Diaquabis(8-quinolinolato-κ²N,O)zinc(II)

The crystal structure of the title compound, [Zn(C₉H₆NO)₂(H₂O)₂], has been redetermined with better R factors (R₁ = 0.0471) and higher accuracy than in previous publications. The molecule is centrosymmetric.

Key indicators

• Single-crystal X-ray study
• T = 294 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.042
• wR factor = 0.117
• Data-to-parameter ratio = 15.8

checkCIF/PLATON results

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Alert level C
PLAT232_ALERT_2_C Hirshfeld Test Diff (M-X)  Zn1    -   O2     =       7.61 su

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   1 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

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

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S1. Comment

8-Quinolinol has been widely used in the quantitative analysis of W and Mo (Marcel & Rene, 1950). The complexes of 8-quinolinol with Nb, Mo, W and Hf emit interesting fluorescence (Schneider & Roselli, 1970). The crystal structure of the title compound, (I), was orginally determined by Merrit et al. (1954) with R₁ = 0.226, and was then refined by Palenik (1964) to R₁ = 0.13. Here, we present the results of a redetermination of the structure of (I) with better R factors (R₁ = 0.0471) and higher accuracy.

In (I), the Zn^II atom is six-coordinated, by one N and one O atom from each of the two 8-quinolinolate ligands and one O atom from each of the two aqua ligands. This ZnO₄N₂ coordination forms an octahedral geometry (Fig. 1). The chelate ligands are connected to the central atom through a Zn—O [1.965 (18) Å] single bond and a Zn—N [2.011 (2) Å] coordinative bond, with a bite angle of 83.88 (8)°, and they occupy the equatorial plane. The two aqua ligands occupy the apical positions of the octahedron, with a Zn—O bond length very close to that of W—O [1.968 (4) Å], but shorter than that of W—N [2.336 (4) Å], in dioxobis(8-quinolinolato-N, O)tungsten (VI) (Raj et al., 1999).

The bond angles in the aromatic ring system of (I) are found to be between 118.2 (5) and 121.7 (5)°. In the 8-quinolinolate ligands, the absence of any unusually long bonds and the marginally longer carbonyl bond [1.355 (6) Å versus 1.28 Å], shorter than the normal single bond in ether and alcohols (>1.4 Å), suggest that the delocalization extends over the entire molecule and will therefore withdraw more negative charge from the cation (Barton et al., 1983).

The coordinated water molecules of (I) interact with the O atom of the 8-quinolinolato ligands via intermolecuar hydrogen bonds (Table 1). These hydrogen bonds interconnect the molecules into chains along the c direction (Fig.2).

S2. Experimental

An ethanolic solution of 8-quinolinol (2 mmol in 20 ml of ethanol) was mixed with Zn(OAc)₂ (1 mmol in 20 ml of H₂O). The resulting solution was left to stand for 5 h and a pale-yellowish solid was obtained. The product was recrystallized from ethanol-water (Ratio?). After several days, pale-yellowish crystals of (I) were harvested. Analysis, found: C 55.41, H 4.23, N 7.42%; calculated: C 55.52, H 4.14, N 7.47%.

S3. Refinement

The H atoms of the water ligands were located in a difference Fourier map and refined with a common isotropic displacement parameter. O—H and H···H distances were restrained to ensure a reasonable geometry for the water molecules. H atoms bound to C atoms were fixed geometrically and were treated as riding on the parent C atoms, with C—H = 0.93 Å and U_iso(H) = 1.2–1.5U_eq(C).

Computing details

Data collection: SMART (Bruker, 1996); cell refinement: SMART; data reduction: SHELXTL (Bruker, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of the molecule of (I) with the atom-numbering scheme and with 30% probability displacement ellipsoids.
	Fig. 2. Packing view of (I).

Diaquabis(8-quinolinolato-κ²N,O)zinc(II)

Crystal data

C18H16N2O4Zn	F(000) = 400
Mr = 389.70	Dx = 1.643 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -p 2ybc	Cell parameters from 2881 reflections
a = 12.955 (2) Å	θ = 1–27.5°
b = 5.5463 (10) Å	µ = 1.59 mm^−1
c = 11.423 (2) Å	T = 294 K
β = 106.288 (4)°	Plate, yellow
V = 787.8 (2) Å^3	0.30 × 0.24 × 0.12 mm
Z = 2

Data collection

Siemens SMART CCD area-detector diffractometer	1820 independent reflections
Radiation source: fine-focus sealed tube	1382 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.035
ϕ and ω scans	θmax = 27.6°, θmin = 3.3°
Absorption correction: multi-scan (SADABS; Sheldrick 1996)	h = −15→16
Tmin = 0.648, Tmax = 0.833	k = −5→7
5060 measured reflections	l = −14→14

