High-spin Ground State Research Articles

Search for Nagaoka ferromagnetism in non-magnetic doped semiconductors

While ferromagnetism at relatively high temperatures is seen in diluted magnetic semiconductors such as Ga 1 - x Mn x As , under certain conditions semiconductors doped with non-magnetic impurities may also exhibit a ferromagnetic ground state. We investigate the possibility of ferromagnetism in a generalized disordered Hubbard model designed to characterize hydrogenic centers in semiconductors. We demonstrate the occurrence of high spin ground states in clusters (e.g. doped quantum dots), and discuss the nature of the single-particle states in a positionally disordered three-dimensional system with a maximally spin-polarized ground state. In particular, we identify the mobility edges, and describe their dependence on impurity density and potential.

Nanoscale ferromagnetism in nonmagnetic doped semiconductors

While ferromagnetism at relatively high temperatures is seen in diluted magnetic semiconductors such as ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$, doped semiconductors without magnetic ions have not shown evidence for ferromagnetism. Using a generalized disordered Hubbard model designed to characterize hydrogenic centers in semiconductors, we find that such systems may also exhibit a ferromagnetic ground state, at least on the nanoscale. This is found most clearly in a regime inaccessible to bulk systems, but attainable in quantum dots as well as heterostructures. We present numerical results demonstrating the occurrence of high spin ground states in both lattice and positionally disordered systems. We examine how the magnetic phases are affected by characteristics of real doped semiconductors, such as positional disorder and electron-hole asymmetry.

Thermally Induced Two-Step, Two-Site Incomplete 6A1 ↔ 2T2 Crossover in a Mononuclear Iron(III) Phenolate−Pyridyl Schiff-Base Complex: A Rare Crystallographic Observation of the Coexistence of Pure S = 5/2 and 1/2 Metal Centers in the Asymmetric Unit

The six-coordinate mononuclear iron(III) complexes [Fe(salpm)2]ClO(4).0.5EtOH, [Fe(salpm)2]Cl, [Fe{(3,5-tBu2)-salpm}2]X (X=ClO4- or Cl-), and [Fe{(3,5-tBu2)-salpm}2]NO(3).2H2O [Hsalpm=N-(pyridin-2-ylmethyl)salicylideneamine; H(3,5-tBu2)-salpm=N-(pyridin-2-ylmethyl)-3,5-di-tert-butylsalicylideneamine] have been synthesized and isolated in crystalline form; their chemical identities have been ascertained by elemental analyses, FAB mass spectrometry, and infrared spectroscopy. The room-temperature effective magnetic moments [(8chiMT)1/2 approximately 5.85-5.90 microB] of these complexes are consistent with the high-spin (S=5/2) ground state. These complexes are intensely colored on account of the strong ppi-->dpi* LMCT visible absorptions. Definitive evidence for the structures of [Fe(salpm)2]ClO(4).0.5EtOH and [Fe{(3,5-tBu2)-salpm}2]NO(3).2H2O has been provided by single-crystal X-ray crystallography. The monomeric complex cations in both compounds comprise two uninegative phenolate-pyridyl tridentate Schiff-base ligands coordinated meridionally to the iron(III) to afford a distorted octahedral geometry with a trans,cis,cis-[FeO2N4] core. Whereas [Fe(salpm)2]ClO(4).0.5EtOH undergoes a thermally induced 6A1<-->2T2 crossover, [Fe{(3,5-tBu2)-salpm}2]NO(3).2H2O retains its spin state in the solid state down to 5 K. However, EPR spectroscopy reveals that the latter complex does exhibit a spin transformation in solution, albeit to a much lesser extent than does the former. The spin crossover in [Fe(salpm)2]ClO(4).0.5EtOH has resulted in an unprecedented crystallographic observation of the coexistence of high-spin and low-spin iron(III) complex cations in equal proportions around 100 K. At room temperature, the two crystallographically distinct ferric centers are both high spin; however, one [Fe(salpm)2]+ complex cation undergoes a complete spin transition over the temperature range approximately 200-100 K, whereas the other converts very nearly completely between 100 and 65 K; approximately 10% of the complex cations in [Fe(salpm)2]ClO(4).0.5EtOH remain in the high-spin state down to 5 K.

