Premium
On the Electronic Structure of Ni II Complexes That Feature Chelating Bisguanidine Ligands
Author(s) -
Roquette Pascal,
Maronna Astrid,
Peters Anastasia,
Kaifer Elisabeth,
Himmel HansJörg,
Hauf Christoph,
Herz Verena,
Scheidt ErnstWilhelm,
Scherer Wolfgang
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200901479
Subject(s) - chemistry , crystallography , excited state , valence (chemistry) , ground state , ligand (biochemistry) , paramagnetism , magnetic susceptibility , density functional theory , computational chemistry , atomic physics , condensed matter physics , physics , biochemistry , receptor , organic chemistry
In this work we report on the syntheses and properties of several new Ni complexes featuring the chelating bisguanidines bis(tetramethylguanidino)benzene (btmgb), bis(tetramethylguanidino)naphthalene (btmgn), and bis(tetramethylguanidino)biphenyl (btmgbp) as ligands. All complexes were structurally characterized by single‐crystal X‐ray diffraction and quantum chemical calculations. A detailed inspection of the magnetic susceptibility of [(btmgb)NiX 2 ] and [(btmgbp)NiX 2 ] (X=Cl, Br) revealed a linear temperature dependence of χ −1 ( T ) above 50 K, which was in agreement with a Curie–Weiss‐type behavior and a triplet ground state. Below approximately 25 K, however, magnetic susceptibility studies of the paramagnetic d 8 Ni complexes revealed the presence of a significant zero‐field splitting (ZFS) that results from spin–orbit mixing of excited states into the triplet ground state. The electronic consequences that might arise from the mixing of states as well as from a possible non‐innocent behavior of the ligand have been explored by an experimental charge density study of [(btmgb)NiCl 2 ] at low temperatures (7 K). Here, the presence of ZFS was identified as one potential reason for the flat ∢Cl‐Ni‐Cl deformation potential and the distinct differences between the ∢X‐Ni‐X valence angles observed by experiment and predicted by DFT. An analysis of the topology of the experimentally and theoretically derived electron‐density distributions of [(btmgb)NiCl 2 ] confirmed the strong donor character of the bisguanidine ligand but clearly ruled out any significant non‐innocent ligand (NIL) behavior. Hence, [(btmgb)NiCl 2 ] provides an experimental reference system to study the mixing of certain excited states into the ground state unbiased from any competing NIL behavior.