Synthesis, crystal structure and magnetic properties of three polynuclear manganese compounds bearing ferrocenecarboxylato ligands

The reactions of sodium ferrocenecarboxylate (FcCO₂Na) and Mn(ClO₄)₂ · 6H₂O in methanol in the presence of ancillary ligands of 1,10-phenanthroline (phen) or 2,2′-bipyridine (2,2′-bpy) produce three discrete polynuclear complexes bearing ferrocenecarboxylato ligands: [Mn₂(FcCO₂)₃(phen)₂](ClO₄) · 2CH₂Cl₂ (1), [Mn₃(FcCO₂)₆(2,2′-bpy)₂] · 2H₂O (2) and [Mn₄O₂(FcCO₂)₇(2,2′-bpy)₂]ClO₄ · 2CH₂Cl₂ · 6H₂O (3). It is shown that their composition and skeletons are tuned by the ancillary ligands and the ratios of starting materials. In dimanganese complex 1, both Mn(II) ions are pentacoordinated in a distorted trigonal bipyramidal geometry and bridged by three ferrocenecarboxylato ligands in a distorted syn-syn bridging mode, which is rare in triply carboxylato-bridged dimanganese complexes. Compound 2 presents a linear trinuclear [Mn₃(μ₂-η¹:η¹-O₂CFc)₄(μ₂-η¹:η²-O₂CFc)₂] core, in which six ferrocencarboxylato ligands show two different bridging modes. The cationic Mn₄O₂ core of 3 has a butterfly structure, in which two Mn(III) ions at “body” sites are bridged by an additional ferrocenecarboxylato ligand and they are further connected to the Mn(III) ions at “wing-tip” sites by ferrocenecarboxylato ligands. Magnetic susceptibilities of 1 and 2 were measured. Both of them mediate a weak antiferromagnetic coupling between the Mn(II) ions bridged by ferrocenecarboxylato ligands.     

Hypercoordinate germanium complexes with phenanthrene-9,10-diolate ligands: synthesis,structure, and electronic properties

The synthesis, molecular structure, and electronic properties of sodium tris(phenanthrene-9,10-diolato)germanate(iv) are described. The germanate complex is readily oxidized in air to produce 9,10-phenanthrenequinone, and the resulting quinones and the ligands reveal intermolecular π-stacking interaction in the polymeric association in the solid state. Addition of phenanthroline to the germanate complex leads to a monomeric structure.     

Polycyclic compounds from aminopolyols and alpha-dicarbonyls: structure and application in the synthesis of exoditopic ligands

The structure and stereochemistry of the crystalline 2 : 2 condensation product ("glytham") of glyoxal and tris(hydroxymethyl)aminomethane was conclusively determined by X-ray diffractometric analysis. The singular disposition of the heteroatoms suggests the employment of glytham as starting material for the synthesis of ditopic ligands for metal ions. Some derivatives of glytham were prepared and their binding properties towards alkaline metal ions were preliminarily investigated by ESI-MS and NMR.     

Diruthenium(III,III) bis(alkynyl) compounds with donor/acceptor-substituted geminal-diethynylethene ligands

Reported in this contribution are the preparation and characterization of a series of Ru(2)(DMBA)(4) (DMBA = N,N'-dimethylbenzamidinate) bis(alkynyl) compounds, trans-Ru(2)(DMBA)(4)(X-gem-DEE)(2) [gem-DEE = σ-geminal-diethynylethene; X = H (1), Si(i)Pr(3) (2), Fc (3); 4-C(6)H(4)NO(2) (4), and 4-C(6)H(4)NMe(2) (5)]. Compounds 1-5 were characterized by spectroscopic and voltammetric techniques as well as the single-crystal X-ray diffraction studies of 2 and 3. Both the single-crystal structural data of compounds 2 and 3 and the spectroscopic/voltammetric data indicate that the gem-DEE ligands are similar to simple acetylides in their impact on the molecular and electronic structures of the Ru(2)(DMBA)(4) core. Furthermore, density functional theory calculations revealed more extensive π delocalization in aryl-donor-substituted gem-DEEs and that the hole-transfer mechanism will likely dominate the charge delocalization in Ru(2)-gem-DEE-based wires.     

