Single-Component Molecular Conductor [Cu(dmdt)(2)] with Three-Dimensionally Arranged Magnetic Moments Exhibiting a Coupled Electric and Magnetic Transition

Crystals of the single-component molecular conductor [Cu(dmdt)(2)] (dmdt = dimethyltetrathiafulvalenedithiolate) were prepared as a molecular system, with three-dimensionally arranged magnetic moments embedded in "sea" of π conduction electrons. [Cu(dmdt)(2)] had fairly large room-temperature conductivity (110 S?cm(-1)) and exhibited weakly metallic behavior near room temperature. Below 265 K, the resistivity (R) increased very slowly with decreasing temperature and then increased rapidly, indicating a transition from a highly conducting state to an insulating state near 95 K. The magnetic susceptibility showed Curie-Weiss behavior at 100-300 K (C = 0.375 emu/mol, Θ = 180 K). The Curie constant and the high-temperature resistivity behavior indicate that conduction electrons and three-dimensionally arranged magnetic moments coexist in the crystal. The ESR intensity increased down to about 95 K. The ESR signal was broadened and decreased abruptly near 95 K, suggesting that electric and antiferromagnetic transitions occurred simultaneously near 95 K. The crystal structure was determined down to 13 K. To examine the stability of the twisted conformation of Cu complex with dithiolate ligands, the dihedral angle dependence of the conformational energy of an isolated M(L)(2)(n-) molecule was calculated, which revealed the dihedral angle dependence on the ligand (L) and the oxidation state of the molecule (n). High-pressure four-probe resistivity measurements were performed at 3.3-9.3 GPa using a diamond anvil cell. The small resistivity increase observed at 3.3 GPa below 60 K suggested that the insulating transition observed at ambient pressure near 95 K was essentially suppressed at 3.3 GPa. The intermolecular magnetic interactions were examined on the basis of simple mean field theory of antiferromagnetic transition and the calculated intermolecular overlap integrals of the singly occupied molecular orbital (SOMO) of Cu(dmdt)(2).     

Magnetic transitions of single-component molecular metal [Au(tmdt)2] and its alloy systems

A single-component molecular conductor [Au(tmdt)2] (tmdt = trimethylenetetrathiafulvalenedithiolate) undergoes an antiferromagnetic phase transition at unprecedentedly high temperature (TN = 110 K). Black microcrystals of alloys, [Ni1-xAux(tmdt)2] (0.0 < x < 1.0) were prepared. The Au-rich system exhibited an antiferromagnetic transition. Metallic single crystal was obtained for x = 0.25.     

Magnetic susceptibility of alkali-tetracyanoquinodimethane salts and extended Hubbard models with bond order and charge density wave phases

The molar spin susceptibilities χ(T) of Na-tetracyanoquinodimethane (TCNQ), K-TCNQ, and Rb-TCNQ(II) are fit quantitatively to 450 K in terms of half-filled bands of three one-dimensional Hubbard models with extended interactions using exact results for finite systems. All three models have bond order wave (BOW) and charge density wave (CDW) phases with boundary V = V(c)(U) for nearest-neighbor interaction V and on-site repulsion U. At high T, all three salts have regular stacks of TCNQ(-) anion radicals. The χ(T) fits place Na and K in the CDW phase and Rb(II) in the BOW phase with V ≈ V(c). The Na and K salts have dimerized stacks at T < T(d) while Rb(II) has regular stacks at 100 K. The χ(T) analysis extends to dimerized stacks and to dimerization fluctuations in Rb(II). The three models yield consistent values of U, V, and transfer integrals t for closely related TCNQ(-) stacks. Model parameters based on χ(T) are smaller than those from optical data that in turn are considerably reduced by electronic polarization from quantum chemical calculation of U, V, and t of adjacent TCNQ(-) ions. The χ(T) analysis shows that fully relaxed states have reduced model parameters compared to optical or vibration spectra of dimerized or regular TCNQ(-) stacks.     

