Heterotrinuclear complexes containing a hexaselenolato-zinc(n), -cadmium(ii), -nickel(ii) or -iron(n) core: Crystal structures of [(OC)3Fe(u-SePh)3M(ji-SePh)3Fe(CO)3] (M = Zn, Cd, Ni or Fe) and [Fe(CO)2(phen)(SePh)2] (phen = 1, 10-phenanthroline)

Article abstract of DOI:10.1039/a705247b

A series of linear trinuclear selenolate complexes of the general type [(OC)₃Fe(μ-SePh)jM(μ-SePh)₃Fe(CO)₃] (M = Zn¹¹ 1. Cd¹¹ 2, Ni¹¹ 3 or Fe¹¹ 4) has been synthesized by reaction of the appropriate [M(H₂O)_n]²⁺ with the chelating metalloligand fac-[N(PPh₃)₂][Fe(CO)₃(SePh)₃] in acetonitrile. Their structures were elucidated on the basis of IR, UV/VIS, NMR spectra and X-ray crystallography. Compounds 1-4 are structurally related, each containing two tridentate metalloligands resulting in a MSe₆ co-ordination environment of virtual O_h symmetry. Further reaction of 4 with 3 equivalents of 1, 10-phenanthroline (phen) initially afforded the intermediate [Fe(phen)₃][Fe(CO)₃(SePh)₃]₂ but eventually neutral [Fe(CO)₂(phen)(SePh)₂] 5 was formed as the sole product. Its crystal structure has been determined. This investigation shows thatyac-[Fe(CO)₃(SePh)₃]^- serves as a tridentate chelating metalloligand and selenolate ligand-transfer reagent.

Full text of DOI:10.1039/a705247b

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Heterotrinuclear complexes containing a hexaselenolato-zinc(II),
-cadmium(II), -nickel(II) or -iron(II) core: crystal structures of
[(OC)3Fe(ì-SePh)3M(ì-SePh)3Fe(CO)3] (M ؍ Zn, Cd, Ni or Fe)
and [Fe(CO)2(phen)(SePh)2] (phen ؍ 1,10-phenanthroline)
Wen-Feng Liaw,*,a Chien-Hong Chen,a Chien-Ming Lee,a Ging-Yi Lin,a Chao-Yi Ching,a
Gene-Hsiang Lee,b and Shie-Ming Pengc
a Department of Chemistry, National Changhua University of Education, Changhua 50058,
Taiwan
b Instrumentation Center, National Taiwan University, Taipei, Taiwan
c Department of Chemistry, National Taiwan University, Taipei 10764, Taiwan
A series of linear trinuclear selenolate complexes of the general type [(OC)3Fe(µ-SePh)3M(µ-SePh)3Fe(CO)3]
(M = ZnII 1, CdII 2, NiII 3 or FeII 4) has been synthesized by reaction of the appropriate [M(H2O)n]2ϩ with the
chelating metalloligand fac-[N(PPh3)2][Fe(CO)3(SePh)3] in acetonitrile. Their structures were elucidated on the
basis of IR, UV/VIS, NMR spectra and X-ray crystallography. Compounds 1–4 are structurally related, each
containing two tridentate metalloligands resulting in a MSe6 co-ordination environment of virtual Oh symmetry.
Further reaction of 4 with 3 equivalents of 1,10-phenanthroline (phen) initially afforded the intermediate
[Fe(phen)3][Fe(CO)3(SePh)3]2 but eventually neutral [Fe(CO)2(phen)(SePh)2] 5 was formed as the sole product.
Its crystal structure has been determined. This investigation shows that fac-[Fe(CO)3(SePh)3]Ϫ serves as a
tridentate chelating metalloligand and selenolate ligand-transfer reagent.
The study of transition-metal selenolate and tellurolate chem-
istry has been actively pursued in several laboratories recently,1
motivated primarily by the bonding diversity,2 reactivity,3
potential use as precursors for M/Se materials,4 and the rele-
vance of such complexes to biomimetic chemistry.5 (e.g., the
structure of the NiFeSe hydrogenase from Desulfovibrio
baculatus revealed that the nickel is ligated to one Se atom, one
or two S/Cl atoms, and three to four N/O atoms;5f the crystal
structure of NiFe hydrogenase isolated from Desulfovibrio gigas
is a Ni᎐Fe binuclear complex bridged by thiocysteines.5g) Some
examples of complexes containing homoleptic hexathiolato-
metal or hexaselenolatometal cores have been reported and
characterized by X-ray crystallography.6,7
Recent work in this laboratory showed that cis-[Mn(CO)4-
(ER)2]Ϫ complexes which contain delocalized lone pairs of elec-
trons around chalcogen atoms are useful in the syntheses of
heterotrimetallic MnI᎐CoIII᎐MnI-chalcogenolate complexes
[(OC)4Mn(µ-ER)2Co(CO)(µ-EЈR)3Mn(CO)3] (E = EЈ = Te, R =
Ph; E = Te, EЈ = Se, R = Ph) and [(OC)3Mn(µ-SePh)3Co-
(µ-SePh)3Mn(CO)3]Ϫ.7,8 In these reactions the complexes cis-
[Mn(CO)4(ER)2]Ϫ act as potential ‘chelating metallo ligands’,
and the chelating properties of these manganese() chalco-
genolate complexes offer novel routes toward heterometallic
chalcogenolate species.
