Tridentate Reduced Schiff Base Ligand Research Articles

Variation of carboxylate binding mode in self-assembled Ni(II) complexes with tridentate reduced Schiff base ligand: Syntheses, structural analysis

Variation of carboxylate binding mode in self-assembled Ni(II) complexes with tridentate reduced Schiff base ligand: Syntheses, structural analysis

Application of two Cu(II)-azido based 1D coordination polymers in optoelectronic device: Structural characterization and experimental studies

Two new azido bridged 1D polymeric Cu(II) chains, [Cu(L1)(μ1,3-N3)]∞ (1) and [Cu2(L2)2(μ1,1-N3)(μ1,3-N3)]∞ (2) have been synthesized by using two different N2O donor tridentate reduced Schiff base ligands, HL1 = 2-[(2-dimethylamino-ethylamino)-methyl]-4-nitrophenol, HL2 = 2-[(2-diethylamino-ethylamino)-methyl]-4-nitrophenol and both are structurally characterized. Cu(II) ions in both complexes occupy distorted pentacoordinated square pyramidal geometry. Both structures form polymeric chains, in 1, via μ1,3-N3− while in 2via both μ1,1-N3− and μ1,3-N3− bridges. The band gaps of the complexes (2.91 eV for 1 and 2.89 eV for 2) suggest that both polymeric chains are semiconducting and thus possess the potential for uses in devices. A detail I–V analysis was performed to measure device related parameters i.e. effective carrier mobility, transit time, carrier concentration, diffusion length and ideality factor. The results show that both polymeric chains behave as Schottky barrier diodes (SBD) and could be used in opto-electronic device. Between the two complexes, 2 performs better than 1 in terms of applicability as indicated by the calculated parameters.

Formation of a carbonato bridged Ni4-complex by atmospheric CO2 fixation: Crystal structure and magnetic properties

Reaction of NiCl2·6H2O with a simple N2O donor tridentate reduced Schiff base ligand, 2-[(3-methylamino-propylamino)-methyl]-4-nitro-phenol (HL) yielded a tetranuclear complex, [Ni4L4Cl2(µ4-CO3)(CH3CN)2]·0.5CH3CN·H2O (1) which was structurally characterized. Complex 1 is an example of atmospheric CO2 fixation model with uniqueness in a new µ4-κ2:κ2:ƞ1:ƞ1-carbonato coordination mode to Ni(II). Involvement of this type of NNO donor ligands for the synthesis of carbonato bridged polynuclear compounds by spontaneous atmospheric CO2 fixation is very rare. All Ni(II) ions are in octahedral environment in 1 with phenoxido and hexadentate µ4-carbonato bridging. Variable temperature magnetic measurements showed overall antiferromagnetic coupling between Ni(II) centers with J1 = −60.32 cm−1, J2 = −19.52 cm−1, J3 = 2.6 cm−1 and J4 = 3.3 cm−1. The magnetic behavior of the complex has been explained considering the carbonato and phenoxido bridging angles.

Ni(II) Dimers of NNO Donor Tridentate Reduced Schiff Base Ligands as Alkali Metal Ion Capturing Agents: Syntheses, Crystal Structures and Magnetic Properties

Three trinuclear Ni(II)-Na(I) complexes,[Ni2(L1)2NaCl3(H2O)]·H2O (1), [Ni2(L2)2NaCl3(H2O)] (2), and [Ni2(L3)2NaCl3(OC4H10)] (3) have been synthesized using three different NNO donor tridentate reduced Schiff base ligands, HL1= 2-[(3-methylamino-propylamino)-methyl]-phenol, HL2= 2-[(3-methylamino-propylamino)-methyl]-4-chloro-phenol, and HL3= 2-[(3-methylamino-propylamino)-methyl]-6-methoxy-phenol that had been structurally characterized. Among these complexes, 1 and 2 are isostructural in which dinuclearNi(II) units act as metalloligands to bind Na(I) ions via phenoxido and chlorido bridges. The Na(I) atom is five-coordinated, and the Ni(II) atom possesses hexacordinated distorted octahedral geometry. In contrast, in complex 3, two -OMe groups from the dinuclear Ni(II) unit also coordinate to Na(I) to make its geometry heptacordinated pentagonal bipyramidal. The magnetic measurements of complexes 1–3 indicate ferromagnetic interactions between dimeric Ni(II) units with J = 3.97 cm−1, 4.66 cm−1, and 5.50 cm−1for 1–3, respectively, as is expected from their low phenoxido bridging angles (89.32°, 89.39°, and 87.32° for 1–3, respectively). The J values have been calculated by broken symmetry DFT method and found to be in good agreement with the experimental values.

