Syntheses, Characterization and X-ray Crystal Structure of Trinuclear Ni II —Na I —Ni II Assembled with Salen-type Schiff Base

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Introduction
Heteronuclear complexes assembled with Schiff bases are widely examined in the past year.Ligands with smaller N 2 O 2 and larger O 2 O 2 cages are suitable for assembling heteronuclear with a 3d metal ions and a s-, p-, d-or f-block metal ions.Schiff bases with two cavities of different sizes which can accommodate metal ions of different sizes have 154 been synthesized using condensation reaction between well-selected keto precursors and diamines [1][2][3].Trinuclear complexes formed by two 3d metals with organic ligand in which the 3d metal atom is situated in the smaller N 2 O 2 cage and one s-, d-or fblockmetal ion is coordinated to larger O 2 O 2 cage have been reported [4][5][6][7][8][9][10][11][12][13].Two different strategies are developed for preparing heteronuclear complexes.The first method called self-assembly method is widely used to prepare 3d/4f complexes with remarkable properties [14][15][16][17][18][19][20].The second method consists in preparing, in first step, a precursor complex called metalloligand, [13,21] which is used in a second step as ligand for preparing the heteronuclear complex.Our synthetic approach consists in using a nickel(II)-based metalloligand [NiL] .(H 2 O) as precursor synthesized from the bicompartmental Schiff ligand bis(2-hydroxy-3-methoxybenzylidene)-1,2-diaminobenzene.

Starting materials and instrumentations
o-Vanillin and 1,3-diaminobenzene, nickel chloride dihydrate, and sodium thiocyanate were purchased from Sigma-Aldrich and used as received without further purification.All solvents used were of reagent grade.The ligand bis(2-hydroxy-3methoxybenzylidene)-1,2-diaminobenzene(H 2 L) was synthesized following the reported procedure [22].Elemental analyses of C, H and N were recorded on a VxRio EL Instrument.Infrared spectra were obtained on an FTIR Spectrum Two of Perkin Elmer spectrometer in the 4000-400 cm -1 region.The molar conductance of 1×10 -3 M in DMSO solutions of the metal complexes was measured at 25 °C using a WTW LF-330 conductivity meter with a WTW conductivity cell.Room temperature magnetic susceptibilities of the powdered samples were measured using a Johnson Mattey scientific magnetic susceptibility balance (Calibrant: Hg[Co(SCN) 4 ]).The compound 1 is obtained following the reported procedure with slight modification [22].In a round bottomed flask, the ligand (H 2 L) (10 mmol, 0.374 g) was dissolved in 5 mL of acetonitrile.A solution of NiCl 2 .6H 2 O (10 mmol, 0.2370 g) in 5 mL of ethanol was added.After two hours under reflux, the brown precipitate was recovered by filtration, washed with ether (2 x 10 mL) and dried in air.The compound was formulated as [NiL]   To a solution of [NiL] .(H 2 O) (1) (1 mmol, 0.4511 g) in 5 mL of DMF was added a solution of NaNO 3 (3 mmol, 0.255 g) in 5 mL of ethanol.The mixture was refluxed for two hours.On cooling yellow solution was filtered.The filtrate was left for slow evaporation.On standing for two weeks, yellow crystals of ( 2

