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MMHMO63OP Microreview
Coordination Structures of Metalloporphyrins with N-Containing Cations in Complexes with Fullerenes
Dmitri V. Konarev,@ and Rimma N. Lyubovskaya
Institute of Problems of Chemical Physics of Russian Academy of Sciences, Chernogolovka, Moscow region, 142432, Russia @Corresponding author E-mail: [email protected]
nopfoupMHbl Porphyrins
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MMHMO63OP Microreview
Ionic complexes of fullerenes with metalloporphyrins attract much attention due to promising photophysical and magnetic properties. We design these complexes using the coordination bonding between metalloporphyrins and N-containing cations (M-N(L+) bonds). In this review we discuss 1). C6g'~ C6g2- and C ~ complexes with (MDABCO+)2-M"TPP units (MDABCO+ is N-methyldiazabicyclooctane cation, M = Zn, Co, Mn, Fe, 1-6) having six-coordinated metal centres; 2). C6g- complexes with (MDABCO+)-M"TMPP (M = Zn (7), Co (8)) and (MDABCO+)-M"OEP units (M = Zn, Co, Mn, Fe, 9-12) having five-coordinated metal centres. We discuss synthesis of the complexes, structures of metalloporphyrins coordinatively bound with N-containing cations formed in the complexes with fullerenes, and the magnetic properties of the complexes.
Keywords: Octaethyl- and tetraphenylporphyrins, complexes, fullerenes, coordination.
Introduction
Fullerenes form variety of molecular and ionic complexes with metalloporphyrins.[1-6] These complexes attract much attention since porphyrin molecules are able to form complexes not only with fullerenes but with variety of endometallofullerenes and chemically modified fullerenes.[17-9] That allows to investigate the molecular and electronic structures of new fullerene families. Design of ionic complexes of fullerenes and metalloporphyrins is a promising approach to study fullerenes in a charged state including anions of endometallofullerenes and chemically modified fullerenes. The other interesting possibility of this approach is the preparation and study of new a-bonded structures from negatively charged fullerenes. Since fullerene
anions have strong tendency for dimerization, polymerization or coordination lead to the new types of fullerene dimers, polymers and coordinatively bound units.[10]
Since fullerenes are relatively weak acceptors (in compare with planar n-acceptors tetracyanoethylene or tetracyanoquinodimethane)[11] most of fullerene complexes with metalloporphyrins have only neutral ground state.[1-5] We developed new approach for the preparation of ionic fullerene-porphyrin complexes which uses the relatively weak coordination bonding between metalloporphyrins and ^-containing cations (the M-N(L+) bonds).[12-17]
For example, ^-methyldiazabicyclooctane cation (MDABCO+, Scheme 1) has a free nitrogen atom capable to coordinate to different metalloporphyrins. Since MDABCO+ can be a counter cation for the fullerene anions, neutral
OMe
MnTPP
N MDABCO
0Me~O
OMe
OMe MnTMPP
Scheme 1.
metalloporphyrin molecules are involved into the ionic complexes with fullerenes in form of positively charged coordination assemblies: {(MDABCO+)n-MIIporphyrin}-•(C60-)n (n = 1 and 2). This approach allows to obtain ionic supramolecular complexes with fullerenes containing dia-magnetic singly bonded (C70-)2 dimers in {(MDABCO+)2-•MnnTPP}-{(MDABCO+)2-{(C70-)2}2-(Solvent)x (TPP is tetraphenylporphyrin, Scheme 1)[12] as well as unusual (C60-)2 dimers bonded by two single bonds having biradical state at room temperature in {(MDABCO+)-MnTMPP}2-(C60-)2-•(Solvent)x (M = Co11, Zn; TMPP is tetrakis(4-methoxyphenyl) porphyrin, Scheme 1).[1314] Fullerene anions can also preserve the monomeric state in the complexes forming antiferromagnetically coupled C60^- chains in {(MDABCO+)2-•MIITPP}^(C60-)2^(Solvent)x[12] and {(MDABCO+)•MIIOEP}• •(C60-V(Solvent)x complexées (M = Zn, Co, Mn, and Fe)[1516] (OEP is octaethylporphyrin, Scheme 1). Recently it was shown that not only fullerene radical anions but fullerene dianions can be involved into the ionic complexes with the coordination assemblies of metalloporphyrins allowing to study the electronic state of more negatively charged fullerenes.[17] The supposed method of synthesis provides interesting possibility to study the coordination assemblies of metalloporphyrins with the coordination cations as well. This field of coordination chemistry of metalloporphyrins is not well studied
In this review we discuss synthesis, structures and magnetic properties of the ionic complexes of fullerenes and metalloporphyrins coordinated by ^-containing cations.
