Complexes built with a scorpion-type tripodal ligand and metal ions: Syntheses, structural features, electrochemical properties and magnetic properties

Article abstract of DOI:10.1007/s11243-013-9693-9

The complexes [Fe(bpz*mpy)₂](ClO₄)₂ (1a), [Cu(bpz*mpy)₂](ClO₄)₂ (1b) and [Ag(bpz*mpy)(Ph₃P)](ClO₄) · H₂O (2) (bpz*mpy = pyridin-2-yl-bis(3,5-dimethylpyrazol-1-yl)methane) have been synthesized and characterized by physicochemical and spectroscopic methods. X-ray crystallographic analysis reveals that the central Fe^II and Cu^II ions in complexes 1a and 1b are located on a twofold rotation axis and have a distorted octahedral coordination sphere, while the Ag ^I center in complex 2 is tetrahedrally coordinated. The electrochemical properties of complex 1b have been investigated. Furthermore, a variable temperature magnetic susceptibility study of complex 1a has also been performed over the measured temperature range 2-300 K.

Full text of DOI:10.1007/s11243-013-9693-9

Transition Met Chem (2013) 38:307–311
DOI 10.1007/s11243-013-9693-9
Complexes built with a scorpion-type tripodal ligand and metal
ions: syntheses, structural features, electrochemical properties
and magnetic properties
•
Chao-Hu Xiao Jia-Cheng Liu Xue-Yan Song
•
•
•
Yun-Xia Yang Dong-Cheng Hu Chang-Dai Si
•
Received: 12 November 2012 / Accepted: 4 January 2013 / Published online: 20 January 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract The complexes [Fe(bpz*mpy)2](ClO4)2 (1a),
[Cu(bpz*mpy)2](ClO4)2 (1b) and [Ag(bpz*mpy)(Ph3P)]-
(ClO4) Á H2O (2) (bpz*mpy = pyridin-2-yl-bis(3,5-dim-
ethylpyrazol-1-yl)methane) have been synthesized and
characterized by physicochemical and spectroscopic methods.
X-ray crystallographic analysis reveals that the central
FeII and CuII ions in complexes 1a and 1b are located on a
twofold rotation axis and have a distorted octahedral
coordination sphere, while the AgI center in complex 2 is
tetrahedrally coordinated. The electrochemical properties
of complex 1b have been investigated. Furthermore, a vari-
able temperature magnetic susceptibility study of complex
1a has also been performed over the measured temperature
range 2–300 K.
[9], [Fe(L)2](BF4)2 (L = 2,6-bis(1H-pyrazol-1-yl)-4-(thio-
cyanatomethyl)-pyridine) [10], [Fe(dppFc)2] (BF4)2 Á 2Et2O
(dppFc = 1-ferrocenyl-2-{(2,6-bis(pyrazolyl)pyridyl)ethyl-
ene})[11].Becauseofboththepyridineandpyrazoleactingas
weakpdonorsandthepyridinebeingastrongerdonorthanthe
pyrazole, a series of related tripodal ligands containing
2-pyridyl substituents have been reported [12–16].
Herein, we report three new complexes employing a
scorpion-type tripodal ligand with 2-pyridyl substituents
and various metal ions (Scheme 1). Complexes 1a and 1b
show coordination by six nitrogen atoms from two ligands
and have a distorted octahedral coordination sphere, com-
plex 2 shows coordination by four atoms and the AgI center
is in a distorted tetrahedral geometry. In addition, the
electrochemical properties of complex 1b and the magnetic
properties of complex 1a are reported.
Introduction
Complexes containing N-heterocyclic rigid scorpion-type
ligands have been well studied because of their interesting
coordination chemistry and potential applications in electro-
chemistry, catalysis and magnetic properties [1–8]. Iron(II)
complexes containing heterocyclic nitrogen ligands are
known for their interesting magnetic properties. Some
examples of such compounds are [FeII{(pz)3CH}2][ClO4]2
Experimental
All reagents and solvents were commercially sourced and
used without further purification. The ligand bpz*mpy was
synthesized by a previously reported procedure [17, 18].
The IR spectra were recorded in the 4,000–400 cm-1
region as KBr pellets on a DIGILAB FTS3000 spectro-
photometer. Elemental analyses (C, H, N) were performed
on a Vario EL-III CHN elemental analyzer. Electrochem-
ical measurements were carried out with a CHI832
instrument, using a three-electrode system, consisting of a
carbon paste working electrode, Ag/AgCl as reference
electrode and platinum wire as counter electrode. Magnetic
susceptibility data (2–300 K) were collected using crushed
crystals of the sample on a Quantum Design MPMS
(SQUID)-XL magnetometer.
