Download New Coordination Compounds of Copper(II) with

Polish J. Chem., 74, 935–944 (2000)
New Coordination Compounds of Copper(II) with
Guanidinopyrimidines in N,N-Dimethylformamide
by H.J. Zawadzki
Department of General Chemistry, Medical University of Gdañsk, Dêbinki 1, 80-211 Gdañsk, Poland
(Received November 5th, 1999; revised manuscript March 16th, 2000)
Several guanidinopyrimidine copper(II) complexes have been prepared in dimethylformamide (DMF) and characterized by elemental analysis, electronic, EPR and vibrational spectra and also by magnetic susceptibility measurements. The structure of the
nearest environment of the central ion has been determined. The general formula of the
complexes is Cu(N-C)L–X, where (N-C) is substituted guanidine, coordinated as a chelating ligand through the guanidinopyrimidine and a formal pseudoaromatic chelate ring
Cu–N bond; L = guanidinopyrimidine, X = ClO-4 .
Key words: copper(II) complexes, guanidinopyrimidines, synthesis, structure, electronic and vibrational spectra, magnetic susceptibility
Biological systems contain a plethora of potential low molecular weight ligands,
and information from simplified systems is of importance for understanding the behavior of transition-metal ions in living organisms. Some observations suggest that
under favorable conditions inter- and intramolecular noncovalent bonds may have
considerable influence on the properties of complexes, increasing the stereoselectivity or ligand selectivity around the central metal ion in a ternary complex by the
steric requirements for the best fit of the interacting groups from both ligands [1–3].
Biological properties of guanidine derivatives confirm the usefulness of studies of
this group of compounds. There are attempts in the synthesis of therapeutically useful
compounds and in search of SAR of coordinative compounds of these substituted
guanidines with metal ions. Continuing our research on the interaction of metal ions
with this biomolecule, we investigated reaction of aminoguanidino-pyrimidines with
copper(II). Previously [4], we described the results of our investigations on Pt(II),
Pd(II) and Cr(III) salts with substituted guanidine. In this paper, the synthesis of substituted guanidinopyrimidines and their chelates with copper(II) in acetonitrile has
been described. The knowledge about substituted guanidines, pyrimidines and coordination compounds is very important, especially for quality control of chemical and
pharmaceutical products. The investigated derivatives and their coordination compounds (type M – ligand) in organic solvent, with a square planar structure, were
tested for their activity in biological systems, giving interesting suggestions for the
synthesis of new chelates with specific biological and physiological activity. Thus, it
seems that the change of the nature of the guanidinopyrimidines ligand, using analogues of the guanidine derivative, could increase the biological and physiological
activities of these coordination compounds. In the case of Cu(II) chelates with
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H.J. Zawadzki
guanidinopyrimidines, the biological and chemical activity is dependent on the structure of the ligand coordinated to the metal ion.
EXPERIMENTAL
Materials: N,N-Dimethylformamide (DMF), the acceptor number –AN = 16.0, manufactured by
VEB Laborchemie Apolda. Copper(II) perchlorate DMF solution was prepared according to [5] by the reaction of metallic copper with nitrosyl perchlorate in dimethylformamide under reduced pressure. The
crystals obtained involved four to six DMF molecules per copper(II) ion, as already noted in [6], and were
dried at 40°C in a vacuum oven for several days and kept in vacuum desiccator over P2O5. Free guanidine
base, 4,6-dichloro-2-guanidinopyrimidine (4,6-DGP), 2,6-dichloro-4-guanidinopyrimidine (2,6-DGP),
4,5,6-trichloro-2-guanidinopyrimidine (4,5,6-TGP), 2,5,6-trichloro-2-guanidinopyrimidine (2,5,6-TGP)
were prepared according to [4,7]. The purified fraction was recrystallized from acetone/methanol mixture: C5H4Cl3N5 (4,5,6-TGP); M = 240.48; H – 1.68, C – 24.97, N – 29.12, Cl – 44.23; M.p. > 360°C.
