Diphenyllead(IV) thiosemicarbazonates and pyrazolonates: Synthesis and characterization

Cyclization of thiosemicarbazones derived from β-keto esters and β-keto amides (HTSC) in the presence of diphenyllead(IV) acetate was explored in methanol solution at room temperature and under reflux. All β-keto ester TSCs underwent cyclization to give the corresponding pyrazolone (HL), which, except in one case, deprotonated and coordinated the PbPh₂²⁺ moiety to form homoleptic [PbPh₂(L)₂] or heteroleptic [PbPh₂(OAc)(L)] derivatives. Cyclization did not occur with β-keto amide TSCs and only [PbPh₂(TSC)₂] or [PbPh₂(OAc)(TSC)] thiosemicarbazonates were isolated. The complexes were characterized by IR spectroscopy in the solid state and by ¹H, ¹³C and ²⁰⁷Pb NMR spectroscopy in DMSO–d₆ solution, in which they evolve and decompose with time. Additionally, crystals of p-acetoacetanisidide thiosemicarbazone (HTSC¹⁰), [PbPh₂(OAc)(L⁵)] · MeOH (HL⁵ = 2,5-dihydro-3,4-dimethyl-5-oxo-1H-pyrazolone-1-carbothioamide), [PbPh₂Cl(L²)] (HL² = 2,5-dihydro-5-oxo-3-phenyl-1H-pyrazolone-1-carbothioamide), [PbPh₂(OAc)(TSC⁸)] · 2MeOH (HTSC⁸ = acetoacetanilide thiosemicarbazone), [PbPh₂(OAc)(TSC¹⁰)] · H₂O and [PbPh₂(OAc)(TSC¹¹)] · 0.75MeOH (HTSC¹¹ = o-acetoacetotoluidide) were studied by X-ray crystallography. The complexes, monomers or dimers with almost linear C–Pb–C moieties, are compared with the corresponding derivatives of Pb(II).     

Be and P NMR analyses on Be complexation with cyclo-tri-μ-imidotriphosphate anions in aqueous solution

Microscopic information on the complexation of Be²⁺ with cyclo-tri-μ-imidotriphosphate anions in aqueous solution has been gained by both ⁹Be and ³¹P NMR techniques at −2.3 °C. Separate NMR signals corresponding to free and complexed species have been observed in both spectra. Based on an empirical additivity rule, i.e., proportionality observed between the ⁹Be NMR chemical shift values and the number of coordinating atoms of ligand molecules, the ⁹Be NMR spectra have been deconvoluted. By precise equilibrium analyses, the formation of [BeX(H₂O)₃]⁺ and [BeX₂(H₂O)₂]⁰ (X = non-bridging oxygen donor as a coordination atom in the phosphate groups) has been verified, and the formation of complexes coordinating with the nitrogen atoms of the cyclic framework in the ligand molecule has been excluded. Instead, the formation of one-to-one (ML) complexes, one-to-two (ML₂), together with two-to-one (M₂L) complexes (L = cP₃O₆(NH)₃) has been disclosed, the stability constants of which have been evaluated as log K_ML = 3.87 ± 0.03 (mol dm⁻³)⁻¹, log K_ML2 = 2.43 ± 0.03 (mol dm⁻³)⁻² and log K_M2L = 1.30 ± 0.02 (mol dm⁻³)⁻², respectively. ³¹P NMR spectra measured concurrently have verified the formation of the complexes estimated by the ⁹Be NMR measurement. Intrinsic ³¹P NMR chemical shift values of the phosphorus atoms belonging to ligand molecules complexed with Be²⁺, together with the ³¹P-³¹P spin-spin coupling constants have been determined.     

Synthesis, structural and spectral properties of novel octakis(3,5-bis-trifluoromethyl-benzylthio) substituted porphyrazine derivatives

[Octakis(3,5-bis-trifluoromethyl-benzylthio)porphyrazinato] magnesium carrying eight (3,5-bis-trifluoromethyl-benzylthio) groups on the peripheral positions have been synthesized by cyclotetramerization of 1,2-bis(3,5-bis-trifluoromethyl-benzylthio)maleonitrile in the presence of magnesium butanolate. Its demetalation by the treatment with trifluoroacetic acid resulted in the metal-free derivative. Further reaction of this product with copper(II) acetate, zinc(II) acetate and cobalt(II) acetate have led to the metallo derivatives M = Cu(II), Zn(II), Co(II). These novel complexes were characterized by elemental analysis, together with FT-IR, ¹H NMR, ¹³C NMR, ¹⁹F NMR, UV-vis and mass spectral data.     