C.-H. Xiao Á J.-C. Liu (&) Á X.-Y. Song Á Y.-X. Yang Á
D.-C. Hu Á C.-D. Si
Key Laboratory of Polymer Materials of Gansu Province, Key
Laboratory of Bioelectrochemistry & Environmental Analysis of
Gansu College of Chemistry and Chemical Engineering,
Northwest Normal University, Lanzhou 730070, People’s
Republic of China
e-mail: jcliu8@nwnu.edu.cn
123

308
Transition Met Chem (2013) 38:307–311
Scheme 1 Chemical structures of [Fe(bpz*mpy)2](ClO4)2 (1a), [Cu(bpz*mpy)2](ClO4)2 (1b) and [Ag(bpz*mpy)(Ph3P)] (ClO4)ÁH2O (2)
Synthesis of [Fe(bpz*mpy)2](ClO4)2 (1a)
X-ray crystallography
To a solution of bpz*mpy (0.2 mmol, 56.3 mg) in 10 ml of
methanol, Fe(ClO4)3 Á 6H2O (0.1 mmol, 46.2 mg), plus
C6H5CO2Na (0.1 mmol, 12.2 mg) were added. The solu-
tion was stirred at r.t. for 30 min. Red block crystals were
obtained by evaporation after 2 weeks and washed with
methanol. Yield: 46 wt %. IR (KBr, cm-1): 3,444 (s),
3,130 (w), 1,635 (m), 1,562 (s), 1,457 (s), 1,419 (m), 1,398
(m), 1,346 (w), 1,315 (m), 1,248 (m), 1,101 (s), 1,075 (s),
905 (w), 871 (m), 819 (w), 776 (m), 688 (m), 623 (s), 527
(w). Anal. Calc. For C32H38N10O8Cl2Fe: C, 47.0; H, 4.7;
N, 17.1. Found: C, 47.6; H, 4.3; N, 17.2 %.
Diffraction intensity data for single crystals of the three
complexes were collected at room temperature on a Bruker
Smart 1000 CCD area detector equipped with graphite-
˚
monochromated Mo-Ka radiation (k = 0.71073 A).
Empirical absorption corrections were applied using the
SADABS program. The structure was solved by direct
methods using the SHELXTL program, and refinement on F2
was carried out by full-matrix least squares with anisotropic
thermal parameters for all non-hydrogen atoms [19–21]. In
addition, hydrogen atoms of the water molecule in complex 2
were not included for the water molecule in complex 2 is
positional disordered, and other hydrogen atoms were placed
at geometrically calculated positions by using a riding
model. The crystallographic data of the three complexes and
refinement details are summarized in Table 1.
Synthesis of [Cu(bpz*mpy)2](ClO4)2 (1b)
A similar procedure to that used for the complex 1a was
followed to obtain the complex 1b. Yield: 51 wt %. IR (KBr,
cm-1): 3,444 (s), 3,140 (w), 1,605 (m), 1,561 (s), 1,460(s),
1,419 (m), 1,393 (m), 1,345 (w), 1,313 (m), 1,245 (m), 1,106
(s), 1,080 (s), 983 (w), 885 (m), 822 (w), 788 (m), 689 (m),
624 (s), 522 (w). Anal. Calc. For C32H38N10O8Cl2Cu: C,
46.6; H, 4.6; N, 16.97. Found: C, 46.8; H, 4.3; N,17.0 %.
Results and discussion
One of the interesting features of complex 1a was that we
obtained iron(II), even in air, starting from an iron(III)
precursor. This may be associated with the sodium ben-
zoate that was added to the reaction mixture, but we have
not explored this redox reaction in any detail and it has
been reported by Anderson et al. [9].
Synthesis of [Ag(bpz*mpy)(Ph3P)] (ClO4)2ÁH2O (2)
A mixture of AgClO4 (20.7 mg, 0.1 mmol), PPh3 (26.2 mg,
0.1 mmol) and bpz*mpy (0.1 mmol, 28.2 mg) was dis-
solved in MeOH (20 mL) and then stirred for 1 h and filtered.
