Crystal structure of bis­{2-[(E)-(4-fluoro­benz­yl)imino­meth­yl]phenolato-κ² N,O}nickel(II)

In the square-planar [Ni(C₁₄H₁₁FNO)₂] complex, weak C—H⋯F and C—H⋯π inter­actions play an important role in the mol­ecular self-assembly, resulting in the formation of 2D mol­ecular sheets which are stacked along the b axis.

Abstract

The asymmetric unit of the title complex, [Ni(C₁₄H₁₁FNO)₂], contains one-half of the mol­ecule with the Ni^II cation lying on an inversion centre coordinated by a bidentate Schiff base anion. The cationic Ni^II center is in a distorted square-planar coordination environment chelated by the imine N and phenolate O donor atoms of the two Schiff base ligands. The N and O donor atoms of the two ligands are mutually trans with Ni—N and Ni—O bond lengths of 1.9242 (10) and 1.8336 (9) Å, respectively. The fluoro­phenyl ring is almost orthogonal to the coordination plane and makes a dihedral angle of 82.98 (7)° with the phenolate ring. In the crystal, mol­ecules are linked into screw chains by weak C—H⋯F hydrogen bonds. Additional C—H⋯π contacts arrange the mol­ecules into sheets parallel to the ac plane.

Chemical context  

Schiff base ligands are well-known and important compounds because of their wide range of biological activities and uses in industrial systems (Feng et al., 2013 ▶; Kumar et al., 2010 ▶; Liu et al., 2005 ▶) as well as being versatile ligands for transition metals. Transition metal complexes with Schiff base ligands, especially those of Pd^II and Ni^II, have been shown to display a variety of structural features and, in some cases, exhibit inter­esting reactivity. In particular they can be photoluminescent (Guo et al., 2013a ▶) and are used as catalysts for many organic reactions such as Heck and Suzuki cross-coupling reactions (Kumari et al., 2012 ▶; Teo et al., 2011 ▶).

In our previous studies, we reported the syntheses and crystal structures of two related Schiff base complexes, bis­{2-[(E)-(4-fluoro­benz­yl)imino­meth­yl]-6-meth­oxy­phenolato-κ² N,O ¹}nickel(II) (Bahron et al., 2011 ▶) and bis­{2-[(E)-(4-meth­oxy­benz­yl)imino­meth­yl]phenolato-κ² N,O ¹}nickel(II) (Bahron et al., 2014 ▶). In this article, we report the successful synthesis of another Schiff base–Ni^II complex, [Ni(C₁₄H₁₁FNO)₂] (1), and its characterization by spectros­copy and elemental analysis. Crystal structure determination confirms the binding mode of the [(4-fluoro­benz­yl)imino­meth­yl]phenolate ligand to the Ni^II cation (Fig. 1 ▶). The title complex was also tested for anti­bacterial activity, and found to be only weakly active.

Figure 1.

The mol­ecular structure of (1), showing 50% probability displacement ellipsoids and the atom-numbering scheme. The labelled atoms are related to the unlabelled atoms of the Schiff base ligands by the symmetry code: 1 − x, −y, 1 − z.

