Dalton Transactions Dynamic Article Links Cite this: Dalton Trans., 2012, 41, 4744 www.rsc.org/dalton COMMUNICATION “Squaring the clusters”: a Mn III 4 Ni II 4 molecular square from nickel(II)-induced structural transformation of a Mn II/III/IV 12 cage† Dimitris I. Alexandropoulos, a Manolis J. Manos, b Constantina Papatriantafyllopoulou, c Shreya Mukherjee, c Anastasios J. Tasiopoulos, b Spyros P. Perlepes, a George Christou* c and Theocharis C. Stamatatos* a,d Received 5th January 2012, Accepted 5th March 2012 DOI: 10.1039/c2dt00030j A Mn III 4 Ni II 4 molecular square exhibiting slow magnetiza- tion relaxation has been prepared from the reaction of a Mn II 4 Mn III 6 Mn IV 2 cluster and a simple Ni II source. Mixed-metal materials are still an attractive research area for many groups worldwide in the fields of solid-state chemistry and condensed-matter physics. 1 Molecular synthetic chemists have also shown an intense interest in mixed-metal complexes during the last two decades. A major reason for this is the search for complexes with interesting magnetic properties, such as single- molecule magnets (SMMs), 2 single-chain magnets (SCMs), 3 and 3D molecule-based magnets. 4 SMMs often possess high spin (S) ground states and easy- axis-type magnetic anisotropy (as reflected in a large and nega- tive zero-field splitting parameter, D), giving a significant energy barrier to reversal of the magnetization vector. To date, the vast majority of SMMs have been found among polynuclear homo- metallic manganese complexes (clusters) containing Mn III atoms. 5 This is due to the often large S values they possess, and the large and negative magnetoanisotropy associated with the presence of Jahn–Teller distorted Mn III centres. Polynuclear het- erometallic 3d–4f and 3d–3d′ complexes occupy a special place among mixed-metal molecular materials because they offer an alternative 6 to homometallic transition-metal SMMs and often exhibit unprecedented metal topologies and beautiful structural motifs. The hope has been that the combination of different metal ions will lead to new molecular species with larger mag- netic anisotropies and higher S values, the latter arising from the different nature and strength of the magnetic exchange inter- actions between the heterospin carriers. Indeed, this approach has successfully led to several 3d–4f high-spin molecules and SMMs, 7 but the 3d–3d′ heterometallic analogues are still not so developed, 8 very likely due to the difficulties encountered in their synthesis. From a synthetic viewpoint, methods must be devised to combine the two different 3d-metal ions within a cluster. One of the common routes is the “one-pot” procedure involving a mixture of 3d- and 3d′-metal salts, and a ligand possessing coordination affinity for both 3d metal ions. A more syntheti- cally logical strategy deals with the use of “3d-metal complexes as ligands” (building blocks) 9 for reactions with an additional 3d′ metal source. A variety of anionic 2-pyridylmonoximes have been widely employed to date in the synthesis of structurally and magnetically interesting homometallic 3d and 3d–4f metal com- plexes, 10 but their use in high-nuclearity 3d–3d′ chemistry is rather limited to a few clusters. 11 These ligands are particularly attractive when one of the 3d metals is divalent, favoring their coordination with the softer N atoms, whereas the harder oximato O atom will favor binding to the trivalent 3d (i.e., Cr III , Mn III , Fe III ) or 4f metal. Distorted octahedral Ni(II) complexes with an S = 1 spin state can have large D values; 12 the magnetic coupling between Ni II and Mn III is known to be stronger than that between Mn II and Mn III , 13 thus preventing complications from low-lying excited states in the analysis of the low-temperature magnetic suscepti- bility data. In addition, polynuclear heterometallic Mn III –Ni II complexes are relatively scarce. 8a,11b,14 For such reasons, we have been targeting new synthetic procedures that might yield large-nuclearity Mn III –Ni II clusters. We have now discovered a synthetic entry into an unusual Mn III 4 Ni 4 molecular square from the reaction between a new Mn II/III/IV 12 oxido–oximato cage-like cluster and a simple Ni II source. We believe this work presages a fruitful new area in high nuclearity 3d–3d′ metal cluster chem- istry with unprecedented architectures and interesting magnetic properties. The reaction of Mn(ClO 4 ) 2 ·6H 2 O, phenyl 2-pyridyl ketone oxime (ppkoH), and NEt 3 in a 1 : 1 : 1 molar ratio in MeCN gave a dark brown solution that upon slow evaporation at room temperature gave brown crystals of [Mn 12 O 8 (OH) 2 ( ppko) 12 - (H 2 O) 2 ](OH)(ClO 4 ) 3 ·2MeCN (1·2MeCN) in 80% yield.† Dissolution of 1 in CH 2 Cl 2 and addition of 6 equivalents of Ni(ClO 4 ) 2 ·6H 2 O gave a dark red precipitate upon overnight stirring. The solid was dissolved in MeCN, and careful layering with Et 2 O afforded red crystals of the heterometallic [Mn 4 Ni 4 - (OH) 8 ( ppko) 8 (H 2 O) 4 ](ClO 4 ) 4 (2) complex in 45% yield.† Note that neither “one-pot” Mn(ClO 4 ) 2 /Ni(ClO 4 ) 2 /ppkoH/NEt 3 † Electronic supplementary information (ESI) available: Details for the preparations of 1 and 2 including microanalytical and IR data, and various structural and magnetic plots for both complexes. CCDC 860120 and 860119. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2dt00030j a Department of Chemistry, University of Patras, 26504 Patras, Greece. E-mail: thstama@chemistry.upatras.gr; Tel: +30-2610-996020 b Department of Chemistry, University of Cyprus, 1678 Nicosia, Cyprus c Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA d Department of General and Inorganic Chemistry, Facultyof Chemistry, Aristotle University of Thessaloniki, P.O. Box 135, 54124 Thessaloniki, Greece 4744 | Dalton Trans., 2012, 41, 4744–4747 This journal is © The Royal Society of Chemistry 2012 Downloaded by University of Florida on 14 December 2012 Published on 06 March 2012 on http://pubs.rsc.org | doi:10.1039/C2DT00030J View Article Online / Journal Homepage / Table of Contents for this issue