Dipyrromethene complexes of transition metals. Part II. Stereochemistry of complexes of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), mercury(II), and palladium(II) and crystal structure analysis of the palladium complex

Abstract

Complexes have been formed between bivalent ions of cobalt, nickel, copper, zinc, mercury, and palladium and the the ligands 4,4'-dicarboxyethyl-3,3',5,5'-tetramethyldipyrromethene (mpmH) and 3,4'-dicarboxyethyl-5-chloro-3',4,5'-trimethyldipyrromethene (cpmH). The stereochemistry of these complexes has been investigated by measurement of magnetic susceptibility, and l H n.m.r. spectra, and U.V. visible spectra. An X-ray determination of the crystal and molecular structure of the complex Pd(mpm), is reported. The palladium atom lies on a crystallographic centre of symmetry and is necessarily coplanar with the four co-ordinated nitrogen atoms of the ligand. The unique bidentate ligand is not planar.THE stereochemistry of transition-metal complexes of dipyrromethenes has been much discussed. Porter,l who reported the preparation of bis(dipyrr0methene) complexes of the divalent ions of cobalt, nickel, palladium, copper, zinc, cadmium, and mercury concluded that steric interactions between groups in the 5-and 5'positions (I) precluded square planar stereochemistry for the metal ions. f 11Recent work has established that some metal ions will achieve tetrahedral configurations in order to overcome intermolecular steric repulsions. from studies of u.v.-visible spectra and magnetism, that It has been t Part I, J. E. Fergusson and C.

Synthesis of quenchers to control the fluorescence of Rhodamine B and improve the contrast ratio of blue filters for LCDs

“…Despite the difference in structure of quenchers 6 and 7, their absorption maxima are similar (557 and 559 nm respectively) and in line with previous studies [16,17]. Their B bands (Soret bands) are in the range of approximately 590-610 and 580-605 nm respectively.…”

Synthesis of meso-phenyl-4,6-dipyrrins, preparation of their Cu(II), Ni(II), and Zn(II) chelates, and structural characterization of bis[meso-phenyl-4,6-dipyrrinato]Ni(II)

“…Regardless of the a substituents present in the dipyrrin ligands, the realization of a tetrahedral coordination sphere poses no interligand steric interactions. Consequently, and in analogy to the stereochemistry of the zinc chelates of alkyldipymns, compound 23 can be assigned a tetrahedral structure (9,22,27,40). The picture is more complex for the nickel and copper chelates.…”

“…The prerequisite that the ligands are flat and coordinate in exactly the same MN, fashion to the complexes to be compared must be strictly fullfilled. Fergusson and coworkers (22), for instance, published the crystal structure analysis of the palladium chelate of 3,3',5,5'-tetramethyl-4,4'-diethoxycarbonyldipyrrin in which the dipyrrin unit was not planar. The tendency for palladium to achieve square-planar coordination geometry is strong enough to distort the planar ligand and to enforce a stepped arrangement of the ligands around the metal centre.…”

“…The stereochemistry of pymn ligands around the metal is dependent on the bulkiness of the substituents in the a and a' positions, and has found interest (22) since Porter (23) called attention to this phenomenon; however, only a limited number of structural data are available (18,22,24,25). Few a-unsubstituted dipymnato complexes have been prepared (26,27) and in no case has a crystal structure been described.…”

Bis{2-[(3,5-diphenyl-1H-pyrrol-2-ylidene-κN)amino]-3,5-diphenylpyrrol-1-ido-κN}palladium(II): a homoleptic four-coordinate tetraphenylazadipyrromethene complex of palladium

“…1b). This stepped geometry has been observed in structurally analogous Pd II dipyrrin and dipyridyliminate complexes (Freeman & Snow, 1965;March et al, 1971;Wood & Thompson, 2007;Hall et al, 2010), with such a geometry predicted to be favoured over the distorted tetrahedron detected in Ni II and Zn II analogues of this ligand (Teets et al, 2008;Palma et al, 2009).…”