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Macrocyclization is a popular method for preparing hosts, but it can have unintended effects, like limiting molecular free rotation to yield mixtures of inseparable isomers. We report a [3 + 3] Schiff-base macrocycle (1) with anthracene bridges. Restricted rotation about the phenyl–anthracene bonds leads 1to exist as a mixture of conformations (1Csand 1C3v). Macrocycle 1was photooxidized to tris(endoperoxide) adduct 4, alleviating restricted rotation. These results were supported by spectroscopic, structural, and computational analyses.

The synthesis and the electrochemical, photophysical, structural, and photoconductive properties of three new heteroleptic Pd(II) complexes with various 3′,5′- disubstituted-2-(2′-pyridil) pyrroles H(N^N) as coordinated ligands are reported. The coordination of the metal center was completed by a functionalized Schiff base H(O^N) used as an ancillary ligand. The [(N^N)Pd(O^N)] complexes showed highly interesting photoconductive properties which have been correlated to their electronic and molecular structures. Theoretical density functional theory (DFT) and time-dependent DFT calculations were performed, and the results were confronted with the organization in crystalline phase, allowing to point out that the photoconductive properties are mainly a consequence of an efficient intramolecular ligand-to-metal charge transfer, combined to the proximity between the central metal and the donor moieties in the solid-state molecular stacks. The reported results confirm that these new Pd(II) complexes form a novel class of organometallic photoconductors with intrinsic characteristics suitable for molecular semiconductors applications.

Novel silver(I) acylpyrazolonato coordination polymers of formula [Ag(QR)]n(1–3) have been synthesized by interaction of silver nitrate with HQRin methanol in the presence of an equivalent quantity of KOH (in general HQR= 1-phenyl-3-methyl-4-RC(O)-5-pyrazolone, in detail HQfb, R = -CF2CF2CF3; HQcy, R = -cyclo-C6H11; HQbe, R = -C(H)C(CH3)2). [Ag(QR)]nreact with 2-ethylimidazole (2EtimH), 1-methylimidazole (Meim), and triphenylphosphine (PPh3), affording the mononuclear Ag(Qfb)(EtimH) (4), Ag(Qcy)(Meim)2(5), Ag(Qbe)(Meim) (6), and Ag(QR)(PPh3)2(7–9). All complexes have been analytically and spectroscopically characterized, and for some of them the X-ray crystal structure has been resolved. In particular, the single crystal molecular structure determination of Ag(Qfb)(EtimH) and Ag(Qbe)(PPh3)2has confirmed the different coordination modes of the HQfband HQbeacylpyrazolone ligands, the former being bound to the silver(I) ion in a monodentate fashion while the latter in the O2-chelating mode. Density functional theory computations suggest new insights about metal–ligand interactions and the observed linkage isomerism. While phosphine-containing complexes Ag(QR)(PPh3)2(7–9) seem not to be able to efficiently inhibit the growth of Escherichia coliand Staphylococcus aureus, the polynuclear complexes [Ag(QR)]n(1–3) and the mononuclear Ag(Qfb)(EtimH) (4), Ag(Qcy)(Meim)2(5), and Ag(Qbe)(Meim) (6) show a high and almost steady in time antibacterial activity, comparable to that of AgNO3. This activity is likely related to the degree of saturation of the silver center and to the presence of different ancillary ligands in the diverse typologies of complexes.

The photochemical reaction between ethyl 2chlorothiazole5carboxylate and benzene gave no product. In contrast, the reaction with ethyl 2iodothiazole5carboxylate gave ethyl 3phenylisothiazole4carboxylate. The same behaviour was observed if the reaction was performed in the presence of furan, thiophene and 2bromothiophene. The products thus obtained were studied for their photophysical properties and it was found that the observed absorptions [λmax=257 nm = 7000 M–1 cm–1 for ethyl 3phenylisothiazole4carboxylate, 278 nm = 7000 M–1 cm–1 for ethyl 32furylisothiazole4carboxylate, 269 and 285 nm = 7500 M–1 cm–1 for ethyl 32thienylisothiazole4carboxylate] are mainly due to π → π transitions from the HOMO to the LUMO+1 orbital. The tested compounds showed fluorescence [λem= 350–400 λexc= 300 nm, 360 and 410 nm λexc= 320 nm, 412 nm λexc= 340 nm for ethyl 3phenylisothiazole4carboxylate, 397 and 460 nm λexc= 300 nm, 381, 394 and 460 nm λexc= 320 nm, 381, 398 and 466 nm λexc= 340 nm for ethyl 32furylisothiazole4carboxylate, 372, 377 and 414 nm λexc= 300, 320 and 340 nm respectively for ethyl 32thienylisothiazole4carboxylate], possibly due to dual emission from different excited states. The use of the compound obtained as a sensitizer in the photooxidation of transα,α′dimethylstilbene showed that all the new compounds are singletoxygen sensitizers.