New insights on the Lewis acidity of diorganolead(IV) compounds: Diphenyllead(IV) complexes with N,O,S-chelating ligands

The reactions of PbPh₂(OAc)₂ with alkylglyoxylate thiosemicarbazones (HRGTSC, R = Et, Bu) afforded complexes of the type [PbPh₂(GTSC)] · H₂O, [PbPh₂(RGTSC)₂] and [PbPh₂Cl(BuGTSC)]. The structures of HRGTSC (R = Me, Et, Bu), [PbPh₂(OAc)(RGTSC)](R = Me, Et, Bu), [PbPh₂Cl(BuGTSC)] and [PbPh₂(GTSC)] · H₂O have been studied by X-ray diffraction. [PbPh₂(OAc)(RGTSC)] and [PbPh₂(GTSC)] · H₂O have [PbC₂NO₃S] kernels and the coordination sphere of the metal is pentagonal bipyramidal. [PbPh₂Cl(BuGTSC)] has a [PbC₂NOSCl] kernel and the coordination geometry around lead is pentagonal bipyramidal with one vacant site. Analysis of the bond distances in [PbPh₂(GTSC)] · H₂O suggests a significant affinity between diphenyllead(IV) and carboxylate donor groups, supporting a borderline acidic character for this organometallic cation. ¹H and ¹³C NMR spectra in DMSO-d₆ suggest the partial dissociation of the acetate in [PbPh₂(OAc)(RGTSC)] solutions and indicate some differences in the coordination mode of the two RGTSC⁻ ligands in [PbPh₂(RGTSC)₂] complexes.     

Preparation of the novel fluorine-18-labeled VIP analog for PET imaging studies using two different synthesis methods

Vasoactive intestinal peptide (VIP) receptors are expressed on various tumor cells in much higher density than somatostatin receptors, which provides the basis for radiolabeling VIP as tumor diagnostic agent. However, fast proteolytic degradation of VIP in vivo limits its clinical application. With the aim to develop and evaluate new ligands for depicting the VIP receptors with positron emission tomography (PET), the structure modified [R^8,15,21, L¹⁷]-VIP analog was radiolabeled with ¹⁸F using two different methods. With the first method, N-4-[¹⁸F]fluorobenzoyl-[R^8,15,21, L¹⁷]-VIP ([¹⁸F]FB-[R^8,15,21, L¹⁷]-VIP 7) was produced in a decay-corrected radiochemical yield (RCY) of 33.6 ± 3%, a specific radioactivity of 255 GBq/μmol (n = 5) within 100 min in four steps. Similarly, N-4-[¹⁸F](fluoromethyl)-benzoyl-[R^8,15,21, L¹⁷]-VIP ([¹⁸F]FMB-[R^8,15,21, L¹⁷]-VIP 8) was synthesized in a RCY of 34.85 ± 5%, a specific radioactivity of 180 GBq/μmol (n = 5) within 60 min in only one step. The two products 7 and 8 were both shown good stability in HSA. Moreover, the low bone uptakes of 7 and 8 in vivo of mice showed good defluorination stability.     

Tin(IV) and organotin(IV) derivatives of bis(pyrazolyl)acetate: Synthesis, spectroscopic characterization and behaviour in solution.: X-ray single crystal study of bis(pyrazol-1-yl)acetatotri-iodotin(IV) [SnI3(bdmpza)]

Novel heteroscorpionate-containing tin and organotin(IV) complexes, [SnR_nX_3 − n(L)], R = Me, Buⁿ, Ph, or cy; X = Cl, Br or I, n = 0, 1, 2 or 3; L = bis(pyrazol-1-yl)acetate (bpza) or bis(3,5-dimethylpyrazol-1-yl)acetate (bdmpza), have been synthesized and characterized by spectral (IR, ¹H, ¹³C and ¹¹⁹Sn NMR, ^119mSn Mössbauer) and analytical data. In [SnI₃(bdmpza)], the ligand is fac-N,N′,O-tridentate, the three iodine atoms thus also fac about the six-coordinate tin(IV) atom. Neutral bpzaH reacts with BuⁿSnCl₃, PhSnCl₃ and SnCl₄ in Et₂O in the absence of base, yielding 1:1 adducts [XSnCl₃(bpzaH)] (X = R or Cl).     

