Formation Of Dinuclear Complex Research Articles

Two new dinuclear complexes with dipicolinate and bridging 2-aminopyrazine ligands: preparation, structural, spectroscopic, and thermal characterizations

Treatment of an aqueous solution of dipicolinic acid (dipicH2) and 2-aminopyrazine (apyz) with Cu(NO3)2 · 3H2O or ZnCl2 (in molar ratio 1 : 1 : 1) led to formation of dinuclear complexes, [M2(H2O)4(dipic)2(µ-apyz)] (M = Cu (1) and Zn (2)). Both complexes were characterized by elemental analyses, IR, and UV-Vis spectroscopy. Their molecular and crystal structures were determined by X-ray crystal structure analysis and their thermal stabilities were confirmed by TGA/DTA methods. Complex 1 crystallizes in the triclinic P-1 space group, while 2 crystallizes in the monoclinic P21/c space group. The dinuclear complexes are analogous and composed of two metal ions bridged by 2-aminopyrazine. Each M(II) is coordinated by one nitrogen atom and two oxygen atoms of tridentate dipicolinate, one heterocyclic nitrogen of 2-aminopyrazine, and two coordinated water molecules. The resulting geometry for the MN2O4 coordination environment can be described as distorted octahedral. Extensive hydrogen-bonding interactions involving all water ligands, dipicolinate oxygen atoms, and amino groups further stabilize the complex units by linking them to form 3-D networks for 1 and 2.

Syntheses, Crystal Structure, and Magnetic Properties of a Self‐assembling Dicopper(II) Helicate with Novel Bipyridine Ligand

AbstractA novel double helical dicopper(II) complex was synthesized by reaction of a polydentate ligand L = 2,2′‐bipyridyl‐6,6′‐bis(2‐acetylpyrazinohydrazone) with copper(II) perchlorate in CH3CN. The self‐assembling process was studied by UV‐Vis spectrometric titration experiments which revealed the formation of dinuclear complexes [Cu2L2](ClO4)4. The structure of dicopper double‐helicate was confirmed by X‐ray diffractometry. Each copper(II) center occupies a distorted octahedral environment. Variable‐temperature magnetic measurements reveal weak antiferromagnetic interactions between Cu(II) ion centers with J = −0.63 cm−1.

Pyrazine bridged Ln2 (La, Nd, Eu and Tb) complexes containing fluorinated β-diketone

Abstract Pyrazine bridged dinuclear lanthanide β-diketonate complexes of the type [(tfaa) 3 Ln(μ-pyz)Ln(tfaa) 3 ] (tfaa is the anion of 1,1,1-trifluoro-2,4-pentanedione; pyz is pyrazine) were isolated by mixing [Ln(tfaa) 3 ] and pyrazine in 2:1 molar ratio in chloroform. The elemental analysis, high yield and only one sharp resonance for the pyrazine moiety in the NMR spectrum are strong enough to support dinuclear complex formation. The oscillator strength of the hypersensitive 4 G 5/2 , 2 G 7/2 ← 4 I 9/2 transition of the neodymium complex is approximately two fold higher than the mononuclear [Nd(tfaa) 3 H 2 O]. It confirms the presence of two neodymium ions both of which contribute to the oscillator strength. The red and green photoluminescence of Eu–Eu and Tb–Tb complexes, respectively, were scrutinized in solution and discussed.

Dinickel(ii) complexes: Preparation and catalytic activity

Ligands (L(a-c)) based on 2,7-bis(3,5-di-R-pyrazol-1-yl)-1,8-naphthyridine (a, R = H; b, R = CH(3); c, R = Ph) were prepared for the construction of a series of dinickel complexes. Treatment of L(x) with NiCl(2) in an anhydrous methanol/THF solution resulted in the formation of dinuclear complexes [(L(x))(μ-Cl)(2)Ni(2)Cl(2)(CH(3)OH)(2)] (3, x = a; 4, x = b; 5, x = c). These new complexes were characterized by elemental analysis, IR and UV-Vis spectroscopic techniques. The structures of complexes 3 and 4 were further confirmed by X-ray diffraction studies. Interestingly, crystals of 4 were obtained as a co-crystallization of 4 and the methanol substituted species [{(L(b))(μ-Cl)(2)Ni(2)Cl(CH(3)OH)(3)}Cl] (4'). These dinickel complexes have been tested in the catalytic homo-coupling of terminal alkynes with the use O(2) as the oxidant, showing excellent activities. A clear improvement on the catalytic activity of these complexes is observed as compared to the mono-nuclear species.

