We present the MBPT(2) and coupled cluster description of the structure, energetics, and vibrational spectra for three isomers of 1,4-diaza-2,5-diboracyclohexadiene. The isomer ring and the acyclic Z- and E-isomers of C2H4B2N2 (with hydrogens attachedto the central CB bond in "cis" or "trans" positions) as well as the transition state between the ring and acyclic Z-isomer have been examined. All three molecules exhibit remarkable thermodynamic stability with respect to two cyanoborane monomers (HCN-BH) and borazirene (HCNBH) and also with respect to the common H2BCN molecule. We demonstrate a necessity for using the coupled cluster approach when reliable energy data are to be obtained. MBPT(2) is not accurate enough. The cyclic isomer is the most stable species. The barrier for the ring formation is acceptably low, suggesting that the synthesis of this novel molecule is possible via its monomeric chain precursors. Bonding analysis and the simulated infrared spectra in the harmonic approximation based upon the MBPT(2) calculations complete the information about these molecules, which may be interesting in connection with their potential use in semiconductor technology.