niques or in a glove-box (argon gas). Solvents were distilled
under nitrogen from appropriate drying agents (diethyl ether
from CaH2; acetonitrile from CaH2–P2O5; hexane and tetra-
hydrofuran (thf) from sodium–benzophenone) and stored in
dried, N2-filled flasks over 4 Å molecular sieves. A nitrogen
purge was used on these solvents before use and transfers to
reaction vessels were via stainless-steel cannula under N2 at a
positive pressure. The reagents iron pentacarbonyl, diphenyl
diselenide, bis(triphenylphosphoranylidene)ammonium chlor-
ide, Zn(BF4)2ؒ6H2O, Ni(NO3)2ؒ6H2O, Cd(NO3)2ؒ4H2O, 1,10-
phenanthroline and Fe(ClO4)2ؒ6H2O (Aldrich) were used as
received. The complex fac-[N(PPh3)2][Fe(CO)3(SePh)3] was
prepared by the literature method.9a Infrared spectra were
recorded on Bio-Rad FTS-185 and FTS-7 FTIR spectro-
meters with sealed solution cells (0.1 mm) and KBr windows,
1
NMR spectra on a Bruker AC 200 spectrometer, H and 13C
chemical shifts being relative to tetramethylsilane and UV/VIS
spectra on a GBC 918 spectrophotometer. Cyclic voltammetric
measurements were performed on a BAS-100B electrochemical
analyzer, using glassy carbon as the working electrode, and
[NBun ][PF6] as the supporting electrolyte. Analyses of carbon,
4
hydrogen and nitrogen were obtained with a CHN analyzer
(Heraeus).
In order to investigate the chelating ability of fac-[Fe(CO)3-
(SePh)3]Ϫ,9 we have studied its reactivity toward [M(H2O)n]2ϩ
fragments. In this paper we report the syntheses and character-
ization of the series of trinuclear clusters [(OC)3Fe(µ-SePh)3-
M(µ-SePh)3Fe(CO)3] (M = Zn 1, Cd 2, Ni 3 or Fe 4), with the
central MII atom co-ordinated by six bridging benzeneseleno-
lates leading to a M(SePh)6 core of virtual Oh symmetry, and
neutral [Fe(CO)2(phen)(SePh)2] 5 (phen = 1,10-phenanthroline).
The formation of complex 5 from the intermediate [Fe-
(phen)3][Fe(CO)3(SePh)3]2 requires the transfer of selenolate
and CO ligands from one iron() center to another.
Preparations
[(OC)3Fe(ì-SePh)3M(ì-SePh)3Fe(CO)3] (M ؍ Zn 1, Cd 2 or
Ni 3). The complex fac-[N(PPh3)2][Fe(CO)3(SePh)3] (0.4 mmol,
0.458 g) dissolved in MeCN (5 cm3) was stirred under N2, and
Zn(BF4)2ؒ6H2O (0.2 mmol, 0.070 g), Cd(NO3)2ؒ4H2O (0.2
mmol, 0.062 g) or fac-[N(PPh3)2][Fe(CO)3(SePh)3] (1 mmol,
1.147 g) and Ni(NO3)2ؒ6H2O (0.5 mmol, 0.146 g) in MeCN
solution added by cannula under a positive pressure of N2 at
ambient temperature. After stirring for 4 h, a brown solid was
precipitated. The mother-liquor was removed via cannula and
the solid washed with MeCN. The brown solid was dried under
vacuum; thf–hexane (1:2 ratio) was added, and the dark brown
solution filtered to remove the insoluble solid. The product was
isolated by removing the solvent. The yield of dark brown
[(OC)3Fe(µ-SePh)3Zn(µ-SePh)3Fe(CO)3] 1 was 0.13 g (50%).
Experimental
Manipulations, reactions, and transfers of samples were con-
ducted under nitrogen according to standard Schlenk tech-
J. Chem. Soc., Dalton Trans., 1998, Pages 353–358
353

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Diffusion of hexane in a thf solution of this complex at
Ϫ15 ЊC for 4 weeks afforded dark brown crystals suitable for
X-ray crystallography. IR (thf): ν(CO) 2070vs and 2019s
cmϪ1. 1H NMR (C4D8O): δ 7.21–7.62 (m, Ph). 13C NMR
(C4D8O): δ 128.5, 129.8, 130.0, 132.1 and 133.4. Absorption
spectrum (thf): λmax/nm (ε/Ϫ1 cmϪ1) 324 (23 920), 606 (470)
(Found: C, 39.60; H, 2.55. Calc. for C42H30Fe2O6Se6Zn: C,
39.36; H, 2.36%). The yield of complex 2 was 0.192 g (72%)
of a dark red solid. Diffusion of hexane into a solution of
[(OC)3Fe(µ-SePh)3Cd(µ-SePh)3Fe(CO)3] in thf at Ϫ15 ЊC for 4
weeks led to dark red crystals suitable for X-ray crystal-
Crystallography
Crystallographic data for complexes 1–5 are collected in Table
1. All crystals were chunky: 1, dark brown, ca. 0.40 × 0.50 ×
0.60 mm; 2, dark red, 0.50 × 0.50 × 0.60 mm; 3, dark red-
brown, 0.35 × 0.50 × 0.60 mm; 4, dark brown, 0.40 × 0.50 ×
0.50 mm; 5, dark red-brown, 0.40 × 0.60 × 0.60 mm. Each was
mounted on a glass fiber and quickly coated in epoxy resin. The
unit-cell parameters were obtained by least-squares refinement
from 25 reflections with 2θ between 19.22 and 24.32Њ for 1,
16.40 < 2θ < 29.60Њ for 2, 20.00 < 2θ < 24.00Њ for 3, 16.22 <
2θ < 29.66Њ for 4, and 18.80 < 2θ < 25.26Њ for 5. Least-squares
refinement of the positional and anisotropic thermal para-
meters for all non-hydrogen atoms and fixed hydrogen atoms
contribution was based on F. Diffraction measurements were
carried out at 25 ЊC on a Nonius CAD 4 diffractometer
with graphite-monochromated Mo-Kα radiation (λ 0.7107 Å)
employing the θ–2θ scan mode.10 A ψ-scan absorption correc-
tion was made. The NRCC-SDP-VAX package of programs
was employed and atomic scattering factors were from ref. 12.
