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

The reaction of FcCOCl (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(η³-C₃H₅)(CO)₂(CH₃CN)₂Br] or [Mo(η³- C₅H₅O)(CO)₂(CH₃CN)₂Br] leading to the new trinuclear complexes [Mo(η³-C₃H₅)(CO)₂(L)₂Br] (C1 for L = L1; C3 for L = L2) and [Mo(η³-C₅H₅O)(CO)₂(L)₂Br] (C2 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(η³-C₅H₅O)(CO)₂(L1)₂Br] 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).     

Reactivities of the coordinated organonitriles in molybdenum(0) and tungsten(0) phosphine complexes: protonation of the nitrile carbon and cleavage of the CN triple bond

The molybdenum and tungsten dinitrogen-organonitrile complexes trans-[M(N₂)(NCR)(dppe)₂] (2, M=Mo; 4, M=W; R=Ph, C₆H₄Me-p, C₆H₄OMe-p, Me; dppe=Ph₂PCH₂CH₂PPh₂) underwent double protonation at the nitrile carbon atom with loss of N₂ and a change in oxidation state to +4 on treatment with hydrochloric acid to afford the cationic imido complexes trans-[MCl(NCH₂R)(dppe)₂]⁺. The solid-state structure of trans-[WCl(NCH₂CH₃)(dppe)₂][PF₆]·CH₂Cl₂ was determined by single-crystal X-ray analysis. Protonation of complexes 2 by fluoroboric acid or hydrobromic acid also formed the similar imido complexes trans-[MoX(NCH₂R)(dppe)₂]⁺ (X=F, Br). In contrast, the dinitrogen complex trans-[Mo(N₂)₂(dppe)₂] reacted with two equiv. of benzoylacetonitrile, a nitrile with acidic CH hydrogen atoms, to give the nitrido complex trans-[Mo(N)(NKCCHCOPh)(dppe)₂] (12), which was accompanied by evolution of dinitrogen and the formation of 1-phenyl-2-propen-1-one in high yields. For complex 12, the zwitterionic structure, where the anionic enolate ligand PhC(O⁺)=CHCN coordinates to the cationic Mo(IV) center through its nitrogen atom, was confirmed by spectroscopic measurements and single-crystal X-ray analysis. A unique intermolecular aromatic C---HO hydrogen bonding was observed in that crystal structure. Complex 12 is considered to be formed via the cleavage of the CN triple bond of benzoylacetonitrile on the metal. A reaction mechanism is proposed, which includes the double protonation of the nitrile carbon atom of the ligating benzoylacetonitrile on a low-valent molybdenum center.     

Reactions of seven coordinate complexes. Synthesis, structure, and copper complex of the novel ligand 3-methyltriazolo(1,5-a)6-acetylsemicarbazonepyridine

The reaction of aquachloro(2,6-diacetylpyridinedisemicarbazone)copper(II) with hydrazine hydrate gave the copper complex of 3-methyltriazolo(1,5-a)6-acetylsemicarbazonepyridine. The free ligand was isolated from the copper complex. The X-ray structures of both the copper complex and the free ligand are reported. The copper complex and the free ligand both crystallize in the triclinic space group with 2 molecules per cell. The Cu complex has cell dimensions of a=8.8574(4), b=10.1764(5), c=10.4434(5) Å, α=71.956(1), β=64.913(1), and γ=81.597(1)°. The Cu ion is in a square pyramidal arrangement, with the Cu, the ligand, and a Cl in the plane and a disordered Cl and H₂O in the apical position. The ligand has cell dimensions of a=7.2696(7), b=8.0516(7), c=9.9326(9) Å, α=110.534(2), β=96.730(2), and γ=100.089(2)°. The ligand is planar with a conformation determined by an internal N-H?H hydrogen bond. The role of the Cu ion in the formation of the triazolopyridine is discussed.     

