Effects of electronic and steric factors on the magnetic properties of novel homo- and heterobinuclear transition-metal complexes with asymmetric 2,6-diformyl-4-R-phenol bis(hydrazones)

Article abstract of DOI:10.1023/A:1014784220867

A series of novel homo- and heterobinuclear copper(II), manganese(II), and VO²⁺ complexes with asymmetric 2,6-diformyl-4-R-phenol bis(hydrazones) are synthesized. The values of exchange parameters of these compounds are determined. The comparison of experimental results with the quantum-chemical calculations of the model fragments of binuclear metal chelates allows one to elucidate the main electronic and geometric factors determining the character of changes in the magnetic properties in systematic series of transition-metal complexes with bis(hydrazones).

Full text of DOI:10.1023/A:1014784220867

Russian Journal of Coordination Chemistry, Vol. 28, No. 3, 2002, pp. 222–225. Translated from Koordinatsionnaya Khimiya, Vol. 28, No. 3, 2002, pp. 234–237.
Original Russian Text Copyright © 2002 by Lukov, Levchenkov, Posokhova, Shcherbakov, Kogan.
Effects of Electronic and Steric Factors on the Magnetic
Properties of Novel Homo- and Heterobinuclear
Transition-Metal Complexes with Asymmetric
2,6-Diformyl-4-R-Phenol Bis(Hydrazones)
V. V. Lukov, S. I. Levchenkov, S. V. Posokhova, I. N. Shcherbakov, and V. A. Kogan
Rostov State University, pr. Stachki 194, Rostov-on-Don, 344104 Russia
Received December 13, 2000
Abstract—A series of novel homo- and heterobinuclear copper(II), manganese(II), and VO2+ complexes with
asymmetric 2,6-diformyl-4-R-phenol bis(hydrazones) are synthesized. The values of exchange parameters of
these compounds are determined. The comparison of experimental results with the quantum-chemical calcula-
tions of the model fragments of binuclear metal chelates allows one to elucidate the main electronic and geo-
metric factors determining the character of changes in the magnetic properties in systematic series of transition-
metal complexes with bis(hydrazones).
In continuation of the syntheses and studies clear complexes III–V was prepared from spe-
into the magnetic properties of homo- and hetero- cially synthesized asymmetric ligand systems I
binuclear metal chelates, a series of novel binu- and II [1–3]:
R1
R1
R1
N
N
O
N
N
N
O
O
N
O
N
N
OH N
HN
NH
R2 H3C
N
N
HN
NH
Ph
Cu
Cu
M
Cl
H3C
N
N
Ph
H3C
N
X
O
CH3
(III)
(I)
(II)
+
R1
+
R1
R1 = OCH3, CO2CH3, CO2C2H5;
R2 = CH3, NH2;
X = O, S;
M = VO2+, Mn2+
N
O
N
X
Cl–
HN
N
N
O
O
N
NO3–
Cu
M
HN
NH
Ph
Cu
Cu
H3C
N
N
R2
Cl
H3C
N
N
O
NO3
CH3
(V)
(IV)
1070-3284/02/2803-0222$27.00 © 2002 åÄIä “Nauka /Interperiodica”