Interpretation of the Photoelectron Spectra of FeS2- by a Multiconfiguration Computational Approach

The ground states of FeS(2) and FeS(2)(-), and several low-lying excited electronic states of FeS(2) that are responsible for the FeS(2)(-) photoelectron spectrum, are calculated. At the B3LYP level an open, quasi-linear [SFeS](-) conformation is found as the most stable structure, which is confirmed at the ab initio CASPT2 computational level. Both the neutral and the anionic unsaturated complexes possess high-spin electronic ground states. For the first time a complete assignment of the photoelectron spectrum of FeS(2)(-) is proposed. The lowest energy band in this spectrum is ascribed to an electron detachment from the two highest-lying 3dpi antibonding orbitals (with respect to the iron-sulfur bonding) of iron. The next-lowest experimental band corresponds to an electron removal from nonbonding, nearly pure sulfur orbitals. The two highest bands in the spectra are assigned as electron detachments from pi and sigma bonding mainly sulfur orbitals.

Time-dependent density functional theory for nonlinear properties of open-shell systems

This paper presents response theory based on a spin-restricted Kohn-Sham formalism for computation of time-dependent and time-independent nonlinear properties of molecules with a high spin ground state. The developed approach is capable to handle arbitrary perturbations and constitutes an efficient procedure for evaluation of electric, magnetic, and mixed properties. Apart from presenting the derivation of the proposed approach, we show results from illustrating calculations of static and dynamic hyperpolarizabilities of small Si(3n+1)H(6n+3) (n=0,1,2) clusters which mimic Si(111) surfaces with dangling bond defects. The results indicate that the first hyperpolarizability tensor components of Si(3n+1)H(6n+3) have an ordering compatible with the measurements of second harmonic generation in SiO2/Si(111) interfaces and, therefore, support the hypothesis that silicon surface defects with dangling bonds are responsible for this phenomenon. The results exhibit a strong dependence on the quality of basis set and exchange-correlation functional, showing that an appropriate set of diffuse functions is required for reliable predictions of the first hyperpolarizability of open-shell compounds.

Theoretical Study of Very High Spin Organic π-Conjugated Polyradicals

Different forms of pi-conjugated polyarylmethyl systems, such as diradicals, polyradicals, spin clusters, and polymers, were studied with valence bond (VB) calculations within the density matrix renormalization group (DMRG) framework. For these systems, the energy gap between the high-spin ground state and the lowest low-spin excited state (DeltaE(L-H)) was computed and found to correlate well with their stability. On the basis of our analysis, medium-sized polyarylmethyl cycles are suggested to be potential key building blocks of very high spin spin clusters and polymers.

Variation of Heterometallic Structural Motifs Based on [W(CN)8]3− Anions and MnII Ions as a Function of Synthetic Conditions

Reactions of [W(CN)(8)](3-/4-) anions with complexes of Mn(2+) ion with tridentate organic ligand 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) lead to a series of heterobimetallic complexes. The crystal structures of these compounds are derived from the same basic structural fragment, namely a W(2)Mn(2) square constructed of alternating cyanide-bridged W and Mn ions. In [Mn(II)(tptz)(OAc)(H(2)O)(2)](2){[Mn(II)(tptz)(MeOH)(1.58)(H(2)O)(0.42)](2)[W(V)(CN)(8)](2)}.5 MeOH.9.85 H(2)O (3), isolated molecular squares are co-crystallized with mononuclear cationic Mn(II) complexes. The structure of {[Mn(II)(tptz)(MeOH)](2)[W(IV)(CN)(8)].2 MeOH}(infinity) (4) is based on an infinite chain of vertex-sharing squares, while {[Mn(II) (2)(tptz)(2)(MeOH)(3)(OAc)][W(V)(CN)(8)].3.5 MeOH0.25 H(2)O}(infinity) (5) and {[Mn(II) (2)(tptz)(2)(MeOH)(3)W(V)(CN)(8)][Mn(II)(tptz)(MeOH)W(V)(CN)(8)].2 H(2).OMeOH}(8) (7) are derived from such an infinite chain by removing one of the W-C[triple bond]N-Mn linkages in each of the squares. The decanuclear cluster [Mn(II) (6)(tptz)(6)(MeOH)(4)(DMF)(2)W(V) (4)(CN)(32)].8.2 H(2)O.2.3 MeOH (6) is a truncated version of structure 4 and consists of three vertex-sharing W(2)Mn(2) squares. The structure of [Mn(II)(tptz)(MeOH)(NO(3))](2)[Mn(II)(tptz)(MeOH) (DMF)](2)[W(V)(CN)(8)](2).6 MeOH (8) consists of a hexanuclear cluster, in which the central W(2)Mn(2) square is extended by two Mn side-arms attached via CN(-) ligands to the W corners of the square. The magnetic behavior of these heterobimetallic complexes (except for 4) is dominated by antiferromagnetic coupling between Mn(II) and W(V) ions mediated by cyanide bridges. Compounds 3, 6, and 8 exhibit high spin ground states of S=4, 13, and 9, respectively, while 5 and 7 exhibit behavior typical of a ferrimagnetic chain with alternating spin centers. Complex 4 contains diamagnetic W(IV) centers but holds promise as a potential photomagnetic solid.