A cyclic diphosphinite by a formal [4+4] cycloaddition reaction of β-phosphaenone

Unstable β-phosphaenones formed by reaction of the phosphanylidene-σ⁴-phosphorane DmpP = PMe₃ (Dmp = 2,6-dimesitylphenyl) with acenaphthenequinone dimerize in hexane by a formal [4+4] cycloaddition reaction to form a cyclic diphosphinite. X-ray crystallographic analysis and variable temperature ¹H NMR spectra of the cyclic diphosphinite are presented.     

Synthesis and characterization of new soluble fluorinated seco-porphyrazines

Magnesium porphyrazinate substituted with eight 3,5-bis(trifluoromethyl)phenyl groups on the peripheral positions has been synthesized by the cyclotetramerization of 3,4-[3,5-bis(trifluoromethyl)phenyl]pyrroline-2,5-diimine in the presence of magnesium butanolate. Acid-mediated demetallation of the magnesium porphyrazine resulted in peripheral oxidation of one pyrrole ring to reveal the seco-porphyrazine, octakis[3,5-bis(trifluoromethyl)phenyl]-2-seco-porphyrazine-2,3-dione. Further reaction of this product with copper (II) acetate, zinc (II) acetate and cobalt (II) acetate has led to the metallo-derivatives, {octakis[3,5-bis(trifluoromethyl)phenyl]-2-seco-2,3-dioxoporphyrazinato} M(II) [M = Cu(II), Zn(II), Co(II)]. These new soluble complexes were characterized by elemental analysis, together with FT-IR, ¹H NMR, ¹³C NMR, ¹⁹F NMR, UV-Vis and mass spectral data.     

Ranking the effect of [1A(ax), 1B(eq)] versus [1A(eq), 1B(ax)] cyclohexane ring substitution on the H chemical shifts of γ-methylene cyclohexane ring protons using 2,2-disubstituted adamantanes as models

When two different substituents are placed in the nonbridgehead position of adamantane, the two [1A(ax), 1B(eq)] and [1A(eq), 1B(ax)] cyclohexane chair conformers are modeled and features of their NMR spectra can be studied from a single spectrum at 298 K. The effect of [1A(ax), 1B(eq)] and [1A(eq), 1B(ax)] cyclohexane ring substitution on the ¹H resonance separation within the γ-CH₂s of cyclohexane ring is compared for various substituent pairs; this aim is approached by measuring the ¹H chemical shift separation within the 4′,9′-H and 8′,10′-H methylenes from the ¹H NMR spectrum of the model 2A,2B-disubstituted adamantane at 298 K.     

Cl/Cl isotope effects in Rh NMR of [RhCln(H2O)6−n] complex anions in hydrochloric acid solution as a unique ‘NMR finger-print’ for unambiguous speciation

A detailed analysis of the ³⁵Cl/³⁷Cl isotope effects observed in the 19.11 MHz ¹⁰³Rh NMR resonances of [RhCl_n(H₂O)_6−n]³⁻ⁿ complexes (n = 3–6) in acidic solution at 292.1 K, shows that the ‘fine structure’ of each ¹⁰³Rh resonance can be understood in terms of the unique isotopologue and in certain instances the isotopomer distribution in each complex. These ³⁵Cl/³⁷Cl isotope effects in the ¹⁰³Rh NMR resonance of the [Rh^35/37Cl₆]³⁻ species manifest only as a result of the statistically expected ³⁵Cl/³⁷Cl isotopologues, whereas for the aquated species such as for example [Rh^35/37Cl₅(H₂O)]²⁻, cis-[Rh^35/37Cl₄(H₂O)₂]⁻ as well as the mer-[Rh^35/37Cl₃(H₂O)₃] complexes, additional fine-structure due to the various possible isotopomers within each class of isotopologues, is visible. Of interest is the possibility of the direct identification of stereoisomers cis-[RhCl₄(H₂O)₂]⁻, trans-[RhCl₄(H₂O)₂]⁻, fac-[RhCl₃(H₂O)₃] and mer-[RhCl₃(H₂O)₃] based on the ¹⁰³Rh NMR line shape, other than on the basis of their very similar δ(¹⁰³Rh) chemical shift. The ¹⁰³Rh NMR resonance structure thus serves as a novel and unique ‘NMR-fingerprint’ leading to the unambiguous assignment of [RhCl_n(H₂O)_6−n]³⁻ⁿ complexes (n = 3–6), without reliance on accurate δ(¹⁰³Rh) chemical shifts.     

