Syntheses, characterization and X-ray crystal structures of Ni(II) complexes of tridentate monocondensed and tetradentate dicondensed Schiff bases

Two octahedral complexes [Ni(HL1)(2)](ClO4)(2) (1) and [Ni(HL2)(2)](ClO4)(2) (2) and a square planar complex [Ni(HL3)]ClO4 (3) have been prepared, where [HL1 = 3-(2-amino-ethylimino)-butan-2-one oxime, HL2 = 3-(2-amino-propylimino)butan-2-one oxime] and H2L3 = 3-[2-(3-hydroxy-1-methyl-but-2-enylideneamino)-1-methyl-ethylimino]-buta n-2-one oxime. All the complexes have been characterized by elemental analyses, spectral studies and room temperature magnetic moment measurements. The molecular structures of all three compounds were elucidated on the basis of X-ray crystallography: complexes 1 and 2 are seen to be the met isomers. (C) 2008 Elsevier Ltd. All rights reserved.

A novel trinuclear nickel(II) complex of an unsymmetrical tetradentate ligand involving bridging oxime and acetylacetone functions

A novel trinuclear nickel(II) complex, [Ni-3(L)(2)(H2O)(2)](ClO4)(2), where L is a bridging unsymmetrical tetradentate ligand, involving o-phenylenediamine, diacetyl monoxime and acetylacetone (H2L = 4-[2-(3-hydroxy-1-methyl-but-2-enylideneamino)-phenylimino]-pentan-2- one oxime) has been synthesized and characterized structurally. In the complex, an octahedral Ni( II) centre is held in the middle by two square planar units with the aid of oxime and ketonic bridges. (c) 2007 Elsevier B. V. All rights reserved.

Tuning of redox potential and visible absorption band of ruthenium(II) complexes of (benzimidazolyl) derivatives: synthesis, characterization, spectroscopic and redox properties, X-ray structures and DFT calculations

Six ruthenium(II) complexes have been prepared using the tridentate ligands 2,6-bis(benzimidazolyl) pyridine and bis(2-benzimidazolyl methyl) amine and having 2,2'-bipyridine, 2,2':6',2 ''-terpyridine, PPh3, MeCN and chloride as coligands. The crystal structures of three of the complexes trans-[Ru(bbpH(2))(PPh3)(2)(CH3CN)I(ClO4)(2) center dot 2H(2)O (2), [Ru(bbpH(2))(bpy)Cl]ClO4 (3) and [Ru(bbpH(2))(terpy)](ClO4)(2) (4) are also reported. The complexes show visible region absorption at 402-517 nm, indicating that it is possible to tune the visible region absorption by varying the ancillary ligand. Luminescence behavior of the complexes has been studied both at RT and at liquid nitrogen temperature (LNT). Luminescence of the complexes is found to be insensitive to the presence of dioxygen. Two of the complexes [Ru(bbpH(2))(bpy)Cl]ClO4 (3) and [Ru(bbpH(2))(terpy]ClO4)(2) (4) show RT emission in the NIR region, having lifetime, quantum yield and radiative constant values suitable for their application as NIR emitter in the solid state devices. The DFT calculations on these two complexes indicate that the metal t(2g) electrons are appreciably delocalized over the ligand backbone. (C) 2006 Elsevier B.V. All rights reserved.

Mononuclear and binuclear ruthenium(II) complexes with 4-(phenyl) thiosemicarbazone of benzaldehyde: a discussion on the relative stabilities of the four-membered and five-membered chelate rings formed by the ligand

Three new ruthenium complexes of the formulae cis-[Ru(PPh3)(2)(BzTscbz)(2)] (1a), [Ru-2(PPh3)(2)(BzTscbz)(4)] (1b) and [Ru(PPh3)(2)(BzTscHbz)(2)](ClO4)(2) (2) [BzTscHbz = 4-(phenyl) thiosemicarbazone of benzaldehyde] have been synthesized and characterized by various physicochemical methods including X-ray structure determinations for 1a and 1b. The relative stabilities of the four-membered versus five-membered chelate rings formed by the deprotonated ligand BzTscbz are discussed on the basis of the experimental results and some semi-empirical as well as DFT calculations. (c) 2005 Elsevier Ltd. All rights reserved.

