A new mixed-valent cobalt pivalate cluster [NaCo112Com2(N3)(N03)2(02CCMe3)4(teaH)2(H20)2] H2O (1) was prepared by the reaction of dinuclear cobalt(II) pivalate cluster [Co2(µ­ OH)2(O2CCMe3)4(HOCCMe3)4] with Dy(NO3)3-6H2O, NaN3 and trietanolamine (teaH3) in acetonit:rile lmder ultrasonic inadiation. The X-ray study revealed the tet:ranuclear cobalt cluster capped with sodium cation, (Fig. 1). The Co atoms in the ve11exes of rhomb are close to common plane within ±0.14 A, and bridged by four carboxylate groups, two teaH ligands and N3- anion. The Co11 ••• Com separations arn in the narrow range 3.070(1) - 3.103(1) A, The analysis of the magnetic properties of this system shows that it comprises two high spin Con ions coupled through the superexchange interaction mediated by the diamagnetic low spin Com ions acting as bridges. The model for the explanation of the magnetic behavior of this complex includes the 4 following intracenter and intercenter interactions: (i) the spin-orbital coupling operating within the T1 ground cubic te1m of each Co11 ion, (ii) the tetragonal c1ystal field that splits this multiplet into an orbital singlet and orbital doublet, (iii) the Co11-Con superexchange interaction and (iv) Zeeman interaction that includes both orbital and spin contributions. In order to describe properly the magnetic anisotropy of the complex we have taken into accmmt the non-colinearity of the anisotropy axes ( coinciding with local C4 ones) of the mononuclear Co11 moieties. The proposed model satisfacto1y explains the observed de magnetic behavior (xT vs. temperature and magnetization vs. magnetic field) of the studied complex (Fig. 2). The obtained best fit local parameters (shown in the Caption for Fig. 2) fall in the typical range of parameters for the axial Co11 ions. The value and the sign of the superexchange arameter seems to be also reasonable be