Five-coordinate cobalt(II) complexes of tris(2-pyridylmethyl)amine (TPA): Synthesis, structural and magnetic characterization of a terephthalato-bridged dinuclear cobalt(II) complex

The cobalt(II) complexes [Co(TPA)Cl]ClO₄ (1), [Co(TPA)Br]ClO₄ (2), [Co(TPA)(H₂O)]Cl(ClO₄) (3) and [Co₂(TPA)₂(μ-tp)](ClO₄)₂ · 2H₂O (4) (TPA = tris(2-methylpyridyl)amine and tp = terephthalate dianion) were synthesized and structurally characterized by UV-vis and IR spectroscopy. The molecular structures of complexes 1 and 4 were determined by X-ray crystallography and their magnetic properties were measured over the temperature range 2-300 K. The coordination geometry around the central Co(II) in these compounds has a distorted trigonal bipyamidal geometry with four nitrogen atoms from the TPA ligand and the fifth coordination site is occupied by Cl⁻ ion in 1, Br⁻ ion in 2, coordinated oxygen atom from H₂O in 3 and by an oxygen atom supplied by the carboxylate group of the bridged terephthalato ligand in 4. The visible spectra of the complexes 1-3 in MeOH show strong distortion toward tetrahedral geometry. For complex 4, analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(monodentate) coordination mode for the bridged tp. X-ray data for 1 and 4 show that the former is mononuclear while the latter is dinuclear. The electronic spectrum of 4 in MeOH is in complete agreement with the assigned X-ray geometry around the Co(II) centers. The magnetic behavior of the mononuclear complex 1 is indicative of a high-spin compound with zero-field splitting. The best fit was obtained with ∣D∣ = 7.3 cm⁻¹, g = 2.25. The dinuclear complex 4 exhibits weak antiferromagnetic coupling with a coupling constant J = −0.8 cm⁻¹. The magnetic properties and the structural parameters of 4 are discussed in relation to the other related μ-terephthalato dinuclear Co(II) compounds. The geometry of the coordination sphere around 4 is unique - the CSD compilation listing only one other compound with such a geometry around the dinuclear Co(II) complex and its composition is far different from that in 4. However, they share a common feature of having a weakly antiferromagnetic coupling between Co(II) centers.     

Luminescent probes for indole-binding proteins derived from ruthenium(II) polypyridine complexes

We report here the synthesis, characterisation, electrochemical, photophysical and protein-binding properties of four luminescent ruthenium(II) polypyridine indole complexes [Ru(bpy)₂(L1)](PF₆)₂ (1), [Ru(bpy)₂(L2)](PF₆)₂ (2), [Ru(L1)₃](PF₆)₂ (1a), and [Ru(L2)₃](PF₆)₂ (2a) (bpy = 2,2′-bipyridine; L1 = 4-(N-(2-indol-3-ylethyl)amido)-4′-methyl-2,2′-bipyridine; L2 = 4-(N-(6-N-(2-indol-3-ylethyl)hexanamidyl)amido)-4′-methyl-2,2′-bipyridine). Their indole-free counterparts, [Ru(bpy)₂(L3)](PF₆)₂ (3) and [Ru(L3)₃](PF₆)₂ (3a) (L3 = 4-(N-(ethyl)amido)-4′-methyl-2,2′-bipyridine), have also been synthesised for comparison purposes. Cyclic voltammetric studies revealed ruthenium-based oxidation at ca. +1.3 V versus SCE and diimine-based reductions at ca. −1.20 to −2.28 V. The indole moieties of complexes 1, 2, 1a and 2a displayed an irreversible wave at ca. +1.1 V versus SCE. All the ruthenium(II) complexes exhibited intense and long-lived orange-red triplet metal-to-ligand charge-transfer ³MLCT (dπ(Ru) → π*(L1-L3)) luminescence upon visible-light irradiation in fluid solutions at 298 K and in alcohol glass at 77 K. The binding of the indole-containing complexes to bovine serum album (BSA) has been studied by quenching experiments and emission titrations.     