Structural variations in Ni(II) complexes of salen type di-Schiff base ligands

Three di-Schiff-base ligands, N,N'-bis(salicylidene)-1,3-propanediamine (H(2)Salpn), N,N'-bis(salicylidene)-1,3-pentanedianiine (H(2)Salpen) and N,N'-bis(salicylidine)-ethylenediamine (H(2)Salen) react with Ni(SCN)(2). 4H(2)O in 2:3 molar ratios to form the complexes; mononuclear [Ni(HSalpn)(NCS)(H2O)]center dot H2O (1a), trinuclear [{Ni(Salpen)}(2)Ni(NCS)(2)] (2b) and trinuclear [{Ni(Salen)}(2)Ni(NCS)(2)] (3) respectively. All the complexes have been characterized by elemental analyses, IR and UV-VIS spectra, and room temperature magnetic susceptibility measurements. The structures of la and 2b have been confirmed by X-ray single crystal analysis. In complex la, the Ni(II) atom is coordinated equatorially by the tetradentate, mononegative Schiff-base, HSalpn. Axial coordination of isothiocyanate group and a water molecule completes its octahedral geometry. The hydrogen atom attached to one of the oxygen atoms of the Schiff base is involved in a very strong hydrogen bond with a neighboring unit to form a centrosymmetric dimer. In 2b, two square planar [Ni(Salpen)] units act as bide mate oxygen donor ligands to a central Ni(II) which is also coordinated by two mutually cis N-bonded thiocyanate ligands to complete its distorted octahedral geometry. Complex 3 possesses a similar structure to that of 2b. A dehydrated form of la and a hydrated form of 2b have been obtained and characterized. The importance of electronic and steric factors in the variation of the structures is discussed. (c) 2007 Elsevier Ltd. All rights reserved.

Influence of counter anions on the structures and magnetic properties of trinuclear Cu(II) complexes containing a mu(3)-OH core and Schiff base ligands

Four trinuclear Cu(II) complexes, [(CuL1)(3)(mu(3)-OH)](NO3)(2) (1), [(CuL2)(3)(mu(3)-OH)](I)(2)center dot H2O (2), [(CuL3)(3)(mu(3)-OH)](I)(2) (3) and [(CuL1)(3)(mu(3)-OH)][(CuI3)-I-1] (4), where HL1 (8-amino-4-methyl-5-azaoct-3-en-2-one), HL2 [7-amino-4-methyl-5-azaoct-3-en-2-one] and HL3 [7-amino-4-methyl-5-azahept-3-en-2- one] are the three tridentate Schiff bases, have been synthesized and structurally characterized by X-ray crystallography. All four complexes contain a partial cubane core, [(CuL)(3)(mu(3)-OH)](2+) in which the three [CuL] subunits are interconnected through two types of oxygen bridges afforded by the oxygen atoms of the ligands and the central OH- group. The copper(II) ions are in a distorted square-pyramidal environment. The equatorial plane consists of the bridging oxygen of the central OH- group together with three atoms (N, N, O) from the Schiff base. The oxygen atom of the Schiff base also coordinates to the axial position of Cu(II) of another subunit to form the cyclic trimer. Magnetic susceptibilities have been determined for these complexes over the temperature range of 2-300 K. The isotropic Hamiltonian, H = -J(12)S(1)S(2) - J(13)S(1)S(3) - J(23)S(2)S(3) has been used to interpret the magnetic data. The best fit parameters obtained are: J = - 54.98 cm(-1) g = 2.24 for 1; J = - 56.66 cm(-1), g = 2.19 for 2; J = -44.39 cm(-1), g = 2.16 for 3; J = - 89.92 cm(-1), g = 2.25 for 4. The EPR data at low temperature indicate that the phenomenon of spin frustration occurs for complexes 1-3. (c) 2007 Elsevier B.V. All rights reserved.

Coordination-driven self-assembly of a novel carbonato-bridged heteromolecular neutral nickel(II) triangle by atmospheric CO2 fixation

Formation of a quasi-symmetrical mu(3)-carbonato-bridged self-assembled heteromolecular triangle of Ni(II), [(mu(3)-CO3){Ni-2(salmeNH)(2)(NCS)(2)}[Ni(salmeNH(2))(2)]center dot Et2O center dot H2O (HsalmeNH = 2-[(3-methylamino-propylimino)-methyl]-phenol) involves atmospheric CO2 uptake in a neutral medium, by spontaneous self-reorganization of the starting mononuclear Ni(II)-Schiff-base complex, [Ni(salmeNH)(2)]. The environment around Ni(II) in two of the subunits is different from the third one. The starting complex, (Ni(salmeNH)(2)], and one of the possible intermediate species, [Ni(salmeNH(2))(2)(NCS)(2)], which has a very similar coordination environment to that in the third Ni(II) center, have been characterized structurally. A plausible mechanism for the formation of such a triangle has also been proposed. The compound shows a very strong antiferromagnetic coupling. Fit as a regular triangular arrangement gave J = -53.1, g = 2.24, and R = 1.5 x 10(-4).