A Bell-Shaped Mn11Gd2 Single-Molecule Magnet

The tridecanuclear heterovalent mixed-metal (Mn11Gd2) complex [MnIII9MnII2GdIII2(O)8(OH)2(O2CR)17(NO3)2(H2O)] has been obtained from the reaction of the hexanuclear compound [Mn6O2(Piv)10(4-Me-py)2.5(PivH)1.5] with Gd(NO3)3·6H2O in CH3CN. The complex presents an unusual “bell”-shaped core with a high-spin ground state and is a new member of the high-nuclearity 3d-4f single-molecule magnets family.

Substituent Effect on Formation of Heterometallic Molecular Wheels: Synthesis, Crystal Structure, and Magnetic Properties

The reaction of manganese(III) Schiff bases of the type salen(2-) (N,N'-ethylenebis(salicylideneaminato)) with X-substituted (X = CH(3), Cl) pyridinecarboxamide dicyanoferrite(III) [Fe(X-bpb)(CN)(2)](-) gave rise to a series of cyanide-bridged Mn(6)Fe(6) molecular wheels, [Mn(III)(salen)](6)[Fe(III)(bpmb)(CN)(2)](6) x 7H(2)O (1), [Mn(salen)](6)[Fe(bpClb)(CN)(2)](6) x 4H(2)O x 2CH(3)OH (2), [Mn(salen)](6)[Fe(bpdmb)(CN)(2)](6) x 10H(2)O x 5CH(3)OH (3), [Mn(5-Br(salpn))](6)[Fe(bpmb)(CN)(2)](6) x 24H(2)O x 8CH(3)CN (4), and [Mn(5-Cl(salpn))](6)[Fe(bpmb)(CN)(2)](6) x 25H(2)O x 5CH(3)CN (5). Compared with [Fe(bpb)(CN)(2)](-), which always gives rise to 1D or polynuclear species when reacting with Mn(III) Schiff bases, the introduction of substituents (X) to the bpb(2-) ligand has a driving force in formation of the novel wheel structure. Magnetic studies reveal that high-spin ground state S = 15 is present in the wheel compounds originated from the ferromagnetic Mn(III)-Fe(III) coupling. For the first time, the quantum Monte Carlo study has been used to modulate the magnetic susceptibility of the huge Mn(6)Fe(6) metallomacrocycles, showing that the magnetic coupling constants J range from 3.0 to 8.0 K on the basis of the spin Hamiltonian [Formula: see text]. Hysteresis loops for 1 have been observed below 0.8 K, indicative of a single-molecule magnet with a blocking temperature (TB) of 0.8 K. Molecular wheels 2-5 exhibit frequency dependence of alternating-current magnetic susceptibility under zero direct-current magnetic field, signifying the slow magnetization relaxation similar to that of 1. Significantly, an unprecedented archlike Mn(2)Fe(2) cluster, [Mn(5-Cl(salpn))](2)[Fe(bpmb)(CN)(2)](2) x 3H(2)O x CH(3)CN (6), has been isolated as an intermediate of the Mn(6)Fe(6) wheel 5. Ferromagnetic Mn(III)-Fe(III) coupling results in a high-spin S = 5 ground state. Combination of the high-spin state and a negative magnetic anisotropy (D) results in the observation of slow magnetization relaxation in 6.