Effect of Nonmagnetic Substitution on the Magnetic Properties and Charge-Transfer Phase Transition of an Iron Mixed-Valence Complex, (n-C(3)H(7))(4)N[Fe(II)Fe(III)(dto)(3)] (dto = C(2)O(2)S(2))

The iron mixed-valence complex (n-C(3)H(7))(4)N[Fe(II)Fe(III)(dto)(3)] exhibits a novel type of phase transition called charge-transfer phase transition (CTPT), where the thermally induced electron transfer between Fe(II) and Fe(III) occurs reversibly at ～120 K, in addition to the ferromagnetic phase transition at T(C) = 7 K. To investigate the mechanism of the CTPT, we have synthesized a series of magnetically diluted complexes (n-C(3)H(7))(4)N[Fe(II)(1-x)Zn(II)(x)Fe(III)(dto)(3)] (dto = C(2)O(2)S(2); x = 0-1), and carried out magnetic susceptibility and dielectric constant measurements and (57)Fe M?ssbauer spectroscopy. With increasing Zn(II) concentration (x), the CTPT is gradually suppressed and disappears at x ≈ 0.13. On the other hand, the ferromagnetic transition temperature (T(C)) is initially enhanced from 7 K to 12 K between x = 0.00 and 0.05, despite the nonmagnetic nature of Zn(II) ions, and then it decreases monotonically from 12 K to 3 K with increasing Zn(II) concentration. This anomalous dependence of T(C) on Zn(II) concentration is related to a change in the spin configuration of the ferromagnetic state caused by the partial suppression of the CTPT.     

Magnetocurrent of charge-polarizable C60-diphenylaminofluorene monoadduct-derived magnetic nanocomposites

We demonstrated the strategy of a nanocomposite design by the incorporation of both a delocalized π-electrons system in a closely bound acceptor-donor analogue chromophore, based on charge-polarizable C(60)(>DPAF-C(9)) nanostructure 1, and spin-polarized d-electrons in the form of γ-FeO(x) nanoparticles. Facile intramolecular electron transfer from the DPAF-C(9) donor moiety to the C(60) acceptor cage of 1 upon activation to the excited state with a long lifetime of the charge-separated state forms a possible mechanism to integrate semiconducting and magnetic properties in a single system. We observed an appreciable magnetocurrent (MC) of C(60)(>DPAF-C(9))-encapsulated magnetic γ-FeO(x) nanoparticles in PMMA matrix upon applying a magnetic field from 0 to 300 mT at either 77 K (12% MC) or 300 K (4.5% MC). Interestingly, the detailed analysis of magnetocurrent curve profiles taken at 77 K allowed us to conclude that the measured magnetocurrent may be attributed to the contributions from magnetic field-dependent excited-state populations in semiconducting structure (density-based MC), magnetism from magnetic structure (mobility-based MC), and product of density and mobility-based MC components (π-d electronic coupling). At the higher temperature region up to 300 K, the semiconducting mechanism dominated the determining factor of measured magnetocurrent. This experimental observation indicated the feasibility of combining delocalized π electrons and spin-polarized d electrons through charge transfer to induce internally coupled dual mobility- and density-based MC through the modulation of spin polarization and excited states in semiconducting/magnetic hybrid materials.     

Scale-free center-of-mass displacement correlations in polymer melts without topological constraints and momentum conservation: a bond-fluctuation model study

By Monte Carlo simulations of a variant of the bond-fluctuation model without topological constraints, we examine the center-of-mass (COM) dynamics of polymer melts in d = 3 dimensions. Our analysis focuses on the COM displacement correlation function C(N)(t)≈?(t) (2)h(N)(t)/2, measuring the curvature of the COM mean-square displacement h(N)(t). We demonstrate that C(N)(t) ≈ -(R(N)∕T(N))(2)(ρ?/ρ)?f(x = t/T(N)) with N being the chain length (16 ≤ N ≤ 8192), R(N) ～ N(1/2) is the typical chain size, T(N) ～ N(2) is the longest chain relaxation time, ρ is the monomer density, ρ(*)≈N/R(N) (d) is the self-density, and f(x) is a universal function decaying asymptotically as f(x) ～ x(-ω) with ω = (d + 2) × α, where α = 1/4 for x ? 1 and α = 1/2 for x ? 1. We argue that the algebraic decay NC(N)(t) ～ -t(-5/4) for t ? T(N) results from an interplay of chain connectivity and melt incompressibility giving rise to the correlated motion of chains and subchains.     

