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DOI:10.1002/ejic.201400126

CLUSTERISSUE

Layered Salts with Iron HexadecachlorophthalocyanineAnions – The Formation of [{FeCl16Pc}2]3– Dimers Containing[FeICl16Pc(2–)]– and Diamagnetic [Fe0Cl16Pc(2–)]2–

Dmitri V. Konarev,*[a] Alexey V. Kuzmin,[b] Manabu Ishikawa,[c]

Yoshiaki Nakano,[c] Maxim A. Faraonov,[a] Salavat S. Khasanov,[b]

Akihiro Otsuka,[c] Hideki Yamochi,[c] Gunzi Saito,[d] andRimma N. Lyubovskaya[a]

Keywords: Molecular design / Iron / Phthalocyanines / Layered compounds / EPR spectroscopy / Magnetic properties

Iron hexadecachlorophthalocyanine (Cl16Pc) salts with a lay-ered arrangement of phthalocyanine (Pc) macrocycles wereobtained by the reduction of FeCl16Pc with sodium fluor-enone ketyl in the presence of PPNCl [PPN+: bis(triphenyl-phosphine)iminium cation] and TBABr (TBA+: tetrabutylam-monium cation). (PPN+)[(FeICl16Pc)–]·0.78C6H4Cl2·0.22C6H14

(1) contains π–π stacking columns formed by dimerized(FeICl16Pc)– anions. The side-by-side arrangement of neigh-boring columns results in the formation of a layered ironhexadecachlorophthalocyanine structure. (TBA+)3{[(FeCl16-Pc)2]3–} (2) contains hexagonal layers formed by [(FeCl16-Pc)2]3– dimers and separated by TBA+ cations. The dimersbear –3 charge and, according to optical and X-ray diffrac-tion data, consist of a [FeI(Cl16Pc)]– monoanion and a[Fe0(Cl16Pc)]2– dianion. These anions are bonded in the di-mer by a Fe–Fe bond of 2.899(4) Å length. It was shown that

IntroductionPhthalocyanines (Pc) form conducting and magnetic

compounds. Most of them were obtained by oxidation ofmetal-free and metal-containing phthalocyanines with io-dine or by electrochemical oxidation of metal–phthalocyan-ines and anionic complexes [MIIIPc(CN–)2]– (M = Co, Fe).The partially oxidized phthalocyanine macrocycles togetherwith a π–π-stacking columnar or layered arrangement leadto the semiconducting or quasi-one-dimensional metallicbehavior of these compounds (in some cases down to4 K).[1–5]

Anionic phthalocyanines with tetracoordinated metalshave not been investigated so much because of their high

[a] Institute of Problems of Chemical Physics RAS,Chernogolovka 142432, RussiaE-mail: konarev@icp.ac.ru

[b] Institute of Solid State Physics RAS, Chernogolovka,Moscow Region 142432, Russia

[c] Research Center for Low Temperature and Materials Sciences,Kyoto University,Kyoto, Sakio-ku 606-8501, Japan

[d] Faculty of Agriculture, Meijo University,1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468-8502, JapanSupporting information for this article is available on theWWW under http://dx.doi.org/10.1002/ejic.201400126.

Eur. J. Inorg. Chem. 2014, 3863–3870 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim3863

the negative charge in both anions is localized on the ironatoms to form FeI and Fe0, respectively, and no electrontransfer to the hexadecachlorophthalocyanine macrocycles isobserved. Magnetic data indicate the presence of only one S= 1/2 spin per [(FeCl16Pc)2]3– dimer. This result is in agree-ment with the formation of iron(I) and iron(0) hexadeca-chlorophthalocyanine anions, which have the iron atoms ind7 and diamagnetic d8 electron configuration, respectively.The spins of the iron(I) atoms are arranged in a hexagonalmanner and only weakly interact, which results in a Weisstemperature of –1 K because of the long distances betweenthem (�18 Å). Previously studied anionic salts with a colum-nar arrangement of [FeI(Cl16Pc)]– do not show EPR signalsfrom FeI. In contrast, salt 2 shows an intense EPR signal withmain components at g� = 2.249 and g� = 1.989, which arecharacteristic of FeI with d7 electron configuration.

air sensitivity.[6–14] Theoretical works predict metallic con-ductivity and even superconductivity for electron-dopedmetal phthalocyanines.[15] However, up to now, they areprepared mainly in the form of powders or films by dopingmetal phthalocyanines with alkali metals.[16–18] Thismethod does not provide single crystals. To extend the fieldof crystalline conducting anionic phthalocyanine com-pounds, new synthetic approaches for the preparation ofsingle crystals should be developed. An important condi-tion for the preparation of conducting phthalocyanine com-pounds is the formation of columns, layers, or 1D chainsfrom phthalocyanine anions. So far, the obtained anionicphthalocyanine compounds do not show noticeable π–πinteractions between the macrocycles.[6–11,14] Recently,compounds with iron(I)–phthalocyanine anions,(Me4P+)[(FeIPc)–](TPC) and (Me4P+)[(FeIPc)–](TBPDA)0.5,have been obtained (Me4P+: tetramethylphosphonium cat-ion; TPC: triptycene; TBPDA: N,N,N�,N�-tetrabenzyl-p-phenylenediamine). The [FeIPc]– anions form {[FeIPc]–}2

dimers packed in layers or 1D chains.[12] However, the over-lap integrals between the neighboring phthalocyanine di-mers are rather low [(0.1–0.2)�10–3], and unpaired elec-

