Syntheses and structures of three complexes of formulas [L 3Co(μ2-O2P(Bn)2) 3CoL′][L″], featuring octahedral and tetrahedral cobalt(II) geometries; Variable-temperature magnetic susceptibility measurement and analysis on [(py)3Co(μ2-O2PBn 2)3Co(py)][ClO4]

Article abstract of DOI:10.1021/ic3004799

The syntheses and structural properties of three dinuclear complexes [L₃Co(μ₂-O₂P(Bn)₂) ₃CoL′][L″] [one ionic L₃ = py₃, L′ = py, L″ = ClO₄^- (1) and two molecular L₃ = py₃, L′ = Cl (2) and L₃ = py, μ₂-NO₃^-, L′ = py (3)] are reported. Complexes feature octahedral Co^II sites bridged by three dibenzylphosphinate ligands to a tetrahedrally ligated Co^II site, with the remaining coordination sites occupied by py, nitrato, and Cl ligands. The Co-Co distances are 4.248 A at 291 K and 4.265 A at 100 K for 1 and 4.278 and 4.0313(7) A for 2 and 3, respectively at 100 K. A fit of the low-temperature magnetic susceptibility data was derived for complex 1 with g = 2.25, TIP = 700 × 10^-6 cm³ mol ^-1, λ = -173 cm^-1, κ = 0.93, ν = -3.9, Δ = 630 cm^-1, J = 0.15 cm^-1, and θ = -1.8 resulting in R(π_M) = 2.5 × 10^-5 and R(π_MT) = 5.8 × 10^-5.

Full text of DOI:10.1021/ic3004799

Communication
pubs.acs.org/IC
Syntheses and Structures of Three Complexes of Formulas [L3Co(μ2-
O2P(Bn)2)3CoL′][L″], Featuring Octahedral and Tetrahedral Cobalt(II)
Geometries; Variable-Temperature Magnetic Susceptibility
Measurement and Analysis on [(py)3Co(μ2-O2PBn2)3Co(py)][ClO4]
John S. Maass,† Matthias Zeller,‡ Tanya M. Breault,§ Bart M. Bartlett,§ Hiroshi Sakiyama,⊥
and Rudy L. Luck*,†
†Department of Chemistry, Michigan Technological University, 1400 Townsend Drive, Houghton, Michigan 49931, United States
‡Department of Chemistry, Youngstown State University, 1 University Plaza, Youngstown, Ohio 44555, United States
§Department of Chemistry, University of Michigan, 930 N. University Avenue, Ann Arbor, Michigan 48109-1055, United States
⊥Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, 1-4-12 Kojirakawa, Yamagata 990-8560,
Japan
S
* Supporting Information
and cobalt have resulted in polymeric species.10−17 In an
ABSTRACT: The syntheses and structural properties of
three dinuclear complexes [L3 Co(μ2 -O2 P-
(Bn)2)3CoL′][L″] [one ionic L3 = py3, L′ = py, L″ =
ClO4− (1) and two molecular L3 = py3, L′ = Cl (2) and L3
extension of this work to prepare clusters of cobalt(III) oxides
or hydroxides,18 we find that this ligand affords dinuclear
clusters of the form [L3Co(μ2-O2P(CH2C6H5)2)3CoL′][L″].
Dark-blue crystals of [(py)3Co(μ2-O2PBn2)3Co(py)][ClO4]
(1) were isolated first from an ethanol solution consisting of
a mixture of Bn2PO2K, Co(ClO4)2·6H2O, pyridine (py), and
H2O2.19 It was later discovered that 1 can be made in good
yield by reacting 3 equiv of the potassium salt of the ligand with
2 equiv of cobalt perchlorate along with excess py in ethanol.
Compound [(py)3Co(μ2-O2P(Bn2)3Co(Cl)] (2) was also first
prepared unintentionally from the reaction of Co(NO3)2·6H2O
with py and Bn2PO2H in dichloromethane (DCM). The
addition of hexanes resulted in the formation of light-pink
crystals, which were found to be the known compound
Co(NO3)2(H2O)2(py)2. The solution was filtered, and the
addition of more hexanes produced dark-blue crystals of 2. The
chloride ion may have been produced from the reaction of py
with DCM,20 and we have discovered that compound 2 can be
produced starting with CoCl2·6H2O. Complex [(py)(μ2-
NO3)Co(μ2-O2PBn2)3Co(py)] (3) was obtained serendip-
itously in a reaction of CoIII(acac)2PyNO2 and Bn2PO2H
under reflux conditions in CHCl3. The addition of pentane,
followed by keeping the solution at 5 °C for 2 weeks, leads to
the formation of dark-purple crystals of 3.