2,5,6-Trichloro-4-guanidinopyrimidine was reacted as described in [4] for 4,5,6-trichloro-2-guanidinopyrimidine. The solid NaCl was removed by filtration. The acetone filtrate was diluted with water
and the resultant solid was collected. On the chromatographic pattern it showed two spots, of which the
lower Rf one corresponds to 4,5,6-trichloro-4-guanidinopyrimidines and a trace of bis (trichloropyrimidinyl) guanidine near solvent front. The solid was further purified by precipitation from methanol
–water solution. Then, it was dissolved in warm acetone, diluted with dichloromethane and chromatographed with 1:1 dichloromethane/acetone to give the product, corresponding to the higher Rf spot. M.p.
300°C. Anal. Calcd. for C5H4Cl3N5 – (2,5,6-TGP); M = 240.48, C, 24.97; H, 1.68; N, 29.12; Cl, 44.23.
All other reagents used were of reagent quality or were purified.
Apparatus: Spectroscopic measurements were carried out in acetonitrile solutions in a 0.5 cm3 flow
cell, which was connected to a titration vessel through teflon and glass tubes. Thermogravimetric analyses have been performed by derivatograph OD-102 (Hungary). The heating rate was 0.083 K s–1 and temperature ranged from 293 to 773 K. Nitrogen was passed over the samples at the rate of 5.6 cm3 × s–1.
Vibrational spectra were recorded by Specord IR-71, UR-10-Carl Zeiss Jena (Germany) and PerkinElmer 325-spectrophotometers, within the range from 400 to 4000 cm–1, using Nujol, hexachlorobutadiene suspension techniques and also were recorded on a Perkin Elmer 580 B spectrophotometer using KBr pellets (4000–250 cm–1). Magnetic susceptibility was measured at room temperature by the
modified Gouy method, using a Johnson Matthey magnetic susceptibility balance and employing
Pascal’s constant [8] for diamagnetic corrections. The effective magnetic moments were calculated using
, where: cM and c coor
are the uncorrected for diamagnetism and corrected molar susmeff = 2.828 c coor
M ×T
M
ceptibility, while cdia is the diamagnetic correction [8]. The visible and UV absorption spectra were recorded by a Hitachi (Japan) double beam spectrophotometer type 356 at room temperature. Electron
paramagnetic resonance measurements were carried out with powdered samples of complexes in E-4
EPR spectrometer. A standard EPR X-band spectrometer with a 100 kHz modulation of the steady magnetic field was used. The steady magnetic field was scaled using the proton NMR technique, while DPPH
served as a frequency marker. The 1H and 13C NMR spectra have been recorded with a Jeol FX 90 or a
Bruker HX 90 instrument.
Preparation of complexes: Syntheses of the coordination compounds were described in [4,7]. Solutions containing the complex were prepared by reaction of Cu(ClO4)2 with DMF. The modifications
were: The reaction of solvocomplex cation [Cu(DMF)4]2+ was carried out with guanidinopyrimidine.
One might expect some properties of DGP, high melting and decomposition temperatures, high reactivity
with metals, and considerable difference in absorption spectra within the visible range, as compared with
DMF and solvocomplex spectra. A solution of DGP in DMF of ca. 0.5 M concentration was obtained from
a sample of DGP, dissolved in hot DMF, and then cooled down to 20°C. A 0.3 M solution of KClO4 in
DMF was used to maintain a constant ionic strength m = 0.1. The solutions prepared were mixed and
heated. The molar ratio M:DGP was higher than 1:1. The post reaction solution contained the product and
non-reacted substrates: [Cu(DMF)2]2+, DGP and KClO4. In order to eliminate them, the solution was concentrated on a rotary evaporator. A precipitate of unreacted [Cu(DMF)4](ClO4)2 was formed and filtered
off. The residue was shaken up with acetone to liberate and remove unreacted KClO4. Acetone from the
New coordination compounds of copper(II)...
937
product solution was evaporated. Unreacted DGP was removed by shaking up the solution of the product
with ether. Ether was evaporated and the product solution was concentrated by evaporation. Since we
failed to find a solvent for recrystallization of the product, the complete removal of acid was impossible.
