Synthesis, crystal structure and spectroscopic properties of some cadmium(II) complexes with three polyamine and corresponding macroacyclic Schiff base ligands

Three Cd(II) macroacyclic Schiff base complexes [CdL⁴(NO₃)₂] (4), [CdL⁵(NO₃)₂] (5), [CdL⁶(NO₃)₂] (6) were prepared by template condensation of 2-pyridinecarboxaldehyde with N1-(2-nitrobenzyl)-N1-(2-aminoethyl)ethane-1,2-diamine (L¹), N1-(2-nitrobenzyl)-N1-(2-aminoethyl)propane-1,3-diamine (L²) or N1-(2-nitrobenzyl)-N1-(3-aminopropyl)propane-1,3-diamine (L³), in the presence of cadmium metal ion, respectively. Three Cd(II) complexes with L¹, L² and L³ were also synthesized. All complexes have been studied with IR, ¹H NMR, ¹³C NMR, DEPT, COSY, HMQC and microanalysis. Two of these complexes, [CdL⁴(NO₃)₂] (4) and [CdL¹(NO₃)₂] (1) have been characterized through X-ray crystallography. In complex 4, the Cd is in a six-coordinate environment comprised of the ligand N₄-donor set and two oxygen atoms of two nitrate groups. In the polyamine complexes (1, 2 and 3) Cd and ligand are in a ratio of 1:1. Supporting ab initio HF-MO calculations have been undertaken using the standard 3-21G^∗ and 6-31G^∗ basis sets.     

Synthesis, crystal structure, spectroscopic and photoluminescence studies of manganese(II), cobalt(II), cadmium(II), zinc(II) and copper(II) complexes with a pyrazole derived Schiff base ligand

Varying coordination modes of the Schiff base ligand H₂L [5-methyl-1-H-pyrazole-3-carboxylic acid (1-pyridin-2-yl-ethylidene)-hydrazide] towards different metal centers are reported with the syntheses and characterization of four mononuclear Mn(II), Co(II), Cd(II) and Zn(II) complexes, [Mn(H₂L)(H₂O)₂](ClO₄)₂(MeOH) (1), [Co(H₂L)(NCS)₂] (2), [Cd(H₂L)(H₂O)₂](ClO₄)₂ (3) and [Zn(H₂L)(H₂O)₂](ClO₄)₂ (4), and a binuclear Cu(II) complex, [Cu₂(L)₂](ClO₄)₂ (5). In the complexes 1-4 the neutral ligand serves as a 3N,2O donor where the pyridine ring N, two azomethine N and two carbohydrazine oxygen atoms are coordinatively active, leaving the pyrazole-N atoms inactive. In the case of complex 5, each ligand molecule behaves as a 4N,O donor utilizing the pyridine N, one azomethine N, the nitrogen atom proximal to the azomethine of the remaining pendant arm and one pyrazole-N atom to one metal center and the carbohydrazide oxygen atom to the second metal center. The complexes 1-4 are pentagonal bipyramidal in geometry. In each case, the ligand molecule spans the equatorial plane while the apical positions are occupied by water molecules in 1, 3 and 4 and two N bonded thiocyanate ions in 2. In complex 5, the two Cu(II) centers have almost square pyramidal geometry (τ = 0.05 for Cu1 and 0.013 for Cu2). Four N atoms from a ligand molecule form the basal plane and the carbohydrazide oxygen atom of a second ligand molecule sits in the apex of the square pyramid. All the complexes have been X-ray crystallographically characterized. The Zn(II) and Cd(II) complexes show considerable fluorescence emission while the remaining complexes and the ligand molecule are fluorescent silent.     