The ReH6[P(C6H5)3]2 ion as a ligand: complexes with M(CO)3 fragments (M = Cr, Mo, W)

The reactions of [(H₅C₆)₃P]₂ReH₆⁻ with (CH₃CN)₃Cr(CO)₃, (diglyme)Mo(CO)₃ or (C₃H₇CN)₃W(CO)₃ led to the formation of [(H₅C₆)₃P]₂ReH₆M(CO)₃⁻ (M = Cr, Mo, W) complexes. These have been characterized by IR and NMR spectroscopies, as well as elemental analyses. A single crystal X-ray diffraction study has also been carried out for the M = Cr complex as a K(18-crown-6)⁺ salt. The complex crystallizes as a THF monosolvate in the monoclinic space group P2₁/n with a = 22.323(6), B = 9.523(2), C = 27.502(5) Å, β = 104.98(2)⁰ and V = 5648 ų for Z = 4. The Re---Cr separation is 2.5745(12) Å, and the two phosphine ligands are oriented unsymmetrically. Although the hydride ligands were not found, the presence of three bridging hydrides and a dodecahedral coordination geometry about rhenium could be inferred. Low temperature ¹H and ³¹P NMR spectroscopic studies did not reveal the low symmetry of the solid state structure.     

Synthesis and characterization of organomolybdenum and organotungsten halides containing the η-pentabenzylcyyclopentadienyl ligand η-Bz5C5M(CO)3X (M = Mo, W; X = Cl, Br, I). The X-ray molecular structure of η-Bz5C5Mo(CO)3I

An improved synthetic procedure for pentabenzylcyclopentadiene Bz₅C₅H was developed. Six new organomolybdenum and organotungsten halides η⁵-Bz₅C₅M(CO)₃X(M = Mo, W; X = Cl, Br, I) were syntesized through the reaction of η⁵-Bz₅C₅M(CO)₃Li (derived from Bz₅C₅H, n-BuLi and M(CO)₆) with PCl₃, PBr₃ or I₂ and characterized by elemental analysis, IR and ¹H NMR spectroscopy. The structure of η⁵-Bz₅C₅Mo(CO)₃I was determined by single-crystal X-ray diffraction techniques. It crystallized in the monoclinic space groupp P2/c with cell parameters a = 13.294(4), B = 15.147(4), C = 19.027(3) Å, β = 108.32(2)°, V = 3637(2) ų, Z = 4 and D_x = 1.50 g cm⁻³. The final R value was 0.035 for 4564 observed reflections.     

Hydrothermal syntheses, structural characterizations and magnetic properties of cobalt(II) and manganese(II) coordination polymeric complexes containing pyrazinecarboxylate ligand

Two novel coordination polymeric complexes [Co(pzca)₂(H₂O)]_n (1) and [Mn(pzca)₂]_n (2) (pzca=2-pyrazinecarboxylate) have been synthesized by hydrothermal reaction of M(CH₃COO)₂·4H₂O (M=Co, Mn) and 2-pyrazinecarboxylic acid. The complex 1 displays an infinite zigzag chain structure in which each cobalt(II) center was coordinated by three nitrogen and three oxygen atoms to generate a CoN₃O₃ octahedral geometry. The existence of hydrogen bond leads to the formation of the interpenetrating stacking structure. Complex 2 indicates a two-dimensional layer structure through the linkage of bridging oxygen atom of pzca ligand. Each Mn(II) center exhibits a distorted octahedral coordination environment with four oxygen atoms and two nitrogen atoms. The distances of adjacent Mn(II) atoms are 3.503 and 5.654 Å, respectively. The magnetic property analyses reveal that both complexes show weak antiferromagnetic exchange interactions between the metal centers.     