Results and Discussion
units (1-6)
C602-andC70 complexeswith(MDABCO+)2-MIITPP
To prepare 1-5 we used the reduction of fullerenes with CH3CH2SNa in the presence ofMDABCO-I excess in C6H4Cl2/ C6H5CN (19:1) mixture. Then (MDABCO+Mfullerene-) salt was precipitated from the solution by hexane in the presence
Table 1. Composition of the complexes.
of corresponding metalloporphyrin. The coordination of MDABCO+ to metalloporphyrin is a key point for the formation of 1 -5 since copper(II) tetraphenylporphyrin which can not coordinate MDABCO+ does not form such complexes. For preparation of 6 an excess of CH3CH2SNa, MDABCO-I and C60 were stirred in acetonitrile (CH3CN). The reduction occurred up to -2 charged state (according to the NIR spectra) and was accompanied by the cationic metathesis reaction. The addition of o-dichlorobenzene (C6H4Cl2) and MnnTPP with further diffusion of hexane into the obtained solution yielded the crystals of 6. The compositions of 1-6 are listed in Table 1. The compositions of 1 and 4 were determined from elemental analyses and those of 2, 3, 5 and 6 from X-ray structural analysis. The compositions of 1-4 are similar and differ only in the content of solvent molecules: {(MDABCO)2-
•M"TPP}.(C60(7o))2-(C6H4Cl2)2,+,-(C6H5CN), (X = 0 - 2.2,
y = 0 - 1.8). Therefore, all these complexes most probably contain the same (MDABCO+)2-M"TPP units and fullerene anions at 1:2 molar ratio. 5 has a composition of another character and involves free non-coordinated MDABCO+ cations additionally to (MDABCO+)2-Mn"TPP units.
Metalloporphyrins coordinate two MDABCO+ cations in both 2 and 3. Therefore, metal atoms are six-coordinated and have the octahedral environment at MII centres (M = Co (Figure 1a) and Mn). Previously such environment was reported for Co"TPP in (piperidine)2-ConTPP[18] and by our knowledge was for the first time found for Mn"TPP since even in a large excess of ^-containing ligands such as pyridine and imidazole (L), MnnTPP forms only five-coordinated L-Mn"TPP species.[19] Most probably, crystal packing forces in the complex with fullerene facilitate the stabilization of six-coordinated metalloporphyrins. The Co- and Mn N(MDABCO+) distances of 2.475(2) and 2.553(2) A indicate weak coordination of MDABCO+ to metalloporphyrins. The elongation of Co-N axial coordination bonds from 2.157(3) to 2.436(2) A was observed when moving from five-coordinated (imidazole)-ConTPP to six-coordinated (piperidine)2-ConTPP. This elongation is a consequence of that an unpaired electron involved in the bonding is located on
N Complex Ref.
1 {(MDABCO)2-ZnTPPHC6o)2<C6H4Cl2)15<C6H5CN)o, [12]
2 {(MDABCOVCoHTPPHCJ^C^C^.^C^CN)^ [12]
3 {(MDABCOVMtfTPPHCJ^mC^y^CN)^ [12]
4 {(MDABCOVFenTPPHC^-mC^y^CN^ [12]
5 {(MDABCO^MtfTPP} •(MDABCO+{(C^^^^C^^^CN^ [12]
6 {(MDABCO+^MtfTPP} <C602->C6H4Cl2V (C^CN^ [17]
7 {(MDABCO+} Co^MPP^ ^o-^ ^^C^y^^CN)^ [13]
8 {(MD^œ+^riTM^^ol^W^^W™),. [14]
9 {(MDABCO+>ZnOEP } •(C^^TOCN^.^TOCyo^ [16]
10 {(MDABCO+>CoIIOEPHC6o-->(C6H5CN)o,/(C6H4Cl2)o,3 [15,16]
11 {(MDABCO^FenOEPHC^^TOCN^^^Cyo^ [16]
12 {(MDABCO+^OEPHC^^^CN^^TOCyo.^ [16]
Figure 1. Coordination units formed with cobalt(II) and manganese(II) tetraphenylporphyrins: (a) (MDABCO+)2-ConTPP in 2 and (b) (MDABCO+)-MnnTPP in 5.[12]
dz2-orbital, which pointed directly to the two nitrogen atoms of axial ligands.[18,20] The removal of the electron from dz2-orbital in CoIIITPP+ leads to the noticeable shortening of axial Co-N bonds in (piperidine)2-CofflTPP+ to 2.060(3) A.[21] For the same reason, the Mn-N axial coordination bond elongates in the (MDABCO)2-Mn"TPP units. This implies that an unpaired electron of Mn"TPP involved in the bonding with MDABCO+ should also localize on dz2-orbital. Additional contribution to the elongation of M-N bonds in (MDABCO+)2-M"TPP (M= Co and Mn) can provide the repulsion between two positive charges of MDABCO+ cations. Porphyrin macrocycles are nearly planar with root mean square deviations (rms) of 0.033 and 0.064 A for 2 and 3. The cobalt atom is in the porphyrin plane with the averaged length of the equatorial Co-N bonds of 1.988(2) A), what is close to that observed for six-coordinated (piperidine)2-Co"TPP (1.987(2) A).[18] The length of equatorial
Mn-N bonds is averaged in 3 at 2.096(2) A and is close to that in high-spin (S = 5/2) MnnTPP-(C6H5CH3)2 (2.084(2) A[22]).
