The polynuclear cobalt complexes are of great current interest due to its wide potential applications such as: catalysts, electron transfer mediators in dye-sensitized solar cells, antiviral agents and nanomagnet molecules. A new Co(II)-containing compound, [Co3(is)6(phen)2] (1) was obtained from the reaction of Co(is)2 (His = isobutyric acid) with 1,10'-phenanthroline (phen) in acetone/dmso (1:1) mixture under ultrasonic treatment. The compound has been characterized by elemental analysis, IR spectroscopy, ESI MS spectrometry, and single-crystal X-ray diffraction studies. The IR spectrum of 1 displays the asymmetric and symmetric C–H stretching vibrations of –CH3 and –CH groups of isobutyrates and phen in the range of 2963–2869 cm─1. These are accompanied by peaks at 1513 and 1469 cm─1 and a doublet at 1368 and 1354 cm─1 arising from asymmetric and symmetric bending vibrations of these groups, respectively. The characteristic strong peaks observed at 1584 and 1415 cm─1 corespond to the asymmetric and symmetric stretching vibrations of the coordinated isobutyrate groups, respectively. Compound 1 crystallizes in the orthorhombic Pbca space group with a = 15.2497(4), b = 16.6307(4), c = 18.9246(5) Å, V = 4799.53 Å3. In the structure, trinuclear complex reside on special position and has a Ci molecular symmetry with central Co1 atom of the trimers located on a crystallographic inversion center and is coordinated octahedrally by six oxygen atoms of six isobutyric carboxylate ligands. Four of these carboxylates form bridges to the peripheral Co2 atoms in the bidentate mode, while the other two in a bidentate chelate-bridging mode in which a single oxygen atom, bridges two Co centers (Fig. 1). The Co–O bond distances are in the narrow range 2.012–2.126 Å except elongated Co2 O5 bonds of 2.367 Å. The peripheral Co2 atoms additionally are chelated by phen ligands with the Co–N bond distances equal 2.099 and 2.173 Å to form a distorted octahedral environment around Co2. The Co1…Co2 separation is 3.458 Å. In the crystal structure trinuclear clusters form supramolecular chain along the b crystallographic axis due to π···π stacking interactions between phen ligands. The interplanar separations are 3.397 Å. a phen)2] (b).