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In the title compound, [Ni(C19H20N2O4)(H2O)2], the Ni atom has a distorted octahedral coordination geometry in which the tetradentate Schiff base ligand acts as a cis-N2O2 donor defining an equatorial plane, and water mol­ecules occupy the axial positions. The two parts of the mol­ecule are related by a mirror plane that passes through the Ni atom and is perpendicular to the equatorial plane. The angular distortions from normal octahedral geometry are in the range 1-6°, and the equatorial plane, defined by the donor atoms of the Schiff base, is almost square planar. The six-membered ring comprising the Ni, the imine N and the propyl­ene C atoms adopts a half-chair conformation. The Ni-O [2.017 (2) Å] and Ni-N [2.071 (2) Å] distances are within the ranges expected for high-spin octahedral nickel complexes.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010001009X/da1141sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S010827010001009X/da1141Isup2.hkl
Contains datablock I

CCDC reference: 152596

Comment top

We are currently investigating the preparation and spectroelectrochemical characterization of modified electrodes with electroactive polymers based on nickel(II) and copper(II) complexes with N2O2-donor Schiff base ligands, which are obtained by the condensation of salicylaldehyde and ethylenediamine derivatives with increasing stereochemical demand (Vilas-Boas et al., 1997, 1998, 2000). The electrochemical characterization of modified electrodes based on nickel complexes with ethylenic bridges has shown that their stability/durability and conductivity in CH3CN/TEAP (0.1 mol dm−3) increase with the bulkiness of the imine bridge substituents, probably a consequence of different film compaction imposed by bulky imine bridges (Santos et al., 2000; Vilas-Boas et al., 2000). We are extending this study to polymers based on similar complexes, but with propylene bridges, in order to assess the influence of the longer imine bridge on the electrochemical performance of polymer modified electrodes. We have prepared the title compound, Ni[{(3-MeO)2salpd}(H2O)2] (I), and studied its oxidative polymerization and redox switching in acetonitrile, and have found that modified electrodes based on {6,6'-dimethoxy-2,2'-[propane-1,3-diylbis(nitrilomethylidyne-N)]diphenolato- O,O'}nickel(II), Ni[((3-MeO)2salpd)] (L1), exhibit high electrochemical stability. We report the molecular structure of the monomer, which is six-coordinate, in contrast with most of the known structures of this type of complexes.

The structure of (I) consists of discrete molecules in which the Ni atom has a distorted octahedral coordination geometry, with the tetradentate Schiff ligand acting as a cis-N2O2 donor and defining the equatorial plane, and with two water molecules occupying the axial positions (Fig. 1). The molecule has crystallographically imposed Cs symmetry, with the Ni atom on a mirror plane which is perpendicular to the general equatorial plane of the molecule. The angular distortions from normal octahedral geometry are in the range 1–6°. The angle subtended at the metal atom in the metallocycle (O1—Ni1—N1) is 88.75 (8)° and that in the propylene bridging moiety (N1—Ni1—N1') is 96.94 (11)°. The O3—Ni1—O2 angle is 175.20 (10)°.

The equatorial plane, defined by the donor atoms of the Schiff base ligand, is essentially planar, and the maximum deviation of the Ni atom from the least-squares equatorial plane is −0.005 (1) Å. The ligand chelate-ring atoms N1—C7—C6—C1—O1 define a plane that makes an angle of 14.58 (3)° with the equatorial plane, and is almost coplanar with the plane defined by the atoms of the benzene ring. The two salicylaldehyde moieties are bent in an umbrella configuration and form, obviously, an angle of 29.16 (5)°. The six-membered ring comprising the Ni, the imine N and propylene C atoms adopts a half-chair conformation; the imine C8 and C9 atoms are 0.288 (4) and −0.361 (5) Å, respectively, from the equatorial coordination plane.

The Ni—O(Schiff base) distance [2.017 (2) Å] is shorter than the Ni—N distance [2.071 (2) Å], as observed in other metal complexes with similar ligands having the same propylene imine bridge (Akhtar & Drew, 1982; Drew et al., 1985; Elerman et al., 1993). This situation is to be contrasted with what is normally found in similar simple complexes with unsubstituted ethylene–imine bridges, for which the Ni—N distances are shorter than the Ni—O distances (Manfredotti & Gasatini, 1983; Akhtar, 1981; Blake et al., 1995), and has been attributed to the steric hindrance of the bulkier trimethylene group between the N groups. As a consequence, ligands with the longer aliphatic chain will cause weaker ligand fields. The Ni—O(water) distance is only slightly longer than the Ni—O(Schiff base) distance, and this observation shows conclusively that the two water molecules are bound axially. The ease of axial coordination in complexes with propylene bridges is a result of the weak ligand field produced by the Schiff base.

