Inorg. Chem. 2007, 46, 619−621
Four-Coordinate Iron(II) Porphyrinates: Electronic Configuration Change
by Intermolecular Interaction
Chuanjiang Hu,† Bruce C. Noll,† Charles E. Schulz,*,‡ and W. Robert Scheidt*,†
Department of Chemistry and Biochemistry, UniVersity of Notre Dame,
Notre Dame, Indiana 46556, and Department of Physics, Knox College, Galesburg, Illinois 61401
Received October 20, 2006
The syntheses and structures of three four-coordinate iron(II)
porphyrinates are reported. The three derivatives are tetraarylpor-
phyrin species, where the aryl is either phenyl, p-methylphenyl, or
p-methoxyphenyl. One of these derivatives, that of tetraphenylpor-
phyrin, Fe(TPP), is a new crystalline phase that is distinct from
the earlier reported phase (Collman, J. P.; et al. J. Am. Chem.
Soc. 1975, 97, 2676). This new phase of Fe(TPP) has a very
saddled porphyrin core; the prior phase was ruffled. The iron atom
susceptibilities.4-8 Fe(TPP)(I4h2d) has a much smaller quad-
rupole splitting value and a larger magnetic moment, which
indicates that it has a different ground state than Fe(Pc). Most
3
2
3
1
2
studies have assigned EgA [(dxy) (dxz,dyz) (dz ) ] as the ground
3
2
2
2
2
state for FeII(Pc)9-12 and A2g [(dxy) (dxz,dyz) (dz ) ] for Fe-
(TPP)(I4h2d).9,13
As part of our investigation of iron(II) porphyrinates, we
have recently isolated and structurally characterized three
four-coordinate FeII(Porph) complexes. These derivatives
(Porph ) TPP, TTP, T-p-OCH3PP) were synthesized by
reduction of the corresponding [Fe(Porph)]2O complex.14
ORTEP diagrams for all three crystalline derivatives are
shown in Figure 1; packing diagrams are given in the
Supporting Information. Solvent interactions are minimal.
Fe(TTP) has crystallographically imposed inversion sym-
has close interactions ( 3.10 Å) with two pyrrole Cb−Cb bonds
∼
above and below the porphyrin plane. Mo¨ssbauer spectra and
magnetic susceptibility measurements, different for the two phases,
provide strong evidence that the two phases of Fe(TPP) have
distinct electronic structures that originate from intermolecular
interactions.
(2) Abbreviations: Porph, a generalized porphyrin dianion; TPP, dianion
of meso-tetraphenylporphyrin; TTP, dianion of meso-tetratolylpor-
phyrin; T-p-OCH3PP, dianion of meso-tetra-p-methoxyphenylporphy-
rin; Pc, phthalocyanine; OEP, 2,3,7,8,12,13,17,18-octaethylporphyri-
nato dianion; OEC, trans-7,8-dihydro-2,3,7,8,12,13,17,18-octaeth-
ylporphyrinato(octaethylchlorinato) dianion; F8TPP, dianion of meso-
tetra(2,6-difluorophenyl)porphyrin; TF5PP, dianion of meso-tetra-
(pentafluorophenyl)porphyrin; TPrPc, 2,7,12,17-tetrapropylporphycene;
Np, porphyrinato nitrogens; THF, tetrahydrofuran.
(3) The original preparation of crystalline Fe(TPP), a crystalline phase
reported by Collman et al.4 in 1975, crystallizes in the tetragonal system
and appears to be the generally studied phase. We denote this phase
as Fe(TPP)(I4h2d).
(4) Collman, J. P.; Hoard, J. L.; Kim, N.; Lang, G.; Reed, C. A. J. Am.
Chem. Soc. 1975, 97, 2676.
(5) (a) Dale, B. W.; Williams, R. J. P.; Johnson, C. E.; Thorp, T. L. J.
Chem. Phys. 1968, 49, 3441. (b) Dale, B. W.; Williams, R. J. P.;
Edwards, P. R.; Johnson, C. E. J. Chem. Phys. 1968, 49, 3445.
(6) Barraclough, C. G.; Martin, R. L.; Mitra, S.; Sherwood, R. C. J. Chem.
Phys. 1970, 53, 1643.
(7) Boyd, P. D. W.; Buckingham, D. A.; Meeking, R. F.; Mitra, S. Inorg.
Chem. 1979, 18, 3585.
(8) Lang, G.; Spartalian, K.; Reed, C. A.; Collman, J. P. J. Chem. Phys.
1978, 69, 5424.
(9) McGarvey, B. R. Inorg. Chem. 1988, 27, 4691.
(10) Li, N.; Su, Z.; Coppens, P.; Landrum, J. J. Am. Chem. Soc. 1990,
112, 7294.
We report that solid-state effects have a significant
influence on the electronic structure of square-planar iron-
(II) porphyrinates. Although the electronic states of iron(II)
porphyrinates have been intensively investigated both ex-
perimentally and theoretically, they are yet far from being
determined (or understood) with certainty. Four-coordinate
iron(II) porphyrinates or phthalocyanines are constrained by
the macrocyclic ligand to square-planar coordination.
In an early theoretical investigation of d6 iron(II) with D4
symmetry, Griffith1 noted that the orbital pattern always
requires that the dx -y orbital be of higher energy than the
other orbitals, and thus the species will always be intermedi-
ate spin (S ) 1). Subsequently, the ground states of the
intermediate-spin four-coordinate iron(II) porphyrins and
phthalocyanines have been studied primarily by Mo¨ssbauer
and magnetic susceptibility. The two most thoroughly
investigated species are Fe(TPP)2,3 and Fe(Pc). Despite their
expected similarities, these two species have significant
differences in their Mo¨ssbauer properties and magnetic
2
2
(11) Sontum, S. F.; Case, D. A.; Karplus, M. J. J. Chem. Phys. 1983, 79,
2881.
(12) Tanaka, K.; Elkaim, E.; Li, L.; Jue, Z. N.; Coppens, P.; Landrum, J.
J. Chem. Phys. 1986, 84, 6969.
(13) Coppens, P.; Li, L. J. Chem. Phys. 1984, 81, 1983.
(14) The four-coordinate species FeII(Porph) was prepared by reduction of
[Fe(Porph)]2O in different solvents with excess ethanethiol (>200 fold)
according to Stolzenberg et al.15 More detail is given in the Supporting
Information.
* To whom correspondence should be addressed. E-mail:
cschulz@knox.edu (C.E.S.), Scheidt.1@nd.edu (W.R.S.).
† University of Notre Dame.
‡ Knox College.
(1) Griffith, J. S. The Theory of Transition-Metal Ions; Cambridge
University Press: London, 1961; pp 370-373.
10.1021/ic0620182 CCC: $37.00
Published on Web 01/03/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 3, 2007 619