cu1—N1—C6	1.40 (18)	C2—C3—C4—C5	0.1 (3)
O1—Cu1—N1—C2	−2.41 (13)	O3—C4—C5—C6	179.52 (18)
O1^i—Cu1—N1—C2	177.59 (13)	C3—C4—C5—C6	−2.4 (3)
Cu1—O1—C1—O2	176.32 (16)	O3—C4—C5—N2	−3.1 (3)
Cu1—O1—C1—C2	−4.1 (2)	C3—C4—C5—N2	175.00 (17)
C6—N1—C2—C3	−3.0 (3)	C2—N1—C6—C5	0.5 (3)
Cu1—N1—C2—C3	−179.66 (16)	Cu1—N1—C6—C5	176.56 (14)
C6—N1—C2—C1	177.69 (16)	C4—C5—C6—N1	2.1 (3)
Cu1—N1—C2—C1	1.0 (2)	N2—C5—C6—N1	−175.38 (17)
O2—C1—C2—N1	−178.33 (17)	C6—C5—N2—O4	−165.03 (19)
O1—C1—C2—N1	2.1 (3)	C4—C5—N2—O4	17.5 (3)
O2—C1—C2—C3	2.3 (3)	C6—C5—N2—O5	18.0 (3)
O1—C1—C2—C3	−177.27 (18)	C4—C5—N2—O5	−159.5 (2)

Symmetry code: (i) −x, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O2^ii	0.79 (3)	1.79 (3)	2.544 (2)	160 (3)
O6—H6A···O2^iii	0.84 (1)	2.28 (2)	3.014 (2)	146 (3)
O6—H6B···O6^iv	0.85 (1)	2.00 (1)	2.836 (3)	170 (5)
O6—H6C···O3^v	0.85 (1)	2.49 (3)	3.109 (2)	130 (3)

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