One-pot syntheses of alkenyl-phosphonio complexes of ruthenium(II), rhodium(III) and iridium(III) bearing p-cymene or pentamethylcyclopentadienyl groups

Reaction of [(p-cymene)RuCl₂(PPh₃)] (1) or [Cp^∗MCl₂(PPh₃)] (Cp^∗ = C₅Me₅) (3a: M = Rh; 4a: M = Ir) with 1-alkynes and PPh₃ were carried out in the presence of KPF₆, generating the corresponding alkenyl-phosphonio complexes, [(p-cymene)RuCl(PPh₃){CHCR(PPh₃)}](PF₆) (2a: R = Ph; 2b: R = p-tolyl) or [Cp^∗MCl(PPh₃){CHCPh(PPh₃)}](PF₆) (5: M = Rh; 6: M = Ir). Similar reactions of complexes [Cp^∗RhCl₂(L¹)] (3a: L¹ = PPh₃; 3c: L¹ = P(OMe)₃) with L² (L² = PPh₃, PMePh₂, P(OMe)₃) gave [Cp^∗RhCl(L¹)(L²)](PF₆) (7bb: L¹ = L² = PMePh₂; 7ca: L¹ = P(OMe)₃, L² = PPh₃; 7cc: L¹ = L² = P(OMe)₃). Alkenyl-phosphonio complex 5 was treated with P(OMe)₃ or 2,6-xylyl isocyanide, affording [Cp^∗RhCl(L){CHCPh(PPh₃)}](PF₆) (8a: L = P(OMe)₃; 8b: L = 2,6-xylNC). X-ray structural analyses of 2a, 6 and 8a revealed that the phosphonium moiety bonded to the C_β atom of the alkenyl group are E configuration.     

New butane-1,2,3,4-tetracarboxylato bridged cobalt(II) complexes

Four butane-1,2,3,4-tetracarboxylato bridged supramolecular complexes [Co₂(H₂O)₅(BTC)]·2H₂O 1, [Co₂(H₂O)₅(BTC)]·2H₂O 2, [Co₂(H₂O)₆(bpy)₂(BTC)]·4H₂O 3 and [Co₂(H₂O)₂(bpy)₂(BTC)] 4, (H₄BTC = butane-1,2,3,4-tetracarboxylic acid, 2,2-bpy = 2,2-bipydine) are synthesized and characterized by single-crystal X-ray diffraction. IR spectroscopy, TG-DTA analyses, elemental analyses, powder X-ray diffraction and magnetic measurements for 3 and 4 are carried out. The dinuclear Co unit in 2 is bridged by BTC⁴⁻ anions into 2D layers, which are assembled via interlayer hydrogen bonds into a 3D (4⁴·6²)(4⁵·6⁵)₂(4⁶·6⁸·8) topological supramolecular architecture. In 3, the [Co₂(H₂O)₆(bpy)₂(BTC)] molecules are aggregated to 2D layers via π-π stacking interactions, the resulting layers are engaged in hydrogen bonding leading to a novel 3D supramolecular architecture with the schläfli symbol of (10².12)₂(4.10²)₂(4².10².12²). The Co atoms in 4 are linked by BTC⁴⁻ anions into a 1D chain, then the hydrogen bonding and π-π stacking interactions result in formation of a 3D novel (4³.6².8)₂(4⁶.6⁶.8³)(6³)₂ topological networks. The variable temperature magnetic characterizations on 3 and 4 suggest weak antiferromagnetic or ferromagnetic coupling exchange via π···π stacking interactions (J = -0.03 cm⁻¹ for 3, J = 0.11 cm⁻¹ for 4).     