Crystal structure determination
Crystals suitable for single-crystal X-ray diffraction, of the reported compounds, were grown by slow evaporation of MeOH solution of the complexes.Details of the crystal structure solution and refinement are given in Table 1.Diffraction data were collected using an ENRAF NONIUS Kappa CCD diffractometer with graphite monochromatized MoKα radiation (λ = 0.71073 Å).All data were corrected for Lorentz and polarization effects.No absorption correction was applied.Complex scattering factors were taken from the program package SHELXTL [23].The structures were solved by direct methods, which revealed the position of all non-hydrogen atoms.All the structures were refined on F 2 by a full-matrix least-squares procedure using anisotropic displacement parameters for all non-hydrogen atoms [24].The hydrogen atoms of water 157 molecules and NH groups were located in the Fourier difference maps and refined.Others H atoms (CH and CH 3 groups) were geometrically optimized and refined as riding model by AFIX instructions.Molecular graphics were generated using ORTEP [25].  .The band at 3319 cm -1 in the metalloligand spectrum is due to the free water molecule.Upon reaction of the metalloligand with Na(I) cation the resulting compound gives a FTIR spectrum which is similar to the spectrum of the metalloligand.All band are slightly shifted to low frequencies.Shifted.The band due to the ν C-O(methyl) is shifted from 1201 cm -1 in the spectrum of (1) to 1192 cm -1 in the spectrum of (2) indicating the involvement of the methoxy oxygen atom to the coordination to the Na(I).New sharp bands appear at 2057 cm -1 , 749 cm -1 and 487 cm -1 and are attributed, respectively, to ν as (CN), ν s (CS) and (SCN) of the uncoordinated thiocyanate moiety [26] present in the trinuclear compound.The molar conductance in DMF of compound 1 is 3 S .cm 2 .mol -1 , while the conductance of 2 is 62 S .cm 2 .mol -1 .These values indicate that the compound 1 is a neutral electrolyte while the compound 2 is 1:1 electrolyte The detailed crystallographic data for the compound is listed in Table 1.Selected interatomic distances and angles are shown in Table 2.The compound crystallizes in the 159 tetragonal system with the space group I4 1 /acd.The crystal structure of the complex is shown in Figure2 and comprises two Ni(II) cation, one Na(I) cation, two di-negative ligand, one free chloride anion and one free thiocyanate anion.Each ligand acts as bridge between one Ni(II) cation and the Na(I).The Ni(II) is coordinated to the ligand through two azomethine nitrogen atoms and two phenoxo oxygen atoms.These two phenoxo oxygen atoms link the Na(II) cation which is also coordinated to two methoxy oxygen atoms.Thus, the two Ni(II) are tetracoordinated while the Na(I) is octacoordinated.In the trinuclear complex, both Ni ions are situated in an N 2 O 2 environment which can be characterized by tetragonality parameter: τ 4 = (360 -α -β) / 141 : α and β are the two largest angles around the central atom; τ 4 = 0 designates a perfect square planar geometry and t 4 = 1 gives a perfect tetrahedron) [29].The τ 4 value of 0.0094 is indicative of a slightly distorted square planar geometry around the Ni atoms.The Ni-O [1.852(4)Å and 1.845( 4) Å] and Ni-N [1.850(5) Å and 1.853( 5) Å] are comparable to the Ni-O and Ni-N bonds lengths reported for the metalloligand complex [30].The Na(I) cation is situated in an O 8 environment.The environment around the Na(I) is best described as a distorted square-antiprism (Figure 3).The two square faces are occupied, respectively, by two phenoxo oxygen atoms of the same ligand and two methoxy oxygen atoms from two different ligand molecules: O2, O3, O1 and O1 i and O2 i , O3 i O4 and O4 i .The bonds lengths of Na-O phenoxo [2.396(4) Å and 2.389(4) Å] are shorter than the distances Na-O methoxy [2.538(4) Å and 2.554(4) Å].These values are comparable to those reported for the complex [Zn(μ-L)Na(NO 3 )(EtOH)] [11].The dihedral angle between the two phenyl rings (C2-C7 and C9-C14) with methoxy group is 3.870(4)°,while these rings form with the central phenyl ring (C16-C21) dihedral angles of 11.1233(4)° and 14.138(3)°, respectively.Each ligand form with the Ni(II) two six membered rings of type NiOCCCN with bites angles of 95.39( 18 3).

Conclusion
In this work, we have successfully synthesized a trinuclear compound formulated as {Ni(-L)Na(-L)Ni} .(SCN) 0.6 .(Cl) 0.4 (2) using the metalloligand [NiL] .(H 2 O)(1) firstly isolated.Suitable crystal for X-ray analyzes was obtained by slow evaporation of methanol solution of 2 for few days.The metalloligand and the complex are studied by FTIR, room temperature magnetic moment measurement and conductance measurement.X-ray data collection, data reduction and structure refinement of complex 2 revealed the structure of the trinuclear complex.The two Ni(II) ions tetracoordinated and are situated in square planar environment defined by O 2 O 2 cavity and the Na(I) which is octacoordinated is situated in a square antiprism environment define by a O 8 inner.Weak inter and intra molecular hydrogen bonds consolidate the structure.

3 . Result and Discussion 3 . 1 .
. of parameters/restraints 295 / 0 Δρ max , Δρ min (e Å -3 ) 1.10, −0.57158 General study The metallo ligand [Ni(L)] .H 2 O (1) was synthesized by mixing the ligand H 2 L and NiCl 2 .6H 2 O in acetonitrile under reflux.The resulting [Ni(L)] .H 2 O (1) was reacted with sodium nitrate and ammonium thiocyanate in molar ratio 1:3:3to yield a trinuclear complex formulated as {Ni(-L)Na(-L)Ni} .(C 2 N 2 S) .(Cl) (2) after slow evaporation of the filtrate.The IR spectrum of the ligand is compared to the spectrum of the metalloligand.The band due to the ν C=N with appears at 1632 cm -1 in the spectrum of the ligand is shifted to low frequency in the spectrum of the metalloligand and appears at 1615 cm -1 .This fact indicates the involvement of the azomethine nitrogen atom to the coordination to the Ni(II) cation.The involvement of the phenoxy oxygen atom to the coordination is assumed by shift of the ν C-O(phenolic) which is pointed at 1248 cm -1 in the spectrum of H 2 L and at 1242 cm -1 in the spectrum of [Ni(L)] .H 2 O.The methoxy oxygen atoms remain uncoordinated as attested by the non-shift of its band pointed in both spectra at 1201 cm -1

Figure 3 .
Figure 3. Plot showing the coordination sphere of the sodium ion in the crystal.

Figure 4 .
Figure 4. View of the title complex along the b axis showing the sheets formed by hydrogen bonding.The sheets separated by chloride anion. 163 ) suitable for X-ray diffraction were isolated.Yield: 74 %.Elemental Anal.Found (Calcd.)for C 46.6 H 36 Cl 0.4 N 4.6 NaNi 2 O 8 S 0.