The instabilities of the Hartree–Fock solutions and the lattice instabilities for conjugated hydrocarbons: The bond-order and bond-length alternations

The instabilities, especially the singlet instabilities, of the conventional Hartree–Fock (HF ) solutions for a variety of alternant and nonalternant hydrocarbons, some of which have been known to show lattice instabilities (bond-length alterations), are examined. The HF solutions for nonalternant hydrocarbons in the pentalene series larger than heptalene and [4n + 2]-annulenes larger than C₂₂H₂₂ are found to be singlet unstable and there appear new solutions lower in energy than the conventional HF solutions and characterized by charge-density waves exhibiting bond-order alterations. It is found that such symmetry-breaking solutions are energetically further stabilized by distorting the nuclear framework so that it may match up with the distribution of bond-order matrix elements of the charge-density wave, which means that in conjugated systems the singlet instability of the HF solution is always accompanied with the lattice instability. Further, it is shown that in conjugated systems, even when the HF solution is singlet stable, if it is not sufficiently stable as, for example, in pentalene and heptalene, there is every possibility for the occurrence of lattice instability. It is also shown that the singlet instability as well as the lattice instability arises from the existence of a sufficiently low-lying singlet excited state.     

A small methanoato ligand in the structural differentiation of copper(II) complexes

Several copper(II) methanoato complexes, namely mononuclear [Cu(O₂CH)₂(2-mpy)₂] (1) (2-mpy = 2-methylpyridine), binuclear [Cu₂(μ-O₂CH)₄(2-mpy)₂] (2), and the polynuclear {[Cu(μ-O₂CH)₂(2-mpy)₂][Cu₂(μ-O₂CH)₄]}_n (3) and {Na₂[Cu(μ-O₂CH)₂(O₂CH)₂][Cu₂(μ-O₂CH)₄]}_n (4), have been synthesized. The mononuclear complex 1 is formed by two asymmetric chelate methanoate anions and two 2-methylpyridine molecules, giving a highly distorted ‘elongated octahedral’ coordination sphere. Complex 1 decomposes outside the mother-liquid, transforming into a regular isolated binuclear paddle-wheel complex 2 with four intra-binuclear bridging methanoates and two axial 2-mpy ligands. The polynuclear complex 3 is formed of alternate mononuclear and binuclear building blocks resembling the central cores of 1 and 2, but with significant differences, especially for the methanoates of the mononuclear units. The oxygen atom of the mononuclear unit in the octahedral axial position in 3 is simultaneously coordinated to the axial position of the binuclear paddle-wheel central core, thus enabling a chain type of structure. A chain of alternate mononuclear and binuclear building blocks, as in the neutral compound 3, are found as well in the ionic polymeric compound 4, though two types of bridges are found in 4, while there is only one type in 3. Namely, the axial position of the octahedral mononuclear unit in 4 is occupied by the methanoate oxygen atom that is already a part of the binuclear paddle-wheel unit, while one equatorial methanoate from the mononuclear unit serves as a triatomic bridge to the axial position of the binuclear building block. A very strong antiferromagnetic interaction is found for all the complexes with the paddle-wheel building blocks [Cu₂(μ-O₂CH)₄] 2–4 (−2J = 444–482 cm⁻¹), attributed to the methanoate intra-binuclear bridges. On the other hand, this strong antiferromagnetism, found already at room temperature, reduces the intensity of the EPR S = 1 spin signals reported for the isolated paddle-wheel complex 2. For the polymeric 3, only the spin S = ½ signals are found in the EPR spectra, and they are assigned to the mononuclear building blocks. No signals with a clear origin are however seen in the room temperature EPR spectrum of the polymeric analogue 4, only the S = ½ signals in the low temperature spectra. This feature is suggested to be due to a specific influence between the adjacent S = 1 (binuclear) and S = ½ (mononuclear) species via their bridges.     