Neutron scattering studies of K(3)H(SO(4))(2) and K(3)D(SO(4))(2): The particle-in-a-box model for the quantum phase transition

In the crystal of K(3)H(SO(4))(2) or K(3)D(SO(4))(2), dimers SO(4)???H???SO(4) or SO(4)???D???SO(4) are linked by strong centrosymmetric hydrogen or deuterium bonds whose O???O length is ≈2.50 A?. We address two open questions. (i) Are H or D sites split or not? (ii) Is there any structural counterpart to the phase transition observed for K(3)D(SO(4))(2) at T(c) ≈ 85.5 K, which does not exist for K(3)H(SO(4))(2)? Neutron diffraction by single-crystals at cryogenic or room temperature reveals no structural transition and no resolvable splitting of H or D sites. However, the width of the probability densities suggest unresolved splitting of the wavefunctions suggesting rigid entities H(L1∕2) -H(R1∕2) or D(L1∕2) -D(R1∕2) whose separation lengths are l(H) ≈ 0.16 A? or l(D) ≈ 0.25 A?. The vibrational eigenstates for the center of mass of H(L1∕2) -H(R1∕2) revealed by inelastic neutron scattering are amenable to a square-well and we suppose the same potential holds for D(L1∕2) -D(R1∕2). In order to explain dielectric and calorimetric measurements of mixed crystals K(3)D((1 - ρ))H(ρ)(SO(4))(2) (0 ≤ ρ ≤ 1), we replace the classical notion of order-disorder by the quantum notion of discernible (e.g., D(L1∕2) -D(R1∕2)) or indiscernible (e.g., H(L1∕2) -H(R1∕2)) components depending on the separation length of the split wavefunction. The discernible-indiscernible isostructural transition at finite temperatures is induced by a thermal pure quantum state or at 0 K by ρ.     

Synthesis, spectroscopy, and electrochemistry of copper(II) complexes with N,N'-bis(3,5-di-t-butylsalicylideneimine)polymethylenediamine ligands

Bulky salen CuL(x) derived from aliphatic polymethylene diamines, H(2)N-(CH(2))(x)-NH(2), where n = 2-6, and 3,5-di-t-butylsalicylaldehyde (H(2)L(x)) and some corresponding tetrahydrosalan complexes (CuL(x)') have been synthesized and characterized by their IR, UV-vis absorption and EPR spectra, by magnetic moments and by cyclic voltammetry in acetonitrile (for H(2)L(x)) and DMF (for CuL(x)). Complexes CuL(x) and CuL(x)' are magnetically normal (mu(exp) = 1.83-1.91 mu(B)). EPR spectra CuL(x) characterized by the axial g and A(Cu) tensors with g parallel > g perpendicular and without (14)N-shf resolution in CHCl(3)/toluene at 300 and 150K. The CV studies on acetonitrile solutions of H(2)L(x) revealed a well-defined quasi-reversible redox wave at E(1/2) = 0.95-1.15 V versus Ag/AgCl but CV of the CuL(x) complexes in DMF exhibit weak pronounced irreversible oxidation waves at E(pa)(1) = 0.51 - 098 V and E(pa)(2) = 1.16 - 1.33 V attributable to metal centered Cu(II/III) and ligand centered CuL(x)/CuL(x)*+ couples, respectively. A poorly defined wave was observed for the quasi-reversible reduction Cu(II)/Cu(I) at potentials less than -1.0 V.     

Constructing single-chain magnets by supramolecular π-π stacking and spin canting: a case study on manganese(III) corroles