A systematic study of a class of divalent transition-metal texaphyrin complexes (M-Tex, M Mn, Fe, Co, Ni, Cu, Zn), recently proposed as active photosensitizers in photodynamic therapy (PDT), was undertaken for the ground and excited electronic states. Geometry optimizations were performed by using the PBE0 exchange-correlation functional coupled with the 6-31G(d) basis set, while electronic excitations energies were evaluated by means of time-dependent density functional response theory (TD-DFT) at the PBE0/6-31G(d) // PBE0/6-31G(d) level of theory. Solvent effects on excitation energies were taken into account in two ways:  by considering solvent molecules explicitly coordinated to the metal center and as bulk effects, within the conductor-like polarizable continuum model (C-PCM). The influence of the metal cation on the so-called Q-band, localized in the near-red visible region of the spectrum, was carefully examined since it plays a basic role in the drug design of new photodynamic therapy photosensitizers. The differences between experimental and computed excitation energies were found to be within 0.3 eV.

The electronic structure of five complexes M(oXHpz) M Ni2; oXHpz2-2,3,7,8,12,13,17,18-octakis-substituted (X CH2, NH, O, S, Se)-5,10,15,20-tetraazaporphyrinate dianion has been investigated using a density functional approach. All the geometries have been obtained minimizing the total intramolecular energy using a nonlocal hybrid functional (B3LYP) at the 6-31g level. The electronic configuration of Ni2is (dx2-y2)0(dxy)2(dxz,dyz)4(dz2)2. Optimized geometries exhibit a planar conformation and are all above the threshold for ruffling, which is described by a Ni−Npbond distance of 1.85−1.87 Å for sterically unhindered porphyrazines. Indeed, the smallest bond distance is 1.880 Å for Ni(oOHpz). Peripheral substituents yield modifications to the “core” of the macrocycle and to the energy levels, changing and interactions. Furthermore, within a time-dependent density functional theory approach, excited states of Ni(oXHpz) X CH2, NH, O, S, Se, complexes have been studied and compared with available experimental UV−vis spectra.

The reactions between L=E donors [L: 1,3-dimethylimidazolyl framework; E: S (1), Se (2)] and halogens X2 (X: Cl, Br, I) to form either “T-shaped” hypervalent chalcogen (TY) or linear charge-transfer-type adducts (CT) have been studied in the density functional theory (DFT) context by considering both thermodynamic and kinetic aspects. Apart from the case of the adducts between sulfur donors and diiodine, hypervalent compounds are calculated to be always more stable than CT ones in the gas phase, in agreement with the experimental results based on spectroscopic and structural determinations. NBO and FMO analyses suggest explanations for this. Reaction mechanism studies reveal that CT adducts are always the first products of the reactions and no transition states connecting the reactants directly to TY adducts have been found. The present calculations indicate that, at least for 1 and 2, TY adducts are obtained from CT adducts and not directly from the reactants.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

This paper reports the synthesis, characterization, photophysical and structural properties of the homologous series of good emitting pentacoordinated GaQ′2L complexes 1–3, where Q′ is 2-methyl-quinolin-8-olate and L is a phenolate substituted in paraposition with respect to the oxygen donor atom. A combined approach between the experimental structural analysis (i.e.the molecular fragments involved in intermolecular π–π interactions) and the computational study (i.e.the nature of the molecular orbitals residing therein) is discussed in order to compare the charge transport aptitude of complexes 1–3, in relation to the facing of their LUMO/LUMO, HOMO/HOMO and HOMO/LUMO arising from the molecular packing. The different phenolate ligands significantly change the packing characteristics of 1–3, with indirect effects on the electron hopping kinetics responsible for conduction in amorphous thin films. The observed preference for pyridyl–pyridyl stacking proves a faster electron conduction in comparison to hole conduction in the three complexes studied.

This paper reports the synthesis, characterisation and photophysical investigation of the homologous series of blue-emitting pentacoordinated AlQ′2L complexes 1–6, where Q′ is 2-methylquinolin-8-olate and L is a phenolate substituted in para to the oxygen donor atom. Both electron attracting and electron releasing substituents have been considered. Also binuclear complexes of formula Q′2Al–L′–AlQ′2, where L′ = OC6H4C6H4O, OC6H4(CH2)3C6H4O and OC6H4C(CH3)2C6H4C(CH3)2C6H4O have been synthesised and characterised. These are interesting blue-emitting materials for OLED (organic light emitting diode) fabrication. A comparison between computational and experimental results allowed the description of the absorption and fluorescence processes. A study of the frontier orbitals involved in the electric conduction and fluorescence emission has been performed. Influences of the phenolate-based ligands on the compounds spectroscopy have been particularly taken into account.

