Pendant Pyridyl Research Articles

Supramolecular liquid-crystalline polyurethane

A novel supramolecular liquid-crystalline polyurethane was prepared by mixing the polyurethane containing a pendant pyridyl unit as H-bond acceptor and 4-dodecyloxybenzoic acid as H-bond donor. Intermolecular hydrogen bond formation was confirmed by Fourier transform infrared spectroscopy. The liquid-crystalline behaviour of the complex formed was established by differential scanning calorimetry, polarizing optical microscopy and X-ray diffractometry. The complex exhibited highly ordered smectic and nematic phases. The smectic-nematic and nematic-isotropic transitions were observed at 89°C and 120°C, respectively.

A reversible NO complex of [Fe II(edampda)] and the [Ni II(edampda)] analogue (edampda 2−= N, N′-bis(pyridylmethyl)ethylenediamine- N, N′-diacetate)

Ni II, Cu II, Zn II and Fe II complexes of edampda 2− ( N, N′-bis(pyridylmethyl)ethylenediamine- N, N′-diacetate) were prepared by the spontaneous chelation of a labile salt of each ion with the H 2edampda in aqueous solution (with the Fe II complex under N 2). edampda 2− is designed to have an intermediate ligand field stronger than edta 4−, but less than tpen ( N, N, N′, N′-tetrakis(pyridylmethyl)ethylenediamine). [Fe II(edampda)] is a high-spin ( S=2) complex at 25°C as shown by its ligand 1H NMR resonances appearing at low field (ortho pyridyl ring protons at 118 ppm, pyridylmethyl CH 2 protons at 57 ppm, coordinated glycinato protons at 44 ppm) as broadened features. The differential pulse voltammogram of [Fe II(edampda)] in solution is consistent with seven-coordinate species [Fe II(edampda)(H 2O)] ( E 1/2=0.44 V) and [Fe II(edampda)Cl] − ( E 1/2=0.37 V) which are analogous to the known [Fe II(edta)(H 2O)] 2− complex. As anticipated from ligand field factors the (II/III) reduction couple is intermediate in the series [Fe II(edta)(H 2O)] 2−; 0.14 V<[Fe(edampda)(H 2O)]; 0.44 V<[Fe(tpen)] 2+; 0.84 V. Admission of NO to [Fe(edampda)(H 2O)] solutions causes a loss of the 0.44 V wave and the appearance of a new wave at 1.08 V in forming [Fe(edampda)NO]. The process is reversed by Ar purging. [Fe(edampda)NO] in a 50:50 ethanol–water glass exhibits an EPR spectrum at 106 K which has components of an S=3/2 species ( g=4.16, 3.44, 2.0) and a second prominent S=1/2 species ( g=2.04). N-shf features reveal a three-line, A N=41G, contact for the S=1/2 species and a five line, A N=65G, contact for the S=3/2 species suggesting of delocalization of spin on to the two adjacent pyridyl ring donors for the S=3/2 species but only on NO for the S=1/2 species. A spin-polarized {Fe(III), NO − triplet} species and low-spin {Fe(I), NO +} entity account for the spin-crossover mixture. The assignments are consistent with the known S=3/2 [Fe(edta)(NO)] 2− and S=1/2 [Fe(tpen)(NO)] 2+ species. Further support for the intermediacy of the ligand field strength of edampda 2− relative to edta 4− and tpen was obtained from the 3A 2g← 3T 1g (F) transition energies of the Ni IIL series: [Ni(edta)] 2− (17 094 cm −1)<[Ni(edampda)] (18 587 cm −1)<[Ni(tpen)] 2+ (19 531 cm −1); the 2E g← 2T 2g transitions for the Cu IIL complexes: [Cu(edta)] 2− (13 605 cm −1)<[Cu II(edampda)] (15 432 cm −1); and the E 1/2 values of the Ni(II)/Ni(III) redox couples: [Ni(edta)] 2− (1.29 V)<[Ni(edampda)] (1.32 V)<[Ni(tpen)] 2+ (≥1.49 V). The [Zn II(edampda)] complex is predominantly octahedrally-coordinated as shown by stereochemically rigid and coordinated glycinato and pyridylmethyl donors exhibiting AB quartets in the 1H NMR spectrum appearing at 4.29 and 3.33 ppm, respectively. Evidence for a trace amount of a [Zn II(edampda)] complex having a dissociated, pendant pyridyl arm is also observed; the species is most probably a pseudo-trigonal bypyramidal structure based on the EPR spectrum of [Cu II(edampda)] (reported elsewhere) which also exhibits features characteristic of distortion from tetragonal symmetry toward a distorted trigonal bipyramidal structure.