A single‐chain magnet (SCM) was constructed from manganese(III) 5,10,15‐tris(pentafluorophenyl)corrole complex [Mn^III(tpfc)] through supramolecular π–π stacking without bridging ligands. In the crystal structures, [Mn(tpfc)] molecules crystallized from different solvents, such as methanol, ethyl acetate, and ethanol, exhibit different molecular orientations and intermolecular π–π interaction or weak Mn ??? O interaction to form a supramolecular one‐dimensional motif or dimer. These three complexes show very different magnetic behaviors at low temperature. Methanol solvate 1 shows obvious frequency dependence of out‐of‐phase alternating‐current magnetic susceptibility below 2 K and a magnetization hysteresis loop with a coercive field of 400 Oe at 0.5 K. It is the first example of spin‐canted supramolecular single‐chain magnet due to weak π–π stacking interaction. By fitting the susceptibility data χ_MT (20–300 K) of 1 with the spin Hamiltonian expression ${\overrightarrow{H}}A single-chain magnet (SCM) was constructed from manganese(III) 5,10,15-tris(pentafluorophenyl)corrole complex [Mn(III) (tpfc)] through supramolecular π-π stacking without bridging ligands. In the crystal structures, [Mn(tpfc)] molecules crystallized from different solvents, such as methanol, ethyl acetate, and ethanol, exhibit different molecular orientations and intermolecular π-π interaction or weak Mn???O interaction to form a supramolecular one-dimensional motif or dimer. These three complexes show very different magnetic behaviors at low temperature. Methanol solvate 1 shows obvious frequency dependence of out-of-phase alternating-current magnetic susceptibility below 2?K and a magnetization hysteresis loop with a coercive field of 400?Oe at 0.5?K. It is the first example of spin-canted supramolecular single-chain magnet due to weak π-π stacking interaction. By fitting the susceptibility data χ(M) T (20-300?K) of 1 with the spin Hamiltonian expression H = -2J Σ(i=1)(n-1) S(Ai) S(Ai+1) + D Σ(i) S((iZ)(2)), the intrachain magnetic coupling parameter transmitted by π-π interaction of -0.31?cm(-1) and zero field splitting parameter D of -2.59?cm(-1) are obtained. Ethyl acetate solvate 2 behaves as an antiferromagnetic chain without ordering or slow magnetic relaxation down to 0.5?K. The magnetic susceptibility data χ(M) T (20-300?K) of 2 was fitted by assuming the spin Hamiltonian H = -2JΣ(i=1)(n-1) S(Ai) S(Ai+1), and the intrachain antiferromagnetic coupling constant of -0.07?cm(-1) is much weaker than that of 1. Ethanol solvate 3 with a dimer motif shows field-induced single-molecule magnet like behavior below 2.5?K. The exchange coupling constant J within the dimer propagated by π-π interaction is -0.14?cm(-1) by fitting the susceptibility data χ(M) T (20-300?K) with the spin Hamiltonian H = -2J S(A) S(B) + β(S((A)g(A)) + S((B)g(B)))H. The present studies open a new way to construct SCMs from anisotropic magnetic single-ion units through weak intermolecular interactions in the absence of bridging ligands.     

Structural features of the modulated BiCu2(P(1-x)V(x))O6 solid solution; 4-D treatment of x = 0.87 compound and magnetic spin-gap to gapless transition in new Cu2+ two-leg ladder systems

The BiCu(2)(P(1-x)V(x))O(6) system shows the appearance of various phenomena that progressively change as a function of the average (P/V)O(4) groups size. Then, from x = 0 to x approximately 0.7, a solid solution exists with respect to the basic orthorhombic unit cell of BiCu(2)PO(6). For greater x values (0.7 < x <0.96), structural modulations with incommensurate q vector that slightly change versus x appear. The 4-D treatment of single-crystal XRD data of the modulated phase corresponding to x = 0.87 at 100 K (orthorhombic, a = 12.379(3)Angstrom, b = 5.2344(9) Angstrom, c = 7.8270(14) Angstrom, q = 0.268(3) b*, super space group: Xbmm(0gamma0) s00, X stands for the nonprimitive centering vector (1/2,0,1/2,1/2), R(obs)(overall) = 5.27%, R(obs)(fundamental) = 4.48%, R(obs)(satellite) = 6.58%) has evidenced strong positional modulated effects within the [BiCu(2)O(2)](3+) ribbons while three XO(4) configurations compete along the x(4) fourth dimension. There is no P/V segregation along x(4) in good agreement with steric-only origins of the modulation. Finally for 0.96 < x <1, two phases coexist, i.e., BiCu(2)VO(6) (X = 1) and a modulated phase of the previous domain.The BiCu(2)VO(6) crystal structure shows a unit cell tripling associated with monoclinic symmetry lowering. The VO(4) orientations between two ribbons proceed with respect to the interribbon distance. Then the full system shows flexible interactions between modulated Bi/M/O-based ribbons and surrounding tetrahedral groups, depending on the average XO(4) size. Furthermore, between two ribbons the Cu(2+) arrangement forms magnetically isolated zigzag copper two-leg ladders. Our preliminary results show a spin-gap behavior likely due to the existence of true S = (1)/(2) Heisenberg two-leg ladders. Modulated compositions are gapless, in good agreement with band-broadening toward a continuum in the magnetic excitation spectrum. The continuous distribution of Cu-Cu distances along the rungs and legs of the ladders should be mainly responsible for this magnetic change.     

