{4-Bromo-2-[2-(5-bromo-2-oxido­benzyl­idene­amino­methyl)­phenyl­imino­methyl]­phenolato-κ⁴O,N,N′,O′}nickel(II)

In the title complex, [Ni(C₂₁H₁₄Br₂N₂O₂)], the Ni^II atom is coordinated by the two imine N and two phenolate O atoms of the Schiff base ligand in a tetrahedrally distorted square-planar geometry. The Ni—N and Ni—O distances are within the ranges expected for Ni–Schiff base derivatives. Intermolecular C—H...O hydrogen bonds link the mol­ecules into centrosymmetric dimers, forming (12) (A) and (10) (B) rings. These dimers combine to form a supramolecular ABAB… aggregate which propagates along the [100] direction.

S1. Comment

Multidentate Schiff base ligands and their nickel(II) complexes have been studied extensively because of their preparative accessibility and structural variability (Garnovskii et al., 1993). In addition to their diverse chelating ability, magnetic properties and applications in catalysis, the Schiff base ligands derived from salicylaldimine can serve as efficient models for biologically important systems (Long, 1995). In general, nickel(II) complexes of diamine Schiff bases display square-planar metal coordination (Elerman et al., 1996; Sony et al., 2004). When the substituents in the imine bridge are bulkier or the substitution is asymmetric, the metal coordination often exhibits tetrahedral distortion (Elmali et al., 2000; de Castro et al., 2001). As part of systematic studies of the characterization of tetradentate nickel(II)–diamine complexes (Datta et al., 2003), and to build up a hierarchy for such systems, the synthesis, spectroscopy and X-ray structural studies of the title complex, (I), were undertaken.

The crystal structure of (I) (Fig. 1) is built from discrete NiL units (where L is the tetradentate Schiff base ligand) in which each Ni^II ion is coordinated by two imine N and two phenolate O atoms. The coordination polyhedron around the metal centre is close to square-planar, the N₂O₂ plane being slightly tetrahedrally distorted [maximum deviation of 0.104 (3) Å for atom N2]. The Ni atom [deviation 0.002 (1) Å] is well within the plane defined by atoms N1, N2, O1 and O2. The distortion of the metal coordination geometry from an ideal square-planar arrangement is revealed by the cisoid O—Ni—O angle of 82.64 (10)° (Table 1) and the dihedral angle of 8.2 (1)° between the two Ni/N/O planes. Similar distortions in the metal coordination geometry have been reported for tetradentate nickel(II)–Schiff base complexes (Arici et al., 2001; Elmali et al., 2000; de Castro et al., 2001) where the substituents in the imine bridge are bulkier.

The tetradentate ligand consists of three essentially planar parts, viz. two 5-bromosalicylideneimine groups [O1/N1/Br1/C1–C7 (L1) and O2/N2/Br2/C15–C21 (L2)], and the bridging benzyl moiety [C8–C14 (L3)]. The maximum deviation of an atom from the L1, L2 and L3 least-squares planes is 0.085 (3) Å for atom C7 in L1; the corresponding deviations of the Ni atom from the L1 and L2 planes are 0.467 (1) and 0.438 (1) Å, respectively. The dihedral angle between L1 and L2 is 8.8 (1)°, indicating a flat arrangement of the two bromosalicylideneimine groups in the molecule. This geometry is similar to that observed in the [Ni(salchd)] (de Castro et al., 2001) and [Ni(-)(chxn)(sal)₂] (Wojtczak et al., 1997) complexes [salchd is bis(salicylidene)cyclohexane-1,2-diaminate, chxn is ?? and sal is salicylidene??] (see Table 3). The pronounced distortion of the planar geometry in [Ni(salpd)] [salpd is bis(salicylidene)-2,2-dimethyl-1,3-propanediaminate; Arici et al., 2001] and [Ni(-)(chxn)(hapi)₂] (hapi is ??; Szlyk et al., 1999) complexes (see Table 3), where the bridging moiety between the two imine N atoms has methyl substitution, is due to the steric requirements imposed by the interaction between the bulky methyl group and other H atoms of the ligand. The whole ligand in (I), however, is not planar; the bridging benzyl moiety (L3) is inclined to the 5-bromosalicylideneimne planes L1 and L2 by 56.2 (1) and 60.7 (1)°, respectively. The bridging chelate ring composed of atoms Ni, N1, C8, C13, C14 and N2 has a distorted boat conformation, with ring puckering parameters (Cremer & Pople, 1975) Q = 0.684 (3) Å, θ = 97.5 (3)° and ϕ = 68.5 (3)°. The distances of the two para-positioned boat atoms, N1 and C14, from the mean plane of the six atoms are 0.435 (2) and 0.715 (3) Å, respectively. The Ni—N and Ni—O bond distances (Table 1) are in good agreement with those observed in similar Ni^II–Schiff base complexs (Santos et al., 2000; Szlyk et al., 1999). ??The fact that the Ni—N bond distances in (I) are slightly longer than those in these related compounds may be attributed to the steric hindrance of the benzyl group between the N atoms, which is bulkier than the bridging groups in these related compounds. The slightly longer Ni—N bond distances in (I) may be attributed to the steric hindrance of the bulky benzyl group between the N atoms. Other bond distances and angles in (I) are within the ranges found for related structures (Elmali et al., 2000; Elerman et al., 1998).