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trons are localized on the iron atoms, which prevents highconductivity in these compounds. The use of bulkieriron(II) hexadecachlorophthalocyanes in the design of an-ionic assemblies provides a π–π-stacking columnar arrange-ment of phthalocyanine macrocycles in the crystalsof (PPN+)[(FeICl16Pc)–], (Ph3MeP+)2[(FeICl16Pc)–](Br–)·C6H4Cl2, and (PPN+)2[(FeCl16Pc)3

2–]·4C6H4Cl2 [PPN+:bis(triphenylphosphine)iminium cation, Ph3MeP+: tri-phenylmethylphosphonium cation]. These salts were ob-tained by zinc-dust reduction of FeIICl16Pc in the presenceof PPNCl or Ph3MePBr in o-dichlorobenzene, which wasfollowed by the precipitation of crystals through additionof hexane. The former two compounds and the last onecontain integer (–1) and partially (–0.66) charged iron hexa-decachlorophthalocyanines arranged in uniform, dimer-ized, and trimerized columns, respectively. High conductiv-ity is not realized in these salts, because the unpaired elec-trons are mainly localized on the iron atoms.[13] However,the significant magnitudes of the intermolecular overlap in-tegrals calculated for these compounds led us to examineanionic iron hexadecachlorophthalocyanines as usefulmodel compounds for the development of different packingmotifs of phthalocyanine anions in a crystal suitable for therealization of high conductivity.

In this work, two anionic iron hexadecachlorophthalocy-anines were obtained by using sodium fluorenone ketyl as areductant. (PPN+)[(FeICl16Pc)–]·0.78C6H4Cl2·0.22C6H14 (1)showed a layered arrangement of phthalocyanine anionsbecause of weak π–π interactions between dimerizedphthalocyanine columns. The stronger reducing power ofthe ketyl compared to that of zinc dust is expected to in-crease the negative charge on FeCl16Pc. In fact, (TBA+)3-[(FeCl16Pc)2

3–] (2) was obtained (TBA+: tetrabutylammo-nium cation), which contains diamagnetic (Fe0Cl16Pc)2–

dianions together with paramagnetic monoanionic(FeICl16Pc)– units. However, even in (Fe0Cl16Pc)2–, thephthalocyanine macrocycles preserved their –2 chargedclosed-shell electronic state. Here, we discuss the crystalstructure as well as the optical and magnetic properties of2 to prove this conclusion.

Results and Discussion

1. Synthesis

Both salts, (PPN+)[(FeICl16Pc)–]·0.78C6H4Cl2·0.22C6H4Cl2 (1) and (TBA+)3[(FeCl16Pc)2

3–] (2), were ob-

Figure 1. (a) View on the iron hexadecachlorophthalocyanine layers formed by the [FeICl16Pc(2–)]– anions in 1. Numbers s1–s3 show thetypes of overlapping modes for Table 1. (b) View along the phthalocyanine layers in 1, which shows that they are surrounded by thePPN+. Disordered C6H4Cl2 and hexane molecules are not shown. Three disordered phenyl substituents of PPN+ are shown in theirmajorly occupied orientation. Carbon is brown, nitrogen is blue, phosphorus is orange, chlorine is green.

Eur. J. Inorg. Chem. 2014, 3863–3870 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim3864

tained by the reduction of FeIICl16Pc with an excess of so-dium fluorenone ketyl in the presence of organic cations.Because sodium fluorenone ketyl is essentially a strongerreductant than zinc dust, iron(II) hexadecachlorophthalo-cyanine is stronger reduced in 1 and 2, which leads to –1and –1.5 charge per phthalocyanine, respectively. In case ofzinc-dust reductant, the phase (PPN+)2[(FeCl16Pc)3

2–]·4C6H4Cl2 is mainly formed, which a formal charge of –0.66on phthalocyanine, whereas the salt (PPN+){[FeICl16Pc]–}with a charge of –1 on phthalocyanine is formed as an ad-mixture only.[13]

2. (PPN+){(FeICl16Pc)–}·0.78C6H4Cl2·0.22C6H14 (1)