Highly conducting crystals based on single-component gold complexes with extended-TTF dithiolate ligands

Highly conducting crystals based on single-component gold complexes with extended-TTF dithiolate ligands [Au(dmdt)(2)](0+) (1) and [Au(tmdt)(2)](0+) (2) were prepared (dmdt = dimethyltetrathiafulvalenedithiolate and tmdt = trimethylenetetrathiafulvalenedithiolate). On the basis of the synchrotron radiation powder diffraction data, the MEM electron density of 2 was successfully obtained. The conductivities of compacted powder samples of 1 and 2 at room temperature were 12 and 15 S cm(-1), respectively. Pauli-like susceptibility of 1 suggested the system to be essentially metallic at least above 50 K, while 2 showed a magnetic transition around 100 K without loss of its high conductivity.     

Unusual oxidation state distributions observed for two mixed-valence heptanuclear manganese disc-like clusters

The synthesis, structures and magnetic properties of two new mixed-valence heptanuclear manganese clusters are described. Both complexes utilize triethanolamine (teaH(3)) as a bridging ligand, displaying near planar, disc-like metal topologies and are of formulae [Mn(II)(4)Mn(IV)(3)(tea)(teaH(2))(3)(peolH)(4)](BF(4))(2)·solv (1) and [Mn(II)(4)Mn(III)(3)F(3)(tea)(teaH)(teaH(2))(2)(piv)(4)(Hpiv)(chp)(3)]·0.5MeCN (2). Compound 1 is a rare mixed-valence compound containing Mn(II) and Mn(IV) ions only and is the first example of a heptanuclear disc with a {Mn(II)(4)Mn(IV)(3)} oxidation state distribution. Compound 2 is a {Mn(II)(4)Mn(III)(3)} complex and displays a unique arrangement of oxidation states within the disc, when compared to other known {Mn(II)(4)Mn(III)(3)} examples. Variable temperature DC and AC magnetic susceptibility studies were carried out for 1 and 2 in the 2-300 K temperature range. Compound 1 displayed an increase in the χ(M)T susceptibility values as the temperature is decreased indicating dominant ferromagnetic interactions are present within the cluster. Fits of the χ(M)T vs. T data reveals an S = 23/2 ground state, with several close lying excited states within 1 cm(-1). Compound 2 displays an overall decrease in the χ(M)T value as the temperature is decreased down to 2 K indicating dominant antiferromagnetic interactions present with a probable S = 4 ground state as determined from the DC and AC susceptibility data.     

Effect of chelate ring expansion on Jahn-Teller distortion and Jahn-Teller dynamics in copper(II) complexes

The expanded ligand N,N'-dimethyl-N,N'-dipyridin-2-yl-pyridin-2,6-diamine (ddpd) coordinates to copper(II) ions in a meridional fashion giving the dicationic complex mer-[Cu(ddpd)(2)](BF(4))(2) (1). In the solid state at temperatures below 100 K the cations of 1 localize in Jahn-Teller elongated CuN(6) polyhedra with the longest Cu-N bond pointing in the molecular x or y directions while the z axis is constrained by the tridentate ddpd ligand. The elongated polyhedra are ordered in an antiferrodistortive way giving an idealized zincblende structure. At higher temperature dynamically averaged (fluxional) polyhedra in the molecular x/y directions are observed by multifrequency variable temperature electron paramagnetic resonance (EPR) and by variable temperature X-ray diffraction studies. Compared to [Cu(tpy)(2)](2+) (tpy = 2,2';6',2″-terpyridine) the Jahn-Teller splitting 4δ(1) of 1 is larger. This is very probably caused by the much more favorable orbital overlap in the Cu-N bonds in 1 which results from the larger bite angle of ddpd as compared to tpy. The "freezing-in" of the Jahn-Teller dynamics of 1 (T ≈ 100 K) occurs at higher temperature than observed for [Cu(tpy)(2)](2+) (T < 77 K) which is also probably due to the larger Jahn-Teller distortion of 1 resulting in a larger activation barrier.     