Complexes of 4- and 5-bromo derivatives of 2-(hydroxymethyl)pyridine with copper(II) and cobalt(II) salts. Synthesis and X-ray crystal structures

Four copper(II) complexes (1–4) and a cobalt(II) complex (5) derived from 4-bromo-2-(hydroxymethyl)pyridine (L¹) or 5-bromo-2-hydroxymethyl)pyridine (L²) with Cu(NO₃)₂·3H₂O, CuCl₂·2H₂O and CoCl₂·6H₂O have been synthesized and their respective crystal structures studied. They show specific influences owing to the different kind of metal cations and counter anions, the hydration as well as the different position of the bromine substitution on both the coordination of the complex unit and the network structure of the crystal lattice. The Cu(II) complexes of L¹ are five-coordinate [Cu(L¹)₂NO₃]NO₃·H₂O (1) and [Cu(L¹)₂Cl]Cl·H₂O (2) species with distorted quadratic pyramidal and trigonal bipyramidal coordination geometries of the N₂O₃ and N₂O₂Cl donor atoms around the Cu(II), respectively. The Cu(II) complexes of L² are six-coordinate [Cu(L²)₂(NO₃)₂] (3) and [Cu(L²)₂Cl(H₂O)]Cl·H₂O (4) species with distorted octahedral coordination geometries of the N₄O₂ and N₂O₃Cl donor atoms. A distorted octahedral coordination geometry of the N₂O₂Cl₂ donor atoms is also found in the complex unit [Co(L²)₂Cl₂] of the Co(II) complex 5 but showing the oxygen atoms of the chelating ligand as well as the chloride ions in a cis-position. Depending on the complex, water molecules and chloride anions are shown to act as stabilizing components of the crystal structure. The comparative structural investigation includes also known structures of the bromine-free ligand analogue 2-(hydroxymethyl)pyridine, illustrating the basic implication of the bromine substitution, mostly perceptible in the different modes of crystal packing.     

Synthesis and crystal structure of a heterometallic tetra-nuclear copper(II)-cadmium(II) complex and its anion modulated conversion into a trinuclear species

A tetra-nuclear, heterometallic copper(II)-cadmium(II) complex, [{CuL(H₂O)}₂(CuL)Cd](ClO₄)₂·H₂O (1) has been synthesized by reacting the “ligand complex” [CuL] with Cd(ClO₄)₂ where H₂L is the tetradentate di-Schiff base derived from 1,3-propanediamine and 2-hydroxyacetophenone. Complex 1 transforms into a trinuclear species, [(CuL)₂Cd(NCS)₂] (2) on treatment with an ammonium thiocyanate solution. Both complexes have been characterized by X-ray single crystal structure analyses. In both structures, the central Cd(II) ion has a six-coordinate distorted octahedral environment being bonded to six oxygen atoms from three Cu(II) units in 1 and to four oxygen atoms from two [CuL] units along with a couple of thiocyanate nitrogen atoms in complex 2. Complex (1) exhibits reversible reductive (Cu(II)/Cu(I); Epc, −1.03 V) and oxidative (Cu(II)/Cu(III); Epa, +1.04 V, respectively) responses in cyclic voltammetry. The generated Cu(I) species for both the complexes are unstable and undergo disproportionation.     

Synthesis of two new tripodal ligands and their cyclocondensation with 2-[2-(2-formylphenoxy)ethoxy]benzaldehyde in the presence of manganese(II) and cadmium(II) metal ions

Two new asymmetric tripodal tetraamine ligands, 2-((bis(2-aminoethyl)amino)methyl)benzenamine (L²) and 2-(((2-aminoethyl)(3-aminopropyl)amino)methyl)benzenamine (L³) were synthesized and characterized. [1+1] Macrocyclic Schiff-base complexes containing 1,2-diphenoxyethane head units and a 2-aminobenzyl pendant arm, were synthesized as [MnL⁴(MeOH)](ClO₄)₂ (1), [MnL⁵(MeOH)](ClO₄)₂ (2), [CdL⁴(H₂O)](NO₃)₂ (3) and [CdL⁵(H₂O)](NO₃)₂ (4) from the metal ion templated cyclocondensation reactions of 2-[2-(2-formylphenoxy)ethoxy]benzaldehyde with the (L²) or (L³) tripodal tetraamine ligands. The crystal structure determination of (1) and (4) showed that the complex cations that had formed consisted of pentagonal bipyramidally coordinated Mn(II) and Cd(II) ions, centrally located in a N₃O₂ macrocycle, with one 2-aminobenzyl pendant arm. Supporting ab initio HF-MO calculations have been undertaken using the standard 3-21G^∗ and 6-31G^∗ basis sets.     

