Recent advances in the stereochemistry of metallotetrapyrroles

Conformational control of cofactors in nature - the influence of protein-induced macrocycle distortion on the biological function of tetrapyrroles

Tetrapyrrole-containing proteins are one of the most fundamental classes of enzymes in nature and it remains an open question to give a chemical rationale for the multitude of biological reactions that can be catalyzed by these pigment-protein complexes. There are many fundamental processes where the same (i.e., chemically identical) porphyrin cofactor is involved in chemically quite distinct reactions. For example, heme is the active cofactor for oxygen transport and storage (hemoglobin, myoglobin) and for the incorporation of molecular oxygen in organic substrates (cytochrome P450). It is involved in the terminal oxidation (cytochrome c oxidase) and the metabolism of H2O2 (catalases and peroxidases) and catalyzes various electron transfer reactions in cytochromes. Likewise, in photosynthesis the same chlorophyll cofactor may function as a reaction center pigment (charge separation) or as an accessory pigment (exciton transfer) in light harvesting complexes (e.g., chlorophyll a). Whilst differences in the apoprotein sequences alone cannot explain the often drastic differences in physicochemical properties encountered for the same cofactor in diverse protein complexes, a critical factor for all biological functions must be the close structural interplay between bound cofactors and the respective apoprotein in addition to factors such as hydrogen bonding or electronic effects. Here, we explore how nature can use the same chemical molecule as a cofactor for chemically distinct reactions using the concept of conformational flexibility of tetrapyrroles. The multifaceted roles of tetrapyrroles are discussed in the context of the current knowledge on distorted porphyrins. Contemporary analytical methods now allow a more quantitative look at cofactors in protein complexes and the development of the field is illustrated by case studies on hemeproteins and photosynthetic complexes. Specific tetrapyrrole conformations are now used to prepare bioengineered designer proteins with specific catalytic or photochemical properties.

Crystal structure of an unknown solvate of (piperazine-κN){5,10,15,20-tetra-kis-[4-(benzo-yloxy)phen-yl]porphyrinato-κ(4) N}zinc

The title compound, [Zn(C72H44N4O8)(C4H10N2)] or [Zn(TPBP)(pipz] (where TPBP and pipz are 5,10,15,20-tetra-kis-[4-(benzo-yloxy)phen-yl]porphyrinato and piperazine ligands respectively), features a distorted square-pyramidal coordin-ation geometry about the central Zn(II) atom. This central atom is chelated by the four N atoms of the porphyrinate anion and further coordinated by a nitro-gen atom of the piperazine axial ligand, which adopts a chair confirmation. The average Zn-N(pyrrole) bond length is 2.078 (7) Å and the Zn- N(pipz) bond length is 2.1274 (19) Å. The zinc cation is displaced by 0.4365 (4) Å from the N4C20 mean plane of the porphyrinate anion toward the piperazine axial ligand. This porphyrinate macrocycle exhibits major saddle and moderate ruffling deformations. In the crystal, the supra-molecular structure is made by parallel pairs of layers along (100), with an inter-layer distance of 4.100 Å while the distance between two pairs of layers is 4.047 Å. A region of electron density was treated with the SQUEEZE [Spek (2015 ▸). Acta Cryst. C71, 9-18] procedure in PLATON following unsuccessful attempts to model it as being part of disordered n-hexane solvent and water mol-ecules. The given chemical formula and other crystal data do not take into account these solvent mol-ecules.

Amino- and Hydroxytetraphenylporphyrins with Activity against the Human Immunodeficiency Virus

A series of amino- and hydroxytetraphenylporphyrin derivatives was found to have activity against the human immunodeficiency virus type 1 (HIV-1) in human peripheral blood mononuclear cells. Activity tends to be associated with increased hydrophilicity of the porphyrins for the porphyrins with one substituent on each phenyl ring but there is no clear pattern for the porphyrins with two substituents on each phenyl ring. The antiviral activity of certain porphyrins has been demonstrated in the absence of light, suggesting a non-photochemical process. Whereas only some of the porphyrins that inhibit HIV-1 in culture inhibit HIV-1 reverse transcriptase in a cell-free system, none of those tested inhibit DNA polymerase α.

