Beta-diketonate Ligands Research Articles

Lead(II) complex with methoxy-substituted beta-diketonate − structure, thermal behavior and unexpected thermolysis byproduct

New complex of lead(II) with beta-diketonate ligand PbL2 is described, where L=CH3COCHCOC(OCH3)(CH3)2, 5-methoxy-5-methylhexan-2,4-dionate). Crystal structure of the compound has been determined and its thermal properties have been studied. Chains of 1D coordination polymers form crystals of the complex, where the molecules are connected through the chelate-bridging oxygen atoms, methoxy groups remain free and form hydrogen bonds between the chains. PbL2 sublimates at 120 °C under reduced pressure (P=10−2 Torr) with partial decomposition. When heated in the condensed phase the complex decomposes with the formation of lead(II) oxide and evolution of a pyran derivative into gas phase. The mechanism of lead(II) complex thermolysis in support of the condensation of two ligands is discussed. A new organic product was identified by 13C and 1H NMR, IR and PL spectroscopy and mass spectrometry; the crystal structure of the product was determined.

Blue-Emitting Zero-Dimensional Inorganic-Organic Hybrids Constructed from Beta-Diketonate Ligands and Bulky Organic Cations.

Two zero-dimensional inorganic-organic hybrids, namely, [C4mim][Cd(TCDPPA)3] (1) and [C4mpy][Cd(TCDPPA)3] (2), where (TCDPPA)- = 2,2,2-trichloro-N-(di(pyrrolidin-1-yl)phosphoryl)acetamide, (C4mim)+ = 1-butyl-3-methylimidazolium, and (C4mpy)+ = 1-butyl-4-methylpyridinium, have been synthesized via metathesis reactions and characterized systematically. These ionic cadmium-containing inorganic-organic hybrid compounds are assembled from a bulky organic cation and a complex anion constructed from the chelation of three TCDPPA ligands to one cadmium ion. These compounds possess wide band gaps and emit in the deep-blue region intensely with a quantum yield as high as 34.04%. The success of this work provides a new method for the design and fabrication of high-efficiency blue-emitting materials.

Models of radiovoltaic batteries based on organo-lanthanide complexes

The complexes of Eu(III) and Tb(III) with beta-diketonate ligands were tested as donor materials in heterojunction radiovoltaic planar devices. The compounds revealed weak ability to directly convert the energy of cathode and X-ray radiation into electricity. However, the use of these complexes as additional radioluminescent layers in radiovoltaic devices has led to design an efficient radio-photovoltaic battery. The highest energy conversion efficiency was achieved when terbium complex with pyrasolonate and triphenylphosphine oxide ligands (Tb(pmip)3(TPPO)2) was used as a phosphor. The device with Tb(pmip)3(TPPO)2 outer layer under cathode radiation of 100 KeV gave output power 94 nW. Under X-ray radiation with photon energy 10 KeV the same device exhibited power of 0.95 nW. In both cases, the energy of accident electrons or X-ray photons causes the emission of the phosphor layer in the visible region, which penetrate through the glass substrate and the anode to the donor/acceptor heterojunction where it is converted into electric current. Thus, the devices operate as radio-photovoltaic devices, although the contribution of the radio-voltaic effect to the overall energy conversion process is very small.

Beta-diketones in the intensification of the luminescence of the silk fibroin films doped rare earth ions

Silk fibroin (SF) is a structural protein found in Bombyx mori cocoons and has properties that are potentially applicable in photonics. This biocompatible matrix is an interesting substrate for different ions and molecules. Furthermore, its variable refractive index allows photons to be guided in this material enabling their use as biocompatible and resorbable waveguides, which can be used to provide optical energy for various applications, e.g., therapy or imaging in living tissue. Rare earth ions (RE) play a widely known role in the field of photonics. However, there are few studies involving the production of light in doped SF with RE ions, and the literature results have shown different sensitization of Eu3+ and Tb3+ ions by the SF matrix. This study presented a consistent work on material synthesis, related studies on spectroscopy of RE ions, and the role of beta-diketonate ligand on the energy transfer mechanisms with the emission improvement in the investigated material. As a result, an intensification of emission was observed for Eu3+ doped sample in the presence of 2-thenoyltrifluoroacetone ligand, but similar results were not carried out with acetylacetone ligand insertion. A possible cause was the different access by beta-diketonate to the lanthanide ion in SF matrix due to the ligand–SF interaction. The results presented have characterized the RE–SF interactions and supported the mechanisms of energy transfer improvement for excitation of different RE ions in this matrix being important for future applications in photonics.