Cyano‐bridged Ln3+‐Cr3+ Binuclear Complexes [Ln(L)x(H2O)yCr(CN)6]·mL·nH2O (Ln=La–Nd, x=5, y=2, m=1 or 2, n=2 or 2.5; Ln=Sm–Dy, Er, x=4, y=3, m=0, n=1.5 or 2.0; L=2‐pyrrolidinone): Structure, Magnetism and Spin Density Map

AbstractIn order to shed light upon the nature and mechanism of 4f‐3d magnetic exchange interactions, a series of binuclear complexes of lanthanide(3+) and chromium(3+) with the general formula [Ln(L)5(H2O)2Cr(CN)6]·mL·nH2O (Ln=La (1), Ce (2), Pr (3), Nd (4); x=5, y=2, m=1 or 2, n=2 or 2.5; L=2‐pyrrolidinone) and [Ln(L)4(H2O)3Cr(CN)6] ·nH2O (Ln=Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Er (10); x=4, y=3, m=0, n=1.5 or 2.0; L2‐pyrrolidinone) were prepared and the X‐ray crystal structures of complexes 2, 6 and 7 were determined. All the compounds consist of a Ln‐CN‐Cr unit, in which Ln3+ in a square antiprism environment is bridged to an octahedral coordinated Cr3+ ion through a cyano group. The magnetic properties of the complexes 3 and 6–10 show an overall antiferromagnetic behavior. The fitting to the experimental magnetic susceptibilities of 7 give g=1.98, J=0.40 cm−1, zJ′=−0.21 cm−1 on the basis of a binuclear spin system (SGd=7/2, SCr=3/2), revealing an intra‐molecular Gd3+‐Cr3+ ferromagnetic interaction and an inter‐molecular antiferromagnetic interaction. For 7 the calculation of quantum chemical density functional theory (DFT), combined with the broken symmetry approach, showed that the calculated spin coupling constant was 20.3 cm−1, supporting the observation of weak ferromagnetic intra‐molecular interaction in 7. The spin density distributions of 7 in both the high spin ground state and the broken symmetry state were obtained, and the spin coupling mechanism between Gd3+ and Cr3+ was discussed.

Dual-mode X-Band EPR and magnetic study of (Cu 2+, Ln 3+) pairs: Investigation of magnetic anisotropy

An experimental and theoretical approach for the determination of the anisotropic exchange interaction constants in (Cu 2+, Ln 3+) pairs where Ln = Tb 3+, Dy 3+ is presented. According to this approach the same phenomenological anisotropic magnetic model was used to simulate the low temperature magnetic behaviour of the pairs as well as their EPR spectra in parallel and perpendicular mode. For the (Cu, Tb), [L 1Cu(O 2COMe)Tb(thd) 2], (L 1 = N, N′-2,2-dimethylpropylenedi(3-methoxysalicylideneiminato; thd– = tetramethylheptanedionato)) and (Cu, Dy) complexes, [L 2Cu-(Me 2CO)Ln(NO 3) 3], (L 2 = N, N′-2-methyl-1,2-propylenedi(3-methoxysalicylideneiminato)), it has been found that the exchange interaction is ferromagnetic with the J z interaction component larger than the other two terms ( J z ≫ J x ∼ J y ). In order to determine the zero-field splitting of the high-spin ground state S = 4 in two ferromagnetic-coupled (Cu, Gd) pairs, [L 1Cu(O 2COMe)Gd(thd) 2] and [L 2Cu(Me 2CO)Gd(NO 3) 3], the EPR spectra in parallel mode were simulated with an appropriate magnetic model. Indeed, one of the most important problems concerning the (Cu, Gd) systems is the complexity of the X-band, perpendicular-mode EPR spectra that renders any simulation procedure difficult. Improvement in analysis of the spectra results from using parallel mode EPR experiments.

IR Spectroscopy of Nb+(N2)n Complexes: Coordination, Structures, and Spin States

Infrared photodissociation spectroscopy in the N-N stretching region is reported for gas-phase Nb+(N2)n complexes (n=3-16). The coordination of nitrogen to the metal cation causes the IR-forbidden N-N stretch of N2 to become active in these complexes. Fragmentation occurs by the loss of intact N2 molecules, and the yield as a function of laser wavelength produces an IR excitation spectrum. The dissociation patterns indicate that Nb+ has a coordination of six ligands. The infrared spectra for all complexes contain bands red-shifted from the N-N stretch in free nitrogen, consistent with ligand-metal charge-transfer interactions such as those familiar for metal carbonyl complexes. Using density functional theory, we investigated the structures and ground electronic states for each of the small cluster sizes. Theory indicates that binding to the low-spin triplet excited state of the metal ion becomes progressively more favorable than binding to its high-spin quintet ground state as additional ligands are added to the cluster. Although the quintet state is the ground state for the n=1-4 complexes, IR spectroscopy confirms that the low-spin triplet electronic state becomes the ground state for the n=5 and 6 complexes. The n=4 complex has a square-planar structure, familiar for high-spin d4 complexes in the condensed phase. The n=5 complex has a geometry that is nearly a square pyramid, while the n=6 complex has a structure close to octahedral.