The geometric parameters of (MDABCO)2-Mn"TPP units in 5 (Figure 1b) and 6 are nearly the same as those in 3. Coordinated nitrogen atoms of two MDABCO+ cations and metal atom lie along a straight line in 2, 3, 5 and 6, which is nearly perpendicular to the porphyrin plane in 2 and 3 (88o) and forms an angle of 85o in 5 and 87.3o in 6. In previously described (piperidine)2-Co"TPP this line forms an angle of about 89o with the porphyrin plane.[18] The Mn-N(MDABCO+) distances in 5 and 6 are long (Table 2) also indicating the essential destabilization of these coordination units. The averaged lengths of Mn-N equatorial bonds in 5 and 6 (Table 2) are close to those in 3 and high-spin Mn"TPP-(C6H5CH3)2.[22] The elongation of Mn-N(TPP) bonds is associated with the singly occupied d(x2-y2)-orbital in
Table 2. Geometric parameters of six-coordinated MnIITPP in high- and low-spin states.[17]
Complex
MnC distances, Displacement of M-N(TPP), A M-N(L), A N atoms from the
difference, A porphyrin plane, A
(MDABCO+)2-MnIITPP-(C60-)2-Solvent
(high-spin)[12]
(MDABCO+)2-MnIITPP-(C70-)4-(MDABCO+)2-Solvent
(high-spin)[12]
(MDABCO+)2-MnIITPP-(C602-)-Solvent
(high-spin)[17]
(MDABCO+)2-MnIITPP-(C602-)-Solvent
(high-spin)[17]
MnIITPP-(C6H5CH3)2
(high-spin)[22]
(NO)-MnTPP-(MPip) (low-spin, S = 1/2)[23]
2.081(2) - 2.110 (2) MnII displaces out of plane by ± 0.127 A
2.097(2) - 2.098(2)
MnII in plane
2.093(1) - 2.094(1)
MnII in plane
2.095(1) - 2.098(1)
MnII in plane
2.082(2) - 2.085(2) MnII displaces out of plane by ± 0.177 A
Aver. 2.028(4) MnII displaces out of plane to NO by ~0.1 A
2.531(2) 2.515(2) 2.545(1) 2.537(1)
3.456(2) - 3.479(2) 0.023
3.446(2) - 3.486(2) 0.040
3.449(3) - 3.469(3) 0.020
3.444(3) - 3.477(3) 0.033
3.466(3)
0.063 - 0.122
0.117 - 0.125
0.104 - 0.118
0.076 - 0.133
0.030 - -0.140
2.206(5) MPip 1.644(5) NO
Figure 2. The structure of MnIITPP porphyrin core in 6. Upper half shows the structurally independent bond lengths and the lower half shows perpendicular displacements of the atoms (in the 0.01 A units) from the mean 24-atom porphyrin plane.[17]
high-spin state of MnIITPP, which is antibonding relative to the Mn-N(TPP) bonds.