The σ-type charge-transfer (CT) interaction between [M(R,R′timdt)2] donors (M = Ni, Pd, Pt; R,R′timdt = formally monoreduced disubstituted imidazolidine-2,4,5-trithione) and diiodine has been thoroughly investigated by a large set of theoretical calculations at different levels of theory (HF, pure and hybrid-DFT with different functionals and basis sets) on I2 (and for the sake of comparison on IBr and Br2), on the model donor dithiolene complexes [M(H2timdt)2], and on the adducts [M(H2timdt)2]·I2 (M = Ni, Pd, Pt). The computations have accounted for the ability of adducts to assume different stoichiometries and to make up polymeric networks based on sulfur−iodine contacts, as in the case of [Ni(Me,iPr-timdt)2]·I2, which was also characterised by single-crystal X-ray diffraction. In addition, the strength of the donor−acceptor interaction has been evaluated through the calculated vibrational features of the model adducts, compared with the experimental FT-Raman spectra recorded on the adducts between [M(Et2timdt)2] and [M(Me,iPr-timdt)2] (M = Ni, Pd, Pt) and diiodine. The frontier-orbital composition, the NBO-charge distribution and bond orders indicate a medium-weak donor ability for the dithiolene donors, which depends only slightly on the nature of the central metal ion, and decreases on passing from M = Ni to M = Pd and Pt, in agreement with the values of the experimental frequencies of the FT-Raman-active I−I stretching vibrations in the adducts [M(Et2timdt)2]·2I2 (M = Ni, Pd, Pt). The ZPE- and CP BSSE-corrected binding energy for [Ni(H2timdt)2]·I2 has been evaluated as −11 kcal/mol. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The reaction between 1,3-dimethyl-4-imidazoline-2-selone (2) and ICN gave the adduct 2·ICN, whose crystal structure features dimers made up of two [2·CN]⁺ and two I⁻ which strongly interact. Hybrid DFT calculations on the adduct 2·ICN, on the cation [2·CN]⁺, and on the dimer (2·ICN)2 account for a partially hypervalent selenium atom in 2·ICN and for the observed structural features. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

A new series of 5-4′-substitutedphenylazo-8-hydroxyquinolines HL–R; R = NCH32, I, C2H5, II, n-C4H9, III, CCH33, IV, H, Vand F, VI has been prepared and the corresponding ZnL–R21a–6a and AlL–R31b–6b complexes successfully synthesized. These compounds have been studied in order to design new molecular materials with enhanced electron transport properties. The obtained species have been extensively characterized by absorption and emission spectra and by cyclic voltammetric measurements. Experimental and computational results show that the ZnL–NCH32·2H2O 1a and AlL–NCH321b complexes only feature luminescence (at 620 and 600 nm), respectively. The unique effects, which are induced by the NN–C6H4–NCH32group, are further proved by a reversible electron transfer process detected by cyclic voltammetry. These outcomes, discussed on the basis of theoretical calculations performed on the HL–NCH32−, HL–NCH32 and HL–NCH32species, suggest that metal complexes formed by 5-4′-N,N-dimethylaminophenylazo-8-hydroxyquinoline should be considered as electron transport materials suitable for applications in photonic devices.

Treatment of octakisoctylthioporphyrazine H2OOSPz with cis-bisbenzonitriledichloroplatinumii in a 1,2,4-trichlorobenzene (TCB)–n-BuOH mixture at 190 °C affords the asymmetric porphyrazine 2H-heptakisoctylthioporphyrazine, H2HOSPz, in ca. 40 yield. In the key synthetic step the two-electron reduced diprotonated porphyrazine, H2OOPz4−H2 hemiporphyrazinogen, forms in nearly quantitative yield. This species undergoes nucleophilic substitution of an octylsulfide group by H−, affording the asymmetric porphyrazine, this process being favoured by the high-temperature induced charge and structural intramolecular rearrangements. The resulting molecule shows mesomorphic behaviour. Interestingly, in the presence of sodium acetate, or in neat TCB, the asymmetric porphyrazine does not form at all. Under these conditions, a PtCl2molecular fragment coordinates both to a porphyrazine aza bridge and to a thioether moiety leading to the formation of the H2OOSPzPtCl2complex. The S,N-coordination of the PtCl2unit was proved by 1H, 195Pt1H, and 13C NMR spectroscopy, and supported by DFT B3LYP calculations. The complex conjugates high asymmetry with strong solvatochromism and, therefore, it is potentially interesting for nonlinear optics.