Diruthenium and diosmium tetracarboxylates: synthesis, physical properties and applications

Dimetal tetracarboxylates, [M₂(O₂CR)₄]ⁿ, have received much coverage in the literature. The metals include Cr, Mo, W, Tc, Re, Ru, Os, Co, Rh, Ir, Ni and Cu with n ranging from −2 to +4 (0 to +2 being most common). Diruthenium and diosmium tetracarboxylates form two of the younger families of these ubiquitous compounds and are known to exist as homovalent Ru₂(II,II) and Os₂(III,III) and mixed-valent Ru₂(II,III) and Os₂(II,III) species. This paper will provide a comprehensive review of these complexes and include such things as their discovery, synthesis and crystal structures; electronic, vibrational (IR and Raman), ESR and photoelectron spectroscopy; magnetic susceptibility; electrochemistry; kinetics; calorimetry; theoretical calculations such as SCF-X-SW and CASSCF; and more recent studies of their mesomorphic behaviour and biological and catalytic applications. The ruthenium compounds, in particular, have shown a potential application as liquid crystals. Current work (including this author's) is also focused on the development of linear chains involving these metal carboxylate units and bidentate bridges with the view to developing ferromagnetic materials and conductive polymers.

There have been no previous reviews on ruthenium (and osmium) carboxylates per se. Cotton and Walton give them some coverage in the context of metal–metal bonds in Multiple Bonds Between Metal Atoms (2nd ed., 1993) however the direct coverage of Ru₂(O₂CR)₄ and Os₂(O₂CR)₄ type complexes is cursory and dispersed throughout the book. As well, the coverage is only comprehensive through December 1990 with some references from 1991. The current review will be complete through to mid-1997.     

Platinum(II) diimine complexes with catecholate ligands bearing imide electron-acceptor groups: synthesis, crystal structures, (spectro)electrochemical and EPR studies, and electronic structure

A series of catechols with attached imide functionality (imide = phthalimide PHT, 1,8-naphthalimide NAP, 1,4,5,8-naphthalenediimide NDI, and NAP-NDI) has been synthesized and coordinated to the Pt (II)(bpy*) moiety, yielding Pt(bpy*)(cat-imide) complexes (bpy* = 4,4'-di- tert-butyl-2,2'-bipyridine). X-ray crystal structures of PHT and NAP complexes show a distorted square-planar arrangement of ligands around the Pt center. Both complexes form "head-to-tail" dimers in the solid state through remarkably short unsupported Pt...Pt contacts of 3.208 (PHT) and 3.378 A (NAP). The Pt(bpy*)(cat-imide) complexes are shown to combine optical (absorption) and electrochemical properties of the catecholate (electron-donor) and imide (electron-acceptor) groups. The complexes show a series of reversible reduction processes in the range from -0.5 to -1.9 V vs Fc (+)/Fc, which are centered on either bpy* or imide groups, and a reversible oxidation process at +0.07 to +0.14 V, which is centered on the catecholate moiety. A combination of UV-vis absorption spectroscopy, cyclic voltammetry, UV-vis spectroelectrochemistry, and EPR spectroscopy has allowed assignment of the nature of frontier orbitals in Pt(bpy*)(cat-imide) complexes. The HOMO in Pt(bpy*)(cat-imide) is centered on the catechol ligand, while the LUMO is localized either on bpy* or on the imide group, depending on the nature of the imide group involved. Despite the variations in the nature of the LUMO, the lowest-detectable electronic transition in all Pt(bpy*)(cat-imide) complexes has predominantly ligand-to-ligand (catechol-to-diimine) charge-transfer nature (LLCT) and involves a bpy*-based unoccupied molecular orbital in all cases. The LLCT transition in all Pt(bpy*)(cat-imide) complexes appears at 530 nm in CH2Cl2 and is strongly negatively solvatochromic. The energy of this transition is remarkably insensitive to the imide group present, indicating lack of electronic communication between the imide and the catechol moieties within the cat-imide ligand. The high extinction coefficient, approximately 6 x 10(3) L mol(-1) cm(-1) of this predominantly LLCT transition is the result of the Pt orbital contribution, as revealed by EPR spectroscopy of the complexes in various redox states. The CV profile of the oxidation process of Pt(bpy*)(cat-imide) in CH2Cl2 and DMF is concentration dependent, as was shown for NDI and PHT complexes as typical examples. Oxidation appears as a simple diffusion-limited process at low concentrations, with an increasing anodic-to-cathodic peak separation eventually resolving as two independent consecutive waves as the concentration of the complex increases. It is suggested that aggregation of the complexes in the diffusion layer in the course of oxidation is responsible for the observed concentration dependence. Overall, the Pt(bpy*)(cat-imide) complexes are electrochromic compounds in which a series of stepwise reversible redox processes in the potential range from 0.2 to -2 V (vs Fc (+)/Fc) leads to tuneable absorbencies between 300 and 850 nm.     

