Stereochemistry and properties of the M(II)N(py) coordination bond in the low-spin dipyridinated iron(II) and cobalt(II) phthalocyanines

Trinuclear coordination assemblies of low-spin dicyano manganese(II) (S = 1/2) and iron(II) (S = 0) phthalocyanines with manganese(II) acetylacetonate, tris(cyclopentadienyl)gadolinium(III) and neodymium(III)

The reaction of Mn^IIPc, Fe^IIPc or Fe^IIPcCl₁₆ with KCN in the presence of cryptand[2.2.2] yielded dicyano-complexes {cryptand(K⁺)}₂{M^II(CN)₂(macrocycle^2-)}^2-·XC₆H₄Cl₂ (M = Mn and Fe, X = 1 and 2) that were used for the preparation of trinuclear assemblies of the general formula {cryptand(K⁺)}₂{M^II(CN)₂Pc·(ML)₂}^2-·nC₆H₄Cl₂ (M^II = Mn^II and Fe^II; n = 1, 4 and 5). These assemblies were formed via coordination of two manganese(II) acetylacetonate (ML = Mn^II(acac)₂, S = 5/2), tris(cyclopentadienyl)gadolinium (ML = Cp₃Gd^III, S = 7/2) or tris(cyclopentadienyl)neodymium (ML = Cp₃Nd^III, S = 3/2) units to the nitrogen atoms of bidentate cyano ligands. The N(CN)-Mn{Mn^II(acac)₂} bond is 2.129(3) Å long but the bonds are elongated to 2.43-2.49 Å for tris(cyclopentadienyl)lanthanides. {Cryptand(K⁺)}₂{Mn^II(CN)₂Pc·(Mn^II(acac)₂)₂}^2-·5C₆H₄Cl₂ (2) contains three Mn(II) ions in different spin states (S = 5/2 and 1/2). Strong antiferromagnetic coupling of spins observed between them with the exchange interaction (J) of -17.6 cm^-1 enables the formation of a high S = 9/2 spin state for {Mn^II(CN)₂Pc·(Mn^II(acac)₂)₂}^2- dianions at 2 K. The estimated exchange interaction between Mn^II (S = 1/2) and Gd^III (S = 7/2) spins in {Mn^II(CN)₂Pc·(Cp₃Gd^III)₂}^2- is only -1.1 cm^-1, and in contrast to 2, nearly independent Gd^III and Mn^II centers are formed. As a result, no transition to the high-spin state is observed in {Mn^II(CN)₂Pc·(Cp₃Gd^III)₂}^2-. The {Mn^II(CN)₂Pc·(Cp₃Nd^III)₂}^2- and{Fe^II(CN)₂Pc·(Cp₃Nd^III)₂}^2- dianions with Cp₃Nd^III show a decrease of χ_MT values in the whole studied temperature range (300-1.9 K). A similar behaviour was found previously for pristine Cp₃Nd^III and Cp₃Nd^III·L complexes (L = alkylisocyanide ligand).

Determining the coordination environment and electronic structure of polymer-encapsulated cobalt phthalocyanine under electrocatalytic CO2 reduction conditions using in situ X-Ray absorption spectroscopy

Encapsulating cobalt phthalocyanine (CoPc) within the coordinating polymer poly-4-vinylpyridine (P4VP) results in a catalyst-polymer composite (CoPc-P4VP) that selectively reduces CO2 to CO at fast rates at low overpotential. In previous studies, we postulated that the enhanced selectively for CO over H2 production within CoPc-P4VP compared to the parent CoPc complex is due to a combination of primary, secondary, and outer-coordination sphere effects imbued by the encapsulating polymer. In this work, we perform in situ electrochemical X-ray absorption spectroscopy measurements to study the oxidation state and coordination environment of Co as a function of applied potential for CoPc, CoPc-P4VP, and CoPc with an axially-coordinated py, CoPc(py). Using in situ X-ray absorption near edge structure (XANES) we provide experimental support for our previous hypothesis that Co changes from a 4-coordinate square-planar geometry in CoPc to a mostly 5-coordinate species in CoPc(py) and CoPc-P4VP. The coordination environment of CoPc-P4VP is potential-independent but pH-dependent, suggesting that the axial coordination of pyridyl groups in P4VP to CoPc is modulated by the protonation of the polymer. Finally, we show that at low potential the oxidation state of Co in the 4-coordinate CoPc is different from that in the 5-coordinate CoPc(py), suggesting that the primary coordination sphere modulates the site of reduction (metal-centered vs. ligand centered) under catalytically-relevant conditions.