Kinetic study of thermal decomposition of new Eu(III), Tb(III) and Gd(III) complexes with beta-diketone ligands and 4,4-diphenyl-2,2-dipyridyl, chloride of 1,10-phenantrolinium

Complexes of general formula [Eu(fod)3·L], [Tb(fod)3·L] and [Gd(fod)3·L] (where fod=6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octadionate; L=4,4-diphenyl-2,2-dipyridyl or/and chloride of 1,10-phenantrolinium) were synthesized by reacting the corresponding salt of terbium and gadolinium with β-diketone(fod) and other ligands, and the precursor Eu(fod)3·2H2O with diphenylbipy and phenCl ligands. The thermal decomposition of these complexes along with description of some emitting materials is discussed in details. We focused on those complexes emitting in the visible region, which can be used in lighting industry (e.g., for the preparation of photo- and electro-luminescent devices) and for biological immunoassays. The thermal decompositions of Eu(fod)3·L, Tb(fod)3·L and Gd(fod)3·L are best described by R2 and R3 kinetic models. Some selected results of our work concerning the synthesis of highly luminescent complexes for application in lighting and light conversion technologies are reported. Such materials have been obtained by combining the peculiar luminescence properties of Eu3+ and Tb3+ antenna complexes with β-diketone (fod).

A novel series of antitumor ruthenium beta‐diketonato compounds

Metal complexes are important chemotherapeutic agents against diseases; cisplatin is a widely used antitumor agent. Other metal centers are promising and ruthenium complexes are already in pre‐clinical trials. Recently, we described the excellent antitumor activity on colon‐rectal tumor cell line of a ruthenium‐curcumin complex and we described the interaction of this complex with the metal binding to guanine N7 of a DNA moiety (Caruso F, Rossi M, Benson A, Opazo C, Freedman D, Monti E, Gariboldi MB, Shaulky J, Marchetti F, Pettinari R, Pettinari C. J Med Chem. 2012 55, 1072). We present here a novel series of Ru compounds where curcumin is replaced with several beta‐diketone ligands. One has particularly strong antitumor activity in vitro; in observing the structure‐activity relationship, we hypothesize a potential intercalation of the ligand naphthalene moiety in between the bases of DNA. We describe a theoretical docking procedure for this species and also include antitumor activity and X‐ray diffraction studies. Supported by HHMI52006322.

Structural and Luminescence Properties of Silica-Based Hybrids Containing New Silylated-Diketonato Europium(III) Complex

A new betadiketonate ligand displaying a trimethoxysilyl group as grafting function and a diketone moiety as complexing site (TTA-Si = 4,4,4-trifluoro-2-(3-trimethoxysilyl)propyl)-1-3-butanedione (C4H3S)COCH[(CH2)3Si(OCH3)3]COCF3) and its highly luminescent europium(III) complex [Eu(TTA-Si)3] have been synthesized and fully characterized. Luminescent silica-based hybrids have been prepared as well with this new complex grafted on the surface of dense silica nanoparticles (28 ± 3 nm) or on mesoporous silica particles. The covalent bonding of Eu(TTA-Si)3 inside the core of uniform silica nanoparticles (40 ± 5 nm) was also achieved. Luminescence properties are discussed in relation to the europium chemical environment involved in each of the three hybrids. The general methodology proposed allowed high grafting ratios and overcame chelate release and tendency to agglomeration, and it could be applied to any silica matrix (in the core or at the surface, nanosized or not, dense or mesoporous) and therefore numerous applications such as luminescent markers and luminophors could be foreseen.

(Invited) Reaction Mechanisms in ALD of Ternary Oxides

Reaction mechanisms underlying the atomic layer deposition (ALD) of ternary oxide films are investigated via the dependence of film stoichiometry on the sequence of ALD pulses. Data on film composition are brought together from experiments on five ternary oxide systems containing La, Mn, Ca, Fe, Sr, or Co, all using beta-diketonate ligands (thd) in the metal precursor and ozone as the oxygen source. These data are compared with the predictions from two possible reaction models: one where all ligands are combusted by ozone, the other where extra ligands are eliminated during the metal precursor pulse due to the availability of surface hydroxyl. The latter reaction is seen to be strongly dependent on the strength of the metal-ligand bond. Differences in cation charge also affect the stoichiometry. In this way, factors dictating the composition of ternary oxides are elucidated, opening the way to improved control of ALD processes and material properties.