Axial coordination influences the Ni—O and Ni—N bond distances of the Schiff base. The values range from 1.84 to 1.90 Å in four-coordinate low-spin Ni complexes with similar Schiff bases having a propylene–imine bridge (Akhtar & Drew, 1982; Drew et al., 1985), and from 1.85 to 1.88%A in the adduct of L1 with SbPh3Cl·H2O (Clarke et al., 1994). In the high-spin five-coordinate Ni complex with a similar Schiff base, but which lacks the methoxy groups, and one axially bound water molecule, the values are 2.034 and 2.034 Å (Elerman et al., 1993), and in the L1·H2O adduct with SbPh3Cl·H2O, the bond distances range from 1.99 to 2.06 Å (Clarke et al., 1994). In the six-coordinate complex of L1, these distances are always longer than 2 Å. These observations suggest that the axial binding of one or two water molecules weakens the equatorial field (the equatorial bond distances are about 0.1 Å longer) and changes the spin state of the nickel to high spin. The high spin state of the complex is confirmed by the diffuse reflectance electronic spectrum that exhibits in the near IR/visible region the three d–d transitions typical of high-spin octahedral nickel complexes.

The crystal packing is depicted in Fig. 2. The packing view down the a axis shows that the molecules are arranged in chains along a twofold screw axis at y + 1/4,z + 1/4. The chains are formed by parallel stacking of benzene moieties (3.7 Å) and with the imine bridges alternating along the axis. Extensive hydrogen bonding is observed between coordinated water molecules: both H2A and H3A (and their symmetry equivalents) appear to be strongly involved in hydrogen bonding to O1 in neighbouring molecules, which progagates a total of eight hydrogen bonds for each molecule in the lattice. Notwithstanding its importance in the packing of these molecules in the crystal, the presence of interactions between the benzene moieties suggests that the crystal packing is also controlled by ππ* interactions between these moieties. This packing is somewhat reminiscent of that found in the similar four-coordinate Ni complex with 2,2'-[propane-1,3-diylbis(nitrilomethylidyne-N)]dinaphthol (Akhtar & Drew, 1982), in which the umbrella-shaped molecules stack parallel to the c axis, with each Ni atom almost directly above the other. In the six-coordinate complexes of L1, the axially bound water molecules prevent such an arrangement and to preserve the stacking of the aromatic moieties, the water–nickel–water fragments are not collinear, but are almost parallel and alternate along the a axis.

Experimental top

The title nickel(II) complex was prepared by refluxing an ethanol/water solution of nickel acetate monohydrate with an equimolar amount of the ligand (obtained by Schiff condensation in ethanol of o-vaniline with 1,3-propanediamine). Upon cooling, a green solid was obtained which was recrystallized from acetonitrile. Crystals of diffractometric quality were obtained by slow evaporation of a dimethylformamide solution.

Refinement top

All H atoms were refined [C—H 0.86 (3)–1.05 (3) Å].

Computing details top

Data collection: Stoe IPDS EXPOSE (Stoe & Cie, 1996); cell refinement: Stoe IPDS CELL (Stoe & Cie, 1996); data reduction: Stoe IPDS INTEGRATE (Stoe & Cie, 1996); program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL93 (Sheldrick, 1993); molecular graphics: ORTEPIII for Windows (Johnson & Burnett, 1998); software used to prepare material for publication: SHELXL93.