Metal complexes of some thiocarbohydrazone ligands: synthesis and structure

The synthesis, structure, physico-chemical investigation and biological studies of some metal complexes of thiocarbohydrazone ligands are described. The ligands were obtained by condensation of N,N′-thiocarbohydrazide with carbonyl compounds such as 2-hydroxyacetophenone or 5-chlorosalicylaldehyde. A variety of binuclear or mononuclear complexes were obtained with the ligands in mono-, bi- and/or tri-deprotonated forms. The bonding sites are the azomethine nitrogen atom, phenolic oxygen atom and thiol sulfur atom. The metal complexes exhibit either tetrahedral or octahedral structures. Preliminary antimicrobial screening showed that the ligands and their metal complexes possess antimicrobial activity towards bacteria and fungi.     

Thermolysis of titanocene methyl compounds bearing t-butyl- and benzyltetramethylcyclopentadienyl ligands

Elimination of methane during thermolysis of title compounds results in the formation of σ-Ti-C bond to t-butyl or benzyl group. The t-butyl-containing titanocene methyl compound [Ti(III)Me(η⁵-C₅Me₄t-Bu)₂] (5) eliminates methane at 110 °C to give cleanly [Ti(III)(η⁵:η¹-C₅Me₄CMe₂CH₂)(η⁵-C₅Me₄t-Bu)] (6). The methyl derivative of analogous benzyl-containing titanocene [Ti(III)Me(η⁵-C₅Me₄CH₂Ph)₂] was not isolated because it eliminated methane at ambient temperature to give [Ti(III)(η⁵:η¹-C₅Me₄CH₂-o-C₆H₄)(η⁵-C₅Me₄CH₂Ph)] (7) with one phenyl ring linked to titanium atom in ortho-position. The corresponding titanocene dimethyl compound [TiMe₂{η⁵-C₅Me₄t-Bu)}₂] (9) eliminates two methane molecules at 110 °C to give the singly tucked-in 1,1-dimethylethane-1,2-diyl-tethered titanocene [Ti{η⁵:η¹:η¹-C₅Me₃(CH₂)(CMe₂CH₂)}(η⁵-C₅Me₄t-Bu)] (11). In distinction, the analogous benzyl derivative [TiMe₂(η⁵-C₅Me₄CH₂Ph)₂] (10) eliminates at 110 °C only one methane molecule to afford [TiMe(η⁵:η¹-C₅Me₄CH₂-o-C₆H₄)(η⁵-C₅Me₄CH₂Ph)] (12) containing one phenyl group attached to titanium in o-position and one methyl group persisting on the titanium atom. This compound is stable at 150 °C for at least 3 h. The crystal structures of 5, 6, 7, and 10 were determined.     

New antitumour active platinum compounds containing carboxylate ligands in trans geometry: synthesis, crystal structure and biological activity

New asymmetric trans-platinum(II) complexes, composed of an isopropylamine, an azole and two carboxylate leaving groups, are presented. The crystal and molecular structures of one of the complexes has been determined and the cytotoxicity and reactivity with 5'-guanosine monophosphate is reported. The complexes show a reduced reactivity, but no decrease in cytotoxic activity compared to their chloro-counterparts. Furthermore the complexes largely overcome cisplatin resistance, they therefore present an interesting class of antitumour active trans-platinum complexes.     

Phenothiazinophanes: synthesis, structure, and intramolecular electronic communication

Ortho-phenylene, ethenylene, and ethylene-bridged phenothiazinophanes are synthesized by Suzuki coupling or McMurry dimerization and catalytic hydrogenation at ambient pressure. Intensive intramolecular electronic communication of the phenothiazinyl subunits is found according to cyclic voltammetry. In addition, the macrocycles display blue to green fluorescence with large Stokes shifts. In the solid state, the cyclophanes are arranged in unidimensional stacks. This orientation appears to be favorable for anisotropic charge transport in hole-transport materials for organic field effect transistors (OFET) applications.     