2.1. Crystal Structure of 1

The main structural motif of 1 is the formation of π–πstacking columns arranged along the a axis (Figure 1, a).The phthalocyanines are weakly dimerized in these col-umns, because the interplane distance in the pair (3.378 Åat s1) is shorter than that between the pairs (3.446 Å at s2).The phthalocyanines are only slightly shifted in the pairs insuch a way that the pyrrole nitrogen atom of one FeCl16Pcunit in the pair weakly coordinates to the iron(I) atom ofneighboring complex with a Fe···N distance of 3.154 Å. Asa result, the iron(I) atom of each FeCl16Pc is displaced outof the 24-atom Pc plane by 0.06 Å towards nitrogen atoms.This type of interaction is characteristic of the salts withiron(I) phthalocyanine and iron(I) hexadecachlorophthalo-cyanine anions.[12,13] Because of a slight shift of the phthalo-cyanines in the pairs, the distance between the iron(I) atomsis only 3.63 Å. Phthalocyanines from the neighboring pairsare essentially stronger shifted in the columns relative toeach other, which leads to a 6.96 Å distance between theiron(I) atoms. In this case, the chlorine atom of a neigh-boring phthalocyanine is located close to the iron(I) atoms(Fe···Cl distance of 3.62 Å). The average length of the equa-torial Fe–N bonds of 1.924(3) Å is close to those in other(FeICl16Pc)– salts [1.927(2)–1.930(2) Å].[13] The phthalocy-anine macrocycles in 1 have a saddle-like conformation,which provides the displacement of the tetrachlorophenyl-ene groups out of the molecular 24-atom Pc plane. Similarconformations were found for other (FeICl16Pc)– anions.[13]

Each pair of Fe–phthalocyanine molecules is surroundedby six PPN+ cations (Figure 1, b), which form multipleshort H,C(PPN+)···C,N[(FeICl16Pc)–] contacts. Neverthe-

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Table 1. Overlap integrals calculated for 1 and 2 (labeled according to Figures 1, a and 2 for 1 and according to Figures 3 and 4 for 2).

Overlap integrals (10–3)

Overlap integrals HOMO–HOMO[a] LUMO–LUMO LUMO–NLUMO NLUMO–NLUMO

(PPN+)[(FeICl16Pc)–]· s1 4.7 1.5 2.2 –8.80.78C6H4Cl2·0.22C6H14 (1) 150 K

s2 9.2 0.7 5.5 1.3s3 0.3 0 0 0.2

(TBA+)3[(FeCl16Pc)23–] (2) 100 K s1 3.8 0.3 –9.1 –0.8

s2 0.2 –0.2 0.1 0s3 0 0 0 0s4 0.1 –0.1 0 0.1s5 0 0.1 0 0s6 0.1 –0.1 0 0

[a] HOMO corresponds to the phthalocyanine π-HOMO in the electronic state of [FeICl16Pc(2–)]–.

less, the phthalocyanine columns are arranged quite closeto each other and form short intercolumn Cl···Cl contactsof 3.30 Å. Moreover, because of the noticeably shiftedphthalocyanine pairs in the columns and their close ar-rangement, weak π–π interactions exist between phthalocy-anines from the neighboring columns (Figure 1, a). This al-lows the formation of layers from phthalocyanine columns.The iron(I) atoms of (FeICl16Pc)– units from neighboringcolumns are locate far from each other, and the shortestFe···Fe distance is of 19.57 Å.

To evaluate the intermolecular interactions, the intermo-lecular overlap integrals were calculated on the basis of thesingle-crystal X-ray diffraction data for frontier-HOMOand LUMO and next-LUMO (NLUMO) orbitals, whichmainly consist of phthalocyanine π orbitals under theapproximation of the extended Hückel method,[19,20]

(Table 1).The values of the overlap integrals depend strongly on

the type of orbitals. The interaction between the phthalocy-anines in the pairs (integral s1, Figure 2, a) is largest forHOMO–HOMO and NLUMO–NLUMO orbitals, whereasthe interaction between phthalocyanines from neighboringpairs (integral s2, Figure 2, b) is largest for HOMO–HOMO and LUMO–NLUMO orbitals. The interaction be-tween phthalocyanines from the neighboring columns (inte-gral s3, Figure 2, c) is non-zero for HOMO–HOMO andNLUMO–NLUMO orbitals. Because the interaction isstrong within the phthalocyanine columns and also betweenphthalocyanines from the neighboring columns, salt 1 canbe considered a layered compound. However, similarly topreviously studied (FeICl16Pc)– salts,[13] the localization of

Figure 2. Types of overlapping between the (FeICl16Pc)– anions in 1. Labels from s1 to s3 are given according to Table 1. Carbon isbrown, nitrogen is blue, and chlorine is green.

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unpaired spins on the metal centers prevents high conduc-tivity.