Metalloporphines: Dimers and Trimers

Procedures for the purification and subsequent crystallization of the slightly soluble four-coordinate metallporphines, the simplest possible porphyrin derivatives, are described. Crystals of the porphine derivatives of cobalt(II), copper(II), platinum(II), and two polymorphs of zinc(II) were obtained. Analysis of the crystal and molecular structures shows that all except the platinum(II) derivative form an unusual trimeric species in the solid state. The isomorphous cobalt(II), copper(II), and one zinc(II) polymorph pack in the unit cell to form dimers as well as the trimers. Interplanar spacings between porphine rings are similar in both the dimers and trimers and range between 3.24 and 3.37 Å. Porphine rings are strongly overlapped with lateral shifts between ring centers in both the dimers and trimers with values between 1.52 and 1.70 Å or in Category S as originally defined by Scheidt and Lee. Periodic trends in the M-Np bond distances parallel those observed previously for tetraphenyl- and octaethylporphyrin derivatives.

Synthesis, FT-IR characterization and crystal structure of aqua-(5,10,15,20-tetra-phenyl-porphyrinato-κ(4) N)manganese(III) tri-fluoro-methane-sulfonate

In the title salt, [Mn(C44H28N4)(H2O)](CF3SO3) or [Mn(III)(TPP)(H2O)](CF3SO3) (where TPP is the dianion of 5,10,15,20-tetra-phenyl-porphyrin), the Mn(III) cation is chelated by the four pyrrole N atoms of the porphyrinate anion and additionally coordinated by an aqua ligand in an apical site, completing the distorted square-pyramidal coordination environment. The average Mn-N(pyrrole) bond length is 1.998 (9) Å and the Mn-O(aqua) bond length is 2.1057 (15) Å. The central Mn(III) ion is displaced by 0.1575 (5) Å from the N4C20 mean plane of the porphyrinate anion towards the apical aqua ligand. The porphyrinate macrocycle exhibits a moderate ruffling and strong saddle deformations. In the crystal lattice, the [Mn(III)(TPP)(H2O)](+) cation and the tri-fluoro-methane-sulfonate counter-ions are arranged in alternating planes packed along [001]. The components are linked together through O-H⋯O hydrogen bonds and much weaker C-H⋯O and C-H⋯F inter-actions. The crystal packing is further stabilized by weak C-H⋯π inter-actions involving the pyrrole and phenyl rings of the porphyrin moieties.

Crystal structure of (4-cyano-pyridine-κN){5,10,15,20-tetrakis[4-(benzoyloxy)phenyl]porphyrinato-κ(4) N}zinc-4-cyano-pyridine (1/1)

In the title compound, [Zn(C72H44N4O8)(C6H4N2)]·C6H4N2 or [Zn(TPBP)(4-CNpy]·(4-CNpy) [where TPBP and 4-CNpy are 5,10,15,20-(tetra-phenyl-benzoate)porphyrinate and 4-cyano-pyridine, respectively], the Zn(II) cation is chelated by four pyrrole-N atoms of the porphyrinate anion and coordinated by a pyridyl-N atom of the 4-CNpy axial ligand in a distorted square-pyramidal geometry. The average Zn-N(pyrrole) bond length is 2.060 (6) Å and the Zn-N(4-CNpy) bond length is 2.159 (2) Å. The zinc cation is displaced by 0.319 (1) Å from the N4C20 mean plane of the porphyrinate anion toward the 4-cyano-pyridine axial ligand. This porphyrinate macrocycle exhibits major saddle and moderate ruffling and doming deformations. In the crystal, the [Zn(TPBP)(4-CNpy)] complex mol-ecules are linked together via weak C-H⋯N, C-H⋯O and C-H⋯π inter-actions, forming supra-molecular channels parallel to the c axis. The non-coordinating 4-cyano-pyridine mol-ecules are located in the channels and linked with the complex mol-ecules, via weak C-H⋯N inter-actions and π-π stacking or via weak C-H⋯O and C-H⋯π inter-actions. The non-coordinating 4-cyano-pyridine mol-ecule is disordered over two positions with an occupancy ratio of 0.666 (4):0.334 (4).