Colorless crystals were obtained from the filtrate after
standing at room temperature for 1 day. Yield: 70 %. IR
(KBr, cm-1): 3,446 (s), 3,057 (w), 1,975 (w), 1,602 (m),
1,561(m), 1,478 (m), 1,436 (s), 1,388 (m), 1,310 (m), 1,254
(m), 1,094 (s), 927 (w), 880 (m), 750 (s), 695 (s), 622 (s), 524
(s), 503 (s). Anal. Calc. For C34H37AgClN5O5P: C, 53.0; H,
4.8; N, 9.1. Found: C, 53.2; H, 4.6; N, 9.0 %.
Description of crystal structures of 1a and 1b
Perspective views of [Fe(bpz*mpy)2](ClO4)2 (1a) and
[Cu(bpz*mpy)2] (ClO4)2 (1b) are given in Fig. 1a and 1b,
respectively. Selected bond distances and angles are given
in Table 2. An X-ray diffraction study performed on com-
plexes 1a and 1b reveals that complex 1a crystallizes in the
123

Transition Met Chem (2013) 38:307–311
309
Table 1 Crystallographic data for complexes 1a–2
Complex
1a
1b
2
Empirical formula
Formula mass
Crystal system
Space group
C32H38Cl2FeN10O8
C32H38Cl2CuN10O8
C68H68Ag2Cl2N10O9P2
1,517.90
Orthorhombic
P2(1)2(1)2(1)
24.840
817.47
825.16
Orthorhombic
Monoclinic
Pbcn
C2/c
hmax (°)
27.550
27.450
˚
a (A)
8.8477(5)
25.1485(8)
14.390(3)
15.703(4)
16.399(4)
90.00
˚
b (A)
20.5923(15)
11.5803(4)
˚
c (A)
19.8105(12)
17.5626(6)
a (°)
b (°)
c (°)
90.00
90.00
90.00
131.652(2)
90.00
90.00
90.00
90.00
3
˚
V (A )
3,609.4(4)
3,821.7(2)
3,705.5(14)
2
Z
4
4
Dcalc (Mg m-3
)
1.504
1.434
1.360
l (mm-1
)
0.631
0.773
0.702
F (000)
1,696.0
1,708.0
1,552.0
No. of measured reflns.
No. of independent reflns.
Rint
17,748
16,687
25,406
4,159
4,337
6,361
0.0365
0.0251
0.0582
No. of parameters
240
240
428
Goodness of fit (GOF)
Final R indices [I [ 2r(I)]
R indices (all data)
1.069
1.070
1.063
R1 = 0.0559, wR2 = 0.1689
R1 = 0.0768, wR2 = 0.1834
R1 = 0.0516, wR2 = 0.1605
R1 = 0.0646, wR2 = 0.1726
R1 = 0.0585, wR2 = 0.1400
R1 = 0.0957, wR2 = 0.1597
orthorhombic system with space group Pbcn and complex 1b
crystallizes in the monoclinic system with space group C2/c.
The asymmetric units of complexes 1a and 1b consist of a
metal cation, two ligands and two uncoordinated perchloric
acid anions. The central Fe and Cu atoms are situated on a
twofold rotation axis and are coordinated by six nitrogen
atoms from two ligands. The Fe–N bond lengths range from
unit of complex 2 consists of an AgI cation, one ligand, one
uncoordinated perchloric acid anion and a half occupancy
uncoordinated water molecule. A perspective view of
complex 2 is given in Fig. 2, and selected bond distances
and angles are given in Table 3. The triphenylphosphine
ligand completes the N3P coordination geometry for Ag.
The Ag center is tetrahedrally coordinated, but the N–Ag–
N angles are significantly less than 90°, range from
77.5(2)° to 82.4(2)°.
˚
1.980(2) to 1.993(2) A which are similar to those observed
for related FeII complexes with similar tripodal type ligands
[9]. Hence, the central iron(II) ion coordination geometry
can be described as a slightly distorted octahedral coordi-
nation environment. In complex 1b, N(1), N(1A), N(5) and
N(5A) atoms form the equatorial plane with bond lengths of
Electrochemical behavior of [Cu(bpz*mpy)2] (ClO4)2
(1b)
˚
Cu–N being in the range of 2.033(2)–2.066(2) A, N(3), and
N(3A) atoms are in apical position with bond length of Cu–N
˚
being 2.320(2) A. Consequently, the complex 1b has a dis-
The electrochemical properties of complex 2 were studied
by cyclic voltammetry in acetonitrile solution using 1 M
tetrabutylammonium hexafluorophosphate as supporting
electrolyte in a potential range of -1.5 to 2.0 V, as shown
in Fig. 3. The cyclic voltammogram of complex 1b
exhibits a one-electron reduction process in the cathodical
potential in Epc = 0.142 V and oxidation peak potential in
Epa = -0.205 V, with ipc = -1.666 lA, ipa = 3.466 lA
and the value of Epa/Epc = 1.44, indicating quasi-revers-
ible behavior. These peaks can be related to the CuII/CuI
redox process.