Characterization of the crystal and magnetic structures of the mixed-anion coordination polymer Cu(HCO2)(NO3)(pyz) {pyz = Pyrazine} by X-ray diffraction, ac magnetic susceptibility, dc magnetization, muon-spin relaxation, and spin dimer analysis

The mixed-anion coordination polymer Cu(HCO2)(NO3)(pyz) was synthesized, its crystal structure was determined by X-ray diffraction, and its magnetic structure was characterized by ac susceptibility, dc magnetization, muon-spin relaxation, and spin dimer analysis. The crystal structure consists of five-coordinate Cu2+ ions that are connected through syn-anti bridging mu-HCO2- and mu-pyz ligands to form a highly corrugated two-dimensional layered network. Bulk magnetic measurements show a broad maximum in chi(T) at 6.6 K. The HCO2- and pyz ligands mediate ferromagnetic and antiferromagnetic spin exchange interactions between adjacent Cu2+ ions with the spin exchange parameters J/kB = 8.17 and -5.4 K, respectively (H = -JSigmaSi x Sj). The muon-spin relaxation data show a transition to a long-range magnetic ordering below TN = 3.66(3) K. For T < TN, the M(H) and chi'ac measurements provide evidence for a field-induced spin-flop transition at 15.2 kOe. That Cu(HCO2)(NO3)(pyz) undergoes a long-range magnetic ordering is an unexpected result because the one-dimensional Cu(NO3)2(pyz) and three-dimensional Cu(HCO2)2(pyz) compounds display linear chain antiferromagnetism with no long-range magnetic ordering down to 2 K.     

Effects of auxiliary complex-forming agents on the rate of metallochromic indicator colour change-IV Mechanism of the colour change of xylenol orange in copper(II)-edta titrations

The rate of ligand substitution of copper(II)-Xylenol Orange (XO) with EDTA (Y) has been determined spectrophotometrically over the pH range 4.8-6.0 at mu = 0.1 (KNO(3)) and at 25 degrees . In 2-(N-morpholino)ethane sulphonic acid buffer, copper forms a 2:1 chelate (Cu(2)XO(2-)) with XO, and the rate-law is expressed as -d[Cu(2)XO(2-)]/dt = 10(2.89)[Cu(2)XO(2)-][Y']- The release of the first copper ion from Cu(2)XO(2-) is the rate-determining step. The resulting CuHXO(3-) or CuH(2)XO(2-) may undergo fast substitution with EDTA. In the presence of hexamine, the copper(II)-XO chelate forms a mixed-ligand complex with hexamine (L). The formation constant K(Cu(2)XOL)(L) = [Cu(2)XOL(2-)]/[Cu(2)XO(2-)] [L] = 10(2.14) (mu = 0.1, 25 degrees ). At 3 x 10(-2)-2 x 10(-1)M hexamine the rate-law is expressed as -d[Cu(2)XOL(2-)]/dt = 5.39[Cu(2)XOL(2-)][Y']/[L']. The dissociation of hexamine from Cu(23)XOL(2-) has to precede the substitution reaction of Cu(2)XO(2-) with EDTA. Hence, hexamine at higher concentrations than 10(-3)M slows down the rate of colour change of XO in the copper-EDTA titration.     

Magnetic single-component molecular conductors exhibiting strong π-d interactions

Single-component molecular conductors [M(tmdt)₂] (tmdt = trimethylenetetrathiafulvalenedithiolate; M = Ni, Au, Pt, Cu), exhibit a variety of electromagnetic properties, which originate from the differences of the metal’s d-orbitals role in the band structure formation. The [Au(tmdt)₂] crystal undergoes an antiferromagnetic transition at 110 K, while maintaining a metallic state at lower temperatures. The Au analog has a high magnetic transition temperature as compared to traditional magnetic molecular conductors due to the strong three-dimensional (3-D) structure and the contribution of the metal d-orbitals. The single-component molecular conductor, [Cu(tmdt)₂], with π- and d-like frontier orbitals is isostructural with other metallic [M(tmdt)₂] systems (M = Ni, Pt, Au). The Cu(tmdt)₂ molecule is planar, which strikingly contrasts the tetrahedral coordination of Cu(dmdt)₂ (dmdt = dimethyltetrathiafulvalenedithiolate) with similarly extended TTF type ligands. Interestingly, unlike other [M(tmdt)₂] with metallic behavior, [Cu(tmdt)₂] shows semiconducting behavior at room temperature (σ(RT) = ∼7 S cm⁻¹). The RT conductivity increased linearly with increased pressure to 110 S cm⁻¹ at 15 kbar despite the compressed pellet sample. The magnetic susceptibility indicates one-dimensional (1-D) Heisenberg behavior with J = 117 cm⁻¹ and shows antiferromagnetic ordering at 13 K. The [Cu(tmdt)₂] is a new multi-frontier π-d system, which introduces a d(σ)-type frontier orbital around the Fermi level of the π-like metal bands.     