Synthesis of uranium complexes incorporating extended azo-imine ligands: Molecular and electronic structure

The new azo-imine ligands 2,4-di-tert-butyl-6-((2-((2-hydroxyphenyl)diazenyl) phenylimino)methyl)phenol, H₂L¹, 1a, and 2,4-di-tert-butyl-6-((2-((2-hydroxyphenyl) diazenyl)p-chlorophenylimino)phenol, H₂L², 1b, were prepared. Reaction of H₂L¹;1a, and H₂L²;1b, with uranyl nitrate hexahydrate afforded the mononuclear complexes of compositions [U(O)₂(L¹)(H₂O)]; 2a, and [U(O)₂(L²)(H₂O)]; 2b, complexes respectively. The newly synthesised ligands (1a and 1b) and the complexes (2a and 2b) were characterised unequivocally. The x-ray structure of 2a was determined. The tetradentate dianionic ligand (L¹)^2- coordinated the uranium ion equatorially with a water molecule in the same plane. Two axially coordinated oxo ligands completed the overall pentagonal bipyramid geometry around U(VI) ion. Structural pattern, electron transfer properties (oxidation near 1.32 ​V vs Ag/AgCl) and electronic transitions of [U(O)₂(L¹)(H₂O)]; 2a, and [U(O)₂(L²)(H₂O)]; 2b have been rationalized by DFT calculations.     

Redox-active ligands as a challenge for electronic structure methods

To improve the catalytic activity of 3d transition metal catalysts, redox-active ligands are a promising tool. These ligands influence the oxidation state of the metal center as well as the ground spin-state and make the experimental determination of both properties challenging. Therefore, first-principles calculations, in particular employing density functional theory with a proper choice of exchange-correlation (xc) functional, are crucial. Common xc functionals were tested on a simple class of metal complexes: homoleptic, octahedral tris(diimine) iron(II) complexes. The spin-state energy splittings for most of these complexes showed the expected linear dependence on the amount of exact exchange included in the xc functionals. Even though varying redox-activity affects the electronic structure of the complexes considerably, the sensitivity of the spin-state energetics to the exact exchange admixture is surprisingly small. For iron(II) complexes with highly redox-active ligands and for a broad range of ligands in the reduced tris(diimine) iron(I) complexes, self-consistent field convergence to local minima was observed, which differ from the global minimum in the redox state of the ligand. This may also result in convergence to a molecular structure that corresponds to an energetically higher-lying local minimum. One criterion to detect such behavior is a change in the sign of the slope for the dependence of the spin-state energy splittings on the amount of exact exchange. We discuss possible protocols for dealing with such artifacts in cases in which a large number of calculations makes checking by hand unfeasible.     

β-Diphenylphosphorylated alkanones and related compounds: synthesis and structure

The reactions of diphenyl(diisopropyl)chlorophosphine with arylidene(heteroarylidene)-acetones and 3-benzylidenepentane-2,4-dione in the presence of acetic acid proceed at a high rate at room temperature to afford the corresponding β-diorganylphosphorylated alkanones and alkanediones in high yields. The reaction of diphenylchlorophosphine with 4-methoxybut-3-en-2-one and dibenzylideneacetone carried out under similar conditions at the equimolar reagent ratio can serve as a convenient method for the synthesis of unique β-diphenylphosphorylalkenones. The structures of compounds obtained were established by IR, Raman, and NMR spectroscopy and X-ray diffraction.     

Organotin compounds bearing mesogenic sidechains: synthesis, X-ray structures and polymerisation chemistry

Organotin compounds R₃Sn(CH₂)_n+2OC₆H₄C₆H₄Y (R₃=Ph₃, Ph₂Bu; Y=H, CN; n=1-3) and RX₂Sn(CH₂)_n+2OC₆H₄C₆H₄Y (R=Ph, Bu; Y=H, CN; X=Br, I; n=1-3) have been synthesised and characterised by ¹H-, ¹³C-, ¹¹⁹Sn-NMR and Mössbauer spectroscopies. X-ray crystallography reveals tetrahedral geometries for Ph₃Sn(CH₂)₄OC₆H₄C₆H₅ and Ph₃Sn(CH₂)₃OC₆H₄C₆H₄CN, a six-coordinated, bromine-bridged dimeric structure for PhBr₂Sn(CH₂)₃OC₆H₄C₆H₅ containing a mer-Br₃C₂OSn coordination sphere about tin and a five-coordinated monomeric structure for PhBr₂Sn(CH₂)₃OC₆H₄C₆H₄CN. In all cases there is strong alignment of mesogenic groups in the solid-state but only PhBr₂Sn(CH₂)₃OC₆H₄C₆H₄CN shows any indication of liquid-crystal behaviour. Wurtz polymerisation of RBr₂Sn(CH₂)₅OC₆H₄C₆H₅ (R=Ph, Bu), both of which contain non-chelating ether functions, generated polystannanes (RR′Sn)_n with M_n 2.3×10⁵; M_w 3.0×10⁵; M_w/M_n 1.30 and M_n 1.3×10⁵; M_w 2.5×10⁵; M_w/M_n 1.96, respectively, while no polymer was obtained from chelated PhBr₂Sn(CH₂)₃OC₆H₄C₆H₅     