Assembling of copper(II) dipicolinate complexes

The role of ancillary ligands, namely imidazole (im), pyridine (py), 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) in the assembly of copper(II) dipicolinate complexes are presented. Mononuclear complexes are observed in the case of monodentate ligands. The mononuclear complex [Cu(im) 3L]·4H 2O ( 1) (L = dipicolinate anion) has a distorted octahedral structure with Z′ = 2, whereas [CuL(py)(H 2O)]·2H 2O ( 2) adopts distorted square pyramidal geometry. The bidentate ligands bpy and phen favor the formation of dinuclear complexes. The dinuclear complex [CuL(bpy)(μ-L)Cu(bpy)(H 2O)]·9H 2O ( 3) has one carbonyl oxygen atom of a carboxylate group of dipicolinate acting as a bridging ligand to the copper site that is devoid of a coordinated water molecule. The complex has an angle of 83.55° between the plane of L and bpy attached to one copper site, whereas it has an angle of 78.13° between the plane L and bpy attached to the other copper site. A 1,10-phenanthroline containing dinuclear copper(II) dipicolinate complex, [Cu(phen)(H 2O)(μ-L)Cu(phen) 2][CuL 2]·12H 2O ( 4), has been structurally characterized. It has an unusual carboxylate bridge.

Synthesis and CuII Coordination Chemistry of a Patellamide Derivative: Consequences of the Change from the Natural Thiazole/Oxazoline to the Artificial Imidazole Heterocycles

The synthesis and Cu(II) coordination chemistry of the cyclic pseudo-octapeptide H(4)pat(1), a dimethyl-imidazole analogue of naturally occurring cyclic peptides (patellamide A-F, ascidiacyclamide) is reported. Substitution of the oxazoline and thiazole heterocycles by dimethyl-imidazoles leads to a slightly different structure of the macrocycle in the solid state. The Cu(II) coordination chemistry of H(4)pat(1), monitored with high-resolution electrospray mass spectrometry, spectrophotometric titrations, and EPR spectroscopy, revealed the presence of both mono- and dinuclear Cu(II) complexes. The dimethyl-imidazole analogue shows a high cooperativity in Cu(II) coordination, that is, the preferred formation of dinuclear complexes. The dinuclear unbridged Cu(II) complexes of H(4)pat(1) have unusual EPR features, reminiscent of those of patellamide D: the dipole-dipole interaction of the Cu(II) centers is negligible due to the "magic angle" orientation of the two Cu(II) ions. Density functional theory calculations (DFT) are used to model the structures of the Cu(II) complexes, and the structural assignments from the spectroscopic investigations are supported by the optimized and by X-ray structures of the metal-free macrocycle and dinuclear Cu(II) complexes of H(4)pat(1). The rigidity of the dimethyl-imidazole rings has a significant effect on the structures of the metal-free ligands and Cu(II) complexes and therefore changes the properties of these compounds. This may explain why Nature has chosen the thiazole-oxazoline combination for the patellamides and ascidiacyclamide.

Self-assembling dicopper(II) complexes of di-2-pyridyl ketone Schiff base ligands derived from S-alkyldithiocarbazates

Condensation of di-2-pyridyl ketone with S-methyldithiocarbazate or S-benzyldithiocarbazate yields potentially bridging ligands of the form Py 2C NNHC(S)SR; Hdpksme (R = Me; the di-2-pyridyl ketone Schiff base of S-methyldithiocarbazate) and Hdpksbz (R = Bz; the di-2-pyridyl ketone Schiff base of S-benzyldithiocarbazate). Complexation of these ligands with Cu(II) in a 1:1 M ratio leads to the formation of dinuclear complexes of the general formula [Cu(NNNS)X] 2 (X = Cl −, NO 3 −, H 2O). X-ray crystallographic structure determinations show that each ligand provides three donor atoms (NNS) in a meridional configuration to one metal, viz. one of the pyridine nitrogen atoms, the azomethine nitrogen atom and the thiolate sulfur, while the nitrogen atom of the second pyridyl group forms a bridge to another copper(II) ion within the dimer. The coordination geometry around each copper(II) ion is approximately square pyramidal, the basal plane of which is composed of one of the pyridine nitrogen atoms, the azomethine nitrogen atom and a chlorido, nitrato or aqua ligand. The apical position of the square pyramid is always occupied by the pyridine nitrogen atom of the second ligand.