CCDC reference number 186/801.
1
lography. IR (thf): ν(CO) 2072vs and 2021s cmϪ1. H NMR
(C4D8O): δ 7.01–7.78 (m, Ph). 13C NMR (C4D8O): δ 132.1,
130.0, 129.6 and 128.5. Absorption spectrum (thf): λmax/nm
(ε/Ϫ1 cmϪ1) 327 (8880) (Found: C, 37.86; H, 2.28. Calc. for
C42H30CdFe2O6Se6: C, 37.97; H, 2.28%). Complex 3 was iso-
lated in 90.6% (0.578 g) yield. Diffusion of hexane–cyclo-
hexane into a solution of [(OC)3Fe(µ-SePh)3Ni(µ-SePh)3-
Fe(CO)3] in thf at Ϫ15 ЊC for 3 weeks afforded dark red-
1
brown crystals. IR (thf): ν(CO) 2070vs and 2019s cmϪ1. H
NMR (C4D8O): δ 13.71 (br), 7.61 (br) and 7.26 (br) (Ph). 13C
NMR (C4D8O): δ 160.0, 132.1, 130.0 and 128.4. Absorption
spectrum (thf): λmax/nm (ε/Ϫ1 cmϪ1) 410 (9622) and 660 (788)
(Found: C, 39.33; H, 2.43. Calc. for C42H30Fe2NiO6Se6: C,
39.57; H, 2.37%).
Results and Discussion
As illustrated in Scheme 1, reaction of fac-[N(PPh3)2]-
[Fe(CO)3(SePh)3] and Zn(BF4)2ؒ6H2O, Cd(NO3)2ؒ4H2O or
Ni(NO3)2ؒ6H2O in a 2:1 molar ratio in MeCN gave trinuclear
[(OC)3Fe(µ-SePh)3M(µ-SePh)3Fe(CO)3] (M = Zn 1, Cd 2 or Ni
3) as a dark brown solid by salt elimination ([N(PPh3)2][BF4]/
[N(PPh3)2][NO3]) without the risk of adduct formation.
Syntheses of 1–3 undertaken in thf solvent at ambient tem-
perature proved unsuccessful. The heterotrimetallic complexes,
which are stable and display no tendency to decompose
under nitrogen at ambient temperature overnight, are sparingly
soluble in common organic solvents like acetonitrile and
hexane.
CAUTION: perchlorate salts of metal complexes with
organic ligands are potentially explosive; only small amounts of
material should be prepared and handled with great caution.
[(OC)3Fe(ì-SePh)3Fe(ì-SePh)3Fe(CO)3] 4. A solution con-
taining fac-[N(PPh3)2][Fe(CO)3(SePh)3] (0.4 mmol, 0.458 g) and
Fe(ClO4)2ؒ6H2O (0.2 mmol, 0.073 g) in acetonitrile (10 cm3) was
stirred under nitrogen at ambient temperature for 1 h. A brown
solution accompanied by a dark brown solid was formed. The
mother-liquor was removed under a positive pressure of N2 and
the dark brown solid was washed twice with acetonitrile.
Tetrahydrofuran was added to extract the product, and then
hexane was slowly added to precipitate a dark brown solid
[yield 0.205 g (80%)]. The dark brown thf solution was layered
with hexane; storage for 4 weeks at Ϫ15 ЊC led to dark brown
crystals of [(OC)3Fe(µ-SePh)3Fe(µ-SePh)3Fe(CO)3] suitable for
X-ray crystallography. IR (thf): ν(CO) 2069vs and 2019s cmϪ1.
1H NMR (C4D8O): δ Ϫ7.82 (br), Ϫ33.23 (br) and 0.94 (br) (Ph).
Absorption spectrum (thf): λmax/nm (ε/Ϫ1 cmϪ1) 611 (644) and
338 (10 638) (Found: C, 39.66; H, 2.44. Calc. for C42H30Fe3-
O6Se6: C, 39.66: H, 2.38%).
The IR carbonyl stretching and 1H and 13C NMR spectra are
consistent with the presence of the six-co-ordination of d10
ZnII, d10 CdII, d8 NiII and low-spin octahedrally co-ordinated d6
FeII with facial tricarbonyls. The electronic spectrum of com-
plex 1 is dominated by ligand-to-metal charge-transfer bands at
approximately 324 and 606 nm. It is notable that fac-
[N(PPh3)2][Fe(CO)3(SePh)3] is an effective tridentate ligand
for stabilizing six-co-ordinated d10 zinc()/cadmium() and
d8 nickel() cores. However, its reaction with Ni(NO3)2ؒ6H2O
or NiCl2 in thf led to decomposition at room temperature.