torted octahedral coordination environment. The bond
lengths and coordination environment of complex 1b are
comparable with those observed in the reported CuII com-
plex [Cu(C16H19N5)2](NO3)2 [22].
Description of crystal structure of 2
In complex 2, [Ag(bpz*mpy)(Ph3P)] (ClO4)2 Á 0.5H2O, the
bpz*mpy functions as a tridentate ligand. The asymmetric
123

310
Transition Met Chem (2013) 38:307–311
Fig. 1 a Perspective view of
the complex cation of 1a.
Hydrogen atoms have been
omitted for clarity. Symmetry
code: (A) = -x, y,1/2 -
z. b Perspective view of the
complex cation of 1b. Hydrogen
atoms have been omitted for
clarity. Symmetry code:
(A) = -x, y,1/2 - z
˚
Table 2 Selected bond distances (A) and angles (°) for complex 1a
and 1b
Fe1–N1
1.980(2)
1.990(2)
N1A–Fe1–N3A
N1–Fe1–N3A
N5A–Fe1–N3A
N5–Fe1–N3A
N1A–Fe1–N3
N1–Fe1–N3
87.41(9)
92.05(10)
89.19(10)
91.35(10)
92.05(10)
87.41(9)
91.35(10)
89.19(10)
179.22(14)
94.81(9)
88.31(9)
82.60(9)
94.37(9)
88.31(9)
94.81(9)
94.37(9)
82.60(9)
175.48(13)
Fe1–N5
Fe1–N3
1.993(2)
N1A–Fe1–N1
N1A–Fe1–N5A
N1–Fe1–N5A
N1A–Fe1–N5
N1–Fe1–N5
N5A–Fe1–N5
Cu1–N5
91.52(14)
88.67(10)
178.75(9)
178.75(9)
88.67(10)
91.18(14)
2.033(2)
N5A–Fe1–N3
N5–Fe1–N3
N3A–Fe1–N3
N5A–Cu1–N3
N5–Cu1–N3
Cu1–N1
2.066(2)
Cu1–N3
2.320(2)
N1–Cu1–N3
N5A–Cu1–N5
N5A–Cu1–N1
N5–Cu1–N1
N5A–Cu1–N1A
N5–Cu1–N1A
N1–Cu1–N1A
92.75(14)
176.94(9)
85.56(10)
85.56(10)
176.94(9)
96.23(14)
N1A–Cu1–N3
N5A–Cu1–N3A
N5–Cu1–N3A
N1–Cu1–N3A
N1A–Cu1–N3A
N3–Cu1–N3A
Fig. 2 Perspective view of the complex cation of 2. Hydrogen atoms
have been omitted for clarity
Symmetry code: (A) = -x, y,1/2 - z
Magnetic susceptibility measurements
˚
Table 3 Selected bond distances (A) and angles (°) for complex 2
of [Fe(bpz*mpy)2](ClO4)2 (1a)
Ag1–N1
Ag1–N4
Ag1–P1
Ag1–N5
2.298(7)
2.328(5)
N1–Ag1–N4
N1–Ag1–P1
N4–Ag1–P1
N1–Ag1–N5
N4–Ag1–N5
P1–Ag1–N5
82.4(2)
135.06(17)
132.00(15)
77.5(2)
Variable temperature magnetic susceptibility data for
compound 1a were measured in the temperature range
2–300 K under fixed fields of 1,000 Oe, and the magnetic
susceptibility versus T plots are shown in Fig. 4. The
vMT product at 300 K has a value of 0.29 emu K mol-1
per FeII ion, which is lower than the spin-only value of an
isolated FeII ion (vMT = 3 emu K mol-1 at 300 K, S = 2
and g = 2.0) and in agreement with the value expected for
a mixture of high-spin (S = 2) and low-spin forms (S = 0).
