Cis-dioxo-bis [3-methoxy-2,2-dimethylpropanediamine] Molybdenum/Surfactant-Modified Electrode for Simultaneous Sensing of Ascorbic Acid and Dopamine.

In this work, the carbon paste electrode (CPE) was modified using the cis-dioxo-bis[3-methoxy-2,2-dimethylpropanediamine] molybdenum(VI) complex and 1-octanaminium,N,N,N-trioctyl bromide. Using the modified electrode, the best separation of anodic peaks for ascorbic acid and dopamine was obtained in solutions with pH 5.0 and the linear range for ascorbic acid is acquired in the range from 3.0 × 10-6 to 6.0 × 10-3 M and for dopamine from 2.0 × 10-6 to 1.0 × 10-2 M. The limits of detection (S/N = 3) were 4 × 10-7 M and 5 × 10-7 M for dopamine and ascorbic acid, respectively. Surface regeneration and the very easy preparation of the modified CPE together with the very good peak resolution and sub-micromolar detection limits designate the prepared carbon paste electrode appropriate for simultaneous voltammetric determination of dopamine and ascorbic acid.

Impedimetric and potentiometric investigation of a sulfate anion-selective electrode: experiment and simulation.

A new anion-selective polyvinyl chloride (PVC) membrane electrode based on {6,6'-diethoxy-2,2'-[2,2-dimethylpropane-1,3-diylbis(nitrilomethylidyne)]diphenolato}nickel(II)monohydrate as a carrier for the sulfate anion is reported. In this work, a new strategy for optimizing membrane components by electrochemical impedance spectroscopy (EIS) is presented. The performance of this electrode was investigated using potentiometric and EIS techniques. The potentiometric results indicated that the prepared electrode had a Nernstian slope of -28.9 ± 0.1 mV in a linear concentrations range of 1.0 × 10(-6) to 3.0 × 10(-1) M, a detection limit of 6.3 × 10(-7) M, an applied pH range of 4.0-9.0, and a response time of less than 15 s; while using the EIS technique, the linear concentrations range was 1.0 × 10(-9) to 1.0 × 10(-1) M and the pH range increased to 4.0-10.0. Finally, the impedance spectra were simulated using the Maple 13 software. A comparison of the experimental data and information obtained from the simulation confirmed the accuracy of the impedance measurement of this electrode.

{4,4',6,6'-Tetrachloro-2,2'-[2,2-dimethyl-propane-1,3-diylbis(nitrilo-methanylyl-idene)]diphenolato}dioxidomolyb-denum(VI).

The asymmetric unit of the title compound, [Mo(C(19)H(16)Cl(4)N(2)O(2))O(2)], comprises two independent mol-ecules (A and B). The geometry around the Mo(VI) atom is distorted octa-hedral in each complex mol-ecule, supported by two oxide O atoms and the N(2)O(2) donor atoms of the coordinating ligand. The dihedral angle between the benzene rings is 74.96 (11) Šfor mol-ecule A and 76.05 (11) Šfor mol-ecule B. In the crystal, the B mol-ecules are linked by pairs of C-H⋯Cl hydrogen bonds, forming inversion dimers. The crystal structure is further stabilized by C-H⋯π inter-actions. An inter-esting feature of the crystal structure is a Cl⋯Cl contact [3.3748 (18) Å], which is shorter than the sum of the van der Waals radii of Cl atoms (3.50 Å).

Dioxido{4,4',6,6'-tetrabromo-2,2'-[2,2-dimethylpropane-1,3-diylbis(nitrilomethanylylidene)]diphenolato}molyb-denum(VI).

The asymmetric unit of the title compound, [Mo(C(19)H(16)Br(4)N(2)O(2))O(2)], comprises two mol-ecules. The coordination environments around the Mo(VI) atoms are distorted octa-hedral, defined by two oxide ligands and an N(2)O(2) donor set of the tetra-dentate Schiff base in each mol-ecule. The dihedral angles between the benzene rings in the mol-ecules are 76.2 (3) and 77.7 (3)°. An inter-esting feature of the crystal structure is the presence of Br⋯Br contacts [3.4407 (11), 3.5430 (11) and 3.6492 (10) Å], which are shorter than the sum of the van der Waals radius of Br atoms (3.70 Å). The crystal structure is further stabilized by inter-molcular C-H⋯Br and C-H⋯π inter-actions. The crystal under investigation was twinned by nonmerohedry in a 0.053 (1):0.947 (1) ratio.

