We report the syntheses and structural studies of two nickel(II) complexes of imidazol-2-ylidene- N′-phenylureate ligand of composition [{Im tBuNCON(H)Ph}2Ni(acac)2](1) and [(C6H5NH2)2Ni(acac)2][ImMes NCON(H)Ph] (2). The nickel complex 1 was readily prepared by the reaction of nickel(II) acetylacetonate [Ni(acac)2] with imidazol-2-ylidene-N′-phenylureate ligand [Im tBuNCON(H)Ph] (L1) in THF under reflux condition for 72 h. The nickel complex 2 was obtained by the reaction of [Ni(acac)2], mesityl derivative of imidazol-2-ylidene-N′-phenylureate ligand [Im MesNCON(H)Ph] (L2) in the presence of aniline as base under reflux condition in THF. Both the paramagnetic complexes have been characterized by FT-IR spectroscopy and elemental analyses. Solid-state structures of both the new complexes were established by single crystal X-ray diffraction analysis. In the molecular structures of complexes 1 and 2, each nickel(II) ion is six fold coordinated and form a distorted octahedral geometry. The optical properties of both complexes have been explored. The Hirshfeld surfaces are used to view and analyze the intermolecular contacts in crystalline state for complex 2. [Figure not available: see fulltext.] © 2015 Indian Academy of Sciences.