Spectroscopic and structural studies of chromate ions in zinc complexes with 2,2′-bipyridine. Analysis of the lowest triplet states in the CrO 42− entity

Abstract

Two novel complexes of Zn(II) chromate with 2,2′-bipyridine have been synthesised: [Zn(bpy) 3]CrO 4·7.5H 2O ( 1) and catena-(μ-CrO 4- O, O′)[Zn(bpy)(H 2O) 2]·2H 2O ( 2). Complex 1 has been characterised by a structural method. The [Zn(bpy) 3]CrO 4·7.5H 2O crystals have a monoclinic symmetry with space group C2/ c and eight chemical units. The chromate ion is not coordinated to the zinc(II) ion. The O(3) and O(4) atoms of CrO 4 2− and O(8) of the water molecule statistically occupy their position with k=0.5, which means that the chromate ions execute reorientational motion between two equilibrium arrangements with equal probability. 4 K electronic spectra ( 1) revealed the vibrational fine structure in ν 3(F 2)=820 cm −1 for the spin-forbidden 1A 1→ 3T 1 transition. The pure electronic 0–0 transition in 1A 1→ 1T 1 was found at 20 270 cm −1. In complex 2 the broad low intensity band at ca. 16 800 cm −1 has been assigned to a forbidden ZnOCr transition in the bridge.