Transfer of chirality by dithiophosphate ligands and chiral discrimination in the stereoselective formation of square-planar Ni(II) complexes

In the formation reaction of Ni(2+) with the chiral racemic ligand, (R)(R)bdtp(-)/(S)(S)bdtp(-), bdtp(-) = [SSPOCH)CH(3))CH(CH(3))O](-), cyclo- O,O'-[1,2-dimethylethylene] dithiophosphato ion, the meso-complex Ni[(R)(R)(lambda)bdtp][(S)(S)(delta)-bdtp] is stereoselectively produced. The meso-complex was compared with the enantiopure crystals of (+)(589)Ni[(R)(R)(lambda)bdtp](2) or (-)(589)Ni[(S)(S)(delta)bdtp](2), as well as racemic crystals, rac-(+/-)Ni[bdtp](2), which were prepared from the solution containing the two enantiomers in a 1:1 ratio. Dissociation constants in solutions indicate different stability of the meso and enantiopure complexes depending on the solvent, whereas a more efficient crystal packing, weak H-bonding, and nonbonding interactions contribute to stabilization of the meso-species over the racemic one. Molecular structures show that the outer five-membered ligand ring adopts the half-chair conformation C(2) with either the lambda or the delta chirality and the methyl groups are in equatorial (e) positions. Enantiopure ligands of (+)(589)Ni[(R)(R)(lambda)bdtp](2) and (-)(589)Ni[(S)(S)(delta)bdtp](2) induce chirality into the symmetric SSNiSS chromophore with slightly helical distortion. Thus, their CD spectra exhibit weak negative or positive Cotton effects at 662 nm. CD spectra in L(+)- and D(-)diethyltartrate of the meso-complex and racemic crystal, rac-(+/-)Ni[bdtp](2), exhibit different weak Cotton effects of opposite sign. Complexes dissociate in methanol; rac-(+/-)Ni[bdtp](2) in methanol undergoes a crystallization-induced second-order asymmetric transformation which finally yields crystals of the meso-Ni[(R)(R)(lambda)bdtp][(S)(S)(delta)bdtp] complex.     

The role of cyclopentadienyl versus indenyl in Mo(II) spirodiene complexes reactivity: A DFT mechanistic study

Spiro[2,4]hepta-4,6-diene and spiro[4,4]nona-1,3-diene react with [Mo(CO)₂Cp’(NCCH₃)₂][BF₄] (Cp’ = Cp, Ind; Ind = η⁵-C₉H₇) to afford the corresponding diene complex [Mo(diene)(CO)₂Cp′]⁺. When Cp’ = Ind, the reaction proceeded forward leading to ring opening in the case of the small spiro ring. Although this and another product resulting from migration of the side arm to the carbonyl were detected when Cp’ = Cp, they did not form from the diene complex. A DFT/PBE1PBE study was carried out and showed a kinetically controlled reaction pathway leading from the [Mo(diene)(CO)₂Ind]⁺ to the reaction product, with an activation barrier of 21.3 kcal mol⁻¹. The thermodynamic preferred species was the non-observed complex (insertion), and its formation required higher barriers. In the presence of Cp, all the barriers increased significantly, explaining the inertness of the initial diene complex. The interpretation of this behaviour is associated with the ease of the η⁵ → η³ haptotropic rearrangement of the indenyl, which helps to lower some relevant barriers. This route is not available for the Cp analogue.     

Multinuclear NMR study of the complexes of 6-phospho-D-gluconic acid with W(VI) and Mo(VI)

Multinuclear ((1)H, (13)C, (17)O, (31)P, (95)Mo, (183)W) magnetic resonance spectroscopy (1D and 2D) has been used to show that 6-phospho-d-gluconic acid forms three complexes with tungsten(VI) and six complexes with molybdenum(VI) in aqueous solution, depending on pH and concentration. Two isomeric 1:2 (metal-ligand) complexes are detected both with tungstate(VI) and molybdate(VI), having MO(2)(2+) centres and involving the carboxylate and the adjacent OH groups in addition to one 2:1 (metal-ligand) complex possessing a M(2)O(5)(2+) centre, with the ligand being coordinated by the carboxylate group and the three consecutive OH groups in positions 2, 3 and 4. Molybdate(VI) forms three additional species, which are not detected with tungstate. One of them is a 2:1 complex with a Mo(2)O(5)(2+) centre, with the ligand being tetradentate via O-3, O-4, O-5 and the phosphate group. The other two are 12:4 species, which can be seen as two 1:2 complexes bound together in a ring through two diphosphomolybdate moieties each derived from heptamolybdate by inclusion of two phosphate groups from the ligands.     