Luminescent Lanthanide (Eu3+, Tb3+) Hybrids with 4‐Vinylbenzeneboronic Acid Functionalized Si‐O Bridges and Beta‐Diketones

4-Vinylphenylboronic acid ligand (VPBA) is functionalized with two crosslinking reagents (3-(triethoxysilyl)-propylisocyanate [TEPIC] and 3-(trimethoxysilyl) propyl methacrylate [TMPMA]) to achieve the two special molecular bridge VPBA-TEPIC and VPBA-TMPMA. Meanwhile, beta-diketone ligands (2-thenoyltrifluoroacetone [TTA], acetyl acetone [ACAC]) as the second ligands play the role of the main energy donor, which absorb abundant energy in ultraviolet-visible extent and then transfer the energy to the corresponding lanthanide ions (Eu(3+), Tb(3+)) to sensitize their emission of them. Eight binary and ternary Eu(3+), Tb(3+) hybrids with VPBA-TEPIC (VPBA-TMPMA) and TTA (ACAC) have been constructed, whose photoluminescence properties are studied in depth and suggest that the ternary hybrids show the favorable characteristic luminescent properties (longer lifetime and higher quantum efficiency).

Computational explorations of mechanisms and ligand-directed selectivities of copper-catalyzed Ullmann-type reactions.

Computational investigations of ligand-directed selectivities in Ullmann-type coupling reactions of methanol and methylamine with iodobenzene by beta-diketone- and 1,10-phenanthroline-ligated Cu(I) complexes are reported. Density functional theory calculations using several functionals were performed on both the nucleophile formation and aryl halide activation steps of these reactions. The origin of ligand-directed selectivities in N- versus O-arylation reactions as described in a previous publication (J. Am. Chem. Soc. 2007, 129, 3490-3491) were studied and explained. The selectivities observed experimentally are derived not from initial Cu(I)(nucleophile) complex formation but from the subsequent steps involving aryl halide activation. The arylation may occur via single-electron transfer (SET) or iodine atom transfer (IAT), depending on the electron-donating abilities of the ligand and nucleophile. Mechanisms involving either oxidative addition/reductive elimination or sigma-bond metathesis are disfavored. SET mechanisms are favored in reactions promoted by the beta-diketone ligand; N-arylation is predicted to be favored in these cases, in agreement with experimental results. The phenanthroline ligand promotes O-arylation reactions via IAT mechanisms in preference to N-arylation reactions, which occur via SET mechanisms; this result is also in agreement with experimental results.

Synthesis of novel β-diketonate bis(bipyridyl) Os(ii) dyes for utilization of infrared light in dye-sensitized solar cells

Bis(bipyridyl) osmium(II) dyes having a beta-diketonate ligand were synthesized in order to utilize visible and infrared light for dye-sensitized solar cells. Compared to black dye, under AM 1.5 irradiation (100 mW cm(-2)), DSCs using our novel Os dyes exhibited a better spectral response in the near-IR region (by 1050 nm) and showed a higher J(SC) value of 23.7 mA cm(-2).

Synthesis and characterization of homo- and heterovalent tetra- hexa- hepta- and decanuclear manganese clusters using pyridyl functionalized β-diketone, carboxylate and triethanolamine ligands

