Half sandwich platinum group metal complexes containing tetradentate N-donor ligand bearing two pyrazolyl-pyridine units linked by an aromatic spacer

Reaction of the bis-bidentate ligand, 1,3-bis((3-(pyridin-2-yl)-1H-pyrazol-1-yl)methyl)benzene (NN∩NN), containing two chelating pyrazolyl-pyridine units connected by an aromatic spacer with platinum group metal complexes results in a series of cationic binuclear complexes, [(η⁶-arene)₂Ru₂(NN∩NN)Cl₂]²⁺ (arene = C₆H₆, 1; p-ⁱPrC₆H₄Me, 2; C₆Me₆, 3), [(η⁵-C₅Me₅)₂M₂(NN∩NN)Cl₂]²⁺ (M = Rh, 4; Ir, 5), [(η⁵-C₅H₅)₂M₂(NN∩NN)(PPh₃)₂]²⁺ (M = Ru, 6; Os, 7), [(η⁵-C₅Me₅)₂Ru₂(NN∩NN)(PPh₃)₂]²⁺ (8) and [(η⁵-C₉H₇)₂Ru₂(NN∩NN)(PPh₃)₂]²⁺ (9). All these complexes have been isolated as their hexafluorophosphate salts and fully characterized by use of a combination of NMR spectroscopy, IR spectroscopy and mass spectrometry. The solid state structures of three complexes, [2][PF₆]₂, [4][PF₆]₂ and [6][PF₆]₂, has been determined by X-ray crystallographic studies.     

Study of half sandwich platinum group metal complexes containing tetradentate N-donor ligand bearing two di-pyridylamine units linked by an aromatic spacer

A general approach for the preparation of dinuclear η⁵- and η⁶-cyclic hydrocarbon platinum group metal complexes, viz. [(η⁶-arene)₂Ru₂(NN∩NN)Cl₂]²⁺ (arene = C₆H₆, 1; p-ⁱPrC₆H₄Me, 2; C₆Me₆, 3), [(η⁵-C₅Me₅)₂M₂(NN∩NN)Cl₂]²⁺ (M = Rh, 4; Ir, 5), [(η⁵-C₅H₅)₂M₂(NN∩NN)(PPh₃)₂]²⁺ (M = Ru, 6; Os, 7), [(η⁵-C₅Me₅)₂Ru₂(NN∩NN)(PPh₃)₂]²⁺ (8) and [(η⁵-C₉H₇)₂Ru₂(NN∩NN)(PPh₃)₂]²⁺ (9), bearing the bis-bidentate ligand 1,2-bis(di-2-pyridylaminomethyl)benzene (NN∩NN), which contains two chelating di-pyridylamine units connected by an aromatic spacer, is reported. The cationic dinuclear complexes have been isolated as their hexafluorophosphate or hexafluoroantimonate salts and characterized by use of a combination of NMR, IR and UV-vis spectroscopic methods and by mass spectrometry. The solid state structure of three derivatives, [2][SbF₆]₂, [3][PF₆]₂ and [4][PF₆]₂, has been determined by X-ray structure analysis.     

Mixed-ligand molecular paneling: dodecanuclear cuboctahedral coordination cages based on a combination of edge-bridging and face-capping ligands

