THE GEOMETRY OF Co(II) COMPLEXES SUPPORTED ON SYNTHETIC CARRIERS

Abstract

The geometry of cobalt(II) complexes anchored on the synthetic supports S (S = NaA, NaX,KA, Al 2 O 3 , and SiO 2 (KSMG)) has been identified by UV-vis spectroscopy. In the UV region, the intensity of the band at 220 nm characteristic of a Оzeol → Со2+ charge transfer in the case of CoCl 2 -KCl/NaХ is quite similar to that for the support itself. In visible region, an absorption band observed at 508 nm (19685 cm-1) corresponds to d-d transition in the Co 2+ ion being in the mixed aqua-chloride ligand field with octahedral symmetry. In the long-wave spectral region, a weak band at 673 nm (14858 cm-1) is characteristic of a d-d transition in the Co 2+ ion being in the tetrahedral ligand field. The spectrum of CoCl 2 -KCl/NaА demonstrates only two bends of the absorption curve at 496 nm (20161 cm-1) and 567 nm (17636 cm-1) characteristic of d-d transitions in the Co 2+ ion in the octahedral ligand field and in the Co 2+ ion with the tetrahedral symmetry, respectively. A band at 480 nm (20833 cm-1) and a bend at 550 nm (18181 cm-1) observed for CoCl 2 -KCl/KА can be attributed to a d-d transition in the Co 2+ ion being in the octahedral ligand surrounding. If Al 2 O 3 finds its use as a support, a wide band extending from 400 to 700 nm with its maximum at 547 nm (18281 cm-1) also may be assigned to a d-d transition in the Co2+ ion being in the octahedral surrounding. Besides a comparatively intense band at 516 nm (19380 cm-1), the spectrum of CoCl 2 -KCl/SiO 2 (KSMG) shows a triplet with well-separated maximums at 619 nm (16155 cm-1), 653 nm (15314 cm-1), and 682 nm (14662 cm-1). The first band is characteristic of a d-d transition in the Co 2+ ion being in the mixed aqua-chloride surrounding with octahedral symmetry. The triplet’s constituent bands may be assigned to d-d transitions in the Co 2+ ion characterized by the tetrahedral symmetry.For the octahedral cobalt(II) complexes, depending on the nature of a support, positions of the band situated at ca . 500 nm shift to the long-wave region in the following order: Co 2+ / NaA (496 nm) Co 2+/ Al 2 O 3 (547 nm) ≈ Co 2+ /KA (550 nm)