81 research outputs found
Magneto-structural studies of monohydroxo-ridged dicopper(II) complexes M[Cu<SUB>2</SUB>L<SUB>2</SUB>(OH)]·2H<SUB>2</SUB>O (M=Na<SUP>+</SUP> (1) and K<SUP>+</SUP> (2); H<SUB>2</SUB>L=2,6-bis[N-(phenyl)carbamoyl]pyridine). Effect of Cu---OH---Cu bridge angle on antiferromagnetic coupling
No full textUsing a tridentate bis-amide ligand 2,6-bis[N-(phenyl)carbamoyl]pyridine (H2L), in its deprotonated form, two new monohydroxo-bridged dicopper(II) complexes M[Cu2L2(OH)]·2H2O (M=Na+ (1) and K+ (2)) have been prepared and characterised by a number of methods, including X-ray crystallography. Each copper(II) ion is terminally coordinated by one pyridyl and two amide nitrogen donors. The two copper(II) centres are bridged by a hydroxo group, with each copper(II) centre assuming a distorted square planar geometry. The observation of short Cu---Npy and long Cu---Namide bonds is caused by the steric requirement of the ligand. Interestingly, each cation Na+/K+ is coordinated to four different [Cu2L2(OH)]- units through the amide O-donors, in an uncommon distorted tetrahedral coordination environment. Temperature-dependent magnetic susceptibility measurements revealed that the compounds have S=0 ground state with singlet-triplet energy separation, 2J=-334 and -296 cm-1 for 1 and 2, respectively. The larger Cu---OH---Cu bridge angle in 1 (131.1(6)°) causes better antiferromagnetic exchange coupling than that in 2 (125.7(6)°)
Synthesis and Characterization of Pyridine Amide Cation Radical Complexes of Iron: Stabilization Due to Coordination with Low-Spin Iron(III) Center<sup>†</sup>
No full textWe reported the synthesis and characterization of peptide complexes of low-spin iron(III) [Fe(bpb)(py)2][ClO4]
(1) and Na[Fe(bpb)(CN)2] (2) [H2bpb = 1,2-bis(pyridine-2-carboxamido)benzene; py = pyridine], where iron is
coordinated to four nitrogen donors in the equatorial plane with two amide nitrogen anions and two pyridine
nitrogen donors (Ray, M.; Mukherjee, R.; Richardson, J. F.; Buchanan, R. M. J. Chem. Soc., Dalton Trans. 1993,
2451). Chemical oxidation of 2 and a new low-spin iron(III) complex Na[Fe(Me6bpb)(CN)2]·H2O (4) [synthesized
from a new iron(III) complex [Fe(Me6bpb)(py)2][ClO4] (3) (S = 1/2)] [H2Me6bpb = 1,2-bis(3,5-dimethylpyridine-2-carboxamido)-4,5-dimethylbenzene) by (NH4)2Ce(NO3)6 afforded isolation of two novel complexes [Fe(bpb)(CN)2] (5) and [Fe(Me6bpb)(CN)2]·H2O (6). All the complexes have been characterized by physicochemical
techniques. While 1−4 are brown/green, 5 and 6 are violet/bluish violet. The collective evidence from infrared,
electronic, Mössbauer, and 1H NMR spectroscopies, from temperature-dependent magnetic susceptibility data,
and from cyclic voltammetric studies provides unambiguous evidence that 5 and 6 are low-spin iron(III) ligand
cation radical complexes rather than iron(IV) complexes. Cyclic voltammetric studies on isolated oxidized complexes
5 and 6 display identical behavior (a metal-centered reduction and a ligand-centered oxidation) to that observed
for complexes 2 and 4, respectively. The Mössbauer data for 6 are almost identical with those of the parent
compound 4, providing compelling evidence that oxidation has occurred at the ligand in a site remote from the
iron atom. Strong antiferromagnetic coupling (|−2J| ≥ 450 cm-1) of the S = 1/2 iron atom with the S = 1/2 ligand
π-cation radical leads to an effectively S = 0 ground state of 5 and 6. The oxidized complexes display 1H NMR
spectra (in CDCl3 solution), characteristic of diamagnetic species
Synthesis and characterization of pyridine amide cation radical complexes of iron: stabilization due to coordination with low-spin iron(III) center