Coordination-induced metal-to-macrocycle charge transfer and effect of cations on reorientation of the CN ligand in the {SnL2Mac}2− dianions (L = CN−, OCN−, Im−; Mac = phthalo- or naphthalocyanine)

Anionic coordination {crypt(M⁺)}₂{SnL₂Mac}²⁻ complexes of tin(ii) phthalo- (Pc) and naphthalocyanines (Nc) were obtained and discussed.

Coordination Complexes of Titanium(IV) and Indium(III) Phthalocyanines with Carbonyl-Containing Dyes: The Formation of Singly Bonded Anionic Squarylium Dimers

Reduction methods for the preparation of coordination complexes of titanium(IV) and indium(III) phthalocyanines (Pc) with organic dyes such as indigo, thioindigo, and squarylium dye III (SQ) have been developed, which allow one to obtain crystalline {cryptand(K⁺ )}{(cis-indigo-O,O)^2- Ti^IV (Pc^2- )}(Cl^- )⋅C₆ H₄ Cl₂ (1), {cryptand(K⁺ )}{(cis-thioindigo-O,O)^2- In^III (Pc^2- )}^- ⋅C₆ H₄ Cl₂ (2), and {cryptand(K⁺ )}{[(SQ)₂ -O,O]^2- In^III (Pc^2- )}^- ⋅3.5 C₆ H₄ Cl₂ (3) complexes. The formation of these complexes is accompanied by the reduction of the starting dyes to the anionic state. Transition of trans-indigo or trans-thioindigo to the cis conformation in 1 and 2 provides coordination of both carbonyl oxygen atoms of the dye to Ti^IV Pc or In^III Pc. SQ is reduced to the radical anion state and forms unusual diamagnetic singly bonded (SQ^- )₂ dimers in 3. These dimers have two closely positioned carbonyl oxygen atoms coordinated to In^III Pc. Dianionic Pc^2- macrocycles have been found in 1-3. The complexes contain two chromophore molecules at one metal center. However, their optical spectra are defined mainly by absorption bands of the metal phthalocyanines.

PVD thin film growth of M(Pc)(CN)2 axially substituted metal-phthalocyanines

We tested the feasibility of in-house synthesized M(Pc)(CN)[Formula: see text] type axially substituted metal-phthalocyanines (M [Formula: see text] metal ion Co or Fe; Pc [Formula: see text] phthalocyanine ligand) for thin film growth via physical vapor deposition. We performed optical and infrared spectroscopy on thin films deposited in high vacuum as well as thermal desorption experiments in ultrahigh vacuum using mass spectrometry. In contradiction to the expectation of a rather strongly bound CN ligand, the results indicate molecular dissociation under the loss of CN groups at a temperature that is below the evaporation temperature of the material needed to form a film on a substrate. Therefore it was concluded that PVD is not a suitable method to grow M(Pc)(CN)[Formula: see text] thin films. However, the obtained data yield valuable insight into the molecules’ stability.

Synthesis and properties of N-methylimidazole solvates of vanadium(ii), chromium(ii) and iron(ii) phthalocyanines. Strong NIR absorption in VII(MeIm)2(Pc2−)

Crystal structures and optical and magnetic properties of N-methylimidazole (MeIm) solvates of vanadium(ii), chromium(ii) and iron(ii) phthalocyanines have been studied.