Thus, the elemental analysis was not possible. Furthermore, an alternative way was used to obtain
[Cu(DMF)4]2+. The mixture was mechanically stirred at 170°C for 8 h. The resulting green solution was
poured onto a cation-exchanger column (SP-Sephadex C-25, Na+ form) and the absorbed complex was
eluted with 0.2 M HClO4. Two bands green and then purple appeared. The second band contained mainly
[Cu(DGP)2]2+. The first eluate has been evaporated to a small volume below 40°C. The resulting green solution was then loaded on a strongly acidic cation exchanger column (Dowex 50W-X8, 2.6 ´ 40 cm,
200–400 mesh, Na+ form) and eluted with HClO4. Yellow-green microcrystals [Cu2(DGP)4](ClO4)4 show
spectral and magnetic behavior typical for binuclear copper(II) compounds, where guanidine groups
serve as a bridge between copper(II) atoms with a nitrogen donor of guanidine. Each complex was additionally purified chromatographically, using the cationic species Dowex-1, X-4, 200-400 mesh, Na+
form; +1,+2,+3 charged ions on Dowex 50W, X-8, 200–400 mesh, Na+ form and the +3 charged complex
by the use of Sephadex C-25.
[CuS4]X2 + L Û [CuS2L]X2 + 2S; [CuS2L]X2 + L Û [CuL2]X2 + 2S;
2[CuL2]X2 Û [Cu2L4]X4; where: L = 2,6-DGP; 4,6-DGP; 2,5,6-TGP; 4,5,6-TGP;
X = ClO-4 , Cl–; S = DMF. [Cu(DMF)4(ClO4)2] + DGP Û [Cu(DMF)2(DGP)](ClO4)2 + 2DMF
[Cu(DMF)2(DGP)](ClO4)2 + DGP Û [Cu(DGP)2](ClO4)2 + 2DMF, 2[Cu(DGP)2](ClO4)2 Û
[Cu2(DGP)4](ClO4)4; [Cu(DMF)4]Cl2 + DGP Û [Cu(DMF)2(DGP)]Cl2 + 2 DMF
[Cu(DMF)2(DGP)]Cl2+ DGP Û [Cu(DGP)2]Cl2 + 2 DMF, 2 [Cu(DGP)2]Cl2 Û [Cu2(DGP)4]Cl4
The chelates of copper(II) ion with guanidinopyrimidines were synthesized by one of the general
methods [4,7]. The chelates were collected, washed with pure solvent and finally with anhydrous ether
and dried in a vacuum over P2O5 in dry nitrogen gas. The content of copper was determined with the
electrogravimetric method. Nitrogen, hydrogen and carbon were determined by a Perkin-Elmer microanalyzer (model 240 CHN).
RESULTS AND DISCUSSION
In this study 16 consecutive chelates have been obtained and analyzed:
(1) – 2,5,6-TGP (C5H4Cl3N5 ); (2) – 4,5,6-TGP (C5H4Cl3N5); (3) – 4,6-DGP (C5H5Cl2N5);
(4) – 2,6-DGP (C5H5Cl2N5); (5) – [Cu2(2,6-DGP)4](ClO4)4; (6) – [Cu2(2,6-DGP)4]Cl4;
(7) – [Cu2(4,6-DGP)4](ClO4)4; (8) – [Cu2(4,6-DGP)4]Cl4; (9) – [Cu2(2,5,6-TGP)4](ClO4)4;
(10)– [Cu2(2,5,6-TGP)4]Cl4; (11) – [Cu2(4,5,6-TGP)4](ClO4)4; (12) – [Cu2(4,5,6-TGP)4]Cl4;
(13) – [Cu(DMF)2(2,6-DGP)](ClO4)2; (14) – [Cu(DMF)2(2,6-DGP)]Cl2;
(15) – [Cu(DMF)2(4,6-DGP)](ClO4)2; (16) – [Cu(DMF)2(4,6-DGP)]Cl2.