1,5-Bis(2-pyridylmethyl-N)-1,5-diazacyclooctane-N,N']chloronickel(II) perchlorate

The structure of the title compound, [NiCl(C 18 H 24 N 4 )]ClO 4 , is comprised of discrete [NiCl(C 18 H 24 N 4 )] + cations and perchlorate anions. The Ni II atom is five-coordinated by the four nitrogen donors of the new miniring macrocyclic ligand 1,5-bis(2-pyridylmethyl)-1,5-diazacyclooctane [Ni-N 2.074 (3)-2.108 (3) A], and by a chloride anion in the apical site [Ni-Cl 2.302 (1) A]. The coordination geometry of the complex could be considered as intermediate between square-pyramidal and trigonal-bipyramidal. The mini-ring macrocyclic ligand has a boat-chair conformation and the two pyridyl pendants are not coplanar.

Copper(II) complexes of new potentially hexadentate N3S3- or N6-donor podand ligands based on the tris(pyrazolyl)borate or tris(pyrazolyl)methane core

The mononuclear copper(II) complexes of the following potentially hexadentate podand ligands have been prepared and crystallographically characterised: tris[3-{2-(methylsulfanyl)phenyl}pyrazol-1-yl]hydroborate [L1]-, phenyltris[3-(2-pyridyl)pyrazol-1-yl]methane (L2), and tris[3-{(6-methyl)-pyrid-2-yl}pyrazol-1-yl]hydroborate [L3]-. Of these, [L1]- [a potentially N3S3 donor with three pyrazolyl and three thioether groups, based on a tris(pyrazolyl)borate core] and L2 [a potentially N6 donor with three pyrazolyl and three pyridyl groups, based on a tris(pyrazolyl)methane core] have been prepared for the first time. In [Cu(L1)][PF6] the Cu(II) centre is in a five-coordinate N3S2 coordination environment which is approximately square pyramidal; the pendant thioether group has a weak, long-range interaction with the sixth coordination site of Cu(II). [Cu(L1)][PF6] undergoes a reversible Cu(I)–Cu(II) redox conversion. In [Cu(L2)(MeOH)][PF6]2 the ligand is four-coordinate via two bidentate pyridyl/pyrazolyl arms, with the third arm pendant; an axial methanol ligand completes the square-pyramidal coordination. In [Cu(L3)(H2O)][PF6], which is five coordinate and approximately trigonal bipyramidal, [L3]- acts as an N4 donor via all three pyrazolyl groups but only one pyridyl group; the two pendant pyridyl groups are involved in O–H···N hydrogen-bonding interactions with the coordinated water molecule. This ‘second-sphere’ stabilisation of a coordinated ligand is strongly reminiscent of the cooperative interactions by which substrates are bound to the active sites of metalloproteins. The EPR spectra of this complex are solvent-dependent, showing a change from a dz2 ground state in non-donor solvents to a dx2-y2 ground state in donor solvents.

Lanthanide complexes of a new sterically hindered potentially hexadentate podand ligand based on a tris(pyrazolyl)borate core; crystal structures, solution structures and luminescence properties

The new podand ligand hydrotris[3-(6-methyl)pyridin-2-ylpyrazol-1-yl]borate [L1]– was prepared which contains three bidentate pyrazolyl/pyridine arms attached to a {BH}– head-group. This ligand differs from an earlier ligand hydrotris[3-(2-pyridyl)pyrazol-1-yl]borate [L2]– by the presence of methyl groups attached to the C6 positions of the pyridyl rings, which would interfere with each other sterically if the ligand co-ordinated in a fully hexadentate manner. Instead, crystallographic analysis of the complexes [M(L1)(NO3)2(H2O)] (M = Eu, Tb or Gd) showed that partial dissociation of the podand occurs to relieve this potential steric problem: either one or two of the pyridyl groups are not co-ordinated, such that [L1]– is penta- or tetra-dentate, but instead are involved in intramolecular N· · ·H–O hydrogen-bonding interactions with the co-ordinated water molecule. The presence of both structural forms in single crystals of the gadolinium and europium complexes shows that interconversion between them in solution must be facile. Variable-temperature 1H NMR spectra of the diamagnetic lanthanum(III) analogue shows that, whereas all three ligand arms are equivalent on the NMR timescale at high temperatures, at –80 °C there is mirror symmetry in the complex such that two arms are equivalent and the third is different from the other two; this is consistent with the crystalline form in which [L1]– is tetradentate with two pendant pyridyl arms, which has pseudo-mirror symmetry. Luminescence studies showed that whereas the ligand-based luminescence is retained in the gadolinium(III) complex, in the europium(III) and terbium(III) complexes the ligand-centred emission is quenched by ligand-to-metal energy transfer, resulting in the usual metal-centred emission spectra. The intensity of the emission from the europium(III) and terbium(III) complexes of [L1]– is substantially reduced compared to the emission from the analogous complexes [M(L2)(NO3)2] (M = Eu or Tb) which we ascribe to the sterically induced poorer co-ordination of the podand ligand, resulting in (i) less efficient ligand-to-metal energy transfer, and (ii) co-ordination of labile solvent molecules (H2O) to the metal centres.