Syntheses, Crystal Structure, and Magnetic Properties of a Self‐Assembling Dinickel(II) Helicate with Novel Bipyridine Ligand

AbstractA novel polydentate ligand, L = 2,2′‐bipyridyl‐6,6′‐bis(2‐acetylpyrazinohydrazone), was synthesized by condensation of 6,6′‐dihydrazine‐2,2′‐bipyridine and 2‐acetylpyrazine. Reaction of L ligand strands with nickel (II) perchlorate in CH3CN generates a double helical dinuclear complex. Its complexation behavior was studied by UV‐Vis spectrophotometric titration experiments that revealed the formation of dinuclear complexes [Ni2L2](ClO4)4. Moreover, the double‐helical structure of [Ni2L2](ClO4)4 was confirmed by X‐ray diffractometer. Each nickel(II) center occupies a distorted octahedral environment. Variable‐temperature magnetic measurements revealed weak antiferromagnetic interactions between Ni(II) ion centers with J = −0.34 cm−1.

Pyrazine-bridged dinuclear complex formation by early lanthanides (LaIII, PrIII, NdIII and SmIII) containing bulky fluorinated β-diketonates

Abstract The reaction of 1 equivalent of pyrazine (pyz) with two equivalents of Ln(fod)3 units led to isolation of first example of pyrazine-bridged dinuclear lanthanide β-diketonate complexes of the form [Ln(fod)3(μ-pyz)Ln(fod)3] (where fod is the anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione and Ln = La, Pr, Nd and Sm). Amazingly only early lanthanides form pyrazine-bridged dinuclear Ln(fod)3 complexes, although the entire series was explored. The high yield, elemental analysis and NMR of the isolated complexes strongly support their dinuclear nature. The solution structure of the complexes was investigated by 1H NMR and 4f–4f absorption spectroscopy which confirm their dinuclear nature. The luminescence of Sm–Sm complex, in solution, has been investigated and discussed.

Different coordination modes of the dimethyldisulfide ligand in trimethylplatinum(IV) complexes

The reaction of [PtMe3(bpy)(Me2CO)](BF4) (2) (prepared from [PtMe3I(bpy)] (1) plus Ag(BF4)) with MeSSMe resulted in the formation of [PtMe3(bpy)(MeSSMe-κS)](BF4) (3). A single-crystal X-ray diffraction analysis revealed in the octahedral Pt(IV) complex (configuration index: OC-6-33), a conformation of the monodentately κS bound MeSSMe ligand (C–S–S–C 92.7(4)°) being very close to that in non-coordinated MeSSMe, thus allowing some hyperconjugative interaction stabilizing the S–S bond. The reaction of [K(18C6)][(PtMe3)2(μ-I)(μ-pz)2] (4; 18C6 = 18-crown-6, Hpz = pyrazole) with Ag(BF4) and MeSSMe resulted in the formation of dinuclear complexes [(PtMe3)2(μ-pz)2(μ-MeSSMe)] existing at room temperature in acetone solution as different fast interconverting isomers. At –40 °C, two isomers with a μ-1κS:2κS (5a) and a μ-1κS:2κS′ (5b) coordinated MeSSMe ligand in the ratio 2:1 could be identified 1H NMR spectroscopically. DFT calculations of type 5 complexes revealed the existence of two conformers with a μ-MeSSMe-1κS:2κS ligand, which differ mainly in the C–S–S–C dihedral angle (66.4 vs. 180.0° 6a/6a′). They have essentially the same energy and a very low activation barrier in acetone as solvent (1.3 kcal/mol) for their mutual interconversion. A further equilibrium structure was identified to be an isomer having a μ-MeSSMe-1κS:2κS′ ligand (6b) that proved to be only 1.9 kcal/mol higher in energy than 6a/6a′.

Thermodynamic Analysis of Reaction Equilibria in Ionic and Molecular Liquid Systems by High-Temperature Raman Spectroscopy

A formalism for correlating relative Raman band intensities with the stoichiometric coefficients, the equilibrium constant, and the thermodynamics of reaction equilibria in solution is derived. The proposed method is used for studying: (1) the thermal dissociation of molten KHSO(4) in the temperature range 240-450 degrees C; (2) the dinuclear complex formation in molten TaCl(5)-AlCl(3) mixtures at temperatures between 125 and 235 degrees C. The experimental and calculational procedures for exploiting the temperature-dependent Raman band intensities in the molten phase as well as (if applicable) in the vapors thereof are described and used for determining the enthalpy of the equilibria: (1) 2HSO(4)(-)(l) <--> S(2)O(7)(2-)(l) + H(2)O(g), DeltaH(0)=64.9 +/- 2.9 kJ mol(-1); and (2) 1/2Ta(2)Cl(10)(l) + 1/2Al(2)Cl(6)(l) <--> TaAlCl(8)(l), DeltaH(0)=-12.1 +/- 1.5 kJ mol(-1).