Elemental analysis confirmed the formulas proposed. The analytical data correspond
to 1:1 or 1:2 (metal:ligand) stochiometry for all chelates. Molecular weight data indicate that the chelates correspond to formulas, i.e., 2[Cu(L)2]X2 Û [Cu2(L)4]X4;
where: L = 2,6-DGP; 4,6-DGP; 2,5,6-TGP; 4,5,6-TGP; X = ClO -4 , Cl–. All obtained
chelates are insoluble in common organic solvents. They are soluble in alcohols and
coordinating solvents.
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H.J. Zawadzki
Analysis of IR vibrational spectra: The spectra of the coordination compounds
of copper(II) with guanidinopyrimidines are very complicated and the entire assignment of all the absorption bands is impossible. However, a careful study might lead to
some important structural conclusions. The frequencies associated with the characteristic functional groups for the free guanidines, biguanidines and other substituted
guanidines [4,9] ligands and their copper(II) complexes are presented in Table 1. In
order to interpret the vibrational spectra, there were investigated: pyrimidine “ring
breathing”, bending >N–H vibration bands, characteristic bands of >C=N– group in
the molecule (–N2C=N– and –N=C–NH2–), as well as bands of C–N stretching. As
ligands, guanidinopyrimidines exhibit two very strong bands. One appears in
1609–1580 cm–1 regions and is assigned to v(C=N) (guanidine) group. The movement in this mode clearly indicates that the guanidine group is participating in the coordination. The other bands become visible in 1225–1240 cm–1, 725 cm–1, 990 cm–1
and 1066 cm–1 are characteristic for the pyrimidine ring. These bands are shifted to
lower frequencies in the spectra of all these complexes (Table 1). The small shifts of
absorption bands, which are specific for the pyrimidine ring in the spectra of copper(II) complexes, are being compared to those of ligands and the changes of their intensities. The bands that occur at ca. 1609 cm–1, 1570 cm–1 and 1508 cm–1, 1480 cm–1,
1467 cm–1, 1225 cm–1, 1066 cm–1, 990 cm–1 and 725 cm–1 in the free guanidinopyrimidine spectrum move to lower wavenumbers after the complex formation.
This is consistent with the binding of guanidinopyrimidine through the nitrogen atom
of the pyrimidine ring. The location of the dNH band at 1618 cm–1 does not change after the complexation. Therefore, the NH group virtually does not contribute to the
ligand–Cu(II) bond. However, a stretching vibration of N=C bond of pyrimidine ring
at 1487 cm–1 is shifted by about 15 cm–1 towards lower frequencies. This shift indicates the interaction between copper(II) and the nitrogen atom. The bands of the ligands in the 1330–1180 cm–1 region may be attributed to the stretching vibration of
C–N (pyrimidine ring) groups. Other bands are due to the ring breathing, C–H bending mode, and out-of-plane vibrations. The positions of these bands in the spectra of
chelates have been changed considerably. Moreover, the intensity of the band at 1120
cm–1 has weakened. The interaction between the donating ligand and the nitrogen
atom is responsible for the observed vibration shift. In the IR spectra of coordination
compounds Cu(II), the new absorption bands at ca. 800–820 cm–1, 915 cm–1,
1020–1025 cm–1 (chelates: 6, 8, 13, 14, 16), 1300–1310 cm–1, 1460 cm–1, 1490–1500
cm–1 (chelates: 5, 7, 9, 10, 11, 12) are present additionally. The latter is probably attributed to the skeleton vibrations of newly generated chelate ring [9]. Formation of
chelate compounds can be achieved due to the coordination of both ligand nitrogen
atoms with one central copper(II) ion, giving the particularly stable six-membered
ring. The most important IR data of copper(II) coordination compounds with aminoguanidinopyrimidines are presented in Table 1.