The syntheses and characterizations are reported for six new homo- and heterovalent manganese clusters, utilizing pyridyl functionalized beta-diketones ligands. The reaction of the trinuclear complex [Mn3O(O2CPh)6(H2O)(Py)2] with 1,3-di(pyridine-2-yl)propane-1,3-dione (dppdH) in CH2Cl2 resulted in a mixed-valence Mn3(II)Mn6(III)Mn(IV) decanuclear cluster of formula [Mn10O7(dppd)3(O2CPh)11] x 4 CH2Cl2 (1). The structure of the core of 1 is based upon a centred tricapped trigonal prism. Reacting Mn(BF4)2 x xH2O with dppdH and triethylamine (NEt3) in CH2Cl2-MeOH gave a rare, homoleptic hexanuclear cluster of formula [Mn(II)6(dppd)8][BF4]4 (2) which has a triangular based core. Reaction of Mn(Y)2 x xH2O, Y = NO3(-) or BF4(-), with dppdH or 1-phenyl-3-(2-pyridyl)propane-1,3-dione (pppdH) in the presence of triethanolamine (teaH3) and NEt3 gave a heptanuclear 'disc' like manganese core of general formula [Mn(II)7(X)6(tea)(OH)3][Y]2 x solv (3) X = pppd- or dppd- and Y = NO3(-) or BF4(-). The addition of N-(2-pyridinyl)acetoacetamide (paaH) to Mn(Y)2 x 4 H2O Y = NO3(-) or ClO4(-) in MeOH gave a second divalent heptanuclear cluster with a 'disc'-like core of general formula [Mn7(paa)6(OMe)6][X]2 x solv (4) (X = NO3(-) or ClO4(-)), whilst the addition of paaH to a mixture of Mn(NO3)2 x 4 H2O, teaH3 and NEt3 in CH2Cl2-MeOH resulted in the formation of a mixed-valence Mn2(II)Mn2(III) tetranuclear 'butterfly' complex of formula [Mn4(paa)4(teaH)2][NO3]2 x 2 MeOH x 2 CH2Cl2 (5). Compound 5 displays the rare Mn(II/III) oxidation state distribution of the body positions being Mn(II) while the wing tips are Mn(III). The in situ formation of the tetranuclear [Mn4(teaH)2(teaH2)2(O2C(CH3)3)2][O2C(CH3)3]2 'butterfly' complex followed by the addition of Mn(O2CMe)2 x 4 H2O resulted in a mixed-valence Mn4(II)Mn(III)Mn(IV) hexanuclear species of formula [Mn6O2(teaH2)4(O2CMe)4][NO3]2[O2CMe] x CH2Cl2 x MeOH x 2 H2O (6). The core of 6 displays a face sharing dicubane topology. Compounds 1 and 6 both display novel trapped-valence metal cores containing three different oxidation states on the manganese ion. Compounds 1, 2 and 3 are the first manganese based dppd clusters, while 4 and 5 are the first with the pyridylamino-substituted beta-diketone ligand (paaH). The magnetic data for 1, 2, 3, 4, and 6 are dominated by antiferromagnetic interactions within the clusters, leading to small ground spin values of S = 1 for 1, S = 3 for 2, S = 5/2 for 3, S = 5/2 for 4 and S = 1/2 for 6. Compound 5, however, displays overall ferromagnetic interactions with the data indicating an S = 6 ground state. 5 also exhibits probable single molecule magnet behaviour as indicated by frequency dependent out-of-phase chiM'' peaks in the AC susceptibility measurements.

Highly efficient luminescent hybrid materials covalently linking with europium(iii) complexes via a novel fluorinated β-diketonate ligand: synthesis, characterization and photophysical properties

A novel highly fluorinated beta-diketonate ligand, 1-(3,5-bis(benzyloxy)phenyl)-4,4,5,5,5-pentafluoropentane-1,3-dione (HBBPPF) and its corresponding europium(III) ternary complex, Eu(BBPPF)(3)(DDXPO) [DDXPO = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene oxide] were synthesized via a dexterously designed routine, characterized and its photophysical properties (PL) investigated. PL measurement results indicated that the europium(III) ternary complex exhibits intense red emission under UV light excitation with a solid-state quantum yield of 39%. An organic-inorganic mesoporous luminescent hybrid material was also constructed by linking the ternary europium(III) complex to the functionalized hexagonal mesoporous MCM-41 through the modified beta-diketonate ligand (SiBBPPF-Na). Beta-diketonate grafted to the coupling agent 3-(triethoxysilyl)propyl isocyanate was used as the precursor for the preparation of mesoporous materials. A modified MCM-41 mesoporous material containing ternary europium(iii) complex covalently bonded to the silica-based network, designated as Eu(BBPPF-Si)(3)(DDXPO)/MCM-41, was obtained by interacting SiBBPPF-Na with europium nitrate, DDXPO and MCM-41 via a ligand-exchange reaction. The new mesoporous hybrid material was characterized by powder X-ray diffraction, nitrogen adsorption-desorption, thermogravimetry, transmission electron microscopy, dynamic light scattering, FT-IR, (29)Si CP MAS NMR and (13)C NMR solid-state techniques, and photoluminescence spectroscopy. Eu(BBPPF-Si)(3)(DDXPO)/MCM-41 exhibits an efficient intramolecular energy transfer process from the silylated beta-diketonate to the central Eu(3+), namely, the "antenna effect", which favours a strong luminescent intensity (quantum yield = 43%). Thermogravimetric analysis on Eu(BBPPF-Si)(3)(DDXPO)/MCM-41 demonstrated that the thermal stability of the lanthanide complex was evidently improved as it was covalently bonded to the mesoporous MCM-41 matrix.

