Solid-State Spin Equilibrium of Ni(cyclam)2 Complex: Magnetostructural Correlations in Two Polymorphs.

Two crystal polymorphs of Ni(cyclam)I2 (cyclam = 1,4,8,11-tetraazacyclotetradecane) were synthesized, and their magnetic properties were investigated. Temperature-dependent X-ray structural analysis and magnetic measurements revealed gradual spin transition in molecular-crystal polymorph trans-[Ni(cyclam)I2] (1a), whereas the zigzag-chain polymorph catena-[Ni(cyclam)(µ-I)]I (1b) did not show an obvious spin transition. The entropy difference between high- and low-spin states of 1a estimated by assuming the spin-equilibrium model is much smaller than those in typical iron(II)-based spin-crossover (SCO) complexes, suggesting that the normal mode softening is less remarkable in 1a. In this system, it is clearly evidenced that the interaction mode responsible to the spin equilibrium in octahedral nickel(II) complexes is highly anistropic, i.e., z-elongation and x,y-shortening of the coordination octahedron.

Synthesis of a Neutral Mononuclear Four-Coordinate Co(II) Complex Having Two Halved Phthalocyanine Ligands That Shows Slow Magnetic Relaxations under Zero Static Magnetic Field.

Syntheses of a novel pseudotetrahedral four-coordinate mononuclear Co(II) complex that has two halved phthalocyanine moieties as the ligands, [Co(half-Pc)2] (1), and its magnetic properties as a single molecule magnet (SMM) are reported. A one pot reaction of phthalonitrile and lithium methoxide followed by the coordination to a Co(II) ion gave 1 as an orange solid in a moderate yield. X-ray crystallography on 1 reveals tetragonally distorted coordination geometry around the Co(II) ion. The M- HT-1 plots suggest that 1 has large axial magnetic anisotropy. The ac magnetic susceptibility data of the magnetically diluted 1 (dil.1) clearly show that the complex acts as an SMM even in the absence of the external static magnetic field ( Hdc). The influence of intermolecular and intramolecular interactions for the magnetic relaxation behaviors has been discussed by comparison of the magnetic data of 1 and dil.1. The Orbach process is suggested as the predominant mechanism of magnetic relaxations in the high-temperature range, and the Arrhenius plots provide the effective relaxation energy barrier and pre-exponential factor of Ueff = 54.0 cm-1 and τ0 = 3.17 × 10-10 s, respectively. The direct estimation of the axial anisotropic parameter of 1 was successfully performed by high-field, multifrequency ESR measurements up to 55 T and 2.5 THz. The evaluated axial zero-field splitting (ZFS) energy of 57.0 cm-1 is comparable to the Ueff energy, confirming that the magnetic relaxations are initiated by the thermal excitation from the ground | M S⟩ = |±3/2⟩ states to the |±1/2⟩ states in the high-temperature range. The results of the ab initio calculations based on the CAS(7,5) SCF wave functions indicate that the ground states of 1 consist mainly of | M S⟩ = |±3/2⟩ states, while the first excited states are the mixture of | M S⟩ = |+1/2⟩ and |-1/2⟩.

Synthesis of a Series of Monophthalocyaninato Cyclen Heavy Lanthanide(III) Complexes with Tetragonal Symmetry.

A series of the new monophthalocyaninato lanthanide complexes, [Ln(Pc)(cyclen)]Cl (Ln = Y, Tb, Dy, Ho, Er, Tm, and Yb; Pc = phthalocyaninato; cyclen = 1,4,7,10-tetraazacyclododecane) was synthesized and characterized. The crystallographic study of monophthalocyaninato complexes with a capping macrocyclic ligand having no π-conjugation while keeping the 4-fold symmetry is presented for the first time. All the six complexes were crystallized in a tetragonal structure of the I4mm space group. In addition to this, the Tb complex exhibited a triclinic crystal structure of the P1̅ space group. All of the complexes are isostructural, where both Pc and cyclen are coordinated to an Ln3+ ion giving an eight-coordinate square-antiprismatic geometry. The skew angle between the Pc and cyclen ligands was 45° in the tetragonal crystals and 41.5° in the triclinic crystal. The metal-nitrogen bond lengths were shorter on the Pc ligand side than cyclen side, presumably due to the difference in the charges of the ligands and the steric factor.

System Composed of Three Types of Electronic Angular Momenta: A J-S-L Triad in a Photoexcited π-Radical Bis(phthalocyaninato)terbium Single-Molecule Magnet.