Synthesis,spectroscopic and structural studies of 2,2,2-trifluoroethyl phosphorodiamidate complexes with tin(IV) chloride

The two octahedral complexes SnCl₄ · 2(O)P(NR₂)₂OCH₂CF₃ (R = Me (1) or Et (2)) have been prepared from SnCl₄ and the ligands (R₂N)₂P(O)OCH₂CF₃ in chloroform solution. Both adducts have been characterised by (³¹P and ¹¹⁹Sn) NMR, IR spectroscopy and elemental analysis. The NMR data show that the complexes exist as mixtures of cis and trans isomers in solution with the latter isomer being the predominant species. The structure of 1 has been determined by X-ray crystallography. Accordingly, the structure is centrosymmetric and the two ligands are bound trans to each other in the octahedral tin complex. DFT/B3LYP calculations show that trans configuration does indeed lead to the lowest energy species. Comparison of the structural, NMR and theoretical data of both complexes with those related to SnCl₄ · 2L (L = (Me₂N)₃P(O) and (Me₂N)₂P(O)F) further supports the important effects of the nature of the substituents in the ligand on the stereochemistry of the complex formed.     

Synthesis,structural characterization and reactivity of copper(I)-nitrile complexes: Crystal and molecular structure of [Cu(BzCN)4][BF4]

Complexes of general formula [CuL₄][BF₄] (L = benzonitrile – PhCN 2 or phenylacetonitrile – BzCN 3) have been prepared and structurally characterized by NMR spectroscopy and X-ray crystallography. Their structure and reactivity have been compared to the well known [Cu(MeCN)₄][BF₄] (1). The ⁶³Cu line width and the ⁶³Cu chemical shift have been evaluated by varying the temperature and the concentration of the complex 2 in benzonitrile solutions. The phenylacetonitrile solutions of the complex 3 give extremely broad signals which are beyond detection. Accordingly, compound 3 has been studied by ⁶³Cu MAS NMR spectroscopy. The solution NMR data are consistent to the prevalence of dynamic equilibrium between tetra- and low-coordinated species in both complexes. The X-ray structure of 3 revealed that the copper(I) atom sits in a slightly distorted tetrahedral geometry, surrounded by four BzCN ligands.     

Oxidation of C-labeled ethyl linoleate monitored and quantitatively analyzed by C NMR

The oxidation of ¹³C-labeled ethyl linoleate (¹³C-EL), a model compound for alkyd resins, was investigated by ¹³C NMR in the presence of Co(II)-2-ethylhexanoate (Co-EH), Mn(acac)₃ (acac = acetylacetonate), and Mn(acac)₃ in combination with 2,2′-bipyridine (bpy), respectively. The use of ¹³C-EL allows us, in an unprecedented way, to reveal the individual evolution of hydroperoxides (ROOH) and peroxy (ROOR) links by ¹³C NMR and to quantify the oxidation intermediates during the oxidation. Mn(acac)₃ appeared to be less effective in decomposing ROOH than Co-EH and the Mn(acac)₃/bpy combination. Quantitative analyses were attempted for a few major ¹³C peaks.     

Cs4P2Se10: A new compound discovered with the application of solid-state and high temperature NMR

The new compound Cs₄P₂Se₁₀ was serendipitously produced in high purity during a high-temperature synthesis done in a nuclear magnetic resonance (NMR) spectrometer. ³¹P magic angle spinning (MAS) NMR of the products of the synthesis revealed that the dominant phosphorus-containing product had a chemical shift of −52.8 ppm that could not be assigned to any known compound. Deep reddish brown well-formed plate-like crystals were isolated from the NMR reaction ampoule and the structure was solved with X-ray diffraction. Cs₄P₂Se₁₀ has the triclinic space group P-1 with a=7.3587(11) Å, b=7.4546(11) Å, c=10.1420(15) Å, α=85.938(2)°, β=88.055(2)°, and γ=85.609(2)° and contains the [P₂Se₁₀]⁴⁻ anion. To our knowledge, this is the first compound containing this anion that is composed of two tetrahedral (PSe₄) units connected by a diselenide linkage. It was also possible to form a glass by quenching the melt in ice water, and Cs₄P₂Se₁₀ was recovered upon annealing. The static ³¹P NMR spectrum at 350 °C contained a single peak with a −35 ppm chemical shift and a ∼7 ppm peak width. This study highlights the potential of solid-state and high-temperature NMR for aiding discovery of new compounds and for probing the species that exist at high temperature.     

