Ni II 20 “Bowls” from the Use of Tridentate Schiff Bases Konstantina I. Alexopoulou, † Aris Terzis, ‡ Catherine P. Raptopoulou, ‡ Vassilis Psycharis,* ,‡ Albert Escuer,* ,§ and Spyros P. Perlepes* ,† † Department of Chemistry, University of Patras, GR-26504 Patras, Greece ‡ Institute of Nanoscience and Nanotechnology, NCSR “Demokritos”, GR-15310 Agia Paraskevi Attiki, Greece § Departament de Quimica Inorganica and Institut de Nanociencia i Nanotecnologia, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain * S Supporting Information ABSTRACT: The reactions of N-salicylidene-o-amino- phenol or its derivatives and excess of nickel(II) acetate in alcohols have led to Ni II 20 clusters with an unprecedented “bowl” metal topology. T he current intense interest in the synthesis and study of high-nuclearity molecular 3d metal clusters (or coordina- tion clusters 1 ) is driven by a variety of reasons, and potential applications of such species are sought in areas such as high- density data storage, 2 magnetic refrigeration, 3 qubits for quantum computation, 4 and molecular spintronics, 5 among others. Nickel(II) clusters have been receiving increasing attention in the field of molecular magnetism. 6a This 3d 8 metal ion has shown promise in the synthesis of both single-molecule magnets (SMMs) 6b and spin-phonon traps. 7 These characteristics justify the interest of our group in the chemistry of nickel(II) coordination clusters. 8 One of the ligand families that we have been using in this chemistry derives from the condensation of derivatives of salicylaldehyde with derivatives of o-aminophenol (Chart 1, left). With all of the above in mind, we decided to employ saphH 2 and samphH 2 , in combination with carboxylate ions (potentially terminal and/or bridging ligands), in nickel(II) chemistry as a means of obtaining large clusters with exciting structures, uncommon metal topologies, and interesting magnetic proper- ties. The reaction of Ni(O 2 CMe) 2 ·4H 2 O and samphH 2 in a 1:1 molar ratio in methanol (MeOH) gave on orange solution that upon storage at room temperature gave brownish-green dichroic crystals of [Ni 4 (samph) 4 (MeOH) 4 ]·0.5MeOH·0.4H 2 O(1· 0.5MeOH·0.4H 2 O) in ∼60% yield. Its molecular structure (Figures S1-S3 in the Supporting Information, SI) is similar to that of [Ni 4 (samph) 4 (EtOH) 4 ]·0.7EtOH (EtOH = ethanol), 9 consisting of tetranuclear cluster molecules with a cubane {Ni 4 (μ 3 -OR) 4 } 4+ core. The precipitation of green crystals from an orange reaction solution made us suspect that there was a “hidden” product in the reaction system, possibly with MeCO 2 - as a coligand; we thus increased the MeCO 2 - /samphH 2 molar ratio. The reactions of Ni(O 2 CMe) 2 · 4H 2 O and samphH 2 in a 2:1 molar ratio (MeCO 2 - :saphH 2 = 4:1) in alcohols (MeOH and EtOH) gave dark-orange-red solutions that upon slow diffusion with Et 2 O afforded red crystals with almost identical IR spectra. The crystals were better from EtOH and were used for single-crystal X-ray analysis to prove that the product (formed in ∼70% yield) is [Ni 20 (samph) 12 (O 2 CMe) 16 (EtOH) 12 ]· 10EtOH·1.8H 2 O (2· 10EtOH·1.8H 2 O). The Ni(O 2 CMe) 2 ·4H 2 O/saphH 2 chemistry (i.e., that with the parent ligand having R = R′ = H; Chart 1, left) is similar, with the products from EtOH being [Ni 4 (saph) 4 (EtOH) 4 ] (3) and [Ni 20 (saph) 12 (O 2 CMe) 16 - (EtOH) 12 ]·5.4EtOH·2.2H 2 O(4·5.4EtOH·2.2H 2 O; Figures S4-S9 in the SI). The saddle-shaped molecule of 2·10EtOH·1.8H 2 O (Figure 1) consists of 20 nickel(II) atoms held together by the 24 phenoxide-type oxygen atoms of the 12 doubly deprotonated η 2 :η 1 :η 2 :μ 3 -samph 2- ligands (Figure S10 in the SI) and 16 oxygen atoms that belong to four η 2 :η 2 :μ 4 - and eight η 1 :η 2 :μ 3 -MeCO 2 - groups. Peripheral ligation is provided by four η 1 : η 2 :μ MeCO 2 - groups, eight terminally ligated oxygen atoms from the η 1 :η 2 :μ 3 acetates, and 12 EtOH ligands. The core (Figure S11 in the SI) is {Ni II 20 (μ-OR) 24 (μ-OR′) 16 }, where 2RO - = samph 2- and R′O - = MeCO 2 - . The molecule is disposed around a crystallographically imposed S 4 axis, and the asymmetric unit is {Ni 5 (samph) 3 (O 2 CMe) 4 (EtOH) 3 ] (Figure S12 in the SI). Each of these Ni 5 units is linked to a neighboring unit through one phenoxide-type oxygen atom (O1) and one oxygen atom (O51) from one η 2 :η 2 :μ 4 -MeCO 2 - group, resulting in a Ni II 20 Received: March 9, 2015 Published: June 2, 2015 Chart 1. Structural Formulas and Abbreviations of the Ligands N-Salicylidene-o-aminophenol (saphH 2 ), N- salicylidene-4-methyl-o-aminophenol (samphH 2 ), and 3- [Benzyl(2-hydroxyethyl)amino]-1-propanol (LH 2 ) a , 11a a The atoms and bonds in bold emphasize the similarity of the regions that contain the three donor atoms in the two ligand types. Communication pubs.acs.org/IC © 2015 American Chemical Society 5615 DOI: 10.1021/acs.inorgchem.5b00521 Inorg. Chem. 2015, 54, 5615-5617