Structural commentary  

The asymmetric unit of (1) contains one-half of the mol­ecule with the Ni^II cation lying on an inversion centre and the Schiff base anion acting as an N,O-bidentate chelate ligand (Fig. 1 ▶). The cation binds to the N and the O atoms of two symmetry-related Schiff base ligand such that the N and O atoms are mutually trans. The N₂O₂ donor sets of the two chelating Schiff base ligands in the equatorial plane around Ni1 adopt a slightly distorted square planar coordination geometry with the angles O1—Ni1—N1 = 92.56 (4)° and O1—Ni1—N1ⁱ = 87.44 (4)° [symmetry code: (i) 1 − x, −y, 1 − z]. As expected under inversion symmetry, the trans angles (N11—Ni1—N1ⁱ and O1—Ni1—O1ⁱ) are found to be linear. The Ni1—N1 and Ni1—O1 distances in the N₂O₂ coordination plane are 1.9242 (10) Å and 1.8336 (9) Å, respectively. These compare well with those observed in the two other closely related Ni^II complexes with N₂O₂ coordinating Schiff base ligands (Bahron et al., 2011 ▶; 2014 ▶). The Ni1/O1/C1/C6/C7/N1 ring adopts an envelope conformation with the Ni1 atom displaced by 0.3885 (5) Å from the O1/C1/C6/C7/N1 plane, with the puckering parameters Q = 0.2429 (10) Å, θ = 65.3 (3) and ϕ = 4.0 (3)°. Other bond lengths and angles observed in the structure are also normal. The fluoro­phenyl ring (C9–C14) makes a dihedral angle of 82.98 (7)° with the phenolate ring (C1–C6).

Supra­molecular features  

In the crystal packing, the mol­ecules are linked into screw chains by weak C2—H2A⋯F1 inter­actions (Fig. 2 ▶, Table 1 ▶). C—H⋯π inter­actions involving both the fluoro­phenyl and the phenolate rings, C5—H5A⋯Cg1 and C13—H13A⋯Cg2, connect the mol­ecules into chains along the c-axis direction (Fig. 3 ▶, Table 1 ▶). They also contribute to the formation of sheets parallel to the ac plane, which are further stacked along the b axis as shown in Fig. 4 ▶.

Figure 2.

Screw chains of mol­ecules of (1) linked by C—H⋯F contacts drawn as dashed lines.

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

Cg1 and Cg2 are the centroids of the C1–C6 and C9–C14 rings, respectively.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C8—H8A⋯O1i	0.99	2.19	2.7300 (18)	113
C14—H14A⋯O1i	0.95	2.52	3.212 (2)	130
C2—H2A⋯F1ii	0.95	2.65	3.5312 (19)	155
C5—H5A⋯Cg1iii	0.95	2.69	3.4010 (18)	133
C13—H13A⋯Cg2iv	0.95	2.69	3.4252 (13)	134

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

Figure 3.

C—H⋯π contacts for (1) drawn as dotted lines with ring centroids shown as coloured spheres. Cg1 and Cg2 are the centroids of the C1–C6 and C9–C14 rings, respectively.

Figure 4.

The packing of (1) viewed along the b axis showing mol­ecular sheets of the Ni^II complex.

Database survey  

A search of the Cambridge Database (Version 5.35, November 2013 with 3 updates) revealed a total of 1191 Ni^II complexes with an NiN₂O₂ coordination sphere. No fewer than 333 of these had the Ni atom chelated by two 3-(imino­meth­yl)phenolate residues. No corresponding structures with a benzyl or substituted benzyl unit bound to the imino N atom were found. However extending the search to allow additional substitution on the phenolate ring resulted in eight discrete structures including the two closely related structures mentioned previously (Bahron et al., 2011 ▶, 2014 ▶), and several other related complexes (see, for example Guo et al. 2013a ▶,b ▶; Senol et al. 2011 ▶; Chen et al. 2010 ▶).