No full textWe reported the synthesis and characterization of peptide complexes of low-spin iron(III) [Fe(bpb)(py)2][ClO4] (1) and Na[Fe(bpb)(CN)2] (2) [H2bpb = 1,2-bis(pyridine-2-carboxamido)benzene; py = pyridine], where iron is coordinated to four nitrogen donors in the equatorial plane with two amide nitrogen anions and two pyridine nitrogen donors (Ray, M.; Mukherjee, R.; Richardson, J. F.; Buchanan, R. M. J. Chem. Soc., Dalton Trans. 1993, 2451). Chemical oxidation of 2 and a new low-spin iron(III) complex Na[Fe(Me6bpb)(CN)2]·H2O (4) [synthesized from a new iron(III) complex [Fe(Me6bpb)(py)2][ClO4] (3) (S =½)] [H2Me6bpb = 1,2-bis(3,5-dimethylpyridine-2-carboxamido)-4,5-dimethylbenzene) by (NH4)2Ce(NO3)6 afforded isolation of two novel complexes [Fe(bpb)(CN)2] (5) and [Fe(Me6bpb)(CN)2]·H2O (6). All the complexes have been characterized by physicochemical techniques. While 1-4 are brown/green, 5 and 6 are violet/bluish violet. The collective evidence from infrared, electronic, Mossbauer, and 1H NMR spectroscopies, from temperature-dependent magnetic susceptibility data, and from cyclic voltammetric studies provides unambiguous evidence that 5 and 6 are low-spin iron(III) ligand cation radical complexes rather than iron(IV) complexes. Cyclic voltammetric studies on isolated oxidized complexes 5 and 6 display identical behavior (a metal-centered reduction and a ligand-centered oxidation) to that observed for complexes 2 and 4, respectively. The Mossbauer data for 6 are almost identical with those of the parent compound 4, providing compelling evidence that oxidation has occurred at the ligand in a site remote from the iron atom. Strong antiferromagnetic coupling (|-2J| ≥ 450 cm-1) of the S = ½ iron atom with the S = ½ ligand π-cation radical leads to an effectively S = 0 ground state of 5 and 6. The oxidized complexes display 1H NMR spectra (in CDCl3 solution), characteristic of diamagnetic species
Manganese(III) complexes of 1,2-bis(2-pyridinecarboxamido)benzene: synthesis, spectra, and electrochemistry
No full textThe synthesis and solution properties of the high-spin (μeff.= 4.78-4.86 at 298 K) manganese(III) complexes [Mn(bpb)X][X = Cl-, N3-, or SCN-; H2bpb = 1,2-bis(2-pyridinecarboxamido)benzene], are described. The brown crystalline complexes display ligand-to-metal charge-transfer transitions at ca. 430 nm, while in the near-infrared region crystal-field transitions are observed. In N,N-dimethylformamide solution the complexes exhibit a quasi-reversible MnIII-MnII couple [E298°-0.03 to + 0.03 V vs. saturated calomel electrode (s.c.e.)]. The complexes [Mn(bpb)Cl] and [Mn(bpb)(N3)] display an additional quasi-reversible MnIV-MnIII couple [E298°+0.87 (Cl-); + 0.49 V (N3-)vs. s.c.e.]
Structural Characterization of an Enantiopure Hydroxo-Bridged Binucleariron(III) Complex with Empty One-Dimensional Helical Channels
No full textA H-bond capable chiral tetradentate ligand, Fe^3^+, and acetate ion assembles into a hydroxo-bridged binuclear complex with the formula [Fe^I^I^I_2(\mu-OH)(\mu-OAc)(S-L)_2]•4H_2O (1) where = S-2-(2-hydroxy-benzylamino)-3-(1-imidazol-4-yl)-propionic acid. The crystal of 1 contains right-handed one-dimensional (1D) helical channels with 7.3-9.8 Å diameter. A similar reaction with a ligand having opposite chirality forms the complex with left-handed helical channels (1a). Heating the crystals of 1 at 95 C under reduced pressure selectively removes three waters from the channel forming an enantiopure porous crystal with empty channels (solvent accessible voids 18% v/v). Intermolecular hydrogen bonding between the imidazole N-H and phenolate oxygen in 1-2 forms a symmetric helix with bridging hydroxo groups pointing inside the channels. All the H-bond capable atoms in the ligand along with one water molecule form an extended H-bonded network throughout the crystal. Exposing the empty channels of 2 to iodine vapor indicates partial filling of the channels with iodine. Crystal data for 1•4 include the following: hexagonal, P61, a = b = 13.164(3) Å, c = 36.305 (11) Å, = \alpha = \beta = 90 ,\gamma = 120 , Z = 6, R1 = 0.0387, wR2 = 0.0842. Crystal data for 1a•2 include the following: hexagonal, P65, a = b = 13.151(4) Å, c = 36.558(2) Å, \alpha = \beta = 90 , \gamma = 120 , Z = 6, R1 = 0.0416, wR2 = 0.1190. Crystal data for 2• include the following: hexagonal, P61, a = b = 13.160(7) Å, c = 36.559 (4) Å, \alpha = \beta = 90 , \gamma = 120 , Z = 6, R1 = 0.0574, wR2 = 0.1423
Synthesis, crystal structure and properties of trigonal bipyramidal [M(L<SUP>5</SUP>)<SUB>2</SUB>(H<SUB>2</SUB>O)]·H<SUB>2</SUB>O complexes [M = cobalt(II) (S = 3/2) or copper(II) (S =½); HL<SUP>5</SUP> = N-(2-chloro-6-methylphenyl)pyridine-2-carboxamide]