Copper(II) complexes with neutral bis(pyrazolyl)methane ligands: The influence of steric hindrance on their structures and properties

By using the neutral bidentate nitrogen-containing ligands; bis(3,5-dimethyl-1-pyrazolyl)methane (L0″), bis(3,5-diisopropyl-1-pyrazolyl)methane (L1″), bis(3-tertiary-butyl-5-isopropyl-1-pyrazolyl)methane (L3″), and bis(3,5-ditertiary-butyl-1-pyrazolyl)methane (L4″), the copper(II) nitrato complexes [Cu(L0″)₂(NO₃)]NO₃ (1NO₃), [Cu(L0″)(NO₃)₂] (2), [Cu(L1″)(NO₃)₂] (3), [Cu(L3″)(NO₃)₂] (4), and [Cu(L4″)(NO₃)₂] (5), chloro complexes [Cu(L0″)₂Cl]₂(CuCl₄) (6CuCl₄), [Cu(L0″)₂Cl]₂(Cu₂Cl₆) (6Cu₂Cl₆), [Cu(L1″)Cl₂] (7), and [Cu(L3″)Cl₂] (8), nitrito complexes [Cu(L0″)(ONO)₂] (9) and [Cu(L1″)(ONO)₂] (10), and the complexes with perchlorate ions [Cu(L0″)₂(CH₃OH)](ClO₄)₂ (11ClO₄) and [Cu(L1″)₂(H₂O)](ClO₄)₂ (12ClO₄) were systematically synthesized and fully characterized by X-ray crystallography and by IR, far-IR, UV–Vis absorption, and ESR spectroscopy. In comparison with the obtained complexes with four bis(pyrazolyl)methanes having different bulkiness at pyrazolyl rings, the second coordination sphere effects on the ligands are discussed in detail. Moreover, the structures and physicochemical properties of these obtained complexes are compared with those of the related complexes with the neutral tridentate tris(pyrazolyl)methane ligand.     

Copper(II) Schiff base complexes derived from 2,2′-dimethyl-propandiamine: Synthesis, characterization and catalytic performance in the oxidation of styrene and cyclooctene

Two new mononuclear copper(II) complexes ([CuL¹]·CHCl₃ (1) and [CuL²] (2)) have been prepared by the reaction of two ONNO type Schiff base ligands, ([bis(2-hydroxy-propiophenone)2,2′-dimethylpropan-diamine] (H₂L¹) and [bis(5-bromosalicylaldehyde)2,2′-dimethyl-propandiamine] (H₂L²)) with Cu(OAc)₂·H₂O in 1:1 molar ratios. The complexes have been characterized by elemental analyses, IR and UV-Vis spectroscopy. The structures have been confirmed by X-ray single crystal analysis at 100 K. The Cu(II) atom in 1 is coordinated equatorially by a N₂O₂ donor set of the tetradentate, dinegative Schiff-base (L¹)²⁻ in a distorted square planar arrangement. While in [CuL²] (2), the Cu(II) ion possesses an additional weak intermolecular contact with one bromine atom of the ligand, thus the coordination sphere of 2 can be described as strongly distorted square pyramidal. The catalytic performance of the prepared copper complexes for the oxidation of styrene and cyclooctene with tert-butyl hydroperoxide has been evaluated.     

Complexes of Co(II), Ni(II) and Cu(II) with lapachol

Complexes of naturally occurring hydroxynaphtho-quinone, lapachol (2-hydroxy-3(3-methyl-2-buthenyl)-1,4-naphthoquinone = HL) with Co(II), Ni(II) and Cu(II) have been prepared by reaction of the corresponding acetates with the ligand (HL) in ethanol. The molecular and crystal structures were determined for [CoL₂(EtOH)₂] (1), [NiL₂(EtOH)₂] (2), and [CuL₂(py)₂] (3). In all cases the deprotonated lapachol behaves as chelating bidentate ligand. The complexes were also characterized by elemental analyses, cyclic voltammetry, and FAB-MS.     