Novel cobalt(II) complexes with pyridyl/ether or pyridyl/thioether ligands. The conversion of pyridyl/thioether cobalt(II) complex to pyridyl/sulfinato cobalt(III) compound

Two new cobalt(II) complexes of symmetric hexadentate mixed-ligand N,O [1,12-bis(2-pyridyl)-5,8-dioxa-2,11-diazadodecane (pydado)] and N,S [1,12-bis(2-pyridyl)-5,8-dithia-2,11-diazadodecane (pydadt)] donor atoms have been synthesized as perchlorate salts. The crystal structures show that [Co(pydado)](ClO₄)₂ · H₂O (1) crystallizes in the triclinic space group and [Co(pydadt)](ClO₄)₂ (2) crystallizes in the monoclinic space group P2_1/c. The cation [Co(pydado)]²⁺ is pseudo-octahedral with the two pyridyl groups in trans position. However, in [Co(pydadt)]²⁺ complex, the size of thioether sulfur atoms imposes a distorted octahedral geometry; the pyridyl groups and the sulfur atoms are in trans position. The reaction of the complex 2 and hydrogen peroxide resulted to the oxidation of Co^II into Co^III and the thioether groups of the ligand to sulfinate groups with elimination of the central ethylenic group of pydadt. Thus, complex 2 was converted to bis[3-(2-pyridylmethylamino)ethanesulfinate] cobalt(III) complex (3) {[Co(pynso)₂](ClO₄) · 0.5H₂O}. The X-ray crystal structure reveals that the compound 3 crystallizes in the triclinic space group with the same donor atoms (N_pyridyl, N_amine and S) belonging to the two ligands in cis-position. In aqueous solution, the stability constants of the Co(II) chelates with these two ligands, determined by potentiometry, show the formation of [Co(LH)]³⁺ and [CoL]²⁺ species in all cases. The chelating power of pydadt ligand is slightly greater than that of pydado.     

Coordination chemistry of pyrazolylbis((alkylthio)methyl)borates: Hybrid nitrogen and sulfur donor ligands

The synthesis of iron(II), cobalt(II) and nickel(II) complexes supported by chelating borate ligands containing one pyrazole and two thioethers, phenyl(pyrazolyl)bis((alkylthio)methyl)borates, [Ph(pz)Bt^R], is described. The six-coordinate complexes [Ph(pz)Bt]₂M, M = Fe (1Fe), Co (1Co) and Ni (1Ni), form exclusively the cis isomers as confirmed by X-ray diffraction analyses. Whereas 1Co and 1Ni are high spin, 1Fe exhibits a room temperature magnetic moment, μ_eff = 4.1 μ_B, consistent with spin-crossover behavior. Quantitative analysis of the electronic spectrum of 2Ni leads to a value of D_q = 1086 cm⁻¹, reflective of a ligand field strength somewhat weaker than those imposed by the related tridentate borate ligands Tp or PhTt. Replacement of the methylthioether substituent with the sterically more demanding tert-butylthioether leads to the isolation of [Ph(pz)Bt^tBu]MX, M = Co, X = Cl (2Co); M = Ni, X = Cl (2Ni) or acac (3). The solid state structures of 2Co and 2Ni are chloride-bridged dimers. Additional high-spin cobalt(II) complexes, accessible under distinct preparative conditions, [κ²-Ph(pzH)Bt^tBu] CoCl₂·THF (4) and [κ²-Ph(pz)Bt^tBu]₂Co (5), have been fully characterized.     

Coordination polymers of manganese(II) and cobalt(II) of a flexible tetradentate pyridine amide ligand: 1D zigzag network and non-covalent interactions

Synthesis and crystal structure of two coordination polymers of composition [Mn^II(H₂bpbn)_1.5][ClO₄]₂ · 2MeOH · 2H₂O (1) and [Co^II(H₂bpbn)(H₂O)₂]Cl₂ · H₂O (2) [H₂bpbn = N,N′-bis(2-pyridinecarboxamido)-1,4-butane], formed from the reaction between [Mn(H₂O)₆][ClO₄]₂/CoCl₂ · 4H₂O with H₂bpbn in MeCN, are described. In 1 each Mn^II ion is surrounded by three pyridine amide units, providing three pyridine nitrogen and three amide oxygen donors. Each Mn^II center in 1 has distorted MnN₃O₃ coordination. In 2 each Co^II ion is coordinated by two pyridine amide moieties in the equatorial plane and two water molecules provide coordination in the axial positions. Thus, the metal center in 2 has trans-octahedral geometry. In both 1 and 2, the existence of 1D zigzag network structure has been revealed. Owing to π-π stacking of pyridine rings from adjacent layers 1 forms 2D network; 2 forms 2D and 3D network assemblies via N-H?Cl and O-H?Cl secondary interactions. Both the metal centers are high-spin.     