Tailored synthesis, spectroscopic, catalytic, and antibacterial studies of dinuclear ruthenium (II/III) chloro sulfoxide complexes with 5-nitro-o-phenanthroline as a spacer

A dinucleating spacer incorporating o-phenanthroline has been synthesized and characterized. The reaction of this spacer with ruthenium precursors resulted in formation of dinuclear complexes, [cis,fac-RuCl2(SO)3 (μ-nphen)cis,cis-RuCl2(SO)2], [trans,mer-RuCl2(SO)3 (μ-nphen)trans, cis-RuCl2(SO)2], and [X]+[trans-RuCl4(SO)(μ-nphen)mer-RuCl3(SO)]−, where SO = dimethylsulfoxide/tetramethylenesulfoxide, nphen = 5-nitro-o-phenanthroline, and X+ = [(dmso)2H]+, Na+, and [(tmso)H]+. These complexes were characterized by elemental analyses, conductivity measurements, magnetic susceptibility, FT-IR, FAB-Mass, 1H-NMR, 13C{1H}-NMR, and electronic spectroscopy. [trans,mer-RuCl2(dmso)3(μ-nphen)trans,cis-RuCl2(dmso)2] was also characterized on the basis of 1H–1H COSY NMR. The coordination of one ruthenium is through heterocyclic nitrogen of the o-phenanthroline and the second is through the oxygen of the nitrito group. Catalytic activity of these complexes has been investigated in hydrolysis of benzonitrile. All the complexes possess antibacterial activity against Escherichia coli and are compared to Chloramphenicol.

Structural studies of new group 6 complexes of salicylidene-2-aminopyridine

Interaction of salicylidene-2-aminopyridine (Hsap) with [M(CO)6], M = Cr, Mo and W, in THF under sunlight resulted in formation of dinuclear complexes [Cr2O4(sap)], 1, [Mo2O4(sap)], 2, and [W2O5(sap)2], 3. Elemental analysis, spectroscopic and magnetic studies of the reported complexes revealed the proposed structures. Magnetic studies of 1 and 2 suggested that the two metal centers have +3 and +6 formal oxidation states, while the tungsten complex 3 has +6 formal oxidation state with d0 electron configuration. The thermal properties of the complexes were investigated by thermogravimetry.

Equilibrium and Kinetic Properties of the Lanthanoids(III) and Various Divalent Metal Complexes of the Heptadentate Ligand AAZTA

The heptadentate ligand 1,4-bis(hydroxycarbonylmethyl)-6-[bis(hydroxycarbonylmethyl)]amino-6-methylperhydro-1,4-diazepine (AAZTA) and its derivatives were recently reported to give stable complexes with Gd(3+) with superior efficiency as MRI contrast agents. Nevertheless, only preliminary data are available on the coordination behavior of this interesting ligand. In this work, thermodynamic and kinetic stability data are determined for the formation of complexes with AAZTA and the lanthanoid metal ions, and other divalent metal ions of interest for this application. The AAZTA ligand binds the lanthanoid ions with log K(ML) values of 17.53-21.85 with its affinity steadily increasing from La(3+) to Lu(3+), suggesting that the seven-membered skeleton is better suited to accommodate smaller metal ions. Even though the denticity is lower, the stability of the heavier lanthanoid complexes is comparable to those of the classical ligand diethylenetriaminepentaacetic acid (DTPA). The transmetalation reactions of [Gd(AAZTA)](-) with Cu(2+) and Eu(3+) predominantly occur through proton-assisted dissociation of the complex. The role of the direct attack of Cu(2+) or Eu(3+) in the exchange reactions is limited, although the formation of dinuclear complexes decreases the proton-assisted dissociation. Near physiological conditions, [Gd(AAZTA)](-) is significantly more inert than [Gd(DTPA)](2-), allowing its potentially safe use as contrast agent in magnetic resonance imaging.