Syntheses,characterization, X-ray crystal structures and emission properties of copper(II), zinc(II) and cadmium(II) complexes of pyridyl–pyrazole derived Schiff base ligand – Metal selective ligand binding modes

The varying coordination modes of the title ligand, L [5-methyl-1-(pyridin-2-yl)-N′-[pyridin-2-ylmethylidene]pyrazole-3-carbohydrazide] towards the different metal centers is reported by preparation and characterization of Cu(II), Zn(II) and Cd(II) complexes, [Cu(L)NO₃.H₂O](NO₃) (1) [Zn(L)₂](ClO₄)₂·2DMF (2) and [Cd(L)(I)₂] (3) respectively. In 1, the neutral ligand serves as tetradentate 4 N donor where both pyridine and pyrazole nitrogen atoms of pyridyl–pyrazole part are coordinatively active, leaving the carbonyl oxygen of the carbohydrazide part inactive. The same pyridine and pyrazole N atoms remain abstained from the coordination process towards the Zn(II) and Cd(II) metal centers. For 2 and 3 the ligand behaves as a tridentate NNO donor where the two nitrogen atoms come from azomethine, pyridine of pyridine-2-carbaldehyde parts and O from carbonyl oxygen atoms (carbohydrazide part). The complex 1 and 2 are distorted octahedral while complex 3 adopts distorted square pyramidal geometry. All the complexes are X-ray crystallographically characterized.     

Copper(II) complexes of N(4)-substituted thiosemicarbazones derived from pyridine-2-carbaldehyde: Crystal structure of a binuclear complex

Ten copper(II) complexes {[CuL¹Cl] (1), [CuL¹NO₃]₂ (2), [CuL¹N₃]₂ · 2/3H₂O (3), [CuL¹]₂(ClO₄)₂ · 2H₂O (4), [CuL²Cl]₂ (5), [CuL²N₃] (6), [Cu(HL²)SO₄]₂ · 4H₂O (7), [Cu(HL²)₂] (ClO₄)₂ · 1/2EtOH (8), [CuL³Cl]₂ (9), [CuL³NCS] · 1/2H₂O (10)} of three NNS donor thiosemicarbazone ligands {pyridine-2-carbaldehyde-N(4)-p-methoxyphenyl thiosemicarbazone [HL¹], pyridine-2-carbaldehyde-N(4)-2-phenethyl thiosemicarbazone [HL²] and pyridine-2-carbaldehyde N(4)-(methyl), N(4)-(phenyl) thiosemicarbazone [HL³]} were synthesized and physico-chemically characterized. The crystal structure of compound 9 has been determined by X-ray diffraction studies and is found that the dimer consists of two square pyramidal Cu(II) centers linked by two chlorine atoms.     

Coordination driven or/and H-bonded Cu(II)-N,N-dialkylisonicotinamide frameworks

Reactions of N,N-diisopropylisonicotinamide (L) with anhydrous CuCl₂, CuBr₂ and Cu(ClO₄)₂·6H₂O yielded: (a) an ionic product with the molecular composition of [CuL₂(H₂O)₄]·2[CuLCl₃] 1; (b) a coordination polymer [CuL₂Br₂]_n2 and (c) a mononuclear complex [CuL₄(C₃H₈O)₂]·(ClO₄)₂] 3, respectively. Similarly, the reaction of N,N-diisobutylisonicotinamide (L′) with Cu(NO₃)₂·3H₂O yielded a coordination polymer [{CuL′₂(H₂O)₂}(NO₃)₂]_n4. The ligands L and L′ coordinate in a monodentate fashion through the pyridine nitrogen atom to the metal centers in complexes 1 and 3. However, complexes 2 and 4 are coordination polymers in which the corresponding ligands (L and L′) act as bridging bidentate between metal centers to form 1D double chains. All the four complexes form networks through coordination polymerization and/or hydrogen bonding.     

