FULL PAPER DOI: 10.1002/ejic.201200612 A Bis(pyrrole) Schiff Base Containing a Flexible Siloxane Bridge and Its Ni II Complex Angelica Vlad, [a] Constantin Turta, [a,b] Maria Cazacu,* [a] Elena Rusu, [a] and Sergiu Shova [a,c] Keywords: Schiff bases / N ligands / Structure elucidation / Siloxanes / Nickel A Schiff base, H 2 L, containing a siloxane bridge was pre- pared by condensation of pyrrole-2-carboxaldehyde with a siloxane diamine, 1,3-bis(3-aminopropyl)tetramethyldisilox- ane. The proper nickel(II) complex, NiL, was obtained by in situ generation of the ligand in the presence of nickel chlor- ide. The synthesized compounds were characterized by ele- mental analysis and common spectroscopic (FTIR, 1 H NMR, Introduction The synthesis and study of siloxane-based compounds having transition metal centers constitute an area of inter- est, because such materials are likely to exhibit attractive and fine-tuned electrical, electrochemical, magnetic, cata- lytic, and optical properties, [1] as a result of the co-existence of two components each having their own particularities. In addition, they would also be of interest as pyrolytic precur- sors to ceramic products [1] containing transition metals or in medicine as biologically active compounds. [2,3] Silicon de- rivatives can be involved either directly with the siloxane bond (i.e. metal siloxides containing Si–O–M linkages) or through the attached organic chelating functions. [4–6] Di- verse organic hydrophilic groups able to act as a chelating agent for metals can be attached to the hydrophobic dior- ganosiloxane moiety that can extend the application range of the products from high-performance materials to phar- maceuticals. [7] One of the most efficient pathways for the preparation metallosiloxane complexes is via Schiff base derivatives, be- cause their synthesis is simple, they are versatile, and they have a diverse range of applications. They can be prepared [a] “Petru Poni” Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41A, 700487 Iasi, Romania E-mail: mcazacu@icmpp.ro Homepage: http://www.icmpp.ro/ [b] Institute of Chemistry of the Academy of Sciences of Moldova (ASM), Academiei str. 3, 2028 Chisinau, Republic of Moldova [c] Institute of Applied Physics of the Academy of Sciences of Moldova (ASM), Academiei str. 5, 2028 Chisinau, Republic of Moldova Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201200612. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Inorg. Chem. 2012, 5078–5084 5078 UV/Vis) techniques. Both compounds were structurally char- acterized by X-ray crystallography. NiL is a discrete mononu- clear nickel complex with a tetrahedrally distorted square- planar N 4 environment. The thermal behavior of the ligand and nickel complex was studied by thermogravimetric analy- sis (TGA) and differential scanning calorimetry (DSC). by starting either from siloxane aldehydes and organic amines or siloxane amines and organic aldehydes. The coor- dination geometry and, as a result, the properties of the formed complexes depend highly on the nature of the com- ponents involved. Some of these transition metal Schiff base complexes with square-planar geometry are of interest especially for anticancer drugs [8] and as catalysts. [9,10] Although of high potential, this direction was not ex- plored sufficiently until now. A relatively small number of compounds of this type [11–13] are reported in the literature, because of the difficulty in their characterization. The high flexibility of the siloxane bond limits the possibility to ob- tain structures that can be investigated by techniques com- mon for classical inorganic and organic chemistry (e.g., sin- gle-crystal X-ray diffraction). We have recently reportedthe synthesis of a series of co- ordination compounds on the basis of ligands containing dimethylsiloxane segments. [14–17] Very recently, we have be- gun a very in-depth study in this direction by approaching different pathways to obtain either low- or high-molecular- weight metallosiloxane structures. The presence of the highly flexible and hydrophobic dimethylsiloxane moiety is expected to induce major changes in the structure and be- havior of the complex as compared with those based on organic ligands. [18] In this paper we report the synthesis as well as the spec- troscopic and structural characterization of a Schiff base ligand, H 2 L, derived from the condensation of pyrrole-2- carboxaldehyde with a siloxane diamine, 1,3-bis(3-amino- propyl)tetramethyldisiloxane, and the corresponding NiL complex. We chose this metal because nickel(II)–diimine complexes have been shown to possess catalytic activity for the polymerization or copolymerization of olefins and vin- ylic monomers [19] and also second-order NLO properties. [20]