Study of Ni(II) and Cu(II) complexeswith Schiff base octadented

The reaction between 3,3-,4,4– tetraaminobiphenyl and o-hydroxy benzaldehyde in 1:4 molar ratio affords a novel tetrabasic octadentate Schiff base (Fig(1) ) . Its reaction with Ni(OAc)2 in 1:2 molar ratio. Leads to the formation of dinuclear complexes of the general formula [Ni2L] and the latter. reacts with the metal halide MX2 ( M= , Ni, Cu, X=Cl or Br ) in 1:2 molar ratio to form tetranuclear complexes of the general formula [ Ni2LM2X4], M=Ni,Cu . The coordination of the Schiff base in the dinuclear complexes seems to occur via N- azomethine and the deprotonated OH groups , while the further coordination in the tetranuclear complexes seems to take place via the lone pair of electrons available on the oxygen atoms . The structural features of the chelates have been confirmed by elemental analysis , IR ,Uv –vis and magnetic measurement .The compounds have been prepared at the room lab Temperature.

New copper(I) and silver(I) triazolato-complexes: Synthesis, reactivity and catalytic activity in olefin cyclopropanation

A new class of azolate ligands, deriving from the equimolar condensation of 3,5-diamino-1,2,4-triazole with salicylaldehyde (H 3L 1) and o-anisaldehyde (H 3L 2) was prepared. In their anionic form, these species act as bridging moieties upon coordination to Cu(I) and Ag(I), giving rise to the formation of dinuclear complexes with the ligand in the typical N, N′-exobidentate conformation. The copper derivative [Cu(H 2L 1)(CH 3CN)] 2 ( 1) showed attractive reactivity in the replacement of the labile acetonitrile molecules. In particular, it was possible to isolate a dinuclear copper(I)-carbonyl complex [Cu(H 2L 1)(CO)] 2 ( 4), by substitution of the nitrile with carbon monoxide. Moreover, the reaction of 1 with ethyl diazoacetate (EDA) in CH 2Cl 2 afforded a mono-carbene product, as established by 13C NMR data. Finally, the copper derivative 1 proved to be a highly diastereoselective catalyst in olefin cyclopropanation in the presence of ethyl diazoacetate. In the case of internal alkenes a trans: cis ratio of up to 97:3 was reached. The X-ray structure of a dinuclear Ag(I) complex, namely [Ag(H 2L 1)(PPh 3)] 2 ( 3), obtained by reacting the polymeric [Ag(H 2L 1)] n ( 2), with triphenylphosphine, is also reported.

Complex formation processes of terminally protected peptides containing two or three histidyl residues. Characterization of the mixed metal complexes of peptides

Copper(II), nickel(II) and zinc(II) complexes of the peptides Ac-HVVH-NH2 and Ac-HAAHVVH-NH2 have been studied by potentiometric, UV-vis, CD, EPR and NMR spectroscopic measurements. Both tetra and heptapeptides can form relatively stable macrochelates with copper(II), nickel(II) and zinc(II) ions, in which the ligands are coordinated via the side-chain imidazole functions. Formation of the macrochelates slightly suppresses, but cannot prevent the copper(II) and nickel(II) ion promoted deprotonation and coordination of the amide functionalities. The overall stoichiometry of the major species is [MH(-3)L]- with a 4N (=N-,N-,N-,Nim) coordination mode. In the case of Ac-HAAHVVH-NH2, coordination isomers of this species can exist with a preference for copper(II) or nickel(II) binding at the internal histidyl residue. In the copper(II)-Ac-HAAHVVH-NH2 system, the presence of the two anchoring sites results in the formation of dinuclear complexes. The existence of these species requires the involvement of amide functions in metal binding. Both equilibrium and spectroscopic data support the fact that the copper(II) ions of the dinuclear species are independent from each other providing a good chance for the formation of various mixed metal complexes. It was found that zinc(II) is not able to significantly alter the copper(II) binding of the heptapeptide, but it can occupy the uncoordinated histidyl sites. The formation of the copper(II)-nickel(II) mixed species was obtained in alkaline solutions and CD spectra suggest the statistical distribution of the two metal ions among the histidyl residues. The binding of HAAHVVH to palladium(II) is exclusive below pH 8 and the mixed metal species of palladium(II) and copper(II) ions are formed only in slightly basic solutions.