Nickel(II) and zinc(II) complexes of N-substituted di(2-picolyl)amine derivatives: Synthetic and structural studies

The interaction of di(2-picolyl)amine (1) and its secondary N-substituted derivatives, N-(4-pyridylmethyl)-di(2-picolyl)amine (2), N-(4-carboxymethyl-benzyl)-di(2-picolyl)amine (3), N-(4-carboxybenzyl)-di(2-picolyl)amine (4), N-(1-naphthylmethyl)-di(2-picolyl)amine (5), N-(9-anthracenylmethyl)-di(2-picolyl)amine (6), 1,4-bis[di(2-picolyl)aminomethyl]benzene (7), 1,3-bis[di(2-picolyl)aminomethyl]benzene (8) and 2,4,6-tris[di(2-picolyl)amino]triazine (9) with Ni(II) and/or Zn(II) nitrate has resulted in the isolation of [Ni(1)(NO₃)₂], [Ni(2)(NO₃)₂], [Ni(3)(NO₃)₂], [Ni(4)(NO₃)₂]·CH₃CN, [Ni(5)(NO₃)₂], [Ni(6)(NO₃)₂], [Ni₂(7)(NO₃)₄], [Ni₂(8)(NO₃)₄], [Ni₃(9)(NO₃)₆]·3H₂O, [Zn(3)(NO₃)₂]·0.5CH₃OH, [Zn(5)(NO₃)₂], [Zn(6)(NO₃)₂], [Zn(8)(NO₃)₂] and [Zn₂(9)(NO₃)₄]·0.5H₂O. X-ray structures of [Ni(4)(NO₃)₂]·CH₃CN, [Ni(6)(NO₃)₂] and [Zn(5)(NO₃)₂] have been obtained. Both nickel complexes exhibit related distorted octahedral coordination geometries in which 4 and 6 are tridentate and bound meridionally via their respective N₃-donor sets, with the remaining coordination positions in each complex occupied by a monodentate and a bidentate nitrato ligand. For [Ni(4)(NO₃)₂]·CH₃CN, intramolecular hydrogen bond interactions are present between the carboxylic OH group on one complex and the oxygen of a monodentate nitrate on an adjacent complex such that the complexes are linked in chains which are in turn crosslinked by intermolecular offset π-π stacking between pyridyl rings in adjacent chains. In the case of [Ni(6)(NO₃)₂], two weak CH?O hydrogen bonds are present between the axial methylene hydrogen atoms on one complex and the oxygen of a monodentate nitrate ligand on a second unit such that four hydrogen bonds link pairs of complexes; in addition, an extensive series of π-π stacking interactions link individual complex units throughout the crystal lattice. The X-ray structure of [Zn(5)(NO₃)₂] shows that the metal centre once again has a distorted six-coordinated geometry, with the N₃-donor set of N-(1-naphthylmethyl)-di(2-picolyl)amine (5) coordinating in a meridional fashion and the remaining coordination positions occupied by a monodentate and a bidentate nitrato ligand. The crystal lattice is stabilized by weak intermolecular interactions between oxygens on the bound nitrato ligands and aromatic CH hydrogens on adjacent complexes; intermolecular π-π stacking between aromatic rings is also present.     

Osmium assisted C-H activation and CN cleavage of N-(2′-hydroxyphenyl) benzaldimines. Synthesis, structure and electrochemical properties of some organoosmium complexes

Reaction of N-(2′-hydroxyphenyl)-4-R-benzaldimines (L-R, R = OCH₃, CH₃, H, Cl and NO₂) with [Os(PPh₃)₃Br₂] in refluxing 2-methoxyethanol in the presence of triethylamine affords two families of organoosmium complexes (1-R and 2-R). In both 1-R and 2-R complexes a benzaldimine ligand is coordinated to the metal center as tridentate C,N,O-donor. In the 1-R complexes, a bidentate N,O-donor imionsemiquinonate ligand, derived from the hydrolysis of another benzaldimine, and a PPh₃ ligand are also coordinated to osmium. In the 2-R complexes, a carbonyl, derived from decarbonylation of 4-R-benzaldehyde (derived from the same hydrolysis stated above), and two PPh₃ ligands take up the remaining coordination sites on osmium. Structures of the 1-Cl and 2-OCH₃ complexes have been determined by X-ray crystallography. All the 1-R and 2-R complexes are diamagnetic, and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on the 1-R complexes shows a reversible Os(III)-Os(IV) oxidation within 0.47-0.67 V (vs SCE), followed by an irreversible oxidation of the imionsemiquinonate ligand within 1.10-1.36 V. An irreversible Os(III)-Os(II) reduction is also displayed by the 1-R complexes within −1.02 to −1.14 V. Cyclic voltammetry on the 2-R complexes shows a reversible Os(II)-Os(III) oxidation within 0.29-0.51 V, followed by a quasi-reversible oxidation within 1.04-1.29 V, and an irreversible reduction of the coordinated benzaldimine ligand within −1.16 to −1.31 V.     