The results suggest that this series of synthetic reactions
are highly dependent on solvent and reactants. Compounds
1–3 are strongly colored and stable to both oxygen and
moisture.
The definitive assignment of the structure of complex 1 was
obtained by X-ray crystallography. An ORTEP13 plot of the
neutral trimetallic compound with its numbering scheme is
shown in Fig. 1, selected bond distances and angles are given in
Table 2. Complex 1 has a linear chain of one zinc() and two
iron() atoms; two outer Fe atoms are co-ordinated by three
bridging SePh ligands and three terminal carbonyls, while the
central ZnII is co-ordinated by six bridging benzeneselenolates
giving a ZnSe6 core of virtual Oh symmetry. Thus, two fac-
[Fe(CO)3(SePh)3]Ϫ act as tridentate ligands to encapsulate the
ZnII. Following the proposal of Stiefel and Brown,14 the six-co-
ordinate polyhedron of D3 symmetry can be defined by the two
parameters Ø and s/h, i.e. the twist angle between two parallel
[Fe(CO)2(phen)(SePh)2] 5.
A solution containing fac-
[N(PPh3)2][Fe(CO)3(SePh)3] (0.458 g, 0.4 mmol) in acetonitrile
(5 cm3) was added to a mixture of 1,10-phenanthroline (0.109 g,
0.6 mmol) and Fe(ClO4)2ؒ6H2O (0.073 g, 0.2 mmol) in thf (5
cm3). The reaction was monitored by FTIR spectroscopy. The
IR spectrum, ν(CO) (MeCN–thf) 2040vs and 1980vs cmϪ1,
indicated the formation of the intermediate [Fe(phen)3][Fe-
(CO)3(SePh)3]2. After stirring overnight at room temperature
the solvent was removed under reduced pressure. The residue
was dissolved in thf (10 cm3) under N2, and the dark red-brown
solution filtered to remove [N(PPh3)2][ClO4]. The filtrate (in thf)
was stored in a refrigerator (Ϫ15 ЊC) for 3 weeks to induce
precipitation of dark red-brown crystals of [Fe(CO)2(phen)-
(SePh)2]. The crystals, suitable for X-ray crystallography, were
recrystallized by vapor diffusion of hexane into a concentrated
thf solution at Ϫ15 ЊC. Yield 0.332 g (91%). IR (thf): ν(CO)
2013vs and 1967s cmϪ1. 1H NMR (C4D8O): δ 9.46 (d), 8.37 (d),
7.83 (s), 7.76 (dd), 7.6 (m), 6.65 (m) and 6.33 (m). 13C NMR
(C4D8O): δ 218.8 (s) (CO), 153.8 (s), 146.6 (s), 137.6 (s), 136.0
(s), 132.1 (s), 131.5 (s), 130.8 (s), 130.0 (s), 128.5 (s), 127.7 (s),
127.3 (s), 125.9 (s) and 125.5 (s). Absorption spectrum (thf):
λmax/nm (ε/Ϫ1 cmϪ1) 330 (8552) (Found: C, 51.58; H, 3.04; N,
4.53. Calc. for C26H18FeN2O2Se2: C, 51.69; H, 3.00; N, 4.66%).
2 fac-[Fe(CO)3(SePh)3]Ϫ ϩ M2ϩ →
[(OC)3Fe(µ-SePh)3M(µ-SePh)3Fe(CO)3]
1 M = Zn
2 M = Cd
3 M = Ni
Scheme 1
354
J. Chem. Soc., Dalton Trans., 1998, Pages 353–358

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Table 1 Crystallographic data for complexes 1–5
1ؒthf
2ؒthf
3ؒ1.5 C6H12ؒ1.5 thf
4ؒthf
5ؒ2H2O
Formula
M
C46H38Fe2O7Se6Zn
1353.62
C46H38CdFe2O7Se6
1400.64
C57H60Fe2NiO7.5Se6
1509.55
C46H38Fe3O7Se6
1344.09
C26H22FeN2O4Se2
636.20
Crystal system
Space group
Triclinic
P1
Triclinic
P1
Cubic
Ia3
Triclinic
P1
Tetragonal
I41/a
¯
¯
¯
¯
a/Å
b/Å
c/Å
α/Њ
11.471(3)
12.830(4)
19.210(8)
72.50(3)
73.86(3)
67.32(3)
2445(1)
2
1.839
55.47
0.053
0.045
11.337(3)
13.266(4)
19.516(6)
70.07(3)
73.29(3)
67.36(3)
2505(1)
2
1.857
53.46
0.037
0.036
28.443(4)
11.465(5)
12.847(3)
19.208(7)
72.51(3)
74.05(4)
67.37(4)
2450(9)
2
1.822
53.3
0.075
0.068
13.953(4)
24.167(8)
β/Њ
γ/Њ
U/Å3
230 11(3)
16
1.743
46.23
0.062
0.073
1.04
4705(2)
8
1.796
37.3
0.069
0.078
3.03
Z
Dc/g cmϪ3
µ/cmϪ1
R
RЈ
Goodness of fit
1.72
1.51
1.74
¹
¹
R = Σ|(Fo Ϫ Fc)|/ΣFo. RЈ = [Σw(Fo Ϫ Fc)2/ΣwFo ]². Goodness of fit = [Σw(Fo Ϫ Fc)2/(M Ϫ N)]² where M = number of reflections and N = number of
2
parameters.
