Received 25 November 2010
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 ) 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-HBr 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.
The synthesis of a broad variety of Ni(Et2en)2X2 compounds is described by Goodgame & Venanzi (1963). The compounds containing NiII in octahedral coordination with axial X ligands have been structurally characterized for X = -O2CCF3 (Senocq et al., 1999), -NCS (Lever et al., 1983) and H2O with non-coordinated Cl- counter-anions (Ihara et al., 1991). [Ni(Et2en)2][ClO4]2 containing a square-planar centrosymmetric cation has been identified as having triclinic (Ikeda et al., 1995; Narayanan & Bhadbhade, 1998) and monoclinic (Hayami et al., 2009) polymorphs.
Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008a); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008a); molecular graphics: SHELXTL (Sheldrick, 2008a); software used to prepare material for publication: SHELXTL.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: WM2433 ).
JPD and JTM gratefully acknowledge Tulane University for support of the Tulane Crystallography Laboratory. Stephen Ashe, Cecilia Burns, Greyson Durr, Andrew Kronfol, Camilla Munson, Whitley Muskwe, Clifford Nelson, Kristy Nguyen, Sarah Oertling, Beau Pritchett and Michael Soforenko (the undergraduate students in the fall 2010 teaching of CHEM 323 at Tulane University) are thanked for their effort in providing the crystalline sample used in this study.
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