A thermal ellipsoid plot of 1 is illustrated in Figure 1. In all
structures, the two Co centers are bridged by three
dibenzylphosphinate ligands. This ligand is very flexible and
is capable of bridging at various lengths, as illustrated in the
Co−Co distances in these compounds, which are 4.265(2),
4.278(1), and 4.0313(7) Å for 1−3, respectively. Complexes 1
and 2 were arranged with the octahedrally coordinated Co
atom arranged on a 3-fold axis and the tetrahedrally
coordinated Co atom located slightly off the 3-fold axis. In 1,
three py ligands complete the octahedral geometry at one end
and the other end has one py coordinated. The complex is
−
= py, μ2-NO3 , L′ = py (3)] are reported. Complexes
feature octahedral CoII sites bridged by three dibenzyl-
phosphinate ligands to a tetrahedrally ligated CoII site,
with the remaining coordination sites occupied by py,
nitrato, and Cl ligands. The Co−Co distances are 4.248 Å
at 291 K and 4.265 Å at 100 K for 1 and 4.278 and
4.0313(7) Å for 2 and 3, respectively at 100 K. A fit of the
low-temperature magnetic susceptibility data was derived
for complex 1 with g = 2.25, TIP = 700 × 10−6 cm3 mol −1
,
λ = −173 cm−1, κ = 0.93, ν = −3.9, Δ = 630 cm−1, J = 0.15
cm−1, and θ = −1.8 resulting in R(χM) = 2.5 × 10−5 and
R(χMT) = 5.8 × 10−5.
inuclear cobalt complexes featuring octahedral and
1,2
D
tetrahedral geometries with CoIII−CoII
and CoII−
3−5
CoII
centers have been reported. Magnetic studies have
been reported for three of the CoII−CoII compounds, which
have very different bridging ligands. First, for compound
[(H2O)(dppm)2Co(μ-CN)CoCl3], high-spin isolation (S =
3/2) pertained, but the linear nature of the data obtained (i.e.,
χMT vs T was linear) could not be satisfactorily analyzed.3
Second, for complex [Co2L2Cl3]Cl, L = 2,6-diamino-3-[(2-
carboxymethyl)phenylazo]pyridine, analysis of the magnetic
data resulted in the conclusion that “two low-spin Co2+ ions
pertained.”4 Third, for compound [(MeCN)5Co(NCS)Co-
(NCS)3] (4), magnetic analysis suggested that the data can be
best fit with the Curie−Weiss expression with gavg = 2.5 and θ =
−15.5 K.5 The Co−Co distances in these compounds were
5.007, 4.800, and 5.732 Å for the first to third, respectively.
Our interest in the complexes reported herein stems from
our discovery that the dibenzylphosphinate ligand stabilizes
tetrameric clusters such as [V4O8]4+, [Mo4O8]4+, and
[W4O8]4+.6−9 Previous research reacting phosphinate ligands
Received: March 2, 2012
Published: April 20, 2012
© 2012 American Chemical Society
4903
dx.doi.org/10.1021/ic3004799 | Inorg. Chem. 2012, 51, 4903−4905

Inorganic Chemistry
Communication
4T1 term.22 The temperature-dependent data χM on 1 were
obtained using a SQUID magnetometer over the temperature
range 2.0−300 K under a 1000 Oe measuring field, and this is
illustrated in Figure 2, together with the χMT dependence. At
Figure 1. Thermal ellipsoid drawing of 1-100K (one orientation).
Selected bond distances (Å) and angles (deg) are as follows: Co1−O1,
2.103(2); Co1−N1, 2.192(2); Co2−O2, 1.813(17); Co2−N2,
2.045(4); O1a−Co1−O1, 91.18(8); O1a−Co1−N1, 86.86(9); O1b−
Co1−N1, 177.33(8); O1−Co1−N1, 87.04(8); N1−Co1−N1a,
94.85(7); O2−Co2−O2b, 125.65(13); O2−Co2−N2, 103.6(7);
O2−Co2−O2a, 106.3(7); O2b−Co2−O2a, 106.0(6); O2b−Co2−N2,
111.3(8); N2−Co2−O2a, 101.6(2). Symmetry transformation codes:
a, −y, x − y, z; b, −x + y, −x, z.
