Pyrazine control of the solid-state supramolecular chemistry of zinc phthalocyanine

Crystals of monoaxially coordinated T-shaped and H-shaped supramolecular zinc(II) phthalocyaninato complexes with pyrazine are obtained. In both types of molecules the central Zn atom of ZnPc complexes with pyrazine exhibits 4 + 1 coordination. The Zn atom is equatorially coordinated by four isoindole N atoms of Pc macrocycle and axially by N atom of pyrazine molecule. The interaction of the central Zn atom of ZnPc with the axial N atom of pyrazine leads to a deviation of Zn from the centre of cavity by 0.371(2) Å in the T-shaped complex and by 0.296(2) Å in the H-shaped complex. Thermogravimetric analysis of the crystals exhibits three slopes down, corresponding to the loss in succession of solvated pyrazine molecules, than the loss of ligated pyrazine molecules from the T-shaped complex and the finally the loss of the bridged pyrazine molecule from the H-shaped complex. Finally the thermal processing leads to the β-ZnPc as residue. The UV–Vis spectrum taken in solution shows the batochromic shift in the polar solvent like α-chloronaphthalene in relation to the spectrum in non-polar solvent like benzene.     

OCTA-ALKYL ZINC PHTHALOCYANINES: POTENTIAL PHOTOSENSITIZERS FOR USE IN THE PHOTODYNAMIC THERAPY OF CANCER

The synthesis, characterization and electronic spectra of a series of nine 1,4,8,11,15,18,22,25-octa-alkyl zinc phthalocyanines (ZnPc), potential photosensitizers for the photodynamic therapy of cancer, are described. The substituents on the phthalocyanine (Pc) macrocycle “red-shift” the absorbance maximum, in cyclohexane, of all nine members of this series to a value of 703 ± 2 nm, with a corrected fluorescence emission maximum for the octadecyl derivative of 715 nm. The solubilities and degree of aggregation of six examples in cyclohexane have been measured. The highest homologue, the octadecyl derivative, remains essentially unaggregated to a concentration of 1.5 ± 10^?4 mol dm^?3. The photostability of this Pc has been examined and the compound shown to be sensitive to photooxidation processes, which lead to its decomposition to 3,6-fcw-decylphthalimide. Known singlet oxygen quenchers inhibit the photodecomposition. In a comparative study, the octadecyl ZnPc underwent a more rapid photodecomposition than the corresponding metal-free derivative.     

Formation of phthalocyanines deprotonated forms and their interaction with Zn Ions in the system 1,8-diazabicyclo[5.4.0]undec-7-ene-acetonitrile at 298 K

The formation of deprotonated forms of tetra(t-butyl)phthalocyanine ((H₂ tButPc) and octa(pentoxy)-phthalocyanine (H₂OAmPc) in the system acetonitrile-1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) at 298 K was studied by the method of spectrophotometric titration. With increasing DBU concentration sequential formation occurs of both mono- and douby deprotonated forms. The introduction of pentoxy groups into the fused benzene rings leads to a significant decrease in the acidity of the tetrapyrrole macrocycle compared with the tert-butyl substitution. The interaction of douby deprotonated forms of the phthalocyanines with zinc diacetate leads to the formation of metal complexes, the chelation constant of the latter is shown to correlate with the acidity of NH-protons in the nucleus of the macrocycle. For the chelation of more acidic tetra(t-butyl)-phthalocyanine an equimolar concentrations of zinc diacetate is sufficient, while the less acidic octa(pentoxy)-phthalocyanine requires almost 6-fold excess.     

Coordination properties of zinc 5,15-di(<Emphasis Type="Italic">ortho</Emphasis>-aminophenyl)octaalkylporphyrin in reactions with mono- an dibasic nitrogen bases

The coordination properties of zinc 5,15-di(ortho-aminophenyl)octaalkylporphyrin in reactions with mono- and dibasic nitrogen bases in benzene are studied by means of computational modeling and spectrophotometric titration. The stability of molecular zinc porphyrinate complexes in solution is estimated and their structure is determined. The correlation between the coordination properties of the compound under investigation and electronic and conformational factors of the macrocycle is established. The base nature is shown to affect the stability of zinc porphyrinate complexes. The correlations between the calculated σ bond energy of the zinc atom with the nitrogen atom of the base (E _b) and the equilibrium constant of the axial coordination reaction are obtained. It is demonstrated that the reaction is accompanied by an increase in steric hindrance and a change in the type of deformation of the porphyrin ligand.     