Synthesis and crystallization  

An ethano­lic solution of 4-fluoro­benzyl­amine (4 mmol, 0.5010 g) was added to salicyl­aldehyde (4 mmol, 0.4970 g), dissolved in absolute ethanol (2 ml), forming a bright-yellow solution. The mixture was heated under reflux for an hour to produce the ligand, (E)-2-[(4-fluoro­benzyl­imino)­meth­yl]phenol. Nickel(II) acetate tetra­hydrate (2 mmol, 0.4983 g) was dissolved separately in absolute ethanol (10 ml) and added to a flask containing the cooled ligand solution. The mixture was stirred and refluxed for 3 h upon which a dark-green solid formed. This was filtered off, washed with ice-cold ethanol and air-dried at room temperature. The solid product was recrystallized from chloro­form, yielding green crystals. Yield 68.6%; m.p. 471–473 K. Analytical data for C₂₈H₂₂F₂N₂O₂Ni: C, 65.28; H, 4.30; N, 5.44. Found: C, 65.87; H, 4.39; N, 5.55. IR (KBr, cm⁻¹): ν(C=N) 1612 (s), ν(C—N) 1390 (w), ν(C—O) 1221 (s), ν(Ni—N) 597 (w), ν(Ni—O) 451 (w). The infrared spectra of the title complex revealed a strong band of 1612 cm⁻¹ in the spectrum assignable to C=N stretching frequency upon complexation (Nair et al., 2012 ▶). The appearance of new bands at 451 and 597 cm⁻¹ in the spectrum of the title complex attributable to Ni—O and Ni—N vibrations, respectively, supports the suggestion above of the participation of the N atom of the imine group and O atom of the phenolic group of the ligand in the complexation with Ni^II cation (Ouf et al., 2010 ▶). Accordingly, it can be deduced that the ligand binds to the Ni^II cation in an N,O-bidentate fashion in 2:1 ratio.

An anti­bacterial activity investigation of the title complex against B. subtilis, S. aureus and E. coli showed very mild or no inhibition with clear inhibition diameters of 7–8 mm at the highest concentration of 50 μM. The negative control of a 9:1 mixture of DMSO:acetone and the positive control of 30 U of chloramphenicol showed inhibition diameters of 6 mm and 20 mm, respectively.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 2 ▶. All H atoms were positioned geometrically and allowed to ride on their parent atoms, with d(C—H) = 0.95 Å for aromatic and 0.99 Å for CH₂ hydrogen atoms. The U _iso values were constrained to be 1.2U _eq of the carrier atoms.

Table 2. Experimental details.

Crystal data
Chemical formula	[Ni(C14H11FNO)2]
M r	515.17
Crystal system, space group	Monoclinic, P21/c
Temperature (K)	100
a, b, c (Å)	13.8611 (3), 5.83340 (1), 16.9942 (3)
β (°)	125.998 (1)
V (Å3)	1111.70 (4)
Z	2
Radiation type	Mo Kα
μ (mm−1)	0.92
Crystal size (mm)	0.47 × 0.19 × 0.11
Data collection
Diffractometer	Bruker APEXII CCD area detector
Absorption correction	Multi-scan (SADABS; Bruker, 2009 ▶)
T min, T max	0.674, 0.906
No. of measured, independent and observed [I > 2σ(I)] reflections	13419, 3235, 2896
R int	0.024
(sin θ/λ)max (Å−1)	0.703
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.028, 0.072, 1.05
No. of reflections	3235
No. of parameters	160
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.45, −0.49

Computer programs: APEX2 and SAINT (Bruker, 2009 ▶), SHELXTL (Sheldrick, 2008 ▶), PLATON (Spek, 2009 ▶), Mercury (Macrae et al., 2006 ▶) and publCIF (Westrip, 2010 ▶).

Supplementary Material

CCDC reference: 1024161

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Crystal data

[Ni(C14H11FNO)2]	F(000) = 532
Mr = 515.17	Dx = 1.539 Mg m−3
Monoclinic, P21/c	Melting point = 471–476 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 13.8611 (3) Å	Cell parameters from 3235 reflections
b = 5.83340 (1) Å	θ = 1.8–30.0°
c = 16.9942 (3) Å	µ = 0.92 mm−1
β = 125.998 (1)°	T = 100 K
V = 1111.70 (4) Å3	Plate, green
Z = 2	0.47 × 0.19 × 0.11 mm

Data collection

Bruker APEXII CCD area detector diffractometer	3235 independent reflections
Radiation source: sealed tube	2896 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.024
φ and ω scans	θmax = 30.0°, θmin = 1.8°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −19→19
Tmin = 0.674, Tmax = 0.906	k = −8→8
13419 measured reflections	l = −23→23