Properties of homo- and heteronuclear mixed biscarbene complexes with conjugated bithiophene units

The syntheses and structures of homo- and heteronuclear biscarbene complexes with bithiophene spacers were investigated. The complexes were synthesized by lithiation of bithiophene followed by metallation using combinations of the metal precursors MnMeCp(CO)₃, W(CO)₆, Mo(CO)₆ and Cr(CO)₆, after which the reaction was quenched with triethyloxonium tetrafluoroborate. This classical Fischer method yielded monocarbene complexes, [ML_nC(OEt)C₄H₂S-C₄H₃S], ([ML_n] = Cr(CO)₅1a, W(CO)₅2a or MnMeCp(CO)₂3a), homonuclear biscarbene complexes, [ML_nC(OEt)C₄H₂S-C₄H₂SC(OEt)ML_n], ([ML_n] = Cr(CO)₅1b, W(CO)₅2b or MnMeCp(CO)₂3b) and heteronuclear biscarbene complexes, [ML_nC(OEt)C₄H₂S-C₄H₂SC(OEt)M′L_n] (1d: [ML_n] = Cr(CO)₅ and [M′L_n] = W(CO)₅; 1e: [ML_n] = MnMeCp(CO)₂ and [M′L_n] = Cr(CO)₅; 1f: [ML_n] = Cr(CO)₅ and [M′] = Mo(CO)₅); 2d: [ML_n] = MnMeCp(CO)₂ and [M′L_n] = W(CO)₅; 3c: [ML_n] = MnMeCp(CO)₂ and [M′L_n] = Mo(CO)₅). Electron density calculations with the gaussian03 software package of 1e revealed a polar rod with the negative pole towards the chromium carbene side, whereas the biscarbenes 1d and 1b showed very little polarity. By-products resulting from activation of the carbene moieties in homonuclear biscarbene complexes included (i) ester-type complexes of the form [ML_nC(OEt)C₄H₂S-C₄H₂SC(O)OEt], ([ML_n] = Cr(CO)₅1c or W(CO)₅2c), formed in situ in the reaction of 1b and 2b, (ii) the organic bis-ester compound [EtOC(O)C₄H₂S-C₄H₂SC(O)OEt] 4, where both metal moieties had been substituted by oxygen and (iii) the carbon-carbon coupled dimeric bithienyl compound [C₄H₃S-C₄H₂SC(O)C(O)C₄H₂S-C₄H₃S] 5. By-products obtained from heteronuclear biscarbene reactions contain the former diketo compound (or a derivative) as spacer between two metal carbonyl fragments and have the general formula [ML_nC(OEt)C₄H₂S-C₄H₂SCR-CR′C₄H₂S-C₄H₂SC(OEt)ML_n] (5a: [M] = Cr(CO)₅, R = OH, R′ = OEt; 5b: [M] = W(CO)₅, R = R′ = O; 5c: [M] = Mo(CO)₅, R = R′ = O). Reaction of 1d, 1e and 1f with hex-3-yne resulted in the formation of benzannulated products 6a, 6b and 6c. All novel complexes were fully characterized using various spectroscopic techniques. The crystal structures of 1b, 2a and 5 are reported.     