Table 2 Selected bond distances (Å) and angles (Њ) for complexes 1–3
Complex 1
Se(1)᎐Zn
Se(2)᎐Zn
Se(3)᎐Zn
Se(1)᎐Fe(1)
Se(2)᎐Fe(1)
Se(3)᎐Fe(1)
2.622(2)
2.643(2)
2.632(2)
2.464(3)
2.464(2)
2.454(2)
Se(4)᎐Zn
Se(5)᎐Zn
Se(6)᎐Zn
Se(4)᎐Fe(2)
Se(5)᎐Fe(2)
Se(6)᎐Fe(2)
2.644(2)
2.613(2)
2.597(2)
2.460(2)
2.461(2)
2.453(2)
Se(1)᎐Zn᎐Se(2)
Se(1)᎐Zn᎐Se(4)
Se)1)᎐Fe(1)᎐Se(2)
Se(1)᎐Fe(1)᎐Se(3)
Se(1)᎐Fe(1)᎐C(2)
Se(2)᎐Fe(1)᎐Se(3)
Zn᎐Se(2)᎐C(13)
78.87(7)
107.37(7)
85.47(8)
84.60(8)
87.3(4)
85.08(8)
119.4(3)
Se(1)᎐Zn᎐Se(3)
Se(1)᎐Zn᎐Se(5)
Se(1)᎐Zn᎐Se(6)
Se(1)᎐Fe(1)᎐C(1)
Se(1)᎐Fe(1)᎐C(3)
Zn᎐Se(2)᎐Fe(1)
Fe(1)᎐Se(2)᎐C(13)
78.10(7)
97.00(8)
171.50(9)
94.1(4)
170.8(4)
81.55(7)
108.6(3)
Complex 2
Cd᎐Se(1)
Cd᎐Se(2)
Cd᎐Se(3)
Cd᎐Se(4)
Cd᎐Se(5)
Cd᎐Se(6)
2.772(1)
2.800(2)
2.852(1)
2.822(1)
2.789(2)
2.758(1)
Fe(1)᎐Se(1)
Fe(1)᎐Se(2)
Fe(1)᎐Se(3)
Fe(2)᎐Se(4)
Fe(2)᎐Se(5)
Fe(2)᎐Se(6)
2.470(2)
2.469(2)
2.457(2)
2.471(2)
2.461(2)
2.463(2)
Se(1)᎐Cd᎐Se(2)
Se(1)᎐Cd᎐Se(4)
Se(1)᎐Cd᎐Se(6)
Se(1)᎐Fe(1)᎐Se(3)
Cd᎐Se(2)᎐Fe(1)
75.09(5)
114.06(4)
168.71(4)
85.72(6)
84.22(5)
Se(1)᎐Cd᎐Se(3)
Se(1)᎐Cd᎐Se(5)
Se(1)᎐Fe(1)᎐Se(2)
Cd᎐Se(1)᎐Fe(1)
Cd᎐Se(3)᎐Fe(1)
73.13(4)
101.32(5)
86.89(6)
84.81(5)
83.33(5)
Fig.
1
An ORTEP13 drawing and labeling scheme of neutral
[(OC)3Fe(µ-SePh)3M(µ-SePh)3Fe(CO)3] (M = Zn 1, Cd 2 or Fe 4 with
thermal ellipsoids drawn at the 20% probability level
lengthening may be due to steric effects of the six benzene-
selenolates. The mean FeII᎐Se bond of length 2.459(2) Å is
comparable with the average of 2.459(2) Å in fac-[N(PPh3)2]-
[Fe(CO)3(SePh)3].9a The cofacial Se᎐Zn᎐Se angles are 78.73(7)Њ
(average). The Se᎐Fe᎐Se angle [average 85.05(8)Њ] is not very
different from that found in fac-[N(PPh3)2][Fe(CO)3(SePh)3]
[average 85.24(8)Њ]9a suggesting that binding to a second metal
(ZnII) has little influence on the Se᎐FeII᎐Se angles.
Complex 3
Ni᎐Se
2.511(2)
Fe᎐Se
2.460(4)
Fe᎐Ni᎐Fe
Se᎐Ni᎐Se
Se᎐Fe᎐Se
Ni᎐Se᎐C(2)
180.0
Se᎐Ni᎐Se
Se᎐Ni᎐Se
Ni᎐Se᎐Fe
Fe᎐Se᎐C(2)
81.83(7)
180.0
80.22(1)
113.3(7)
98.18(7)
83.92(17)
116.0(7)
Complex 2 (Fig. 1, selected bond distances and angles in
Table 2) is essentially isostructural with 1. The six-co-ordinated
CdII bearing six bridging selenolate ligands has the longest
CdII᎐Se bonds [2.799(2) Å, average] among the reported
cadmium complexes bearing bridging selenolate ligands, e.g.