Figure 2. Temperature dependence of χM vs T and χMT vs T for 1
with data represented by open circles and the solid-line fit obtained
using the parameters described in the text.
300 K, the χMT value for 1 was 5.813 emu K mol−1 compared
to 5.575 emu K mol−1 reported for 4.5 As shown in Figure 2,
χMT versus T for 1 decreases slowly from 5.813 emu K mol−1 at
300 K to 4.575 emu K mol−1 at 50 K and then more rapidly to
2.254 emu K mol−1 at 2 K. We were unable to determine a
satisfactory fit to the data using the Curie−Weiss equation, but
this is not surprising because analysis of high-spin cobalt(II)
complexes is known to be difficult.23−30
positively charged and is balanced by a [ClO4]− anion, as
illustrated in Figure 1.
Compound 2 has a similar octahedral geometry with three py
ligands, but at the other site, one chloride ligand completes the
tetrahedral arrangement. This complex also has the Co atoms
and the Cl ligand situated on a 3-fold axis, but both benzyl
groups are disordered. Compound 3 has a nitrato ligand
coordinated in a bidentate manner together with one py ligand
at the octahedral Co site and one py ligand at the other. Ring
strain in the four-membered ring of the nitrato ligand is
responsible for the longer Co−O distances at Co2−O7,
2.188(3) Å, and Co2−O8, 2.211(3) Å, compared to the
other Co−O distances at the octahedral site in 3, which range
from 2.031(2) to 2.069(2) Å.21 This complex did contain the
shortest Co−Co distance at 4.0313(7) Å within compounds 1−
3, and all feature octahedral and tetrahedral Co centers. The
bridging phosphinate ligands are asymmetrically bonded in that
the Co−O distances are significantly longer at the octahedral
site in comparison to those at the tetrahedral end, i.e., 2.103(2)
and 2.102(4) Å compared to 1.813(17) and 1.973(5) Å for 1
and 2, respectively. The disorder in these molecules hindered a
more accurate determination, but for 3, the distances at
2.031(2), 2.032(3), and 2.069(2) Å at the octahedral end were
also significantly longer than those at the tetrahedral site at
1.955(2), 1.933(2), and 1.940(2) Å for Co−O bonds on
phosphinate ligands P1, P2, and P3, respectively, all presumably
because of steric reasons.
A fit of the data for 1 and 4 was calculated using the
equations presented as Supporting Information; see Table 1.
This analysis involved consideration of the g factor and
temperature-independent paramagnetism (TIP) for the tetra-
hedral CoII ion, the spin−orbit coupling factor λ, the orbital
reduction factor κ, and a distortion parameter ν defined as Δ/
κλ for the octahedral CoII ion, and the intramolecular exchange
interaction J and the Weiss constant θ to describe the
intermolecular exchange interaction. In general, it is difficult
to separate the intramolecular interaction from the intermo-
lecular interaction. In particular, when J is negative, it is almost
impossible to determine J and θ correctly. If the calculation for
the fit of the low-temperature data modified J without
consideration of θ, the quality of the fit was not good;
however, this improved when θ was used instead of J.
