Cobalt(II) triazene 1-oxide bis(chelates). A case of planar (low spin)–tetrahedral (high spin) isomerism

Abstract

High-and low-spin cobalt( ti) triazene 1 -oxide bis(chelates) have been isolated. The low-spin complexes possess square-planar structure whilst the high-spin complexes are tetrahedral. The_molecular structure of high-spin [Co(OMeN,C,H,Me-4),] has been determined: triclinic, space group P1, Z = 2, a = 7.970(5), b = 10.1 74(5), c = 11.676(5) A, a = 87.1 8(4), p = 74.31 (4) and y = 74.06(4)". For some complexes the isolation of both planar (low-spin) and tetrahedral (high-spin) isomers or of their conglomerates is possible depending on the synthesis conditions. The crystal structure of square-planar [ Ni(OMeN,C,H,-Me-4),], which is isomorphous wiLh the low-spin isomer of [Co(OMeN3C,H,Me-4),], has been determined: triclinic, space group P1, 2 = 1, with a = 7.495(2), b = 7.694(5), c = 8.61 2(3) A, a = 64.64(5), p = 87.84(2) and y = 78.64(3)". The complexes exhibit a planar-tetrahedral equilibrium in non-co-ordinating solvents, the AH * and AS* values of which, determined from solution magnetic susceptibility measurements, are in the range 1-15 kJ mol-' and 5-30 J K-l moIV, respectively. The electrochemical properties of the complexes are given.The first report on metal complexes of triazene I-oxides appeared as early as in 1938.' Since that time some interest has centred around the formation and properties of these compounds.' The synthesis of the ligands is quite straightforward and involves coupling the diazotised aromatic amines and Nalkylor aryl-hydroxylamines, the latter prepared by reduction of the corresponding nitro compounds. A host of differently substituted starting materials is available. Hence it is possible to introduce into a ligand system a number of substituents of different size and polar effects. In a previous communication 2 j we reported the formation of both high-and low-spin cobalt(I1) complexes, the spin state being dependent on the ligand substituents. The structure of low-spin [Co(OEtN,Ph),] was shown to be square-planar centrosymmetrk2j The formation of low-spin bis(che1ate) cobalt(r1) systems with an N 2 0 2 chromophore indicates rather strong o-donor properties of triazen-1 -olato anions. We also pointed out the possibility of conversion of some of the high-spin complexes into low-spin isomers upon dissolution in non-co-ordinating solvents or by recystallisation from dimethylformamide (dmf)-water.This paper describes the isolation, magnetic, electrochemical and spectroscopic properties of cobalt@) chelates of systematically substituted triazene I-oxides. The molecular structure of high-spin, tetrahedral [Co(OMeN,C6H,Me-4),] has been determined, The formation of high-and low-spin complexes and their interconversions have been found to be due to tetrahedralplanar isomerism. This phenomenon is well documented for four-co-ordinate nickel(I1) bis(che1ates) but is very scarce for analogous cobalt(r1) systems4 Experimental Details of the magnetic, spectroscopic and electrochemical instrumentation are given in refs. 2(k) and 2(n). Magnetic susceptibility measurements in CDCl, and C,D,CD, solutions...

Geometry and Spin Change at the Heart of a Cobalt(II) Complex: A Special Case of Solvatomorphism

“…In 1‐orange , the mean CoO bond length (1.951(7) Å) is similar to the corresponding values reported for tetrahedral (HS) cobalt(II) complexes of fluorinated alkoxide ligands14a (1.952(3) Å), and α ‐iminoketone‐type ligands (compound 10 , Table 1). The mean CoN bond length 1.989(8) Å is comparable to those found in tetrahedral cobalt complexes of triazene 1‐oxide ligands6 (compound 9 , Table 1) and β ‐ketoaminato ligands18 (compound 11 , Table 1). The CoO and CoN bond lengths are longer by 0.11(1) and 0.09(1) Å in 1‐orange (tetrahedral) versus 1‐green (square planar), as was expected based on crystal‐ and ligand‐field theory 19.…”

“…They present characteristic low‐molar absorptivity values 19. 24 The bands at λ =540, 970, and 1266 nm are indicative of the tetrahedral form 6. 30 Similar features were identified for tetrahedral cobalt(II) N,O ‐bis‐chelates of AMOXs,7, 31 triazene‐1‐oxides,6 and β‐ketoamine30 ligands.…”

“…[g] Compound 8 : Co(L) 2 , L=carbohydrazide‐type (DOBYEA) 17. [h] Compound 9 : Co(L) 2 , L=triazene 1‐oxide‐type (YANWOZ) 6. [i] Compound 10 : Co(L) 2 , L= α ‐iminoketone‐type (YIPHIP) 22.…”

“…In the electronic spectra of 1‐green and 1‐orange , recorded in the solid state at room temperature (Figure 7), the bands at λ =644 and 944 nm are indicative of the square‐planar form, whereas the bands at 540 and 970 nm are characteristic of the tetrahedral form 3b. 6…”

Triazene: vielseitige Verbindungen für die organische Synthese

“…Eine bemerkenswerte Arbeit befasst sich mit der Umsetzung disubstituierter Triazene mit Metallperchloraten. [9,107] Zu den Metallen, die Triazene binden, z‰hlen Nickel, [108] Kupfer, [109] Platin, [110] Cobalt, [111,112] Ruthenium [9] und Osmium. [105] Wenn man bedenkt, dass die Verwendung vieler Triazene in der Krebstherapie an ihrer Unbest‰ndigkeit in vivo scheitert und dass diese Metallionen in der Blutbahn und im gesamten Kˆrper vorhanden sind, kommt diesen Ergebnissen Bedeutung zu.…”