Experimental spin density in the high spin ground state of the Fe 8pcl cluster

The induced spin density was determined by polarised neutron diffraction in the S = 10 ground state of [(tacn) 6Fe 8O 2(OH) 12]Br 4.3(ClO 4) 3.7 · 6H 2O, Fe 8pcl, which differently from the bromide analogous, Fe 8Br 8, presents a centre of symmetry. The relative spin arrangement is in agreement with the model proposed from classical magnetic measurements and with the previous spin density study in the noncentrosymmetrical Fe 8Br 8 compound. The experimental spin populations on the iron atoms are in good quantitative agreement with calculations using exact diagonalisation of the exchange Hamiltonian with experimental J values obtained from magnetic susceptibility measurements on Fe 8Br 8. This determination confirms that the spin density determination provides a valuable evaluation of the relative strengths (and sign) of the intracluster magnetic interactions and that the dissymmetry observed on the spin populations in the Fe 8Br 8 compound with respect to quasi-D 2 symmetry of the molecular frame was an artefact due to the data refinement method for non centrosymmetrical structures.

Kondo screening of a high-spin Nagaoka state in a triangular quantum dot

We study transport through a triangle triple quantum dot connected to two noninteracting leads using the numerical renormalization group (NRG). The triangle has a high-spin ground state of S = 1 caused by a Nagaoka ferromagnetism, when it is isolated and has one extra electron introduced into a half-filling. The results show that the conduction electrons screen the local moment via two separate stages with different energy scales. The half of the S = 1 is screened first by one of the channel degrees, and then at very low temperature the remaining half is fully screened to form a Kondo singlet. The transport is determined by two phase shifts for quasi-particles with even and odd parities, and then a two-terminal conductance in the series configuration is suppressed g series ≃ 0 , while plateau of a four-terminal parallel conductance reaches a unitary limit value g parallel ≃ 4 e 2 / h of two conducting modes.

Dissociative and associative attachment of NO to iron clusters

Electronic and geometrical structures of iron clusters with associative (FeNO, Fe2NO, Fe3NO, Fe4NO, Fe5NO, and Fe6NO) and dissociative (OFeN, OFe2N, OFe3N, OFe4N, OFe5N, and OFe6N) attachments of NO, as well as the corresponding singly negatively and positively charged ions, are computed using density functional theory with generalized gradient corrections. Both types of isomers are found to be stable and no spontaneous dissociation was observed during the geometry optimizations. The ground states correspond to dissociative attachment of NO for all iron clusters Fe(n), except for Fe and Fe+. All of the OFe(n)N clusters have ferrimagnetic ground states, except for OFe2N, OFe2N-, OFe4N, and OFe4N-, which prefer the ferromagnetic coupling. In the ferrimagnetic states, the excess spin density at one iron atom couples antiferromagnetically to the excess spin densities of all other iron atoms. Relative to the high-spin Fe(n) ground state, the lowest energy ferrimagnetic state quenches the total magnetic moments of iron clusters by 7, which is to be compared with a reduction in the magnetic moment of one in the lowest energy ferromagnetic states. Dissociation of NO on the iron clusters has a pronounced impact on the energetics of reactions; the Fe(n)NO+CO-->Fe(n)N+CO2 channels are exothermic while the OFe6N+CO--> Fe6N+CO2 channels are nearly thermoneutral.

Magnetic properties of the ferromagnetic ring-shaped single-molecule magnet Cu6

The magnetic properties of the ferromagnetic ring-shaped single-molecule magnet (n-BuNH3)12[(CuCl)6 (AsW9O33)2] · 6H2O, known as Cu6, have been studied by electron spin resonance (ESR). The ESR spectra show several sharp absorptions, which originates from the multiplet splitting of the high spin ground state S = 3. Meanwhile, the frequency-field plot of the observed ESR shows a gap at zero-field suggesting the existence of an anisotropic exchange interaction in the system. Moreover, forbidden ESR transitions of ΔSz = ±2 have been also observed where the origin comes from the mixing of the spin state by virtue of the transverse field component of the anisotropy.

