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Synthesis, Characterization, Solvatochromic Behavior and Crystal Structures of Complexes
the one used for (1) except that thiobenzamide was used lone pair of the central sulfur atom and as a result, the C-N
instead of thioacetamide. Recrystallization from chloroform stretching frequency is raised while the C=S stretching
furnished dark red crystals of a CHCl3 solvate of (2) with a frequency is lowered relative to the free ligands. As we have
solvent content of ca. 1 molecule per Co. Yield: 55%. Anal. recently reported [13], the thioacetamide binds to cobalt
calcd. for C34H28ClN4O6S2Co: C, 54.66; H, 3.78; N, 7.50; through the S atom in trans-[CoIII((BA)2en)(ta)2]PF6 and trans-
found: C 53.07, H 3.57, N 7.25. 2max/cm-1 (KBr): 3403 (m, N- [CoIII(acacen)(ta)2]ClO4 complexes. The IR spectrum of the
H), 1609 (s, C=N), 703 (m, C=S), 1322 (m, C-N), 1095 (s, free ligand exhibits the characteristic band of an imine at 1614
1
ClO4). H NMR (500 MHz, (CD3COCD3) ꢆ: 6.76 (br t, 2H, cm-1 [15]. This band is shifted to lower frequencies by 5-6 cm-1
Hd), 7.37-7.69 (m, 18H, HPh,h,b,c,e), 8.50 (m, 2H, Hg) , 8.99 (br s, in the corresponding cobalt complexes, due to the coordination
2H, Hf), 10.20 (br s, 2H, NHi), 11.48 (br s, 2H, NHj).
of the imine nitrogen [21]. Also, a band at 3300-3400 cm-1,
characteristic of the OH group in the free ligand, is absent in
the IR spectrum of the complex which indicates that the Schiff
X-Ray Crystallography for (1) and (2)
Dark red crystals suitable for X-ray crystallography were base is coordinated in its deprotonated form. The ꢈ(CS),
obtained by slow evaporation of chloroform solutions of the appearing at 705 cm-1 for the free thiobenzamide, appears at
complexes at room temperature. X-ray data were collected on a 703 cm-1 in (1) and 692 cm-1 in (2). The small increase in
Bruker Smart APEX CCD diffractometer with graphite ꢈ(CN) and the small decrease in ꢈ(CS) of the coordinated
monochromated Mo K& (04= 0.71073 Å) radiation and 0.3° ꢇ- thioacetamide and thiobenzamide, are consistent with the metal
scan frames covering approximately the whole sphere of the sulfur coordination of the thione forms, and conform to the X-
-
reciprocal space. Cell refinement and data reduction were made ray molecular structures. The stretching vibration of ClO4
with the help of the SAINT program [17]. Corrections for anion is observed at 1083 cm-1 in (1) and at 1095 cm-1 in (2)
absorption were made with the multi-scan method and program [22].
SADABS [17]. The structures were solved using direct
The 1H NMR spectral data are presented under the heading
methods (SHELXS-97) and refined against F2 using the ‘Experimental’. The low field signal, which appears at ꢆ = 13.1
SHELXL-97. [18]. Both solids were CHCl3 solvates with in the free ligand, due to the extensive hydrogen bond
disordered solvent and an approximate solvent content of 1 formation, is absent in the NMR spectra of the complexes
CHCl3 per Co. Therefore, the solvent was squeezed with which clearly indicates that the salophen Schiff base is
program PLATON [19] prior to the final refinement. A coordinated as a dianionic ligand. The 1H NMR spectrum of (1)
summary of the crystal data along with further details of the in CD3COCD3 is shown in Fig. 1A (assignment as in Scheme
1
structure determinations are given in Table 1.
RESULTS AND DISCUSSION
Spectral Studies
1). The signal appearing as a singlet at ~2.22 ppm in the H
NMR spectrum of (1) is assigned to the two CH3 groups of
thioacetamide ligands. The two =CH protons, Hf, adjacent to
the iminic nitrogens appear at 8.88 ppm. The two N-H protons
of the coordinated thioacetamide, Hi and Hj, appear at 9.89 ppm
Ambidentate ligands can bond to a metal center through and 10.99 ppm, respectively. The aromatic protons of the
more than one kind of atom. The classic examples are the phenyl rings in the coordinated Schiff base ligand appear in the
thioamide ligands which can bind in a monodentate fashion appropriate region. The 1H NMR spectral data of (2) in
through the S or the N atom [13,20]. For example, CD3COCD3 show features similar to those observed for
thioacetamide and thiobenzamide exist as the two resonance complex (1), Fig. 1B. The two =CH protons, Hf, adjacent to the
structures presented in Scheme 2.
iminic nitrogens appear at the ~8.99 ppm. The aromatic protons
In form (I) the ligand binds through the lone pair of the of the phenyl rings in the coordinated Schiff base ligand and
nitrogen atom and consequently the C-N stretching frequency the thiobenzamide appear at 6.8-8.5 ppm range. The two
is lowered while the C=S stretching frequency is raised relative signals at 10.19 ppm and 11.48 ppm, are assigned to the two N-
to the free ligands. In form (II), the ligand binds through the H protons of the coordinated thiobenzamide, Hi and Hj,
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