(4‐Aminopyridine‐κN1)(phthalocyaninato‐κ4N)zinc(II) tetrahydrofuran disolvate

The title compound, [Zn(C₃₂H₁₆N₈)(C₅H₆N₂)]·2C₄H₈O, consists of one (phthalocyaninato)zinc (ZnPc) unit, a coordinated 4‐aminopyridine (4‐ap) molecule and two tetrahydrofuran (THF) solvent molecules. The central Zn atom is (4+1)‐coordinated by four isoindole N atoms of the Pc core and by the pyridine N atom of 4‐aminopyridine. The Zn atom is displaced by 0.4464 (8) Å from the isoindole N₄ plane towards the pyridine N atom. The crystal structure is stabilized by intermolecular amine–phthalocyaninate N—H...N hydrogen bonds and π–π interactions between the aggregated Pc rings, which form molecular layers, and by weak van der Waals interactions between the layers. As well as hindering the aggregation of ZnPc molecules by occupying an axial position, the amino group will add new interactions which will favor applications of ZnPc, for example, as a sensitizer of photodynamic therapy.     

Optically active tetraazamacrocycles analogous to cyclam

The syntheses of enantiopure tetraazamacrocycles analogous to cyclam, (S,S)-3, (R,R)-3 and (S,S,S,S)-4, have been carried out. NMR and semiempirical studies of 3 have revealed that this compound presents a rigid conformation with C₂ symmetry, which is stabilized by intramolecular bifurcated hydrogen bonds. Structural studies for macrocycle 4 have shown that the presence of two cyclohexane rings of (S,S) configuration leads to the loss of the D₂ symmetry in solution, which is in agreement with the AM1 calculated structure.     

The photodegradation of a zinc phthalocyanine

A water-soluble zinc phthalocyanine (Pc), ZnPc (3), bearing 12 dimethylamino groups, which enhance the solubility of the macrocycle was synthesized and characterized. Photobleaching of the compound was examined both in vivo and in vitro. Laser irradiation causes photo-oxidation of the newly synthesized ZnPc. A photobleachable phthalocyanine can be an alternative in imaging; phthalocyanine dyes are used in imaging the cardiovascular system. Besides, it can be used in fluorescein angiography in some cases. When compared to stable ones, a photobleaching ZnPc (3) might be an attractive compound for imaging in medicine.     

Synthesis,thermal stability and structural characterisation of iron(II) phthalocyanine complex with 4-cyanopyridine

A new complex of bis-axially coordinated iron(II) phthalocyanine by 4-cyanopyridine (4-CNpy) has been obtained in crystalline form as an adduct with two 4-CNpy molecules. The [FePc(4-CNpy)₂] · 2(4-CNpy) crystallises in the monoclinic system, space group P2₁/c with two molecules in the unit cell. The iron(II) coordinates four isoindole nitrogen atoms of the almost planar phthalocyaninato(2−) macroring and axially two nitrogen atoms of 4-CNpy molecules. The coordination polyhedron around the Fe(II) atom approximates to a tetragonal by-pyramid. Four equatorial Fe–N bonds are shorter (1.936(2) Å) than two axial Fe–N bonds (2.027(2) Å). The centrosymmetric FePc(4-CNpy)₂ molecules form alternating sheets parallel to the bc crystallographic plane and solvated 4-CNpy molecules that are anti-parallel oriented by their polar cyano groups are located between the sheets of FePc(4-CNpy)₂ molecules. Ligation of the intermediate-spin iron(II) phthalocyanine by 4-CNpy molecules leads to the low spin Fe(II) complex. The importance of the d(π) → π^∗(Pc) back donation is manifested in the difference between the values of C–N isoindole and C–N azamethine bond lengths of the Pc macrocycle. The thermal analysis of the crystals of [FePc(4-CN)₂] · 2(4-CNpy) shows two steps responsible for a loss of solvated (∼170 °C) and coordinated (∼235 °C) 4-CNpy molecules.     

The crystal and molecular structure of triphenylphosphoniodithio-carboxylato-ss'-carbonylbis (trikphenylphosphine) iridium(I) tetrafluoroborate [Ir(S2CPPh3) (CO) (PPh3)2]BF4.