Refinement

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.028	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.072	H-atom parameters constrained
S = 1.05	w = 1/[σ2(Fo2) + (0.0322P)2 + 0.7123P] where P = (Fo2 + 2Fc2)/3
3235 reflections	(Δ/σ)max = 0.001
160 parameters	Δρmax = 0.45 e Å−3
0 restraints	Δρmin = −0.49 e Å−3

Special details

Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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
Ni1	0.5000	0.0000	0.5000	0.01062 (7)
F1	1.07321 (8)	−0.19874 (17)	0.63754 (7)	0.0297 (2)
N1	0.58764 (8)	0.26207 (18)	0.50481 (7)	0.01200 (19)
O1	0.41017 (8)	−0.01507 (15)	0.36693 (7)	0.01520 (18)
C1	0.38843 (10)	0.1456 (2)	0.30461 (9)	0.0133 (2)
C2	0.29659 (11)	0.1091 (2)	0.20455 (9)	0.0160 (2)
H2A	0.2528	−0.0303	0.1840	0.019*
C3	0.27066 (11)	0.2756 (2)	0.13703 (9)	0.0174 (2)
H3A	0.2085	0.2490	0.0704	0.021*
C4	0.33373 (12)	0.4832 (2)	0.16425 (10)	0.0175 (2)
H4A	0.3147	0.5959	0.1168	0.021*
C5	0.42385 (11)	0.5206 (2)	0.26118 (9)	0.0151 (2)
H5A	0.4676	0.6600	0.2804	0.018*
C6	0.45190 (10)	0.3546 (2)	0.33205 (8)	0.0125 (2)
C7	0.55207 (10)	0.3936 (2)	0.43090 (9)	0.0125 (2)
H7A	0.5968	0.5294	0.4434	0.015*
C8	0.70465 (10)	0.3283 (2)	0.59589 (9)	0.0134 (2)
H8A	0.7024	0.3042	0.6524	0.016*
H8B	0.7198	0.4930	0.5933	0.016*
C9	0.80423 (10)	0.1869 (2)	0.60823 (8)	0.0133 (2)
C10	0.86635 (11)	0.2669 (2)	0.57233 (9)	0.0166 (2)
H10A	0.8456	0.4110	0.5402	0.020*
C11	0.95823 (11)	0.1396 (3)	0.58258 (10)	0.0202 (3)
H11A	1.0010	0.1957	0.5588	0.024*
C12	0.98511 (11)	−0.0701 (3)	0.62825 (10)	0.0196 (3)
C13	0.92625 (11)	−0.1569 (2)	0.66508 (9)	0.0174 (2)
H13A	0.9471	−0.3019	0.6965	0.021*
C14	0.83553 (11)	−0.0255 (2)	0.65471 (9)	0.0152 (2)
H14A	0.7942	−0.0816	0.6798	0.018*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Ni1	0.01005 (10)	0.01029 (11)	0.01063 (11)	−0.00089 (7)	0.00557 (8)	0.00019 (7)
F1	0.0240 (4)	0.0360 (5)	0.0340 (5)	0.0125 (4)	0.0197 (4)	0.0035 (4)
N1	0.0105 (4)	0.0115 (5)	0.0129 (4)	−0.0003 (3)	0.0063 (4)	−0.0010 (4)
O1	0.0168 (4)	0.0142 (4)	0.0122 (4)	−0.0036 (3)	0.0072 (3)	0.0005 (3)
C1	0.0123 (5)	0.0149 (5)	0.0138 (5)	0.0010 (4)	0.0084 (4)	0.0009 (4)
C2	0.0141 (5)	0.0177 (6)	0.0148 (5)	−0.0015 (4)	0.0077 (5)	−0.0003 (4)
C3	0.0141 (5)	0.0218 (6)	0.0136 (5)	0.0016 (4)	0.0066 (4)	0.0010 (5)
C4	0.0176 (6)	0.0188 (6)	0.0157 (6)	0.0029 (4)	0.0096 (5)	0.0049 (5)
C5	0.0153 (5)	0.0144 (6)	0.0167 (6)	0.0012 (4)	0.0100 (5)	0.0022 (4)
C6	0.0115 (5)	0.0133 (5)	0.0135 (5)	0.0014 (4)	0.0077 (4)	0.0010 (4)
C7	0.0122 (5)	0.0115 (5)	0.0158 (5)	−0.0002 (4)	0.0093 (4)	−0.0005 (4)
C8	0.0119 (5)	0.0116 (5)	0.0140 (5)	−0.0017 (4)	0.0062 (4)	−0.0020 (4)
C9	0.0103 (5)	0.0149 (5)	0.0114 (5)	−0.0012 (4)	0.0045 (4)	−0.0015 (4)
C10	0.0154 (5)	0.0179 (6)	0.0156 (5)	−0.0010 (4)	0.0086 (5)	0.0007 (4)
C11	0.0174 (6)	0.0271 (7)	0.0192 (6)	−0.0004 (5)	0.0126 (5)	−0.0003 (5)
C12	0.0139 (5)	0.0249 (7)	0.0182 (6)	0.0039 (5)	0.0085 (5)	−0.0020 (5)
C13	0.0139 (5)	0.0162 (6)	0.0161 (6)	0.0013 (4)	0.0054 (5)	−0.0002 (4)
C14	0.0123 (5)	0.0152 (6)	0.0155 (5)	−0.0018 (4)	0.0068 (4)	−0.0008 (4)