Synthesis and purification of metallooctachlorophthalocyanines

A detailed synthetic procedure based on the use of urea, dichlorophthalic acid, respective transition metal halides and [NH4]2[MoO4] as a catalyst in the melt or by using 1,2,4-trichlorobenzene as a high-boiling inert solvent is described to gain 2,3,9,10,16,17,23,24-metallooctachlorophthalocyanines (MPcCl8 compounds with M=Mn, Fe, Co, Ni, Cu). In cases that a first purification by subsequent treatment of the crude materials with HCl, NaOH and HCl would not give rise to analytically pure compounds, a second novel purification by using pyridine is described. The degree of purity, exceeding always 98%, is determined by thermogravimetric analysis. Comparative IR, UV/Vis and PXRD studies of the MPcCl8 compounds are reported.

CASSCF-based explicit ligand field models clarify the ground state electronic structures of transition metal phthalocyanines (MPc; M = Mn, Fe, Co, Ni, Cu, Zn)

Multireference electronic structure methods are used to assign ground state electronic configurations for a series of metallophthalocyanines. Ligand orbital occupancies remain constant across the period and are consistent with a formal 2– charge on the ligand. The d electron configurations of some metallophthalocyanines are straightforward and can be unambiguously assigned, (dxy)2(dxz,dyz)2,2( [Formula: see text])2([Formula: see text])n, with n = 2, 1, 0, respectively, for ZnPc, CuPc, and NiPc. Controversies over ground state electronic structure assignments for other metallophthalocyanines arise due to multiple complicating factors: accidental near-degeneracies, environmental effects, and different ligand field models used in interpreting experimental spectra. We demonstrate that explicit ligand field models provide more reliable and consistent interpretations of experimental data than implicit, parameterized alternatives. On this basis, we assign gas-phase electronic ground states for MnPc, (dxy)2(dxz,dyz)1,1([Formula: see text])1 and CoPc, (dxy)2(dxz,dyz)2,2([Formula: see text])1, and show that the ground state of FePc cannot be resolved to a single state, with two near-degenerate states that are likely spin-orbit coupled: (dxy)2(dxz,dyz)1,1( [Formula: see text])2 and (dxy)2(dxz,dyz)2,1([Formula: see text])1. Remaining differences between computational predictions and experimental observations are small and may be ascribed primarily to environmental effects but are also partly due to incomplete modelling of electron correlation.

Structure and optical properties of fullerene C60 complex with dipyridinated iron(II) phthalocyanine [Fe(II)Pc(C5H5N)2]·C60·4C6H4Cl2: First structure of bisaxially coordinated iron(II) phthalocyanine complex with acetonitrile Fe(II)Pc(CH3CN)2

The complex of fullerene C 60 with dipyridinated iron(II) phthalocyanine [ Fe ( II ) Pc ( C 5 H 5 N )2]· C 60·4 C 6 H 4 Cl 2 (1) has been obtained as single crystals. According to the IR- and UV-visible-NIR spectra, 1 is molecular solid with no charge transfer from Fe ( II ) Pc ( C 5 H 5 N )2 to C 60· C 60 molecules form closely packed linear columns in 1 along the b axis with a uniform interfullerene center-to center distance of 9.99 Å and multiple short van der Waals (vdW) C … C contacts between fullerenes of 3.10–3.18 Å. Totally each Fe ( II ) Pc ( C 5 H 5 N )2 unit is surrounded by four C 60 molecules two of which form short vdW C … C contacts with the phthalocyanine plane locating near two adjacent phenylene substituents of Fe ( II ) Pc . The Fe ( II ) Pc ( C 5 H 5 N )2 geometry remains almost unchanged as compared with that of fullerene free Fe ( II ) Pc ( C 5 H 5 N )2. The iron(II) atoms are located exactly in the Pc plane, the Fe - N ( C 5 H 5 N ) bond length is 2.038(3) Å and the averaged of the Fe - N ( Pc ) bond length is 1.935(3) Å. Bisaxially coordinated iron(II) phthalocyanine complex with acetonitrile Fe ( II ) Pc ( CH 3 CN )2 does not cocrystallize with C 60. Nevertheless, good quality crystals of [ Fe ( II ) Pc ( CH 3 CN )2]·2 C 6 H 4 Cl 2 (2) were isolated in this synthesis. That is the first structure of bisaxially coordinated metal phthalocyanine complex with nitrile containing solvent. Acetonitrile unusually strongly coordinates to Fe ( II ) Pc with the Fe – N ( CH 3 CN ) bond length of 1.938(1) Å. The iron(II) atoms are located in the Pc plane and the averaged length of the Fe - N ( Pc ) bonds is 1.934(1) Å.