Receptor versus Counterion: Capability of N,N′‐Bis(2‐aminobenzyl)‐diazacrowns for Giving Endo‐ and/or Exocyclic Coordination of ZnII

AbstractThe structure of ZnII complexes with receptors L1 and L2[L1 = N,N′‐bis(2‐aminobenzyl)‐1,10‐diaza‐15‐crown‐5 and L2 = N,N′‐bis(2‐aminobenzyl)‐4,13‐diaza‐18‐crown‐6] was studied both in the solid state and in acetonitrile solution. Both receptors form mononuclear ZnII complexes in this solvent, while no evidence for the formation of dinuclear complexes was obtained. This is in contrast with previous investigations that demonstrated the formation of dinuclear complexes of L2 with first‐row transition metals such as NiII, CoII and CuII. Compounds of formula [Zn(L1)](ClO4)2 (1), [Zn(L1)](NO3)2·2CH3CN (2), [Zn(L2)](ClO4)2 (3) and [Zn(L2)(NO3)2] (4) were isolated and structurally characterised by X‐ray diffraction analyses. L1 forms seven‐coordinate ZnII complexes in the presence of both nitrate and perchlorate anions, as a consequence of the good fit between the macrocyclic cavity and the ionic radius of the metal ion. The ZnII ion is deeply buried into the receptor cavity and the anions are forced to remain out of the metal coordination sphere. The cation [Zn(L1)]2+ present in 1 and 2 is one of the very few examples of seven‐coordinate Zn complexes. Receptor L2 provides a very rare example of a macrocyclic receptor allowing endocyclic and exocyclic coordination on the same guest cation, depending on the nature of the anion present. Thus, in 3 the ZnII ion is endocyclically coordinated, placed inside the crown hole coordinated to four donor atoms of the ligand in a distorted tetrahedral environment, whereas in 4, the presence of a strongly coordinating anion such as nitrate results in an exocyclic coordination of ZnII, which is directly bound only to the two primarily amine groups of L2 and two nitrate ligands. Spectrophotometric titrations of [Zn(L2)]2+ with tetrabutylammonium nitrate in acetonitrile solution demonstrate the stepwise formation of 1:1 and 1:2 adducts with this anion in acetonitrile solution. The [Zn(L1)]2+, [Zn(L2)]2+ and [Zn(L2)(NO3)2] systems were characterised by means of DFT calculations (B3LYP model). The calculated geometries show an excellent agreement with the experimental structures obtained from X‐ray diffraction analyses. Calculated binding energies of the macrocyclic ligands to ZnII are also consistent with the experimental data.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)

Thermodynamic and Structural Characterization of the Copper(II) Complexes of Peptides Containing Both Histidyl and Aspartyl Residues

Terminally protected pentapeptides with 2 histidines (Ac-HHVGD- and Ac-HVGDH-) and the terminally free peptides containing both internal aspartyl and C-terminal histidyl residues (FDAH and VIDAH) have been synthesized, and copper(II) complexes studied by potentiometric, UV-Vis, CD, and EPR spectroscopic techniques in solution. Both thermodynamic and spectroscopic data reveal that side chain donor atoms of aspartyl and histidyl residues have a significant contribution to the metal binding affinity of peptide molecules. In the case of terminally protected peptides, the role of the imidazole-N donor functions is reflected in the enhanced stability of the 3N and 4N coordinated copper(II) complexes. The amino and -carboxylate groups of FDAH and VIDAH create a very effective metal binding site with the (, , ) and (, , , ) coordination modes including the N-termini, while the histidine sites are available for the formation of the (, , ) binding mode resulting in the preference of dinuclear complex formation.

Organotins as a Locking Agent in the Formation of Dinuclear Complexes

In this paper the synthesis and characterization of new heterobimetallic compounds with a ligand derived from diacetylpyridine, hydrazine and salicylaldehyde has been reported. The open end of the ligand was locked with R2SnCl2 followed by the insertion of a transition metal ion in the cavity thus formed by locking the ligand. These compounds are characterized by TGA/DSC, IR, 1H and 13CNMR, electronic spectra, magnetic moment and conductivity measurements. The disappearance of ν(O–H) and appearance of ν(Sn–O) in the IR spectrum of the Sn(saldp)R2 {where saldp = bis(salicylaldehydehydrazone)diacetylpyridine and R = –CH3, –C4H9} suggests the complex formation with R2SnCl2. The IR spectra of the complexes exhibited a blue shift in ν(C=N) indicating coordination of the azomethine nitrogen. The complexes are non-electrolytes in DMSO. The 1HNMR and 13CNMR spectra of the complexes are not much different from that of the free ligand except for the disappearance of the signal at 9 ppm due to phenolic protons. The methyl or butyl protons attached to the tin appear at their usual places. The TGA profile of the ligand and its mononuclear complexes exhibit a three-step pyrolysis, although the binuclear complexes decompose in two steps leaving behind tin oxide as the final product.