Treatment of octakis(octylthio)porphyrazine (H₂OOSPz) with cis-bis(benzonitrile)dichloroplatinum(ii) in a 1,2,4-trichlorobenzene (TCB)–n-BuOH mixture at 190 °C affords the asymmetric porphyrazine 2H-heptakis(octylthio)porphyrazine, H₂HOSPz, in ca. 40% yield. In the key synthetic step the two-electron reduced diprotonated porphyrazine, [H₂OOPz(4−)(H+)₂] (hemiporphyrazinogen), forms in nearly quantitative yield. This species undergoes nucleophilic substitution of an octylsulfide group by H−, affording the asymmetric porphyrazine, this process being favoured by the high-temperature induced charge and structural intramolecular rearrangements. The resulting molecule shows mesomorphic behaviour. Interestingly, in the presence of sodium acetate, or in neat TCB, the asymmetric porphyrazine does not form at all. Under these conditions, a PtCl₂ molecular fragment coordinates both to a porphyrazine aza bridge and to a thioether moiety leading to the formation of the [H₂OOSPz]PtCl₂ complex. The S,N-coordination of the PtCl₂ unit was proved by 1H, 195Pt{1H}, and 13C NMR spectroscopy, and supported by DFT (B3LYP) calculations. The complex conjugates high asymmetry with strong solvatochromism and, therefore, it is potentially interesting for nonlinear optics.

With the aim of preparing new dyes for Q-switching and/or mode-locking Nd-based lasers, such as Nd:YLF and Nd:YAG (emission wavelengths 1053 and 1064 nm, respectively), the syntheses of about 30 new neutral dithiolenemetal complexes belonging to the class [M(R,R'timdt)2] have been carried out [M = Ni (4a−c; 4g−j), Pd (5a−j), Pt (6a−j); R,R'timdt = monoreduced form of disubstituted imidazolidine-2,4,5-trithione]. The examination of the effects induced on the intense NIR absorption by changing M, R, and R' has allowed for the recognition of the additive contributions (Δλ) of the central metal ion and of the substituents to the λ^M,R,R'max position of the NIR absorption maximum, which is in the region of 1000 nm. The high Δλ values due to aromatic substituents have been elucidated by means of Hybrid-DFT calculations performed on the model compound [Ni(H2timdt)(Ph,H-timdt)]. Both the λ^M,R,R'max values and the molar extinction coefficients vary with the solvent. Complex 5f [M = Pd, R = p-F-C6H4, R' = m,m,p-(MeO)3-C6H2] shows that it has been possible to exactly match the emission wavelength of the Nd:YLF and Nd:YAG lasers in chloroform and toluene, respectively (by choosing the appropriate combination of metal ion and substituents). The highest extinction coefficient ever observed for a metal-dithiolene (120000 M⁻¹·cm⁻¹ at 1034 nm in toluene) is also reported for complex 6g [M = Pt, R = p-F-C6H4, R' = naphthyl]. Time-resolved absorption dynamics measurements on 5f have also been carried out by means of pump-probe experiments, with a picosecond Nd:YAG Q-switched and mode-locked laser. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The synthesis and spectroscopic characterisation of the products obtained by treatment of N,N′‐dimethylimidazolidine‐2‐thione (1), N,N′‐dimethylimidazolidine‐2‐selone (2), N,N′‐dimethylbenzoimidazole‐2‐thione (3) and N,N′‐dimethylbenzoimidazole‐2‐selone (4) with Br2in MeCN are reported, together with the crystal structures of the 10‐E‐3, T‐shaped adducts 2⋅Br2(12), 3⋅Br2(13) and 4⋅Br2(14). A conductometric and spectrophotometric investigation into the reaction between 1–4and Br2, carried out in MeCN, allows the equilibria involved in the formation of the isolated 10‐E‐3 (E=S, Se) hypervalent compounds to be hypothesised. In order to understand the reasons why S and Se donors can give different product types on treatment with Br2and I2, DFT calculations have been carried out on 1–8, 19and 20, and on their corresponding hypothetical [LEX]+cations (L=organic framework; E=S, Se; X=Br, I), which are considered to be key intermediates in the formation of the different products. The results obtained in terms of NBO charge distribution on [LEX]+species explain the different behaviour of 1–8, 19and 20in their reactions with Br2and I2fairly well. X‐ray diffraction studies show 12–14to have a T‐shaped (10‐E‐3; E=S, Se) hypervalent chalcogen nature. They contain an almost linear Br‐E‐Br (E=S, Se) system roughly perpendicular to the average plane of the organic molecules. In 12, the Se atom of each adduct molecule has a short interaction with the Br(1) atom of an adjacent unit, such that the Se atom displays a roughly square planar coordination. The Se−Br distances are asymmetric [2.529(1) vs. 2.608(1) Å], the shorter distance being that with the Br(1) atom involved in the short intermolecular contact. In contrast, in the molecular adducts 13and 14, which lie on a two‐fold crystallographic axis, the Br‐E‐Br system is symmetric and no short intermolecular interactions involving chalcogen and bromine atoms are observed. The adducts are arranged in parallel planes; this gives rise to a graphite‐like stacking. The new crystalline modification of 10, obtained from acetonitrile solution, confirms the importance of short intermolecular contacts in determining the asymmetry of Br‐E‐Br (E=S, Se) and I‐Se‐I groups in hypervalent 10‐E‐3 compounds. The analogies in the conductometric and spectrophotometric titrations of 1and 2–4with Br2, together with the similarity of the vibrational spectra of 11–14, also imply a T‐shaped nature for 11. The vibrational properties of the Br‐E‐Br (E=S, Se) systems resemble those of the Br3−and IBr2−anions: the Raman spectrum of a symmetric Br‐E‐Br group shows only one peak near 160 cm−1, as found for symmetric Br3−and IBr2−anions, while asymmetric Br‐E‐Br groups also show an antisymmetric Br‐E‐Br mode at around 190 cm−1, as observed for asymmetric Br3−and IBr2−ions. Therefore, simple IR and Raman measurements provide a useful tool for distinguishing between symmetric and asymmetric Br‐E‐Br groups, and hence allow predictions about the crystal packing of these hypervalent chalcogen compounds to be made when crystals of good quality are not available.

