Synthesis, magnetic properties and theoretical calculations of novel nitronyl nitroxide and imino nitroxide diradicals grafted on terpyridine moiety Giorgio Zoppellaro, Anela Ivanova, Volker Enkelmann, Ahmed Geies, Martin Baumgarten * Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany Received 6 October 2002; accepted 2 January 2003 Abstract The synthetic route based on Stille coupling between tributyltinpyridyl derivatives and bromo substituted mono- and dipyridyl- carbaldehyde is used for the synthesis of 5,5ƒ-diformyl-2,2?:6?,2ƒ-terpyridine (8). A sequence of Ullman coupling with 2,3- bis(hydroxylamino)-2,3-dimethylbutane followed by oxidation under phase transfer conditions affords either 5,5ƒ-Bis(1-oxyl-3-oxo- 4,4,5,5-tetramethylimidazolidin-2-yl)2,2?:6?,2ƒ-terpyridine (10) (diNN-Terpy) or the related 5,5ƒ-Bis(1-oxyl-4,4,5,5-tetramethylimi- dazolidin-2-yl)2,2?:6?,2ƒ-terpyridine (11) (diIN-Terpy), where both biradicals display clear intramolecular ferromagnetic interaction between the single spin units as evidenced by ESR spectroscopy. Quantum chemical calculations (ROHF/AM1) are performed showing the triplet ground-state for both 10 and 11 radicals. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Terpyridine; Organic based magnets; EPR radicals; Open-shell molecules; Nitronyl nitroxide; Semiempirical (AM1) calculations 1. Introduction There is growing interest in developing novel synthetic routes for functionalized 2,2?:6?,2ƒ-terpyridines [1a] due to their rich coordination chemistry [1b,1c], for supra- molecular assembly [2], in molecular biology [3] and even in photochemistry [4]. In addition much attention has been devoted over the last decade to develop different sets of molecular units carrying either free radicals or luminophoric centers for use as novel magnetic materials or optical devices [5]. In that vein terpyridine based radicals offer both advantages, although relatively few examples of those are available up to now in literature [6]. Since the discovery of nitronyl nitroxide (NIT) by Ullman [7] this class of radicals was widely used as building block constituents for the preparation of molecular based magnets, due to their exceptional stability, facile preparation, versatility in coordination properties and ability to generate cooperative magnetic properties [8]. In the nitronyl nitroxide radical the spin density of the unpaired electron is delocalized over two sites of coordination, leaving open the possibility to arrange the molecular unit into a supramolecular network. This assumption may be regarded as the ‘condicio sine qua non ’ to achieve high Curie-temperatures (T c ) below which materials behave like magnets [9]. In fact the first example of pure organic ferromagnets is based on the b-phase of p - nitrophenyl-nitronyl nitroxide radical with T c / 0.64 K [10]. Thus the first point to consider in designing novel organic-based magnets, if more than one radical unit is connected through a spacer or coupling unit, is the clear * Corresponding author. Tel.:  /49-6131-37-9142; fax:  /49-6131- 37-9370. E-mail address: baumgart@mpip-mainz.mpg.de (M. Baumgarten). Polyhedron 22 (2003) 2099  /2110 www.elsevier.com/locate/poly 0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0277-5387(03)00258-4