Different reaction behaviour of molybdenum and tungsten - Reactions of the dichloro dioxo dimethyl-bispyridine complexes with thiophenolate

The reaction of the metal complexes MO₂Cl₂(mebipy) (M = Mo, W) with two equivalents thiophenol by the exact same procedure leads to two different products for molybdenum [Mo₂O₄(SPh)₂(mebipy)₂] and tungsten [WO₂(SPh)₂(mebipy)]. To understand why this is the case the redox potentials of the starting materials were measured showing that the redox potential for thiophenol is lower than the redox potentials (M^V ↔ M^VI) for both of the metal precursors. A reduction of the metal and oxidation of the sulfur should be possible for both reactions but occurs only for the molybdenum compound. Theoretical calculations show that different metal-sulfur bond strengths are as well and equally responsible for the differing reaction behaviour as are the redox potentials.     

A hemiacetalate complex of Ru(II)

Reaction of cis-Ru(bisox)₂Cl₂, where bisox is 4,4,4′,4′-tetramethyl-2,2′-bisoxazoline, with excess of pyridine-2-carboxaldehyde (py-2-al) in 1:1 (v/v) methanol-water mixture under nitrogen atmosphere and subsequent addition of excess of NH₄PF₆ give [Ru(bisox)₂(py-2-al)](PF₆)₂ · H₂O (1). Refluxing of 1 in dehydrated methanol in presence of triethylamine yields the corresponding hemiacetalate complex: [Ru(bisox)₂ (pyridine-2-(α-methoxymethanolato))]PF₆ · 1.5H₂O (2). Both the complexes have been characterised by single crystal X-ray crystallography, FTIR and NMR. In cyclic voltammetry in acetonitrile at a glassy carbon electrode, 2 displays a quasireversible Ru(II/III) couple at 1.08 V versus NHE which is not observed in 1. A tentative mechanism is proposed for the conversion of 1 to 2. DFT calculations with the LanL2DZ basis set have been performed to investigate these observations theoretically.     

Chiroptical properties of anionic and neutral nickel(II) bis(dithiolene) complexes based on methyl and dimethyl-dddt ligands

Racemic and enantiopure nickel(II) bis(dithiolene) anionic and neutral complexes based on the methyl-5,6-dihydro-1,4-dithiin-2,3-dithiolate (me-dddt) and dimethyl-5,6-dihydro-1,4-dithiin-2,3-dithiolate (dm-dddt) ligands have been experimentally and theoretically investigated with a special focus on their chiroptical properties. According to the time-dependent density-functional theory (TD-DFT) calculations, the strong near-infrared absorption bands typical for such complexes are only weakly active in circular dichroism (CD), and moreover, they have opposite signs for the axial and equatorial conformations, due to the variation of the angle between the transition electric and magnetic dipole moments, thus leading to the mutual cancellation of their contributions and the absence of these bands in the experimental CD spectra. The influence of the number of stereogenic centers and of the oxidation state of the complexes on their chiroptical properties is highlighted. The solid-state structure of the complex (TMA)[Ni(rac-me-dddt)₂] (TMA = tetramethylammonium), determined by single-crystal X-ray diffraction analysis, shows a rather unusual cis arrangement of the two dithiolene ligands, with the methyl substituents adopting an axial conformation, which is not the most stable one in the gas phase.     

Examining the impact of steric and electronic variation in N2S scorpionate ligands on the properties of zinc(II) and cadmium(II) complexes