Characterization of the mixed axial ligand complex (4-cyanopyridine)(imidazole)(tetramesitylporphinato)iron(iii) perchlorate. Stabilization by synergic bonding

The reaction of [Fe(TMP)(OClO[Formula: see text]], where TMP is the dianion of tetramesitylporphyrin, with a combination of a strong [Formula: see text]-acceptor ligand and a [Formula: see text]-donating imidazole can lead to the preparation of mixed-ligand complexes [Fe(Porph)(4-CNPy)(L)][Formula: see text] where L is imidazole itself or 1-acetylimidazole and 4-cyanopyridine is the strong [Formula: see text] acceptor ligand. The stability of the new mixed-ligand pair is the presumed result of synergic bonding between the two axial ligands. The molecular structure and other characterization of the new mixed axial ligand complex, [Fe(TMP)(4-CNPy)(HIm)]ClO4 is described. The axial ligands have a relative perpendicular arrangement with Fe–N(imidazole) = 1.945 Å and Fe–N(pyridine) = 2.021 Å. The average equatorial Fe–N[Formula: see text] distance is 1.963 Å, which is consistent with the S4-ruffled TMP core. Despite the relative perpendicular arrangement of axial ligands, the EPR spectrum of the complex is a rhombic signal and not a large gmax signal. The EPR g-values are [Formula: see text] 3.05, [Formula: see text] 2.07, and [Formula: see text] 1.22. A quadrupole doublet was seen in the Mössbauer spectrum with an isomer shift of 0.197 mm/s and quadrupole splitting of 1.935 mm/s. Two crystalline forms of [Fe(TMP)(4-CNPy)(HIm)]ClO4 have been characterized; the two forms differ only in the solvent content of the lattice. Crystal data for form A: [Formula: see text] 15.432 (12) Å, [Formula: see text] 20.696 (2) Å, [Formula: see text] 19.970 (5) Å, and [Formula: see text] 99.256 (14)[Formula: see text], monoclinic, space group P21/n, V [Formula: see text] 6295 (2) Å3, Z [Formula: see text] 4, formula FeCl3O4N8C[Formula: see text]H[Formula: see text], 8397 observed data, [Formula: see text] 0.086, [Formula: see text] 0.210, refinement on [Formula: see text]. Crystal data for form B: [Formula: see text]15.267 (3) Å, [Formula: see text]20.377 (6) Å, [Formula: see text] 19.670 (4) Å, and [Formula: see text] 98.14 (1)[Formula: see text], monoclinic, space group P[Formula: see text]/n, V = 6058 (4) Å3, Z = 4, formula C[Formula: see text]H[Formula: see text]Cl[Formula: see text]FeN8O4, 5464 observed data, [Formula: see text] 0.096, [Formula: see text] 0.112, refinement on F.

Time dependent DFT investigation of the optical properties of artificial light harvesting special pairs

Simulated absorption spectra of (ZnTriPP)₂DPB dimer in which Q band is enhanced 50 times for visibility.

Improved light absorbance does not lead to better DSC performance: studies on a ruthenium porphyrin–terpyridine conjugate

Despite having a good spectral response, a bis(tpy)ruthenium complex with peripheral porphyrin and phosphonate anchoring domains gives poor photoconversion efficiency due to a triplet–triplet energy transfer process.

Solid-state Porphyrin Interactions with Oppositely Charged Peripheral Groups

The crystallization and the crystal and molecular structure of a very slightly soluble electrostatically interacting pair of porphyrins is described. The tetra-anion 5,10,15,20-tetrakis-(4-sulfonatophenyl)-21,23H-porphyrin [H2TPPSO3]4- and the tetra-cation 5,10,15,20-tetra(N-methylpyridyl)21H,23H-porphyrin [H2TMePyP]4+ are found to form an alternating one-dimensional stack that is stabilised by electrostatic interactions between the porphyrin rings but also by π-π interactions between all substituted phenyl rings in the ensemble. The resulting interactions between the porphyrins is exceptionally tight.

Field-Induced Slow Magnetic Relaxation in a Mononuclear Manganese(III)-Porphyrin Complex