Iridium(III) bis-terpyridine complexes displaying long-lived pH sensitive luminescence

A bis-terpyridine complex of iridium(III) incorporating a pendent pyridyl group displays long-lived emission at pH 7 in air-equilibrated aqueous solution, but both the lifetime and intensity are reduced by a factor of >8 upon protonation of the pyridyl nitrogen; structurally similar complexes with pendent phenolic groups are only weakly emissive and their ground-state absorption spectra show a new, low-energy band (λ = 468 nm) upon deprotonation.

Cis-(2,2'-Bipyridyl-N,N')carbonyl(methanoato-C)(η2-2,2':6',2''-terpyridyl-N,N')ruthenium(II) Hexafluorophosphate

The title compound, [Ru(CHO2)(C10H8N2)(C15H11N3)(CO)]PF6 or cis-[Ru(bpy)(η2-tpy)(CO)(COOH)]PF6 (where bpy is 2,2′-bipyridyl and tpy is 2,2′:6′,2′′-terpyridyl), has distorted octahedral geometry about the Ru atom, a bidentate terpyridyl ligand and a fully chelated bipyridyl ligand. The terminal carbonyl and carboxyl groups are cis. The Ru—C—O angle (terminal carbonyl) is distorted from linearity [173.7 (4)°] by the pendant pyridyl group of the N,N′-bound tpy ligand, which is hydrogen bonded to the hydroxyl proton of the carboxyl group.

Synthesis and Characterization of Binuclear Lanthanide Complexes of 1,4,7,10-Tetrakis(2-Pyridylmethyl)-1,4,7,10-Tetraazacyclododecane

A series of new dinuclear lanthanide complexes with a macrocyclic tetramine ligand containing 4-pyridyl pendants has been synthesized by the reaction of 1,4,7,10-tetrakis-(2-pyridylmethyl)-1,4,7,10-tetraazacyclododecane (L) and lanthanide nitrates (where Ln = Ce, Nd, Eu, Gd, Tb, Ho, Yb). The complexes have the general formula [Ln2(L)(NO3)4](NO3)2. L acts as an octadentate donor ligand to bond two lanthanide(III) ions in these complexes. The electronic and steric requirements of the lanthanide ion appear to be fully satisfied by coordination of the two nitrogens of the macrocyclic ring, the two nitrogens of the pyridyl pendants of L, and the oxygens of two bidentate chelating nitrate ions. The coordination number of the metal ions is therefore 8. The electronic spectra of the Nd and Ho complexes in the visible region have been analyzed, and the spectral parameters (β, b1/2, δ, ωλ) have been calculated and discussed. The emission spectra of the Eu and Tb complexes show strong luminescence, and the spectra from methanol and aqueous solutions are obviously different. The variable-temperature magnetic susceptibility (4-300 K) of the Gd(III) complex reveals a weak antiferro-magnetic spin exchange with J = - 0.23 cm−1 between the Gd3+ ions.

Synthetic resins as designable supports for metal‐based chemistry: The issue of their nanomorphology and molecular accessibility

AbstractMacromolecular cross‐linked ligands containing pyridyl pendant groups are characterized by a combination of inverse steric exclusion chromatography, ESR and NMR spectrometries in water and methanol. On the basis of the relevant results, methanol is seen to be clearly the best swelling agent and it is chosen as medium for CuII coordination.