On the detection of both carbonyl and hydroxyl oxygens in amino acid derivatives: a O NMR reinvestigation

The hypothesis and the conclusions of previous ¹⁷O NMR studies on the detection of both oxygens of the carboxylic group of Boc-[¹⁷O]Tyr(2,6-diClBzl)-OH in DMSO-d₆ solution (Tetrahedron Lett.2000, 41, 8651) are reconsidered. The appearance of two discrete resonances at 340 and 175 ppm of this protected amino acid is not now attributed: (a) to the reduction of the intramolecular conformational exchange rate, due to the effect of intramolecular hydrogen bonding of the hydroxy part of the carboxyl with the carbonyl oxygen of the Boc-group, and (b) to the effect of solvent viscosity, suggested in the mentioned study. The cause of this phenomenon is now attributed to a strong hydrogen bonding of the polar proton acceptor solvent DMSO with the carboxy group, which effectively reduces the proton exchange rate, thus becoming slow on the ¹⁷O NMR time scale.     

Structural investigations on diorgano- and triorganotin(IV) derivatives of [meso-tetra(4-sulfonatophenyl)porphine] metal chlorides

Several new complexes of organotin(IV) moieties with MCl_n[meso-tetra(4-sulfonatophenyl)porphine], (R₂Sn)₂MCl_n[meso-tetra(4-sulfonatophenyl)-porphinate]s and (R₃Sn)₄MCl_n [meso-tetra(4-sulfonatophenyl)porphinate]s, [M = Fe(III), Mn(III): n = 1, R = Me, n-Bu; Ph; M = Sn(IV): n = 2, R = Me, n-Bu] have been synthesized and their solid state configuration investigated by infrared (IR) and Mössbauer spectroscopy, and by ¹H and ¹³C NMR in D₂O.The electron density on the metal ion coordinated inside the porphyrin ring is not influenced by the organotin(IV) moieties bonded to the oxygen atoms of the side chain sulfonatophenyl groups, as it has been inferred on the basis of Mössbauer spectroscopy and, in particular, from the invariance of the isomer shift of the Fe(III) and Sn(IV) atoms coordinated into the porphyrin square plane of the newly synthesized complexes, with respect to the same atoms in the free ligand.As far as the coordination polyhedra around the peripheral tin atoms are concerned, infrared spectra and experimental Mössbauer data would suggest octahedral and trigonal bipyramidal environments around tin, in polymeric configurations obtained, respectively, in the diorganotin derivatives through chelating or bridging sulfonate groups coordinating in the square plane, and in triorganotin(IV) complexes through bridging sulfonate oxygen atoms in axial positions.The structures of the (Me₃Sn)₄Sn(IV)Cl₂[meso-tetra(4-sulfonatophenyl)porphinate] and of the two model systems, Me₃Sn(PS)(HPS) and Me₂Sn(PS)₂ [HPS = phenylsulfonic acid], have been studied by a two layer ONIOM method, using the hybrid DFT B3LYP functional for the higher layer, including the significant tin environment. This approach allowed us to support the structural hypotheses inferred by the IR and Mössbauer spectroscopy analysis and to obtain detailed geometrical information of the tin environment in the compounds investigated.¹H and ¹³C NMR data suggested retention of the geometry around the tin(IV) atom in D₂O solution.     

Comparability of composition of carbon functional groups in humic acids between inverse-gated decoupling and cross polarization/magic angle spinning 13C nuclear magnetic resonance techniques

To find a certain relation between the composition of carbon functional groups of humic acids derived from liquid state ¹³C nuclear magnetic resonance (NMR) spectra acquired with inverse-gated decoupling (IGD), known as a quantitative pulse sequence, and that by solid-state ¹³C NMR with cross polarization/magic angle spinning (CPMAS) techniques, fifteen soil humic acid samples with a wide range of aromaticity were analyzed. Relationships between the proportions of humic acid carbon as alkyl, O-alkyl, and aromatic carbon assessed by the two methods could be regressed to y = ax (r = 0.932-0.956; P < 0.005), respectively. The contents of alkyl, O-alkyl, and aromatic carbon assessed by CPMAS method were larger than those found by IGD method. However, the differences between the two methods were small and exclusive regression to y = x was also significant (r = 0.775-0.941; P < 0.005). Aromaticity calculated from ¹³C CPMAS NMR data also did not differ significantly from those computed from ¹³C NMR spectra with IGD. These observations indicated the comparability of the relative content of carbon functional groups in humic acids except for carboxyl and carbonyl carbon.     