Anion directed template synthesis of Cu(II) complexes of a N,N,O donor mono-condensed Schiff base ligand: A molecular scaffold forming highly ordered H-bonded rectangular grids

Anion directed, template syntheses of two dinuclear copper(II) complexes of mono-condensed Schiff base ligand Hdipn (4-[(3-aminopentylimino)-methyl]-benzene-1,3-diol) involving 2,4- dihydroxybenzaldehyde and 1,3-diaminopentane were realized in the presence of bridging azide and acetate anions. Both complexes, [Cu-2(dipn)(2)(N-3)(2)] (1) and [Cu-2(dip(n))(2)(OAc)(2)] (2) have been characterized by X-ray crystallography. The two mononuclear units are joined together by basal-apical, double end-on azido bridges in complex 1 and by basal-apical, double mono-atomic acetate oxygen-bridges in 2. Both complexes form rectangular grid-like supramolecular structures via H-bonds connecting the azide or acetate anion and the p-hydroxy group of 2,4- dihydroxybenzaldehyde. Variable-temperature (300-2 K) magnetic susceptibility measurements reveal that complex 1 has antiferromagnetic coupling (J = -2.10 cm (1)) through the azide bridge while 2 has intra-dimer ferromagnetic coupling through the acetate bridge and inter-dimer antiferromagnetic coupling through H-bonds (J = 2.85 cm (1), J' = -1.08 cm (1)). (C) 2009 Elsevier B. V. All rights reserved.

Structural and spectroscopic properties of Ru(II) complexes of 4-(aryl)thiosemicarbazones of thiophen-2-carbaldehyde

Six Ru(II) complexes of formula [Ru(L)(2)(PPh3)(2)] have been prepared where LH = 4-(aryl)thiosemicarbazones of thiophen-2-carbaldehyde. X-ray crystal structures of five of the complexes are reported. In all the complexes ruthenium is six coordinate with a distorted octahedral cis-P-2, cis-N-2, trans-S-2 donor environment, and each of the two thiosemicarbazone ligands are coordinated in a bidentate fashion forming a four membered chelate ring. The complexes undergo a one-electron oxidation at similar to 0.5 V vs. Ag/AgCl. The EPR spectrum of the electrochemically oxidized solution at 100 K shows a rhombic signal, with transitions at g(1) = 2.27, g(2) = 2.00 and g(3) = 1.80. DFT calculations on one of the complexes suggest that there is 35% ruthenium and 17% sulfur orbital contribution to the HOMO. These results suggest that the assignment of metal atom oxidation states in these compounds is not unambiguous. (C) 2009 Elsevier Ltd. All rights reserved.

Palladium(II) and platinum(II) complexes with tridentate iminophosphine ligands; synthesis and structural studies

The previously synthesised Schiff-base ligands 2-(2-Ph2PC6H4N = CH) - R' - C6H3OH (R' = 3-OCH3, HL1; 5-OCH3, HL2; 5-Br, HL3; 5-Cl, HL4) were prepared by a faster, more efficient route involving a microwave assisted co-condensation of 2-(diphenylphosphino) aniline with the appropriate substituted salicylaldehyde. HL1-4 react directly with (MCl2)-Cl-II (M = Pd, Pt) or (PtI2)-I-II(cod) affording neutral square-planar complexes of general formula [(MCl)-Cl-II(eta(3)-L1-4)] (M = Pd, Pt, 1 - 8) and [(PtI)-I-II(eta(3)-L1-4)] (M = Pd, Pt, 9 - 12). Reaction of complexes 1 - 4 with the triarylphosphines PR3 (R = Ph, p-tolyl) gave the novel ionic complexes [Pd-II(PR3)(eta(3)- L1-4)] ClO4 (13 - 20). Substituted platinum complexes of the type [Pt-II(PR3)(eta(3)- L1-4)] ClO4 (R = P(CH2CH2CN)(3) 21 - 24) and [Pt-II( P(p-tolyl)(3))(eta(3)-L-3,L-4)] ClO4 ( 25 and 26) were synthesised from the appropriate [(PtCl)-Cl-II(eta(3)-L1-4)] complex (5 - 8) and PR3. The complexes are characterised by microanalytical and spectroscopic techniques. The crystal structures of 3, 6, 10, 15, 20 and 26 were determined and revealed the metal to be in a square-planar four-coordinate environment containing a planar tridentate ligand with an O, N, P donor set together with one further atom which is trans to the central nitrogen atom.