Synthesis and structural characterization of copper(II), cadmium(II) and zinc(II) complexes with 4,5-diazaspirobifluorene and bis-9-biphenyl-4,5-diazafluorenyl peroxide

The synthesis and structural chemistry of four new divalent transition metal complexes of the fluorene ligands 4,5-diazaspirobifluorene (L1) and bis-9-biphenyl-4,5-diazafluorenyl peroxide (L2), [Cu₃(L1)₄(NO₃)₆(H₂O)₂] · 2CH₃CN (1), [Cu(L1)(CH₃CO₂)₂(H₂O)] · 2H₂O (2), [Cd(L1)₂(NO₃)₂] · DMF (3) (DMF = N,N-dimethylformamide) and [Zn₂(L2)(μ-Cl)₂Cl₂]_∞ (4) are described. Single-crystal X-ray diffraction analysis reveal that the four complexes exhibit various frameworks due to diverse coordination modes and different conformations of ligands L1 or L2, as well as nitrate, acetate or chloro counterions. L1 in complexes 1, 2 and 3 present an asymmetric rigid bidentate ligand with two nitrogen atoms as the donor sites. Novel complex 4 was formed through complexation between conformationally bent shaped peroxide ligands and zinc(II) dichlorides that adopt a linear coordination geometry, which can also give rise to extended polymeric chains with a zigzag secondary structure.     

Self assembly of asymmetric tetranuclear Cu(II) [2 × 2] grid-like complexes and of a dinuclear Ni(II) complex from pyridyl-phenol Schiff base ligands

Self assembly of N-salicylidene 2-aminopyridine (L1H) with Cu(NO₃)₂·3H₂O affords [Cu₄(L1)₄(NO₃)₃(CH₃OH)][Cu(L1)(NO₃)₂](2-aminopyridinium)(NO₃)·5CH₃OH (1) which is composed of an asymmetric [2 × 2] grid-like cationic complex that co-crystallizes with a Cu(II) mononuclear anion. This remarkable tetranuclear unit presents three penta-coordinated and one hexa-coordinated Cu(II) sites. This quadruple helicate structure reveals strong anti-ferromagnetic coupling (J = −340(2) cm⁻¹) between Cu(II) ions through a double alkoxo bridge. Reacting L1H with Cu(NO₃)₂·3H₂O in slightly different conditions affords however a more symmetric tetranuclear grid-like complex: [Cu₄(L1)₄(NO₃)₂(OH)₂](2-aminopyridinium)(OH)·CH₃OH) (2). A dinuclear Ni(II) complex, [Ni₂(L2)₂(L2H)₂(NCS)₂(CH₃OH)₂]·2CH₃OH (3), obtained with another related donor ligand (L2H = N-salicylidene 3-aminomethylpyridine) was also prepared.     

Synthesis, characterization and structural analysis of new copper(II) complexes incorporating a pyridoxal-semicarbazone ligand

The reaction between 3-hydroxy-5-hydroxymethyl-2-methyl-4-pyridinecarboxaldehyde semicarbazone (pyridoxal-semicarbazone or PLSC) and appropriate chloride, sulfate, nitrate or thiocyanate Cu(II) salts in water/alcohol mixtures resulted in the formation of new copper(II) complexes: [Cu(PLSC)Cl₂] (1), [Cu(PLSC)(H₂O)(SO₄)]₂·3H₂O (2), [Cu₂(PLSC)₂(NCS)₂](NCS)₂ (3), [Cu(PLSC)(NO₃)₂(CH₃OH)] (4) and [Cu(PLSC-2H]NH₃·H₂O (5). The complexes were characterized by elemental analysis, conductometric measurements and IR spectroscopy, while complexes 1, 2, 3 and 4 were further characterized by single crystal X-ray diffraction.     