Geometry of MnnTPP macrocycle is defined to a great extent by the spin state of Mn" atoms. We analyzed the geometric parameters of (MDABCO+)2-MnnTPP units in the complexes with fullerenes (Figure 2, Table 2). The degree of radial distortion of the porphyrin core can be estimated from the difference in the length of two Mn C distances, and the perpendicular displacements of the atoms from the 24-atom porphyrin plane (Figure 2). The largest displacements were found for the nitrogen atoms of pyrrole rings (these values are listed in Table 2). The Mnn atoms are positioned exactly in the porphyrin plane in (MDABCO+)2-Mn"TPP when it forms
complex 5 ,[12] That results in the largest radial expansion of the porphyrin core (Table 2). For (MDABCO+)2-Mn"TPP units in 3, the thermal parameter of Mn11 atom for the vibration perpendicular to the porphyrin plane is essentially higher than that of N atoms, and the disorder model in which Mn11 atom was distributed between two symmetry equivalent out-of-plane positions with isotropic temperature factors can be applied. However, the accuracy of the crystal structure determination does not allow one to refine simultaneously the position of Mn11 atoms with anisotropic temperature factors because they show large correlations.[12] The out-of-plane displacement of Mn11 atoms from the mean porphyrin plane estimated using this model was ± 0.127 Â. In this case moderate radial expansion of the porphyrin core is realized (Table 2). The Mn11 atoms arranged exactly in the porphyrin plane in both crystallographically independent (MDABCO+)2-MnIITPP units in 6 since they are located in the centres of symmetry, whereas the radial expansion of the porphyrin core has moderate values (Table 2). Thus, all (MDABCO+)2-MnIITPP units manifest radial expansion of the porphyrin core. As this takes place MnII atoms can locate in the porphyrin plane or displace out of this plane. The transition of MnIITPP to the low-spin state in (NO)-MnTPP-(MPip) decreases in the length of M-N(TPP) bonds (2.028(4) Â), however, the data of the radial expansion of the porphyrin core is absent for this compound.[23]
Magnetic properties of 3 and 4 are defined by the contribution from C60^ radical anions and the high-spin MnIITPP and FeIITPP porphyrins whereas those of 1 are defined by the contribution from C60^ radical anions only. The Weiss temperatures were estimated to be -13 K for 1 and -2 K for 2 and 3. The (C70-)2 dimers as well as the C602-dianions are diamagnetic and the magnetic behaviour of 5 and 6 is defined only by the contribution of high-spin MnIITPP
Figure 3. Fragment of the crystal structure of 7 showing the cage from the (MDABCO+)-CoIITMPP units accommodating the doubly bonded (C60-)2 dimer.[13]
molecules which are isolated by the diamagnetic (C70-)2 dimers or C602- anions. As a result the Weiss temperatures for these complexes are close to 0.
The formation of (C~) dimers in the complexes with (MDABCO+) •MIITMI6P units
An ionic complexes 7 and 8 contain negatively charged (C60-)2 dimers, bonded by two C-C bonds, and the coordination (MDABCO+>M"TMPP units (M = Co and Zn). The composition of the complexes was determined by X-ray diffraction on a single crystal (Table 1).
The MDABCO+ cation is a monodentate ligand and coordinates to CoIITMPP in 7 by nitrogen atom with the Co N distance of 2.385 Â. Cobalt atom is five-coordinated and deviates by 0.084 Â from the plane of four nitrogen atoms towards MDABCO+. Coordination between
The magnetic properties of (C60-)2 dimers, bonded by two C-C bonds, are of a special interest since they have triplet state at 300 K. Magnetic moment of 7 at this temperature is equal to 3.47 (xB at 300 K and close to that calculated for a system of four noninteracting 1/2 spins (M-eff = 3.46 |xB) per a formula unit. These spins are localized on CoIITMPP and C60- (four units in total). Taking into account that the dimer is a single molecule, the presence of spins on both C60- units implies that this dimer should have a biradical state at 300 K. The presence of paramagnetic ConTMPP and (C60^)2 is justified by EPR since both species show individual signals. Intense EPR signal with g = 1.9997 and the linewidth (AH) of 3.46 mT at RT, which is close to those of the radical anions of C60 derivatives (2.0000[24]), was attributed to the (C6;-)2 dimers and broad signal with g = 2.2638 and AH = 30 mT (19 K) was assigned to Co"TMPP. Pure Lorentz shape of the signal from the (C60")2 dimers is most probably the result of
ConTMPP and (C60-)2 dimers is absent, the shortest Co C exchange interaction between ConTMPP and (C6(/ )2, which
distances of 2.757 and 2.940 A are close to those distances in neutral ConTMPP-(C60)2-(C6H5CH3)3 complex (2.65-2.67 A).[5] A porphyrin cage accommodates (C60-)2 dimers in 7 and completely isolates them one from another (Figure 3). Each cage consists of six {(MDABCO+) • ConTMPP} units, two of which contact with dimer by free ConTMPP surface, four other units contact with dimer by MDABCO+ cations with short C(MDABCO+)-C((C60-)2) contacts in the 3.0823.390 A range (only two of four such units are shown in Figure 3 for clarity).