Crystal and molecular structures of the title compound have been determined from a three-dimensional X-ray analysis using diffractometer data. The crystals are monoclinic, space group P2₁/c, with Z = 4 in a unit cell of dimensions a = 10.5876(9), b = 31.518(10), c = 16.2164(5) Å, β = 92.521(1)°. The observed and calculated densities are 1.38 and 1.374 g cm^-1 respectively. The crystals decompose under X-rays, and three crystals were required to complete data collection. The structure was solved and refined by convetional methods to final residuals R and R_w of 0.087 and 0.107 respectively.The crystals contain monomeric cations, and BF₄ anions. The iridium atom is in a distorted trigonal bipyramidal environment consisting of the two sulphur atoms (one axial, one equatorial) of a bidentate triphenylphosphoniodi-thiocarboxylate ligand, two triphenylphosphine groups (equatorial) and the carbonyl ligand (axial). The non-equivalent Ir-s distances are 2.377 and 2.307(5) Å, the Ir-P distances are 2.334, 2.331(5) Å. Within the zwitterion, the C-S distances are 1.66 and 1.70(2) Å, while P-C is 1.78(2) Å. The condensation of PPh₃ and CS₂ to form the PH₃P⁺-CS₂ zwitterion is in contrast to that predicted previously.It is probable that the other complexes of iridium and rhodium prepared in a similar manner [2] should now be reformulated as containing Ph₃P⁺-CS₂^- ligands.     

Photolysis of 10,10-difluorophenanthren-9(10H)-one. Evidence for solvent-assisted α-cleavage

The photolysis of 10,10-difluorophenanthren-9(10H)-one 1 in different solvents shows that the major competing reaction of the diradical formed by α-cleavage: recombination and hydrogen atom abstraction depends on the hydrogen atom donating ability of the solvent. Photolysis of 1 in cyclohexane in the presence of air or oxygen leads mainly to α-cleavage while photoreduction with the formation of 10-fluoro-9-phenanthrol occurs when the solution is deaerated prior to irradiation. In acetonitrile, a poor hydrogen donor, recombination of the diradical back to starting compound 1 is the sole process.     

A Novel Sulfur‐bridged Dimeric Zinc(II) Complex with 2, 6‐Diacetylpyridine Bis(thiosemicarbazone)

The reaction of zinc bromide with the pentadentate chelating ligand 2, 6‐diacetylpyridine bis(thiosemicarbazone) (H₂L¹) yields the formation of a novel complex. Recrystallization in a acetone/water solution leads us to isolate the mixed ligand complex of [Zn(H₂L¹)Br_0.49(OH)_0.51]₂·(HSO₄)₂·6H₂O, structurally characterized. The complex is a dimer in which each zinc atom is seven‐co‐ordinated with the SNNNS‐chelating ligand occupying the five equatorial positions, a bromine atom or hydroxo group in one of the two axial positions and a sulfur atom of the centrosymmetrical molecule occupies the other axial site making a bridge between the two zinc atoms. To the best of our knowledge is the first S‐bridged dimeric Zinc(II) complex derived from 2, 6‐diacetylpyridine bis(thiosemicarbazone) ligand. The MALDI‐TOF mass, solid state IR and ¹H NMR (in DMSO solution) spectra are also discussed.     

1,4,10,13-tetraoxa-7,16-diaza(diphenylphosphinylmethyl)cyclooctadecane (L). As a prototype of supramolecular machine: Synthesis, crystal structure, and vibrational spectra of the sodium thiocyanate complex with L [NaL](NCS)

A new method of synthesis of the lariat crown ether 1,4,10,13-tetraoxa-7,16-diaza(diphenylmethyl)cyclooctadecane (L) has been described. The sodium thiocyanate complex with L [NaL](NCS) has been studied by X-ray crystallography, and the major vibrational frequencies in its IR spectrum have been assigned. The crystals of the complex are monoclinic: a = 11.538(2) Å, b = 9.796(2) Å, c = 7.564(2), Å, β = 90.38(3)°, Z = 2, space group P2₁/c, R1 = 0.0486 for 1733 reflections with I > 2σ(I). The compound has an ionic structure. In the centrosymmetric cation [NaL]⁺, both the macrocyclic part and the side groups of the ligand L are involved in coordination with the metal atom. The coordination polyhedron of the Na atom is a hexagonal bipyramid in which the equatorial plane is formed by six donor atoms of the substituted diaza-18-crown-6 ether (DA18C6) (av. Na-O_ether, 2.682 Å; Na-N, 2.861 Å). The phosphoryl oxygen atoms of the side chains of the ligand occupy the axial positions (Na-O_P, 2.325 Å). It is demonstrated that the cationic complexes of L can be, in principle, used as components of supramolecular machines.     