Figures top
[Figure 1] Fig. 1. The molecular structure of [Ni{(3-MeO)2salpd}(H2O)2] with the atom-labelling scheme. Displacement ellipsoids are plotted at the 50% probability level and H atoms are shown as spheres of arbitrary radii.
[Figure 2] Fig. 2. The crystal packing of [Ni{(3-MeO)2salpd}(H2O)2] viewed down the a axis.
(I) top
Crystal data top
[Ni(C19H20N2O4)(H2O)2]F(000) = 912
Mr = 435.12Dx = 1.526 Mg m3
Orthorhombic, PnmaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2nCell parameters from 2000 reflections
a = 7.4077 (11) Åθ = 4.8–28.2°
b = 22.064 (3) ŵ = 1.06 mm1
c = 11.585 (2) ÅT = 293 K
V = 1893.5 (5) Å3Needle, light green
Z = 40.4 × 0.1 × 0.1 mm
Data collection top
Stoe Image Plate Detector System
diffractometer
1898 independent reflections
Radiation source: fine-focus sealed tube1583 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.096
Area–detector scansθmax = 26.1°, θmin = 3.3°
Absorption correction: numerical
(Stoe IPDS FACEIT; Stoe & Cie, 1996)
h = 99
Tmin = 0.458, Tmax = 0.930k = 2723
9095 measured reflectionsl = 1414
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.037Hydrogen site location: geom and difmap for H3 H2
wR(F2) = 0.093All H-atom parameters refined
S = 1.05Calculated w = 1/[σ2(Fo2) + (0.0533P)2]
where P = (Fo2 + 2Fc2)/3
1847 reflections(Δ/σ)max = 0.002
183 parametersΔρmax = 0.86 e Å3
0 restraintsΔρmin = 0.62 e Å3
Crystal data top
[Ni(C19H20N2O4)(H2O)2]V = 1893.5 (5) Å3
Mr = 435.12Z = 4
Orthorhombic, PnmaMo Kα radiation
a = 7.4077 (11) ŵ = 1.06 mm1
b = 22.064 (3) ÅT = 293 K
c = 11.585 (2) Å0.4 × 0.1 × 0.1 mm
Data collection top
Stoe Image Plate Detector System
diffractometer
1898 independent reflections
Absorption correction: numerical
(Stoe IPDS FACEIT; Stoe & Cie, 1996)
1583 reflections with I > 2σ(I)
Tmin = 0.458, Tmax = 0.930Rint = 0.096
9095 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0370 restraints
wR(F2) = 0.093All H-atom parameters refined
S = 1.05Δρmax = 0.86 e Å3
1847 reflectionsΔρmin = 0.62 e Å3
183 parameters
Special details top