509 (m)
516 (m)
501 (m)
512 (m)
518 (w)
502 (m)
511 (m)
516 (w)
(3), (4)
(9), (11)
(13), (15)
(6), (8)
(10), (12)
(14), (16)
1615 (w)
1615 (w)
1618 (w)
1615 (w)
1615 (w)
1618 (w)
1650
1615 (w)
1650 (w)
1618 (w)
1022 (sh)
1022 (sh)
1007,
1022 (sh)
1015
1017 (sh)
1010 (sh)
1021 (sh)
1011 (sh)
d(N–H)asym n(C–N)sym
1240 (m)
1233 (m)
1225 (m)
1240 (m)
1236 (m)
1232 (m)
1240
1232 (m)
1225 (m)
n(C–N)as
1565 (vs)
1565 (s)
1585 (s)
1550 (sh)
1590 (s, br)
1590 (vs)
1609 (sh)
n(C=N)
pyrimidine
725 (w), 770 (s), 850 (m), 990 (b),
1066 (b)
1330
850 (m), 1225 (s), 1467 (sh), 1487 (m),
1570 (sh)
1356 (w) 720 (w), 810 (m), 980 (b), 1058 (m),
1220 (s), 1490 (m), 1560 (s)
1380 (sh) 720 (w), 812 (m), 978 (b), 1060 (m),
1220 (s), 1475 (m), 1558 (s)
1390 (s) 720 (w), 810 (m), 978 (b), 1060 (m),
1370 (w) 1218 (s), 1475 (m), 1560 (s)
1370 (w) 718 (w), 812 (m), 915 (b), 975 (b),
1220 (s), 1470 (m), 1560 (s)
1390 (w) 720 (w), 812 (m), 915 (b), 978 (b),
1220 (s), 1480 (m), 1558 (s)
1380 (sh) 720 (w), 812 (m), 915 (b), 978 (b),
1220 (s), 1470 (m), 1560 (s)
1330 (s)
n(C–N)
Relative intensities: s = strong; m = medium; w = weak; v = very; sh = shoulder, b = breathing.
(5), (7)
499 (m)
d(C–N)
(1), (2)
Compound
Table 1. Infrared data of guanidinopyrimidines and their Cu(II) complexes in cm–1.
360 w
365 m
356 w
365 w
334 m
323 m
n(M–N)
n4
1090 s 625 m
1082 s 620 s
1085 s 620 s
n3
ClO-4
New coordination compounds of copper(II)...
939
940
H.J. Zawadzki
Magnetic susceptibility: The magnetic moments of Cu(II) complexes at room
temperature were 1.80 B.M. In order to obtain more detailed information on the
structure of these compounds, the magnetic susceptibility was measured between
77–302 K. The magnetic parameters can be estimated as g = 2.08, Na = 60 ×10–6 cgs
emu and –J = 19 cm–1 from the best fit of the cA values to the modified BleaneyBowers equation [8,10]
cA =
Nb 2 g 2
1
´
+ Na
3kT
1 + 1 / 3exp( -2 J / kT )
(1)
where J denotes the exchange integral between copper(II) ions in binuclear copper(II)
2
complexes. N 2b = Nm b . J = 19 cm–1 shows that there is an antiferromagnetic exchange
interaction between the two copper(II) ions in the complexes. This value is close to
other pyrimidinoguanidines copper(II) chelates J values of 20–90 cm–1 [11]. It is,
therefore, concluded that the present compounds exhibit a guanidine–bridged
dimeric structure, in which guanidinopyrimidine is coordinated around each copper(II) through the terminal amino nitrogen, deprotonated amide nitrogen and the nitrogen of pyrimidine guanidine group and the pseudoheterocyclic ring- nitrogen.
This mode of coordination may be well accepted, due to studies of guanidinosubstituted coordination compounds (5–7). The same type of binuclear copper(II) coordination compounds with oligopeptide, glicyl-b-alanine, imidazole, dipeptides
[14,15], pyrazolo-derivatives has been isolated. This compound exhibits a similar
magnetic property (–J = 17 cm–1) to the compounds (9) – [Cu2(2,5,6-TGP)4](ClO4)4,
and (11) – [Cu2(4,5,6-TGP)4](ClO4)4. Kivelson and Neiman [13,15] theory calculated their molecular orbital coefficients. The effective magnetic moments and a regular run of the reciprocal of the mole magnetic susceptibility on temperature, in the
case of binuclear pyrimidinoguanidine complexes with Cu(II), point on the lack of interaction of the unpaired electrons of the two different copper atoms. All investigated
coordination compounds are paramagnetic and have a partially deformed octahedral
structure.
