Effect of Ligand Deprotonation on the Spin Transition in Fe(II) Complexes.

The effect of deprotonation of the ligands forming the second coordination sphere of the iron(II) ion on its spin crossover behavior is examined. Due to the pronounced changes in the observed magnetic characteristics of the iron(II) ion, the proton removal from the ligand in the second coordination sphere is modeled by the appearance of a negative charge on one of the neutral nitrogens in the nearest surrounding of the metal ion, thus significantly changing the crystal field acting on this ion and, respectively, the conditions for observation of the spin transition. Different symmetries of the nearest nitrogen surrounding of the iron(II) ion and different locations of the negative charge in this surrounding are examined in the frames of the crystal field model.

Modeling of the Charge-Transfer-Induced Spin Transition in the Tetranuclear Cyanide-Bridged [CoFe] Complex.

The course of the charge-transfer-induced spin transition demonstrated by the cyanide-bridged tetranuclear [CoFe(bpy*)(CN)(tp*)](PF)·2CP·8BN complex has been followed by DFT calculations of the single-point energies for different total spin values of the complex in a wide temperature range. With the aid of these calculations, the picture of spin conversion, that the compound undergoes, has been restored. It has been demonstrated that at 100 K the two crystallographically unique tetranuclear FeCo subunits A and B present in the structure contain diamagnetic low-spin Fe and low-spin Co ions.

Modeling of Spin Crossover in Linear Trinuclear Complexes: Effects of External Pressure.

In the present study, a model is suggested to explain the course of spin transformation in crystals containing linear trinuclear iron(II) clusters as structural units. The energy spectrum of an isolated trimer is described with due allowance of the effects of the cubic crystal field formed by the nearest surrounding of each Fe ion as well as by consideration of intracluster interactions in the nearest neighbor approximation. The intercluster cooperative interaction promoting the spin transition is assumed to arise from the coupling of molecular modes with phonons, that is, a feature characteristic for molecular crystals containing as a structural element single spin-crossover ions or complexes formed by these ions.

Modeling Spin Interactions in a Triangular Cobalt(II) Complex with Triaminoguanidine Ligand Framework: Synthesis, Structure, and Magnetic Properties.

The new tritopic triaminoguanidine-based ligand 1,2,3-tris[(pyridine-2-ylmethylidene)amino]guanidine (Hpytag) was synthesized. The reaction of a mixture of cobalt(II) chloride and cobalt(II) perchlorate with the ligand Hpytag in pyridine solution leads to the formation of the trinuclear cobalt(II) complex [Co(pytag)(py)Cl]ClO. Three octahedrally coordinated high-spin cobalt(II) ions are linked through the bridging triaminoguanidine backbone of the ligand leading to an almost equilateral triangular arrangement.

Tetranuclear {CoCo}, Octanuclear {CoCo}, and Hexanuclear {CoDy} Pivalate Clusters: Synthesis, Magnetic Characterization, and Theoretical Modeling.

New tetranuclear and octanuclear mixed-valent cobalt(II/III) pivalate clusters, namely, [NaCo(OCCMe)(HOCCMe)(teaH)(N)]·2HO (in two polymorphic modifications, 1 and 1a) and [Co(OCCMe)(teaH)(N)](MeCCO)·MeCN·HO (2) have been synthesized by ultrasonic treatment of a dinuclear cobalt(II) pivalate precursor with sodium azide and triethanolamine (teaH) ligand in acetonitrile. The use of Dy(NO)·6HO in a similar reaction led to the precipitation of a tetranuclear [NaCo(OCCMe)(teaH)(N)(NO)(HO)]·HO (3) cluster and a heterometallic hexanuclear [CoDy(OH)(OCCMe)(teaH)(HO)](NO)·HO (4) cluster. Single-crystal X-ray analysis showed that 1 (1a) and 3 consist of a tetranuclear pivalate/teaH mixed-ligand cluster [CoCo(OCCMe)(teaH)(N)] decorated with sodium pivalates [Na(OCCMe)(HOCCMe)] (1 or 1a) or sodium nitrates [Na(NO)] (3) to form a square-pyramidal assembly.

Iridates from the molecular side.

New exotic phenomena have recently been discovered in oxides of paramagnetic Ir(4+) ions, widely known as 'iridates'. Their remarkable properties originate from concerted effects of the crystal field, magnetic interactions and strong spin-orbit coupling, characteristic of 5d metal ions. Despite numerous experimental reports, the electronic structure of these materials is still challenging to elucidate, and not attainable in the isolated, but chemically inaccessible, [IrO6](8-) species (the simplest molecular analogue of the elementary {IrO6}(8-) fragment present in all iridates).

A magnetooptical study of (4-(2-dibutylaminoethanolato-N,O,O,O) chlorido copper(II)): a cubane complex with dominant ferromagnetic interactions.

This paper reports the experimental and theoretical study of a tetranuclear (CuClOCH2CH2N(C4H9)2)4 complex. Analysis of the magnetic circular dichroism spectrum was performed based on the Hamiltonian that includes the crystal field of the nearest ligands and the spin-orbit interaction. The crystal field parameters were evaluated in the framework of the exchange charge model that accounts for the exchange and covalence effects.

Microscopic theory of cooperative spin crossover: Interaction of molecular modes with phonons.

In this article, we present a new microscopic theoretical approach to the description of spin crossover in molecular crystals. The spin crossover crystals under consideration are composed of molecular fragments formed by the spin-crossover metal ion and its nearest ligand surrounding and exhibiting well defined localized (molecular) vibrations. As distinguished from the previous models of this phenomenon, the developed approach takes into account the interaction of spin-crossover ions not only with the phonons but also a strong coupling of the electronic shells with molecular modes.

Enhancing the blocking temperature in single-molecule magnets by incorporating 3d-5d exchange interactions.

We report the first single-molecule magnet (SMM) to incorporate the [Os(CN)(6)](3-) moiety. The compound (1) has a trimeric, cyanide-bridged Mn(III)-Os(III)-Mn(III) skeleton in which Mn(III) designates a [Mn(5-Brsalen)(MeOH)](+) unit (5-Brsalen=N,N'-ethylenebis(5-bromosalicylideneiminato)). X-ray crystallographic experiments reveal that 1 is isostructural with the Mn(III)-Fe(III)-Mn(III) analogue (2).