[{Cd(SeC6H2But-2,4,6)2}2] [average 2.646(4) Å],2d [{Cd2-
(µ-SePh)2(SePh)2(Et2PC2H4PEt2)}∞] (2.678 Å)4c and [Cd8-
(µ-S)(µ-SePh)12(SePh)4]2Ϫ (2.638 Å).19
triangular faces of the polyhedron and the ratio of the side of
the triangle to the distance between the triangles.15,16 In the
Zn(SePh)6 core of complex 1 Ø = 48.4Њ and s/h = 1.47, indicat-
ing that the structure is elongated along one of the pseudo-C3
axes, and adopts a conformation in which two adjacent tri-
angles are almost staggered. The Fe ؒ ؒ ؒ Zn distances, average
3.32(2) Å [Zn ؒ ؒ ؒ Fe(1) 3.338(3) and Zn ؒ ؒ ؒ Fe(2) 3.302(3) Å],
exclude any direct metal–metal interactions. The ZnII᎐SePh
bond distances [average 2.625(2), range from 2.597(2) to
2.644(2) Å] are significantly longer than the average of 2.515(3)
Compound 3 displays intense charge-transfer transitions at
1
410 and 660 nm. The H NMR spectrum exhibits broadening
and shifting of resonances, indicative of two unpaired spins for
d8 nickel() in a distorted Oh ligand field.
Å
in [(thf)4Eu(µ-SePh)3Zn(SePh)],2b 2.469(2)
[Zn(SePh)4]2Ϫ,17 and 2.477(3) Å in [Zn4(SePh)10]2Ϫ.18 This
Å
in
The X-ray structural analysis (Fig. 2) of complex 3 reveals a
J. Chem. Soc., Dalton Trans., 1998, Pages 353–358
355

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Table 3 Selected bond distances (Å) and angles (Њ) for complexes 4
and 5
Complex 4
Fe᎐Se(1)
Fe᎐Se(3)
Fe᎐Se(5)
Fe(1)᎐Se(1)
Fe(1)᎐Se(3)
Se(2)᎐C(13)
2.627(10)
2.628(3)
2.618(3)
2.469(3)
2.457(5)
1.949(14)
Fe᎐Se(2)
Fe᎐Se(4)
Fe᎐Se(6)
Fe(1)᎐Se(2)
Se(1)᎐C(7)
Se(3)᎐C(19)
2.640(3)
2.641(3)
2.594(10)
2.463(5)
1.878(17)
1.938(14)
Se(1)᎐Fe᎐Se(2)
Se(1)᎐Fe᎐Se(4)
Se(1)᎐Fe᎐Se(6)
Fe᎐Se(1)᎐C(7)
78.79(10)
107.01(10)
171.51(12)
116.6(5)
Se(1)᎐Fe᎐Se(3)
Se(1)᎐Fe᎐Se(5)
Fe᎐Se(1)᎐Fe(1)
78.37(10)
96.87(10)
81.81(15)
Fe(1)᎐Se(1)᎐C(7) 113.0(5)
Complex 5
Fe᎐Se
Fe᎐C(1)
2.474(1)
1.773(12)
Fe᎐N
Se᎐C(8)
1.989(8)
1.935(10)
Se᎐Fe᎐SeЈ
Se᎐Fe᎐NЈ
Se᎐Fe᎐C(1Ј)
NЈ᎐Fe᎐C(1)
C(1)᎐Fe᎐C(1Ј)
175.46(11)
91.8(3)
88.1(4)
176.2(4)
89.0(5)
Se᎐Fe᎐N
91.6(3)
88.7(4)
94.8(4)
81.3(3)
Se᎐Fe᎐C(1)
N᎐Fe᎐C(1)
N᎐Fe᎐NЈ
Fig. 2 An ORTEP drawing and labeling scheme of [(OC)3Fe(µ-SePh)3-
Ni(µ-SePh)3Fe(CO)3] 3 with thermal ellipsoids drawn at the 30%
probability level
MeCN gave trinuclear [(OC)3Fe(µ-SePh)3Fe(µ-SePh)3Fe(CO)3]
1
4 as a dark brown solid. Complex 4 exhibits a diagnostic H
centrosymmetric trinuclear iron–nickel–iron selenolate complex
in which the NiII is in a distorted octahedral arrangement with
the selenium atoms of benzeneselenolates in two parallel faces
of the octahedron capped by tricarbonyliron() fragments. The
structure of complex 3 contains two symmetrically independent
NMR spectrum with the aryl proton resonances well removed
from the diamagnetic region. The o- and p-protons resonate
upfield, δ Ϫ7.8 and Ϫ33.2, while the m-protons are at δ 0.94
which is consistent with the central FeII having a high-spin and
the two terminal FeII having low-spin configurations as
observed in the analogue [(OC)3Fe(µ-SPh)3Fe(µ-SPh)3-
Fe(CO)3].22 Comparing 4 and [(OC)3Fe(µ-SPh)3Fe(µ-SPh)3-
Fe(CO)3], the increase in the upfield shift of the p-, o-protons of
the thiolate ligands (δ Ϫ12.2 and Ϫ43.8) compared to those of
the selenolate ligands (δ Ϫ7.8 and Ϫ33.2) reflects the nature
of the bonding between the metal and chalcogenolate ligands,
i.e. weaker orbital overlap in the Fe᎐Se bonds.23 The Mössbauer
spectrum exhibited two doublets in a 2:1 intensity ratio. The
isomer shifts occur at 0.23 and 0.35 mm sϪ1 with quadrupole
splittings of 0.31 and 0.93 mm sϪ1 respectively for complex 4.
The molecular structure of complex 4 is shown in Fig. 1 and
selected bond distances and angles are summarized in Table 3.