Molecules of (I) are linked by two different C—H····O hydrogen bonds (Table 2) into centrosymmetric dimers, in which one of the phenolate O atoms acts as a double acceptor. Phenyl atom C9 at (x, y, z) acts as a hydrogen-bond donor to O2 at (-x, −y + 1, −z + 1), thus forming a dimer characterized by an R₂²(12) motif (A) with an inversion centre at (0, 1/2, 1/2). Similarly, atom C14 at (x, y, z) acts as a donor to atom O2 at (-x + 1, −y + 1, −z + 1), generating an R₂²(10) ring (B) with an inversion centre at (1/2, 1/2, 1/2). These two dimers combine to form a supramolecular aggregate, ABAB···, which propagates along [100] (Fig. 2). The observed Ni···Ni distance, 3.480 (3) Å, in (I) is well within the values reported [3.201 (1)–3.582 (1) Å] for analogous Schiff base complexes (de Castro et al., 2001; Encan et al., 1997; Wojtczak et al., 1997) with Ni···Ni interactions.

S2. Experimental

The ligand 4-bromo-2-[2-(5-bromo-2-hydroxybenzylideneaminomethyl)phenyliminomethyl]phenol (H₂L) was prepared by condensation of 5-bromosalicylaldehyde (10 mmol, 2.01 g) and 2-aminobenzylamine (5 mmol, 0.61 g) in methanol (50 ml). The reaction mixture was stirred for 1 h and the resulting solution was used without further purification. Ni(ClO₄)₂·6H₂O (1 mmol, 0.366 g) was dissolved in methanol (20 ml) and the methanol solution of the ligand (H₂L, 1 mmol) was added dropwise. A brown compound, NiL, (I), was obtained on keeping the solution at room temperature (298 K) for three days. Recrystallization from dichloromethane yielded single crystals of (I), which were collected by filtration and air-dried (yield 65%). Analysis found: C 46.31, H 2.55, N 5.16%; calculated for C₂₁H₁₄Br₂N₂O₂NI; C 46.24, H 2.57, N 5.14%. IR (cm⁻¹): 1605 (C—N), 1320 (C—O), 2300–2840 (N—H), 535 (Ni—N), 405 (Ni—O). The broad band around 620 nm in the UV spectrum can be assigned to d–d transition in the complex and suggests an approximate square-planar or tetrahedral metal coordination.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SMART (Bruker, 1998); data reduction: SMART; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and CAMERON (Watkin et al., 1993); software used to prepare material for publication: SHELXL97 and PARST95 (Nardelli, 1995).

Figures

	Fig. 1. : An ORTEP-3 (Farrugia, 1997) view (50% probability level) of the molecule of (I).
	Fig. 2. : A view of the packing of the unit cell of (I), along the c axis, showing the formation of dimers.

{4-Bromo-2-[2-(5-bromo-2- oxidobenzylideneaminomethyl)phenyliminomethyl]phenolato- κ⁴O,N,N',O'}nickel(II)

Crystal data

[Ni(C21H14Br2N2O2)]	Z = 2
Mr = 544.87	F(000) = 536
Triclinic, P1	Dx = 1.873 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.228 (5) Å	Cell parameters from 110 reflections
b = 10.834 (7) Å	θ = 1.2–26.0°
c = 12.831 (8) Å	µ = 5.16 mm^−1
α = 100.09 (1)°	T = 293 K
β = 99.83 (1)°	Needle, brown
γ = 95.63 (1)°	0.35 × 0.12 × 0.10 mm
V = 966.2 (11) Å^3