Synthesis,structure, thermal studies on Zn(II), Cd(II) complexes of N-(2-pyridylmethyl)pyridine-2-carbaldimine and N-(2-pyridylmethyl)pyridine-2-methylketimine

The bivalent zinc and cadmium complexes of two Schiff bases N-(2-pyridylmethyl)pyridine-2-carbaldimine (L1), N-(2-pyridylmethyl)pyridine-2-methylketimine (L2), tridentate ligands with an N₃ chromophore and coordinating with two five-membered chelate rings, were synthesized. Complexes [Zn(L1)(NO₃)₂] (1), [Zn(L2)(NO₃)₂] (2), [Cd(L1)(NO₃)₂(H₂O)] (3) and [Cd(L2)(NO₃)₂(CH₃OH)] (4) were characterized by X-ray crystallography. In 1 and 2, Zn(II) has a distorted square-pyramidal geometry where as in 3 and 4, Cd(II) possesses a pseudo-pentagonal-bipyramidal geometry. The following trends in the bond lengths are observed: M–N_im < M–N_py; Zn–N > Zn–O; Cd–N < Cd–O. The final residues from the thermogravimetric analysis are ZnO and CdO, the SEM studies revealed, respectively, their porous and spherical natures. The average activation energy (E) for the loss of pyridine rings obtained from the Friedman fitting of the DSC data, for 1, 2, 3, and 4 are 193.8(2), 114.5(3), 127.1(4), and 63.7(3) kJ mol⁻¹ and their logarithmic pre-exponential factor (A) are 11.22, 5.31, 6.88, and 2.09, respectively.     

Experimental and computational investigations of cadmium(II) complexes incorporating 2-benzoylpyridine

Three novel cadmium(II) complexes of 2-benzoylpyridine [Cd(bopy)₂Cl₂] (1), {[Cd(bopy)(μ_1,1-N₃)₂]·bopy}_n (2) and [Cd(bopy)₂(SCN)₂] (3) were synthesized and characterized by spectroscopic and crystallographic methods. Azide ions of 2 act as bridging ligands generating a 1D chain running along [0 1 0]. The zig-zag chains consisting of {Cd(bopy)(N₃)₂} units are separated by 2-benzoylpyridine molecules. The fluorescence properties of the complexes 1, 2 and 3 were examined both in solid state and solution, and compared with the free ligand. Additionally, the electronic spectrum of 3 were investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.     

Copper(II) complexes of symmetrical and unsymmetrical tetradentate Schiff base ligands incorporating 1-benzoylacetone: Synthesis,crystal structures and electrochemical behavior

Three new copper(II) complexes [CuL¹]₂(ClO₄)₂ (1), [CuL²]ClO₄ (2) and [CuL³] (3) with three Schiff base ligands [HL¹ = 1-phenyl-3-{3-[(pyridin-2-ylmethylene)-amino]-propylimino}-butan-1-one, HL² = 1-phenyl-3-[3-(1-pyridin-2-yl-ethylideneamino)-propylimino]-butan-1-one and H₂L³ = 3-[3-(1-methyl-3-oxo-3-phenyl-propylideneamino)-propylimino]-1-phenyl-butan-1-one] have been synthesized and structurally characterized by X-ray crystallography. The mono-negative tetradentate asymmetric Schiff base ligands (L¹)⁻ and (L²)⁻ are chelated in complexes 1 and 2 to form square planar copper(II) complexes. In complex 1, the two units are associated weakly through ketonic oxygen of benzoylacetone fragment to form the dimeric entity. The square planar geometry of complex 3 is unusually distorted towards tetrahedral one. All three complexes exhibit reversible cyclic voltammetric responses in acetonitrile solution corresponding to the Cu^II/Cu^I redox process. The E_1/2 (−0.47 V versus SCE) of 3 shows significant anodic shift due to the tetrahedral distortion around Cu(II) compare to that of 1 and 2 (−0.82 and −0.87 V versus SCE, respectively).