FULL PAPER DOI: 10.1002/ejic.201000824 Distortional Isomerism in Copper(II) Nitrato Complexes of N,N,N-Tris{[(para-nitrobenzyl)phenyl]aminoethyl}amine Ann Almesåker, [a,b] Patrick Gamez, [b,c] Janet L. Scott, [a][‡] Simon J. Teat, [d] Jan Reedijk,* [b,e] and Leone Spiccia* [a] Keywords: Copper / Tripodal ligands / Coordination modes / Hydrogen bonds / Distortional isomerism The tris(aminoethyl)amine derivative tris{[(para-nitrobenz- yl)phenyl]aminoethyl}amine [(p-NO 2 BP) 3 tren] was reacted with copper(II) nitrate in thf to yield three different solvates of [Cu(p-NO 2 BP) 3 trenNO 3 ]NO 3 (C1) in the solid state, namely α-C1·2thf (C2), β-C1·2.5thf (C3) and α-C1·(thf) 1.5 · (iPr 2 O) 0.25 (C4). The light green-yellow coloured complexes, C2 and C4, are different solvates of the one distortion isomer, while the dark-green C3 is a different distortion isomer. The spectral properties of these distortion isomers were exam- ined, and the structures of C3 and C4 were determined by X- ray crystallography. The difference in the physical properties (EPR and reflectance electronic spectra) of the light and dark Introduction The coordination chemistry of the tripodal ligand tris- (aminoethyl)amine (tren) and more elaborate structures thereof continues to be of significant interest. [1] These li- gands can adopt mono-, di-, tri- or tetradentate coordina- tion modes when reacted with a variety of metal ions, the last being the most common. [1] Ligands based on tren have often been applied in the synthesis of copper(II) complexes, and the majority of them adopt a trigonal-bipyramidal ge- ometry in which these tripodal ligands use all four nitrogen atoms to bind to the copper(II) ion, leaving one open coor- [a] School of Chemistry and Centre for Green Chemistry, Monash University, Victoria 3800, Australia Fax: +61-3-9905-4597 E-mail: leone.spiccia@monash.edu [b] Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P. O. Box 9502, 2300 RA Leiden, The Netherlands Fax: +31-71-527-4671 E-mail: reedijk@chem.leidenuniv.nl [c] ICREA, Universitat de Barcelona, Departament de Química Inorgànica, Diagonal 647, 08028 Barcelona, Spain [d] Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [e] Department of Chemistry, King Saud University, P. O. Box 2455, Riyadh 11451, Saudi Arabia [‡] Current address: Centre for Sustainable Chemical Technologies, University of Bath, Bath, BA2 7AY, UK © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Inorg. Chem. 2010, 5394–5400 5394 green solids of C1 (α-C1·2thf and β-C1·2.5thf) can be attrib- uted to a change in the coordination mode of the ligand to the Cu II centre. While the coordination sphere and orienta- tion of the donor atoms in C3 and C4 are similar and the axial Cu–N and Cu–O distances identical, their equatorial bond lengths [Cu(1)–N eq ] differ significantly. Compound C4 was found to have a more uniform distribution of Cu(1)–N eq bond lengths [2.166(3)–2.232(3) Å] than C3 [2.077(3)–2.352(3) Å], one Cu–N eq distance being unusually long, when compared with similar bonds in a range of copper(II) complexes of tren derivatives. dination site in the trigonal bipyramid for an exchangeable monodentate ligand. [1] This open coordination site has often been used in the stabilization of highly reactive spe- cies, such as copper–dioxygen complexes, [2,3] or the stabili- zation of redox-active anions, such as thiosulfates and thiosulfonates. [4] Copper(II) is sometimes found to adopt different geome- tries with the same ligand due to the “plasticity” of the copper(II) ion. [5,6] Distortion isomers have been reported, which have distinctly different colours arising from only slight distortions in the coordination sphere of the cop- per(II) ion, [6,7] and, in some cases, distortion isomers have been isolated as differently solvated species. [8] We recently reported that the [Cu(p-NO 2 BP) 3 trenF]BF 4 complex can be formed by reaction of a tren-based ligand, (p-NO 2 BP) 3 tren, with Cu(BF 4 ) 2 ·6H 2 O. The fluoride ligand can be generated from the hydrolysis of a BF 4 – anion or introduced by the addition of a fluoride salt. Analysis of the structure of this compound revealed the shortest ever reported Cu II –F distance, indicating very strong binding of fluoride to the Cu II centre. [9] The bulky para-nitrobenz- ylphenyl N-substituents on (p-NO 2 BP) 3 tren were found to create a tight hydrophobic cavity that prevented the fluoride ion from forming bridged complexes and from accepting hydrogen bonds from hydrophilic molecules. This finding led us to postulate that the presence of bulky N-substituents on the tren moiety could be exploited in the synthesis of further complexes with interesting crystallographic features