Treatment of 2,3,7,8,12,13,17,18-octakis(ethylsulfanyl)-5,10,15,20-porphyrazine (H₂OESPz) with CrCl₂ in a 1,2,4-trichlorobenzene–n-BuOH mixture resulted in one ethylsulfanyl branch at the pyrrolic β positions of the macrocycle being replaced by an hydrogen atom with >40% yield. The structure of the asymmetric pyrrolic subunit and of the nearest pyrrolic subunits have been determined by NMR spectroscopy. The reaction path leading to the asymmetric porphyrazine implies the formation of a two-electron reduced diprotonated porphyrazine, [H₂OESPz(−4)(2H⁺)], that, as a consequence of charge and structural intramolecular rearrangements at high temperature, undergoes nucleophilic substitution of an ethyl sulfide group by H⁻. UV-Vis and near-IR results suggest that the asymmetric substitution modifies the (sulfanyl)porphyrazine π and n_Sulfur levels. On the contrary, ESR spectroscopy shows that the electronic properties of the coordinated Cu²⁺ ion are affected only marginally. The half-waves of the ligand first reductive processes sensibly shift towards cathodic potentials in the asymmetric metal porphyrazines, but not in the asymmetric free-base porphyrazine, probably due to conflicting electronic and structural effects induced by removal of an ethylsulfanyl tail.

The syntheses of the first examples of selenoparabanic acid derivatives (dialkylimidazolidine-2-selone-4,5-dione, 3eRR = Me, Et, Bu) are presented along with the X-ray crystal structure determination of 3eEt. To gain an insight in the properties of parabanic acid derivatives on the basis of their electronic structures, we report the results of comparative hybrid-DFT calculations performed on parabanic, thioparabanic, and selenoparabanic acids (3aH, 3bH, and 3eH) and on their N,N' -dimethyl derivatives (3aMe, 3bMe, and 3eMe). Calculations show that the different nature of the frontier orbitals of 3aRcompared to those of 3bRand 3eR, might account for the different reactivities of these compounds. Moreover, the weak donor character of 3bRand 3eRtowards molecular di-iodine, estimated by FT-Raman measurements is in agreement with the calculated NBO-charge distribution.Key words: selenation, selenoparabanic derivatives, crystal structure, DFT calculations.