Geometric parameters (Å, º)

Ni1—O1i	1.8336 (9)	C5—H5A	0.9500
Ni1—O1	1.8336 (9)	C6—C7	1.4351 (16)
Ni1—N1i	1.9242 (10)	C7—H7A	0.9500
Ni1—N1	1.9242 (10)	C8—C9	1.5133 (16)
F1—C12	1.3613 (15)	C8—H8A	0.9900
N1—C7	1.2967 (16)	C8—H8B	0.9900
N1—C8	1.4915 (15)	C9—C14	1.3943 (17)
O1—C1	1.3097 (15)	C9—C10	1.3960 (17)
C1—C6	1.4130 (17)	C10—C11	1.3937 (18)
C1—C2	1.4187 (17)	C10—H10A	0.9500
C2—C3	1.3801 (18)	C11—C12	1.378 (2)
C2—H2A	0.9500	C11—H11A	0.9500
C3—C4	1.4031 (19)	C12—C13	1.3834 (19)
C3—H3A	0.9500	C13—C14	1.3926 (17)
C4—C5	1.3794 (18)	C13—H13A	0.9500
C4—H4A	0.9500	C14—H14A	0.9500
C5—C6	1.4100 (17)
O1i—Ni1—O1	180.0	N1—C7—C6	126.56 (11)
O1i—Ni1—N1i	92.56 (4)	N1—C7—H7A	116.7
O1—Ni1—N1i	87.44 (4)	C6—C7—H7A	116.7
O1i—Ni1—N1	87.44 (4)	N1—C8—C9	110.45 (9)
O1—Ni1—N1	92.56 (4)	N1—C8—H8A	109.6
N1i—Ni1—N1	180.00 (6)	C9—C8—H8A	109.6
C7—N1—C8	114.48 (10)	N1—C8—H8B	109.6
C7—N1—Ni1	123.90 (8)	C9—C8—H8B	109.6
C8—N1—Ni1	121.62 (8)	H8A—C8—H8B	108.1
C1—O1—Ni1	129.03 (8)	C14—C9—C10	118.57 (11)
O1—C1—C6	123.23 (11)	C14—C9—C8	121.18 (11)
O1—C1—C2	118.67 (11)	C10—C9—C8	120.25 (11)
C6—C1—C2	118.10 (11)	C11—C10—C9	121.36 (12)
C3—C2—C1	120.18 (12)	C11—C10—H10A	119.3
C3—C2—H2A	119.9	C9—C10—H10A	119.3
C1—C2—H2A	119.9	C12—C11—C10	117.89 (12)
C2—C3—C4	121.73 (12)	C12—C11—H11A	121.1
C2—C3—H3A	119.1	C10—C11—H11A	121.1
C4—C3—H3A	119.1	F1—C12—C11	118.81 (12)
C5—C4—C3	118.79 (12)	F1—C12—C13	118.24 (13)
C5—C4—H4A	120.6	C11—C12—C13	122.95 (12)
C3—C4—H4A	120.6	C12—C13—C14	118.04 (12)
C4—C5—C6	120.87 (12)	C12—C13—H13A	121.0