We report on a novel manganese(III)-porphyrin complex with the formula [Mn(III) (TPP)(3,5-Me2 pyNO)2 ]ClO4 ⋅CH3 CN (2; 3,5-Me2 pyNO=3,5-dimethylpyridine N-oxide, H2 TPP=5,10,15,20-tetraphenylporphyrin), in which the Mn(III) ion is six-coordinate with two monodentate 3,5-Me2 pyNO molecules and a tetradentate TPP ligand to build a tetragonally elongated octahedral geometry. The environment in 2 is responsible for the large and negative axial zero-field splitting (D=-3.8 cm(-1) ), low rhombicity (E/|D|=0.04) of the high-spin Mn(III) ion, and, ultimately, for the observation of slow magnetic-relaxation effects (Ea =15.5 cm(-1) at H=1000 G) in this rare example of a manganese-based single-ion magnet (SIM). Structural, magnetic, and electronic characterizations were carried out by means of single-crystal diffraction studies, variable-temperature direct- and alternating-current measurements and high-frequency and -field EPR spectroscopic analysis followed by quantum-chemical calculations. Slow magnetic-relaxation effects were also observed in the already known analogous compound [Mn(III) (TPP)Cl] (1; Ea =10.5 cm(-1) at H=1000 G). The results obtained for 1 and 2 are compared and discussed herein.

Coordination and acid-base properties of meso-nitro derivatives of β-octaethylporphyrin

Spectrophotometric method is used to study the acid-base and coordination properties of a series of porphyrins with a continuously increasing degree of macrocycle deformation resulting from the introduction of strong electron — withdrawing substituents: 2,3,7,8,12,13,17,18-octaethylporphyrin (1), 5-nitro-2,3,7,8,12,13,17,18-octaethylporphyrin (2), 5,15-dinitro-2,3,7,8,12,13,17,18-octaethylporphyrin (3), 5,10,15-trinitro-2,3,7,8,12,13,17,18-octaethylporphyrin (4), and 5,10,15,20-tetranitro-2,3,7,8,12,13,17,18-octaethylporphyrin (5). It is found that the values of total basicity constants obtained for the investigated compounds consistently diminish with an increase in the number of meso-substituents: 11.85 (1) < 10.45 (2) < 10.31 (3) < 10.23 (4) < 9.56 (5). The values of the combined acidity constants of porphyrins (4–5) obtained in acetonitrile-DBU system at 298 K are pKa = 10.90 and 10.40 respectively. The reaction of complex formation between the porphyrins and their dianionic forms with zinc acetate was studied. It is shown that two opposing factors, the steric and electronic effects of the substituents, change the acid-base and coordination properties of the above series of compounds.

Crystal structure of chlorido-(5,10,15,20-tetra-phenyl-porphyrinato-κ(4) N)manganese(III) 2-amino-pyridine disolvate

In the title compound, [Mn(C44H28N4)Cl]·2C5H6N2, the Mn(III) centre is coordinated by four pyrrole N atoms [averaged Mn-N = 2.012 (4) Å] of the tetra-phenyl-porphyrin mol-ecule and one chloride axial ligand [Mn-Cl = 2.4315 (7) Å] in a square-pyramidal geometry. The porphyrin macrocycle exhibits a non-planar conformation with major ruffling and saddling distortions. In the crystal, two independent solvent mol-ecules form dimers through N-H⋯N hydrogen bonding. In these dimers, one amino N atom has a short Mn⋯N contact of 2.642 (1) Å thus completing the Mn environment in the form of a distorted octa-hedron, and another amino atom generates weak N-H⋯Cl hydrogen bonds, which link further all mol-ecules into chains along the a axis.

Geometric and electronic structures of five-coordinate manganese(ii) “picket fence” porphyrin complexes

The X-ray structural investigation rationalized the variable axial ligand distances. EPR revealed five resonance positions and the simulations gave reasonable zero field splitting parameters.

Acid–base equilibria and coordination chemistry of the 5,10,15,20-tetraalkyl-porphyrins: implications for metalloporphyrin synthesis

Easy formation of metalloporphyrins from the doubly deprotonated porphyrin P²⁻ is reported.

Molecular structures and solvation of free monomeric and dimeric ferriheme in aqueous solution: insights from molecular dynamics simulations and extended X-ray absorption fine structure spectroscopy