Syntheses and molecular structures of Co-Na and Co-K coordination polymers constructed using mono- and bis-chelated cobalt(III) complexes of bis(2-pyridylcarbonyl)amide ion

Four new hetero-bimetallic Co³⁺-Na⁺ and Co³⁺-K⁺ coordination polymers having the molecular formulae [Na(H₂O)Co(L)(N₃)₃]_n (1), [Na₂Co(L)(N₃)₃(H₂O)₅][Co(L)(N₃)₃] (2), K[Co(L)(NCS)₃]·H₂O (3) and K[Co(L)₂][Co(NCS)₄]·0.5H₂O (4), were synthesized. Compounds 1-4 were characterized by single crystal X-ray diffraction, IR, UV-Vis, and thermogravimetric methods. These bimetallic systems have EE, EO azide bridge (1, 2) as well as bent (1, 2, 3) and linear (1, 4) aquo bridges. Important features observed among them were: a Z-shaped and diamond-shaped Co₂Na₂ clusters in 1, a centrosymmetric double ladder like polymer based on Na₄ cluster in 2, and a linear KOK core having paddle-wheel structure in 4.     

Influence of the phosphine arrangement on the reactivity of palladium(II) and platinum(II) polyphosphine complexes with copper(I) chloride

The distorted square-planar complexes [Pd(PNHP)Cl]Cl (1) (PNHP = bis[2-(diphenylphosphino)ethyl]amine), [M(P₃)Cl]Cl [P₃ = bis[2-(diphenylphosphino)ethyl]phenylphosphine; M = Pd (2), Pt (3)] and [Pt(NP₃)Cl]Cl (5) (NP₃ = tris[2-(diphenylphosphino)ethyl]amine), coexisting in the later case with a square-pyramidal arrangement, react with one equivalent of CuCl to give the mononuclear heteroionic systems [M(L)Cl](CuCl₂) [L = PNHP, M = Pd (1a); L = P₃, M = Pd (2a), Pt (3a); L = NP₃, M = Pt (5a)]. The crystal structure of 3a confirms that Pt(II) retains the distorted square-planar geometry of 3 in the cation with P₃ acting as tridentate chelating ligand, the central P atom being trans to one chloride. The counter anion is a nearly linear dichlorocuprate(I) ion. However, the five-coordinate complexes [Pd(NP₃)Cl]Cl (4), [M(PP₃)Cl]Cl (M = Pd (6), Pt (7); PP₃ = tris[2-(diphenylphosphino)ethyl] phosphine) containing three fused five-membered chelate rings undergo a ring-opening by interaction with one (4, 6, 7) and two (6, 7) equivalents of CuCl with formation of neutral MCu(L)Cl₃ [L = NP₃, M = Pd (4a); L = PP₃, M = Pd (6a), Pt (7a)] and ionic [MCu(PP₃)Cl₂](CuCl₂) [M = Pd (6b), Pt (7b)] compounds, respectively. The heteronuclear systems were shown by ³¹P NMR to have structures where the phosphines are acting as tridentate chelating ligands to M(II) and monodentate bridging to Cu(I). Further additions of CuCl to the neutral species 6a and 7a in a 1:1 ratio resulted in the achievement of the ionic complexes 6b and 7b with ions as counter anions. It was demonstrated that the formation of heterobimetallic or just mononuclear mixed salt complexes was clearly influenced by the polyphosphine arrangement with the tripodal ligands giving the former compounds. However, complexes [M(NP₃)Cl]Cl constitute one exception and the type of reaction undergone versus CuCl is a function of the d⁸ metal centre.     