Data collection

Bruker SMART CCD area-detector diffractometer	3752 independent reflections
Radiation source: fine-focus sealed tube	2981 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.024
ϕ and ω scans	θmax = 26.0°, θmin = 1.6°
Absorption correction: multi-scan (SADABS; Sheldrich, 1996)	h = −8→8
Tmin = 0.299, Tmax = 0.597	k = −13→13
9936 measured reflections	l = −15→15

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)] = 0.033	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.082	H-atom parameters constrained
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0412P)^2 + 0.2635P] where P = (Fo^2 + 2Fc^2)/3
3752 reflections	(Δ/σ)max = 0.001
253 parameters	Δρmax = 0.74 e Å^−3
0 restraints	Δρmin = −0.39 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Br1	0.15193 (6)	0.31365 (4)	0.97644 (3)	0.06638 (14)
Br2	0.38440 (6)	0.88639 (4)	0.06741 (3)	0.06703 (14)
Ni	0.25506 (5)	0.48784 (4)	0.46153 (3)	0.03464 (12)
O1	0.2083 (3)	0.5570 (2)	0.59536 (16)	0.0418 (5)
O2	0.3168 (3)	0.6568 (2)	0.45556 (16)	0.0437 (5)
N1	0.1594 (3)	0.3215 (2)	0.47186 (19)	0.0354 (6)
N2	0.3346 (3)	0.4315 (2)	0.33175 (19)	0.0364 (6)
C1	0.1910 (4)	0.5004 (3)	0.6751 (2)	0.0372 (7)
C2	0.1931 (5)	0.5738 (3)	0.7784 (3)	0.0449 (8)
H2	0.2016	0.6614	0.7870	0.054*
C3	0.1829 (5)	0.5190 (3)	0.8651 (3)	0.0476 (8)
H3	0.1874	0.5693	0.9324	0.057*
C4	0.1657 (4)	0.3880 (3)	0.8536 (2)	0.0437 (8)
C5	0.1528 (4)	0.3124 (3)	0.7554 (2)	0.0439 (8)
H5	0.1353	0.2249	0.7481	0.053*
C6	0.1659 (4)	0.3674 (3)	0.6646 (2)	0.0384 (7)
C7	0.1380 (4)	0.2877 (3)	0.5618 (2)	0.0402 (7)
H7	0.1005	0.2022	0.5582	0.048*
C8	0.0813 (4)	0.2291 (3)	0.3753 (2)	0.0396 (7)
C9	−0.0956 (5)	0.1594 (3)	0.3643 (3)	0.0490 (8)
H9	−0.1649	0.1718	0.4191	0.059*
C10	−0.1669 (6)	0.0710 (3)	0.2698 (3)	0.0617 (10)
H10	−0.2827	0.0214	0.2625	0.074*
C11	−0.0674 (6)	0.0565 (3)	0.1871 (3)	0.0605 (10)
H11	−0.1166	−0.0022	0.1240	0.073*
C12	0.1062 (5)	0.1292 (3)	0.1977 (3)	0.0482 (8)
H12	0.1717	0.1201	0.1410	0.058*
C13	0.1825 (5)	0.2155 (3)	0.2923 (2)	0.0403 (7)
C14	0.3681 (5)	0.2981 (3)	0.3073 (3)	0.0436 (8)
H14A	0.4576	0.2795	0.3662	0.052*
H14B	0.4204	0.2824	0.2422	0.052*
C15	0.3598 (4)	0.4982 (3)	0.2605 (2)	0.0395 (7)
H15	0.3887	0.4568	0.1966	0.047*
C16	0.3472 (4)	0.6300 (3)	0.2708 (2)	0.0379 (7)
C17	0.3652 (4)	0.6861 (3)	0.1820 (3)	0.0446 (8)
H17	0.3762	0.6364	0.1170	0.054*