Electron correlation in weakly coupled transition metal dimers: Bimetallocenylenes and bimetallocenes

The Hartree-Fock (HF) instabilities in a series of bimetallocenes (1) and bimetallocenylenes (2) with Fe, Co, Ni and Cr as 3d centers have been investigated by means of a semiempirical INDO Hamiltonian. The HF picture is only valid in the case of the iron dimers. Strong correlation effects are encountered in the Co, Ni and Cr complexes. The necessary conditions for singlet, non-singlet (triplet) and non-real variations of the HF orbitals are discussed in detail. Singlet fluctuations are the result of intraatomic angular correlation (short-range) at each 3d center. The violation of the spin symmetry corresponds to a long-range interaction between the transition metal centers. Only for MOs with large 3d _xz amplitudes there exists a channel for the interatomic spin decoupling. Consequences for polymetallocenes are shortly discussed.     

Synthesis,chemical characterization,X-ray crystal structure and magnetic properties of oxalato-bridged copper(II) binuclear complexes with 2,2′-bipyridine and diethylenetriamine as peripheral ligands

Two new μ-oxalato binuclear copper(II) complexes, [{Cu(NO₃)(H₂O)(bipy)}₂(ox)] (1) and [{Cu(dien)}₂(ox)](NO₃)₂ (2), with ox=oxalate, dien=diethylenetriamine and bipy=2,2′-bipyridine, have been synthesized and their crystal and molecular structures have been determined by single-crystal X-ray diffraction methods. The crystal structure of 1 consists of centrosymmetric neutral dimers where the copper atoms lie in a strongly elongated octahedral environment, surrounded by two nitrogen atoms of a bipy molecule and two oxygen atoms of the bridging oxalato group in the equatorial plane and oxygen atoms of water molecules and nitrate ions in the axial positions. Crystal structure of 2 is made up of non-coordinated nitrate anions and asymmetric binuclear cations in which copper atoms are in a distorted square–pyramidal coordination with three atoms of a diethylenetriamine ligand and an oxygen atom of the asymmetrically coordinated oxalato bridge building the basal plane and the other oxygen atom of the oxalato ligand filling the apical position. Both compounds have been also characterized by Fourier transform infrared (FT-IR) and electron spin resonance (ESR) spectroscopies, thermal analysis and variable temperature magnetic susceptibility measurements. The two compounds exhibit antiferromagnetic exchange with a singlet–triplet separation of −382 and −6.5 cm⁻¹ for 1 and 2, respectively. Magnetic and ESR results are discussed with respect to the crystal structure of the compounds.     

Coordination chemistry of 1,4-bis(carboxymethyl)-1,4,7-triazacyclononane: Synthesis and characterization of mononuclear and binuclear μ-oxo-bridged iron(III) complexes,and a 1D-helical copper(II) chain

The syntheses of the pentadentate ligand 1,4-bis(carboxymethyl)-1,4,7-triazacyclononane (LH₂) and its use in the preparation of [LHCu]ClO₄ (1), and a mononuclear iron(III) complex ([LFeCl] (2)) are reported. The hydrolysis of 2 in the presence of an excess of NaClO₄ resulted in the crystallization of a binuclear complex, [Fe₂(μ-O)L₂] · (NaClO₄)₃ · CH₃OH · 3H₂O (3). The crystal structures of 1–3 have been determined by single-crystal X-ray crystallography. In complex 1, the Cu(II) centre is in square based pyramidal environment, with two nitrogen atoms from the tacn ring and two oxygen atoms from two different carboxylate groups lying in the basal plane and the third nitrogen atom occupying the apical position. One pendant acetic acid group is protonated and, instead of coordinating to the copper(II) centre, participates in hydrogen bonding interactions with the perchlorate counter-ion. The coordinated carboxylate group forms a bridge to the copper atom of an adjacent [LHCu]⁺ molecule, thus generating 1D-helical chains. The compound exhibits weak ferromagnetic coupling probably due to weak interactions between [LHCu]⁺ molecules. In complex 2, the iron(III) centre is in a distorted octahedral geometry, with the fac-coordinated triamine ring, two carboxylate groups and one chloride ligand occupying the coordination sphere. In the binuclear complex 3, two iron(III) centres are bridged by one oxygen atom to form a μ-oxo-diiron(III) complex with an Fe?Fe distance of 3.423(3) Å and a non-linear Fe–O–Fe angle of 144.4°. This binuclear complex features strong antiferromagnetic coupling between the two iron(III) centres.     