Synthesis, characterisation and crystal structures of a few coordination complexes of nickel(II), cobalt(III) and zinc(II) with N′-[(2-pyridyl)methylene]salicyloylhydrazone Schiff base

Four new coordination complexes, Ni^II(L)₂ (1), [Co^III(L)₂]ClO₄ (2), [Zn(HL)(L)]ClO₄ · H₂O (3) and [Zn(L)₂][Zn(L)(HL)]ClO₄ · 7H₂O (4) (where L is a monoanion of a Schiff base ligand, N′-[(2-pyridyl)methylene]salicyloylhydrazone (HL) with NNO tridentate donor set), have been synthesised and systematically characterised by elemental analysis, spectroscopic studies and room temperature magnetic susceptibility measurements. Single crystal X-ray diffraction analysis reveals that 1 is a neutral complex, while 2-4 are cationic complexes. Among them, 4 is a rare type of cationic complex with two molecules in the asymmetric unit. The ligand chelates the metal centre with two nitrogen atoms from the pyridine and imino moieties and one oxygen atom coming from its enolic counterpart. All the reported complexes show distorted octahedral geometry around the metal centres, with the two metal-N (imino) bonds being significantly shorter than the two metal-N (Py) bonds.     

Lewis acidity of platinum(II)-based Baeyer-Villiger catalysts: An electrochemical approach

The electrochemical behavior of the Pt(II)-based Baeyer-Villiger catalysts of the general formulae [Pt(μ-OH)(P^∩P)]₂(BF₄)₂ (P^∩P = dppe (1a), 2Fdppe (1 b), 4Fdppe (1c), dfppe (1d), dmpe (1e), depe (1f), dippe (1g), dtbpe (1h)) and [Pt(OH₂)₂(P^∩P)](OTf)₂ (P^∩P = dppe (2a), 2Fdppe (2b), 4Fdppe (2c), dfppe (2d)) is reported. They exhibit irreversible reduction processes whose potentials reflect the Lewis acidity of the metal centres, showing (for the aromatic diphosphine complexes) overall relations with the number of fluorine atoms, with J_Pt-P, with the ν(CN) coordination shift of a ligand isocyanide probe and with the catalytic activity. Single-crystal X-ray diffraction analyses were carried out for [Pt(μ-OH)(4Fdppe)]₂(BF₄)₂ (1c) and [Pt(μ-OH) (dippe)]₂(BF₄)₂ (1g).     

Syntheses and structures of cobalt(III) alcoholate complexes formed by addition of a water molecule across 2-pyridyl substituted imine function

Schiff bases L1-L5 {N-[1-pyridine-2-ylethylidene]pyridine-2-amine (L1), 3-methyl-N-[1-pyridine-2-ylmethylidene]pyridine-2-amine (L2), 3-methyl-N-[1-pyridine-2-ylethylidene]pyridine-2-amine (L3), 4-methyl-N-[1-pyridine-2-ylmethylidene]pyridine-2-amine (L4), 4-methyl-N-[1-pyridine-2-ylethylidene]pyridine-2-amine (L5)} were synthesized and on reaction with Co(NO₃)₂·6H₂O, complexes having the molecular formulae [Co(L1O)₂]NO₃ (1), [Co(L2O)₂]NO₃·xH₂O (2a, x = 2; 2b, x = 3), [Co(L3O)₂]NO₃ (3), [Co(L4O)₂]NO₃·4H₂O (4), [Co(L5O)₂]NO₃ (5) were isolated from the respective imines. The salt [Co(L2O)₂]PF₆ (2c) was obtained by treating 2 with KPF₆. Complexes 1-5 were formed as a result of addition of a water molecule across the imine function and the resultant alcohol binds in its deprotonated form. The alcoholate ion remained bound in a facial tridentate fashion to the low-spin cobalt(III). X-ray crystal structure determination confirmed the presence of trans-trans-trans-N_AN_PO (A = aminopyridyl and P = pyridyl) disposition in 2a and cis-cis-trans-N_AN_PO in 2b, 2c and 4. Water dimers in 2a, 2b, 4 and water-nitrate ion network in 2a were other notable features.     