A series of LZn(II)Br (1-4) and LCd(II)Cl complexes (9-11) has been prepared by the reaction of metal halide precursors with the lithium salts of the N₂S⁻ ligands bis(3,5-diisopropylpyrazol-1-yl)dithioacetate (L¹), bis(3,5-di-tert-butylpyrazol-1-yl)dithioacetate (L²), N-phenyl-2,2-bis(3,5-diisopropylpyrazol-1-yl)thioacetamide (L³) and N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide (L⁴). Characterization by X-ray crystallography and DOSY NMR studies indicate that LZnBr complexes 1-4 are mononuclear both in the solid state and in solution. Steric differences between ligands L¹-L⁴ result in distortion from an ideal tetrahedral geometry for each complex, with the degree of distortion depending on the bulk of the ligand substituents. In contrast, the related complex L³CdCl was shown by X-ray crystallography to dimerize in the solid state to form the chloride-bridged five-coordinate complex [L³CdCl]₂ (10). Despite 10 having a dinuclear structure in the solid state, DOSY NMR studies indicate 9-11 exist as mononuclear LCdCl species in solution. In addition, Zn(II) cyanide complexes of the form LZnCN [L = L¹ (5), L³ (7), L⁴ (8)] have been characterized and the X-ray structure of 8 determined. Moreover, density functional theory calculations have been conducted which yield important insight into the bonding in 1-4 and 5-8 and the electronic impact of ligands L¹-L⁴ on the zinc(II) ion and its ability to function as a Lewis acid catalyst.     

Carbonylmolybdenum complexes with di(imino)pyridine and related ligands: Reduction of a di(imino)pyridine to an aminoiminopyridine system under mild conditions

The reactions of [Mo(CO)₆] towards a 2,6-di(imino)pyridine L¹ and related ligands were studied. The reaction with L¹ afforded two new complexes, [Mo(CO)₄L¹] (1) and [Mo(CO)₄L²] (2), where L² is the 2-amino-6-iminopyridine ligand arising from the hydrogenation of one imine function of L¹; similar reaction with a 2-acetyl-6-iminopyridine ligand L³ afforded [Mo(CO)₄L³] (3). Compounds 1, 2 and 3 have been fully characterised by IR, ¹H NMR and X-ray crystallography; they present a metal ion in a pseudo-octahedral environment, the three organic ligands acting with bidentate N₂ coordination modes. One of the imine functions in 1, the amine function in 2, and the ketone function in 3 are uncoordinated.     

Re(V) complexes formed by metal-assisted solvolysis of di-(2-pyridyl)ketone: Synthesis, X-ray studies, redox behavior and DFT calculations

The complexes {ReOCl₂[(py)₂C(O)(OR)]}, (R = CH₂CH₃ (1), CH₂CH₂CH₃ (2)) were obtained from the metal-assisted alcoholysis reaction of di-2-pyridylketone. Their crystal structures were determined by single-crystal X-ray diffraction. The structures of 1 and 2 consist of neutral mononuclear molecules containing the [ReO]³⁺ core. In both compounds the Re(V) central ion is also bonded to an oxygen and both nitrogens from the organic ligand and two chlorides in a distorted octahedral environment. Cyclic voltammograms in CH₃CN solutions showed two main redox responses, both of them involving one electron transfer. Comparative theoretical studies on equilibrium geometries and electronic properties were conducted in the framework of the density functional theory (DFT).     

Heterobimetallic platinum(II)-palladium(II) complexes bridged by fluorobenzenethiolates. Structure and equilibria

Synthesis of the heterobimetallic platinum(II)-palladium(II) complexes with poly fluorinated benzenethiolates as intermetallic bridges, [(dppe)Pd(μ-SR_F)₂Pt(dppe)](SO₃CF₃)₂ with SR_F = p-SC₆F₄(CF₃) (1), SC₆F₅ (2), p-SC₆HF₄ (3) and o-SC₆H₄(CF₃) (4), have been accomplished either by a redistribution reaction in mixtures of the homonuclear bimetallic species, [(dppe)Pd(μ-SR_F)₂Pd(dppe)]²⁺/[(dppe)Pt(μ-SR_F)₂Pt(dppe)]²⁺ or by assembling the monometallic building blocks [(dppe)M(μ-SR_F)₂]/[(dppe)M′(solvent)₂]²⁺, M, M′ = Pd or Pt. Both experimental systems reach an equilibrium state which is independent of the temperature within the probed range, −90 °C to +50 °C. A single crystal of the heterobimetallic compound [(dppe)Pd(μ-SC₆F₅)₂Pt(dppe)](SO₃CF₃)₂(acetone)₂ (2) was isolated and analyzed by X-ray diffraction. Comparison with the corresponding structures exhibited by the homobimetallic analogous, [Pd₂(μ-SC₆F₅)₂(dppe)₂](SO₃CF₃)₂(acetone)₂ (5) and [Pt₂(μ-SC₆F₅)₂(dppe)₂](SO₃CF₃)₂(acetone)₂ (6) shows that all three structures are isostructural in space group . All three compounds exhibit a centrosymmetric planar [M₂(μ-S)₂] ring in which the sulfur substituents are arranged in an anti configuration.     