The synthesis and characterization of a side-by-side iron phthalocyanine dimer

The QCA paradigm is one of the approaches to decrease the size scale of computing devices. When molecules are used as QCA cells, they may be able to perform computing at room temperature. This paper describes a novel molecular QCA cell candidate which is a side-by-side iron phthalocyanine dimer, and an investigation of its optical and redox properties. The new dodeca(pentyloxy) substituted side-by-side iron phthalocyanine dimer, along with the octa(pentyloxy) iron phthalocyanine monomer, are soluble in non-polar organic solvents. These compounds were isolated by gel permeation chromatography (GPC) and high-performance liquid chromatography (HPLC) to final purities of 98% and 99%, respectively. The NMR spectra of both compounds in CDCl3 are broad due to aggregation, but become well resolved after the addition of the coordinating solvent pyridine-d5. Addition of pyridine also gives changes in the UV-vis spectra and electrochemical peaks of both monomer and dimer in dichloromethane indicative of axial iron coordination. The electrochemical data indicates the loss of pyridine ligands from the oxidized products of both monomer and dimer. The comproportionation constant of side-by-side phthalocyanine dimer shows that its oxidized and reduced mixed-valence complexes are fairly stable. The dimer is thus a candidate for molecular QCA systems.

Axial ligand exchange reaction on ruthenium phthalocyanines

Bis(4-methylpyridine)phthalocyaninato ruthenium(II) has been synthesized. It was proved by single-crystal X-ray diffraction that the central Ru(II) atom is bonded to six N atoms in an elongated octahedral configuration, and the axial ligands have a significantly longer Ru - N bond distance, 2.101(4) Å, than the independent pyrrol Ru - N bond, 1.99 Å. Therefore, the axial ligands can be exchanged by other ligands. The ligand exchange reactions with diethyl pyridyl-4-phosphonate and diethyl pyridylmethyl-4-phosphonate were studied in high boiling-point solvents at elevated temperatures, ca 160 °C. Mono-ligand as well as double-ligand replaced complexes were obtained. The complexes have been isolated by column chromatography. These complexes have potential applications, such as in dye sensitized solar cells.

Effects induced by axial ligands binding to tetrapyrrole-based aromatic metallomacrocycles

The axial positions of planar metallomacrocycles are unoccupied. The positively charged metal is thus a potential binding site for electron-donating groups. The binding strength is affected by the central metal, the ligand, and the macrocycle. One ligand leads to the out-of-plane displacement of the central metal, whereas two ligands from two sides structurally neutralize each other. The axial ligand donates charge to the central metal and the macrocycle when the lone pair orients along the interaction axis. The frontier orbital levels are elevated because of the charge donated to the macrocycle. Even though the singlet-triplet gap and the absorption maximum do not change significantly upon binding, the redox chemistry is considerably affected by the shifts of orbital levels. The macrocyclic M-N bonds are weakened by the binding, but their natures remain almost unchanged. Calcium phthalocyanine is a special case, as the central calcium is too large to fit the cavity. Accordingly, multiple ligands facilely bind to the calcium from one side. The aluminum phthalocyanine halogen is another special case, as it has a halogen ligand coordinating to the aluminum through a nondative bond. This leads to some effects different from those caused by dative binding. When there is no considerable steric demand, the lone pair points along the interaction axis to facilitate the donation. When in a stacked dimer, the electron-rich group is part of a large molecule, and the orientation of the lone pair is approximately perpendicular to the interaction axis. This induces the charge loss of the central metal. Because metallomacrocycles are widespread in the biological, medical, and material sciences, the results from this study are expected to bring useful insights to these fields.