EFFECTS OF ELECTRONIC AND STERIC FACTORS
Table 1. Elemental analysis of complexes III–V
223
Content (found/calcd), %
H
Complex
R1
R2
X
M
Empirical formula
C
N
III
III
IV
IV
IV
V
OCH3
CO2C2H5
OCH3
CO2CH3
CO2C2H5
CH3
Cu
Cu
C25H21N6O4Cu2
50.7/50.3
51.1/50.8
41.3/41.6
41.8/41.6
41.9/42.4
41.1/40.5
37.5/37.2
41.7/41.4
3.2/3.5
3.3/3.6
3.0/3.2
3.3/3.1
3.1/3.3
3.1/3.2
3.2/2.9
3.4/3.3
13.9/14.1
13.5/13.2
15.2/15.5
15.2/14.9
14.9/14.7
15.2/14.9
17.3/16.9
15.5/15.2
C27H23N6O5Cu2
C25H23N8O10Cu2
C26H23N8O11Cu2
C27H25N8O11Cu2
C19H18Cl2N6O3CuV
C18H17Cl2N7O2SCuV
C19H18Cl2N6O2CuMn
CH3
NH2
CH3
O
VO
VO
Mn
V
CH3
S
V
CH3
O
Compositions and structures of complexes III–V on the magnetic properties of the complexes [8, 9]. This
were determined on the basis of elemental analysis, IR suggestion is supported by the magnetic properties of
spectroscopy, conductometry, and magnetochemistry complexes IV (Table 3). A slight reduction in the 2J
data.
values is obviously caused by axial coordination of one
of the two nitrate ions to the copper atom. This coordi-
nation is confirmed by the aforementioned data on the
electric conductivity of solutions of complexes IV.
Reactions of asymmetric bis(hydrazones) with cop-
per(II) acetate and copper(II) nitrate result in the forma-
tion of binuclear complexes of Cu2L(OCH3) and
Cu2(H2L)(NO3)2(OCH3) composition, respectively,
where L3– and H2L– are the tri- and monodeprotonated
forms of the corresponding bis(hydrazones) I (Table 1).
Recently, we analyzed in detail the effect the elec-
tronic nature of periphery donor atoms in the model
fragment VI (X = O, N, S; Y = O) on the exchange
interaction and gave a quantum-chemical interpretation
of this dependence [3, 10].
The absorption band due to “amide-I” of the
hydrazide fragment [4] disappears from the IR spectra
of complexes III and shifts to lower frequencies (by
20–25 cm–1) for complexes IV as compared to the posi-
tion of this band in the spectra of the initial bis(hydra-
zones) I (~1660 cm–1). In addition, broadening and
growth in the intensity of the ν(C=N) band at 1625 cm–1
in the spectra of complexes III can be explained in
terms of an increase in the number of azomethin
groups.
N
N
O
N
X
M
Cu
Y
(VI)
In this work, similar calculations were carried out
(using the PMX method) to determine the effect of the
nature of one of the bridging atoms (Y = Cl) along with
the effect of the metal nature (M = VO2+, Mn2+) and X
atoms on the magnetic properties. Table 4 presents cal-
culations of the HOMO and LUMO relative energies
for fragments VI, as well as the square of the energy
splitting ∆ between these orbitals at successively varied
M and X. It is known that the value of ∆2 is proportional
to the antiferromagnetic component of exchange
effects between paramagnetic centers [11]; therefore,
The values of conductivity of 0.001 M solutions of
complexes IV in DMF (Table 2) allow one to classify
them as 1 : 1 electrolytes; it can also be seen that one of
the nitrate ions is in the outer sphere [5].
The temperature dependence of magnetic suscepti-
bility of complexes III and IV shows a significant
exchange interaction of the antiferromagnetic type
(Table 3). The values of the exchange parameters for
compounds III are in good agreement with the reported
values for similar homobinuclear complexes that differ
in the electronic nature of substituents R1 [1]; they are
noticeably lower than the corresponding parameters for
symmetric systems [6, 7].
Table 2. Molar conductivities of 0.001 M solutions of com-
plexes III–V in DMF
λ,
Com-
plex
R1
R2
X
M
Ω–1 cm2 mol–1
Therefore, our study of the systematic series of
binuclear copper(II) complexes with 2,6-diformyl-4-R-
phenol bis(hydrazones) suggests that the transition
from symmetric bis(acylhydrazone) derivatives to
asymmetric derivatives (type III) reveals the predomi-
nant effect of the geometric factor, determining the
structures of both chelate cores and the whole binuclear
complex molecule, as compared to electronic factors,
III
CO2C2H5
CO2CH3
Cu
2.9
87.3
75.5
83.3
90.4
IV
IV
V
CO2C2H5 CH3
O
S
CH3
CH3
NH2
CH3
VO
VO
V
O
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 28 No. 3 2002