{4,4',6,6'-Tetra-iodo-2,2'-[(2,2-dimethyl-propane-1,3-di-yl)bis-(nitrilo-methanylyl-idene)]diphenolato}nickel(II).

The asymmetric unit of the title compound, [Ni(C(19)H(16)I(4)N(2)O(2))], comprises half of a Schiff base complex. The Ni(II) atom is located on a twofold rotation axis which also bis-ects the central C atom of the 2,2-dimethyl-propane group of the ligand. The geometry around the Ni(II) atom is distorted square-planar, with a dihedral angle of 21.7 (3)° between the symmetry-related N/Ni/O coordination planes. The dihedral angle between the symmetry-related benzene rings is 27.9 (3)°. In the crystal, short inter-molecular I⋯I [3.8178 (9) and 3.9013 (10) Å] inter-actions are present.

Aqua{4,4',6,6'-tetrachloro-2,2'-[(2,2-dimethylpropane-1,3-diyl)bis(nitrilomethanylylidene)]diphenolato}zinc.

The asymmetric unit of the title compound, [Zn(C(19)H(16)Cl(4)N(2)O(2))(H(2)O)], comprises two crystallographically independent mol-ecules. The geometry around the Zn(II) atoms is distorted trigonal-bipyramidal, supported by the N(2)O(2) donor atoms of the tetradentate Schiff base and a coordinating water mol-ecule. The dihedral angles between the benzene rings in the two mol-ecules are 34.10 (15) Šand 30.61 (15) Å. In the crystal, neighbouring independent mol-ecules are linked by pairs of O-H⋯O hydrogen bonds, forming dimers with R(2) (2)(6) ring motifs, and by O-H⋯Cl hydrogen bonds. There are short Cl⋯Cl [3.4728 (16), 3.4863 (16), and 3.388 (1) Å] contacts present, and mol-ecules are also linked by C-H⋯O and π-π [centroid-centroid distance = 3.671 (2) Å] inter-actions.

4-Amino-2-hy-droxy-benzohydrazide.

The asymmetric unit of the title compound, C(7)H(9)N(3)O(2), comprises two crystallographically independent mol-ecules (A and B). In each mol-ecule there is an intra-molecular O-H⋯O hydrogen bond making an S(6) ring motif. In the crystal, a pair of N-H⋯N hydrogen bonds link the two mol-ecules (A and B) into a dimer with an R(2) (2)(6) ring motif. The B mol-ecules are linked via pairs of N-H⋯O hydrogen bonds, forming inversion dimers with an R(2) (2)(10) ring motif. The mol-ecules are further linked via other N-H⋯O hydrogen bonds, forming undulating two-dimensional networks lying parallel to the bc plane. These networks are finally linked via N-H⋯O hydrogen bonds, forming a three-dimensional structure.

(E)-4-Amino-N'-(5-chloro-2-hy-droxy-benzyl-idene)benzohydrazide.

In the title hydrazide Schiff base compound, C(14)H(12)ClN(3)O(2), the conformation around the C=N double bond is E. The dihedral angle between the benzene rings is 41.57 (14) Å. An intra-molecular O-H⋯N hydrogen bond makes an S(6) ring motif. In the crystal, mol-ecules are linked by N-H⋯O (bifurcated acceptor) and N-H⋯N hydrogen bonds, forming chains along the a axis. The inter-esting feature of the crystal structure is the short inter-molecular C⋯O [3.216 (3), 3.170 (3), and 2.992 (3) Å] contacts, one of which is significantly shorter than the sum of the van der Waals radii of these atoms [3.22 Å].

(E)-4-Amino-N'-(5-bromo-2-hy-droxy-benzyl-idene)benzohydrazide mono-hydrate.

In t the title compound, C(14)H(12)BrN(3)O(2). H(2)O, the conformation of the C=N double bond in the hydrazide Schiff base mol-ecule is E. The dihedral angle between the benzene rings is 48.01 (11) °. An intra-molecular O-H⋯N hydrogen bond makes an S(6) ring motif. In the crystal, mol-ecules are linked through N-H⋯O (bifurcated acceptor) and O-H⋯O hydrogen bonds, forming two-dimensional networks lying parallel to (100).