In the FeSe6 core, Ø = 48.4 and s/h = 1.47.14 The Fe ؒ ؒ ؒ Fe dis-
tance averages to 3.32(2) Å [Fe(1) ؒ ؒ ؒ Fe(2) 3.306(5) and
¯
molecules of 3 and both molecules locate at 3 with the same
geometry. The arrangement of the selenolate substituents is
symmetrical so that the Fe᎐Ni᎐Fe vector lies on a three-fold
rotation axis. Neutral 3 appears to have no precedent in iron–
nickel–selenolate chemistry. In concordance with the earlier
discussion, the Ni(SePh)6 core has Ø = 60Њ and s/h = 1.53. The
Fe᎐Ni᎐Fe angle of 180.0Њ and the staggered conformation of
two parallel triangular benzeneselenolate faces promise the best
minimization of interactions between the selenolates.20 The
Se᎐Ni᎐Se angles are divided into two groups (Table 2), 81.95(7)
(average) and 98.05(7)Њ (average, different facial groups). The
NiII᎐Se bond distance is 2.509(2) Å (average), which is signifi-
cantly longer than that in [Ni2(µ-2,4,6-Me3C6H2Se)2(2,4,6-
Me3C6H2Se)4]2Ϫ [2.341(2)
Å
average],5b in [Ni(SePh)4]2Ϫ
[2.401(3) Å average],5b and in [{Ni(µ-SePh)(SePh)(dmphen)}2]
(dmphen = 2,9-dimethyl-1,10-phenanthroline) [2.432(1) Å].21
The NiII ؒ ؒ ؒ FeII distance [3.201(6) Å] is not short enough to
suggest a bonding interaction between the two metals.5g
Reaction of [Ni(η-C5H5)(C5H6)]ϩ and fac-[Fe(CO)3(SePh)3]Ϫ
in a 1:2 molar ratio in MeCN also yields complex 3. In a sense,
the triangular selenium atoms of the benzeneselenolates in the
tridentate metallo ligand fac-[Fe(CO)3(SePh)3]Ϫ act like
cyclopentadienyl, a six-π-electron donor ligand. We are cur-
rently pursuing this relationship.
Fe(2) ؒ ؒ ؒ Fe(3) 3.338(5) Å]. The average FeII ᎐Se distance (ter-
t
minal FeII᎐SePh) of 2.462(6) Å is close to the value of 2.459(2)
Å observed in fac-[Fe(CO)3(SePh)3]Ϫ.9a However, the six-co-
ordinated FeII bearing six bridging selenolate ligands has longer
FeII᎐Se bonds [2.625(3) Å, average], e.g. [Fe12(SePh)24] (average
2.441 Å).24 This lengthening effect might result in cleavage of
Fe᎐Se bonds under neutral Lewis-base ligands.
The reaction of complex 4 with 3 equivalents of 1,10-
phenanthroline in MeCN solution initially affords the inter-
mediate [Fe(phen)3][Fe(CO)3(SePh)3]2, but eventually neutral
[Fe(CO)2(phen)(SePh)2] 5 is formed as the sole product [Scheme
2(b)].† In order to clarify the formation of 5, as illustrated
in Scheme 2(c), a straightforward synthetic reaction was
conducted by addition of 2 equivalents of fac-[N(PPh3)2]-
[Fe(CO)3(SePh)3] to a mixture of Fe(ClO4)2ؒ6H2O and 3 equiv-
alents of 1,10-phenanthroline, in MeCN–thf under a nitrogen
atmosphere at ambient temperature. The reaction finally led to
the isolation of the dark red-brown complex 5. Its formation
from [Fe(phen)3][Fe(CO)3(SePh)3]2 requires the transfer of
As illustrated in Scheme 2(a), reaction of fac-[N(PPh3)2]-
[Fe(CO)3(SePh)3] and Fe(ClO4)2ؒ6H2O in a 2:1 molar ratio in
(a)
2 fac-[Fe(CO)3(SePh)3]Ϫ
[(OC)3Fe(µ-SePh)3Fe(µ-SePh)3Fe(CO)3]
ϩFe2ϩ
4
(b)
ϩ 3 phen
3[Fe(CO)2(phen)(SePh)2] ← [Fe(phen)3][Fe(CO)3(SePh)3]2
5
ϩ 2 fac-[Fe(CO)3(SePh)3]Ϫ
(c)
† Crystals of [Fe(phen)3][Fe(CO)3(SePh)3]2ؒ3H2OؒMeCN form in the
monoclinic space group C2/c with cell dimensions a = 25.280(5),
b = 14.802(2), c = 22.453(7) Å, β = 110.28(3)Њ, U = 7881(3) Å3, Z = 4,
R = 0.042 and RЈ = 0.037.
Fe(ClO4)2ؒ6H2O ϩ 3 phen
Scheme 2
356
J. Chem. Soc., Dalton Trans., 1998, Pages 353–358

View Article Online
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2 (a) S. P. Wuller, A. L. Seligson, G. P. Mitchell and J. Arnold, Inorg.
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3 C. P. Gerlach, V. Christou and J. Arnold, Inorg. Chem., 1996, 35,
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Fig.
3
An ORTEP drawing and labeling scheme of neutral
[Fe(CO)2(phen)(SePh)2] with thermal ellipsoids drawn at the 30%
probability level
selenolate and CO ligands from one iron() center to another.
