Long-Range Exchange Interactions and Integer-SpinS_t= 2 EPR Spectra of a Cr^IIIZn^IICr^IIISpecies with Multiplet Mixing

Abstract

Synthesis, structural, and spectroscopic characterization of the linear cationic complex [LCr(III)(mu-[dmg)(3)Zn(II))Cr(III)L](2+) (1) in which L = 1,4,7-trimethyl-1,4,7-triazacyclononane and dmg is the dimethylglyoximato anion are reported. The Cr...Cr distance of 1 is 7 A. SQUID magnetic susceptibility measurements reveal the presence of long-range exchange interaction of the Cr(III) terminal ions, mediated by the diamagnetic Zn(II)(dmg)(3) "bridging ligand" (J(0) = -4.4 cm(-1), H(ex) = -2J(0)S(1)S(2), S(i) = 3/2). Multifrequency EPR measurements (S-, X-, Q-band) on frozen solutions were used to establish the intramolecular nature of the exchange coupling and to determine the zero-field splitting (ZFS) parameters and the anisotropic contributions of spin coupling. An effective spin Hamiltonian description was applied for interpretation of the spectra originating from the S(t) = 2 total spin manifold which included up to fourth-order terms for the ZFS. By the help of alternative simulations with the full coupling matrix for two spins S(i) = 3/2 (16 x 16) it could be shown that the higher-order terms in the effective description owe their origin to multiplet mixing due to competing single-ion ZFS (the absolute value of D(i) = 0.2 cm(-1)) and isotropic exchange interaction. The magnetic anisotropy related to dimer properties could be readily explained by dipolar coupling (j(z) = -0.012 cm(-1)). Implications for the interpretation of other integer-spin EPR spectra are discussed.

Magnetic Anisotropy of the Antiferromagnetic Ring [Cr8F8Piv16]

“…A large number were derived from measurements of mononuclear complexes,44, 45 or Cr III doped in inorganic lattices,46 with absolute values ranging between practically negligible to ≈0.7 cm −1 . For dimeric complexes, typical values range from | D zz Cr |=0.198(2) cm −1 ,42 to D zz Cr =−0.658 cm −1 22. The single‐ion axial anisotropy found for 1 fits into this range.…”

“…In fact, large deviations from this behavior were clearly observed in dinuclear copper( II ) complexes 15. Indeed, some authors attribute the spin–spin ZFS contribution in chromium( III ) compounds completely to dipolar interactions,42 while in other cases the dipolar interaction does not account completely for the axial ZFS found 39, 41. However, in these latter cases, the axial ZFS parameters were of the order of a few hundredths of a wavenumber, which makes the relative error quite large.…”

Heptapyridinebis(μ-dimethylglyoximato)tricopper(II) diperchlorate: a novel trinuclear copper complex bridged by glyoximate groups

“…The oximate group can behave as a bridge binding one metal atom through the imine N atom and another one through the deprotonated O atom to generate dinuclear, trinuclear, tetranuclear and polymeric chain metal complexes (Chen et al, 2003;Liu et al, 2002;Li et al, 2002). Although many bidentate and tridentate ligands are utilized as terminal ligands to synthesize these complexes (Burdinski et al, 2001;Birkelbach et al, 1998), the chemistry of bis-dioximate complexes with monodentate ligands has not been much explored (Fraser et al, 1994;Kubiak et al, 1995;Solans et al, 1996). With this idea in mind, we designed and synthesized a copper(II) trinuclear complex, (I), with the double oximate bridges in cis arrangement, and pyridine as the terminal ligands.…”

Metallomacrocycles as ligands: synthesis and characterisation of aluminium-bridged bisglyoximato complexes of palladium and iron

“…39,40 Additionally there are several examples of cryptands consisting of tris-glyoximato moieties with the oxygen donors bound to antimony, tin, iron, manganese, or chromium. [41][42][43][44][45][46][47] Given the utilization of macrocycles for many applications including biomimetic chemistry, catalysis, and solar fuels, facile synthetic access to diverse metallomacrocycles is of interest as a complementary strategy for tuning of the electronic and steric environment of coordinated metal centers. We report herein on the synthesis of metallomacrocycles based on aluminium bridged bisglyoximato frameworks and their coordination chemistry with iron and palladium.…”