3. (TBA+)3[(FeCl16Pc)23–] (2)

3.1. Crystal Structure of 2

There are three TBA+ cations per two crystallographi-cally independent FeCl16Pc molecules, which form[(FeCl16Pc)2]3– dimers bonded by a Fe···Fe bond of2.899(4) Å (Figure 3). This type of bonding is for the firsttime observed in anionic iron phthalocyanines, whereasin previously studied structures only nitrogen atoms ofneighboring phthalocyanines are weakly coordinated to theiron(I) atoms with Fe···N distances of 2.98–3.34 Å.[12,13]

The Fe–Fe bonding provides short interplane Pc distancesin the dimers (3.22 Å) and is accompanied by a 0.16 Å dis-placement of the iron atoms from the 24-atom Pc planetowards the neighboring iron atoms. The phthalocyaninesin the dimers are rotated relative to each other around theFe–Fe bond by about 50°. Because 2 contains three TBA+

cations per (FeCl16Pc)2 dimer, the total charge of the dimeris –3. In this case, one phthalocyanine can be in amonoanionic state and another phthalocyanine can be in adianionic state or the –3 charge can be equally distributedover two phthalocyanines, which would provide a charge of–1.5 for each unit. The presence of two crystallographycallyindependent phthalocyanines within the dimer and a strongdifference in their geometry points to the existence of twodifferently charged phthalocyanines. First, the phthalocyan-ines have a slightly different length of the average equatorial

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Fe–N bonds [1.915(16) and 1.932(16) Å], but this is withinthe experimental error for the lengths of these bonds. Thephthalocyanine with shorter Fe–N bonds has a saddle-likeconformation, whereas the phthalocyanine with longer Fe–N bonds has a concave conformation. The surrounding ofthese phthalocyanines is also different. One TBA+ cation islocated close to the iron atom of the phthalocyanine withshorter Fe–N bonds [the Fe···N(TBA+) distance is 4.41 Å].

Figure 3. (a) Cation surrounding of one [(FeCl16Pc)2]3– dimer in 2;view of the [(FeCl16Pc)2]3– dimer along the Fe–Fe bond (b) andphthalocyanine planes (c). s1 marks the overlapping mode forTable 1. Only majorly occupied orientations of the alkyl substitu-ents of TBA+ are shown. Carbon is brown, nitrogen is blue, andchlorine is green.

Figure 4. (a) View of the hexagonal phthalocyanine layers con-sisting of [{FeCl16Pc}2]3– dimers; (b) view along the phthalocyaninelayers arranged parallel to the ac plane. s2–s6 mark overlappingmodes for Table 1. Carbon is brown, nitrogen is blue, and chlorineis green.

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Two other TBA+ cations are closer to another phthalocyan-ine and have essentially longer Fe···N(TBA+) distances of6.56 and 7.04 Å. Thus, the tendency of Fe–N bond lengths,the strict differences in the molecular shape, and the ar-rangement of the nearby located cations points to the coex-istence of differently charged FeCl16Pc units. The differ-ences in the Fe–N bond lengths do not allow to distinguishmono- and dianions of FeCl16Pc.[6] However, the saddle-like conformation of the Pc macrocycle is characteristic ofthe (FeICl16Pc)– monoanions in previously studied salts[13]

and in 1. The charge disproportionation feature is also sup-ported by the optical spectra and magnetic data discussedin the following sections.

On the whole, 2 has a layered structure, in which hexago-nal phthalocyanine layers consisting of [(FeCl16Pc)2]3– di-mers (Figure 4, b) are separated by TBA+ layers. The inter-molecular overlap integrals for 2 were calculated by usingthe extended Hückel method[22,23] on the basis of single-crystal X-ray diffraction data. The interactions between theFeCl16Pc skeletons were evaluated by overlap integralsamong the frontier HOMO, frontier LUMO, and NLUMOorbitals (Table 1). The overlap integrals are labeled accord-ing to Figures 3 and 4. Only the face-to-face s1 interactionis effective enough for all types of orbitals. Whereas thissystem is a layered system from the viewpoint of the pack-ing motif of the FeCl16Pc units, the weak side-by-side s2–s6 interactions (Table 1) along with the long distances be-tween the iron centers (�18 Å) inhibit the magnetic interac-tions between the units.

3.2. UV/Visible-NIR Spectrum of 2

It was found[13] that the metal centers in the (FeCl16Pc)–

monoanions are iron(I) atoms, and no electron transferfrom these atoms to the phthalocyanine macrocycles is ob-served. The estimated degree of electron density transfer tothe phthalocyanine macrocycles is less than 1%. Potentially,upon the formation of the (FeCl16Pc)2– dianions, the secondelectron can be localized on the iron atoms to form[Fe0Cl16Pc(2–)]2–, or it can be transfered to the phthalocy-anine macrocycles to form [FeICl16Pc(3–)]2–. The formationof negatively charged phthalocyanine macrocycles in thesalts with radical anions of metal-free phthalocyanine(H2Pc·–) and some metal(II) phthalocyanines is ac-companied by the appearance of an intense band in theNIR range[9,21] [for example, in the spectrum of

Figure 5. Spectra of the (H2Pc·–)(TOA+)·C6H4Cl2 salt (a) withmetal-free phthalocyanine radical anions,[9] salt 2 (b), and parentFeIICl16Pc (c) in KBr pellets.