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 on F2 for ALL reflections except for 51 with very negative F2 or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The observed criterion of F2 σ(F2) is used only for calculating R_factor_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 (Å2) top
xyzUiso*/Ueq
Ni10.01893 (4)0.25000.39890 (3)0.0186 (2)
O10.0060 (2)0.31207 (7)0.27138 (13)0.0255 (4)
N10.0297 (2)0.32028 (9)0.5172 (2)0.0251 (4)
O30.2629 (3)0.25000.4184 (2)0.0289 (5)
H3A0.315 (4)0.2749 (17)0.387 (3)0.063 (11)*
O40.0438 (2)0.36440 (8)0.07423 (15)0.0354 (4)
O20.3010 (3)0.25000.3946 (2)0.0252 (5)
H2A0.341 (4)0.2750 (15)0.364 (3)0.050 (10)*
C10.0532 (3)0.36858 (9)0.2752 (2)0.0219 (4)
C20.0760 (3)0.40055 (9)0.1692 (2)0.0261 (5)
C30.1262 (3)0.45995 (11)0.1654 (2)0.0352 (5)
H30.141 (4)0.4805 (17)0.093 (3)0.065 (10)*
C40.1536 (3)0.49237 (11)0.2676 (3)0.0388 (6)
H40.193 (4)0.5323 (15)0.260 (2)0.043 (7)*
C50.1326 (3)0.46382 (11)0.3715 (2)0.0335 (5)
H50.145 (4)0.4850 (15)0.436 (3)0.046 (8)*
C60.0845 (3)0.40195 (10)0.3777 (2)0.0247 (5)
C70.0634 (3)0.37595 (10)0.4915 (2)0.0277 (5)
H70.087 (4)0.4078 (13)0.557 (2)0.036 (7)*
C80.0027 (4)0.30784 (13)0.6404 (2)0.0387 (6)
H8A0.055 (4)0.3416 (17)0.680 (3)0.051 (8)*
H8B0.133 (4)0.3021 (14)0.661 (2)0.044 (7)*
C90.0942 (5)0.25000.6804 (3)0.0389 (8)
H9A0.208 (4)0.25000.666 (3)0.015 (7)*
H9B0.088 (7)0.25000.761 (5)0.074 (15)*
C100.0576 (5)0.39064 (15)0.0363 (2)0.0483 (7)
H10A0.029 (4)0.4214 (19)0.047 (3)0.058 (10)*
H10B0.025 (4)0.356 (2)0.086 (3)0.056 (10)*
H10C0.186 (5)0.4073 (18)0.051 (3)0.075 (11)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ni10.0242 (2)0.0123 (2)0.0194 (2)0.0000.00044 (12)0.000
O10.0389 (7)0.0114 (7)0.0260 (9)0.0032 (6)0.0042 (6)0.0013 (6)
N10.0293 (9)0.0208 (10)0.0253 (9)0.0006 (7)0.0012 (7)0.0027 (8)
O30.0250 (10)0.0170 (12)0.0447 (13)0.0000.0034 (10)0.000
O40.0630 (10)0.0170 (9)0.0262 (8)0.0041 (7)0.0038 (7)0.0035 (7)
O20.0265 (10)0.0191 (13)0.0301 (12)0.0000.0039 (9)0.000
C10.0221 (8)0.0118 (9)0.0317 (11)0.0025 (7)0.0007 (8)0.0015 (8)
C20.0299 (10)0.0141 (10)0.0343 (12)0.0045 (8)0.0036 (9)0.0010 (9)
C30.0417 (12)0.0164 (11)0.0474 (15)0.0004 (9)0.0056 (10)0.0105 (10)
C40.0433 (12)0.0127 (11)0.060 (2)0.0056 (10)0.0016 (11)0.0048 (11)
C50.0367 (11)0.0156 (12)0.0482 (15)0.0015 (9)0.0066 (10)0.0064 (10)
C60.0245 (9)0.0137 (10)0.0359 (12)0.0000 (8)0.0009 (8)0.0023 (8)
C70.0312 (10)0.0220 (11)0.0300 (12)0.0002 (9)0.0033 (9)0.0088 (9)
C80.061 (2)0.031 (2)0.0240 (12)0.0025 (12)0.0032 (10)0.0065 (11)
C90.053 (2)0.041 (2)0.022 (2)0.0000.0071 (15)0.000
C100.078 (2)0.037 (2)0.0302 (14)0.011 (2)0.0043 (13)0.0121 (12)
Geometric parameters (Å, º) top
Ni1—O1i2.017 (2)C3—H30.96 (3)
Ni1—O12.017 (2)C4—C51.368 (4)
Ni1—N12.071 (2)C4—H40.93 (3)
Ni1—N1i2.071 (2)C5—C61.413 (3)
Ni1—O22.090 (2)C5—H50.89 (3)
Ni1—O32.100 (2)C6—C71.446 (3)
O1—C11.295 (3)C7—H71.05 (3)
N1—C71.289 (3)C8—C91.518 (3)
N1—C81.467 (3)C8—H8A0.96 (4)
O3—H3A0.76 (3)C8—H8B1.04 (3)
O4—C21.380 (3)C9—C8i1.518 (4)
O4—C101.409 (3)C9—H9A0.86 (3)
O2—H2A0.72 (3)C9—H9B0.94 (5)
C1—C61.417 (3)C10—H10A0.94 (4)
C1—C21.425 (3)C10—H10B0.99 (4)
C2—C31.363 (3)C10—H10C1.03 (4)
C3—C41.398 (4)
O1i—Ni1—O185.55 (9)C5—C4—C3119.6 (2)
O1i—Ni1—N1174.30 (7)C5—C4—H4123.3 (16)
O1—Ni1—N188.75 (8)C3—C4—H4117.0 (16)
O1i—Ni1—N1i88.75 (8)C4—C5—C6121.2 (2)
O1—Ni1—N1i174.30 (7)C4—C5—H5119 (2)
N1—Ni1—N1i96.94 (11)C6—C5—H5120 (2)
O1i—Ni1—O291.70 (6)C5—C6—C1120.1 (2)
O1—Ni1—O291.70 (6)C5—C6—C7117.2 (2)
N1—Ni1—O288.70 (6)C1—C6—C7122.7 (2)
N1i—Ni1—O288.70 (6)N1—C7—C6127.6 (2)
O1i—Ni1—O391.82 (7)N1—C7—H7120.3 (16)
O1—Ni1—O391.82 (7)C6—C7—H7112.0 (16)
N1—Ni1—O388.11 (6)N1—C8—C9113.1 (2)
N1i—Ni1—O388.11 (6)N1—C8—H8A106 (2)
O2—Ni1—O3175.20 (10)C9—C8—H8A109 (2)
C1—O1—Ni1128.02 (14)N1—C8—H8B112.2 (15)
C7—N1—C8115.5 (2)C9—C8—H8B105.0 (17)
C7—N1—Ni1124.6 (2)H8A—C8—H8B112 (2)
C8—N1—Ni1119.9 (2)C8i—C9—C8114.5 (3)
Ni1—O3—H3A117 (3)C8i—C9—H9A112.2 (9)
C2—O4—C10118.3 (2)C8—C9—H9A112.2 (9)
Ni1—O2—H2A115 (2)C8i—C9—H9B106.4 (15)
O1—C1—C6124.9 (2)C8—C9—H9B106.4 (15)
O1—C1—C2118.6 (2)H9A—C9—H9B104 (4)
C6—C1—C2116.4 (2)O4—C10—H10A112 (2)
C3—C2—O4125.2 (2)O4—C10—H10B101 (2)
C3—C2—C1122.4 (2)H10A—C10—H10B108 (3)
O4—C2—C1112.3 (2)O4—C10—H10C111 (2)
C2—C3—C4120.3 (2)H10A—C10—H10C110 (3)
C2—C3—H3121 (2)H10B—C10—H10C114 (3)
C4—C3—H3119 (2)
Symmetry code: (i) x, y+1/2, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2—H2A···O1ii0.72 (3)2.15 (3)2.810 (3)152 (4)
O3—H3A···O1iii0.76 (3)2.41 (3)3.107 (3)152 (4)
Symmetry codes: (ii) x+1/2, y, z+1/2; (iii) x1/2, y, z+1/2.

