Electron Paramagnetic Resonance Studies of the Electronic Structures of Bis(maleonitriledithiolato)copper(II), -nickel(III), -cobalt(II), and -rhodium(II) Complexes

Abstract

Vol. 86 Fig. 10.-Rotatory dispersion curve of the L-histidine-copper complex resolved into a simple Cotton effect and a Cotton effect similar to those of the cobalt, nickel, and zinc complexes.the many-electron model to this chromophoric electron. Looking at complex I (imidazole plane), it would be reasonable to take the most polarizable 2-direction in the direction of charge transfer. The y-direction would be in the imidazole plane and the x-direction would be perpendicular to that plane. All of the groups lie in H Complex I (imidazole plane) or very near a plane except the carboxylate anion which is clearly the principal perturbation of the "chromophoric ellipsoid.'' As it is a negative group, the product Axyz would be positive in this direction, that is, the static charge effect is assumed to be dominant, and as xyz is negative, must be negative, i.e., a negative Cotton effect might be expected. Figure 10 shows that the curve for the L-histidinocopper(II) can be resolved into a curve similar to those of the other transition metals and a negative Cotton effect curve.Acknowledgment.-The authors express appreciation to the National Science Foundation under Grant GP-415 for financial support of this research and to Dr. D. J. Caldwell for helpful discussions on theoretical aspects of optical rotation.

Theory of the Spin Hamiltonian Parameters for Low Spin Cobalt(II) Complexes

“…Using the above coordinate system the ground state of (dX2-Y2)2(dXZ)2(dZ2)2(dyz) has been reported for four cobalt complexes (10,12,13,21 has been attributed to most other complexes (1 1, 14, 16, 17, 22-24). In the case of one type of CON,complex,Engelhardt et al (23) have proposed a (d,,)2(dy,)2(d,2)2(dx2~y2) ground state while Urbach et al (1 5) have proposed the more usual (dX2-y2)2(dXZ)2(dyZ)2(dZ2) ground state.…”

“…No regular pattern is observed in the hyperfine A values. In the few single crystal studies done (9)(10)(11)(12)(13), the large g value is always'found to be in the plane deCan. J. Chem.…”

Single Crystal Electron Spin Resonance Of Low Spin Co(II) And Of Cu(II) Schiff Base Complexes

“…Five single crystal studies of low spin Co(I1) complexes are known to the authors (1,(12)(13)(14)(15) and only two (1, 15) are of complexes having oxygen and nitrogen bonding to the cobalt ion. Zelewsky and Fierz (1) in their study of N, N1-ethylenebis(salicylideneiminato)cobalt(II), [Co(salen)], claimed that only a ' B, ground state would explain their results but they provided no details.…”

“…The axis normal to the molecular plane or z axis is taken to be that axis with the large g value and A value in the copper system and is found to be in the 23 plane of the crystal. The x axis has been assigned by an analogy with similar Co(I1) complexes (1, 13,14) in which the large g value is always associated with the x axis. The growth habits of this crystal also support this assignment, since growth of the crystal along the long axis or y axis of molecule would be poor, which is the case for the 1 axis of the crystal.…”

Synthesis and electron spin resonance studies of a Co(II) complex with a tetradentate macrocyclic Schiff base ligand

“…result in an electronic T I too short to allow observation of esr spectra even a t 77 K. The magnetic susceptibility measured in the solution and 63 the paramagnetic shifts observed in the nmr spectrum of the complex are strong indications [5] A, = K + P that there is indeed a paramagnetic species here 4 57 which is not a pure S = 112 state. The magnetic is defined likewise.…”