Interestingly, when J and θ were simultaneously optimized, J
became positive (but small at 0.15 cm−1) and the lowest Rχ
value (i.e., even higher fitting quality) was obtained. The value
for the spin−orbit parameter λ of −173 cm−1 for 1 is
noteworthy for the theoretical value for the free CoII ion is
expected to be ∼−172 cm−1.31 That for κ at 0.93 is also close to
that for the free CoII ion.32 Both of these parameters were
calculated to be slightly less in complex 4.5 The values for Δ at
630 and 510 cm−1 for 1 and 4, respectively, are normal for
octahedral high-spin cobalt(II) complexes (∼200 to ∼800
cm−1).33 For 1, the negative ν value of −3.9 and the Δ value of
630 cm−1 suggest that the octahedral CoII ion is trigonally
compressed, and this is also consistent with the crystal structure
of 1, where O1a−Co1−O1 and N1−Co1−N1a are larger than
The χMT data for 1 and 2 were determined at room
temperature (ca. 290 K) using a Johnson Matthey Gouy
balance to be 5.56 and 6.59 emu K mol−1, respectively. These
values are larger than the spin-only value for two high-spin CoII
sites (3.75 emu K mol−1) and suggests that there is a
contribution of orbital angular momentum typical of the local
4904
dx.doi.org/10.1021/ic3004799 | Inorg. Chem. 2012, 51, 4903−4905

Inorganic Chemistry
Communication
a
Table 1. Magnetic Parameters
b
c
complex
g
TIP, emu mol−1
λ, cm−1
κ
ν
Δ, cm−1
J, cm−1
θ, K
Rχ, ×10−5
R
χT, ×10−5
1
2.25
2.17
0.0007
0.0007
−173
−155
0.93
0.89
−3.9
−3.7
630
0.15
−1.8
−0.1
2.5
15
5.8
16
d
4
510
c
−2.62
a
b
d
Calculated as in the Supporting Information. Rχ = ∑(χM,calc − χM,obs)2/∑(χM,obs)2. RχT = ∑(χM,calcT − χM,obsT)2/∑(χM,obsT)2. L = MeCN, L′ =
NCS.5
90° and O1a−Co1−N1 and O1−Co1−N1 are smaller than
90°.34 In conclusion, for complex 4,5 if J is assumed to be 0, |θ|
becomes large and unreasonable. Therefore, the sign and
magnitude of the J value at −2.62 cm−1 in Table 1 are
suggestive of antiferromagnetic interactions. However, in the
case of 1, the magnitude of J at 0.15 cm−1 is small and indicative
of very weak exchange interactions.
(11) Chandrasekhar, V.; Boomishankara, R.; Sasikumara, P.;
Nagarajan, L.; Cordes, A. W. Z. Anorg. Allg. Chem. 2005, 631,
2727−2732.
(12) Eichelberger, J. L.; Gillman, H. D. Inorganic coordination
polymers. XXI. Manganese(II), cobalt(II), nickel(II), copper(II), and
zinc(II) bis(N-phenylaminomethyl) phosphinates. Effects of coordinating
side groups; Pennwalt Corp.: Philadelphia, PA, 1977; p 18 pp.
(13) Giancotti, V.; Ripamonti, A. Chim. Ind. (Milan) 1966, 48, 1065−
1070.
ASSOCIATED CONTENT
(14) Giancotti, V.; Ripamonti, A. J. Chem. Soc. A 1969, 706−713.
(15) Gillman, H. D.; Eichelberger, J. L. Inorg. Chim. Acta 1977, 24,
31−34.
■
S
* Supporting Information
Preparations, FTIR spectra, equations for magnetic analysis,
and CIF files for 1-291K, 1-100K, 2-100K, and 3-100K (CCDC
869796−869799). This material is available free of charge via
the Internet at http://pubs.acs.org. The atomic coordinates for
these structures have also been deposited with the Cambridge
Crystallographic Data Centre. They can be obtained, upon
request, from the Director, Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.
(16) Giordano, F.; Randaccio, L.; Ripamonti, A. Chem. Commun.
1967, 19−20.
(17) Rose, S. H.; Block, B. P. J. Am. Chem. Soc. 1965, 87, 2076−2077.
(18) McAlpin, J. G.; Stich, T. A.; Ohlin, C. A.; Surendranath, Y.;
Nocera, D. G.; Casey, W. H.; Britt, R. D. J. Am. Chem. Soc. 2011, 133,
15444−15452.
(19) Crystal data for 1: C62H62Co2N4O6P3·ClO4, M = 1269.38,
hexagonal, a = b = 13.5260(10) Å, c = 57.341(4) Å, V = 9085.2(11)
Å3, T = 100(2) K, space group R3, Z = 6, 14927 reflections measured,
̅
5028 independent reflections (Rint = 0.0311). R1 = 0.0518 [I > 2σ(I)]
and wR2(F2) = 0.1126 [I > 2σ(I)]. GOF on F2 =1.018.
(20) Rudine, A. B.; Walter, M. G.; Wamser, C. C. J. Org. Chem. 2010,
75, 4292−4295.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: rluck@mtu.edu. Tel: (906)487 2309.