Interactions of three different types of electronic angular momenta, namely, spin, orbital, and total angular momenta from different origins in a photoexcited neutral bis(phthalocyaninato)terbium single-molecule magnet (Pc2Tb, where Pc2- denotes a phthalocyaninato anion) have been studied. We have conducted varied-temperature and varied-magnetic-field magnetic circular dichroism (MCD) measurements on the highest occupied molecular orbital-lowest unoccupied molecular orbital electronic transition in the ligand side of the neutral Pc2Tb to reveal the quantum nature of the system composed of a π-radical with a spin angular momentum S, the 4f system with a total angular momentum J, and the cyclic π conjugate system with a photoinduced orbital angular momentum L. We have constructed a new theoretical model that gives a quantitative agreement to the temperature and magnetic field dependence of MCD. The theoretical analysis revealed that the system takes eight quantum states that can be expressed as | J z S z L z⟩ = |±±±⟩, where the three angular momenta are quantized along the fourfold symmetry axis. Thus, we have identified the existence of the magnetic interactions among the three angular momenta and quantitatively determined their magnitudes for the first time.

Selective Stabilization of the Spin States of a Magnetically Anisotropic Dysprosium Ion Induced by Photo-Excitation of the Associated Cyclic π-Conjugated System.

The presence of a new electronic interaction, which couples a 4 f-electronic system with a total angular momentum J and a photoexcited cyclic π-conjugated system with an orbital angular momentum L, in the bis(phthalocyaninato)dysprosium single-molecule magnet ([DyPc2 ]- ) is reported. Two π-π* excited states in the visible spectral region of the [DyPc2 ]- complex, which are denoted here as QL and QH , showed significantly different temperature and field dependences of the magnetic circular dichroism (MCD) A-term intensity. This phenomenon not only indicates the presence of a "J-L" interaction, but also that the interaction generates two different preferred orientations of the J-L pair, either parallel (for the QH band) or antiparallel (for the QL band), depending on the excitation energy. We have constructed a theoretical model that reproduces the temperature and field dependences, and quantitatively evaluated the J-L interaction.

Synthesis of a Series of Heavy Lanthanide(III) Monoporphyrinato Complexes with Tetragonal Symmetry.

A series of heavy lanthanide(III) and yttrium(III) monoporphyrinato complexes formulated in [Ln(TPP)(cyclen)]Cl (Ln = Tb, Dy, Ho, Er, Tm, Yb, and Y; TPP = 5,10,15,20-tetraphenylporphyrinato), with cyclen, 1,4,7,10-tetraazacyclododecane, as a capping ligand, have been prepared in mild conditions and studied using single-crystal X-ray diffraction crystallography. The complexes exhibit an electronic absorption band (B(0,0)) in the range of 421-423 nm, showing a bathochromic shift associated with the increase of the ionic radii of the lanthanide, as well as two peaks of Q(1,0) and Q(0,0) bands between 548-586 nm. All of the complexes are isostructural, where both TPP and cyclen are coordinated to a lanthanide(III) or yttrium(III) ion giving an eight-coordinate square-antiprismatic (SAP) geometry (average skew angles are in the range of 43.01°-43.67°). The mean plane of the four nitrogen atoms of TPP (N4t) and that of the cyclen (N4c) are virtually parallel with a dihedral angle of less than 1°. The lanthanide(III) or yttrium(III) ions lie between N4t and N4c. The position of the metal ion is closer to the N4t plane, which is presumably caused by the different charges of the ligands, the size of the N4 square ligands, and the steric factor. The average Ln-N and interplanar distances (dN) decrease with decreasing lanthanide(III) ionic radii, showing the effect of lanthanide contraction. The skew angles, opening angles, and N-N distances are nearly unchanged, keeping the rigid square antiprismatic geometry throughout the series.

Crystal structure of a second polymorph of tetra-kis-(pyridin-2-yl)methane.

A second polymorph of the title compound, C21H16N4, is reported. The original polymorph was solved by our group [Matsumoto et al. (2003 ▶). Tetra-hedron Lett. 44, 2861-2864] in the monoclinic space group C2/c and refined to R = 0.050. Now the crystal structure of a tetra-gonal polymorph (space group P-421 c) has been solved and refined to R = 0.036. In the crystal, there are no strong inter-molecular inter-actions. Reflecting the high symmetry of the mol-ecular structure, the asymmetric unit is a quarter of the mol-ecule, and the mol-ecule exhibits S4 symmetry along the c axis in the crystal.

catena-Poly[[bis-(ethanol-κO)mangan-ese(II)]-µ-2,5-di-chloro-3,6-di-oxo-cyclo-hexa-1,4-diene-1,4-bis-(olato)-κ(4) O (1),O (6):O (3),O (4)].