Electronic spectra: Electronic spectra of copper(II) coordination compounds
with investigated substituted of pyrimidinoguanidines were resolved into spectra of
individual copper(II) chloride complexes by knowing the formation constants of the
copper(II) chloride complexes. The electronic spectra of the coordination compounds Cu(II) with DGF and TGP exhibit two characteristic absorption bands. The
first band at l = 400–450 nm represents the L ® Me charge-transfer (C-T) band. The
second broad band at lower energy of medium intensity in the visible range 630–670
nm (Table 2) may be assigned to spin-allowed d-d transition band. The d-d transition
band implies hexa- or penta- metal coordination. The chelates are in the ground state
dx2 – y2 (term 2B1g) and the effective ligand field octahedral symmetry (D4h) or very
close to D4h. But generally, such chelates exhibit a broad structureless band with or
without shoulder between 600–660 nm depending upon the strength of the field of lig-
New coordination compounds of copper(II)...
941
ands. The appearance of a single broad band in guanidinopyrimidines with copper(II)
complexes investigated is not unexpected, because of the steric hindrance caused by
the bulky ligand molecules. Since only single broad bands have been observed in
these chelates, one can conclude that all three transitions are present within this broad
envelope. Considerable width of the d-d bands is a result of the Jahn-Teller effect.
The bands from these transitions are partly splitted in the spectrum of 2[Cu(L)2](X)2
Û [Cu2(L)4](X)4; where: L = 2,6-DGP, 4,6-DGP, (compounds 5, 7, and 6, 8),
whereas they are probably overlapped in the spectrum of 2[Cu(L)2](X)2 Û
[Cu2(L)4](X)4, where: L = 2,5,6-TGP; 4,5,6-TGP; X = ClO -4 , Cl– (compounds: 9, 11
and 10, 12). However, literature data [4,11,16] show that the maximum of the experimental spectrum corresponds to 2B1g ® 2B2g. Using the different method of resolution
it was found, that 2B1g ® 2B2g transition energy corresponds exactly to the maximum
of multiple bands. On that basis we have assumed that the highest point of single
broad band corresponds to 2B1g ® 2B2g transition.
Table 2. Electronic spectral data of the copper(II)–guanidinopyrimidines complexes.
Electronic spectral
bands in nm
Compound
5, 6
430
630
440
630
430
640
430
630
430
630
430
640
7, 8
9, 10
11, 12
13, 14
15, 16
Assignment
440
640
440
620
430
640
430
630
440
630
430
630
Charge transfer
2
B1g ® 2B2g
Charge transfer
2
B1g ® 2B2g
Charge transfer
2
B1g ® 2B2g
Charge transfer
2
B1g ® 2B2g
Charge transfer
2
B1g ® 2B2g
Charge transfer
2
B1g ® 2B2g
Electron spin resonance spectra. The copper(II) cation has nine d electrons.
Because the d shell holds only 10 electrons, all but one must be paired; thus, this ion in
the 2D state has L = 2, S = 1/2, I = 3/2. The spectra of coordination compounds Cu(II)
with 2,6-dichloro-4-guanidinopyrimidine (2,6-DGP), 4,6-dichloro-2-guanidinopyrimidine (4,6-DGP), 2,5,6-trichloro-2-guanidinopyrimidine (2,5,6-TGP), 4,5,6-trichloro-2-guanidinopyrimidine (4,5,6-TGP) can be interpreted using a spin
Hamiltonian theory [8,17].
