Propeller-like [Fe(4)(L)(2)(dk)(6)] complexes, in which Hdk is a β-diketone and H(3)L is a tripodal alcohol, R-C(CH(2)OH)(3), exhibit tunable magnetic anisotropy barriers and retain their magnetic memory effect when chemically anchored on metal surfaces. Heteronuclear analogues of these M(4) complexes have been sought to afford a library of compounds with different total spin (S) values, but synthetic efforts described so far gave solid solutions containing M(4) in addition to the desired M(3)M' species. We now present a novel synthetic route to M(3)M' complexes featuring a central chromium(III) ion. The three-step preparation goes through coordination of Cr(III) by two equivalents of tripodal alkoxide (R = Et and Ph), followed by reaction of this complex "core" with the peripheral +III metal ions. Products have been characterised by chemical analyses together with (1)H-NMR, FTIR, W-band EPR, DC/AC magnetic susceptibility measurements and single crystal X-ray diffractometry. Due to the chemical inertness of Cr(III), this route yields 100% pure Fe(3)Cr complexes without metal scrambling; what is more, it is suitable for designing novel heteronuclear single molecule magnets (SMMs) with a variety of d- and f-metals and R groups.

The selective replacement of the central iron(III) ion with vanadium(III) in a tetrairon(III) propeller-shaped single-molecule magnet has allowed us to increase the ground spin state from S=5 to S=13/2. As a consequence of the pronounced anisotropy of vanadium(III), the blocking temperature for the magnetization has doubled. Moreover, a significant remnant magnetization, practically absent in the parent homometallic molecule, has been achieved owing to the suppression of zero-field tunneling of the magnetization for the half-integer molecular spin. Interestingly, the contribution of vanadium(III) to the magnetic anisotropy barrier occurs through the anisotropic exchange interaction with iron(III) spins and not through single ion anisotropy as in most single-molecule magnets.

The reversible thermochromic behaviour of homoleptic [{V(OR)(4)}(n)] complexes in solution [R = Pr(i) (product I), Bu(s) (B(s)), Nep (N) and Cy (C)] is accounted for the existence of an aggregation equilibrium involving dimeric and monomeric species in which vanadium(iv) is respectively five- and four-coordinate. Bulky R groups such as Bu(t) and Pe(t) (tert-pentoxide) prevent aggregation and therefore give rise to exclusively mononuclear compounds (B(t) and P(t), respectively) that are not thermochromic. The complexes and their temperature-dependent interconversion were characterised by single crystal X-ray diffractometry, magnetic susceptibility measurements and electronic, FTIR and EPR spectroscopies in a wide temperature range. Equilibrium constants and enthalpy and entropy changes for the dimerization reactions have been determined and compared with literature data.

Dois complexos contendo vanádio e lítio, [V 6 Li 10 O 8 (ONep) 14 {OSi(Me) 2 (ONep)} 2 ] (1) e [V(ONep) 3 (μ-ONep) 2 Li(thf) 2 ] (2), Nep = neopentila, Me = metila e thf = tetraidrofurano, foram isolados em alto rendimento e caracterizados por diversas técnicas incluindo espectroscopias de ressonância paramagnética eletrônica (RPE, banda X) e ressonância magnética nuclear (RMN) de 29 Si, medidas de susceptibilidade magnética e difratometria de raios X de monocristal. A despeito das condições similares de preparação, os dois produtos apresentam características estruturais admiravelmente distintivas: o complexo binuclear não-oxo 2 é um simples produto de adição de "V(ONep) 4 " e "Li(ONep)(thf) 2 ", enquanto 1 é um agregado de valência mista com 16 centros metálicos. O oxoalcóxido molecular 1 também contém grupos silanolatos, {OSi(Me 2 )(ONep)} − , produzidos por ataque nucleofílico de neopentóxidos à graxa de silicone dissolvida acidentalmente no meio de reação. Ambos os produtos têm aplicações promissoras em síntese orgânica e inorgânica, incluindo a preparação de óxidos mistos pouco comuns contendo vanádio, lítio e/ou silício.Two complexes containing both vanadium and lithium, [V 6 Li 10 O 8 (ONep) 14 {OSi(Me) 2 (ONep)} 2 ] (1) and [V(ONep) 3 (μ-ONep) 2 Li(thf) 2 ] (2), Nep = neopentyl, Me = methyl and thf = tetrahydrofuran, have been isolated in high yield and characterised by a number of techniques including X-band electron paramagnetic resonance (EPR) and 29 Si{ 1 H} nuclear magnetic resonance (NMR) spectroscopies, magnetic susceptibility measurements and single crystal X-ray diffractometry. Despite the similar preparation conditions, the two products present remarkably distinctive structural features: complex 2 is a binuclear adduct of "V(ONep) 4 " and "Li(ONep)(thf) 2 ", while 1 is a mixed-valence, 16-metal aggregate. The large molecular oxoalkoxide 1 also contains silanolate units, {OSi(Me 2 )(ONep)} − , produced by nucleophilic attack of neopentoxide groups on Si-O bonds of silicone grease accidentally dissolved in the reaction media. Both products have promising applications in organic and inorganic synthesis, including the preparation of uncommon V-Li and/or Si containing oxides. Keywords: vanadium(IV), lithium, alkoxide, silicone grease, neopentoxide IntroductionThe literature on vanadium alkoxide chemistry describes a number of high valence, vanadium(V) compounds prepared from commercially available VOCl 3 , V 2 O 5 , (NH 4 )VO 3 or VO(OR) 3 (R = alkyl). These species have received attention because of their applications as catalysts in polymerization reactions 1 and as precursors of industrially applied homo-and mixed-metal oxides.2 There is also an increasing interest on the preparation of lower oxidation state vanadium alkoxides, such as non-oxo vanadium(III)/ (IV) compounds, to be employed as direct precursors of less common oxides without the use of reducing reaction conditions.3 However, these syntheses have been hampered by the lack of suitable non-oxo starting materials, as the very stable v...

Unsymmetric porphyrins containing both pentafluorophenyl (PFP = A) and 3,4-dimethoxyphenyl (DMP = B) substituents at the meso positions were prepared using Lindsey's methodology.