The vMT values decreases a very little with decreasing
2.3321(15)
2.400(6)
78.2(2)
130.01(16)
temperature, down to a value of 0.19 at 200 K and reaches
a minimum value of 0.12 at 2.0 K. The vMT values of
complex 1a mean that at 300 K about 90 % of molecules
123

Transition Met Chem (2013) 38:307–311
311
Supplementary material
Full crystallographic details are deposited with the Cam-
bridge Structural Database Centre (CCDC No. 848436,
848438 and 854857) for complexes 1a, 1b and 2, respec-
tively. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk.
References
´
1. Arroyo N, Torre FG, Jalon FA, Manzano BR, Moreno-Lara B,
´
Rodrıguez AM (2000) J Organomet Chem 603:174–184
2. Halcrow MA (2009) Coord Chem Rev 249:2880–2980
3. Zhang J, Li A (2009) Andy Hor TS. Organometallics 28:
2935–2937
Fig. 3 Cyclic voltammogram of complex 1b. Scan rate: 100 Mv s-1
4. Zhang J, Li A (2009) Andy Hor TS. Dalton Trans 2009:
9327–9333
5. Morin TJ, Wanniarachchi S, Gwengo C, Makura V, Tatlock HM,
Lindeman SV, Bennett B, Long GJ, Grandjean F, Gardinier JR
(2011) Dalton Trans 40:8024–8034
6. Tandon SS, Thompson LK, Bridson JN, Dewan JC (1994) Inorg
Chem 33:54
7. Anderson TJ, Jones GD, Vicic DA (2004) J Am Chem Soc
126:8100–8101
8. McCarthy CJ, Thompson LK, Newlands MJ, Hynes RC (1992)
Acta Crystallogr SectC 48:430
9. Anderson PA, Astley T, Hitchman MA (2000) Richard Keene F,
Moubaraki B, Murray KS, Skelton BW, Tiekink ERT, Toftlund
H, White AH. J Chem Soc, Dalton Trans 2000:3505–3512
10. Haryono M, Heinemann FW, Petukhov K, Gieb K, Mu¨ller P,
Grohmann A (2009) Eur J Inorg Chem 2009:2136–2143
11. Nihei M, Han L, Oshio H (2007) J Am Chem Soc 129:5312–5313
12. Keene FR, Snow MR, Stephenson PJ, Tiekink ERT (1988) Inorg
Chem 27:2040–2045
13. Hafeli TA, Keene FR (1988) Aust J Chem 41:1379
14. Morin TJ, Bennett B, Lindeman SV, Gardinier JR (2008) Inorg
Chem 47:7468–7470
Fig. 4 vMT versus T plot for complex 1a from 2.0 to 300 K with a
1,000 Oe applied dc magnetic field
15. Morin TJ, Merkel A, Lindeman SV, Gardinier JR (2010) Inorg
Chem 49:7992–8002
16. Astley T, Canty AJ, Hitchman MA, Rowbottom GL, Skelton BW,
White AH (1991) J Chem Soc, Dalton Trans 1991:1981–1990
are in the low-spin state, and there may be a very small
amount of spin crossover down to 2 K (about 4 % of the
molecules). This indicates that the FeII ions in complex 1a
are magnetically isolated from their neighbors in the solid
state. This is not surprising and can be ascribed to the
structure of complex 1a.
´
´
´
´
17. Carmen Carrion M, Dura G, Jalon FA, Manzano BR, Rodrıguez
AM (2012) CrystGrowth Des 12:1952–1969
18. Byers PK, Canty AJ, Honeyman RT (1990) J Organomet Chem
385:417
19. Bruker (2008) SADABS, SAINT and APEX2. Bruker AXS Inc.,
Madison
20. Sheldrick GM (2000) SHELXTL, crystallographic software
package, version 6.10. Bruker-AXS, Madison, WI
21. Sheldrick GM (2008) Acta Crystallogr A64:112
22. Liu JC, Guo GZ, Xiao CH, Song XY, Li M (2011) Acta Crys-
tallogr Sect E67:m1691
Conclusion
Three new complexes have been prepared and characterized
by X-ray diffraction analysis. Complexes 1a and 1b have a
distorted octahedral coordination sphere, and complex 2 has
a distorted tetrahedral geometry. Variable temperature
magnetic measurements show gradual spin crossover over
the measured temperature range in the FeII case.
123