Synthesis, properties, and crystal structure of the tin(IV) complex with N-(2-hydroxyethyl)ethylenediaminetriacetic acid [Sn(μ-Hedtra)(μ-OH)SnCl3(H2O)] · 3H2O

The binuclear tin(IV) complex with N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (H₄Hedtra) is synthesized. The compound is characterized by elemental analysis, thermogravimetry, and IR spectroscopy. An X-ray diffraction analysis of complex Sn(μ-Hedtra)(μ-OH)SnCl₃(H₂O)] · 3H₂O (I) is carried out. Structure I is formed by the binuclear complexes and molecules of water of crystallization. One of the tin atoms coordinates six “active” sites Hedtra^4? (the alcohol branch is deprotonated and forms a bridge between two tin atoms) and the bridging hydroxo group. The polyhedron is a pentagonal bipyramid. The octahedral environment of the second tin atom is formed by two bridging oxygen atoms, three chlorine atoms (fac isomer), and a coordination water molecule.     

Synthesis,structure, and fungicidal activity of mono- and binuclear mixed-ligand copper complex with <Emphasis Type="Italic">p</Emphasis>-nitrobenzoic acid and monoethanolamine

Mixed-ligand metal complexes based on ethanolamines and simple monosubstituted benzoic acids, in particular, mono- and binuclear copper complexes with monoethanolamine (MEA) and p-nitrobenzoic acid (PNBA), [Cu²⁺((PNBA)₂ ^-(MEA)₂)] (I) and [2Cu²⁺((PNBA)₄ ^-(MEA)₂(H₂O)₂)] (II), were prepared for the first time. The structures of the complexes were characterized by FT IR spectroscopy and X-ray diffraction (CIF files CCDC no. 1497849 (I) and no. 1497848 (II)). The doubly charged copper ions are coordinated at the vertices of octahedra, which are highly distorted due to the Jahn–Teller effect. In the crystals of the mononuclear complex I, the molecules are joined into columns, whereas in the binuclear compound II, a three-dimensional framework is formed owing to intermolecular H-bonds involving the nitro group. Fungicidal activities were found for compounds I, II, MEA, PNBA, previously obtained single-ligand copper complexes with MEA and PNBA, and MEA- and PNBA-based organic salt. The biological activity gradually increases in the series: ligand, single-ligand metal complex, organic salt, mono- and binuclear mixed-ligand complex, i.e., some ligands and copper ions show a synergistic effect.     

Synthesis, characterization, and biological properties of N-phenolato-N′-(3-dimethylaminopropyl)oxamide and its binuclear copper(II) complexes

A new asymmetric N,N′-bis(substituent)oxamide ligand, N-phenolato-N′-(3-dimethylaminopropyl)oxamide (H₃pdmapo), and two of its binuclear Cu(II) complexes with different terminal ligands, namely [Cu₂(pdmapo)(phen)(H₂O)](ClO₄) (1) and [Cu₂(pdmapo)(bpy)(CH₃OH)](ClO₄) (2), where phen = 1,10-phenanthroline and bpy = 2,2′-bipyridine, have been synthesized and characterized. The crystal structures of both complexes have been determined by single-crystal X-ray diffraction. Both structures contain binuclear Cu(II) cationic complexes with pdmapo^3? ligands. The asymmetric pdmapo^3? ligands bridge two Cu(II) atoms in the cis conformation and the Cu···Cu separations through the oxamide bridge are 5.2046(18) and 5.207(2) Å for complexes 1 and 2, respectively. The coordination environments of the two Cu(II) atoms in each binuclear complex are different. The copper occupying the inner site of the pdmapo^3? ligand is four-coordinated in a CuN₃O distorted square-planar environment, while the other is five-coordinated in a square pyramid geometry. In complex 1, O–H···O and C–H···O hydrogen bonds link the complex into a one-dimensional chain. In complex 2, O–H···O hydrogen bonds link the molecules to form a dimer, together with two types of strong π–π interactions, giving a two-dimensional network structure. The cytotoxicities and DNA-binding properties of H₃pdmapo and the two complexes were studied. The experimental evidence suggests that the ligand binds to DNA via a groove binding mode, while the binuclear complexes bind intercalatively to DNA.     

