Mononuclear Fe(iii) complexes commonly exist in high-spin or low-spin states, whereas their occurrence in the intermediate-spin state (S = 3/2) is scarce. The magnetic anisotropy in two trigonal-bipyramidal mononuclear Fe(iii) complexes, (PMe3)2FeCl3 (1) and (PMe2Ph)2FeCl3 (2), in their intermediate-spin ground state has been examined by ab initio electronic structure calculations. The calculations successfully reproduce the experimental magnetic anisotropic barrier, Ueff in 1 (81 cm−1) and 2 (42 cm−1), which is shown to arise due to thermally assisted quantum tunneling of magnetization from the second Kramer’s doublets. The magnetic anisotropy in both the complexes is found to be significantly influenced by the axial ligands, while the equatorial ligands have negligible contribution. The large reduction in Ueff of 2 has been shown to arise due to the phenyl groups, which results in the lifting of orbital degeneracy of e″ and e′ frontier orbitals and leads to a net quenching of the orbital angular momentum of the metal center causing a diminished spin-orbit splitting in 2. While the crystal structure of 2 shows two phenyl rings out of plane to each other, the present study discovered another stable conformation of 2, where the two phenyl rings are in the same plane (2a). Unlike 2, the planarity of the two phenyl rings in 2a restores the degeneracy of the frontier orbitals, thereby increasing the spin-orbit splitting and a consequent rise in Ueff from 42 to 80 cm−1 in 2a.

1.
E.
Edler
and
M.
Stein
,
Eur. J. Inorg. Chem.
2014
,
3587
.
2.
A.
Begum
and
S.
Sarkar
,
Eur. J. Inorg. Chem.
2012
,
40
.
3.
D. J.
Harding
,
P.
Harding
, and
W.
Phonsri
,
Coord. Chem. Rev.
313
,
38
(
2016
).
4.
P.
Guaetlich
,
Eur. J. Inorg. Chem.
2013
,
581
.
5.
M.
Swart
,
Int. J. Quantum Chem.
113
,
2
(
2013
).
6.
R.
Poli
and
J. N.
Harvey
,
Chem. Soc. Rev.
32
,
1
(
2003
).
7.
J. N.
Harvey
,
Wiley Interdiscip. Rev.: Comput. Mol. Sci.
4
,
1
(
2014
).
8.
D. H.
Dolphin
,
J. R.
Sams
, and
T. B.
Tsin
,
Inorg. Chem.
16
,
711
(
1977
).
9.
T.
Sakai
 et al.,
J. Am. Chem. Soc.
125
,
13028
(
2003
).
10.
M.
Nakamura
,
Coord. Chem. Rev.
250
,
2271
(
2006
).
11.
P. J.
van Koningsbruggen
,
Y.
Maeda
, and
H.
Oshio
, “
Iron(iii) spin crossover compounds
,” in
Spin Crossover in Transition Metal Compounds I
, edited by
P.
Gütlich
and
H.
Goodwin
(
Springer Berlin Heidelberg
,
Berlin, Heidelberg
,
2004
), pp.
259
324
.
12.
H.
Keutel
 et al.,
Inorg. Chem.
38
,
2320
(
1999
).
13.
S.
Mossin
 et al.,
J. Am. Chem. Soc.
134
,
13651
(
2012
).
14.
X.
Feng
 et al.,
J. Am. Chem. Soc.
139
,
16474
(
2017
).
15.
A.
Rudavskyi
,
C.
Sousa
,
C.
de Graaf
,
R. W. A.
Havenith
, and
R.
Broer
,
J. Chem. Phys.
140
,
184318
(
2014
).
16.
S.
Stepanovic
 et al.,
Inorg. Chem.
52
,
13415
(
2013
).
17.
M.
Swart
and
M.
Gruden
,
Acc. Chem. Res.
49
,
2690
(
2016
).
18.
M.
Swart
,
J. Chem. Theory Comput.
4
,
2057
(
2008
).