Reaction of a tris-bidentate ligand L(1) (which can cap one triangular face of a metal polyhedron), a bis-bidentate ligand L(2) (which can span one edge of a metal polyhedron), and a range of M(2+) ions (M = Co, Cu, Cd), which all have a preference for six coordination geometry, results in assembly of the mixed-ligand polyhedral cages [M12(mu(3)-L(1))4(mu-L(2))12](24+). When the components are combined in the correct proportions [M(2+):L(1):L(2) = 3:1:3] in MeNO2, this is the sole product. The array of 12 M(2+) cations has a cuboctahedral geometry, containing six square and eight triangular faces around a substantial central cavity; four of the eight M3 triangular faces (every alternate one) are capped by a ligand L(1), with the remaining four M3 faces having a bridging ligand L(2) along each edge in a cyclic helical array. Thus, four homochiral triangular {M3(L(2))3}(6+) helical units are connected by four additional L(1) ligands to give the mixed-ligand cuboctahedral array, a topology which could not be formed in any homoleptic complex of this type but requires the cooperation of two different types of ligand. The complex [Cd3(L(2))3(ClO4)4(MeCN)2(H2O)2](ClO4)2, a trinuclear triple helicate in which two sites at each Cd(II) are occupied by monodentate ligands (solvent or counterions), was also characterized and constitutes an incomplete fragment of the dodecanuclear cage comprising one triangular {M3(L(2))3}(6+) face which has not yet reacted with the ligands L(1). (1)H NMR and electrospray mass spectrometric studies show that the dodecanuclear cages remain intact in solution; the NMR studies show that the Cd 12 cage has four-fold (D2) symmetry, such that there are three independent Cd(II) environments, as confirmed by a (113)Cd NMR spectrum. These mixed-ligand cuboctahedral complexes reveal the potential of using combinations of face-capping and edge-bridging ligands to extend the range of accessible topologies of polyhedral coordination cages.     

Boxes, helicates, and coordination polymers: a structural and magnetochemical investigation of the diverse coordination chemistry of simple pyridine-alcohol ligands

A structurally diverse array of polynuclear complexes has been identified and structurally characterized from the reaction of 6-methylpyridine-2-methanol (1) with a range of cobalt(II) salts under a variety of reaction conditions. A tetranuclear cubane, [Co4(1-H)4Cl4(H2O)3(CH3OH)], was isolated from the reaction of 1 with CoCl2.6H2O and NaOH in MeOH, and a tetranuclear double cubane, [Co4(1-H)6(NO3)2], was isolated from the reaction of 1 with Co(NO3)2.6H2O and NEt3 in MeOH. A bowl-shaped trinuclear complex, [Co3(1-H)3Cl3(dmso)], which features a triply bridging dmso ligand, assembled upon mixing 1 and CoCl2.6H2O in dmso. A 1-D coordination polymer, [Co(1)2(SO4)](infinity), where the sulfate ligands bridge "[Co(1)2]" units in a mu2:eta1 fashion to build up the polymer structure, was isolated from the reaction of 1 with CoSO4.7H2O. The reaction of the structurally related ligand 8-hydroxyquinaldine (2) with a mixture of CoCl2.6H2O and Co(OAc)2.4H2O lead to the formation of the tetranuclear double cubane, [Co4(2-H)6Cl2]. Temperature-dependent magnetic measurements have also been performed for these five complexes along with the hydrogen-bonded helicate [Co2(1)2(1-H)2]. The hydrogen bonds of the helicate mediate antiferromagnetic interactions between the cobalt(II) centers (J = -3.18(9) cm(-1), g = 2.25(2)). The sulfate bridging ligands of [Co(1)2(SO4)](infinity) are poor mediators of magnetic exchange. The Co(II) centers in the double-cubane complexes [Co4(1-H)6(NO3)2] and [Co4(2-H)6Cl2] are strongly antiferromagnetically coupled to each other at low temperature to give an S = 0 ground state. [Co4(1-H)4Cl4(H2O)3(MeOH)] exhibits rather complicated magnetic behavior; however, we did not observe any evidence for single-molecule magnetism as was seen for structurally related complexes.     

A cyclic oligophenylene containing two 1,8-naphthalene units bridged by two face-to-face biphenyl linkages exhibiting unusual strain and pi-pi interaction

1,8-[1,8-Naphthalenediylbis(4',4-biphenyldiyl)]naphthalene, a very stable strained cyclophane, has been synthesized in moderate yield using the copper-catalyzed coupling of 1, 8-bis(4-(tributylstannyl)phenyl)naphthalene. The X-ray analysis of the titled compound discloses bent p,p'-biphenylylene chains with splayed naphthalene rings, and the p,p'-biphenylylene chains located face-to-face indicate a fairly strong pi-pi interaction.     

