Dalton Transactions Dynamic Article Links Cite this: Dalton Trans., 2011, 40, 10090 www.rsc.org/dalton PAPER Tuning of spin crossover behaviour in iron(III) complexes involving pentadentate Schiff bases and pseudohalides† Ivan Nemec,* a,c Radovan Herchel, b Roman Boˇ ca, a Zdenˇ ek Tr´ avn´ ıˇ cek, c Ingrid Svoboda, d Hartmut Fuess d and Wolfgang Linert e Received 18th April 2011, Accepted 2nd August 2011 DOI: 10.1039/c1dt10696a Investigations on a series of eight novel mononuclear iron(III) Schiff base complexes with the general formula [Fe(L 5 )(L 1 )]·S (where H 2 L 5 = pentadentate Schiff-base ligand, L 1 = a pseudohalido ligand, and S is a solvent molecule) are reported. Several different aromatic 2-hydroxyaldehyde derivatives were used in combination with a non-symmetrical triamine 1,6-diamino-4-azahexane to synthesize the H 2 L 5 Schiff base ligands. The consecutive reaction with iron(III) chloride resulted in the preparation of the [Fe(L 5 )Cl] precursor complexes which were left to react with a wide range of the L 1 pseudohalido ligands. The low-spin compounds were prepared using the cyanido ligand: [Fe(3m-salpet)(CN)]·CH 3 OH (1a), [Fe(3e-salpet)(CN)]·H 2 O(1b), while the high-spin compounds were obtained by the reaction of the pseudohalido (other than cyanido) ligands with the [Fe(L 5 )Cl] complex arising from salicylaldehyde derivatives: [Fe(3Bu5Me-salpet)(NCS)] (2a), [Fe(3m-salpet)(NCO)]·CH 3 OH (2b) and [Fe(3m-salpet)- (N 3 )] (2c). The compounds exhibiting spin-crossover phenomena were prepared only when L 5 arose from 2-hydroxy-1-naphthaldehyde (H 2 L 5 = H 2 napet): [Fe(napet)(NCS)]·CH 3 CN (3a, T 1/2 = 151 K), [Fe(napet)(NCSe)]·CH 3 CN (3b, T 1/2 = 170 K), [Fe(napet)(NCO)] (3c, T 1/2 = 155 K) and [Fe(napet)(N 3 )], which, moreover, exhibits thermal hysteresis (3d, T 1/2 ↑ = 122 K, T 1/2 ↓ = 117 K). These compounds are the first examples of octahedral iron(III) spin-crossover compounds with the coordinated pseudohalides. We report the structure and magnetic properties of these complexes. The magnetic data of all the compounds were analysed using the spin Hamiltonian formalism including the ZFS term and in the case of spin-crossover, the Ising-like model was also applied. Introduction Spin-crossover (SCO) materials can be reversibly switched between reference electronic states with different spin multiplicity by exter- nal stimuli, such as temperature, pressure, and light irradiation. 1,2 a Institute of Inorganic Chemistry, Slovak University of Technology, Radlinsk´ eho 9, SK-812 37, Bratislava, Slovakia. E-mail: ivan.nemec@ stuba.sk, ivan.nemec@upol.cz b Department of Inorganic Chemistry, Faculty of Science, Palack´ y Univer- sity, Tˇ r. 17. listopadu 12, CZ-77900, Olomouc, Czech Republic E-mail: radovan.herchel@upol.cz c Regional Centre of Advanced Technologies and Materials, Department of In- organic Chemistry, Faculty of Science, Palack´ y University, Tˇ r. 17. Listopadu 12, CZ-77146, Olomouc, Czech Republic. E-mail: zdenek.travnicekl@ upol.cz d Materials Science, Darmstadt University of Technology, D-64287, Darm- stadt, Germany. E-mail: hfuess@tu-darmstadt.de e Institute of Applied Synthetic Chemistry, Vienna University of Technology, 1060, Vienna, Austria. E-mail: wlinert@mail.zserv.tuwien.ac.at † Electronic supplementary information (ESI) available: Thermal ellipsoid graphics, selected crystallographic data, calculation of Hirschfield surfaces and fingerplots, 29 cif files and details of magnetic data interpretation. CCDC reference numbers 823940–823952 and 836987. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c1dt10696a In hexacoordinated mononuclear complexes with the d 5 electronic configuration of the central metal ion, there are three possible spin isomers: low-spin (LS) with S = 1/2, intermediate spin (IS) with S = 3/2 and high-spin (HS) with S = 5/2 with the spin-only effective magnetic moment m eff = 1.7, 3.9, and 5.9 m B , respectively. With the regular octahedral geometry, only the S = 1/2 to S = 5/2 transition comes into play. In previous work 3 it was shown that chlorido-containing precursor complexes [FeL 5 Cl] of the pentadentate Schiff-bases L 5 (Fig. 1) are appropriate compounds for the “bottom-up” synthetic strategy aimed at the synthesis of dinuclear 4 and tetranuclear 5 complexes. Even heptanuclear spin-crossover compounds are achievable when the ferrocyanide anion is used as a bridging unit. 6 Recently, we have reported on a new group of dinuclear cyanido- bridged iron(III) complexes with gradual SCO behaviour. 7 The spin transition is significantly affected by the strong exchange interaction in these compounds and thereby it is of a gradual character. However, our main task is to find appropriate ligands or complexes, which preserve the SCO behaviour of the compound and exhibit pronounced abruptness of the spin transition. Reactions of various 2-hydroxybenzaldehydes with aliphatic triamines, such as dpt or pet (dpt = N-(3-aminopropyl)propane-1, 10090 | Dalton Trans., 2011, 40, 10090–10099 This journal is © The Royal Society of Chemistry 2011 Published on 09 September 2011. Downloaded by Univerzita Palackého v Olomouci on 22/09/2013 15:43:48. View Article Online / Journal Homepage / Table of Contents for this issue