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V. Enchev et al. / Journal of Molecular Structure 595 82001) 67±76
1
anhydride with 0.05 M acetylacetone. The mixture
was heated under re¯ux until the phthalic anhydride
was completely dissolved. Then it was cooled to 808C
and 0.15 M triethylamine was added. After 12±14 h,
the reaction mixture was poured on 150 g ice with
50 ml concentrated HCl. The resulting precipitate
was ®ltered and washed with water until neutral
reaction. The precipitate was dissolved in 500 ml
3% solution of NaOH, and ®ltered again. The ®ltrate
was acidi®ed with HCl ꢀ1:1) resulting in the formation
of a precipitate of 2AID. The product was twice
recrystalized from ethanol; mp 109±1108C; yield
71%.
The complexes were obtained by mixing metha-
nolic solution of the corresponding metal acetate
with ethanolic solution of the ligand. The reaction
mixtures were re¯uxed for about 30 min at 908C
until precipitates were obtained. The latter were
washed with ethanol and dried for four weeks above
P4O10. The presence of two water molecules in the
ZnꢀII) and CdꢀII) complexes was proved using ther-
mogravimetric analysis. All chemicals were analy-
tical grade reagents.
performed. The 2D H±13C multiple bond connec-
tivity ꢀHMBC) spectra were recorded with a spectral
width of ca. 2000 Hz for H and 15 000 Hz for 13C,
relaxation delay 1.5 s, FT size 2K £ 256W.
1
2.3. Quantum-chemical calculations
The PM3 [12,13] calculations were performed for
2AID and its MꢀII) complexes with Zn, Cd and Pb
using the mopac 6.0 program [14]. Geometries were
optimized without any constrains. The analytic
gradient minimization method implemented within
an extrapolation procedure called eigenvector
following ꢀEF) was used. The mean gradient threshold
Ê 21
was 0.01 kcal mol21
A . The vibrational analysis of
the obtained structures was carried out. The calculated
wavenumbers of all normal modes were scaled by a
factor of 0.893.
The ab initio structure optimizations for 2AID and
its Zn, Cd and Pb complexes were performed at the
RHF level. The geometry optimization of the CuꢀII)
complex was performed at UHF level. Geometric
structures were optimized within C1 symmetry. The
calculations described herein were carried out with
the Stevens±Basch±Krauss±Jasien effective core
potentials ꢀECP) and their concomitant basis sets for
all the atoms ꢀECP-31G) [15,16]. The ab initio
calculations were performed using the gamess
program package [17]. The IR frequencies for the
metal complexes were not calculated because
numerical differentiation is a very time-consuming
procedure.
2.2. IR, EPR and NMR measurements
The IR spectra were recorded on a Perkin±Elmer
FTIR-1600 spectrophotometer ꢀKBr tablets). EPR
spectra were measured on a Bruker B-ER 420 X-
band spectrometer ꢀtemperature range 100±300 K).
The DTG data were obtained on a Perkin±Elmer
TGS-2 instrument.
Cross polarization ꢀCP) magic angle spinning
ꢀMAS) solid state 13C NMR spectra were recorded
on a Bruker MSL-300 instrument at 75.5 MHz.
Powder samples were spun at 8.4 kHz in 4 mm ZrO2
rotor, a contact time of 4 ms, a repetition time of 6 s
and a spectral width of 20 kHz were used for accumu-
lation of 300±600 scans. Chemical shifts were
calibrated indirectly through the glycine CyO signal
recorded at 176.0 ppm relative to TMS.
3. Results and discussion
The X-ray [4] determined and ab initio calculated
structure of 2AID is shown in Fig. 1. There is reason-
able agreement between the results obtained by PM3,
ab initio ꢀECP-31G) calculations and crystallographic
data ꢀTable 1). According to Antipin et al. [6], the
experimental O12´´´O17 distance in 2AID ꢀat
Ê
21208C) is 2.650 A indicating the presence of the
The NMR spectra for DMF-d7 solutions were
measured at ambient temperature on a Bruker DRX-
250 spectrometer, operating at 250.13 and 62.90 MHz
for 1H and 13C, respectively, using a dual 5 mm probe
head. Standard 1D experiments with 308 pulses, 1 s
relaxation delay, 16K time domain points, zero-®lled
to 64K for the protons and 32K for the carbons were
O±H´´´O intramolecular hydrogen bond. The PM3
and ECP-31G calculations predict this distance to be
2.683 and 2.730 A, respectively. The 13C NMR data
Ê
of the solid compound and in DMF-d7 solution at
room temperature are listed in Table 2. A signi®cant
down®eld shift of the resonance peak of the carbonyl
Enchev, Venelin