C18	0.3666 (5)	0.8132 (3)	0.1905 (3)	0.0484 (8)
C19	0.3590 (5)	0.8884 (3)	0.2881 (3)	0.0543 (9)
H19	0.3633	0.9755	0.2939	0.065*
C20	0.3453 (5)	0.8360 (3)	0.3762 (3)	0.0507 (8)
H20	0.3431	0.8882	0.4416	0.061*
C21	0.3343 (4)	0.7036 (3)	0.3701 (2)	0.0392 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0905 (3)	0.0754 (3)	0.0369 (2)	0.0132 (2)	0.01485 (19)	0.01729 (18)
Br2	0.0848 (3)	0.0696 (3)	0.0559 (2)	0.0092 (2)	0.0183 (2)	0.0327 (2)
Ni	0.0384 (2)	0.0337 (2)	0.0302 (2)	0.00363 (16)	0.00510 (16)	0.00402 (16)
O1	0.0528 (13)	0.0383 (12)	0.0337 (11)	0.0064 (10)	0.0098 (10)	0.0040 (9)
O2	0.0593 (14)	0.0367 (12)	0.0341 (12)	0.0024 (10)	0.0095 (10)	0.0062 (9)
N1	0.0385 (14)	0.0347 (14)	0.0317 (13)	0.0034 (11)	0.0060 (11)	0.0047 (11)
N2	0.0363 (13)	0.0367 (14)	0.0347 (14)	0.0057 (11)	0.0060 (11)	0.0033 (11)
C1	0.0299 (15)	0.0440 (18)	0.0360 (17)	0.0042 (13)	0.0056 (13)	0.0039 (14)
C2	0.053 (2)	0.0424 (19)	0.0379 (18)	0.0085 (15)	0.0094 (15)	0.0010 (14)
C3	0.0491 (19)	0.058 (2)	0.0332 (17)	0.0092 (16)	0.0082 (14)	0.0002 (15)
C4	0.0426 (18)	0.056 (2)	0.0330 (17)	0.0067 (15)	0.0073 (14)	0.0107 (15)
C5	0.0485 (19)	0.047 (2)	0.0365 (18)	0.0052 (15)	0.0069 (14)	0.0116 (15)
C6	0.0353 (16)	0.0432 (18)	0.0340 (17)	0.0032 (14)	0.0038 (13)	0.0042 (14)
C7	0.0428 (18)	0.0371 (17)	0.0396 (18)	0.0047 (14)	0.0065 (14)	0.0066 (14)
C8	0.0466 (18)	0.0347 (17)	0.0342 (16)	0.0040 (14)	0.0026 (14)	0.0033 (13)
C9	0.054 (2)	0.0430 (19)	0.0444 (19)	−0.0040 (16)	0.0050 (16)	0.0042 (15)
C10	0.067 (2)	0.048 (2)	0.057 (2)	−0.0114 (18)	−0.0020 (19)	0.0004 (18)
C11	0.083 (3)	0.043 (2)	0.043 (2)	−0.003 (2)	−0.0016 (19)	−0.0034 (16)
C12	0.071 (2)	0.0385 (19)	0.0352 (17)	0.0136 (17)	0.0084 (16)	0.0047 (14)
C13	0.0528 (19)	0.0322 (17)	0.0351 (17)	0.0115 (14)	0.0049 (14)	0.0046 (13)
C14	0.052 (2)	0.0412 (18)	0.0393 (17)	0.0141 (15)	0.0129 (15)	0.0049 (14)
C15	0.0346 (16)	0.050 (2)	0.0313 (16)	0.0039 (14)	0.0022 (13)	0.0062 (14)
C16	0.0329 (15)	0.0430 (18)	0.0368 (17)	0.0027 (13)	0.0023 (13)	0.0105 (14)
C17	0.0401 (18)	0.055 (2)	0.0380 (18)	0.0041 (15)	0.0037 (14)	0.0124 (15)
C18	0.0474 (19)	0.056 (2)	0.047 (2)	0.0035 (16)	0.0083 (15)	0.0259 (17)
C19	0.066 (2)	0.0412 (19)	0.060 (2)	0.0049 (17)	0.0154 (19)	0.0189 (17)
C20	0.064 (2)	0.0401 (19)	0.050 (2)	0.0069 (17)	0.0191 (17)	0.0087 (16)
C21	0.0384 (17)	0.0408 (18)	0.0372 (17)	0.0021 (14)	0.0042 (13)	0.0090 (14)