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(H2Pc·–)(TOA+)·C6H4Cl2 (TOA+ is the tetraoctylammo-nium cation) this band is observed at 1024 nm, Figure 5, a].The spectrum of salt 2 is shown in Figure 5 (b). It containsbands in the visible range at 800, 676, 542, and 328 nm.The low-energy absorption band in the NIR range is absentin the spectrum of 2. This is the evidence that no electrontransfer from the iron atoms to the phthalocyanine macro-cycles occurs and that [Fe0Cl16Pc(2–)]2– dianions withiron(0) atoms are formed. Bands at 800 and 542 nm wereobserved in the spectra of salts with [FeICl16Pc(2–)]–

monoanions,[13] whereas the band at 676 nm is reproducedin the spectrum of neutral FeIICl16Pc, which has a maxi-mum at 686 nm (Figure 5, c). Thus, the UV/Vis-NIR spec-trum of 2 also supports the formation of [FeICl16Pc(2–)]–

monoanions and [Fe0Cl16Pc(2–)]2– dianions with iron(I,0)atoms. A weak band in the spectrum of 2 in the NIR range(Figure 5, b) at 1400 nm can be attributed to a charge trans-fer in the [(FeCl16Pc)2]3– dimers.

3.3. Magnetic Properties of 2

The magnetic properties of 2 were analyzed by SQUIDand EPR techniques. The effective magnetic moment of 2is 1.69 μB per formula unit at 300 K (Figure 6, a). Thatcorresponds to the presence of one S = 1/2 spin per[(FeCl16Pc)2]3– dimer. This spin originates from the[FeICl16Pc(2–)]– monoanions, because the iron(I) atomshave d7 electron configuration with a S = 1/2 ground state.The [Fe0Cl16Pc(2–)]2– dianions are diamagnetic and do notcontribute to the magnetic moment, which is in agreementwith the diamagnetic d8 electron configuration for theiron(0) atoms. It should be noted that an electron transferfrom the iron(0) atoms to the phthalocyanine macrocycleswould strongly increase the magnetic moment, becauseparamagnetic iron(I) and a phthalocyanine radical anion(both have S = 1/2 spin state) would form as a result ofsuch an electron transfer in the diamagnetic {Fe0Cl16Pc-(2–)}2– units. The magnetic behaviour of 2 can be describedwell by the Curie–Weiss law with a Weiss temperature ofonly –1 K (Figure 6, b), which shows the absence of notice-able magnetic intraction between the [(FeCl16Pc)2]3– dimersbecause of the long distances between the iron(I) atoms.The magnetic moment is nearly temperature-independentdown to 12 K. It increases slightly below 12 K and drops

Figure 6. Temperature dependencies of the effective magnetic moment (a) and reciprocal molar magnetic susceptibility (b) for polycrystal-line 2.

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below 10 K, which is most probably due to weak antiferro-magnetic interaction of spins manifested at low tempera-tures.

The EPR spectrum of 2 at 300 K is shown in Figure 7.There are a relatively intensive component at g� = 2.249, aless prominent component at g� = 1.989, and a number oflower-intensity lines. The spectrum only slightly changeswhen the temperature decreases down to 100 and 4 K (seeSupporting Information, Figure S2). A similar spectrum of[FeIPc]– was observed in the case of the electrochemical re-duction of FeIIPc in pyridine (with hyperfine splitting frompyridine) and chemical reduction of FeIIPc in THF.[22,23]

The EPR spectrum of 2 (Figure 7) is similar in shape andparameters to those of FeI porphyrins and corresponds tothe electron configuration of FeI: (dxy)2(dxz,dyz)4(dz2)1.[24–26]

In addition to the major components with g� = 2.249 andg� = 1.989, split and weak signals are also observed in themagnetic field from 292 up to 322 mT (the signal separationvaries in the range 2.1–3.4 mT at 300 K, Figure 7). Suchsplitting can be attributed to the hyperfine interaction of anunpaired spin from FeI with phthalocyanine nitrogenatoms. However, because of the anisotropy of these interac-tions and a possible overlapping of the lines, the simulationof these spectra is almost impossible. The appearance ofsuch lines was observed upon the reduction of FeIIPc bysodium in THF.[27] The iron(0) atoms bonded to the para-magnetic iron(I) centers most probably cannot split theEPR signal due to the hyperfine interactions, since iron hasa non-magnetic nucleus. Another possible reason for theappearance of weak components in the 292–322 mT range

Figure 7. EPR spectrum of polycrystalline 2 measured under anaer-obic conditions at 300 K.