Synthesis and Crystal Structure of N-(2-Pyridylmethyl)-L-Alanine) Isothiocyanate Cobalt(III)

The title compound, [N-(2-pyridylmethyl)-(L)-alanine]Co(III) thiocyanate (1) was obtained from the reaction of Co(OOCH3)2·H2O with the tridentate reduced Schiff base ligand, N-(2-pyridylmethyl)-(L)-alanine (L) and NH4SCN and characterized by elemental analysis, IR, UV-visible, TGA and single- crystal X-ray diffraction. Structural and spectroscopic analyses reveal [Co(L)2)]SCN to be monomeric with Cobalt(III) adopting a pseudo-octahedral geometry, coordinating to two reduce Schiff base ligands. In the crystal lattice, the thiocyanate anion forms an intermolecular SCN···HNamine hydrogen bond, while adjacent monomers are linked by intermolecular Ocarboxyl···HNamine···H-bonds to form a supramolecular network. This work is therefore undertaken in an attempt to construct coordination framework structures of varying properties using the mixed-ligand strategy involving reduced Schiff bases and the thiocyanate ion.

Formation of a dinuclear and a trinuclear Ni(II) complex on slight variation of experimental conditions: Structural analysis and magnetic properties

A diphenoxido bridged dinuclear Ni(II) complex [Ni2L2(NO2)2] (1) and a μ2 and μ3-phenoxido, μ3-hydroxido, and μ2-nitrito (1κO:2κN) bridged trinuclear Ni(II) complex [Ni3L3(OH)(NO2)]·ClO4 (2), have been synthesized using a tridentate reduced Schiff base ligand HL (HL=2-[(2-dimethylamino-ethylamino)-methyl]-phenol). Both complexes were characterized by X-ray structure determination and variable-temperature magnetic susceptibility measurements. In both complexes the nickel atoms are six-coordinated with a distorted octahedral environment. The interesting feature of the trimeric complex 2 is that the three mononuclear units are assembled around a μ3-hydroxido ion in such a way that the three phenoxido groups and one nitrito group form a cyclic bridge that markedly modify the magnetic properties. Complex 1 presents a moderate antiferromagnetic Ni–Ni coupling (J=−39cm−1) through the phenoxido bridges with a wide Ni–O–Ni bond angle of 101.77(6)° whereas the lower Ni–O–Ni bond angles, in the range 86.66(6)–96.07(7)°, lead to a moderate ferromagnetic coupling (J=+18.2cm−1) in the trimeric complex 2 with a weak antiferromagnetic contribution (J′=−0.51cm−1) via the 1κO:2κN nitrito bridge.

Deactivation of catecholase-like activity of a dinuclear Ni(II) complex by incorporation of an additional Ni(II)

A new dinuclear Ni(II) complex [Ni2L2(PhCOO)(H2O)2]ClO4 (1) has been synthesized by reacting Ni(ClO4)2·6H2O with a reduced Schiff base ligand [(3-dimethylamino-propylamino)-methyl]-phenol (HL) in presence of benzoic acid in 1:1:1 ratios. Structural analysis reveals that complex 1 is a di-μ2-phenoxo-bridged dinuclear Ni(II) complex and has an additional syn-syn benzoate bridge. Enzyme kinetic studies reflect that it (1) is effective in mimicking catecholase like activity with 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate. Kinetic measurements suggest that the rate of catechol oxidation follows first order kinetics with respect to the catalyst. The possible intermediates during the course of reaction are identified from ESI–MS spectra. The characteristic EPR spectra of the complex in the presence of 3,5-DTBC supports the formation of nickel(II)-semiquinonate as an intermediate species during the catalytic oxidation. When the synthesis is carried out with Ni(II) : HL ratio of 3:2, a different compound [Ni3L2(PhCOO)4] (2) is produced incorporating an additional Ni(II)-benzoate. 2 possesses a linear trinuclear structure with the tridentate reduced Schiff base ligand coordinated to the terminal nickel atoms which are linked to the central Ni(II) by phenoxo and carboxylate bridges. Unlike 1, it does not show any catalytic activity towards catechol oxidation. Variable temperature magnetic susceptibility measurements have also been performed for 1 and 2. Complex 1 indicates the presence of intradimer antiferromagnetic interactions (J=−5.65cm−1). In contrast to complex 1, ferromagnetic coupling (J=3.55cm−1) is observed in complex 2.