Experimental details

Crystal data
Chemical formula[Ni(C19H20N2O4)(H2O)2]
Mr435.12
Crystal system, space groupOrthorhombic, Pnma
Temperature (K)293
a, b, c (Å)7.4077 (11), 22.064 (3), 11.585 (2)
V3)1893.5 (5)
Z4
Radiation typeMo Kα
µ (mm1)1.06
Crystal size (mm)0.4 × 0.1 × 0.1
Data collection
DiffractometerStoe Image Plate Detector System
diffractometer
Absorption correctionNumerical
(Stoe IPDS FACEIT; Stoe & Cie, 1996)
Tmin, Tmax0.458, 0.930
No. of measured, independent and
observed [I > 2σ(I)] reflections
9095, 1898, 1583
Rint0.096
(sin θ/λ)max1)0.620
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.037, 0.093, 1.05
No. of reflections1847
No. of parameters183
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.86, 0.62

Computer programs: Stoe IPDS EXPOSE (Stoe & Cie, 1996), Stoe IPDS CELL (Stoe & Cie, 1996), Stoe IPDS INTEGRATE (Stoe & Cie, 1996), SHELXS86 (Sheldrick, 1990), SHELXL93 (Sheldrick, 1993), ORTEPIII for Windows (Johnson & Burnett, 1998), SHELXL93.

Selected geometric parameters (Å, º) top
Ni1—O12.017 (2)Ni1—O22.090 (2)
Ni1—N12.071 (2)Ni1—O32.100 (2)
O1i—Ni1—O185.55 (9)N1—Ni1—O288.70 (6)
O1i—Ni1—N1174.30 (7)O1—Ni1—O391.82 (7)
O1—Ni1—N188.75 (8)N1—Ni1—O388.11 (6)
N1—Ni1—N1i96.94 (11)O2—Ni1—O3175.20 (10)
O1—Ni1—O291.70 (6)
Symmetry code: (i) x, y+1/2, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2—H2A···O1ii0.72 (3)2.15 (3)2.810 (3)152 (4)
O3—H3A···O1iii0.76 (3)2.41 (3)3.107 (3)152 (4)
Symmetry codes: (ii) x+1/2, y, z+1/2; (iii) x1/2, y, z+1/2.
 

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