(E)-4-Amino-N'-(2-hy-droxy-5-methyl-benzyl-idene)benzohydrazide.

The asymmetric unit of the title compound, C(15)H(15)N(3)O(2), comprises two crystallographically independent mol-ecules (A and B), each having an E conformation around the C=N bond. In each mol-ecule, there is an intra-molecular O-H⋯N hydrogen bond making an S(6) ring motif. The dihedral angles between the substituted phenyl rings are 17.49 (9) and 10.03 (9)°. In the crystal, N-H⋯O hydrogen bonds link neighbouring independent mol-ecules into infinite chains, of the type -A-B-A-B-, along the a axis, enclosing R(2) (1)(7) ring motifs. The chains are linked by N-H⋯O hydrogen bonds and C-H⋯O inter-actions, leading to the formation of a three-dimensional network.

{4,4'-Dimethyl-2,2'-[2,2-dimethyl-propane-1,3-diylbis(nitrilo-methanylyl-idene)]diphenolato}copper(II) monohydrate.

The asymmetric unit of the title compound, [Cu(C(21)H(24)N(2)O(2))]·H(2)O, comprises half of a Schiff base complex and half of a water mol-ecule. The whole compound is generated by crystallographic twofold rotation symmetry. The geometry around the Cu(II) atom, located on a twofold axis, is distorted square-planar, which is supported by the N(2)O(2) donor atoms of the coordinating Schiff base ligand. The dihedral angle between the symmetry-related benzene rings is 47.5 (4)°. In the crystal, the water mol-ecule that is hydrogen bonded to the coordinated O atoms links the mol-ecules via O-H⋯O inter-actions into chains parallel to [001]. The crystal structure is further stabilized by C-H⋯π inter-actions, and by π-π inter-actions involving inversion-related chelate rings [centroid-centroid distance = 3.480 (4) Å].

4-Bromo-2-[(E)-(2-{2-[(2-{[(E)-5-bromo-2-hy-droxy-benzyl-idene]amino}-phen-yl)sulfan-yl]ethyl-sulfan-yl}phen-yl)imino-meth-yl]phenol.

The asymmetric unit of the title compound, C(28)H(22)Br(2)N(2)O(2)S(2), comprises half of a Schiff base ligand, the whole mol-ecule being generated by a crystallographic inversion center located at the mid-point of the C-C bond of the central methyl-ene segment. Intra-molecular O-H⋯N and O-H⋯S hydrogen bonds make S(6) and S(5) ring motifs, respectively. In the crystal, there are no significant inter-molecular inter-actions.

{4,4'-Dichloro-2,2'-[2,2-dimethyl-propane-1,3-diylbis(nitrilo-methanylyl-idene)]diphenolato}copper(II).

In the title Schiff base complex, [Cu(C(19)H(18)Cl(2)N(2)O(2))], the Cu(II) ion is coordinated in a distorted square-planar environment by two N atoms and two O atoms of the tetra-dentate ligand. The dihedral angle between the benzene rings is 36.86 (14)°. In the crystal, mol-ecules are linked into inversion dimers by pairs of weak C-H⋯O hydrogen bonds. In addition, π-π [centroid-centroid distance = 3.7279 (16) Å] and weak C-H⋯π inter-actions are observed.

(E)-4-Amino-N'-(2-hy-droxy-5-meth-oxy-benzyl-idene)benzohydrazide monohydrate.

In the title compound, C(15)H(15)N(3)O(3)·H(2)O, the hydazide Schiff base mol-ecule shows an E conformation around the C=N bond. An intra-molecular O-H⋯N hydrogen bond makes an S(6) ring motif. The dihedral angle between the substituted phenyl rings is 23.40 (11)°. The water mol-ecule mediates linking of neighbouring mol-ecules through O-H⋯(O,O) hydrogen bonds into infinite chains along the a axis, which are further connected together through N-H⋯O hydrogen bonds, forming a two-dimensional network parallel to (001). C-H⋯O inter-actions aso occur.

{4,4'-Dimethyl-2,2'-[(2,2-dimethyl-propane-1,3-di-yl)bis-(nitrilo-methanylyl-idene)]diphenolato}nickel(II) monohydrate.