The self-organizing capability of a family of newly synthesized ‘free-base’, H₂(OASPz), and metal porphyrazines, M(OASPz) (OASPz²⁻ = 2,3,7,8,12,13,17,18-octakis(alkenylthio)-5,10,15,20-tetraazaporphyrinato dianion, n = 4, 5, 6, 8; M = Co, Ni, Cu), into columnar, discotic liquid crystals, has been investigated by differential scanning calorimetry (DSC), optical microscopy and X-ray diffraction. It is found that of the metal-free porphyrazines only those with n = 4 or 5 show, as indicated by X-ray and optical microscopy studies, characteristic stable and discotic nematic mesophases. All the metallated porphyrazines show a discotic liquid crystalline behavior and those with the largest values of n present, consistent with the X-ray results, hexagonal columnar packing. Comparing the mesomorphic behavior of these compounds with those of the parent compounds peripherally substituted with saturated alkyl(sulfanyl)-chains it is seen that the effect of the increased stiffness at the periphery of the chains, induced in the title tetrapyrroles by the terminal double bonds, results in a decrease of the clearing temperature, T_i, and also of the mesophase temperature stability range, ΔT. This effect is larger in H₂ and Ni than in Cu and especially in Co porphyrazines, where the axial coordinating capability of the Co seems to counterbalance the effect of this perturbation.

Spread monolayers and Langmuir–Blodgett films were prepared with 2,3-bis(N-(3-thiopropyl)phthalimido)-7,8,12,13,17,18-hexakis(octylthio)-5,10,15,20-tetraazaporphyrinate palladium(II) (PdR6R2′TAP). Although monolayers at the water/air interface tend to aggregate, transfer as multilayer films onto quartz slides was possible when the proper experimental conditions were chosen. The properties of the Langmuir–Blodgett films were investigated by UV-Vis and FTIR spectroscopy. Their structures were markedly influenced by transfer temperature. When the monolayer was transferred at T=309 K, the corresponding LB film showed a different packing structure with respect to the films transferred at lower temperatures. This resulted in a better homogeneity, as revealed by optical microscopy. The monolayer thickness and the refractive index were respectively determined by means of ellipsometry and with the aid of dark m-lines spectroscopy for LB films transferred at T=309 K.

The synthesis, spectroscopic and electrochemical properties of the Lu(oepz)2(oepz ≡ 2,3,7,8,12,13,17,18-octakis(ethyl)-5,10,15,20-porphyrazinato) complex are reported. The complex, as inferred from UV-vis spectra recorded at different concentrations, strongly aggregates in solution, the most likely association mode being dimerization. The complex shows a weak near-IR absorption (λmax= 834 nm) that is considerably blue-shifted compared with the near-IR absorption of bis(π-radical) lutetium analogues. The Lu(oepz)2neutral species is electrochemically stable between 0.73 and -0.98 V (vsAg/AgCl), which is the largest range of stability for neutral lutetium di- tetrapyrrole complexes. Lu(oepz)2shows excellent Type IIphotodynamic activity, as indicated by the value of the singlet oxygen generation quantum yield φΔof 0.94 obtained by comparison with meso-tetraphenylporphyrin.

Summary. We have analyzed equilibrium solvent effects on some isomerization reactions, chosen as the most representative of this wide class of reaction in organic and inorganic chemistry. Solvent effects were modeled by the self-consistent reaction field approach, in the framework of the density functional computational scheme, as implemented in the ADF package. We have investigated as “organic reactions” the formamide/formamidic acid and 2-pyridone/2-hydroxypyridine tautomerization reactions, whereas the linkage isomerization of pentaamminenitro cobalt(II) to pentaamminenitrito cobalt(II) was chosen as representative of inorganic isomeric equilibria. The three examples point out three different limiting behaviors deriving from the interplay of electrostatic and polarization contributions to the total energy.

Reaction of the oespz²⁻ ligand (oespz = 2,3,7,8,12,13,17,18-octakis (ethylsulfanyl)-5,10,15,20-porphyrazinato) with trivalent lanthanide ions, such as Nd³⁺, Eu³⁺, Dy³⁺, Yb³⁺ and Lu³⁺, leads to the direct synthesis of the corresponding sandwich complexes, in the radical, ligand-oxidized green form, whereas the reaction with La³⁺ affords the sandwich complex in the protonated, blue form. It is found that the ligand-oxidized complexes show rather weak electronic absorptions in the range 850–1150 nm and are, compared to lanthanide diporphyrins and diphthalocyanines, very stable both to oxidation and to reduction. © 1998 John Wiley & Sons, Ltd.

As a first step toward a detailed study of solvent effects on inorganic reaction mechanisms, we have introduced the self-consistent reaction field in a density functional scheme. To test our results, we have studied the thermodynamics of the tautomerization reactions of formamide and 2-pyridone, for which several experimental and theoretical works are available. Our results are in agreement with experimental results and sophisticated ab initio computations. As a further application, we have studied the linkage isomerization of pentaamminenitritocobalt(III) ion, [Co(NH3)5ONO]2+, to pentaamminenitrocobalt(III) ion, [CO(NH3)5NO2]2+. This process was studied in detail experimentally, but there is a lack of theoretical characterization. Our results indicate the nitrito as the most stable form in aqueous solution, in agreement with experiment.