A multinuclear NMR study in the solid state and in solution of thallium(I) tris-(pyrazol-1-yl)borates (thallium scorpionates)

The ¹H, ¹³C and ¹⁵N NMR spectroscopic properties of six thallium tris-(pyrazol-1-yl)borates, including a tetrakis derivative, were determined. The results in solution were necessary to understand those, more complicated, in the solid state. A collection of ²⁰⁵Tl-¹⁵N and ²⁰⁵Tl-¹³C couplings was measured in the latter state. Among those, a very large coupling constant (between 194 and 282 Hz) has been measured on the carbon at the position 4 of the pyrazole ring in several compounds and particularly for the cyclobutyl derivative [Tl(Tp^Cbu)]. It has been assigned to a direct interaction of the 4-C-H ? Tl type and related to the X-ray structures, when available.     

(27)Al NMR and Raman spectroscopic studies of alkaline aluminate solutions with extremely high caustic content - Does the octahedral species Al(OH)(6)(3-) exist in solution?

²⁷Al NMR and Raman spectra of alkaline aluminate solutions with 0.005 M ≤ [Al(III)]_T ≤ 3 M in various M′OH solutions (M′⁺ = Na⁺, K⁺ and Li⁺) were recorded and analysed. Caustic concentrations up to 20 M were used to explore whether higher aluminium hydroxo complexes are formed at extremely high concentrations of hydroxide. A single peak was observed on the ²⁷Al NMR spectrum of each solution. The chemical shift of this peak shifts significantly upfield with increasing [M′OH]_T in solutions with [Al(III)]_T < 0.8 M. This variation shows a strong dependence on the cation of the solution and practically disappears in systems with [Al(III)]_T ≥ 0.8 M. For Raman spectra of solutions with [Al(III)]_T = 0.8 M and [NaOH]_T ≥ 10 M, the peak maximum of the symmetric ν₁-AlO₄ stretching of Al(OH)₄⁻ shifted progressively from ∼620 to ∼625 cm⁻¹ and decreased in intensity with increasing [NaOH]_T. In parallel, modes centred at ∼720 and ∼555 cm⁻¹ (cf. ∼705 and ∼535 cm⁻¹ at lower [NaOH]_T, ascribed to a dimeric aluminate species appeared, and their intensities increased with increasing [NaOH]_T. These variations in the ²⁷Al NMR and Raman spectra can be interpreted in terms of contact ion-pairs formed between the cation of the medium and the well-established Al(OH)₄⁻ or the dimeric aluminate species. Assumption of higher aluminium hydroxo complex species (e.g., Al(OH)₆³⁻) is not necessary to explain the spectroscopic effects observed.     

Reactions of the metallocene dichlorides [M(Cp)2Cl2] (M = Zr, Hf) and [Ti(MeCp)2Cl2] with the pyridine-2,6-dicarboxylate(−2) ligand: Synthesis, spectroscopic characterization and X-ray structures of the products

The reactivity pattern of the 16-electron species [M(Cp)₂Cl₂] (M = Zr, Hf; Cp⁻ = η⁵-C₅H₅⁻) and [Ti(MeCp)₂Cl₂] (MeCp⁻ = η⁵-C₅H₄CH₃⁻) towards the dipicolinate(−2) (dipic²⁻) ligand under mild (ambient temperature) and convenient (aerobic reactions, aqueous media) conditions have been investigated. The syntheses, molecular structures and spectroscopic (IR, ¹H NMR) characterization are reported for the 18-electron products [Zr(Cp)₂(dipic)] (1), [Hf(Cp)₂(dipic)] (2) and [Ti(MeCp)₂(dipic)] (3). The dipic²⁻ ion behaves as N,O,O′-chelating ligand in the three complexes, while the centroids of the Cp⁻ (1, 2) and MeCp⁻ (3) rings formally occupy the fourth and fifth coordination sites about the central metal. The two identical/very similar bite angles of only ∼70° make the dipic²⁻ ligand particularly suited to form stable metallocene derivatives with 5-coordinate geometry. IR and ¹H NMR data are discussed in terms of the known structures and the tridentate chelating mode of the dipic²⁻ ligand.