Synthesis and dynamic NMR studies of fluxionality in rhenium(I), platinum(II) and platinum(IV) complexes of ‘back-to-back’ 2,2′∶6′,2″-terpyridine ligands

Syntheses are given for the following transition metal complexes, [{ReBr(CO)3}2L] (L = L1, L2 or L3), [(PtClMe3)2L1], [(PtIMe3)2L] (L = L2 or L3), [ReBr(CO)3L1], [Pt(C6F5)2L3], [Pt(C6F4CF3)2L] (L = L1 or L2), [{Pt(C6F4CF3)2}2L] (L = L1 or L2) and [ReBr(CO)3PtIMe3L1] where the ligands, L, are the ‘back-to-back’ terpyridine ligands, 6′,6″-bis(2-pyridyl)-2,2′∶4′,4″∶2″,2‴-quaterpyridine (L1), 1,4-bis(2,2′∶6′,2″-terpyridin-4′-yl)benzene (L2) and 6′,6″-bis{2-(4-methylpyridyl)}-2,2′∶4′,4″∶2″,2‴-quaterpyridine (L3). All the complexes undergo 1,4-metallotropic shifts in solution at above-ambient temperatures and restricted rotations of the pendant pyridyl rings at below-ambient temperatures. Activation energies for these processes have been computed from variable temperature one-dimensional bandshape analysis and 2D-exchange spectroscopy (2D-EXSY) NMR experiments. The metallotropic shift energies are very metal-dependent being in the order PtIV < ReI < PtII, with ΔG ‡ (298.15 K) values ranging from 62 to 101 kJ mol–1. The fluxions are sensitive only to the local metal-coordination environment, there being negligible electronic interaction between the metal centres in the dinuclear complexes. In the mixed-metal dinuclear complex [ReBr(CO)3PtIMe3L1] it proved possible to measure the different rates of fluxion of the ReI and PtIV moieties.

New dioxocyclam ligands appended with 2-pyridylmethyl pendant(s): synthesis, properties and crystal structure of their copper(II) complexes (dioxocyclam = 1,4,8,11-tetraazacyclotetradecane-12,14-dione) ‡

Two new dioxocyclam ligands, 4-(pyridin-2-ylmethyl)-1,4,8,11-tetraazacyclotetradecane-12,14-dione (L1) and 4,8-bis(pyridin-2-ylmethyl)-1,4,8,11-tetraazacyclotetradecane-12,14-dione (L2), have been synthesized and characterized. The solution chemistry of the CuII complexes with these ligands have been studied by potentiometric and spectroscopic titration, cyclic voltammetry (CV), UV/VIS and ESR spectral techniques. The CuII complex of L2 has been isolated as single crystals and the structure has been determined by X-ray diffraction analysis to be [CuL2][ClO4]2 1. In complex 1, the CuII atom is five-co-ordinate with the two pendant pyridyl nitrogens and the two tertiary amines forming a distorted trigonal-bipyramidal configuration in which the backbone oxygen O(2) co-ordinates to CuII while the two amido nitrogen groups remained non-deprotonated and non-co-ordinated. To our knowledge, this is the first example of CuII complexes of dioxotetraamines in which the backbone oxygen co-ordinates to the central metal by twisting the backbone.

Synthesis and dynamic NMR studies of fluxionality in palladium(II) and platinum(II) complexes of 2,4,6,-tris(2-pyridyl)-1,3,5-triazine (TPT) and 2,4,6-tris(2-pyridyl)-pyrimidine (TPP)

Complexes of general formulae cis-[M(C 6F 4CF 3) 2L] (M = Pd II, Pt II; L = 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPT) and 2,4,6-tris(2-pyridyl)-pyrimidine (TPP) were isolated as air-stable solids. In all cases cis square-planar complexes were formed with the nitrogen ligands acting as bidentate chelates towards each metal moiety. The complexes exhibited various modes of fluxionality in solution, namely 1,4-metallotropic shifts, a new ‘metal hurdling’ fluxion and, at below-ambient temperatures, restricted rotation of the pendant pyridyl ring adjacent to the metal chelate ring. Dynamic NMR experiments (one-dimensional bandshape analysis and two-dimensional EXSY experiments) provided activation energy data for these processes. Gibbs free energy values ( ΔG ≠ (298.15 K)) were in the ranges 74–113 (metal hurdling). 69–118 (metal 1,4-shifts) and 37–43 (pendant pyridyl rotations) kJ mol −1. Energies of any of these fluxions were considerably higher in the Pt II complexes than in the Pd II complexes. To aid understanding of the low temperature fluxionality of the TPT complexes, the complex [Pd(C 6F 4CF 3) 2(mstd)] (mstd = meso-stilbenediamine) was synthesised. At low temperatures, C 6F 4CF 3 ring rotations and five-membered ring puckering in this complex were arrested, ΔG ≠ (208K) for the latter process being 42.8 kJ mol −1.