Improved preparation of indenyl molybdenum(II) and tungsten(II) compounds

Oxidative addition of 1-bromo-1H-indene to [Mo(CO)₃(NCMe)₃] and [W(CO)₃(NCEt)₃] is a suitable method for preparation of the indenyl compounds [IndMo(CO)₃Br] and [IndW(CO)₃Br], respectively. These products were fully characterised using spectroscopic methods. Structure of [IndW(CO)₃Br] was determined by single crystal X-ray diffraction analysis.     

Stereochemically non-rigid helical mercury(II) complexes

Reactions of the 1:2 condensate (L) of benzil dihydrazone and 2-acetylpyridine with Hg(ClO₄)₂ · xH₂O and HgI₂ yield yellow [HgL₂](ClO₄)₂ (1) and HgLI₂ (2), respectively. Homoleptic 1 is a 8-coordinate double helical complex with a Hg(II)N₈ core crystallising in the space group Pbca with cell dimensions: a = 16.2250(3), b = 20.9563(7), c = 31.9886(11) Å. Complex 2 is a 4-coordinate single helical complex having a Hg(II)N₂I₂ core crystallising in the space group P2₁/n with cell dimensions a = 9.8011(3), b = 17.6736(6), c = 16.7123(6) Å and β = 95.760(3)^o. In complex 1, the N-donor ligand L uses all of its binding sites to act as tetradentate. On the other hand, it acts as a bidentate N-donor ligand in 2 giving rise to a dangling part. From variable temperature ¹H NMR studies both the complexes are found to be stereochemically non-rigid in solution. In the case of 2, the solution process involves wrapping up of the dangling part of L around the metal.     

Syntheses, characterizations and crystal structures of four zinc(II) and cadmium(II) complexes constructed by ligand bearing poly-coordination atoms

Treatment of 3-(4-carboxyphenylhydrazono)pentane-2,4-dione (HL) with transition metal ions afforded four novel complexes, [Zn(L)(μ₂-OOCCH₃)(H₂O)]_n (1), [Zn(L)₂(MeOH)₄] (2), {[Cd₄(η²-L)₄(μ₂-η²-L)₄(H₂O)₄(MeOH)₂]·MeOH} (3) and [Cd(η²-L)(μ₂-η²-OOCCH₃)(H₂O)₂]_n (4). Their crystal structures have been characterized by single-crystal X-ray crystallography. In polymer 1, the acetate anions bridge the Zn(II) ions forming an infinite one-dimensional (1-D) chain with L⁻ units acting as monodentate ligands in the side chain. In mononuclear complex 2, two L⁻ ligands act as monodentate fashion to coordinate to the Zn(II) ion. In its solid-state structure, [Zn(L)₂(MeOH)₄] groups are joined together by hydrogen bonds forming a three-dimensional (3-D) supramolecular network. In tetranuclear complex 3, four Cd(II) ions are linked by four μ₂-η²-L⁻ ligands, and chelated by another four L⁻ ligands, respectively. In polymer 4, the acetate anions bridge the Cd(II) ions leading to a 1-D chain containing chelating L⁻ units in the side chain.