No full textUsing a bidentate ligand N-(2-chloro-6-methylphenyl)pyridine-2-carboxamide (HL5), in its deprotonated form, two new five-co-ordinate complexes of composition [M(L5)2(H2O)]·H2O (M = CoII 1 or CuII 2) have been prepared and characterized including X-ray crystallography. The co-ordination geometry at CoII and CuII is approximately trigonal bipyramidal (two deprotonated amide nitrogens and a water molecule in the equatorial plane and two pyridines in the axial positions), being more distorted in the case of CuII. The observed distortion is caused by (i) a small bite angle of the chelating ligand and (ii) the presence of two ortho substituents, a chloro and a methyl group, on the phenyl ring (steric effect). To the best of our knowledge, 1 represents the first structurally characterized mononuclear high-spin cobalt(II) complex with a pyridine amide ligand. The magnetic moments of 1 and 2 at 300 K reveal that the compounds are paramagnetic (1 has S = 3/2 and 2 has S =½), both as solids and in dmf solution. Temperature dependent magnetic susceptibility measurements confirmed their spin state. The stereochemistry of the cobalt(II) centre in 1 does not change to any measureable extent on dissolution in dmf (cf. solid and solution state absorption spectra). The geometry of the copper(II) centre in 2 observed in the solid state is not retained in dmf solution (absorption spectra), changing to a tetragonal stereochemistry. Cyclic voltammetric measurements (dmf solution; glassy carbon electrode) on 1 reveal an oxidative response at 0.48 V vs. saturated calomel electrode (SCE) and a reductive response at -1.66 V corresponding to CoIII-CoII and CoII-CoI redox couples, respectively. For 2 the CuII-CuI process was observed at -0.53 V vs. SCE
Synthesis of a Self-Assembled Molecular Capsule that Traps Pyridine Molecules by a Combination of Hydrogen Bonding and Copper(II) Coordination
No full textMolecule and molecular assemblies with cavities of different
size and shape to encapsulate guest molecules have been
synthesized in view of their potential use as selective hosts for anion sensing, catalysis, selective recognition, and separation of guest molecules
Intelligent instrumentation: principles and applications
No full textWith the advent of microprocessors and digital-processing technologies as catalyst, classical sensors capable of simple signal conditioning operations have evolved rapidly to take on higher and more specialized functions including validation, compensation, and classification. This new category of sensor expands the scope of incorporating intelligence into instrumentation systems, yet with such rapid changes, there has developed no universal standard for design, definition, or requirement with which to unify intelligent instrumentation. Explaining the underlying design methodologies of intelligent instrumentation, Intelligent Instrumentation: Principles and Applications provides a comprehensive and authoritative resource on the scientific foundations from which to coordinate and advance the field. Employing a textbook-like language, this book translates methodologies to more than 80 numerical examples, and provides applications in 14 case studies for a complete and working understanding of the material. Beginning with a brief introduction to the basic concepts of process, process parameters, sensors and transducers, and classification of transducers, the book describes the performance characteristics of instrumentation and measurement systems and discusses static and dynamic characteristics, various types of sensor signals, and the concepts of signal representations, various transforms, and their operations in both static and dynamic conditions. It describes smart sensors, cogent sensors, soft sensors, self-validating sensors, VLSI sensors, temperature-compensating sensors, microcontrollers and ANN-based sensors, and indirect measurement sensors. The author examines intelligent sensor signal conditioning such as calibration, linearization, and compensation, along with a wide variety of calibration and linearization techniques using circuits, analog-to-digital converters (ADCs), microcontrollers, ANNs, and software. The final chapters highlight ANN techniques for pattern classification, recognition, prognostic diagnosis, fault detection, linearization, and calibration as well as important interfacing protocols in the wireless networking platform
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