Structure and O2 uptake properties of a novel nickel(II) complex of pyridyl-pendant dioxocyclam [1-(2-pyridyl)methyl-5,7-dioxo-1,4,8,11-tetraazacyclotetradecane

Novel potentially five-coordinate pyridyl–pendant dioxocyclam [1-(2-pyridyl)methyl-5,7-dioxo-1,4,8,11-tetraazacyclotetradecane (H2L) and its homologs (6-methyl and 6,6-dimethyl derivatives)] have been synthesized to study nickel(II) complexation. A purple nickel(II) complex with a deprotonated amide (NiHL) was isolated from aqueous equimolar solution of H2L and Ni(ClO4)2. A yellow nickel(II) complex with two deprotonated amides (NiL) was crystallized from an H2O/CH3CN solution of H2L and Ni(OH)2. The X-ray crystal study of NiL showed a square-planar nickel(II) complex with the pyridyl–pendant remaining uncoordinated. It is concluded from the visible absorption and NMR study of NiL in aqueous solution that the four-coordinate NiL is in equilibrium with a five-coordinate square-pyramidal nickel(II) complex with the apical coordination of the pyridyl–pendant. A voltammetric study disclosed a low nickel(II/III) redox potential of +0.29 V vs SCE for NiL at pH 9.5 and 25 °C with 0.10 M Na2SO4. The nickel(II) complex NiL absorbed an equimolar amount of O2 at pH 9.5 and 25 °C, and the O2 was activated to cleave plasmid DNA.

Ruthenium tris-(bipyridyl) complexes with pendant protonatable and deprotonatable moieties: pH sensitivity of electronic spectral and luminescence properties

A. M. W. Cargill Thompson, M. C. C. Smailes, J. C. Jeffery and M. D. Ward, J. Chem. Soc., Dalton Trans., 1997, 737 DOI: 10.1039/A607181C

Preparation and Characterization of Nitrogen and Oxygen Containing Graphite-like Pyropolymers from 5-(2-Pyridyl)-2,4-pentadiyn-1-ol

5-(2-Pyridyl)-2,4-pentadiyn-1-ol was polymerized over NbCl5- or TaCl5-based catalysts followed by pyrolysis to obtain graphite-like pyropolymers. The black metathesis polymer, poly[5-(2-pyridyl)-2,4-pentadiyn-1-ol], has the structure of a fully conjugated backbone and was converted into a polyacene-based polymer having pyridyl pendant groups. The pyropolymers prepared by vacuum pyrolysis over 700 °C have nitrogen atoms incorporated into graphene sheets. The polymers were characterized by elemental analysis, TGA, FT-IR, laser Raman, NMR, XPS, X-ray diffraction, temperature-programmed desorption experiments, charge/discharge experiments, and SEM and TEM studies.

Synthesis of triosmium alkylidyne clusters incorporating pendant pyridyl ligands. Crystal structures of [Os 3( μ-H) 2(CO) 9{ μ3-C(4,4′-bipy)}] · H 2O and [Os 3( μ-H 2(CO) 9{ μ3-C(2,4′-bipy)}] (4,4′-bipy = 4,4′-bipyridine; 2,4′-bipy = 2,4′-bipyridine)

Reaction of [Os 3( μ-H) 3(CO) 9( μ 3-CCl)] with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in the presence of an excess of 4,4′-bipyridine (4,4′-bipy) or 2,4′-bipyridine (2,4′-bipy) yields [Os 3( μ-H) 2(CO) 9{ μ 3-C(4,4′-bipy)}] ( 1) and [Os 3( μ-H) 2(CO) 9{ μ 3-C(2,4′-bipy)}] ( 2), respectively, in good yields. Both complexes, which contain externally directed pendant pyridyl groups capable of ligation to other metal centres, have been fully characterised by spectroscopic and X-ray diffraction methods. Chemical reactivities of 1 with H +, AuPPh 3 + and [Os 3( μ-H) 3(CO) 9( μ 3-CCl)] are also described.

