| Summary: | The structure of the title compound, [Ni(C6H16N2)2]Br2 or [Ni(Et2en)2]Br2 (Et2en is asymmetric N,N-diethylethylenediamine), containing an NiII atom (site symmetry overline{1}) in square-planar NiN4 coordination, is described and contrasted with related structures containing NiII in octahedral coordination with axial X− ligands (X− = variable anions). The dialkylated N atom has an appreciably longer bond length to the NiII atom [1.9666 (13) Å] than does the unsubstituted N atom [1.9202 (14) Å]. The Ni—N bond lengths in [Ni(Et2en)2]Br2 are significantly shorter than corresponding values in tetragonally distorted [Ni(Et2en)2X2] compounds (X = −O2CCF3, OH2, or −NCS), which have a triplet ground state. The electronic configuration in these axially ligated [Ni(Et2en)2X2] compounds populates the metal-based dx2-y2 orbital, which is Ni—N antibonding in character. Each Et2en ligand in each [Ni(Et2en)2]2+ cation forms a pair of N—H...Br hydrogen bonds to the Br− anions, one above and below the NiN4 square plane. Thus, a ribbon of alternating Br− pairs and [Ni(Et2en)2]2+ cations that are canted at 65° relative to one another is formed by hydrogen bonds.
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