Similar doubly bonded (C60-)2 dimers are formed in 8. However, in this case the shortest Zn C((C60-)2) distances are longer (3.02-3.17 A). That is due to the stronger coordination of MDABCO+ to ZnTMPP (Figure 4a) since N(MDABCO+)-Zn distance is noticeably shorter (2.280(4) A) and the displacement of Zn atom from the plane of four nitrogen atoms towards MDABCO+ is larger (0.265 A). Short Co-C((C60-)2) contacts provide complete order of (C60-)2 dimers in 7 whereas weaker Zn- C((C60-)2) interaction results in the disorder of these dimers in 8 even at 120(2) K in spite of the Van-der-Waals interaction with the porphyrin plane is nearly the same in both complexes. These data allow to suppose that namely metal-fullerene interaction is responsible for the ordering of the fullerene dimers.
averages D and E parameters and leads to the disappearance of triplet features of the signal. In contrast to 7 complex 8 contains diamagnetic and EPR silent (MDABCO+)-ZnTMPP units. That allows us to observe the narrow Lorentz signal from the (C60-)2 dimers (g=2.0024 and AH = 0.277 mT) which narrows at temperature decrease (0.17 mT at 100 K). The data of SQUID measurements for 8 can be fitted according to the Heisenberg model for the pairs of antiferromagnetically interacting spins with exchange interaction between them of J/kB = - 44.7 K. Therefore, dimers have singlet (S =0) ground state and exited (S = 1) triplet state.
C^- complexes with (MDABCO+)M"OEP units
The complexes 9-12 were obtained by the reduction of C60 by CH3CH2SNa in the presence of MDABCO-I with following precipitation of the obtained salt in the presence of MnOEP. The composition of the complexes 9, 10 and 12 was determined by X-ray diffraction study on a single crystal whereas that of 11 by elemental analysis (Table 1). The MDABCO+ cations coordinate to MIIOEP as monodentate ligands forming positively charged coordination assemblies (MDABCO+)-MnOEP (M = Zn, Co, Mn, and Fe). The M" atoms are five-coordinated in these assemblies (Figure 4b).
Figure 4. Coordination (MDABCO+>ZnTMPP units in 8 (a) and (MDABCO+>MnnOEP units in 12 (b). Макрогетер0циmbl /Macroheterocycles 2009 2(3-4) 190-197
b
Figure 5. The view on the crystal structure of 9 along c-axis and zigzag fullerene chains (a); the view on the zigzag fullerene chains along ¿-axis (b). Solvent molecules are not depicted for clarity.
The length of M-N(MDABCO+) bonds changed in the following order: Zn (2.237(2)) < Mn" (2.301(1)) < Co" (2.340(3) A). Mn atoms deviate from the plane of four nitrogen atoms towards MDABCO+ cation by 0.042 A in 10, 0.239 A in 9 and 0.274 A in 12. The weaker M-N bonds lead to smaller deviation of the metal atom from the plane of four nitrogen atoms. Since one coordination position is free in Mn atom C60^ can be a second ligand for MnOEP.
The main structural motif of these complexes is zigzag chains of fullerenes, which occupy channels formed by four MnOEP molecules (Figure 5a). Due to the zigzag arrangement of fullerenes vacancies are formed in the chains, accommodating small MDABCO+ cations (Figure 5b). The centre-to-centre distances between fullerenes in the chains are defined by the cation size. They are rather large (10.297 A for 10, 10.560 A for 9 and 10.703 A for 12) and do not allow the formation of Van-der-Waals CC contacts
between C„•" in the chains.