Methylene bridge regulated geometrical preferences of ligands in cobalt(iii) coordination chemistry and phenoxazinone synthase mimicking activity

Two new azide bound cobalt(III) complexes, [Co(L(1))(N3)3] (fac-1) and [Co(L(2))(N3)3] (mer-2), where L(1) is bis(2-pyridylmethyl)amine and L(2) is (2-pyridylmethyl)(2-pyridylethyl)amine, derived from tridentate reduced Schiff-base ligands have been reported. Interestingly, a methylene bridge regulated preferential coordination mode of ligands is noticed in their crystal structures: it is found in a facial arrangement in fac-1 and has a meridional disposition in mer-2. Both complexes show phenoxazinone synthase-like activity and the role of the structural factor on the catalytic activity is also explored. Moreover, the easily reducible cobalt(III) center in mer-2 favors the oxidation of o-aminophenol. The ESI-MS positive spectra together with UV-vis spectroscopy clearly suggest the formation of a catalyst-substrate adduct by substitution of the coordinated azide ions in the catalytic cycle.

Solvomorphism and catecholase activities of bis(μ-phenoxido)dicopper(II) complexes

Two phenoxido bridged dinuclear Cu(II) complexes, [Cu2(L1)2(NCO)2] (1), and [Cu2(L2)2(NCO)2]·2CH3OH (2), have been synthesized using the tridentate reduced Schiff-base ligands 2-[(2-dimethylamino-ethylamino)-methyl]-phenol (HL1) and 2-[(2-diethylamino-ethylamino)-methyl]-phenol (HL2) respectively. Re-crystallization of compound 2 from dichloromethane produced desolvated complex [Cu2(L2)2(NCO)2] (3). The compounds 2 and 3 are pseudopolymorphs or solvomorphs which differ in the crystal system (orthorhombic, Pbca for 2 and monoclinic, P21/n for 3). The complexes have been characterized by X-ray structural analyses and spectroscopic methods. In all three complexes Cu(II) is penta-coordinated having the geometry intermediate between distorted square pyramid and trigonal bipyramid with Addison parameter (τ)=0.33, 0.48 and 0.53 for 1, 2 and 3 respectively. Using 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate, the catecholase activity of complexes 1 and 2 has been studied in methanol solution; compound 2 shows slightly higher catecholase activity (kcat=98.4h−1) than compound 1 (kcat=64.2h−1).

Insertion of a Hydroxido Bridge into a Diphenoxido Dinuclear Copper(II) Complex: Drastic Change of the Magnetic Property from Strong Antiferromagnetic to Ferromagnetic and Enhancement in the Catecholase Activity

A diphenoxido-bridged dinuclear copper(II) complex, [Cu(2)L(2)(ClO(4))(2)] (1), has been synthesized using a tridentate reduced Schiff base ligand, 2-[[2-(diethylamino)ethylamino]methyl]phenol (HL). The addition of triethylamine to the methanolic solution of this complex produced a novel triple bridged (double phenoxido and single hydroxido) dinuclear copper(II) complex, [Cu(2)L(2)(OH)]ClO(4) (2). Both complexes 1 and 2 were characterized by X-ray structural analyses, variable-temperature magnetic susceptibility measurements, and spectroscopic methods. In 1, the two phenoxido bridges are equatorial-equatorial and the species shows strong antiferromagnetic coupling with J = -615.6(6.1) cm(-1). The inclusion of the equatorial-equatorial hydroxido bridge in 2 changes the Cu···Cu distance from 3.018 Å (avg.) to 2.798 Å (avg.), the positions of the phenoxido bridges to axial-equatorial, and the magnetic coupling to ferromagnetic with J = 50.1(1.4) cm(-1). Using 3,5-di-tert-butylcatechol as the substrate, the catecholase activity of the complexes has been studied in a methanol solution; compound 2 shows higher catecholase activity (k(cat) = 233.4 h(-1)) than compound 1 (k(cat) = 93.6 h(-1)). Both complexes generate identical species in solution, and they are interconvertible simply by changing the pH of their solutions. The higher catecholase activity of 2 seems to be due to the presence of the OH group, which increases the pH of its solution.