CHARMM force field parameters have been developed to model nonprotein bound five-coordinate ferriheme (ferriprotoporphyrin IX) species in aqueous solution. Structures and solvation were determined from molecular dynamics (MD) simulations at 298 K of monomeric [HO-ferriheme](2-), [H2O-ferriheme](-), and [H2O-ferriheme](0); π-π dimeric [(HO-ferriheme)2](4-), [(H2O-ferriheme)(HO-ferriheme)](3-), [(H2O-ferriheme)2](2-), and [(H2O-ferriheme)2](0); and μ-oxo dimeric [μ-(ferriheme)2O](4-). Solvation of monomeric species predominated around the axial ligand, meso-hydrogen atoms of the porphyrin ring (Hmeso), and the unligated face. Existence of π-π ferriheme dimers in aqueous solution was supported by MD calculations where such dimers remained associated over the course of the simulation. Porphyrin rings were essentially coplanar. In these dimers major and minor solvation was observed around the axial ligand and Hmeso positions, respectively. In μ-oxo ferriheme, strong solvation of the unligated face and bridging oxide ligand was observed. The solution structure of the μ-oxo dimer was investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy. The EXAFS spectrum obtained from frozen solution was markedly different from that recorded on dried μ-oxo ferriheme solid. Inclusion of five solvent molecules obtained from spatial distribution functions in the structure generated from MD simulation was required to produce acceptable fits to the EXAFS spectra of the dimer in solution, while the solid was suitably fitted using the crystal structure of μ-oxo ferriheme dimethyl ester which included no solvent molecules.

Crystal structure of 5,10,15-triphenyl-20-(4,4,5,5-tetra-methyl-1,3,2-dioxaborolan-2-yl)porphyrin

In the title compound, C44H37BN4O2, the dihedral angle between the plane of the porphyrin macrocycle ring system [r.m.s. deviation = 0.159 (1) Å] and those of three phenyl rings are 66.11 (4), 74.75 (4) and 57.00 (4)°. The conformational distortion is characterized by a mixture of ruffled, saddle and in-plane distortion modes. In the crystal, the porphyrin mol-ecules are linked by C-H⋯π inter-actions into supra-molecular chains running along the a-axis direction. A pair of bifurcated N-H⋯(N,N) hydrogen bonds occur across the central region of the macrocycle.

(5-n-Butyl-10,20-diiso-butyl-porphyrin-ato)nickel(II)

The asymmetric unit of the title compound, [Ni(C₃₂H₃₆N₄)], contains two independent mol­ecules exhibiting an overall ruffled conformation of the porphyrin macrocycle and differing mainly in the positions of the methyl groups. The average Ni—N bond lengths are 1.912 (2) and 1.910 (2) Å in the two mol­ecules. The mol­ecules form a closely spaced lattice structure in which neighbouring porphyrins are oriented in a nearly perpendicular fashion to each other. The compound was prepared via nucleophilic substitution of (5,15-diiso­butyl­porphyrinato)nickel(II) with n-butyl­lithium.

Iron nitrosyl "natural" porphyrinates: does the porphyrin matter?

The synthesis and spectroscopic characterization of three five-coordinate nitrosyliron(II) complexes, [Fe(Porph)(NO)], are reported. These three nitrosyl derivatives, where Porph represents protoporphyrin IX dimethyl ester, mesoporphyrin IX dimethyl ester, or deuteroporphyrin IX dimethyl ester, display notable differences in their properties relative to the symmetrical synthetic porphyrins such as OEP and TPP. The N–O stretching frequencies are in the range of 1651–1660 cm^–1, frequencies that are lower than those of synthetic porphyrin derivatives. Mössbauer spectra obtained in both zero and applied magnetic field show that the quadrupole splitting values are slightly larger than those of known synthetic porphyrins. The electronic structures of these naturally occurring porphyrin derivatives are thus seen to be consistently different from those of the synthetic derivatives, the presumed consequence of the asymmetric peripheral substituent pattern. The molecular structure of [Fe(PPIX-DME)(NO)] has been determined by X-ray crystallography. Although disorder of the axial nitrosyl ligand limits the structural quality, this derivative appears to show the same subtle structural features as previously characterized five-coordinate nitrosyls.

The synthesis and characterization of three five-coordination {FeNO}₇ porphyrin derivatives based on natural porphyrin substitution patterns show that there are systematic differences compared to synthetic porphyrin derivatives with more symmetric substitution patterns. Characterization includes high-field Mössbauer spectroscopy and a crystal structure of the protoporphyrin IX dimethyl ester derivative.

Isomorphous free-base, Ni(ii)- and Cu(ii)-5,10,15,20-tetra(4-hydroxyphenyl)porphyrin nitrobenzene hexasolvates with tetragonal 3D hydrogen-bonded network structures

The crystal structures of 5,10,15,20-tetra(4-hydroxyphenyl)-21,23H-porphyrin nitrobenzene hexasolvate (1), 5,10,15,20-tetra(4-hydroxyphenyl)porphyrinatonickel(ii) and -copper(ii)nitrobenzene hexasolvates (2and3) are described.