Geometric parameters (Å, º)

Br1—C4	1.904 (3)	C8—C9	1.391 (5)
Br2—C18	1.905 (3)	C9—C10	1.391 (5)
Ni—O1	1.850 (2)	C9—H9	0.9300
Ni—O2	1.859 (2)	C10—C11	1.376 (5)
Ni—N2	1.875 (3)	C10—H10	0.9300
Ni—N1	1.901 (3)	C11—C12	1.387 (5)
O1—C1	1.299 (4)	C11—H11	0.9300
O2—C21	1.306 (4)	C12—C13	1.387 (4)
N1—C7	1.299 (4)	C12—H12	0.9300
N1—C8	1.439 (4)	C13—C14	1.501 (5)
N2—C15	1.286 (4)	C14—H14A	0.9700
N2—C14	1.477 (4)	C14—H14B	0.9700
C1—C6	1.414 (5)	C15—C16	1.423 (5)
C1—C2	1.417 (4)	C15—H15	0.9300
C2—C3	1.359 (5)	C16—C17	1.401 (4)
C2—H2	0.9300	C16—C21	1.403 (4)
C3—C4	1.392 (5)	C17—C18	1.361 (5)
C3—H3	0.9300	C17—H17	0.9300
C4—C5	1.361 (4)	C18—C19	1.382 (5)
C5—C6	1.411 (4)	C19—C20	1.364 (5)
C5—H5	0.9300	C19—H19	0.9300
C6—C7	1.416 (4)	C20—C21	1.416 (5)
C7—H7	0.9300	C20—H20	0.9300
C8—C13	1.387 (4)
O1—Ni—O2	82.64 (10)	C10—C9—H9	120.6
O1—Ni—N2	172.20 (10)	C11—C10—C9	120.4 (4)
O2—Ni—N2	92.46 (10)	C11—C10—H10	119.8
O1—Ni—N1	92.65 (10)	C9—C10—H10	119.8
O2—Ni—N1	172.06 (10)	C10—C11—C12	120.2 (3)
N2—Ni—N1	92.87 (11)	C10—C11—H11	119.9
C1—O1—Ni	127.9 (2)	C12—C11—H11	119.9
C21—O2—Ni	127.22 (19)	C13—C12—C11	120.4 (3)
C7—N1—C8	115.7 (3)	C13—C12—H12	119.8
C7—N1—Ni	124.0 (2)	C11—C12—H12	119.8
C8—N1—Ni	119.82 (19)	C12—C13—C8	119.0 (3)
C15—N2—C14	116.6 (3)	C12—C13—C14	122.6 (3)
C15—N2—Ni	125.8 (2)	C8—C13—C14	118.4 (3)
C14—N2—Ni	117.6 (2)	N2—C14—C13	108.4 (2)
O1—C1—C6	123.4 (3)	N2—C14—H14A	110.0
O1—C1—C2	119.4 (3)	C13—C14—H14A	110.0
C6—C1—C2	117.2 (3)	N2—C14—H14B	110.0
C3—C2—C1	121.4 (3)	C13—C14—H14B	110.0
C3—C2—H2	119.3	H14A—C14—H14B	108.4
C1—C2—H2	119.3	N2—C15—C16	125.8 (3)
C2—C3—C4	120.3 (3)	N2—C15—H15	117.1
C2—C3—H3	119.8	C16—C15—H15	117.1
C4—C3—H3	119.8	C17—C16—C21	120.8 (3)
C5—C4—C3	120.9 (3)	C17—C16—C15	118.2 (3)
C5—C4—Br1	119.6 (3)	C21—C16—C15	120.7 (3)
C3—C4—Br1	119.4 (2)	C18—C17—C16	120.2 (3)
C4—C5—C6	119.7 (3)	C18—C17—H17	119.9
C4—C5—H5	120.2	C16—C17—H17	119.9
C6—C5—H5	120.2	C17—C18—C19	120.2 (3)
C5—C6—C1	120.4 (3)	C17—C18—Br2	119.3 (3)
C5—C6—C7	118.9 (3)	C19—C18—Br2	120.5 (3)
C1—C6—C7	120.5 (3)	C20—C19—C18	120.5 (3)
N1—C7—C6	126.7 (3)	C20—C19—H19	119.7
N1—C7—H7	116.6	C18—C19—H19	119.7
C6—C7—H7	116.6	C19—C20—C21	121.4 (3)
C13—C8—C9	121.1 (3)	C19—C20—H20	119.3
C13—C8—N1	118.5 (3)	C21—C20—H20	119.3
C9—C8—N1	120.4 (3)	O2—C21—C16	123.6 (3)
C8—C9—C10	118.9 (3)	O2—C21—C20	119.6 (3)
C8—C9—H9	120.6	C16—C21—C20	116.8 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C9—H9···O2^i	0.93	2.68	3.484 (4)	145
C14—H14A···O2^ii	0.97	2.51	3.403 (4)	152

Symmetry codes: (i) −x, −y+1, −z+1; (ii) −x+1, −y+1, −z+1.