C4—C5—H5A	119.6	C14—C13—H13A	121.0
C6—C5—H5A	119.6	C13—C14—C9	121.18 (12)
C5—C6—C1	120.33 (11)	C13—C14—H14A	119.4
C5—C6—C7	118.85 (11)	C9—C14—H14A	119.4
C1—C6—C7	120.62 (11)
O1i—Ni1—N1—C7	−161.69 (10)	C8—N1—C7—C6	171.36 (11)
O1—Ni1—N1—C7	18.31 (10)	Ni1—N1—C7—C6	−8.09 (17)
O1i—Ni1—N1—C8	18.90 (9)	C5—C6—C7—N1	177.97 (11)
O1—Ni1—N1—C8	−161.10 (9)	C1—C6—C7—N1	−7.20 (18)
N1i—Ni1—O1—C1	158.63 (10)	C7—N1—C8—C9	−97.31 (12)
N1—Ni1—O1—C1	−21.37 (10)	Ni1—N1—C8—C9	82.15 (11)
Ni1—O1—C1—C6	12.98 (17)	N1—C8—C9—C14	−87.37 (13)
Ni1—O1—C1—C2	−166.89 (9)	N1—C8—C9—C10	92.19 (13)
O1—C1—C2—C3	179.45 (11)	C14—C9—C10—C11	−0.29 (18)
C6—C1—C2—C3	−0.42 (17)	C8—C9—C10—C11	−179.86 (12)
C1—C2—C3—C4	0.48 (19)	C9—C10—C11—C12	0.9 (2)
C2—C3—C4—C5	−0.03 (19)	C10—C11—C12—F1	178.90 (12)
C3—C4—C5—C6	−0.47 (19)	C10—C11—C12—C13	−0.9 (2)
C4—C5—C6—C1	0.52 (18)	F1—C12—C13—C14	−179.49 (11)
C4—C5—C6—C7	175.37 (11)	C11—C12—C13—C14	0.3 (2)
O1—C1—C6—C5	−179.94 (11)	C12—C13—C14—C9	0.31 (19)
C2—C1—C6—C5	−0.07 (17)	C10—C9—C14—C13	−0.32 (18)
O1—C1—C6—C7	5.30 (18)	C8—C9—C14—C13	179.25 (11)
C2—C1—C6—C7	−174.83 (11)

Symmetry code: (i) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, º)

Cg1 and Cg2 are the centroids of the C1–C6 and C9–C14 rings, respectively.

D—H···A	D—H	H···A	D···A	D—H···A
C8—H8A···O1i	0.99	2.19	2.7300 (18)	113
C14—H14A···O1i	0.95	2.52	3.212 (2)	130
C2—H2A···F1ii	0.95	2.65	3.5312 (19)	155
C5—H5A···Cg1iii	0.95	2.69	3.4010 (18)	133
C13—H13A···Cg2iv	0.95	2.69	3.4252 (13)	134

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