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Abstract

High-frequency as well as X-band electron spin resonance (ESR) spectroscopy, and static magnetization measurements of correlated electron systems and metal-organic spins systems are presented. ESR data of the honeycomb-lattice spin systems Na3Ni2SbO6 and Li3Ni2SbO6 reveal uniaxial and orthorhombic antiferromagnetic resonances (AFMR), respectively, in the ordered state. In both materials, AFMR gaps of 358 GHz and 200 GHz, respectively, are found. The bilayer Kagome lattice Ca10Cr7O28, which is a frustrated spin system, demonstrates g anisotropy (gb = 1.94, gc = 2.01) depending on the crystallographic axes on high-frequency ESR data. X-band ESR data show a similar temperature dependence of the linewidths for the different axes. The two Ni dimer compounds [Ni2L(dppba)]ClO4 and [Ni2L(dppba)AuPh]BPh4 (1) have a similar ligand except an Au atom attached to the phosphorus atom of (1). In both materials, ferromagnetic coupling and uniaxial anisotropy of about -12 GHz is found. The Au ligand however does not significantly affect the magnetic properties. Results presented for the mixed valence complex [Ni(III)Ni(II)(LDA)](BPh4)2 demonstrate a total spin S = 3/2 which implies ferromagnetic coupling between the Ni2+ ion (S = 1) and the low spin Ni3+ ion (S = 1/2). Again, there is an uniaxial anisotropy which amounts to -49 GHz. ESR measurements of (HNEt3)2Cu(II)[12-MCCu(II)N(Shi)-4] with Cu5-clusters organized in a metal-organic framework show typical powder spectra which are described by a S = 1/2 spin-Hamiltonian and gx = 2.03, gy = 2.04 and gz = 2.23. [Gd(III)2L(OAc)4]PF6 has a magnetic anisotropy which can be ascribed to dipolar coupling between the Gd ions.