Effect of Different Alkyl Groups at the N-Position on the Luminescence of Carbazole-Based β-Diketonate Europium(III) Complexes

A series of carbazole-based beta-diketone derivatives and their europium(III) ternary complexes Eu(N-Cx)(3)phen were designed and synthesized, where N-Cx denotes carbazole-based beta-diketonates with different alkyl substituents at N-position of the carbazole ring and phen is 1,10-phenethroline. Thermogravimetric analysis (TGA) shows that the decomposition temperature of the complexes is over 360 degrees C. UV-visible absorption spectroscopy, photoluminescence (PL), and the luminescence quantum yield of the Eu(III) complexes were measured and compared with each other, and the effect of different substituted-alkyls at N-position in the carbazole ring on the photoluminescence was discussed in details, indicating there exists a competition between the absorption capacity and the energy transfer efficiency for the complexes when the structure of the substituted-alkyls changes. The triplet state energy levels of the beta-diketonate ligands in the complexes are higher than that of the lowest excited level of Eu(3+) ion, (5)D(0), so the photoluminescence mechanism of the Eu(III) complexes was proposed as a ligand-sensitized luminescence process. Red LEDs were fabricated by precoating the complexes onto 395 nm emitting InGaN chips. All the results show that this series of Eu(III) complexes is a promising candidate as a red component in fabrication of NUV-based white LEDs.

Reduced Efficiency Roll-Off in Organic Light-Emitting Diodes by a Novel Short-Lived Organoeuropium Emitter

In this paper, we report a novel organoeuropium complex [Eu(DPDBM)(3)DPPZ] based on a triphenylamine-derived beta-diketone ligand for short-lived emitter exploration. The (5)D(0) --> (7)F(2) ( approximately 610 nm) luminescence lifetime of Eu(DPDBM)(3)DPPZ is only 30 mus, which is 1 order of magnitude shorter than that of a typical Eu(3+) complex. The electroluminescence device using Eu(DPDBM)(3)DPPZ as the emitter achieves a maximum current efficiency of 3.0 cd/A, and the efficiency roll-off is largely reduced because of the emitter's short luminescence lifetime.

A series of Eu(III) emitters with a novel triphenylamine-derived beta-diketone ligand

In this paper, a series of Eu(III)complexes with a novel triphenylamine-derived beta-diketone ligand are synthesized. Systematical research reveals that these Eu(III) complexes take an occasional antenna mechanism by transferring energy between singlet state of ligand and central Eu(III), which leads to much shortened excited state lifetimes of the corresponding Eu(III) complexes.

Structural and Photoluminescence Studies of a Europium(III) Tetrakis(β-diketonate) Complex with Tetrabutylammonium, Imidazolium, Pyridinium and Silica-Supported Imidazolium Counterions

Tetrakis(naphthoyltrifluoroacetonato)lanthanate(III) complexes (Ln = Eu, Gd) containing the cations tetrabutylammonium, [NBu(4)](+); 1-butyl-3-methylimidazolium, [C(4)mim](+); and 1-butyl-3-methylpyridinium, [C(4)mpyr](+), have been prepared and structurally characterized by single-crystal X-ray diffraction. The {EuO(8)} coordination sphere in [NBu(4)][Eu(NTA)(4)] is best described as a distorted dodecahedron, where the metal ion is located at the 4-fold inversion axis with only one crystallographically independent NTA residue. In [C(4)mim][Eu(NTA)(4)] and [C(4)mpyr][Gd(NTA)(4)], the central Ln(3+) ions are coordinated by eight oxygen atoms from four distinct beta-diketonate ligands, in an overall distorted square-antiprismatic geometry. Besides electrostatic interactions, the crystal packing in all three structures is stabilized by offset pi-pi interactions involving the naphthyl rings of neighboring complexes (and, for [C(4)mim][Eu(NTA)(4)] and [C(4)mpyr][Gd(NTA)(4)], neighboring naphthyl/imidazolium and naphthyl/pyridinium rings) and C-H...pi contacts. The photoluminescence properties of the three Eu(III) complexes were studied at room temperature and -259 degrees C by measuring emission and excitation spectra, (5)D(0) emission decay curves, and absolute emission quantum yields. Under ligand excitation (lambda(ex) = 290-395 nm), the quantum yields (room temperature) were in the range 0.72-0.77 for the 1-butyl-3-methylimidazolium salt. An immobilized analogue of this complex was prepared by supporting [Eu(NTA)(4)](-) on an ordered mesoporous silica derivatized with 1-propyl-3-methylimidazolium groups. The disappearance of the intra-4f(6) lines in the excitation spectrum of the supported material indicated an increase in the ligand's sensitization process of the Eu(3+) ions, relative to direct intra-4f(6) excitation. The emission quantum yield measured for the supported material (0.32-0.40, for excitations between 265 and 360 nm) is the highest so far reported for lanthanide-containing ordered mesoporous silicas.