Synthesis and properties of new trinuclear Mo(II) complexes containing imidazole and benzimidazole ferrocene units

The reaction of FcCOC1 (Fc = (C5H5) Fe(C5H4)) with benzimidazole or imidazole in 1: 1 ratio gives the ferrocenyl derivatives FcCO(benzim) (L1) or FcCO(im) (L2), respectively. Two molecules of L1 or L2 can replace two nitrile ligands in [Mo(eta(3)-C3H5)( CO)(2)(CH3CN)(2)Br] or [Mo(eta(3)-C5H5O)(CO)(2)(CH3CN)(2)Br] leading to the new trinuclear complexes [Mo(eta(3)-C3H5)(CO)(2)(L)(2)Br] (C1 for L = L1; C3 for L = L2) and [Mo(eta(3)-C5H5O)(CO)(2)(L)(2)Br] (C-2 for L = L1; C4 for L = L2) with L1 and L2 acting as N-monodentade ligands. L1, L2 and C2 were characterized by X-ray diffraction studies. [Mo(eta(3)-C5H5O)(CO) 2(L1)(2)Br] was shown to be a trinuclear species, with the two L1 molecules occupying one equatorial and one axial position in the coordination sphere of Mo(II). Cyclic voltammetric studies were performed for the two ligands L1 and L2, as well as for their molybdenum complexes, and kinetic and thermodynamic data for the corresponding redox processes obtained. In agreement with the nature of the frontier orbitals obtained from DFT calculations, L1 and L2 exhibit one oxidation process at the Fe(II) center, while C1, C3, and C4 display another oxidation wave at lower potentials, associated with the oxidation of Mo(II). (C) 2007 Elsevier B. V. All rights reserved.

Different supramolecular hydrogen bond structures and significant changes in magnetic properties in dinuclear mu(2)-1,1-N-3 copper(II) complexes with very similar tridentate Schiff base blocking ligands

Three new basal-apical, mu(2)-1,1-azide bridged complexes, [CuL1(N-3)](2) (1), [CuL2(N-3)](2) (2) and [CuL3(N-3)]2 (3) with very similar tridentate Schiff base blocking ligands [L-1=N-(3-aminopropyl) salicylaldimine, L-2=7-amino-4-methyl-5-azahept-3-en-2-one and L-3=8-amino-4-methyl-5-azaoct-3-en-2-one) have been synthesised and their molecular structures determined by X-ray crystallography. In complex 1, there is no inter-dimer H-bonding. However, complexes 2 and 3 form two different supramolecular structures in which the dinuclear entities are linked by strong H-bonds giving one-dimensional systems. Variable-temperature (300-2 K) magnetic susceptibility measurements and magnetization measurements at 2 K reveal that complexes 1 and 2 have antiferromagnetic coupling while 3 has ferromagnetic coupling which is also confirmed by EPR spectra at 4-300 K. Magnetostructural correlations have been made taking into consideration both the azido bridging ligands and the existence of intermolecular hydrogen bonds in complexes 2 and 3.

Supramolecular hydrogen-bond structures and magnetic interactions in basal-apical, dinuclear, azide-bridged copper(II) complexes

