A New Class of Ferromagnetically‐Coupled Mixed Valence Vanadium(IV/V) Polyoxometalates

Abstract

Reaction of [V(VI)OCl(2)(thf)(2)] with a bidentate nitrogen-donor ligand (L: phen=1,10-phenanthroline, 5-mephen=5-methyl-1,10-phenanthroline, bipy=2,2'-bipyridine, 5,5'-me(2)bipy=5,5'-dimethyl-2,2'-bipy) in methyl alcohol, in the presence of triethylamine, leads to the formation of hexameric [V(2) (IV)V(4) (V)] oxo-alkoxo-vanadates of the general formula [V(6)O(12)(mu(2)-OCH(3))(4)(L)(4)].x H(2)O [L=phen (1.4 H(2)O), 5-mephen (2.6 H(2)O), bipy (3.4 H(2)O), 5,5'-me(2)bipy (4.H(2)O)]. X-ray structure analysis of 1.2 H(2)O and 4.8 CH(3)OH revealed a pair of V(3)O(13)N(4) trimeric units sharing two corners, with a centrosymmetric planar V(6)-core. In addition, a fully oxidized V(V) species [V(V) (4)O(8)(OCH(3))(2)(mu(3)-OCH(3))(2)(5,5'-me(2)bipy)(2)].3 CH(3)OH (5.3 CH(3)OH) was isolated from the reaction mixture used for the synthesis of 4.H(2)O. The crystal structure of 5.3 CH(3)OH revealed a dicubane-like framework with two missing vertices. Electron paramagnetic resonance (EPR) and variable temperature magnetic susceptibility studies for the hexamers 1.4 H(2)O and 3.4 H(2)O showed the complete localization of the single 3d electrons on the V(IV) ions and unusual ferromagnetic interaction between the two paramagnetic vanadium(IV) ions separated by a distance of about 5.1 A. Furthermore, intermolecular antiferromagnetic interactions through pi-contacts of phenyl rings were observed for these species below 8 K. The ferromagnetic exchange coupling observed in the hexanuclear compounds 1.4 H(2)O and 3.4 H(2)O is also discussed using ab initio UHF calculations on a model compound. The value of the exchange coupling constant (3.7 cm(-1)) for this model compound, calculated using the broken symmetry approach, is in good agreement, both in sign and magnitude, with the experimental J values (6.00 cm(-1) for 1.4 H(2)O and 8.54 cm(-1) for 3.4 H(2)O).

An Interesting Array of Cyclic Tetramer Water in the Molecular Structure of [V6O12(phen)4(CH3O)4] · 4H2O

“…Although the complex was reported by Themistoklis A. Kabanos and coworkers, [16] the reaction routes are different from each other as follows:…”

“…4H 2 O, namely the hexanuclear oxo-methoxo-vanadates complex [V 2 IV V 4 V ], the structure and magnetic property of which have been reported briefly by Themistoklis A. Kabanos and co-workers. [16] In this paper, we will report a new way to synthesize the title complex and analyze the structure in detail. What is most intriguing is the interesting array of water cluster in the lattice between the molecular frameworks.…”

Ferromagnetic Coupling in a Mixed‐Valence Hexavanadate Core: Quantum‐Chemical Forecast

“…Only a few examples of ferromagnetic coupling between the vanadium(IV) sites in oxovanadium complexes are known in the literature. [41][42][43] Among them, the octanuclear vanadium complex with the ligand 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci) is the most exciting one. [43] The peculiar chelating properties of the ligand enforce a mutually orthogonal orientation of the V-O t bonds favoring ferromagnetic coupling between the vanadium(IV) centers.…”

Density functional study of magnetic exchange of dinuclear manganese complexes with the heteropolymolyanion: [MnII 2(X n+Mo9O33)2]2(n−10)− (X = PV, AsV, SeVI)

“…In the past years, several theoretical calculations on POM systems were known in the literature, however, the magnetic properties have been mainly considered for reduced (blue) species [18][19][20][21][22][23][24] and the description of the exchange coupling between two magnetic centers in the POM framework is seldom [25,26] . Furthermore, theoretical studies of magnetic coupling between paramagnetic ions encapsulated in the sandwichtype polyoxometalates have not been reported so far.…”