In the title coordination polymer, [Mn(C6Cl2O4)(C2H5OH)2] n , the Mn(II) atom and the chloranilate [systematic name: 2,5-di-chloro-3,6-dioxo-cyclo-hexa-1,4-diene-1,4-bis-(olate)] ion lie on crystallographic inversion centers. The geometry around the Mn(II) atom is a distorted octa-hedron involving four O atoms of two chloranilate ions and two O atoms from two ethanol mol-ecules. The chloranilate ion serves as a bridging ligand between the Mn(II) ions, leading to an infinite linear chain along the b-axis direction. The chains are linked by O-H⋯O hydrogen bonds between the apically coordinating ethanol mol-ecule and the chloranilate ion, affording a two-dimensional layer expanding parallel to the ab plane.

Bis[tetra-kis-(pyridin-2-yl)methane-κ(3) N,N',N'']cobalt(II) tetra-kis-(thio-cyanato-κN)cobaltate(II) methanol monosolvate.

The title complex, [Co(C21H16N4)2][Co(NCS)4]·CH3OH, consists of one [Co{C(py)4}2](2+) complex cation [C(py)4 = tetra-kis-(pyridin-2-yl)methane], one [Co(NCS)4](2-) complex anion and a methanol solvent mol-ecule. In the cation, the Co(II) atom is coordinated by six N atoms of two C(py)4 ligands in a distorted octa-hedral geometry. In the anion, the Co(II) atom is coordinated by the N atoms of four NCS(-) ligands in a distorted tetra-hedral geometry. The methanol mol-ecule is disordered and was modelled over three orientations (occupancies 0.8:0.1:0.1). There are two weak hydrogen-bond-like inter-actions between the methanol solvent mol-ecule and NCS(-) ligands of the anion [O⋯S = 3.283 (3) and 3.170 (2) Å].

Control of Exchange Interactions in π Dimers of 6-Oxophenalenoxyl Neutral π Radicals: Spin-Density Distributions and Multicentered-Two-Electron Bonding Governed by Topological Symmetry and Substitution at the 8-Position.

The tri-tert-butylphenalenyl (TBPLY) radical exists as a π dimer in the crystal form with perfect overlapping of the singly occupied molecular orbitals (SOMOs) causing strong antiferromagnetic exchange interactions. 2,5-Di-tert-butyl-6-oxophenalenoxyl (6OPO) is a phenalenyl-based air-stable neutral π radical with extensive spin delocalization and is a counter analogue of phenalenyl in terms of the topological symmetry of the spin density distribution. X-ray crystal structure analyses showed that 8-tert-butyl- and 8-(p-XC6H4)-6OPOs (X=I, Br) also form π dimers in the crystalline state. The π-dimeric structure of 8-tert-butyl-6OPO is seemingly similar to that of TBPLY even though its SOMO-SOMO overlap is small compared with that of TBPLY. The 8-(p-XC6H4) derivatives form slipped stacking π dimers in which the SOMO-SOMO overlaps are greater than in 8-tert-butyl-6OPO, but still smaller than in TBPLY. The solid-state electronic spectra of the 6OPO derivatives show much weaker intradimer charge-transfer bands, and SQUID measurements for 8-(p-BrC6H4)-6OPO show a weak antiferromagnetic exchange interaction in the π dimer. These results demonstrate that the control of the spin distribution patterns of the phenalenyl skeleton switches the mode of exchange interaction within the phenalenyl-based π dimer. The formation of the relevant multicenter-two-electron bonds is discussed.

catena-Poly[[[(2,2'-bipyridine-κ(2)N,N')manganese(II)]-µ-(2,5-dichloro-3,6-dioxocyclo-hexa-1,4-diene-1,4-diolato)-κ(4)O(1),O(6):O(3),O(4)] ethanol disolvate].

The asymmetric unit of the title coordination polymer, {[Mn(C(6)Cl(2)O(4))(C(10)H(8)N(2))]·2C(2)H(5)OH}(n), consists of one Mn(II) ion, one 2,2'-bipyridine (bpy) ligand, one chloranilate (CA(2-)) ligand and two ethanol solvent mol-ecules. The Mn(II) ion is octa-hedrally coordinated by two N atoms of one bpy ligand and four O atoms of two chloranilate ions. The chloranilate ion serves as a bridging ligand between the Mn(II) ions, leading to an infinite zigzag chain along [101]. π-π stacking inter-actions [centroid-centroid distance = 4.098 (2) Å] is observed between the pyridine rings of adjacent chains. The ethanol mol-ecules act as accepters as well as donors for O-H⋯O hydrogen bonds, and form a hydrogen-bonded chain along the a axis. The H atoms of the hy-droxy groups of the two independent ethanol mol-ecules are each disordered over two sites with equal occupancies.