Trivalent actinide and lanthanide separations by tetradentate nitrogen ligands: a quantum chemistry study

Although a variety of tetradentate ligands, 6,6'-bis(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2'-bipyridines (BTBPs), have been proved as effective ligands for selective extraction of Am(III) over Eu(III) experimentally, the origin of their selectivity is still an open question. To elucidate this question, the geometric and electronic structures of the actinide and lanthanide complexes with the BTBPs have been investigated systematically by using relativistic quantum chemistry calculations. We show herein that in 1:1 (metal:ligand) type complexes substitution of electron-donating groups to the BTBP molecule can enhance its coordination ability and thus the energetic stability of the formed Am(III) and Eu(III) complexes in the gas phase. According to our results, Eu(III) can coordinate to the BTBPs with higher stability in energy than Am(III), no matter whether there are nitrate ions in the inner-sphere complexes. The presence of nitrate ions leads to formation of the probable Am(III) and Eu(III) complexes, M(NO(3))(3)(H(2)O)(n) (M = Am, Eu), in nitric acid solutions. It has been found that the changes of Gibbs free energy play an important role for Am(III)/Eu(III) separation. In fact, the weaker complexing ability of Am(III) with nitrate ions and water molecules makes the decomposition of Am(NO(3))(3)(H(2)O)(4) more favorable in energy, which may thus increase the possibility of formation of Am(BTBPs)(NO(3))(3). Our work may shed light on the design of novel extractants for Am(III)/Eu(III) separation.     

Complexes of Ag(I), Hg(I) and Hg(II) with multidentate pyrazolyl-pyridine ligands: From mononuclear complexes to coordination polymers via helicates, a mesocate, a cage and a catenate

The coordination chemistry of a series of di- and tri-nucleating ligands with Ag(I), Hg(I) and Hg(II) has been investigated. Most of the ligands contain two or three N,N'-bidentate chelating pyrazolyl-pyridine units pendant from a central aromatic spacer; one contains three binding sites (2 + 3 + 2-dentate) in a linear sequence. A series of thirteen complexes has been structurally characterised displaying a wide range of structural types. Bis-bidentate bridging ligands react with Ag(I) to give complexes in which Ag(I) is four-coordinate from two bidentate donors, but the complexes can take the form of one-dimensional coordination polymers, or dinuclear complexes (mesocate or helicate). A tris-bidentate triangular ligand forms a complicated two-dimensional coordination network with Ag(I) in which Ag...Ag contacts, as well as metal-ligand coordination bonds, play a significant role. Three dinuclear Hg(I) complexes were isolated which contain an {Hg2}2+ metal-metal bonded core bound to a single bis-bidentate ligand which can span both metal ions. Also characterised were a series of Hg(II) complexes comprising a simple mononuclear four-coordinate Hg(II) complex, a tetrahedral Hg(II)4 cage which incorporates a counter-ion in its central cavity, a trinuclear double helicate, and a trinuclear catenated structure in which two long ligands have spontaneously formed interlocked metallomacrocyclic rings thanks to cyclometallation of two of the Hg(II) centres.     

The coordination chemistry ofN,N′-ethylenebis(2-acetylpyridine imine) andN,N′-ethylenebis(2-benzoylpyridine imine); two potentially tetradentate ligands containing four nitrogen atoms

Summary New complexes of the general formulae [ML_A(H₂O)₂]-Cl₂ (M=Ni or Cu), [ML_AX₂] (M=Co or Cu; X=Cl or Br), [NiL_ABr₂]·H₂O, [ML_A] [MCl₄] (M=Pd or Pt), [NiL_B(H₂O)₂]Cl₂·2H₂O, [ML_BCl₂] (M=Co, Ni, Cu, Pd or Pt; X=Cl or Br) and [ML_B] [MCl₄] (M=Pd or Pt), where L_A=N,N-ethylenebis(2-acetylpyridine imine) and L_B=N, N-ethylenebis(2-benzoylpyridine imine), have been isolated. The complexes were characterized by elemental analyses, conductivity measurements, t.g./d.t.g. methods, magnetic susceptibilities and spectroscopic (i.r., far-i.r., ligand field,¹Hn.m.r.) studies. Monomeric pseudo-octahedral stereochemistries for the Co^II, Ni^II and Cu^II complexes andcis square planar structures for the compounds [ML_BX₂] (M=Pd or Pt; X=Cl or Br) are assigned in the solid state. The molecules L_A and L_B behave as tetradentate chelate ligands in the Co^II, Ni^II, Cu^II and Magnus-type Pd^II and Pt^II complexes, bonding through both the pyridine and methine nitrogen atoms. A bidentateN-methine coordination of the Schiff base L_B is assigned in the [ML_BX₂] complexes (M=Pd or Pt; X=Cl or Br). The anomalous magnetic moment values of the Co^II complexes are discussed.     