Novel carbonyl complexes of ruthenium with α-substituted oxime derivatives of terpenes

The reactions of Ru₃(CO)₁₂ with 1R,4S,6S-4-dimethylamino-4,7,7-trimethylbicyclo[4.1.0]heptane-3-one oxime (dimethylaminocaraneoxime) (I), 1R,4S,6S-4-methylamino-4,7,7-trimethylbicyclo[4.1.0]heptane-3-one oxime (methylaminocarane oxime) (II), and 1R,2R,5R-2-benzylthio-2,6,6-trimethylbicyclo[3.1.1]heptane-3-one oxime (benzylthiopinaneoxime) (III) were studied. The binuclear complex Ru₂(CO)₄{μ-η³(O,N,X)-L}₂ was formed as the main product in every reaction, when Ru₃(CO)₁₂ was heated with terpenoid to 80°C. In the above complex, two terpene ligands are coordinated in the form of ‘head-to tail’ bridge by the oxime groups at a binuclear metal fragment Ru-Ru. The heteroatom of the second functional group of every bridging ligand (nitrogen of amino group in I and II, sulfur of the thio group in III) is additionally coordinated to the ruthenium atom to give the chelate five-membered ring. Also the reactions of terpenoids I, II, III with Ru₃(CO)₁₂ were performed at room temperature using Me₃NO. In this case, as in the thermal reactions, the main product was the binuclear complex. However, in the reactions of Ru₃(CO)₁₂ with I and II, the trinuclear clusters were isolated that readily transformed to binuclear complexes in a solution. The complexes synthesized can exist as two diasteromers due to their chiral metal core. However, in all the cases, only one diastereomer was isolated, which indicates stereospecific nature of the above reactions. The compounds obtained were characterized by IR, ¹H-, ¹³C{¹H}-, COSY, and HXCOBI-NMR spectroscopy, the specific optical rotation angles were measured. For the binuclear complexes with ligands I, III and for trinuclear cluster with ligand II, single crystals were obtained and studied by X-ray diffraction.     

Crystal structure of tetra(μ-acetato)-bis{[1-ethyl-3-(pyridine-2-yl)carbamide]copper}

The crystal structure of tetra(μ-acetato)-bis{[1-ethyl-3-(pyridine-2-yl)carbamide]copper} Cu₂(L)₂(CH₃COO)₄ (I), where L is 1-ethyl-3-(pyridine-2-yl)carbamide, is determined. The asymmetric unit cell of the crystal structure of I contains a copper complex with two acetate ions and a monodentate molecule of 1-ethyl-3-(pyridine-2-yl)carbamide, which is coordinated via the pyridine nitrogen atom. Due to the symmetry center, binuclear complexes form in the crystal, in which the acetate ions act as bridges between the metal atoms. In them, the coordination polyhedron of the central copper atoms represents an almost ideal tetragonal pyramid. Its base is formed from the oxygen atoms of acetate ions. In the crystal of the binuclear complex, hydrogen bonds form between the acetate ions and the L ligand along with an intramolecular hydrogen bond, which stabilize the conformation of the organic L molecule. Between the neighboring complexes in the crystal, the van der Waals interaction occurs.     

Fe–Hg Interactions and P Chemical Shifts in [Fe(CO)3 (PPh2R)2(HgCl2)] (R=pym, fur, py, thi)