Metal-free and transition-metal tetraferrocenylporphyrins part 1: synthesis, characterization, electronic structure, and conformational flexibility of neutral compounds

H(2)TFcP [TFcP = 5,10,15,20-tetraferrocenyl porphyrin(2-)] was prepared by a direct tetramerization reaction between pyrrole and ferrocene carbaldehyde in the presence of a BF(3) catalyst, while the series of MTFcP (M = Zn, Ni, Co and Cu) were prepared by a metallation reaction between H(2)TFcP and respective metal acetates. All compounds were characterized by UV-vis and MCD spectroscopy, APCI MS and MS/MS methods, high-resolution ESI MS and XPS spectroscopy. Diamagnetic compounds were additionally characterized using (1)H and (13)C NMR methods, while the presence of low-spin iron(ii) centers in the neutral compounds was confirmed by M?ssbauer spectroscopy and by analysis of the XPS Fe 2p peaks, revealing equivalent Fe sites. XPS additionally showed the influence on Fe 2p binding energies exerted by the distinct central metal ions. The conformational flexibility of ferrocene substituents in H(2)TFcP and MTFcP, was confirmed using variable-temperature NMR and computational methods. Density functional theory predicts that alpha,beta,alpha,beta atropisomers with ruffled porphyrin cores represent minima on the potential energy surfaces of both H(2)TFcP and MTFcP. The degree of non-planarity is central-metal dependent and follows the trend: ZnTFcP < H(2)TFcP approximately CuTFcP < CoTFcP < NiTFcP. In all cases, a set of occupied, predominantly ferrocene-based molecular orbitals were found between the highest occupied and the lowest unoccupied, predominantly porphyrin-based molecular orbitals. The vertical excitation energies of H(2)TFcP were calculated at the TDDFT level and confirm the presence of numerous predominantly metal-to-ligand charge-transfer bands coupled via configurational interaction with expected intra-ligand pi-pi* transitions.     

The electronic structure of polyenes and unsaturated carbonyl compounds

PE spectra of polyene aldehydes are reported and discussed on the basis of a semiempirical LCFO-MO treatment within the π electron approximation. The necessary parameter values including the CC bond alternation were obtained by fitting PPP orbital and transition energies to the PE and UV data of diphenyl polyenes and polyene aldehydes. Thus, for planar systems the assignment of a PE band near 13.5 eV to the π orbital of the CO group could be given, which could be confirmed by the LCFO-MO calculations and by results from ab initio calculations, and which forms the basis of a discussion and comparison of π orbital interactions in planar unsaturated carbonyl compounds and hydrocarbons.     

Allyl strontium compounds: synthesis, molecular structure and properties

The synthesis and attempted isolation of neutral bis(allyl)strontium [Sr(C(3)H(5))(2)] (1) resulted in the isolation of potassium tris(allyl)strontiate K[Sr(C(3)H(5))(3)] (2). In situ generated 1 shows a pronounced Br?nsted basicity, inducing polymerisation of THF. Ate complex 2 crystallises as [K(THF)(2){Sr(C(3)H(5))(3)}(THF)](∞) (2·(THF)(3)). The salt-like solid state structure of 2·(THF)(3) comprises a two-dimensional network of (μ(2)-η(3):η(3)-C(3)H(5))(-) bridged potassium and strontium centres. Synthesis of allyl complexes 1 and 2 utilised SrI(2), [Sr(TMDS)(2)] (3) (TMDS = tetramethyldisilazanide), and [Sr(HMDS)(2)] (HMDS = hexamethyldisilazanide) as strontium precursors. The solid state structure of previously reported [Sr(TMDS)(2)] (3) was established by X-ray single crystal analysis as a dissymmetric dimer of [Sr(2)(TMDS)(4)(THF)(3)] (3·(THF)(3)) with multiple Si-HSr agostic interactions. The presence of ether ligands (THF, 18-crown-6) influenced the Si-HSr resonances in the NMR spectra of the amido complex 3.