X-ray Structures and Homolysis of Some Alkylcobalt(III) Phthalocyanine Complexes

The first crystallographic data for sigma-bonded alkylcobalt(III) phthalocyanine complexes are reported. A single-crystal X-ray structure of CH(3)CH(2)Co(III)Pc (Pc = dianion of phthalocyanine) reveals that the solid consists of centrosymmetric face-to-face dimers in which the CH(3)CH(2)Co(III)Pc units retain their square pyramidal geometry. The structure appears to be the first one reported for a five-coordinate RCo(III)(chelate) complex with an electron-deficient equatorial system. The Co-C bond in CH(3)CH(2)Co(III)Pc (2.031(5) A) is the longest found in five-coordinate RCo(III)(chel) complexes (R = simple primary alkyl group). Another X-ray study demonstrates that CH(3)Co(III)Pc(py) has a distorted octahedral geometry with axial bonds of very similar length to those in methylcobalamin. The axial bonds are shorter than those in its octaethylporphyrin analogue, in accordance with a weaker trans axial influence in six-coordinate complexes containing an electron-deficient phthalocyanine equatorial ligand. A different trend has been observed for five-coordinate RCo(III)(chel) complexes: electron-rich equatorial systems seem to make the Co-C axial bond shorter. Kinetic data for the homolysis of RCo(III)Pc complexes (R = Me, Et) in dimethylacetamide are also reported. Homolysis of ethyl derivatives is faster. The Co-C bond dissociation energies (BDEs) for the pyridine adducts of the methyl and the ethyl derivative are 30 +/- 1 and 29 +/- 1 kcal/mol, respectively. The BDE for CH(3)CoPc(py) is considerably lower than that for MeCbl despite the very similar lengths of the axial bonds in the two complexes. The results of this work do not support any correlation between the Co-C bond length and the bond strength as defined by BDE.

UV photostability of metal phthalocyanines in organic solvents

Kinetic studies of photochemical reactions induced by UV radiation in solutions of metal phthalocyanines have been carried out to determine the factors which might have influenced the stability of photosensitized phthalocyanines. Complexes of the molecular type Mpc, M'(2)pc, and Lnpc(2) (where M = Li, Mg, Fe, Co, Zn, Pb; M'= Tl; Ln = rare earth; pc = phthalocyanine ligand, C(32)H(16)N(8)(2-)) were investigated in DMF, DMSO, and pyridine. Progressive decay of the phthalocyanine macrocycle due to absorption of UV light was observed. Phthalimide found in the final photolysis product may indicate some chemically bonded oxygen involved in the solid phthalocyanine material. Fluorescence lifetimes determined for the studied compounds (2.91-5.98 ns) have shown no particular relation to the stability of the excited macrocyclic system. The bonding strength of the photosensitized phthalocyanine moiety appears to rely on typical chemical factors, rather than on the properties of the excited states. Kinetics of the degradation process has proved to depend on the molecular structure of the complex and seems to be controlled by interactions of the macrocycle bridging nitrogen atoms with the solvent molecules. The use of electron acceptor solvents such as DMSO may enhance the molecular stability of phthalocyanines excited by UV radiation. Sandwich-type rare earth diphthalocyanines dissolved in DMSO displayed the highest photostability.