The Electronic Properties and Stereochemistry of the Copper(ir) Ion.Part VI. t Bis( bipyridyl)copper(ii) Complexes.

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The principal and mean magnetic moments of Fe acac3 (acac = acetylacetonate) and K3Fe(oxalate),,3H,0 are reported over the temperature range 80--300%. This appears to be the first time that anisotropy of the 6Alp ground-state of the iron( Ill) ion has been detected by crystal magnetic susceptibility measurements. The anisotropy is interpreted in terms of the zero-field splitting of the ground state arising from a low-symmetry ligand-field and spin-orbit coupling ; values of the zero-field splitting are reported and discussed with reference to the molecular structures of the two complexes.THE origin of the zero-field splitting in 3d5 systems to explain ground-state splittings of the order of 0.001 and the effect of such splitting on the magnetic properties cm.-l in nearly cubic systems were based on highof FeIII and MnII have long been of interest in studies order perturbations due to the cubic field and spinof specific heats, adiabatic demagnetisation, and, orbit coupling.lS2 Such an explanation was queried by more recently, paramagnetic resonance. Early attempts Meijer who found that the discrepancy between the 4

The e.s.r. and electronic spectra and magnetic moments of Cu(NH,),Ag(SCN), and [Cu(tren)NCS]SCN (tren = 2,2',2"-triaminotriethylamine) are reported and compared with the previously reported data for trigonal bipyramidal complexes of the copper(l1) ion. Theoretical expressions for the g-values for a copper(l1) ion in a trigonal bipyramidal configuration are derived and are shown to apply only to the Cu(NH,),Ag(SCN), complex. The energy levels 2€" and 2E' are shown to be separated by less than 2000 cm.-I and the magnetic moments of the trigonal bipyramidal complexes are in the range normally observed for copper(l1) complexes with a n orbitally non-degenerate ground state.

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The X-ray powder photographs, magnetic susceptibilities, infrared spectra, electronic spectra (as reflectance), and electronspin resonance spectra of nine hexanitro complexes of divalent iron, cobalt, nickel, and copper are reported. They are of the form KsM'tM'XNOah] where M" is a divalent transition metal ion and M' is a divalent cation (lead or barium, and, in the case of the copper complex, calcium). All the complexes were confirmed as having face-centered cubic crystal structures except for the barium-copper and the calcium-copper complexes, which were shown to be weakly tetragonal. The unit cell dimension a of the cubic lead complexes shows a systematic increase from iron to copper corresponding to an increase in the metal to nitrogen distance in this sequence, consistent with the increasing repulsion experienced by the ligands as electrons are added to the eg orbitals. The electronic reflectance spectra of the iron and nickel complexes are consistent with a regular octahedral coordination and a crystal field splitting of 13,590 cm-1 is indicated for the nickel complex, the highest value yet reported for a spin-free octahedral nickel(II) complex. The electronic spectra of the cobalt and copper complexes closely resemble one another and are only consistent with a tetragonal environment for the transition metal ions. The observation of an isotropic electron spin resonance spectrum for the lead-copper, the lead-cobalt, and the barium-cobalt complexes, but an anisotropic spectrum for the barium-copper and calcium-copper complexes, suggests that the former complexes may be undergoing a dynamic Jahn-Teller distortion.

The theoretical behaviour of principal and average magnetic moments of octahedral cobalt( 11) complexes perturbed by spin-orbit coupling and a Dqh symmetry crystal-field distortion is presented. Calculations have been performed using a complete spin-quartet basis. The crystal field is parameterized by the fourth-order quantities Dq and Dt, and by the second-order term Ds.The magnetic moment of dichlorotetrakis(thiourea)cobalt(ll) and dichlorotetra-aquocobalt(ii) tetrahydrate as powders and crystals are reported in the temperature range 300-90 K. Attempts to fit these results to the theoretical model do not yield unique values of the parameters and some general observations on the interpretation of cobalt(l1) magnetic susceptibilities are made.second-, fourth-, and fourth-order harmonics in the the ac plane are independent of temperature. We have made this assumption, based on our own and others' experi-M.

The magnetic susceptibilities of single crystals of tetraethylammonium tetrachloronickelate( 11) and bis-(N-isopropylsalicylaldiminato) nickel (11) have been measured over the temperature range 90--300°K. The anisotropy of the chloro-complex is characterized by a reversible discontinuity at ca. 21 8" associated with a small thermal hysteresis. The principal susceptibilities have been fitted to a theoretical spin-triplet model. The CI-Ni-CI angles calculated from the magnetic data of the chloro-compound above the transition temperature agree very well with those deduced from the room-temperature X-ray structure analysis. Orbital reduction factors and spinorbit coupling coefficients for both complexes have been determined and are discussed. THE general magnetic properties of a complete spintriplet model for tetrahedral nickel(I1) ions were discussed in Part 1.1 We now describe measurements of the principal magnetic moments of tetraethylammonium tetrachloronickelate(I1) and bis-(N-isopropylsalicylaldiminato)nickel(II) and their interpretation within the framework of the general theory. In a previous paper,2 we have reported the magnetic properties of the analogous copper(I1) compounds and considered them within the framework of the complete 2D model.3 EXPERIMENTAL Both complexes were prepared by the literature meth0ds.~*5 Tetragonal blue crystals of the chloro-complex grown by slow evaporation of a nitromethane solution at room temperature showed well developed [OOl] faces. Dark green orthorhombic crystals of the Schiff-base compound grown similarly from ethanolic solution displayed well formed [OlO] faces. Crystal axes were identified in all cases by conventional X-ray methods.Powder susceptibilities of the Schiff -base complex were