Syntheses,structures, and properties of two mononuclear cobalt(III) azido complexes containing a tetradentate N-donor Schiff base as end-capping ligand

Two hexacoordinated mononuclear Co(III) compounds of the type cis-[Co(L)(N₃)₂] X [1, X = ClO₄; 2, X = PF₆; L = N,N′-(bis(pyridine-2-yl)benzylidine)-1,4-butanediamine] have been synthesized and characterized by physicochemical and spectroscopic methods. The crystal structures of complexes 1 and 2 both have distorted octahedral geometry with two terminal azides in mutual cis orientations. In the crystalline state, two mononuclear units of 1 are associated by weak C–H…π interactions to produce a dimeric unit, which packs through C–H…O hydrogen bonds and π…π interactions leading to a 2-D continuum. The mononuclear units in 2 are engaged in weak cooperative intermolecular C–H…π interactions and multiple C–H…F hydrogen bonds giving rise to a 3-D network structure. These diamagnetic compounds are redox active and show luminescence in DMF solutions.     

Novel unsymmetric chiral Schiff bases possessing two different donor moieties: unique tetradentate ligands from combination of salicylaldehyde and acetylacetone units

A new class of novel chiral Schiff base ligands has been developed using a stepwise approach. The key feature of these new ligands is that they possess two different donor units, one of them is aromatic while the other is non-aromatic.     

Imino sulfinamidines: synthesis and coordination chemistry of a novel class of chiral bidentate ligands

The new imino sulfinamidine ligand PhS(NHt-Bu)=NC(Me)=N(C6H3-2,6-iPr2), LH (11) was synthesized from N-(2,6-diisopropylphenyl)acetamidine (9) and N-tert-butyl phenylsulfinimidoyl chloride (10). Reaction of LH (11) with ZnEt2 or AlMe3 gave the complexes LZnEt (12) and LAlMe2 (13), respectively. The structures of 12 and 13 were determined by X-ray diffraction and were shown to contain L as a kappa2-N1,N5 bidentate ligand in a six-membered chelate. Formation of the magnesium complex (LMgN(TMS)2 x L2Mg) (14) from 11, MgI2, and KN(SiMe3)2 highlighted a secondary coordination mode of L, binding through the sulfinamidine nitrogens in a four-membered chelate.     

Coordination stability between metal/ligands interaction by modern spectroscopic studies: IR, electronic, EPR and cyclic voltammetry of cobalt(II) complexes with organic skeleton containing cyclic ligands

A comparative investigation of the interaction of two pyrrole-substituted, mixed oxygen and nitrogen donor, macrocycles ligands have been designed and their coordination interaction with cobalt(II) is studied. Cobalt(II) salts combine with a tetradentate and hexadentate macrocyclic nitrogen/oxygen donor ligands and formed novel cobalt(II) complexes which are characterized by elemental analysis, molar conductance, magnetic moments, mass, (1)H NMR, IR, electronic and EPR spectral studies. At the room temperature magnetic moment for cobalt(II) complexes lie in the range 4.70-5.01BM, which is higher than the spin-only value. All the complexes are high-spin type and have three unpaired electrons. Therefore, the electronic confutation and the splitting of the orbital will be t(2g)(5)eg(2). The electrochemical behaviour of the cobalt(II) complexes, the Co(III)/Co(II) couple are observed. Their positive potential indicates that metal in lower oxidation state is strongly bound to these ligands. The difference between the potential of the anodic peak and cathodic peak remains constant in all complexes. Also, the ratio between the cathodic peak current and square root of the scan rate is practically constant for the studied complexes.     