In order to study the effects of R group on Fe–Hg interactions and 31P chemical shifts, the structures of mononuclear complexes Fe(CO)₃(PPh₂R)₂ (R=pym:1, fur: 2, py: 3,thi: 4; pym=pyrimidine, fur=furyl, py=pyridine, thi=thiazole) and binuclear complexes [Fe(CO)₃(PPh₂R)₂(HgCl₂)] (R=pym: 5, fur: 6, py: 7, thi: 8) were studied using the density functional theory (DFT) PBE0 method. The 31P chemical shifts were calculated by PBE0-GIAO method. Nature bond orbital (NBO) analyses were also performed to explain the nature of the Fe–Hg interactions. The conclusions can be drawn as follows: (1) The complexes with nitrogen donor atoms are more stable than those with O or S atoms. The more N atoms there are, the higher is the stabilility of the complex. (2) The Fe–Hg interactions play a dominant role in the stabilities of the complexes. In 5 or 6, thereisa σ-bond between Fe and Hg atoms. However, in 7 and 8, the Fe–Hg interactions act as σ_P–Fe→n_Hg and σ_C–Fe→n_Hg delocalization. (3) Through Fe→Hg interactions, there is charge transfer from R groups towards the P, Fe, and Hg atoms, which increases the electron density on P nucleus in binuclear complexes. As a result, compared with their mononuclear complexes, the 31P chemical shifts in binuclear complexes show some reduction.     

Structural,theoretical and multinuclear NMR study of mercury(II) complexes of phosphorus ylides: Mono and binuclear complexes

Reaction of phosphorus ylide Ph₃PCHC(O)C₆H₄Cl (Y₁) with HgX₂ (X = Cl, Br and I) and ylide (p-tolyl)₃PCHC(O)CH₃ (Y₂) with HgI₂ in equimolar ratios using methanol as solvent leads to binuclear products. The bridge-splitting reaction of binuclear complex [(Y₁) · HgCl₂]₂ by DMSO yields a mononuclear complex containing DMSO as ligand. O-coordination of DMSO is revealed by single crystal X-ray analysis in mononuclear complex of [(Y₁) · HgCl₂ · DMSO]. C-coordination of ylides is confirmed by X-ray structure of binuclear complex [(Y₂) · HgI₂]₂. Characterization of the obtained compounds was also performed by elemental analysis, IR, ¹H, ³¹P, and ¹³C NMR. Theoretical studies on mercury(II) complexes of Y₁ show that formation of mononuclear complexes in DMSO solution in which DMSO acts as a ligand, energetically is more favorable than that of binuclear complexes.     

Bi- and trinuclear oxalamidinate complexes of palladium as catalysts in the copper-free Sonogashira reaction and in the Negishi reaction

The binuclear complex [(acac)Pd(oxam)Pd(acac)] 1 (oxam: tetraphenyl oxalic amidinate) has been prepared from H₂oxam and Pd(acac)₂ in excellent yield. The complex was characterized by elemental analyses, mass spectroscopy, ¹H NMR, ¹³C NMR spectroscopy and in the solid state by X-ray single crystal diffraction analyses. 1 consists of a bimetallic centrosymmetric unit in which the planar oxam ligand acts in a bis-chelating fashion. Each palladium center is in a planar environment.The complex 1 acts as highly selective pre-catalyst in the copper-free Sonogashira reaction between 4-bromoacetophenone and phenylacetylene. Its long-time catalytic activity is higher than that of the related binuclear complex 2 (oxam: tetra-p-tolyl oxalic amidinate) or that of the trinuclear compound [(acac)Pd(oxam)Zn(oxam)Pd(acac)] (3), the solid-state structure of which was also determined by an X-ray structural analysis of single crystals. In addition, 2 is an active and extremely selective pre-catalyst for the Negishi reaction between 3,5,6,8-tetrabromophenanthroline and R-CC-ZnCl (R: Ph, (ⁱprop)₃Si) to form tetra-alkyne-substituted derivatives.     

Geometries and properties of bimetallic phosphido-bridged complex Cp(CO)2W(μ-PPh2)W(CO)5 and Cp(CO)3W(μ-PPh2)W(CO)5

Complete geometry optimizations were carried out by HF and DFT methods to study the molecular structure of binuclear transition-metal compounds (Cp(CO)₃W(μ-PPh₂)W(CO)₅) (I) and (Cp(CO)₂W(μ-PPh₂)W(CO)₅) (II). A comparison of the experimental data and calculated structural parameters demonstrates that the most accurate geometry parameters are predicted by the MPW1PW91/LANL2DZ among the three DFT methods. Topological properties of molecular charge distributions were analyzed with the theory of atoms in molecules. (3, −1) critical points, namely bond critical point, were found between the two tungsten atoms, and between W1 and C10 in complex II, which confirms the existence of the metal–metal bond and a semi-bridging CO between the two tungsten atoms. The result provided a theoretical guidance of detailed study on the binuclear phosphido-bridged complex containing transition metal–metal bond, which could be useful in the further study of the heterobimetallic phosphido-bridged complexes.     