Bis[µ-3,5-bis-(pyridin-2-yl)-1H-pyrazole]-bis-[di-bromido-iron(III)].

The title dinuclear complex, [Fe2Br4(C13H9N4)2], which lies on an inversion center, features two approximately planar bis-(pyridin-2-yl)pyrazole (bpypz(-)) ligands [maximum deviation = 0.082 (3) Å] and four bromide ions. Each Fe(III) ion is octa-hedrally coordinated by four N atoms of two bpypz(-) ligands and two Br ions. π-π stacking inter-actions [centroid-centroid distances = 3.7004 (17)-4.0123 (18) Å] are observed between pyridyl and pyrazole rings, and between pyridyl and pyridyl rings of adjacent complex mol-ecules.

Bis[µ-3,5-bis-(pyridin-2-yl)pyrazolato]bis-[(hexa-fluoro-phosphato)copper(II)].

The title dinuclear complex mol-ecule, [Cu2(C13H9N4)2(PF6)2], lies about an inversion center. The Cu(II) atom shows a square-pyramidal coordination geometry with the basal plane formed by four N atoms of the two bis-chelating 3,5-bis-(pyridin-2-yl)pyrazolate ions and with one F atom of the hexa-fluoro-phosphate ion in the apical position. Mol-ecules are stacked in a column along the a axis through C-H⋯F hydrogen bonds. The columns are further linked by other C-H⋯F hydrogen bonds, forming a three-dimensional network.

Effect of chain length on thermal conversion of alkoxy-substituted copper phthalocyanine precursors.

A series of dialkoxy-substituted copper phthalocyanine (CuPc) precursors (4a-4d) have been prepared by treating phthalonitrile with the corresponding lithium alkoxide under mild conditions. The precursors exhibited high solubilities in common organic solvents, including acetone, toluene, tetrahydrofuran (THF), CH(2)Cl(2), and CHCl(3). Elongation of the alkoxy chains improved the solubilities of the precursors effectively, and accordingly, the butoxy-substituted derivative (4d) showed the highest solubility among 4a-4d. X-ray crystallography clarified that the conjugated skeletons of 4a-4d are all isostructural, and have two alkoxy groups in a syn-conformation fashion, leading to highly bent structures. Thermal conversions of the precursors examined by thermogravimetry (TG) and differential thermal analysis (DTA) demonstrate that 4a was converted into CuPc via two distinct exothermic processes in the 200-250 °C temperature range, while 4d exhibits only one exothermic signal in the DTA. In the field emission scanning electron microscopy (FESEM) images of 4a, the presence of two types of distinct crystal morphology (prismatic and plate-like crystals) can be recognized, implying that the two observed exothermic processes in the DTA can be attributed to the different crystal morphologies of the samples rather than the step-by-step elimination of the alkoxy groups. The thermal formation of CuPc from the precursors has been unambiguously confirmed by X-ray powder diffraction, UV-vis spectroscopy, and elemental analysis. The precursors were converted into CuPc at lower temperature with increasing chain length, presumably because of the increased void volume in the crystals. Thermal conversion performed in the solution phase results in a bright blue-colored solution with prominent absorption bands in the 650-700 nm region, strongly supporting the formation of CuPc.

Bis[µ-3,5-bis-(2-pyrid-yl)pyrazolato]bis-(hydrogensulfato)-dicopper(II) methanol disolvate.

The title compound, [Cu(2)(C(13)H(9)N(4))(2)(HSO(4))(2)]·2CH(3)OH, consists of discrete centrosymmetric dinuclear complex mol-ecules and methanol solvent mol-ecules. The Cu(II) atom shows a square-pyramidal coordination geometry and is bonded to four N atoms of the two bis-chelating 3,5-bis-(2-pyrid-yl)pyrazol-ate ions (bpypz(-)) and one O atom of the hydrogensulfate ion. The bpypz(-) ligands in the complex mol-ecule are virtually coplanar [dihedral angle between the mean ligand planes = 0.000(1)°] with the Cu(II) atom deviating in opposite directions from their best plane by 0.2080 (12) Å. π-π stacking inter-actions between the pyridyl and pyrazole rings [centroid-centroid distance = 3.391 (3) Å] and strong O-H⋯O hydrogen bonds between the hydrogensulfate ligands and the methanol mol-ecules assemble the mol-ecules into a one-dimensional polymeric structure extending along the a axis. The methanol mol-ecule acts both as an accepter and a donor in the hydrogen bonding.