19.
C. J.
Cramer
and
D. G.
Truhlar
,
Phys. Chem. Chem. Phys.
11
,
10757
(
2009
).
20.
H.
Paulsen
,
L.
Duelund
,
H.
Winkler
,
H.
Toftlund
, and
A. X.
Trautwein
,
Inorg. Chem.
40
,
2201
(
2001
).
21.
M.
Reiher
,
O.
Salomon
, and
B.
Artur Hess
,
Theor. Chem. Acc.
107
,
48
(
2001
).
22.
23.
S.
Ye
and
F.
Neese
,
Inorg. Chem.
49
,
772
(
2010
).
24.
O. S.
Siig
and
K. P.
Kepp
,
J. Phys. Chem. A
122
,
4208
(
2018
).
25.
L. M.
Lawson Daku
,
F.
Aquilante
,
T. W.
Robinson
, and
A.
Hauser
,
J. Chem. Theory Comput.
8
,
4216
(
2012
).
26.
K.
Pierloot
and
S.
Vancoillie
,
J. Chem. Phys.
125
,
124303
(
2006
).
27.
K.
Pierloot
and
S.
Vancoillie
,
J. Chem. Phys.
128
,
034104
(
2008
).
28.
M.
Radoń
,
K.
Gassowska
,
J.
Szklarzewicz
, and
E.
Broclawik
,
J. Chem. Theory Comput.
12
,
1592
(
2016
).
29.
C.
Sousa
,
C.
de Graaf
,
A.
Rudavskyi
, and
R.
Broer
,
J. Phys. Chem. A
121
,
9720
(
2017
).
30.
G.
Alcover-Fortuny
,
C.
de Graaf
, and
R.
Caballol
,
Phys. Chem. Chem. Phys.
17
,
217
(
2015
).
31.
K. P.
Kepp
,
Coord. Chem. Rev.
257
,
196
(
2013
).
32.
R.
Sessoli
 et al.,
J. Am. Chem. Soc.
115
,
1804
(
1993
).
33.
R.
Sessoli
,
D.
Gatteschi
,
A.
Caneschi
, and
M. A.
Novak
,
Nature
365
,
141
(
1993
).
34.
M. R.
Pederson
and
S. N.
Khanna
,
Phys. Rev. B
60
,
9566
(
1999
).
35.
D.
Gatteschi
,
R.
Sessoli
, and
J.
Villain
,
Molecular Nanomagnets
(
Oxford University Press
,
New York
,
2006
).
36.
H. L. C.
Feltham
and
S.
Brooker
,
Coord. Chem. Rev.
276
,
1
(
2014
).
37.
M.
Murrie
,
Chem. Soc. Rev.
39
,
1986
(
2010
).
38.
G.
Aromí
and
E. K.
Brechin
, “
Synthesis of 3d metallic single-molecule magnets
,” in
Single-Molecule Magnets and Related Phenomena
, edited by
R.
Winpenny
(
Springer Berlin Heidelberg
,
Berlin, Heidelberg
,
2006
), pp.
1
67
.
39.
J.
Cirera
,
E.
Ruiz
,
S.
Alvarez
,
F.
Neese
, and
J.
Kortus
,
Chem. - Eur. J.
15
,
4078
(
2009
).
40.
F.
Neese
and
D. A.
Pantazis
,
Faraday Discuss.
148
,
229
(
2011
).
41.
O.
Waldmann
,
Inorg. Chem.
46
,
10035
(
2007
).
42.
Y.
Meng
,
S.
Jiang
,
B.
Wang
, and
S.
Gao
,
Acc. Chem. Res.
49
,
2381
(
2016
).
43.
N.
Ishikawa
,
M.
Sugita
,
T.
Ishikawa
,
S.
Koshihara
, and
Y.
Kaizu
,
J. Am. Chem. Soc.
125
,
8694
(
2003
).
44.