Cis–trans isomerism in diphenoxido bridged dicopper complexes: role of crystallized water to stabilize the cis isomer, variation in magnetic properties and conversion of both into a trinuclear species

The trans-[Cu(2)L(2)Cl(2)] (1), and cis-[Cu(2)L(2)Cl(2)]·H(2)O (2) isomers of a diphenoxido bridged Cu(2)O(2) core have been synthesized using a tridentate reduced Schiff base ligand 2-[(2-dimethylamino-ethylamino)-methyl]-phenol. The geometry around Cu(II) is intermediate between square pyramid and trigonal bipyramid (Addison parameter, τ = 0.463) in 1 but nearly square pyramidal (τ = 0.049) in 2. The chloride ions are coordinated to Cu(II) and are trans oriented in 1 but cis oriented in 2. Both isomers have been optimized using density functional theory (DFT) calculations and it is found that the trans isomer is 7.2 kcal mol(-1) more favorable than the cis isomer. However, the hydrogen bonding interaction of crystallized water molecule with chloride ions compensates for the energy difference and stabilizes the cis isomer. Both complexes have been converted to a very rare phenoxido-azido bridged trinuclear species, [Cu(3)L(2)(μ(1,1)-N(3))(2)(H(2)O)(2)(ClO(4))(2)] (3) which has also been characterized structurally. All the complexes are antiferromagnetically coupled but the magnitude of the coupling constants are significantly different (J = -156.60, -652.31, and -31.54 cm(-1) for 1, 2, 3 and respectively). Density functional theory (DFT) calculations have also been performed to gain further insight into the qualitative theoretical interpretation on the overall magnetic behavior of the complexes.

Synthesis, crystal structures and magnetic properties of two bis(μ-phenoxido)dicopper(II) complexes derived from reduced Schiff base ligands

Two phenoxido bridged dinuclear Cu(II) complexes, [Cu 2(L 1) 2(NCNCN) 2] ( 1) and [Cu 2(L 2) 2(NCNCN) 2]·2H 2O ( 2) have been synthesized using the tridentate reduced Schiff-base ligands 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL 1) and 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL 2), respectively. The complexes have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Both the complexes present a diphenoxido bridging Cu 2O 2 core. The geometries around metal atoms are intermediate between trigonal bipyramid and square pyramid with the Addison parameters ( τ) = 0.57 and 0.49 for 1 and 2, respectively. Within the core the Cu–O–Cu angles are 99.15° and 103.51° and average Cu–O bond distances are 2.036 and 1.978 Å for compounds 1 and 2, respectively. These differences have marked effect on the magnetic properties of two compounds. Although both are antiferromagnetically coupled, the coupling constants ( J = −184.3 and −478.4 cm −1 for 1 and 2, respectively) differ appreciably.

Synthesis, structure and magnetic properties of two end-on double azido bridged nickel(II) dinuclear entities incorporating N, N, N-coordinating tridentate reduced Schiff base ligands

Complexes of the general formula [Ni 2L 2(μ 1,1-N 3) 2(N 3) 2] have been synthesised in good yields by reacting Ni(NO 3) 2 · 6H 2O with L in the presence of excess of sodium azide in methanol at room temperature. Here L is N, N-bis(2-pyridylmethyl)amine (L 1) and N-(2-pyridylmethyl)- N′, N′-diethylethylenediamine (L 2). The X-ray structures of both compounds reveal that the N, N, N coordinating reduced Schiff bases are ligated facially. The Ni–N azido–Ni angle is ∼100° and the Ni⋯Ni separation is ∼3.2 Å. The variable temperature magnetic susceptibility measurements of the two complexes show ferromagnetic behavior.

Structure and magnetic properties of a neutral dimeric copper (II) complex of N-(2-hydroxybenzyl)glycinamide ligand

A copper (II) complex ([Cu2(sglym)2(NO3)2]) of tridentate reduced Schiff base ligands, namely, (N-(2-hydroxybenzyl)-glycinamide (Hsglym) was synthesized and characterized in the solid state by single crystal x-ray diffraction techniques. The two Cu(II) atoms are bridged by two phenolate oxygen atoms in the neutral dimers and the geometry of Cu(II) can be described as a distorted square pyramid. The Cu–Cu distances are 3.020(2) Å. The magnetic properties of the complex were studied at variable temperatures. Transition of spin state (from spin zero to spin one) was observed due to thermal excitation. This transition of spin state observed in the temperature range 100–400 K was accompanied by magnetic viscosity.

Study of Mono- and Bi-nuclear Copper(ii) Complexes of Tridentate Reduced Schiff Bases

Spectral, electrochemical and magnetic studies of mononuclear complexes CuL·nH2O, Cu(L)A and binuclear complexes Cu2L2·nH2O and Li(Cu2L22A–H) where L is a tridentate reduced Schiff base ligand and A is imidazole, reveal strong antiferromagnetic interactions in the binuclear complexes.