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)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.117	H atoms treated by a mixture of independent and constrained refinement
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0725P)^2] where P = (Fo^2 + 2Fc^2)/3
1820 reflections	(Δ/σ)max < 0.001
115 parameters	Δρmax = 0.60 e Å^−3
0 restraints	Δρmin = −0.37 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
Zn1	0.5000	0.5000	0.5000	0.02949 (18)
O2	0.50256 (19)	0.2156 (4)	0.33660 (19)	0.0455 (6)
H2A	0.5172	0.0717	0.3613	0.055*
H2B	0.4901	0.2173	0.2595	0.055*
O1	0.56840 (15)	0.7428 (3)	0.42094 (17)	0.0301 (4)
N1	0.65223 (18)	0.3964 (4)	0.57992 (19)	0.0282 (5)
C1	0.7222 (2)	0.5406 (5)	0.5430 (2)	0.0276 (6)
C2	0.6746 (2)	0.7249 (5)	0.4561 (2)	0.0277 (6)
C3	0.7427 (2)	0.8711 (6)	0.4150 (3)	0.0389 (7)
H3	0.7143	0.9907	0.3581	0.047*
C4	0.8539 (2)	0.8422 (6)	0.4576 (3)	0.0446 (8)
H4	0.8980	0.9440	0.4281	0.053*
C5	0.9005 (2)	0.6691 (6)	0.5412 (3)	0.0403 (7)
H5	0.9750	0.6560	0.5690	0.048*
C6	0.8349 (2)	0.5114 (5)	0.5847 (3)	0.0327 (6)
C7	0.8730 (2)	0.3211 (6)	0.6687 (3)	0.0406 (7)
H7	0.9465	0.2949	0.7000	0.049*
C8	0.8020 (3)	0.1775 (6)	0.7034 (3)	0.0423 (8)
H8	0.8266	0.0520	0.7581	0.051*
C9	0.6913 (2)	0.2195 (5)	0.6561 (3)	0.0345 (6)
H9	0.6436	0.1181	0.6797	0.041*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0244 (3)	0.0300 (3)	0.0321 (3)	0.00157 (17)	0.00474 (19)	0.00763 (18)
O2	0.0730 (17)	0.0278 (11)	0.0322 (11)	0.0081 (10)	0.0088 (11)	−0.0004 (9)
O1	0.0266 (10)	0.0295 (10)	0.0319 (10)	0.0020 (8)	0.0045 (8)	0.0088 (8)
N1	0.0283 (12)	0.0292 (12)	0.0250 (11)	0.0025 (10)	0.0039 (10)	0.0010 (10)
C1	0.0249 (14)	0.0305 (15)	0.0255 (13)	0.0013 (10)	0.0038 (11)	−0.0038 (10)
C2	0.0281 (14)	0.0283 (14)	0.0253 (13)	−0.0016 (11)	0.0051 (11)	−0.0019 (10)
C3	0.0364 (17)	0.0416 (19)	0.0374 (16)	−0.0044 (13)	0.0083 (14)	0.0068 (14)
C4	0.0362 (17)	0.051 (2)	0.0479 (19)	−0.0133 (14)	0.0149 (15)	−0.0024 (15)
C5	0.0258 (15)	0.0492 (19)	0.0444 (18)	−0.0027 (13)	0.0076 (13)	−0.0077 (14)
C6	0.0260 (14)	0.0390 (17)	0.0299 (15)	0.0014 (12)	0.0023 (12)	−0.0063 (12)
C7	0.0297 (16)	0.0458 (18)	0.0410 (17)	0.0087 (13)	0.0013 (13)	−0.0004 (14)
C8	0.0444 (19)	0.0396 (17)	0.0361 (16)	0.0145 (14)	0.0000 (14)	0.0035 (13)
C9	0.0357 (16)	0.0331 (16)	0.0322 (15)	0.0045 (12)	0.0054 (13)	0.0045 (12)

Geometric parameters (Å, º)