Coordination chemistry of a new imine-ether ligand,N,N′-bis(2-pyridylmethylene)-2,2′-(ethylenedioxy)bis(ethylamine): mono-helical and single-helical-strand coordination modes identified by X-ray crystallography

A new Schiff base ligand, N,N′-bis(2-pyridylmethylene)-2,2′-(ethylenedioxy)bis(ethylamine), L, and the complexes, [AgL](BF₄) (1), [Zn₂LCl₄] (2), [Hg₂LCl₄] (3), [Cd₂LI₄] (4), [Ni₂L₃](BF₄)₄ (5), and [M₂L₃](ClO₄)₄ with M=Co(II) (6) Fe(II) (7) and Zn(II) (8), have been synthesised and characterised crystallographically and spectroscopically. The silver(I) complex 1 consists of a mono-helical structure where one ligand molecule, coordinating in a tetradentate manner, wraps itself around the Ag(I) ion, giving rise to a distorted tetrahedral arrangement. Single-helical-strand binuclear complexes were obtained with zinc(II), mercury(II) and cadmium(II), 2, 3 and 4, respectively. Complexes 2 and 3 are isomorphous and both contain one ligand molecule coordinating to two metal atoms via the two pyridylimine N-atoms. The two remaining coordination sites on the metals are occupied by chlorine atoms. In the fivefold coordinate cadmium(II) complex, 4, the ligand coordinates in a bis-tridentate manner via the two pyridylimine units and the two oxygen atoms. The two remaining coordination sites on the metals are occupied by iodine atoms. It was possible to combine both coordination modes of the ligand, mono-helical and single-helical-strand, in the isomorphous binuclear octahedrally coordinated nickel(II), cobalt(II), iron(II) and zinc(II) complexes, 5–8, respectively. One ligand molecule is wrapped around each metal ion, which in turn are linked by a third ligand molecule, so forming mono-bridged species.     

Binuclear Triphenylantimony(V) Catecholate Based on Redox-Active Bis-<Emphasis Type="Italic">o</Emphasis>-Benzoquinone,a Bis-Catechol-Aldimine Derivative

The oxidative addition of bis-o-benzoquinone Q–(CH=N–N=CH)–Q (L), in which two 3,5-ditert-butyl-o-benzoquinones are linked to each other in positions 6 via the CH=N–N=CH group, to triphenylstibine gave a new binuclear triphenylantimony(V) bis-catecholate complex, Ph₃Sb(Cat–(CH=N–N=CH)–Cat)SbPh₃ (I). Recrystallization of I from a methanol–trichloromethane mixture resulted in an additional coordination of a methanol molecule to each antimony atom to give the binuclear complex, (CH₃OH)Ph₃Sb(Cat–(CH=N–N=CH)–Cat)SbPh₃(CH₃OH) (I · 2CH₃OH), the crystals of which (I · 2CH₃OH) · 2CH₃OH · CHCl₃ (II) contain additionally two methanol solvate molecules, which fix the geometry of the nitrogen-containing bridging group, and a trichloromethane molecule. The molecular structure of compound II in the crystalline state was determined by X-ray diffraction (CIF file CCDC no. 1560840).     

Crystal structure and magnetic properties of the binuclear copper(II) complex with 2,6-diformyl-4-tert-butylphenol bis(imidazolinylhydrazone)

The binuclear copper(II) complex with 2,6-diformyl-4-tert-butylphenol bis(imidazolinylhydrazone) (H₃L), [Cu₂(H₂L)Br₂]ClO₄ (I), was synthesized. The structure of complex I was determined by X-ray diffraction analysis. The antiferromagnetic exchange interaction (2J = ?108 cm^?1) translated through the phenoxide oxygen atom is observed between the copper(II) ions. The exchange parameter was calculated by the quantum-chemical “broken symmetry” method.     