Electronic Structure of Four-Coordinate C3v Nickel(II) Scorpionate Complexes: Investigation by High-Frequency and -Field Electron Paramagnetic Resonance and Electronic Absorption Spectroscopies

A series of complexes of formula TpNiX, where Tp*- = hydrotris(3,5-dimethylpyrazole)borate and X = Cl, Br, I, has been characterized by electronic absorption spectroscopy in the visible and near-infrared (NIR) region and by high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy. The crystal structure of TpNiCl has been previously reported; that for TpNiBr is given here: space group = Pmc2(1), a = 13.209(2) A, b = 8.082(2) A, c = 17.639(4) A, alpha = beta = gamma = 90 degrees , Z = 4. TpNiX contains a four-coordinate nickel(II) ion (3d8) with approximate C3v point group symmetry about the metal and a resulting S = 1 high-spin ground state. As a consequence of sizable zero-field splitting (zfs), TpNiX complexes are "EPR silent" with use of conventional EPR; however, HFEPR allows observation of multiple transitions. Analysis of the resonance field versus the frequency dependence of these transitions allows extraction of the full set of spin Hamiltonian parameters. The axial zfs parameter for TpNiX displays pronounced halogen contributions down the series: D = +3.93(2), -11.43(3), -22.81(1) cm(-1), for X = Cl, Br, I, respectively. The magnitude and change in sign of D observed for TpNiX reflects the increasing bromine and iodine spin-orbit contributions facilitated by strong covalent interactions with nickel(II). These spin Hamiltonian parameters are combined with estimates of 3d energy levels based on the visible-NIR spectra to yield ligand-field parameters for these complexes following the angular overlap model (AOM). This description of electronic structure and bonding in a pseudotetrahedral nickel(II) complex can enhance the understanding of similar sites in metalloproteins, both native nickel enzymes and nickel-substituted zinc enzymes.

Stable iminonitroxide biradicals: Building blocks for organic heterospin, heteromolecular complexes

A stable cationic biradical has been designed and synthesized, and its magnetic property and crystal structure have been examined. An iminonitroxide derivative of 3,5-disubstituted pyridine ( 1) with a triplet ground state has been cationized by a reaction with methyl trifluoromethanesulfonate (MeTfO), which gave a salt of N-methylated pyridinium 2 +, 2 + · TfO −. The ground state of the cation 2 + has been found to be triplet with 2 J/ k B = 7.5 K from magnetic susceptibility measurements for 2 + · TfO − in a magnetically diluted organic matrix. The magnetic susceptibility of neat crystalline solids of 2 + · TfO − has been explained by an exchange coupling model based on the X-ray crystal structure. It is well known that the energy preference for a high-spin ground state for a m-phenylene coupling unit is disturbed by heteroatomic substitution and an ionic charge. The present experimental results show that the high-spin preference in 1 is little affected by the ionic charge in 2 +. The ground-state triplet biradical serves as building blocks for molecule-based magnets of S > 1/2 of molecular assemblages based on electrostatic interactions between molecular ions.

Theoretical Design of High-spin Organic Molecules with [sbnd]˙ N [sbnd]S [sbnd] as a Spin-containing Fragment and Heterocycle as End Groups

Novel stable high-spin molecules possessing three different arranging fashions were designed with ˙N S as a spin-containing (SC) fragment, an aromatic group, such as benzene (1), pyridine (2), pyridazine (3), pyrimidine (4), pyrazine (5) or triazine (6) as end groups (EG), and phenyl as a ferromagnetic coupling (FC) unit. The effects of different EG on the spin multiplicities of the ground states and their stabilities were investigated by means of the AM1-CI approach. All the investigated molecules corresponded to the FC and possessed high-spin ground states. The spin on the two atoms of the SC fragment was not in agreement with the delocalization results in the specific stability of ˙N S . In those molecules, the stabilities of the triplet states decreased when the distance between the atoms of central SC fragments ( N ) increased. The stabilities of the triplet states of compounds 1 a- n , 1 b- n and 1 c- n , with heterocycles as EG were higher than those of the triplet states of those compounds with phenyl as EG. Furthermore, the stabilities of the triplet states of the compounds with pyrimidine and triazine as EG were higher than those with pyridine, pyridazine or pyrazine as EG.

High-Spin M2+ Carboxylate Triangles from the Microwave

The reaction of M(O2CMe)2.4H2O (M = Ni, Co) with NaN3 in pyridine/MeOH under microwave irradiation and controlled pressure/temperature leads to the formation of the trimetallic species [M3(N3)3(O2CMe)3(py)5] (M = Ni, 1; Co, 2) in 4 min and in high yields. Both complexes display dominant ferromagnetic interactions and high-spin ground states.