A novel europium(iii) complex with versatility in excitation ranging from infrared to ultraviolet

One- and two-photon absorption properties of a novel europium(III) complex containing a hemicyanine cation are investigated in this paper; in which the sensitization wavelength of europium(III), induced by beta-diketonate ligands, is in the ultraviolet range, and the hemicyanine(aminostyrylpyridinium) cation extends the sensitization wavelength of Eu(III) to visible region. Furthermore, under 1.06 microm ultrashort pulse laser excitation, the complex exhibits effective europium(III) luminescence induced by the two-photon absorption of the hemicyanine cation. Therefore, this new europium(III) complex with excitation bands in the near infrared, visible and ultraviolet ranges. Since the 1.06-microm ultrafast laser is one of the most frequently used laser sources and 1.06 microm is an 'optical window' for cells and tissues, the results suggest that this kind of complex has promising applications in deep-penetrating and high quality bioimaging in vivo.

Luminescence spectroscopy of europium(III) and terbium(III) penta-, octa- and nonanuclear clusters with β-diketonate ligands

A series of Eu(III) and Tb(III) clusters as well as their Y(III) analogues with increasing nuclearities of 5, 8 and 9 have been synthesised using beta-diketonate ligands with decreasing steric hindrance. Their molecular structures have been established from X-ray diffraction on single crystals for most clusters and studied by luminescence and Raman spectroscopy. The Raman spectra have distinctive patterns for each nuclearity in accordance with their crystal structure. The luminescence spectra of the Eu(III) and Tb(III) clusters also show distinctive features.

Synthesis and characterization of redox-active tris(pyrazolyl)borate cobalt complexes

The reaction of CoX2 (X = Cl, Br, NO3) with KTp(Ph2) in tetrahydrofuran (THF) yields the half-sandwich compounds [Tp(Ph2)CoX] (X = Cl 1, Br 2, NO3 3). The reaction of [Tp(Ph2)CoBr] with NaX (X = N3, NO2) or potassium thiocyanate (KNCS) permits isolation of [Tp(Ph2)CoX] (X = N3 4, NCS 5, NO2 6). In contrast, the reaction of cobalt(II) acetate with KTp(Ph2) yields [Tp(Ph2)CO(OAc)(Hpz(Ph2))] 7 as a result of B-N bond cleavage. Subsequent reaction of 7 with a range of beta-diketones in the presence of NaOMe produces the beta-diketonate complexes, [Tp(Ph2)Co(beta-diketonate)] (beta-diketonate = acac 8, hfac 9, dbm 10, tmhd 11). IR spectroscopy suggests that the Tp(Ph2) ligands are kappa3-coordinated and that the beta3-diketonate ligands adopt a bidentate coordination mode. Electronic spectra are consistent with four- or five-coordinate species in solution. X-Ray crystallographic studies of 7 reveal an intermediate five-coordinate cobalt centre with a hydrogen bonding interaction between the pyrazole hydrogen and the acetate carbonyl oxygen. The molecular structures of 9 and 10 show cobalt centres with square pyramidal coordination geometries and kappa2-coordinated beta-diketonate ligands. Cyclic voltammetric studies of 6 reveal irreversible one-electron reduction to Co(I). However, the beta-diketonate complexes, 8, 10 and 11 undergo irreversible one-electron oxidation. The redox potential and reversibility increases as the steric bulk of the substituent on the beta-diketonate ligand increases.