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is the strong asymmetry of the g� component of the EPRsignal, which are due to the polycrystallinity of the sample.Such effects were observed in some anionic fullerenecompounds containing paramagnetic [Cp*2Cr]+ or(MDABCO+)2MnIITPP cations, where [Cp*2Cr] is deca-methylchromocene and MDABCO+ is the N-methyldiazabi-cyclooctanium cation.[28,29] Narrow EPR signals with g-fac-tors close to 2.0035, which are characteristic of negativelycharged phthalocyanine macrocycles in H2Pc·�,[9] are notobserved, and this supports the absence of a charge transferfrom the iron(I,0) atoms to the phthalocyanine macrocycles.

3.4. Electronic State of the FeIICl16Pc and Its Anions

According to the calculations[30] FeIIPc has the electronconfiguration (b2g)2(a1u)2(a1g)2(1eg)2 with two unpaired elec-trons on the metal centered 1eg orbitals. The formation of(FeIPc)– anions is accompanied by the switching of the or-der of the a1g and 1eg orbitals and the filling of the a1g

orbital, which is also metal centered and has 86% contri-bution from the iron dz2 orbital. As a result, the [FeIPc]–

anions have a d7 electron configuration with a [(1eg)4(b2g)2-(a1g)1] ground state in agreement with the EPR spec-tra.[25–29] Our calculations show that perchlorination ele-vates the energy of the a1u orbital delocalized over theCl16Pc macrocycle (Figure 8). However, if the a1u orbitalbecomes the HOMO, we should observe a π spin (S = 1/2)in the EPR spectrum of the (FeICl16Pc)– monoanions. If ad spin is responsible for the EPR spectra, the situation mustbe similar to original FeIIPc, and the electronic state of[FeICl16Pc]– can be close to that of [FeIPc]–. Our opticaland EPR data support second possibility (Figure 8). The

Figure 8. Electron configuration for neutral [FeIICl16Pc(2–)], the[FeICl16Pc(2–)]– monoanions, and the [Fe0Cl16Pc(2–)]2– dianions.For distributions of MO145, MO146, MO147, and MO148 orbitalsover the phthalocyanine macrocycle see Supporting Information,Figure S3.

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(Fe0Cl16Pc)2– dianions should have a diamagnetic [(1eg)4-(b2g)2(a1g)2] ground state with d8 electron configuration forthe iron(0) atoms (Figure 8). This is also in agreement withthe experiment.

3.5. The Nature of the Fe–Fe Bond in the [(FeCl16Pc)2]3–

Dimers According to DFT Calculations

To gain a deeper insight into the nature of the Fe–Fe bondin the [(FeCl16Pc)2]3– dimers of 2, DFT investigations at theBLYP, B3LYP, CAM-B3LYP, and ωB97X-D levels oftheory were performed for the doublet state of the[(FeCl16Pc)2]3– dimer with and without point charges of +1at the position of nitrogen in tetrabutylammonium cations.The total energies and �S2� values are listed in the Sup-porting Information (Table S2), although the �S2� valuesof unrestricted methods are much larger than that of thepure doublet state (0.75), which indicates that the unrestric-ted wavefunctions are severely contaminated by the highermultiplet states. The frontier orbitals relevant to the Fe(1)–Fe(2) bond are shown in Figure 9. The SOMO, (HO–4)MO,and (HO–17)MO can be characterized as π-type Fe(1)–Fe(2) antibonding, σ-type bonding, and π-type bonding in-teractions, respectively, although the π-type bonding andantibonding interactions seem to be considerably weak. Tofurther evaluate the strength of the Fe(1)–Fe(2) bond, Wib-erg bond indices (WBIs)[31] were computed, which are sum-marized in Table S3. The WBIs of the Fe(1)–Fe(2) bond arein the range 0.10–0.36 depending on the calculation meth-ods. They are smaller than those of the corresponding Fe–N equatorial coordinative bonds (0.44–0.67), which con-firms that the Fe(1)–Fe(2) bond is effective but weaker thanthe Fe–N bonds. The charge and spin densities on the Fe

Figure 9. Selected frontier orbitals for the doublet state of the[(FeCl16Pc)2]3– dimer with point charges calculated at theROωB97X-D/LanL2DZ/6-31G(d) level of theory.

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atoms could not be explained reasonably by using presentDFT methods, because different levels of theory providedifferent distributions of charge and spin densities on theFe atoms.

Conclusions

Two new salts with iron hexadecachlorophthalo-cyanine anions were obtained as single crystals.(PPN+)[(FeICl16Pc)–]·0.78C6H4Cl2·0.22C6H4Cl2 (1) con-tains π–π stacking columns from dimerized [FeICl16Pc]–

anions, which form a layered phthalocyanine structure be-cause of the weak overlapping between phthalocyaninesfrom the neighboring columns. (TBA+)3[(FeCl16Pc)2

3–] (2)contains (FeCl16Pc)2

3– dimers bonded by Fe–Fe bonds. Thisis the first example of an anionic phthalocyanine com-pound simultaneously containing the [FeICl16Pc(2–)]–

monoanion and the [Fe0Cl16Pc(2–)]2– dianion. In bothanions, there is no electron transfer from the iron(I,0) atomsto the phthalocyanine macrocycles. Magnetic data show thepresence of only one S = 1/2 spin per (FeCl16Pc)2

3– dimerand, correspondingly, the diamagnetic ground state for the[Fe0Cl16Pc(2–)]2– dianions, in which the iron(0) atoms haved8 electron configuration. The spins on the iron(I) atomsare arranged in a hexagonal manner and only weakly inter-act because of the long distances between them. The EPRspectrum of the (FeICl16Pc)– monoanions was observed forthe first time. It has main components at g� = 2.249 and g�

= 1.989, which are characteristic of FeI with a d7 electronconfiguration.