The synthesis, characterisation, X-ray single crystal structures and magnetic properties of three new basal-apical mu(2)-1,1-azide-bridged complexes [(CuLN3)-N-1](2) (1), [(CuLN3)-N-2](2) (2) and [(CuLN3)-N-3](2) (3) with very similar tridentate Schiff-base blocking ligands {HL1 = N-[2-(ethylamino) ethyl] salicylaldimine; HL2 = 7-(ethylamino)-4-methyl-5-azahept-3-en-2-one; HL3 = 7-amino-4-methyl-5-azaoct-3-en-2-one} have been reported [complex 1: monoclinic, P2(1)/c, a = 8.390(2), b = 7.512(2), c = 19.822(6) Angstrom, beta = 91.45(5)degrees; complex 2: monoclinic, P2(1)/c, a = 8.070(9), b = 9.787(12), c = 15.743(17) A, beta = 98.467(10)degrees; complex 3: monoclinic, P2(1)/n, a = 5.884(7), b = 16.147(18), c = 11.901(12) Angstrom, beta = 90.050(10)degrees]. The structures consist of neutral dinuclear entities resulting from the pairing of two mononuclear units through end-on azide bridges connecting an equatorial position of one copper centre to an axial position of the other, The copper ions adopt a (4+1) square-based geometry in all the complexes. In complex 2, there is no inter-dimer hydrogen-bonding. However, complexes 1 and 3 form two different supramolecular structures in which the dinuclear entities are linked by H-bonds giving one-dimensional systems. Variable temperature (300-2 K) magnetic-susceptibility measurements and magnetisation measurements at 2 K reveal that all three complexes have antiferromagnetic coupling. Magneto-structural correlations have been made taking into consideration both the azido bridging ligands and the existence of intermolecular hydrogen bonds. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).

Trinuclear Cu(II) complexes containing peripheral ketonic oxygen bridges and a mu(3)-OH core: steric influence on their structures and existence

Two tridentate Schiff bases, HL1(6-amino-3-methyl-1-phenyl-4-azahex-2-en-1-one), and HL2 (6-atnino-3,6-dimethyl-1-phenyl-4-azahex-2-en-1-one) on reaction with Cu(II) perchlorate in the presence of triethyl amine yielded two new trinuclear copper(II) complexes, [(CuL1)(3)(mu(3)-OH)](ClO4)(2) (1) and [(CuL2)(3)(mu(3)-OH)](ClO4)(2) center dot 0.75H(2)O (2), whereas another tridentate ligand HL3 (7-amino-3-methyl-1-phenyl-4-azahept-2-en-1-one) underwent hydrolysis under the same reaction conditions to result in the formation of a mononuclear complex, [Cu(bn)(pn)ClO4] (3) [where bn = 1-benzoylacetonate and pn = 1,3-propanediamine]. All three complexes have been characterized by X-ray crystallography. For both 1 and 2 the cationic part is trinuclear with a [Cu3OH] core held by three carbonyl oxygen bridges between each pair of copper(II) atoms. The structure of 3 is a monomer with a chelating 1,3-propanediamine and a benzoyl acetone moiety. Magnetic measurements of I and 2 have been performed in the 2-300 K temperature range. The experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -J(S1S2 + S2S3 + S1S3), yielding as best fit parameters: J = -25.6 cm(-1), g = 2.21 for 1 and J = 11.2 cm(-1), g = 2.10 for 2. The EPR spectra at low temperature could be indicative of spin frustration in complex 1. (C) 2006 Elsevier Ltd. All rights reserved.

Copper(II) complexes of tetradentate N2S2 donor sets: synthesis, crystal structure characterization and reactivity

Two mononuclear and one dinuclear copper(II) complexes, containing neutral tetradentate NSSN type ligands, of formulation [Cu-II(L-1)Cl]ClO4 (1), [Cu-II(L-2)Cl]ClO4 (2) and [Cu-2(II)(L-3)(2)Cl-2](ClO4)(2) (3) were synthesized and isolated in pure form [where L-1 = 1,2-bis(2-pyridylmethylthio)ethane, L-2 = 1,3-bis(2-pyridylmethylthio)propane and L-3 = 1,4-bis(2-pyridylmethylthio)butane]. All these green colored copper(II) complexes were characterized by physicochemical and spectroscopic methods. The dinuclear copper(II) complex 3 changed to a colorless dinuclear copper(I) species of formula [Cu-2(1)(L-3)(2)](ClO4)(2),0.5H(2)O (4) in dimethylformamide even in the presence of air at ambient temperature, while complexes I and 2 showed no change under similar conditions. The solid-state structures of complexes 1, 2 and 4 were established by X-ray crystallography. The geometry about the copper in complexes 1 and 2 is trigonal bipyramidal whereas the coordination environment about the copper(I) in dinuclear complex 4 is distorted tetrahedral. (C) 2008 Elsevier Ltd. All rights reserved.