Gallium and Indium Complexes of Hexadentate Ligands Containing Pendant Pyridyl and Phenolate Groups

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGallium and Indium Complexes of Hexadentate Ligands Containing Pendant Pyridyl and Phenolate GroupsErnest Wong, Shuang Liu, Steve Rettig, and Chris OrvigCite this: Inorg. Chem. 1995, 34, 11, 3057–3064Publication Date (Print):May 1, 1995Publication History Published online1 May 2002Published inissue 1 May 1995https://doi.org/10.1021/ic00115a036RIGHTS & PERMISSIONSArticle Views764Altmetric-Citations34LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (955 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

Synthesis, Structure and Properties of Five-Coordinate Copper(II) Complexes of Pentadentate Ligands with Pyridyl Pendant Arms

Synthesis, Structure and Properties of Five-Coordinate Copper(II) Complexes of Pentadentate Ligands with Pyridyl Pendant Arms

Synthesis, structure and properties of cobalt(III) complexes of pentadentate ligands with pyridyl pendant arms

Cobalt(III) complexes of the pentadentate ligands 3-[4-(2-pyridyl)-3-azabut-3-enyl]-3-azapentane-1,5-diamine (L1), 3-[4-(2-pyridyl)-3-azabutyl]-3-azapentane-1,5-diamine (L2) and 1,4-bis(2-pyridylmethyl)-1,4,7-triazacyclononane (L4) have been synthesized. Various characterization studies have confirmed the formation of the complexes [CoL4(OH2)]3+, [Co(L4)Cl]2+, [Co(L1)Cl]2+, [Co(L2)Cl]2+ and [Co(HL3)Cl]2+(HL3= 3-{2-[hydroxy(2-pyridyl)methyleneamino]ethyl}-3-azapentane-1,5-diamine) the product of oxidation of [Co(L1)Cl]2+ in acidic solution. The structure of [CoL4(OH2)][ClO4]3·H2O has been determined by single crystal X-ray diffraction. The complex crystallizes in the orthorhombic space group P212121, with a= 15.090(3), b= 16.659(4), c= 10.192(4)A and Z= 4. Refinement gave final R and R′ values of 0.045 and 0.043, respectively, for 1708 observed reflections. The pyridyl pendant arms were found to introduce significant distortion from ideal octahedral geometry. The Co–N(tacn) distances are shorter than in related complexes of ligands derived from 1,4,7-triazacyclononane (tacn). The complex [Co(HL3)Cl][ClO4]2·H2O crystallizes in the monoclinic space group P21/c with a= 13.496(5), b= 10.253(3), c= 15.371(6)A, β= 101.65(3)° and Z= 4. Refinement gave final R and R′ values of 0.054 and 0.054, respectively, for 1686 observed reflections. The bond lengths within the amide portion of the pentadentate ligand are intermediate between keto and enol resonance forms. Protonation of the amide oxygen is implied by the number of counter ions present. No evidence of imine oxidation was observed in electrochemical studies. These studies indicated that some stabilization of the CoII state relative to CoIII arises from the presence of pyridyl and imine π acceptors.

The synthesis and X-ray structures of ytterbocene(II) complexes containing pendant pyridyl groups, [Yb(Cp x) 2] (Cp x=η 5-C 5H 3(R)[CMe 2(CH 2) nC 5H 4N-2]-1,3; R  H or SiMe 3 and n = 0 or 1

Metallation of C 5H 5[C(Me) 2CH 2C 5H 4N-2] ( Cp pyH), C 5H 4(SiMe 3)[{C(Me) 2CH 2 C 5H 4N-2}-3] ( Cp′ pyH), C 5H 5-[C(Me) 2C 5H 4N-2](Cp py(s)H, and C 5H 4[(SiMe 3){C(Me) 2C 5H 4N-2}-3] [Cp′ py(s)H] with KH in THF yielded the potassium complexes KCp py ( 1), KCp′ py ( 2), KCp py(s) ( 3), or KCp′ py(s) ( 4). Compounds 1–4 were readily converted into their homoleptic solvent-free ytterbium(II) complexes [Yb(Cp py) 2] ( 5), [Yb(CP′ py) 2] ( 6), [Yb(Cp py(s) 2 ( 7) and [Yb(Cp′ py(s) 2] ( 8). The crystal structures of 5 and 8 show that both of the pyridyl groups in each complex are coordinated to the ytterbium. Some angles in 5 are Cp(1)-Yb-Cp(2) 137.7° and N(1)-Yb-N(2) 100.8(2)°, and the corresponding angles in 8 are Cp(1)-Yb-Cp(2) 136.9° and N(1)-Yb-N(2) 84.0(4)° (where Cp refers to the centroid of the cyclopentadienyl ring).