Structural and Conformational Aspects of Equatorial and Axial Trifluoromethyl,Difluoromethyl, and Monofluoromethyl Groups

The X‐ray crystal structures of cis‐ and trans‐1‐(indol‐3‐yl)‐4‐methyl cyclohexane and its congeners with stepwise fluorination of the methyl group are reported. The trans‐configured compounds adopted diequatorial conformations, whereas the cis analogues adopted regular cyclohexane chair conformations with the methyl group preferentially assuming the axial position, even in the case of the CF₃ group. Surprisingly, although the axial CF₃ derivative displayed distinct valence deformations in the cyclohexane moiety, the observed structural changes were relatively modest. The cis derivatives with axial mono‐ and difluorinated methyl groups exhibited conformational disorder in the crystals with significant population levels for the staggered conformations that had one fluorine atom in the endo position; their respective trans counterparts adopted unique conformations, but again with one fluorine atom in the endo position. Theoretical calculations for a series of cis‐ and trans‐1,4‐dimethyl cyclohexane model compounds with stepwise fluorination of one equatorial or axial methyl group reproduced the experimentally observed structural response patterns very well, reproduced the experimentally determined nonlinear correlation of the axial–equatorial energy difference with the degree of methyl fluorination in a satisfactory manner, and provided further insights into important conformational aspects of partially fluorinated methyl groups.     

The Influence of Substituent Orientation on the Photovoltaic Performance of Phthalocyanine‐Sensitized Solar Cells

Phthalocyanines (Pcs) are used as sensitizers in dye‐sensitized solar cells (DSSCs) because of their stability and intense absorption in the red and near‐IR regions. Impressive progress has been made in photovoltaic efficiencies by introduction of bulky peripheral substituents to help suppress macrocycle aggregation. To reach benchmark efficiencies reported for other related dyes, new designs need to be explored. Single carboxy‐ZnPc regioisomers substituted at the non‐peripheral positions by rigid aryl groups have now been studied, which has shed light on the influence of steric hindrance and/or orientation of the substituent around the anchoring group on the photovoltaic response. The regioisomer bearing the aryl group far away from the anchoring group produces a more effective sensitization of the TiO₂ films and higher short‐circuit photocurrent density (J_sc). Taking advantage of the good photovoltaic performance in the near‐IR region of this ZnPc, it was combined with another appropriate dye for panchromatic sensitization of the mesoporous photoelectrode and an increase of the overall device efficiency.     

Structural effect of the competition of 4-picoline and water molecules to form complexes with Be,Mg and Zn phthalocyanines

The BePc(4-Mepy), MgPc(4-Mepy)₂ were recrystallised from wet 4-picoline and the aqua M((II) phthalocyaninato complexes, BePcH₂O · (4-Mepy) (Ia), (MgPcH₂O · (4-Mepy))₂ (IIa) and (MgPcH₂O · (4-Mepy)₂) · (4-Mepy) (IIb), have been obtained. Recrystallisation of ZnPc(4-Mepy) in wet 4-picoline yields the β-ZnPc in microcrystalline form. The Ia, IIa and IIb complexes were obtained in crystalline form. The composition of the Mg complexes (IIa and IIb) depends on the crystallisation temperature. The BePcH₂O · (4-Mepy) compound crystallises in the centrosymmetric space group of the triclinic system, while both Mg complexes crystallise in the P2₁/n space group of the monoclinic system. In all crystals the central M(II) atom (Be and Mg) is 4 + 1 coordinated, equatorially by four N-isoindole atoms of Pc macrocycle and axially by O atom of water molecule. Interaction of the central M atom of MgPc with axially ligated water molecule leads to the saucer-shape of the Pc ring and deviates the central M(II) atom from the N₄-isondole plane by 0.308(2), 0.482(2) and 0.537(2) Å in Ia, IIa and IIb, respectively. The molecules in the Ia and IIa crystals are linked together by a pair of O–H?N hydrogen bonds between the H atom of water molecule and the azamethine N atom of the other Pc into a dimeric structure, and the 4-picoline molecules are linked to the (MPcH₂O)₂ dimeric structure. In IIb crystal the MgPcH₂O molecule is linked by O–H?N hydrogen bonds with two 4-picoline molecules, while the third 4-picoline molecule interacts only by the van der Waals forces. The O–H?N hydrogen bonding system and the π–π interactions between the aromatic Pc macrocyles are the key for the molecular arrangement and stabilisation of the structure. The stability of the solid-state complexes was analysed by thermogravimetric measurements. Only the solid-state spectrum of IIa complex exhibits an intense near IR absorption band. The spectra of IIa and IIb in solution are identical, the Q band is blue shifted in O-donor solvents comparing with the spectrum in N-donor solvents.     

