Octahedral–Tetrahedral Systems [Co(<i>dppm</i>^{<i>O</i>,<i>O</i>})₃]²⁺[CoX₄]^2– Showing Slow Magnetic Relaxation with Two Relaxation Modes

Three compounds with octahedral–tetrahedral Co­(II) moieties of [Co­(<i>dppm</i>^{<i>O</i>,<i>O</i>})₃]­[CoX₄] type, where X = SCN (<b>1</b>), Cl (<b>2</b>), or I (<b>4</b>) have been synthesized and characterized by the X-ray structure analysis (<b>1</b> and <b>4</b>), and spectroscopic methods. The dc magnetic measurements show high magnetic anisotropy for octahedral centers whereas tetrahedral sites possess moderate <i>D</i> values. These results are confirmed by the ab initio calculations. The ac susceptibility data reveals a slow magnetic relaxation for <b>2</b> and <b>4</b>, similar to that of the X = Br analogue (<b>3</b>), whereas <b>1</b> displays no ac-absorption signal. There are two relaxation channels; the slower for <b>2</b> (<b>4</b>) possesses a relaxation time as long as τ_LF= 178 (588) ms at <i>T</i> = 1.9 K and <i>B</i>_dc = 0.7 T. Also, the half-Zn analogue, [Co­(<i>dppm</i>^{<i>O</i>,<i>O</i>})₃]­[ZnI₄], shows slow magnetic relaxation with two relaxation channels conditioned by the cationic unit [Co­(<i>dppm</i>^{<i>O</i>,<i>O</i>})₃]²⁺

Structure and Mechanism Revision of a Catalyzed Cyclization of Benzaldehyde Bearing Alkyne-Nitrile

Pt­(II)-catalyzed carbocyclization of benzaldehyde containing a keto-nitrile functionality resulted in the formation, respectively, of isochromenes and spiro-lactones instead of fused lactams and spiro-lactams as was previously reported. The reaction mechanism was proposed, and the products were identified by multidimensional NMR, IR, and X-ray analysis. The structure of these new products was also confirmed by their synthesis in an unambiguous manner using practical and short approaches

Mixed-Valence Heptanuclear Iron Complexes with Ferromagnetic Interaction

Three new Prussian blue analogues, heptanuclear mixed-valence iron complexes of the type [Fe^II(CN)₆{Fe^III(1_–2H)}₆]­Cl₂·<i>n</i>H₂O, were synthesized and structurally and spectrally characterized, and their magnetic properties were investigated (1_–2H corresponds to doubly deprotoned Schiff-base pentadentate ligands <b>1a</b>, <i>N</i>,<i>N</i>′-bis­(2-hydroxybenzylidene)-1,5-diamino-3-azapentane, <b>1b</b>, <i>N</i>,<i>N</i>′-bis­(3-ethoxy-2-hydroxybenzylidene)-1,7-diamino-4-azaheptane, or <b>1c</b>, <i>N</i>,<i>N</i>′-bis­(3-methoxy-2-hydroxybenzylidene)-1,6-diamino-3-azahexane). These compounds were formed by assembling the [Fe­(CN)₆]^4– building block with mononuclear complexes of the [Fe­(1_–2H)­Cl] type. X-ray structure analysis revealed that the complexes adopt a star-like architecture: the Fe­(II) ion lies at the very center, and on its octahedral nodes the Fe­(III) sites are coordinated in the Fe^II–CN–Fe^III manner. The Schiff-base pentadentate ligand moiety 1_–2H coordinates a single Fe­(III) center in two complexes <b>3b</b> and <b>3c</b>. Ligands 1a_–2H in the complex cation of <b>3a</b> adopt an unusual coordination mode: three donor atoms of the same ligand (one O and two N) coordinate one Fe­(III), whereas the remaining N′ and O′ donor atoms coordinate the neighboring Fe­(III) center creating the {Fe­(ON₂)­(N′O′)­N″} chromophore involving two 1a_–2H ligand moieties. Moreover, three Fe­(III) centers are interconnected with three 1a_–2H ligands in such a manner that two {Fe^III₃(1a_–2H)₃} units form two intramolecular rings. Magnetic investigation of the heptanuclear complexes revealed the high-spin state of all six Fe­(III) coordination sites (<i>s</i> = 5/2), while the very central Fe­(II) site is in the low-spin state (<i>s</i> = 0). At low temperature, the ferromagnetic exchange interactions stay evident for all three complexes. Mössbauer spectra of compounds <b>3a</b> and <b>3b</b> revealed a presence of two different doublets for both compounds: the major doublet is related to six Fe­(III) high-spin coordination sites and the minor doublet refers to the low-spin very central Fe­(II)