[(dpp‐bian)GaGa(dpp‐bian)] and [(dpp‐bian)ZnGa(dpp‐bian)]: Synthesis, Molecular Structures, and DFT Studies of These Novel Bimetallic Molecular Compounds

Abstract1,2‐Bis[(2,6‐diisopropylphenyl)imino]acenaphthene) (dpp‐bian) stabilizes gallium–gallium and zinc–gallium bonds (compounds 1–3). The compound [(dpp‐bian)GaGa(dpp‐bian)] (2) was prepared by the reaction of GaCl3 with K3[dpp‐bian] and the heterometallic [(dpp‐bian)ZnGa(dpp‐bian)] (3) was prepared by a simple one‐pot reaction of [{(dpp‐bian)ZnI}2] with GaCl3 and K4[dpp‐bian]. In contrast to [(dpp‐bian)ZnZn(dpp‐bian)] (1) and 3, compound 2 is ESR silent, thus proving the dianionic character of both dpp‐bian ligands. The solution ESR spectrum of 3 reveals the coupling of an unpaired electron with the gallium nuclei 69Ga and 71Ga (A(69Ga)=0.97, A(71Ga)=1.23 mT), thus confirming the presence of ZnGa bonds in solution. According to the results of the X‐ray crystal structure analyses the metal–metal bond lengths in 2 (2.3598(3) Å) and 3 (2.3531(8) Å) are close to that found in 1 (2.3321(2) Å). The electronic structures of compounds 2 and 3 were studied by DFT (B3 LYP/6–31G* level). The metal–metal π bond in 2 is mainly formed by overlap of the p orbitals of Ga in the HOMO and HOMO−1, the latter showing a stronger interaction. The s and p orbitals of Ga overlap in the deeper located HOMO−17 producing a GaGa σ bond. In contrast to the ZnZn bond in 1, which has 95 % s character, the NBO (natural bond order) analysis of 2 reveals 67.8 % s, 32.0 % p, and 0.2 % d character for the GaGa bond. Compound 3 has a doublet electronic ground state. The unpaired electron occupies the α HOMO−1 localized at the Zn‐containing fragment. The GaZn bond is mainly formed by overlap of the metal orbitals in the α HOMO−6 and β HOMO−5. According to the results of the NBO analysis, the Zn wave functions are responsible for 28.7 % of the ZnGa bond, with 96.7 % s, 1.0 % p, and 2.3 % d character.