Structure, magnetic properties and nuclease activity of pyridine-2-carbaldehyde thiosemicarbazonecopper(II) complexes

New complexes of formulae [Cu(HL²)(H₂O)(NO₃)](NO₃) (1), [{Cu(L¹)(tfa)}₂] (2), [{Cu(L¹)}₂(pz)](ClO₄)₂ (3) and {[{Cu(L¹)}₂(dca)](ClO₄)}_n (4), where HL¹ = pyridine-2-carbaldehyde thiosemicarbazone, HL² = pyridine-2-carbaldehyde 4N-methylthiosemicarbazone, Htfa = trifluoroacetic acid (CF₃COOH), pz = pyrazine (C₄H₄N₂) and dca = dicyanamide [N(CN)₂]⁻, have been synthesized and characterized. The crystal structures of these compounds are built up of monomers (1), dinuclear entities with the metal centers bridged through the non-thiosemicarbazone coligand (2 and 3) and 1D chains of dimers (4). In all the cases, square-pyramidal copper(II) ions are present, except for the square-planar ones in 3. Magnetic measurements show antiferromagnetic couplings in 2, 3 and 4. The susceptibility data were fitted by the Bleaney-Bowers’ equation for copper(II) dimers derived from H = -2JS₁S₂ being the obtained J/k values −4.8, −4.3 and −5.1 K for compounds 2-4, respectively. The magnetic susceptibility of the already known [{Cu(HL¹)(tfa)}₂](tfa)₂ compound has been also measured for the first time. The J/k value is -0.3 K, lower than that in 2. The nuclease activity of 3 and 4 has been analyzed.     

Difference in bonding behaviour of azide and thiocyanate to Hg(II)-azoimidazoles

Mercury(II) acetate reacts with the 1-alkyl-2-(arylazo)imidazoles [RaaiR′ where R = H (a), Me (b); R′ = Me (1/3/5), Et (2/4/6)] and sodium azide in methanol solution to afford azido bridged polymeric complexes [Hg(RaaiR′)(N₃)₂]_n (3/4). On setting up similar reaction condition, the reaction of Hg(OAc)₂ with RaaiR′ and NH₄SCN has yielded, instead of polymer, an ion-pair [Hg(RaaiR′)₄][Hg(SCN)₄] (5/6). The complexes are characterised by elemental analysis, IR, UV-Vis, ¹H NMR spectral data and single-crystal X-ray structures of [Hg(HaaiEt)(μ-1,1-N₃)₂]_n (4a) and [Hg(HaaiEt)₄][Hg(SCN)₄] (6a). The complex 4a is a coordination polymer with end-on (μ-1,1) azido bridge and 6a has tetrahedral structure.     

Anion-directed supramolecular assembly of cobalt(II)-fluconazole coordination polymers: Structural diversity, fluorescent and magnetic properties

Six fluconazole-bridged cobalt(II) coordination polymers, namely [Co(HFlu)₂(H₂O)₂](ClO₄)₂ (1), [Co(HFlu)₂(H₂O)(AcO)](AcO)·2C₂H₅OH (2), [Co(HFlu)₂Cl₂]·2C₂H₅OH (3), [Co₃(Flu)₂(acac)₄]·C₂H₅OH (4), [Co(HFlu)₂(malo)(H₂O)]·3H₂O (5), and [Co(HFlu)₂(fum)(H₂O)₂]·H₂O (6) (HFlu = 2-(2′,4′-difluorophenyl)-1,3-bis(1,2,4-triazol-1-yl)-propan-2-ol, AcOH = acetate acid, Hacac = acetylacetonate, H₂malo = malonate acid, H₂fum = fumaric acid), have been synthesized and structurally characterized, and the thermal, fluorescent and magnetic properties investigated. The crystal structures display the one-dimensional cationic double-bridged chain consisting of 20-membered macrocycles to be parallel in 1 and perpendicular in 2. The structure of 3 consists of two-dimensional neutral rhombic grid in bc plane with (4,4) topology and alternative P/M helices intersecting at the Co sites along b direction. Complex 4 shows one-dimensional polymeric chain, in which binuclear Co₂(Flu)₂(acac)₂ units act as bridging blocks to link Co(acac)₂ nodes through triazolyl nitrogen atoms. The structure of 5 shows dimeric 20-membered macrometallacyclic motif. Complex 6 shows HFlu-bridged one-dimensional chain, which is stabilized by hydrogen-bonding interactions to produce alternative hydrophobic and hydrophilic architecture. Complexes 1-3 and 5-6 exhibit the similar electronic absorption and fluorescent spectra as those of HFlu, while complex 4 shows a fluorescent quenching phenomenon. Fluorescence titration of HFlu suggests that the fluorescent intensities at the maximal emission decrease upon the addition of Co(acac)₂. The variable-temperature magnetic measurement of 4 reveals weak ferromagnetic interaction combined with the spin-orbit coupling effect in the 1-D Co(II) chain.     