Syntheses and structures of three Mn(II) coordination polymers assembled from a dithiocarboxylic acid and N-donor ligands

Three new complexes, {[Mn(dtb)(bpe)·2H₂O]·H₂O} _n (1), {[Mn(dtb)(bpa)·2H₂O]·H₂O} _n (2), and {[Mn(dtb)(phen)]} _n (3) [H₂dtb?=?5,5′-dithiobis(2-nitrobenzoic acid), bpe?=?1,2-bis(4-pyridyl)ethene, bpa?=?1,2-bi(4-pyridyl)ethane, phen?=?1,10-phenanthroline], have been synthesized under hydrothermal conditions with Mn(OAc)₂·4H₂O, dtb, and different N-donor ligands. X-ray structure analyses of 1 and 2 reveal analogous structures with 1D helical chains and 2D 4⁴ chiral layers. The structure of 3 shows a 1D chain which is outwardly decorated with phen ligands. These neutral polymeric complexes exhibit structural diversity due to the different coordination modes of the flexible dtb ligand and the N-donor ligands. The thermogravimetric analyses and X-ray powder diffractions of 1–3 are also presented.     

Coordination chemistry of bis(2-pyridylimine) ligands with Ag(I): formation of two structurally different coordination polymers and one metallocycle controlled by linker and the solvent system

Reaction of equimolar amounts of AgClO₄ and bis[4-(2-pyridylmethyleneamino)phenyl] methane (L¹) or bis[4-(2-pyridylmethyleneamino)phenyl] ether (L²) in a 1:1 solvent mixture of CH₃CN and CH₂Cl₂ leads to the formation of two infinite coordination polymers of the composition {[Ag(L¹)]ClO₄·CH₃CN}_n (1) and {[Ag(L²)]ClO₄·CH₂Cl₂}_n (2). Whereas 1 represents a homochiral single-stranded helicate the related complex 2 shows a typical zigzag chain arrangement. Both structures are characterized by a distorted tetrahedral coordination environment of the Ag(I) centres each based on a N₄ coordination pattern of two ligand molecules. The resulting strands are connected by a hydrogen bonding network including ClO₄ ^? anions and solvent molecules forming 2-D layers. Additional ?ШC?? and CH?C?? interactions between the aromatic parts of the ligand molecules give a 3-D arrangement of the packing. In contrast, a discrete dinuclear metallocycle, [Ag₂(L²)₂](ClO₄)₂·CH₃OH (3), has been formed by reaction of AgClO₄ with L² when CH₂Cl₂ in the solvent mixture was replaced by CH₃OH. Again each Ag(I) has a distorted tetrahedral geometry and is coordinated to two pyridylimine units of two ligand molecules. Additional weak hydrogen bonds involving perchlorate and solvent molecules as well as edge-to-face and face-to-face ?ШC?? interactions allow a 3-D packing arrangement.     

The fixation of linear versus loop-type peptidic structures by metal coordination: the coordination chemistry of Val-Val- and Val-Val-Val-bridged dicatechol ligands

The Val-Val-bridged dicatechol ligand L1-H4 forms triplybridged dinuclear complexes with titanium(IV) ions, while the more flexible Val-Val-Val derivative L2-H4 leads to mixtures of complexes containing species with a cyclic arrangement of the ligand; with [cis-MoO2]2+ on the other hand, a well-defined macrocycle [(L2)MoO2]2- is formed which possesses a loop-type structure in the peptidic part of the ligand.     

Synthesis, characterization, and coordination chemistry of two new tartaric acid-derived bis(phosphite) ligands

The syntheses of two chiral bis(phosphite) ligands with tartaric acid-derived backbones: 1 (from dimethyl tartrate) and 2 (from dipyrollidene tartramide), three complexes of 1: cis-Mo(CO)₄(1), cis-PtCl₂(1), and cis-PdCl₂(1) and two complexes of 2: cis-Mo(CO)₄(2) and cis-PdCl₂(2) are described. Each ligand and complex has been fully characterized by ¹H, ¹³C, and ³¹P NMR spectroscopy, and the coordination ³¹P NMR chemical shifts have been compared to those observed for complexes of related ligands. The X-ray crystal structures of each of the metal complexes have also been determined. The X-ray crystal structures indicate that the conformation of the seven-membered chelate ring varies depending on the substituents on the tartrate backbone. However, the conformations of the seven-membered rings do not change when the metal center is changed or when the coordination environment around the metal center is changed.     