Reaction of the oespz2−ligand (oespz = 2,3,7,8,12,13,17,18-octakis (ethylsulfanyl)-5,10,15,20-porphyrazinato) with trivalent lanthanide ions, such as Nd3+, Eu3+, Dy3+, Yb3+and Lu3+, leads to the direct synthesis of the corresponding sandwich complexes, in the radical, ligand-oxidized green form, whereas the reaction with La3+affords the sandwich complex in the protonated, blue form. It is found that the ligand-oxidized complexes show rather weak electronic absorptions in the range 850–1150 nm and are, compared to lanthanide diporphyrins and diphthalocyanines, very stable both to oxidation and to reduction.

The synthesis, spectroscopic and electrochemical properties of the Lu(oepz)2 (oepz ≡ 2,3,7,8,12,13,17,18-octakis(ethyl)-5,10,15,20-porphyrazinato) complex are reported. The complex, as inferred from UV-vis spectra recorded at different concentrations, strongly aggregates in solution, the most likely association mode being dimerization. The complex shows a weak near-IR absorption (λmax = 834 nm) that is considerably blue-shifted compared with the near-IR absorption of bis(π-radical) lutetium analogues. The Lu(oepz)2 neutral species is electrochemically stable between 0.73 and −0.98 V (vs Ag/AgCl), which is the largest range of stability for neutral lutetium di– tetrapyrrole complexes. Lu(oepz)2 shows excellent Type II photodynamic activity, as indicated by the value of the singlet oxygen generation quantum yield φΔ of 0.94 obtained by comparison with meso-tetraphenylporphyrin. © 1998 John Wiley & Sons, Ltd.

Some phenylpyridines and bipyridines have been studied by UV photoelectron spectroscopy and quantum-chemical methods. This study, together with some new computations on the previously reported bipyrimidines, has allowed a comprehensive analysis of general trends along the whole series of biphenyl-like molecules. Several physico-chemical characteristics have been considered in this respect, including geometric structure, conformational behaviour, relative stabilities, dipole moments and ordering of ionic states.The results obtained have been analysed in terms of conjugative and steric interactions by means of fragment analysis. On these grounds simple thumb-rules have been suggested, which may prove useful for a better understanding of polyphenyl-like molecules.

The first Pd dithiolene [Pd(Et2timdt)2] 4a belonging to the new class of metal dithiolenes deriving from the R12timdt (R12timdt 4;= 4;monoanion of 1,3-dialkylimidazolidine-2,4,5-trithione) ligand has been characterised by X-ray crystal structure determination on a single crystal [monoclinic, space group P21/n, a 4;= 4;9.545(2), b 4;= 4;5.417(2), c 4;= 4;20.093(4) Å, β 4;= 4;93.40(2)°, Z 4;= 4;2], UV–VIS–NIR, diffuse solid state reflectance, FTIR, FT-Raman spectroscopies, solid state 13C NMR and cyclic voltammetry and the results have been comparatively discussed with those obtained for the analogous [Ni(Et2timdt)2] 4b. The UV–VIS–NIR spectrum of 4a is dominated by a very intense absorption band at 1010 nm (ɛ 4;= 4;70 4;000 dm3 mol–1 cm–1). The NIR features of 4a and 4b have been examined on the basis of the electronic structure of their ground-state configurations, investigated by DFT calculations. The co-crystallisation of 4a with I2 yielded the [Pd(Et2timdt)2]·I2·CHCl3 6 adduct [monoclinic, space group C2/m, a 4;= 4;21.724(9), b 4;= 4;12.901(4), c 4;= 4;11.004(6) Å, β 4;= 4;102.83(4)°, Z 4;= 4;4]. No short metal–metal interaction was observed in both 4a and 6 (Pd  · 4;· 4;·  Pd 5.42 Å in 4a and 5.25 Å in 6), since each palladium ion is almost ‘sandwiched’ between two imidazolidine rings of parallel adjacent molecules.