Experimental SectionMaterials: FeIICl16Pc (80%), PPNCl (97 %), and TBABr (99%)were purchased from Aldrich. Sodium fluorenone ketyl was pre-pared as described elsewhere.[32] All manipulations for the synthesesof 1 and 2 were carried out in a MBraun 150B-G glove box witha controlled atmosphere, and the content of H2O and O2 was lessthan 1 ppm. Solvents were purified under an argon atmosphere. o-Dichlorobenzene (C6H4Cl2) was distilled from CaH2 under reducedpressure, and hexane was distilled from Na/benzophenone. Thecrystals of 1 and 2 were stored in a glove box. KBr pellets for themeasurement of IR and UV/Visible-NIR spectra of 2 were alsoprepared in a glove box. EPR and SQUID magnetic measurementswere performed on a sample (10 mg) of polycrystalline 2 sealed in2 mm quartz tubes under 10–5 Torr.

Synthesis: FeIICl16Pc (40 mg, 0.0352 mmol), an excess of PPNCl(50 mg, 0.0871 mmol), and more than two molar equivalents ofsodium fluorenone ketyl (16 mg, 0.079 mmol) were heated in o-dichlorobenzene (16 mL) at 100 °C for 2 h. The color of the solu-tion changed from pale green to deep-violet, and FeIICl16Pccompletely dissolved. Then it was cooled down to room tempera-ture and stirred for two more hours. The final deep-violet solutionwas filtered in a 50 mL glass tube of 1.8 cm diameter with a groundglass plug, and hexane (30 mL) was layered over the solution. Thecrystals of the salts precipitated during 2 months. The solvent wasdecanted from the crystals, and they were washed with hexane(yield 54%). The analysis of the obtained crystals under a micro-scope in a glove box showed the presence of two phases. Thin,

Eur. J. Inorg. Chem. 2014, 3863–3870 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim3869

nearly transparent, brown-black plates were attributed accordingto their unit-cell parameters to previously described (PPN+)-[(FeICl16Pc)–],[13] whereas rather thick, rhombic crystals were foundto belong to a new phase. The composition of the rhombic crystalswas determined by single-crystal X-ray diffraction analysis{(PPN+)[(FeICl16Pc)–]·0.78C6H4Cl2·0.22C6H14 (1)}.

FeIICl16Pc (40 mg, 0.0352 mmol), an excess of TBABr (50 mg,0.155 mmol), and more than two molar equivalents of sodium fluor-enone ketyl (16 mg, 0.079 mmol) were heated in o-dichlorobenzene(16 mL) at 100 °C during 2 h. The solution color changed fromslightly green to deep-violet, and FeIICl16Pc completely dissolved.Then, it was cooled down to room temperature and stirred for twomore hours. The final deep-violet solution was filtered in a 50 mLglass tube, and hexane (30 mL) was layered over the solution. Thecrystals of the complexes precipitated during 1.5 months. The sol-vent was decanted from the crystals, and they were washed withhexane (yield 34%). The analysis of the obtained crystals under amicroscope in a glove box showed the presence of only one phase.The crystals were thick rhombuses of dark gold color. The compo-sition of the crystals, determined from single-crystal X-ray diffrac-tion data, was (TBA+)3[(FeCl16Pc)2

3–] (2). Several crystals testedfrom the synthesis had the same unit-cell parameters, which provedthe presence of only one crystal phase.

X-ray Crystal Structure Determination: X-ray diffraction data for 1were collected on an Oxford diffraction “Gemini-R” CCD dif-fractometer with graphite-monochromated Mo-Kα radiation at lowtemperatures using an Oxford Instrument Cryojet cooler. Experi-mental data were processed using CrysAlisPro software, OxfordDiffraction Ltd. X-ray diffraction data for 2 were collected on aBruker Smart Apex II CCD with graphite monochromated Mo-Kα

radiation using a Japan Thermal Engineering Co. cooling systemDX-CS190LD. Raw data reduction to F2 was carried out usingBruker SAINT.[33] The structures were solved by a direct methodand refined by a full-matrix least-squares method against F2 usingSHELX-2013.[34] Non-hydrogen atoms were refined in the aniso-tropic approximation. Positions of hydrogen atoms were calculatedgeometrically and refined by the “riding” model with Uiso = 1.2Ueq

of the connected non-hydrogen atom or as ideal CH3 groups withUiso = 1.5Ueq.