(21) Driessen, W. L.; de Graaff, R. A. G.; Parlevliet, F. J.; Reedijk, J.;
de Vos, R. M. Inorg. Chim. Acta 1994, 216, 43−49.
(22) Sakiyama, H.; Adams, H.; Fenton, D. E.; Cummings, L. R.;
McHugh, P. E.; Okawa, H. Open J. Inorg. Chem. 2011, 1, 33−38.
(23) Kahn, O. Molecular Magnetism; VCH: Berlin, 1993; p 380 pp.
(24) Lloret, F.; Julve, M.; Cano, J.; Ruiz-Garcia, R.; Pardo, E. Inorg.
Chim. Acta 2008, 361, 3432−3445.
(25) Sakiyama, H. J. Chem. Software 2001, 7, 171−178.
(26) Sakiyama, H. Inorg. Chim. Acta 2006, 359, 2097−2100.
(27) Sakiyama, H. J. Comput. Chem. Jpn 2007, 6, 123−134.
(28) Sakiyama, H. Inorg. Chim. Acta 2007, 360, 715−716.
(29) Tone, K.; Sakiyama, H.; Mikuriya, M.; Yamasaki, M.; Nishida, Y.
Inorg. Chem. Commun. 2007, 10, 944−947.
(30) Borta, A.; Gillon, B.; Gukasov, A.; Cousson, A.; Luneau, D.;
Jeanneau, E.; Ciumacov, I.; Sakiyama, H.; Tone, K.; Mikuriya, M. Phys.
Rev. B 2011, 83, 184429.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support by the Michigan Technological University is
gratefully acknowledged. The variable-temperature magnetic
data for [Co(NCMe)5Co(NCS)4] were supplied by Jack Guy
DaSilva from the laboratory of Professor Joel S. Miller. “SQUID
magnetometry at the University of Michigan is supported by an
NSF grant, CHE-1040008. The X-ray diffractometer was
funded by NSF Grant 0087210, Ohio Board of Regents
Grant CAP-491, and by Youngstown State University.
REFERENCES
(31) Figgis, B. N.; Hitchman, M. A. Ligand Field Theory and Its
Application; Wiley-VCH: New York, 2000.
■
(1) Chiari, B.; Cinti, A.; Crispu, O.; Demartin, F.; Pasini, A.;
Piovesana, O. J. Chem. Soc., Dalton Trans. 2001, 3611−3616.
(2) Panja, A.; Eichhorn, D. M. J. Coord. Chem. 2009, 62, 2600−2609.
(3) Li, W.; Zhan, S.-z.; Wang, J.-g.; Yan, W.-y.; Deng, Y.-f. Inorg.
Chem. Commun. 2008, 11, 681−683.
(32) Lines, M. E. J. Chem. Phys. 1971, 55, 2977−2984.
(33) Figgis, B. N.; Gerloch, M.; Lewis, J.; Mabbs, F. E.; Webb, G. A. J.
Chem. Soc. A 1968, 2086−2093.
(34) Stiefel, E. I.; Brown, G. F. Inorg. Chem. 1972, 11, 434−436.
(4) Tan, X.-w.; Xie, X.-h.; Chen, J.-y.; Zhan, S.-z. Inorg. Chem.
Commun. 2010, 13, 1455−1458.
(5) Shurdha, E.; Moore, C. E.; Rheingold, A. L.; Miller, J. S. Inorg.
Chem. 2011, 50, 10546−10548.
(6) Feng, L.; Maass, J. S.; Luck, R. L. Inorg. Chim. Acta 2011, 373,
85−92.
(7) Jimtaisong, A.; Feng, L.; Sreehari, S.; Bayse, C. A.; Luck, R. L. J.
Cluster Sci. 2008, 19, 181−195.
(8) Maass, J. S.; Chen, Z.; Zeller, M.; Luck, R. L. Dalton Trans. 2011,
40.
(9) Maass, J. S.; Zeller, M.; Holmes, D.; Bayse, C. A.; Luck, R. L. J.
Cluster Sci. 2011, 22, 193−210.
(10) Brechin, E. K.; Coxall, R. A.; Parkin, A.; Parsons, S.; Tasker, P.
A.; Winpenny, R. E. P. Angew. Chem., Int. Ed. 2001, 40, 2700−2703.
4905
dx.doi.org/10.1021/ic3004799 | Inorg. Chem. 2012, 51, 4903−4905