Treatment of H2oetpz [oetpz2-= 2,3,7,8,12,13,17,18-octakis(ethylthio)-5,10, 15,20-tetraazaporphyrinato dianion] with Zr(NEt)2afforded the double-decker complex [Zr(oetpz)2] which has been characterized by FAB-MS, 1H and 13C NMR, electronic spectra and cyclic voltammetry. The most relevant features of UV-vis spectra and the electrochemical behaviour of [Zr(oetpz)2] are related both to the dimensions of the ionic radius of ZrIVand to the hybrid structure of the porphyrazinato ring. The reaction of the complex with oxidizing and reducing agents has been followed spectrophotometrically. It has been found that [Zr(oetpz)2] is oxidized reversibly by the nitrosonium cation NO+to form the EPR and near-IR-active [Zr(oetpz)2]+-radical cation; in contrast, [Zr(oetpz)2] is irreversibly reduced by TDAE leading to charge-transfer green-blue compounds, [Zr (oetpz)2](TDAE)x, with 0.7⪯ x ⪯1.5. The donor capability of the peripheral sulfur atoms towards coordinatively unsaturated metallic centres has been studied in benzene. Spectroscopic changes following the treatment of [Zr(oetpz)2] with [Pd(DMSO)2Cl2] suggest that the formation of oligomers of zirconium diporphyrazine units and PdCl2bridging fragments is a possible process. Copyright © 1996 Elsevier Science Ltd

Reaction of [Mn(oespz)] [oespz2– 4;= 4;2,3,7,8,12,13,17,18-octakis(ethylsulfanyl)-5,10,15,20-tetraazaporphyrinate dianion (porphyrazinate)] with CS2 and, subsequently, with THF, afforded the hydrogensulfido(1–)manganese(III) ethylsulfanylporphyrazinate [Mn(oespz)(SH)], in high yield. The S–H stretching absorptions are not observed in the IR spectrum of the complex, whereas a peak at δ 10.3 (vs. SiMe4) ascribed to the hydrogensulfido proton resonance, is observed in the 1H NMR spectrum. The complex was shown to be isostructural with [M(oespz)Cl] (M 4;= 4;Fe or Mn) by X-ray crystallography. The crystal packing of the complex consists of slipped stacks of dimeric units with the monomers positioned in a trans fashion with respect to the Mn–Sapical bond. Magnetic data are consistent with weakly antiferromagnetically coupled high spin (S 4;= 4;2) manganese(III) centers. A possible pathway to the oxidative addition of CS2 to the manganese(II) center has been proposed. In CHCl3 [Mn(oespz)(SH)] reacts reversibly through the axial hydrosulfido ligand with the sterically hindered base 2,4,6-trimethylpyridine, whereas the complex co-ordinates 1-methylimidazole reversibly on the vacant site of manganese. Treatment of the complex with 1-methylimidazole in benzene leads to a MnIII–MnII redox process, as deduced from the UV/VIS spectra.

New discotic metallomesogens of 2,3,7,8,12,13,17,18-octakis (alkyl-thio) 5,10,15,20 tetraaza porphyrin (H2Pn) and some related complexes, obtained by reaction of first row transition metal ions Ni(II), Co(II), Cu(II), Zn(II) with the free porphyrin, have been prepared. All materials were characterized by DSC measurements and optical observations.The microscopic structure of all mesophases was checked and characterized by X-ray diffraction. Except for H2P(7-12), all of the compounds are mesogenic; a few of them exhibit mesomorphic polymorphism. Melting (C→D) temperatures range from 40 to 85°C. Only NiP4, CoP4 and CuP4 show higher values. Both temperature and ΔH of isotropization (D→I) show a regular trend with respect to the number of carbon atoms in the alkyl chains and of the nature of the metal. ΔH values for complexes with partially filled d-shell metals are very similar and show definite differences with respect to those of Zn(II).Optical and X-ray data in the case of n ≥ 7 indicate a columnar mesophase with hexagonal packing whereas in complexes with n < 7 the observed mesophase shows a non-hexagonal columnar packing.CuP6 and NiP6 probably show both mesophases which are connected by a phase transition, presumably of second order or with exceedingly low enthalpy change but easily detected by polarizing microscopy because of sharp texture changes. As expected, no odd-even effect is detectable on the properties of the liquid-crystalline phases as a function of the number of carbon atoms in the aliphatic chains.

The synthesis and the physico-chemical properties of the bis(2,3,7,8,12,13,17,18-octakis-(octhylthio)-5,10,15,20-tetraazaporphyrinato)lutetium(III) double-decker complex, Lu(OOTTAP)2, are described, ESR, 1H and 13C NMR, UV-visible and NIR studies show that radical nature of this compound and suggest that the unpaired electron cannot be assigned to a specific tetra-azaporphyrinic ring on the time scales available. Some relevant UV-visible spectroscopic and redox features of Lu(OOTTAP)2resemble closely those of diphthalocyanine complexes, while the intensity and vibrational structure of the NIR spectra are rather reminiscent of those of bis-porphyrin systems.