A. K.
Bar
,
C.
Pichona
, and
J.
Sutter
,
Coord. Chem. Rev.
308
,
346
(
2016
).
45.
S.
Gómez-Coca
,
D.
Aravena
,
R.
Morales
, and
E.
Ruiz
,
Coord. Chem. Rev.
289-290
,
379
(
2015
).
47.
P. P.
Power
,
Chem. Rev.
112
,
3482
(
2012
).
48.
J. M.
Zadrozny
 et al.,
Chem. Sci.
4
,
125
(
2013
).
49.
J. M.
Zadrozny
 et al.,
Nat. Chem.
5
,
577
(
2013
).
50.
J. M.
Zadrozny
 et al.,
Inorg. Chem.
52
,
13123
(
2013
).
51.
S.
Roy Chowdhury
and
S.
Mishra
,
Eur. J. Inorg. Chem.
2017
,
659
.
52.
X.
Yao
 et al.,
J. Am. Chem. Soc.
139
,
373
(
2017
).
53.
R.
Maurice
 et al.,
J. Chem. Theory Comput.
5
,
2977
(
2009
).
54.
D.
Brazzolotto
 et al.,
Chem. - Eur. J.
22
,
925
(
2016
).
55.
F.
Weigend
and
R.
Ahlrichs
,
Phys. Chem. Chem. Phys.
7
,
3297
(
2005
).
56.
F.
Weigend
,
Phys. Chem. Chem. Phys.
8
,
1057
(
2006
).
57.
J. P.
Perdew
,
Phys. Rev. B
33
,
8822
(
1986
).
58.
A. D.
Becke
,
Phys. Rev. A
38
,
3098
(
1988
).
59.
J. P.
Perdew
 et al.,
Phys. Rev. B
46
,
6671
(
1992
).
60.
J. P.
Perdew
 et al.,
Phys. Rev. B
48
,
4978
(
1993
).
61.
C.
Adamo
and
V.
Barone
,
J. Chem. Phys.
110
,
6158
(
1999
).
62.
A. D.
Becke
,
J. Chem. Phys.
98
,
5648
(
1993
).
63.
C.
Lee
,
W.
Yang
, and
R. G.
Parr
,
Phys. Rev. B
37
,
785
(
1988
).
64.
A. D.
Becke
,
J. Chem. Phys.
104
,
1040
(
1996
).
65.
A. D.
Becke
,
J. Chem. Phys.
107
,
8554
(
1997
).
66.
J. P.
Perdew
and
W.
Yue
,
Phys. Rev. B
33
,
8800
(
1986
).
67.
J. P.
Perdew
,
Phys. Rev. B
34
,
7406
(
1986
).
68.
T.
Yanai
,
D. P.
Tew
, and
N. C.
Handy
,
Chem. Phys. Lett.
393
,
51
(
2004
).
69.
M. J.
Frisch
 et al., gaussian 09, Revision C.01,
Gaussian, Inc.
,
Wallingford, CT
,
2009
.
70.
B. O.
Roos
,
P. R.
Taylor
, and
P. E. M.
Siegbahn
,
Chem. Phys.
48
,
157
(
1980
).
71.
B. O.
Roos
 et al.,
J. Phys. Chem. A
112
,
11431
(
2008
).
72.
K.
Andersson
,
P.
Malmqvist
,
B. O.
Roos
,
A. J.
Sadlej
, and
K.
Wolinski
,
J. Phys. Chem.
94
,
5483
(
1990
).
73.
K.
Andersson
,
P.
Malmqvist
, and
B.
Roos
,
J. Chem. Phys.
96
,
1218
(
1992
).
74.
B.
Roos
and
P.
Malmqvist
,
Phys. Chem. Chem. Phys.
6
,
2919
(
2004
).
75.
L. F.
Chibotaru
and
L.
Ungur
,
J. Chem. Phys.
137
,
064112
(
2012
).
76.
F.