60
C60^ radical anions are arranged from the opposite site of the porphyrin macrocycle relative to the ^-containing cation. The shortest M-C(C60^") distance among these complexes was found in 10 (2.508(4) A at 100 K) and in this case the reversible formation of Co-C coordination bond is observed. M."C(C60~) distances in 9 and 12 are essentially longer (3.037 and 3.049 A at 100 K, respectively) indicating the absence of coordination of C6(/- to (MDAB CO+) -ZnOEP or (MDABCO+)-MnnOEP units. Nevertheless, C6(/- radical anions form multiple short Van-der-Waals NC and CC contacts with the porphyrin macrocycles in these complexes since the macrocycles are concave-shaped and conform well to the spherical shape of C60.
The averaged length of M-N(OEP) bonds in (MDABCO+)-MnnOEP (12) is 2.107(2) A and indicates the high-spin state of MnIIOEP. Close length of Mn-N (porphyrin) bonds was found in high-spin MnnTPP-(1-MeIm) (2.128(7) A[26]) and (MDABCO+)2-MnnTPP
(2.081(1)-2.110(2) A).[12-17]
Magnetic properties of the complexes range from diamagnetic behaviour of 10 at low temperature (due to the
formation of Co-C(C60-) bond) to strong antiferromagnetic interaction of spins in 9, 11 and 12 (the Weiss temperatures were estimated to be -18, -42 and -2.5 K, respectively). Complexes 9 and 12 contain chains of C60" radical anions, whereas 12 additionally contains high-spin (MDABCO+)•MnIIOEP units. Both complexes show AF interaction of spins, which is most probably realized in the fullerene chains. Additionally, each C60" has face-to-face interaction with the porphyrin macrocycle. Therefore, magnetic interaction between Mn11 centres and C60" is also expected in 12. The EPR spectrum of 9 justifies the presence of exchange coupling between (MDABCO+)-Mn"OEP and C60^. Complex 11 manifests strongest antiferromagnetic interaction of spins. However, the absence of structural information does not allow the detailed interpretation of the magnetic data for this compound.
Conclusions
The tendency of metalloporphyrins, MII porphyrin, to extra-coordination can be successfully used in the design of supramolecular ionic MII porphyrin-C60 complexes: {(MDABCO+)n-Mnporphyrin}-(C60-)-(Solvent)x (n = 1 and 2). The driving force for the formation of these complexes is the coordination of MDABCO+ to MII porphyrin (M = Zn, Co, Mn and Fe). Porphyrins, which cannot coordinate this cation, for example CuII porphyrins, do not form such complexes.
The synthesis of the series of complexes allows for the first time to study the coordination of MDABCO+ and C60^ to MIIOEP and compare their coordination ability. There is a competition between fullerenes and ^-containing cations for the coordination to MIIOEP. From structural data we can conclude that fullerenes are weaker ligands than MDABCO+. As a result, the M" atoms display out of the porphyrin plane towards ^-containing ligand forming rather short M-N(L+) bonds of 2.237(2)-2.340(3) A length and that prevents the formation of stable coordination bonds between fullerenes and MII porphyrins. The smaller is the displacement of the
metal(II) atom from the porphyrin plane towards MDABCO+ the shorter M-C(C60~) contacts are formed. The smallest displacement of Co" atom and the shortest Co- C(C60-) distance were found namely in 10. It should be emphasized that the Co-C coordination bonds are really formed in 10 below 50 K.[15] In 9 and 12 the larger M-C(C60/-) distances (> 3 A) for ZnOEP and Mn"OEP indicate the absence of coordination at 100 K.
Coordination assemblies were found in a series of {(MDABCO+)2-MnTPP}-(C60")2-(Solvent)x complexes with metal(II) tetraphenylporphyrins (M=Zn, Co, Mn and Fe).[12] However, in this case two MDABCO+ cations coordinate to each M"TPP with the formation of (MDABCO+)2-M"TPP units and, as a result, the central metal(II) atoms of porphyrins are shielded from bonding with C60". In the case of six-coordinated metalloporphyrins M-N(L+) bonds are rather long (2.475(2)-2.553(2) A) indicating essential destabilization of these coordination units. The Mn" and Fe" porphyrins are in high-spin state (S = 5/2) and (S = 2), respectively both for five- and six-coordinated porphyrins in the complexes with fullerenes. That was confirmed by the magnetic measurments.
The developed method of synthesis demonstrates high potential for the preparation of different c-bonded structures of negatively charged fullerenes and coordinatively bound structures of metalloporphyrins with ^-containing cations as well to obtain complexes with antiferromagnetic interaction of spins ranging from weak to strong.
Acknowledgements. The work was supported by RFBR grant N 06-03-32824.
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Received 12.05.2009 Accepted 22.06.2009