In the title compound, [Ni(C(21)H(24)N(2)O(2))]·H(2)O, both the complex mol-ecule and the water mol-ecule lie on a twofold rotation axis. The Ni(II) ion is coordinated in a distorted square-planar geometry by the tetra-dentate ligand. The dihedral angle between the two symmetry-related benzene rings is 47.12 (8)°. In the crystal, pairs of symmetry-related O-H⋯O hydrogen bonds form R(2) (2)(6) ring motifs. In addition, there are weak inter-molecular C-H⋯O hydrogen bonds, and π-π stacking inter-actions with a centroid-centroid distance of 3.4760 (8) Å.

4,6-Dichloro-2-{[(E)-(3-{[(E)-3,5-dichloro-2-hy-droxy-benzyl-idene]amino}-2,2-dimethyl-prop-yl)imino]-meth-yl}phenol.

In the title compound, C(19)H(18)Cl(4)N(2)O(2), a potential tetra-dentate Schiff base ligand, the dihedral angle between the two benzene rings is 48.01 (10)°. The configuration about the two C=N bonds is E and two intra-molecular O-H⋯N hydrogen bonds make S(6) ring motifs. In the crystal, mol-ecules are linked along the b axis via inter-molecular C-H⋯Cl inter-actions. The crystal structure is further stabilized by an inter-molecular π-π inter-action [centroid-centroid distance = 3.5744 (12) Å].

{4,4',6,6'-Tetra-iodo-2,2'-[2,2-dimethyl-propane-1,3-diylbis(nitrilo-methanylyl-idene)]diphenolato}copper(II).

In the title compound, [Cu(C(19)H(16)I(4)N(2)O(2))], the Cu(II) atom and the substituted C atom of the diamine segment lie on a crystallographic twofold rotation axis. The geometry around the Cu(II) atom is distorted square-planar, which is supported by the N(2)O(2) donor atoms of the coordinated Schiff base. The dihedral angle between the symmetry-related substituted benzene rings is 29.40 (19)°. In the crystal, a short I⋯I [3.8766 (6) Å] contact is present and links neighbouring mol-ecules into chains propagating along the a axis.

{4,4',6,6'-Tetra-bromo-2,2'-[2,2-dimethyl-propane-1,3-diylbis(nitrilo-methanylyl-idene)]diphenolato}nickel(II).

The asymmetric unit of the title compound, [Ni(C(19)H(16)Br(4)N(2)O(2))], comprises half of a Schiff base complex. The geometry around the Ni(II) atom, located on a twofold rotation axis, is distorted square-planar, which is supported by the N(2)O(2) donor atoms of the coordinated ligand. The dihedral angle between the substituted benzene rings is 23.19 (17)°. In the crystal, a short inter-molecular Br⋯Br [3.6475 (7) Å] inter-action is present.

{4,4',6,6'-Tetra-bromo-2,2'-[(2,2-dimethyl-propane-1,3-di-yl)bis-(nitrilo-methanylyl-idene)]diphenolato}copper(II).

In the title compound, [Cu(C(19)H(16)Br(4)N(2)O(2))], the Cu(II) ion and the substituted C atom of the diamine fragment lie on a crystallographic twofold rotation axis. The geometry around the Cu(II) ion is distorted square-planar, which is defined by the N(2)O(2) donor atoms of the coordinated Schiff base ligand. The dihedral angle between the symmetry-related substituted benzene rings is 25.33 (14)°. The crystal structure is stabilized by an inter-molecular π-π inter-action [centroid-centroid distance = 3.8891 (18) Å].

(E)-3-[(3-Eth-oxy-2-hy-droxy-benzyl-idene)amino]-benzoic acid.

In the title compound, C(16)H(15)NO(4), a potential bidentate N,O-donor Schiff base ligand, the benzene rings are inclined to one another by 4.24 (12)°. The mol-ecule has an E conformation about the C=N bond. An intra-molecular O-H⋯N hydrogen bond makes an S(6) ring motif. In the crystal, pairs of O-H⋯O hydrogen bonds link the mol-ecules, forming inversion dimers with R(2) (2)(8) ring motifs. These dimers are further connected by C-H⋯O inter-actions, forming a sheet in (104). There is also a C-H⋯π inter-action present involving neighbouring mol-ecules.