Crystallographic Data for 1: C74H36.2Cl17.56FeN9P2, Mr =1791.55 gmol–1, black rhombic plates, triclinic, P1, a = 9.810(1) Å,b = 17.703(1) Å, c = 21.104(1) Å, α = 102.097(4)°, β = 102.612(7)°,γ = 94.408(7)°, V = 3468.2(5) Å3, Z = 2, dcalcd. = 1.680 gcm–3, μ =0.991 mm–1, F(000) = 1759, T = 150.0(1) K, max. 2θ = 59.662°,Rint = 0.0567, 34066 reflections collected, 16668 independent; R1

= 0.0638 for 11235 observed reflections [� 2σ(F)] with 317 re-straints and 885 parameters; wR2 = 0.1734 (all data); final GoF =1.048.

Crystallographic Data for 2: C112H108Cl32Fe2N19, Mr =2966.27 gmol–1, dark gold plate, monoclinic, P 21/n, a =18.635(2) Å, b = 21.797(3) Å, c = 29.969(4) Å, β = 95.454(1)°, V =12118(3) Å3, Z = 4, dcalcd. = 1.626 gcm–3, μ = 1.004 mm–1,F(000) = 6036, T = 100(2) K, max. 2θ = 43.11°, Rint = 0.0682,40806 reflections collected, 13939 independent; R1 = 0.1461 for8674 observed reflections [� 2σ(F)] with 1380 restraints and 1605parameters; wR2 = 0.3889 (all data); final GoF = 1.055.

CCDC-982157 (for 1) and -983511 (for 2) contain the supplemen-tary crystallographic data for this paper. These data can be ob-tained free of charge from The Cambridge Crystallographic DataCentre via www.ccdc.cam.ac.uk/data_request/cif.

Disorder in the Crystal Structures of 1 and 2: Salt 1 contains onecrystallographically independent, ordered [FeICl16Pc]– anion and

www.eurjic.org FULL PAPER

the PPN+ cation. Three of six phenyl substituents of the PPN+

cation are disordered between two positions with occupancies of0.477(10)/0.523(10), 0.448(8)/0.552(8), and 0.679(8)/0.321(8). Thereare two positions occupied by solvent molecules. One position, oc-cupied by C6H4Cl2 molecules, only has an occupancy of 0.5. An-other position is shared by C6H4Cl2 and hexane molecules at a0.28/0.22 ratio. Because both positions of the solvent moleculesare in the inversion centers, all solvent molecules are statisticallydisordered between two orientations. Totally, 317 restraints wereused for the refinement of the crystal structure of 1. This numberof restraints results from the SHELXL instructions. The restraintsare given for the disordered C6H4Cl2 and hexane molecules as 5DFIX, 44 SAME/SADI, 21 FLAT, 180 SIMU, 66 ISOR, and 1SUMP instructions to keep the bond lengths and angles close toaverage values.

The X-ray diffraction experiment was carried out at 100 K. How-ever, no reflections were observed at high angles (dmin is 0.97 Å–1

and 2θ is only 43.11°). A similar behaviour was found for severalcrystals tested by X-ray diffraction from the synthesis. As a result,the (sinθ)/λ ratio and the bond precision are low, and the R1 andwR2 values are rather high enough for this compound. Neverthe-less, the structure of 2 is solved and refined stably with low residualelectron density. In spite of the low temperature of the experiment(100 K) and the slow cooling rate, several alkyl substituents of theTBA+ cations are disordered between two positions. Several mis-takes are shown in the CIF check as short intra H···H contactsbetween hydrogen atoms. These mistakes appear because of the dis-order of the alkyl substituents of TBA+, and in all cases, thesehydrogen atoms belong to different disordered parts of one alkylchain. In total, 1380 restraints are used for the refinement of thecrystal structure of 2. This number of restraints results from theSHELXL instructions. The restraints are given for the disorderedalkyl substituents of the TBA+ cations as 80 DFIX, 22 SAME/SADI, 509 DELU, 342 SIMU, 426 ISOR, and 1 SUMP instruc-tions to keep the bond lengths and angles close to average values.

Supporting Information (see footnote on the first page of this arti-cle): IR and EPR spectra, MO calculations and computational de-tails, calculated total energies, charge and spin densities, andWiberg bond indices.

Acknowledgments

This work was supported by the Russian Foundation for Basic Re-search (RFBR) (grant number 13-03-00769), by the Japan Societyfor the Promotion of Science (JSPS KAKENHI) (grant numbers23225005, 26288035), and by the Ministry of Education, Culture,Sports, Science and Technology, Japan (MEXT KAKENHI) (grantnumber 20110006). Y. N. is indebted to the Chubei Itoh Founda-tion. Theoretical calculations were partly performed at the Re-search Center for Computational Science, Okazaki, Japan.

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Received: January 30, 2014Published Online: May 7, 2014