Stereosensitive formation and interconversion of sulfur-bridged cobalt(III)-mercury(II) polynuclear complexes with d- and/or l-penicillaminates

The reaction of trans(N)-[Co(d-pen)₂]⁻ (pen = penicillaminate) with HgCl₂ or HgBr₂ in the molar ratios of 1:1 gave the sulfur-bridged heterodinuclear complex, [HgX(OH₂){Co(d-pen)₂}] (X = Cl (1a) or Br (1b)). A similar reaction in the ratio of 2:1 produced the trinuclear complex, [Hg{Co(d-pen)₂}₂] (1c). The enantiomers of 1a and 1c, [HgCl(OH₂){Co(l-pen)₂}] (1a′) and [Hg{Co(l-pen)₂}₂] (1c′), were also obtained by using trans(N)-[Co(l-pen)₂]⁻ instead of trans(N)-[Co(d-pen)₂]⁻. Further, the reaction of cis · cis · cis-[Co(d-pen)(l-pen)]⁻ with HgCl₂ in the molar ratio of 1:1 resulted in the formation of [HgCl(OH₂){Co(d-pen)(l-pen)}] (2a). During the formations of the above six complexes, 1a, 1b, 1c, 1a′, 1c′, and 2a, the octahedral Co(III) units retain their configurations. On the other hand, the reaction of cis · cis · cis-[Co(d-pen)(l-pen)]⁻ with HgCl₂ in the molar ratio of 2:1 gave not [Hg{Co(d-pen)(l-pen}₂] but [Hg{Co(d-pen)₂}{Co(l-pen)₂}] (2c), accompanied by the ligand-exchange on the terminal Co(III) units. The X-ray crystal structural analyses show that the central Hg(II) atom in 1c takes a considerably distorted tetrahedral geometry, whereas that in 2c is of an ideal tetrahedron. The interconversion between the complexes is also examined. The electronic absorption, CD, and NMR spectral behavior of the complexes is discussed in relation to the crystal structures of 1c and 2c.     

Synthesis and characterisation of a series of 1,2-phenylenedioxoborylcyclopentadienyl-metal complexes [Ti(IV), Zr(IV), Hf(IV), La(III), Ce(III), Yb(III), Sn(II) and Fe(II)]

The preparation of a series of 1,2-phenylenedioxoborylcyclopentadienyl-metal complexes is described. These are of formula [M{η⁵-C₅H₄(BX)}Cl₃] [M = Ti and X = CAT (2a), CAT^t (2b) or CAT^tt (2c); X = CAT^tt and M = Zr (4a) or Hf (4b)], [M{η⁵-C₅H₄(BX)}₂Cl₂] [M = Zr, X = CAT (3a) or CAT^t (3c); or M = Hf, X = CAT (3b) or CAT^t (3d)], [M{(μ-η⁵-C₅H₃BCAT)₂ SiMe₂}Cl₂] [M = Zr (5a) or Hf (5b)], [M{η⁵-C₅H₃(BCAT)₂}Cl₃] [M = Zr (6a) or Hf (6b)], [M{η⁵-C₅H₄BCAT}₃(THF)] [M = La (7a), Ce (7b) or Yb (7c)], [Sn{η⁵-C₅ H₄(BCAT^t)}Cl](8) and [Fe{η⁵-C₅H₄(BCAT^t)}₂] (9). The abbreviations refer to BO₂C₆H₄-1,2 (BCAT) and the 4-Bu^t (BCAT^t) and the (BCAT^tt) analogues. The compounds 2a-9 have been characterised by microanalysis, multinuclear NMR and mass spectra. The single crystal X-ray structure of the lanthanum compound 7a is presented.     