DFT calculation of benzoazacrown ethers and their complexes with calcium perchlorate

The complexation constants of several azacrown ethers with Ca(ClO₄)₂ were determined and turned out to be the higher, the large the macrocycle. The structures of free ligands and their complexes and the complexation energies were calculated by the DFT method. In the aza-12(15)-crown-4(5) ether complexes with Ca(ClO₄)₂, the metal cations lie outside the averaged plane of heteroatoms of the macrocycle, and the coordination of both counterions is V-like. In the complexes of aza-18-crown-6 ethers, the counterions are in the axial position relatively to the macrocycle in the center of which the Ca²⁺ ion is localized. The complexation energies increase with an increase in the size of the azacrown ether macrocycle. The involvement of the nitrogen atom in binding with the Ca²⁺ ion decreases with the expansion of the macrocycle. Two methods for quantitative estimation of the degree of pre-organization of ligands to complexation were considered: geometric and energetic methods. Benzoaza-15-crown-5 ether is a ligand which is more pre-organized to complexation than N-phenylaza-15-crown-5 ether.     

Rearrangements des halohydrines en presence de carbonate d'argent sur celite-II: Halohydrines cyclohexaniques substituees

Silver carbonate on Celite reacts with trans-diaxial halohydrins of the cyclohexane series, giving epoxides. cis-Bromohydrins, where the bromine atom is axial, lead to ketones.     

Structure and properties of lithium n-butyl amidinates

Lithium n-butyl amidinates (formally lithium salts of N',N-disubstituted amidoimides of pentanoic acid) with various substituents were prepared and characterized in solution by ¹H, ⁷Li, ¹³C and ¹⁵N NMR spectra parameters in C₆D₆, THF-d₈ and Et₂O-d₁₀. The characteristic spectral parameters were compared with parent carbodiimides and amidines prepared by hydrolysis, where large solvent effects were described. Five of studied compounds were studied by X-ray diffraction techniques in the solid state. Lithium n-butyl amidinates containing less bulky substituents like isopropyl or cyclohexyl crystallize with Et₂O or THF as centrosymmetric dimers with mutually parallel amidinate moieties. The lithium N,N'-bis[2,6-di(propan-2-yl)phenyl]n-butylamidinate crystallizes from Et₂O solution as an asymmetric dimer. The first unit is composed by one ligand coordinated to one of lithium atoms. The lithium atom is also coordinated by one of the nitrogen atoms of the second ligand. The second nitrogen atom of the same ligand is coordinated to the second lithium atom which is also connected to the Et₂O molecule and the aromatic ring of the ligand in a η³-fashion. The same compound crystallizes from the THF solution as a monomeric bis-tetrahydrofuranate.     

An unusual oligomerization/oxidation reaction of a 3‐boron‐substituted 1‐phenylbuta‐1,3‐diene produces 6,9,16,19‐tetraphenyl‐5,15‐distyryl‐3,13,25,26‐tetraoxa‐2,12‐diborapentacyclo[16.2.2.28,11.12,5.112,15]hexacosa‐1(20),7,10,17‐tetraene

The unusual title macrocyclic structure, C₆₀H₅₄B₂O₄, has been isolated from exposure of 3‐BF₃‐1‐phenylbuta‐1,3‐diene to both air and moisture in an attempt to obtain crystals of the starting butadiene compound. Formation of the macrocycle from six molecules of the starting butadiene material is rationalized and its structural features are compared with those of other B(OR)₂‐substituted cyclohexane and benzene ring containing structures. Molecules reside on crystallographic centers of inversion and there are no intermolecular interactions of note in the crystal structure.     

Preparation,characterization and X-ray structures of 1-methylisatin 3-thiosemicarbazone copper,nickel and cobalt complexes

Copper, nickel and cobalt complexes of 1-methylisatin 3-thiosemicarbazone (HL) have been synthesized and characterized by means of spectroscopic techniques. The X-ray crystal structures of [CuClL]_n (1), [NiL₂] (2), [CoL₂]₂[CoCl₄]·2EtOH (3) were also determined. In all compounds the monodeprotonated ligand behaves as O, N, S terdentate. In the copper complex the coordination geometry is square-pyramidal with the ligand and a chlorine atom lying on the basal plane; a bridging sulphur atom in axial position forms polymeric chains. The nickel atom of complex 2 is surrounded by six donor atoms of two ligand moieties in a distorted octahedral fashion. The molecular structure of compound 3 consists of octahedral [CoL₂]⁺ cations, [CoCl₄]²⁻ anions and solvate ethanol molecules.