Experimental and Theoretical Study of the Antisymmetric Magnetic Behavior of Copper inverse-9-Metallacrown-3 Compounds Tereza Afrati, † Catherine Dendrinou-Samara, † Catherine Raptopoulou, ‡ Aris Terzis, ‡ Vassilis Tangoulis,* ,† Athanassios Tsipis,* ,| and Dimitris P. Kessissoglou* ,† Department of Chemistry, Aristotle UniVersity of Thessaloniki, Thessaloniki 54124, Greece, NCSR “Demokritos”, Institute of Materials Science, 15310 Aghia ParaskeVi Attikis, Greece, and Laboratory of Inorganic and General Chemistry, Department of Chemistry, UniVersity of Ioannina, 45110 Ioannina, Greece Received February 21, 2008 Use of PhPyCNO - /X - “blends” (PhPyCNOH ) phenyl 2-pyridyl ketoxime; X - ) OH - , alkanoato, ClO 4 - ) in copper chemistry yielded trinuclear clusters that have been characterized as inverse-9-metallacrown-3 compounds and accommodate one or two guest ligands. The magnetic behavior showed a large antiferromagnetic interaction and a discrepancy between the low-temperature magnetic behavior observed experimentally and that predicted from a magnetic model. The discrepancy between the Brillouin curve and the experimental result provides clear evidence of the influence of the antisymmetric interaction. Introducing the antisymmetric terms derived from the fit of the susceptibility data into the magnetization formula caused the simulated curve to become nearly superimposable on the experimental one. The EPR data indicated that the compound [Cu 3 (PhPyCNO) 3 (µ 3 -OH)(2,4,5-T) 2 ](1), where 2,4,5-T is 2,4,5-trichlorophenoxyacetate, has isosceles or lower magnetic symmetry (δ * 0), that antisymmetric exchange is important (G * 0), and that ΔE > hν. The structures of the complexes 1 and [Cu 3 (PhPyCNO) 3 (µ 3 -OH)(H 2 O)(ClO 4 ) 2 ](2) were determined using single- crystal X-ray crystallography. Theoretical calculations based on density functional theory were performed using the full crystal structures of 1, 2, [Cu 3 (PhPyCNO) 3 (OH)(CH 3 OH) 2 (ClO 4 ) 2 ](3), and [Cu 3 (PhPyCNO) 3 (µ 3 -OMe)(Cl)(ClO 4 )] (4). The geometries of the model compounds [Cu 3 (κ 3 N,N,O-HNCHCHNO) 3 (µ 3 -OH)(µ 2 -HCOO)(HCOO)] (5), [Cu 3 (κ 3 N,N,O- HNCHCHNO) 3 (µ 2 -HCOO)(HCOO)] + (6), [Cu 3 (κ 3 N,N,O-HNCHCHNO) 3 (µ 3 -O)] + (7), and [Cu 3 (κ 3 N,N,O-HNCHCHNO) 3 ] 3+ (8) were optimized at the same level of theory for both the doublet and quartet states, and vibrational analysis indicated that the resulting equilibrium geometries corresponded to minima on the potential energy surfaces. Both e g and t 2g magnetic orbitals seem to contribute to the magnetic exchange coupling. The latter contribution, although less important, might be due to overlap of the t 2g orbitals with the p-type orbitals of the central triply bridging oxide ligand, thereby affecting its displacement from the Cu 3 plane and contributing to the antiferromagnetic coupling. The crucial role of the triply bridging oxide (µ 3 -O) ligand on the antiferromagnetic exchange coupling between the three Cu(II) magnetic centers is further evidenced by the excellent linear correlation of the coupling constant J with the distance of the µ 3 -O ligand from the centroid of the Cu 3 triangle. Introduction It has been remarked that the attention of coordination chemists is increasingly directed to polynuclear systems. Metallacrowns (MCs), 1 the inorganic structural and func- tional analogues of crown ethers, are usually formed with transition-metal ions and a nitrogen replacing the meth- ylene carbons. MCs exhibit selective recognition of cations and anions, and these complexes can display intramo- lecular magnetic exchange interactions. 1,2 There is also a renewed interest in the coordination chemistry of oximes. These research efforts are being driven by a number of * Corresponding authors. E-mail: vtango@upatras.gr (V.T.), attsipis@ uoi.gr (A.T.), kessisog@chem.auth.gr (D.P.K.). † Aristotle University of Thessaloniki. ‡ NCSR “Demokritos”. | University of Ioannina. (1) (a) Mezei, G.; Zaleski, C. M.; Pecoraro, V. L. Chem. ReV. 2007, 107, 4933–5003. (b) Pecoraro, V. L.; Stemmler, A. J.; Gibney, B. R.; Bodwin, J. J.; Wang, H.; Kampf, J. W.; Barwinski, A. Prog. Inorg. Chem. 1997, 45, 83–177. Inorg. Chem. 2008, 47, 7545-7555 10.1021/ic8003257 CCC: $40.75  2008 American Chemical Society Inorganic Chemistry, Vol. 47, No. 17, 2008 7545 Published on Web 08/06/2008