Diastereoisomerically pure pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2-bipyridine: structural, electrochemical and spectral studies

Pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2^′-bipyridine of composition [(bpy)₂Ru(pzdc)Ru(bpy)₂](ClO₄) · H₂O (1) and [(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄) · H₂O (2) have been obtained in high yield and have been separated to their homochiral (ΛΛ/ΔΔ) rac (1a, 2a) and heterochiral (ΛΔ/ΔΛ) meso (1b, 2b) diastereoisomers. The distinctive structural features of these diastereoisomers have been characterized by 1-D and 2-D ¹H NMR spectroscopy. The X-ray crystal structure of rac-[(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄) · H₂O (2a) has been determined. The electrochemical and electronic spectral studies have established that there remain difference in properties and hence difference in intermetallic communication between the diastereoisomeric forms in each case.     

Interaction of Pt(II) and Pd(II) complexes of terpyridine with 1-methylazoles: A combined experimental and density functional study

The synthesis and characterization of several complexes of the composition [{M(terpy)}_n(L)](ClO₄)_m (M = Pt, Pd; L = 1-methylimidazole, 1-methyltetrazole, 1-methyltetrazolate; terpy = 2,2′:6′,2″-terpyridine; n = 1, 2; m = 1, 2, 3) is reported and their applicability in terms of a metal-mediated base pair investigated. Reaction of [M(terpy)(H₂O)]²⁺ with 1-methylimidazole leads to [M(terpy)(1-methylimidazole)](ClO₄)₂ (1: M = Pt; 2: M = Pd). The analogous reaction of [Pt(terpy)(H₂O)]²⁺ with 1-methyltetrazole leads to the organometallic compound [Pt(terpy)(1-methyltetrazolate)]ClO₄ (3) in which the aromatic tetrazole proton has been substituted by the platinum moiety. For both platinum(II) and palladium(II), doubly metalated complexes [{M(terpy)}₂(1-methyltetrazolate)](ClO₄)₃ (4: M = Pt; 5: M = Pd) can also be obtained depending on the reaction conditions. In the latter two compounds, the [M(terpy)]²⁺ moieties are coordinated via C5 and N4. X-ray crystal structures of 1, 2, and 3 are reported. In addition, DFT calculations have been carried out to determine the energy difference between fully planar [Pd(mterpy)(L)]²⁺ complexes Ip-IVp (mterpy = 4′-methyl-2,2′:6′,2″-terpyridine; L = 1-methylimidazole-N3 (I), 1-methyl-1,2,4-triazole-N4 (II), 1-methyltetrazole-N3 (III), or 3-methylpyridine-N1 (IV)) and the respective geometry-optimized structures Io-IVo. Whereas this energy difference is larger than 70 kJ mol⁻¹ for compounds I, II, and IV, it amounts to only 0.8 kJ mol⁻¹ for the tetrazole-containing complex III, which is stabilized by two intramolecular C-H?N hydrogen bonds. Of all complexes under investigation, only the terpyridine-metal ion-tetrazole system with N3-coordinated tetrazole appears to be suited for an application in terms of a metal-mediated base pair in a metal-modified oligonucleotide.     

8-Quinolinolato complexes of ruthenium(II) and (III)

Reduction of RuQ₃ (1a, Q = 8-quinolinolato) with Zn/Hg in the presence of various π-acceptor ligands in ethanol affords RuQ₂L₂ (L₂ = (dimethylsulfoxide)₂ (2); (4-picoline)₂ (3); N,N′-dimethyl-1,4-diazabuta-1,3-diene, dab (4); cyclooctadiene, COD (5); norborna-2,5-diene, nbd (6)). Compound 6 is isolated as an equimolar mixture of cis,trans (6a) and trans,cis (6b) isomers, which can be separated by column chromatography. DFT calculations have been performed on 6a and 6b. Oxidation of 3 and 6b affords the corresponding ruthenium(III) species 7 and 8, respectively. The structures of 2, 3, 4 and 6 have been determined by X-ray crystallography.