This redistribution reaction suggests that the complex fac-
[Fe(CO)3(SePh)3]Ϫ serves as an intermetal selenolate-transfer
reagent.25 A carbon monoxide atmosphere prevents the forma-
tion of 5 when a mixture of [Fe(phen)3][Fe(CO)3(SePh)3]2 is
exposed to 1 atm (101 325 Pa) CO in MeCN at room tempera-
ture. Complex 5 is a stable, diamagnetic species soluble in
organic solvents. Its IR spectrum shows two strong CO stretch-
ing bands, supporting a cis position of two CO ligands. The
electrochemistry of complex 5, in thf with 0.05  [NBun ][PF6]
as supporting electrolyte, reveals two irreversible oxidations at
Ϫ0.01 and 1.00 V (vs. Ag–AgCl).
4
The definitive assignment of the structure of complex 5
was obtained by X-ray crystallography. An ORTEP plot of
the neutral complex with its numbering scheme is shown in
Fig. 3. The molecules possess a crystallographic two-fold axis
as defined by the equivalent atoms shown. The geometry
about the Fe can be described as distorted octahedral with
bond angles of 89.0(5)Њ for C(1)᎐Fe᎐C(1Ј), 81.3(3)Њ for
N᎐Fe᎐N and 175.46(11)Њ for Se᎐Fe᎐Se confirming the spec-
troscopic assignment of a cis-cis-trans (cct) configuration.
The Fe᎐SePh distances [2.474(1) Å] are comparable with
terminal Fe᎐SePh of 2.459(2) Å in fac-[Fe(CO)3(SePh)3]Ϫ,9a
the Fe᎐SePh distance of 2.460(12) Å in tetrahedral [Fe-
(SePh)4]2Ϫ,1b and the Fe᎐SeMe distance of 2.448(1) Å in cct-
[Fe(CO)2(SeMe)2(PMe3)2].9d Distances to the least-squares
planes (1,10-phenanthroline ligand) from the carbon atoms
of the phenyl rings range from 3.043(6) to 3.922(8) Å with an
average value of 3.500(9) Å.
6 P. M. Boorman, H.-B. Kraatz, M. Parvez and T. Ziegler, J. Chem.
Soc., Dalton Trans., 1993, 433.
7 W.-F. Liaw, W.-Z. Lee, C.-Y. Wang, G.-H. Lee and S.-M. Peng,
Inorg. Chem., 1997, 36, 1253.
8 W.-F. Liaw, D.-S. Ou, Y.-S. Li, W.-Z. Lee, C.-Y. Chuang, Y.-P. Lee,
G.-H. Lee and S.-M. Peng, Inorg. Chem., 1995, 34, 3747; W.-F. Liaw,
C.-Y. Chuang, W.-Z. Lee, C.-K. Lee, G.-H. Lee and S.-M. Peng,
Inorg. Chem., 1996, 35, 2530.
9 (a) W.-F. Liaw, C.-H. Lai, C.-K. Lee, G.-H. Lee and S.-M. Peng,
J. Chem. Soc., Dalton Trans., 1993, 2421; (b) W.-F. Liaw,
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1536; (c) W.-F. Liaw, C.-H. Lai, M.-H. Chiang, C.-K. Hsieh, G.-H.
Lee and S.-M. Peng, J. Chin. Chem. Soc. (Taipei), 1993, 40, 437;
(d) W.-F. Liaw, D.-S. Ou, Y.-C. Horng, C.-H. Lai, G. H. Lee and
S.-M. Peng, Inorg. Chem., 1994, 33, 2495.
It is of interest that the benzeneselenolates occupy trans
co-ordination sites, and the phenyl groups attached to seleni-
ums lie above and below the 1,10-phenanthroline ligand in
complex 5.26 When viewed along the Se᎐Fe᎐Se direction, the
phenyl rings at Se and 1,10-phenanthroline are seen in an off-
center face-to-face arrangement. This configuration lends
itself to optimize intramolecular ring–ring displaced face-to-
face and intramolecular non-bonded, weakly polar ring–ring
interactions.27
10 A. C. T. North, D. C. Philips and F. S. Mathews, Acta Crystallogr.,
Sect. A, 1968, 24, 351.
11 E. J. Gabe, Y. LePage, J. P. Charland, F. L. Lee and P. S. White,
J. Appl. Crystallogr., 1989, 22, 384.
12 International Tables for X-Ray Crystallography, Kynoch Press,
Birmingham, 1974, vol. 4.
13 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National
Laboratory, Oak Ridge, TN, 1976.
14 E. I. Stiefel and G. F. Brown, Inorg. Chem., 1972, 11, 434.
15 J. A. McCleverty, Prog. Inorg. Chem., 1968, 10, 49; R. Eisenberg,
Prog. Inorg. Chem., 1970, 12, 295.
16 D. L. Kepert, Prog. Inorg. Chem., 1977, 23, 1.
Acknowledgements
We thank Professor Teng-Yuan Dong (National Sun Yat-sen
University) for the Mössbauer spectra. The support of the
National Science Council (Taiwan) is gratefully acknowledged.
17 N. Ueyama, T. Sugawara, K. Sasaki, A. Nakamura, S. Yamashita,
Y. Wakatsuki, H. Yamazaki and N. Yasuoka, Inorg. Chem., 1988,
27, 741.
18 J. J. Vittal, P. A. W. Dean and N. C. Payne, Can. J. Chem., 1992, 70,
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19 G. S. Lee, K. J. Fisher, D. C. Craig, M. L. Scudder and I. G. Dance,
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20 E. I. Stiefel, R. Eisenberg, R. C. Rosenberg and H. B. Gray, J. Am.
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