224
LUKOV et al.
Table 3. Magnetic properties of complexes III–V
R1
R2
X
M
T, K
–2J**, cm–1
g
*
Complex
µeff , µB
III
OCH3
Cu
290
83
1.59
1.02
1.60
1.01
1.70
1.20
1.65
1.22
1.72
1.35
1.74
1.27
1.56
1.00
5.83
5.26
145.4
2.03
III
IV
IV
IV
V
CO2C2H5
OCH3
CO2CH3
CO2C2H5
CH3
Cu
294
83
138.8
107.4
98
2.00
2.13
2.04
2.11
2.18
2.00
288
82
291
83
295
83
85.6
CH3
NH2
CH3
O
S
VO
VO
Mn
293
83
106.4
147.8
28.4
V
CH3
296
83
V
CH3
O
293
g1 = 2.00
g2 = 2.08
81.8
* The value of µ for the binuclear molecule is given in the case of a complex with M = Mn; µ calculated for one metal ion is given in
eff
eff
the case of complexes with M = Cu, VO.
** The value of the parameter –J is given for the complex with M = Mn.
the above values of ∆2 may be qualitatively compared of the chlorine atoms [5], which is in agreement with
to the values of exchange parameters (2J).
the above scheme.
Comparison of the exchange parameters 2J of the
earlier synthesized homobinuclear complexes V (X =
O, M = Cu, 2J ≈ –85 cm–1; X = S, M = Cu, 2J ≈
−131 cm–1 [3]) with the values of ∆2 (Table 4) shows
that in the case of compounds V, like in the systems
with a dioxygen bridge (structure VI, Y = O) with an
analogous structure of the binuclear complex as a
whole, the interrelated change in electronegativity of
the X atoms and in the value of ∆2 determines the char-
acter of changes in the exchange interaction.
A similar tendency may be noted, when going to the
heterobinuclear complexes V with M = Mn2+. Analysis
of the J value for this compound (Table 3) in terms of
the theory of one-electron exchange channels [13, 14]
allows one to state that the antiferromagnetism of the
complex is higher than that of homobinuclear systems;
this is in good agreement with the larger value of ∆2
(Table 4). At the same time, the agreement between the
experimental data and the results of quantum-chemical
calculations for complexes V with M = MÓ2+, VO2+ is
accidental rather than regular, because we assumed in
our calculations that the ferromagnetic contribution to
the total value of the exchange parameter J for the het-
eropair Cu2+–Mn2+ to be the same as that for the
homobinuclear system Cu2+–Cu2+, which, of course, is
not a rigid assumption [11].
For practical application of this correlation, we car-
ried out the target synthesis of binuclear complexes V.
It was found that reactions of Cu(II)-containing ligands
with manganese(II) and VO2+ chlorides result in binu-
clear complexes of the CuMHLCl2 composition, where
HL2– is the doubly deprotonated form of bis(hydra-
zones) (Table 1).
In the IR spectra of the complexes, the amide-I or
ν(C=S) bands of the thiosemicarbazone fragment
(~840 cm–1 [12]) disappear, while the relative intensity
of the ν(C=N) band increases. The values of conductiv-
ity for 0.001 M solutions of the complexes in DMF
(Table 2) make it possible to assign them to the 1 : 1
electrolytes and reveal the outer-sphere character of one
Table 4. Relative energies of molecular orbitals of model
fragments VI
X
M
E
, eV
E
, eV
∆2*
LUMO
HOMO
O
Cu
–11.251
–11.136
–10.193
–10.192
–11.532
.
–11.412
–11.395
–11.404
–11.401
–11.848
0.026
0.067
1.467
1.462
0.100
S
Cu
O
S
VO
VO
Mn
O
The requirement of a more accurate consideration of
the ferromagnetic component is supported by a com-
2
* ∆ = E
– E
HOMO
LUMO
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 28 No. 3 2002

EFFECTS OF ELECTRONIC AND STERIC FACTORS
225
1/2
parative analysis of the experimental values of
n
r =
(χi – χ0i )2χ–i 2
,
1
--
n
exchange parameters 2J and the results of quantum-
chemical calculations for heterobinuclear complexes V
with M = VO2+. Despite the significantly larger value of
∆2 for these complexes as compared to the homobinu-
clear copper(II) complexes, the values of 2J are compa-
rable in both cases. At the same time, the abnormal,
from the point of view of potential orthogonality of
∑
1
where χi and χ0i are the experimental and calculated
molar magnetic susceptibilities at the ith point, respec-
tively, and n is the number of points.
Quantum-chemical calculations were performed
in accordance with the PMX method using the CACAO
program package.
copper(II) and vanadium(IV) magnetic orbitals (dx2
– y2
and dxy, respectively [11]), antiferromagnetism of the
above, as well as of the earlier reported, Cu(II) and
VO2+ complexes [2] is not an accidental phenomenon
and needs further studies first of all, X-ray diffraction
study of the systematic series.
ACKNOWLEDGMENTS
The work was supported by the Russian Foundation
for Basic Research, project no. 99-03-32535a.
EXPERIMENTAL
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RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 28 No. 3 2002