Five-coordination. VI. Low-spin cobalt(II) complexes with with bidentate ligands

Abstract

Stable, crystalline complexes containing the five-coordinate [CoL2X]+ species, where X = Cl, Br, or I and L is one of the bidentate ligands diphenyl(o-methylthiophenyl)phosphine (I, SP), diphenyl(o-methylselenophenyl)phosphine (II, SeP), or diphenyl(o-diphenylarsinophenyl)phosphine (III, AP), have been isolated and characterized by magnetism and conductivity measurements, electronic and infrared spectra, and elemental analyses. All of the complexes are deep red and possess one unpaired electron (pett = 2.1-2.5 BM). The electronic spectra exhibit three distinct bands below 22,000 cm-1 which may be assigned to ligand-field transitions.Research interest and activity in five-coordinate com-.plexes has accelerated dramatically during the past 4 years. Whereas five-coordination is now fairly common for nickel(II), when polydentate ligands containingbonding donor atoms, such as arsenic, phosphorus, sulfur, or selenium, are used,3-6 well-characterized examples of five-coordinate complexes of a d7 ion have not been observed so frequently. One authentic, low-spin example is [Co(HPPh2)3Br2].7 Also, Venanzi and co-workers8 have prepared five-coordinate co-(1964).

Spectral and electrochemical characterization of bimetallic complexes of a novel 32-membered unsymmetrical [N12] macrocycle

“…Electronic spectra of Co II complexes (3) in DMSO solution as well as the solid state reflectance spectrum in barium oxide diluent exhibit ligand field bands in the visible region whose nature and positions are nearly identical and are comparable to that reported [26] for low-spin square-pyramidal Co II complexes. The reflectance spectrum contains an additional band in low energy region.…”

“…l eff $ 5.5 BM per Co 2+ ) expected [28] for two S = 2 uncoupled spins (in highspin state of Co 2+ ion) in square-pyramidal geometry. High-spin five coordinate Co II complexes having identical donor sites with C 4v symmetry of the basal plane usually adopt [23,26,28] a regular square-pyramidal geometry. Distortion from the perfect C 4v symmetry of the basal plane reduces [26] the magnetic moment value in monomeric Co(II) complexes of the type [CoL 2 X] + [(where L = diphenyl (o-diphenyl arsinophenyl) phosphine or diphenyl (o-methyl selenophenyl) phosphine and X = Cl, Br or I)].…”

A Tetraphosphane Imine Ligand Which Enforces Square‐Pyramidal Coordination

“…The properties of a number of low-spin cobalt() complexes of the type [CoL 2 X]Y (L = bidentate neutral ligand with variable donor set, X = coordinating anion; Y = noncoordinating anion) have been published. [8][9][10] Meek and coworkers reported the series of complexes [(dppe) 2 Co…”

Copper(II), nickel(II) and cobalt(II) complexes of oxaldihydrazide and succindihydrazide Schiff bases with salicylaldehyde ando-hydroxyacetophenone

“…The colour of the cobalt(ll) complex (3) and a weak band present at 1200 nm is suggestive of square planar stereochemistry. The spectral features of complexes (6, 9 and 12), which show strong absorption bands between 500 and 800 nm, correspond closely to five-coordinate cobalt(ll) (9).…”

“…and 2.0-2.5 B.M. ranges have been reported for cobalt(ll) complexes with low-spin square planar and pentacoordinate stereochemistry (9). There is no firm demarcation between the observed magnetic moments for the square pyramidal and trigonal-bipyramidal pentacoordinate cobalt(Ill complexes.…”