Aquilante
,
P.
Malmqvist
,
T. B.
Pedersen
,
A.
Ghosh
, and
B. O.
Roos
,
J. Chem. Theory Comput.
4
,
694
(
2008
).
77.
F.
Aquilante
 et al.,
J. Comput. Chem.
37
,
506
(
2016
).
78.
H.
Paulsen
and
A. X.
Trautwein
,
Density Functional Theory Calculations for Spin Crossover Complexes
(
Springer Berlin Heidelberg
,
2004
), pp.
197
219
.
79.
A.
Droghetti
,
D.
Alfe
, and
S.
Sanvito
,
J. Chem. Phys.
137
,
124303
(
2012
).
80.
J.
Sirirak
,
D.
Sertphon
,
W.
Phonsri
,
P.
Harding
, and
D. J.
Harding
,
Int. J. Quantum Chem.
117
,
e25362
(
2017
).
81.
I.
Bersuker
,
The Jahn-Teller Effect
(
Cambridge University Press
,
2006
).
82.
M.
Gruden-Pavlovic
,
M.
Peric
,
M.
Zlatar
, and
P.
Garcia-Fernandez
,
Chem. Sci.
5
,
1453
(
2014
).
83.
R.
Boča
,
Coord. Chem. Rev.
248
,
757
(
2004
).
84.
R.
Boča
,
Theoretical Foundations of Molecular Magnetism
(
Elsevier
,
1999
), Vol. 1.
85.
R.
Ruamps
 et al.,
Chem. Sci.
5
,
3418
(
2014
).
86.
J. M.
Frost
,
K. L. M.
Harriman
, and
M.
Murugesu
,
Chem. Sci.
7
,
2470
(
2016
).
87.
F.
Neese
,
J. Chem. Phys.
127
,
164112
(
2007
).
88.
F.
Neese
,
Wiley Interdiscip. Rev.: Comput. Mol. Sci.
2
,
73
(
2012
).
89.
A.
Kubica
,
J.
Kowalewski
,
D.
Kruk
, and
M.
Odelius
,
J. Chem. Phys.
138
,
064304
(
2013
).
90.
A.
Abragam
and
B.
Bleaney
,
Electron Paramagnetic Resonance of Transition Ions
(
Oxford University Press
,
New York
,
1970
).
91.
L.
Ungur
and
L. F.
Chibotaru
,
Phys. Chem. Chem. Phys.
13
,
20086
(
2011
).
92.
S. K.
Gupta
,
T.
Rajeshkumar
,
G.
Rajaraman
, and
R.
Murugavel
,
Chem. Commun.
52
,
7168
(
2016
).
93.
S. K.
Singh
,
T.
Gupta
,
L.
Ungur
, and
G.
Rajaraman
,
Chem. - Eur. J.
21
,
13812
(
2015
).
94.
S.
Roy Chowdhury
and
S.
Mishra
,
Phys. Chem. Chem. Phys.
19
,
16914
(
2017
).
95.
N. F.
Chilton
,
C. A. P.
Goodwin
,
D. P.
Mills
, and
R. E. P.
Winpenny
,
Chem. Commun.
51
,
101
(
2015
).
96.
L.
Ungur
and
L. F.
Chibotaru
,
Inorg. Chem.
55
,
10043
(
2016
).
97.
T. H.
Dunning
, Jr.
,
B. H.
Botch
, and
J. F.
Harrison
,
J. Chem. Phys.
72
,
3419
(
1980
).
98.
K.
Andersson
and
B. O.
Roos
,
Chem. Phys. Lett.
191
,
507
(
1992
).
99.
K.
Pierloot
, “
Nondynamic correlation effects in transition metal coordination compounds
,” in
Computational Organometallic Chemistry
, edited by
T. R.
Cundari
(
Marcel Dekker, Inc.
,
New York, NY
,
2001
), pp.
123
158
.

Supplementary Material

You do not currently have access to this content.