Linkage isomerism of the oximato group: The characterization of some mono- and binuclear square planar nickel(II) complexes of vicinal oxime-imine ligands

The reactions of the Schiff-base N,N-ethylenebis-(isonitrosoacetylacetoneimine), (H₂L), with Ni(II) acetate led to the formation of the yellow-orange complex LNi (I) in water and the red complex LNi (II) in ethanol. Both oximato groups in I are coordinated to the metal through the oximino-oxygen whereas in II one group is similarly coordinated while the other is coordinated through the oximino-nitrogen. Complex I was converted to complex II by boiling in chloroform and the conversion was reversed by reacting complex II with either piperidine or ethylenediamine. H₂L neutralized by ammonia reacted with Ni(II) chloride (1:1) and the complex formed was characterized as the red square planar bis-(4-iminopentane-2,3-dione 3-oximato)Ni(II);(III). This trans complex reacted with piperidine (1:4) to produce its cis configuration (IV). Complex III reacted with ethylenediamine (2:1) and 1,3-diaminopropane (1:1) to produce complexes II and V respectively of the identical structure. Attempted similar reaction (1:1) with either 1,4-diaminobutane or 1,5-diaminopentane led to the formation of the binuclear complexes VI and VII in which two molecules of complex III are linked together by -(CH₂)₄- and -(CH₂)₅-Moieties respectively. The suggested structures of the square planar Ni(II) complexes are based on analytical, spectral and magnetic moment evidence.     

Synthesis,characterization and magnetostructural correlation studies on three binuclear copper complexes of pyrimidine derived Schiff base ligands

Three binuclear Cu(II) complexes of two pyrimidine derived Schiff base ligands, 2-S-methyl-6-methyl-4-formyl pyrimidine-N(4)-ethyl thiosemicarbazone (HL₁) and salicyl hydrazone of 2-hydrazino-4,6-dimethylpyrimidine (HL₂), have been prepared. HL₁ produces a bis(μ-thiolato) Cu(II) complex co-crystallizing with its mononuclear analog, [Cu₂(L₁)₂(NO₃)₂][Cu(L₁)(NO₃)] (1). On the other hand HL₂ shows versatility by producing two different classes of binuclear Cu(II) complexes, a bis(μ-phenoxo) complex [Cu₂(L₂)₂(NO₃)₂] (2) and another a (μ-4,4′-bipyridyl) complex, [Cu₂(L₂)₂(μ-4,4′-bipyridyl)(NO₃)₂] (3) under suitable conditions. All the three complexes show distorted square pyramidal geometry around each Cu atom but to a varied extent. Magnetic behavior of complex 1 shows that it is strongly ferromagnetic in nature whereas compounds 2 and 3 are weakly antiferromagnetic in nature. A magnetostructural correlation study combined with molecular modelling on complexes 1 and 2 has thrown light on the difference on magnetic interaction between the Cu atoms in these two complexes. Various factors that may be responsible for such differences are also explored. A novel and potentially useful pH dependant conversion of 3 to 2 has also been noticed.     

Reactions of benzyldiphenylphosphine with Pd(II) sources on silica gel

Depending on the conditions used, reactions of benzyldiphenylphosphine (HL¹) with Na₂PdCl₄ on silica gel or with Pd(OAc)₂ on the same absorbent followed by treatment with LiCl provide one or more of the four compounds: the cyclopalladated binuclear complex [(μ-Cl)PdL¹]₂ (1), cis and trans isomers of the coordination complex PdCl₂(HL¹)₂ (3), the binuclear coordination complex [(μ-Cl)PdCl(HL¹)]₂ (4), and compound PdCl₂(HL¹)₃ (5). The 56% yield of complex 1 achieved using the reaction with Na₂PdCl₄ and NaOAc on SiO₂ is higher than that reported for the direct cyclopalladation of PBnPh₂ with Pd(OAc)₂ in AcOH. X-ray diffraction studies of the cyclopalladated dimer 1 and the coordination complex cis-3 are reported.