Reaction of nickel(II) nitrate with the dpyatriz ligand, namely 2,4,6-tris(bis(pyridin-2-yl)amino)-1,3,5-triazine, in acetonitrile produces a tetranuclear NiII coordination compound, [Ni4(dpyatriz)2(NO3)8(CH3CN)2(H2O)2].2CH3CN (1), the crystal structure of which has been determined by X-ray diffraction using a synchrotron source. 1 has been characterized by IR and UV-vis spectroscopy, elemental and thermogravimetric analyses, and magnetic susceptibility measurements. Its solid-state structure exhibits remarkable anion...pi interactions between coordinated nitrate ions and the triazine rings. In addition, a thorough X-ray powder diffraction study has revealed a number of pseudopolymorphic phases (2-5), resulting from various degrees of hydration/solvation of the [Ni4(dpyatriz)2] core. The interconversion scheme among the different phases has been determined using controlled heating, and the basic structural features of the different pseudopolymorphs have been assessed through ab initio powder diffraction methods.