Synthesis, crystal structures and spectroscopic characterization of Co(II) bis(4,4′-bipyridine) with meso-porphyrins α,β,α,β-tetrakis(o-pivalamidophenyl) porphyrin (α,β,α,β-TpivPP) and tetraphenylporphyrin (TPP)

The reaction of the starting materials [ Co II ( Porph )] (Porph = α,α,α,α-tetrakis(o-pivalamidophenyl)porphyrin (TpivPP) and the meso-tetraphenylporphyrin (TPP)) with an excess of 4,4′-bipyridine in chlorobenzene leads to the creation of two cobalt(II) derivatives: [ Co II (α,β,α,β- TpivPP )(4,4′- bpy )2]· C 6 H 5 Cl · C 6 H 14(1) and [ Co II ( TPP )(4,4′- bpy )2]·2 bpy (2). These compounds have been characterized by UV-vis, IR, 1 H NMR and MALDI-TOF spectroscopy. The proton NMR spectra of (1) and (2) clearly indicated that these derivatives are paramagnetic while the UV-vis data confirmed creation of a new six-coordinated or penta-coordinated Co ( II )-meso-porphyrin complexes by displaying red shifted Soret bands. The determined X-ray structures of (1) and (2) show that in the solid state these species are considered as coordination polymers which consist of 1D chains of alternating [ Co II ( Porph )] and 4,4′-bipyridine molecules located at the axial positions of the cobalt(II) coordination sphere. The coordination geometry of Co ( II ) in (1) and (2) is octahedral; the porphyrin (TpivPP or TPP) acts as a tetradentate chelating ligand with four nitrogen atoms from the pyrrole moieties occupying the equatorial positions along the porphyrin core. The N -donor atoms of the 4,4′-bipyridine create the axial ligands. It is noteworthy that for complex (1) the starting porphyrin is the α,α,α,α-TpivPP atropisomer but the final coordination polymer contains the α,β,α,β-TpivPP conformer.

5,15-Bis(4-pentyl-oxyphen-yl)porphyrin

In the title compound, C₄₂H₄₂N₄O₂, the complete molecule is generated by a crystallographic inversion centre. The porphyrin system exhibits a near planar macrocycle conformation with an average deviation from the least-squares plane of the 24 macrocycle atoms of 0.037 (5) Å. The phenyl ipso C atoms are positioned above and below the porphyrin plane by 0.35 (1) Å and the macrocycle shows evidence of in-plane rectangular elongation with N⋯N separations of 3.032 (5) and 2.803 (5) Å. Two intramolecular N—H⋯N hydrogen bonds occur.

Aqua-(5,10,15,20-tetra-phenyl-porphyrin-ato-κ(4) N)cadmium(II)-18-crown-6 (1/1)

The title compound, [Cd(C44H28N4)(H2O)]·(C12H24O6), was made by the reaction of the [Cd(TPP)] with an excess of 18-crown-6 in chloro-benzene (where TPP is tetra-phenyl-porphyrinate). The Cd(II) cation is chelated by a TPP anion and coordinated by a water mol-ecule in a distorted N4O square-pyramidal geometry, the Cd(II) cation being displaced by 0.7533 (9) Å from the mean plane of four N atoms of TPP anion. The porphyrin core presents a significant distortion, the maximum atomic deviation from the 24-atom mean plane is 0.1517 (2) Å. The 18-crown-6 mol-ecule is linked with the Cd(II) complex via classical O-H⋯O hydrogen bonds. In the crystal, weak C-H⋯π inter-actions link the complex and 18-crown-6 mol-ecules into a three-dimensional supra-molecular architecture.

[5,15-Bis(2-methyl-prop-yl)porphyrinato]nickel(II)

The title compound, [Ni(C(28)H(28)N(4))], crystallizes with two independent mol-ecules in the unit cell, one of which is located on an inversion center. Both macrocycles exhibit a planar conformation with average deviation from the least-squares-plane of the 24 macrocycle atoms of Δ24 = 0.043 Å for the first mol-ecule and 0.026 Å for the mol-ecule located on an inversion center. The average Ni-N bond lengths are 1.955 (2) and 1.956 (2) Å in the two mol-ecules. The mol-ecules form π-π dimers of inter-mediary strength with a mean plane separation of 3.36 (2) Å.