Halide copper(II) complexes of aromatic N-donor containing ligands: Structural,magnetic and reactivity studies

The preparation of four new copper(II) complexes with different N-donor ligands [CuBr₂(2-benzylpyridine)₂] (1), [CuBr₂(2-benzylpyridine)(2,2′-bipyridine)]·H₂O (2), [CuBr₂(3-methyl-2-phenylpiridine)₂] (3), [Cu(picolinate)₂]·KI (4) from copper(I) halides as starting material is described. During the preparation of compound 4 a ligand oxidation reaction took place to give the picolinate ligand starting from 2-(2-methylaminoethyl)pyridine. The complexes were characterized by elemental analyses, IR spectroscopy and crystallographic studies. Single crystal X-ray diffraction analysis of the complexes reveals their monomeric penta- and tetracoordinated nature. For all compounds, the copper(II) present a common square planar coordination except for compound 2 which is five coordinated in a quasi-square pyramidal configuration with τ of 0.29. The Cu–N distances for these compounds are in the range of 1.959(4)-2.041(3) Å, Cu–O distance was 1.961(3) Å and Cu–Br distances were in the range of 2.4052(4)-2.4381(6) Å for the square base configuration while for apical distance it was 2.6745(7) Å. Magnetic properties have been investigated for all compounds in the temperature range 2-300 K. Compound 1 shows weak antiferromagnetic intermolecular interaction.     

Polynuclear lanthanide complexes of a series of bridging ligands containing two tridentate N,N',O-donor units: structures and luminescence properties

A set of three potentially bridging ligands containing two tridentate chelating N,N',O-donor (pyrazole-pyridine-amide) donors separated by an o, m, or p-phenylene spacer has been prepared and their coordination chemistry with lanthanide(III) ions investigated. Ligand L(1) (p-phenylene spacer) forms complexes with a 2:3 M:L ratio according to the proportions used in the reaction mixture; the Ln(2)(L(1))(3) complexes contain two 9-coordinate Ln(III) centres with all three bridging ligands spanning both metal ions, and have a cylindrical (non-helical) 'mesocate' architecture. The 1:1 complexes display a range of structural types depending on the conditions used, including a cyclic Ln(4)(L(1))(4) tetranuclear helicate, a Ln(2)(L(1))(2) dinuclear mesocate, and an infinite one-dimensional coordination polymer in which metal ions and bridging ligands alternate along the sequence. ESMS studies indicate that the 1:1 complexes form a mixture of oligonuclear species {Ln(L(1))}(n) in solution (n up to 5) which are likely to be cyclic helicates. In contrast, ligands L(2) and L(3) (with o- and m-phenylene spacers, respectively) generally form dinuclear Ln(2)L(2) Ln(III) complexes in which the two ligands may be arranged in a helical or non-helical architecture about the two metal ions. These complexes also contain an additional exogenous bidentate bridging ligand, either acetate or formate, which has arisen from hydrolysis of solvent molecules promoted by the Lewis-acidity of the Ln(III) ions. Luminescence studies on some of the Nd(III) complexes showed that excitation into ligand-centred pi-pi* transitions result in the characteristic near-infrared luminescence from Nd(III) at 1060 nm.     

A family of coordination polymers derived from a flexible dicarboxylic acid and auxiliary N-donor ligands: solvothermal synthesis,crystal structure and dye adsorption properties

Transition Metal Chemistry - Four novel coordination polymers [Cd2(oba)2(phen)2]n (1), [Mn3(oba)3(phen)2]n (2), [Zn(oba)(phen)]n (3) and [Mn(oba)(dmphen)]n (4)...