Zn1—O1	1.9655 (18)	C2—C3	1.375 (4)
Zn1—O1^i	1.9655 (18)	C3—C4	1.394 (4)
Zn1—N1^i	2.011 (2)	C3—H3	0.9300
Zn1—N1	2.011 (2)	C4—C5	1.370 (5)
Zn1—O2^i	2.451 (2)	C4—H4	0.9300
Zn1—O2	2.451 (2)	C5—C6	1.404 (4)
O2—H2A	0.8500	C5—H5	0.9300
O2—H2B	0.8501	C6—C7	1.419 (4)
O1—C2	1.324 (3)	C7—C8	1.357 (5)
N1—C9	1.315 (4)	C7—H7	0.9300
N1—C1	1.362 (4)	C8—C9	1.402 (4)
C1—C6	1.412 (4)	C8—H8	0.9300
C1—C2	1.438 (4)	C9—H9	0.9300
O1—Zn1—O1^i	180.0	O1—C2—C3	124.3 (3)
O1—Zn1—N1^i	96.12 (8)	O1—C2—C1	118.1 (2)
O1^i—Zn1—N1^i	83.88 (8)	C3—C2—C1	117.6 (3)
O1—Zn1—N1	83.88 (8)	C2—C3—C4	120.9 (3)
O1^i—Zn1—N1	96.12 (8)	C2—C3—H3	119.6
N1^i—Zn1—N1	180.0	C4—C3—H3	119.6
O1—Zn1—O2^i	90.75 (8)	C5—C4—C3	122.2 (3)
O1^i—Zn1—O2^i	89.25 (7)	C5—C4—H4	118.9
N1^i—Zn1—O2^i	86.60 (8)	C3—C4—H4	118.9
N1—Zn1—O2^i	93.40 (8)	C4—C5—C6	119.4 (3)
O1—Zn1—O2	89.25 (7)	C4—C5—H5	120.3
O1^i—Zn1—O2	90.75 (8)	C6—C5—H5	120.3
N1^i—Zn1—O2	93.40 (8)	C5—C6—C1	118.7 (3)
N1—Zn1—O2	86.60 (8)	C5—C6—C7	124.9 (3)
O2^i—Zn1—O2	180.0	C1—C6—C7	116.4 (3)
Zn1—O2—H2A	113.6	C8—C7—C6	119.9 (3)
Zn1—O2—H2B	138.0	C8—C7—H7	120.0
H2A—O2—H2B	108.4	C6—C7—H7	120.0
C2—O1—Zn1	111.90 (16)	C7—C8—C9	119.6 (3)
C9—N1—C1	118.5 (2)	C7—C8—H8	120.2
C9—N1—Zn1	131.3 (2)	C9—C8—H8	120.2
C1—N1—Zn1	110.18 (17)	N1—C9—C8	122.8 (3)
N1—C1—C6	122.9 (2)	N1—C9—H9	118.6
N1—C1—C2	115.9 (2)	C8—C9—H9	118.6
C6—C1—C2	121.2 (3)
N1^i—Zn1—O1—C2	179.56 (17)	C6—C1—C2—O1	−179.9 (2)
N1—Zn1—O1—C2	−0.44 (17)	N1—C1—C2—C3	−178.8 (2)
O2^i—Zn1—O1—C2	92.90 (17)	C6—C1—C2—C3	0.2 (4)
O2—Zn1—O1—C2	−87.10 (17)	O1—C2—C3—C4	179.3 (3)
O1—Zn1—N1—C9	−177.9 (3)	C1—C2—C3—C4	−0.8 (4)
O1^i—Zn1—N1—C9	2.1 (3)	C2—C3—C4—C5	0.1 (5)
O2^i—Zn1—N1—C9	91.7 (3)	C3—C4—C5—C6	1.1 (5)
O2—Zn1—N1—C9	−88.3 (3)	C4—C5—C6—C1	−1.6 (4)
O1—Zn1—N1—C1	1.01 (18)	C4—C5—C6—C7	178.3 (3)
O1^i—Zn1—N1—C1	−178.99 (18)	N1—C1—C6—C5	179.9 (3)
O2^i—Zn1—N1—C1	−89.38 (18)	C2—C1—C6—C5	1.0 (4)
O2—Zn1—N1—C1	90.62 (18)	N1—C1—C6—C7	0.0 (4)
C9—N1—C1—C6	−1.3 (4)	C2—C1—C6—C7	−178.9 (3)
Zn1—N1—C1—C6	179.6 (2)	C5—C6—C7—C8	−179.1 (3)
C9—N1—C1—C2	177.7 (2)	C1—C6—C7—C8	0.8 (4)
Zn1—N1—C1—C2	−1.4 (3)	C6—C7—C8—C9	−0.3 (5)
Zn1—O1—C2—C3	179.7 (2)	C1—N1—C9—C8	1.8 (4)
Zn1—O1—C2—C1	−0.2 (3)	Zn1—N1—C9—C8	−179.3 (2)
N1—C1—C2—O1	1.1 (4)	C7—C8—C9—N1	−1.0 (5)

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2A···O1^ii	0.85	1.99	2.841 (3)	174
O2—H2B···O1^iii	0.85	1.99	2.829 (3)	169

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