Construction of a novel topological frustrated system: a frustrated metal cluster in a helical space.

A novel topologically frustrated pentanuclear cluster helicate [{Cu(II)(µ-L)(3)}(2)Cu(II) (3)(µ(3)-OH)](3+) (L(-)=3,5-bis(2-pyridyl)pyrazolate) has been synthesized and characterized. This cluster has a helical arrangement of ligands around the central metal core. Dzyaloshinsky-Moriya interactions are essential components to observe a gradual magnetization and forbidden transitions of high-field/multi-frequency (HF/MF)-ESR. The origin of the magnetic anisotropy of this compound is influenced by its helical spin structure, and consequently, the Cu(5)-cluster helicate introduces a unique magnetic anisotropy. This observation is a direct evidence of the topological part of the new spin phase in a magnetic system.

Complete enantioseparation through supramolecular complex formation between tris(1,3-diaminopropane)cobalt(III) phosphate and ß-cyclodextrin, [Co(tn)3]PO4·ß-CDX.

The supramolecular complex [Co(tn)(3)]PO(4)·ß-CDX (tn = 1,3-diaminopropane; ß-CDX = ß-cyclodextrin) was prepared through ß-CDX, rac-[Co(tn)(3)]Cl(3), and Na(3)PO(4) in a mole ratio of 1:2:2. After one recrystallization process, the circular dichroism spectrum confirmed that complete enantioseparation of [Co(tn)(3)]PO(4) is achieved in this system. X-ray crystal structure analysis reveals the presence of the only Λ-enantiomer in the unit cell and the head-to-head chiral discrimination structure of this system. Thus, we found that the present diastereomer formation with ß-CDX affords the very convenient and effective optical resolution procedure of [Co(tn)(3)](3+).

Stabilization of long-lived metastable state in long alkylated spin-crossover cobalt(II) compound.

The A mixed crystal compound [Co(0.8)Fe(0.2)(C16-terpy)(2)](BF(4))(2) (2) (C16-terpy is 4'-hexadecyloxy-2,2':6',2''-terpyridine) with long alkyl chains was prepared by mixing [Co(C16-terpy)(2)](BF(4))(2) (1), which exhibits unique magnetic behavior, and the diamagnetic iron(II) compound [Fe(C16-terpy)(2)](BF(4))(2) (3). The long-lived metastable state in the frozen-in effect was observed for the first time in the spin-crossover cobalt(II) compound 2. Furthermore, relaxation from metastable to stable states was very slow because of a large structural transition resulting from the long alkyl chains.

Determination of ligand field splitting in lanthanide(iii) monoporphyrinato complexes.

The 4f-electronic structures of the ground multiplet states of a series of lanthanide(iii) monoporphyrinato complexes with a cyclen as the capping ligand [Ln(TPP)(cyclen)]Cl (Ln = Tb, Dy, Ho, Er, Tm, and Yb; TPP = 5,10,15,20-tetraphenylporphyrinato; cyclen = 1,4,7,10-tetraazacyclododecane) have been determined using experimental NMR and magnetic susceptibility data. Magnetic susceptibilities of the microcrystalline samples of [Ln(TPP)(cyclen)]Cl were measured in the range of 1.8-300 K. NMR signals corresponding to the protons on the porphyrin ring show marked paramagnetic shifts (lower = Tb, Dy, Ho, and Yb; higher = Er and Tm) in comparison with the diamagnetic Y congener. A set of ligand-field parameters that simultaneously reproduces the magnetic susceptibilities and the paramagnetic shifts has been determined by using a self-developed multidimensional optimization program. In addition, CASSCF calculations were carried out for further insight into their electronic structures.

Calorimetric study of correlated disordering in [Hdamel]2[Cu(II)(tdpd)2] x 2 THF crystal.

The heat capacity of [Hdamel]2[Cu(II)(tdpd)2] x 2 THF was measured from 6 to 250 K by adiabatic calorimetry. There are four heat anomalies around 150 K associated with disordering in the orientation of the uncoordinated THF molecules and in the conformation of the out-of-plane allyl groups of [Hdamel](+) units. The total entropy of transition was determined to be 19.8 J K(-1) mol(-1), less than the 4R ln 2 (R = gas constant) expected from the crystal structure at room temperature. The smallness of the total entropy change on phase transitions proves the presence of the strong motional correlation between the adjacent allyl groups. The calorimetric conclusion agreed with the crystal structure at 200 K re-examined in this study.