Hs = g × b × H ×S
(2)
g = ge – k
l
D
(3)
ge – is the free electron g factor, l – is the spin-orbit coupling constant for the free ion,
D – is the crystal field splitting, and k – is a factor that depends on the type of transition
942
H.J. Zawadzki
ion and on its orientation. For ions, in which the d shell is less than half filled, l > 0,
hence usually g < ge; for ions in which the d shell is greater than half filled g > ge
[17,18]. If the molecule contains a single threefold or higher axis of symmetry (Z), X
and Y are equivalent. This is called axial symmetry and gXX = gYY ¹ gZZ. It is common
in such cases to designate the g factors as g||, the g factor parallel to the symmetry axis
(i.e., g|| = gZZ), and g^ for the g factor perpendicular to this axis (i.e., g^ = gXX = gYY).
g÷÷ = 2 –
8l
2l
g, g^ = 2 ,
D0
D1
(4)
The complete Hamiltonian described is:
HSS = b(gxHxSx + gyHySy + gzHzSz) + D[S x2 - 1 / 3S ( S + 1)] + E ( S x2 - S y2 )
(5)
where: H is the Hamiltonian operator,
D = Dzz –
DXX + DYY
,
2
1 é
1
ù
S = l êg z - (g x + g y ) ú
2 ë
2
û
E=
DXX - DYY
2
(6)
1
E = l (g x - g y )
4
(7)
(The electron has an intrinsic angular momentum or spin)
HS = g|| bHzSz + g^db(HxSx + HySy) + D(S2/z – 1/3S(S + 1) + E(S x2 – S y2 )
(8)
D – is the axial zero-field splitting parameter, tensor of fines splitting [12–14]. The
spectra of coordination compounds (5–8) and (9–12) were obtained at 77 K. A typical
electron spin resonance spectrum of chelate copper ion with DGP (5, 6) is presented
in Figure 1.
In the spectrum in Figure 1 six-absorption signals separated by 80 gauss interval
can be observed. In a simple spectrum, containing fourteen lines, two sets of seven
lines could be expected in the parallel signal for such binuclear chelates. It is apparent
that the two sets of seven lines overlap to get less than fourteen lines. The highest field
peak of the high field set of seven peaks is not readily visible perhaps due to low intensity and/or overlapping with the perpendicular signal. For the chelates investigated
the g|| component (2.380) > g^ component (2.068) indicating that the unpaired electron occupies predominantly the dx2 – y2 orbital giving 2B1g ground state with g|| > g^ in
the square planar and elongated octahedral coordination compounds. If the complex
is formed as a compressed octahedral one, the unpaired electron is in dz2 giving
New coordination compounds of copper(II)...
943
Figure 1. EPR spectrum of copper(II) ion with DFG measured at 77 K.
ground state 2A1g with g|| component < g^ component. The values G = 6.7 (compounds
5 and 7) and 4.9 (compounds 6 and 8), in Table 3, indicate considerable contribution
of the dx2 – y2 orbital in the ground state of the copper(II) ion. The distinct hyperfine
structure A||, which is rather a rare case for “pure” copper coordination compounds,
indicates that in Cu(II)–DFG the exchange coupling is relatively small and that the
substances are magnetically diluted. The exchange energy must be lower than the
splitting constant A||, J < 0.015 cm–1. Otherwise the structure characteristic for magnetic diluted systems would not be observed.
Table 3. Spin Hamiltonian and orbital reduction parameters of compounds guanidinopyrimidines with
copper(II) ion.
Compound
(5), (7)
(6), (8)
(9), (11)
(10), (12)
(13), (15)
(14), (16)
g||
2.29
2.24
2.45
2.27
2.30
2.34
g^
2.04
2.05
1.96
2.04
2.06
2.08
gave
2.12
2.11
2.12
2.16
2.16
2.17
A|| (a)
121
135
88
126
126
126
A^ (a)
29
28
77
31
77
77
Aave (a)
59
63
81
63
81
81
K2
0.532
0.662
–
0.578
0.535
0.535
G
6.7
4.9
10.6
7.0
7.0
7.0
(a) units ´ 10–4 cm–1.
Acknowledgments
I express my thanks to Dr. Bart³omiej Ciesielski, Medical School, for valuable suggestion and discussion
and to Mr. Maciej Zawadzki,Wichita State University, USA, for assistance in the experiments.
944
H.J. Zawadzki
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