Copper(II) carboxylate dimers prepared from ligands designed to form a robust π···π stacking synthon: supramolecular structures and molecular properties

The reactions of bifunctional carboxylate ligands (1,8-naphthalimido)propanoate, (L(C2)(-)), (1,8-naphthalimido)ethanoate, (L(C1)(-)), and (1,8-naphthalimido)benzoate, (L(C4)(-)) with Cu(2)(O(2)CCH(3))(4)(H(2)O)(2) in methanol or ethanol at room temperature lead to the formation of novel dimeric [Cu(2)(L(C2))(4)(MeOH)(2)] (1), [Cu(2)(L(C1))(4)(MeOH)(2)]·2(CH(2)Cl(2)) (2), [Cu(2)(L(C4))(4)(EtOH)(2)]·2(CH(2)Cl(2)) (3) complexes. When the reaction of L(C1)(-) with Cu(2)(O(2)CCH(3))(4)(H(2)O)(2) was carried out at -20 °C in the presence of pyridine, [Cu(2)(L(C1))(4)(py)(4)]·2(CH(2)Cl(2)) (4) was produced. At the core of complexes 1-3 lies the square Cu(2)(O(2)CR)(4) "paddlewheel" secondary building unit, where the two copper centers have a nearly square pyramidal geometry with methanol or ethanol occupying the axial coordination sites. Complex 4 contains a different type of dimeric core generated by two κ(1)-bridging carboxylate ligands. Additionally, two terminal carboxylates and four trans situated pyridine molecules complete the coordination environment of the five-coordinate copper(II) centers. In all four compounds, robust π···π stacking interactions of the naphthalimide rings organize the dimeric units into two-dimensional sheets. These two-dimensional networks are organized into a three-dimensional architecture by two different noncovalent interactions: strong π···π stacking of the naphthalimide rings (also the pyridine rings for 4) in 1, 3, and 4, and intermolecular hydrogen bonding of the coordinated methanol or ethanol molecules in 1-3. Magnetic measurements show that the copper ions in the paddlewheel complexes 1-3 are strongly antiferromagnetically coupled with -J values ranging from 255 to 325 cm(-1), whereas the copper ions in 4 are only weakly antiferromagnetically coupled. Typical values of the zero-field splitting parameter D were found from EPR studies of 1-3and the related known complexes [Cu(2)(L(C2))(4)(py)(2)]·2(CH(2)Cl(2))·(CH(3)OH), [Cu(2)(L(C3))(4)(py)(2)]·2(CH(2)Cl(2)) and [Cu(2)(L(C3))(4)(bipy)]·(CH(3)OH)(2)·(CH(2)Cl(2))(3.37) (L(C3)(-) = (1,8-naphthalimido)butanoate)), while its abnormal magnitude in [Cu(2)(L(C2))(4)(bipy)] was qualitatively rationalized by structural analysis and DFT calculations.     

Hydride reduction of NAD+ analogues by isopropyl alcohol: kinetics, deuterium isotope effects and mechanism

Observed pseudo-first-order rate constants (k(obs)) of the hydride-transfer reactions from isopropyl alcohol (i-PrOH) to two NAD(+) analogues, 9-phenylxanthylium ion (PhXn(+)) and 10-methylacridinium ion (MA(+)), were determined at temperatures ranging from 49 to 82 degrees C in i-PrOH containing various amounts of AN or water. Formations of the alcohol-cation ether adducts (ROPr-i) were observed as side equilibria. The equilibrium constants for the conversion of PhXn(+) to PhXnOPr-i in i-PrOH/AN (v/v = 1) were determined, and the equilibrium isotope effect (EIE = K(i-PrOH)/K(i-PrOD)) at 62 degrees C was calculated to be 2.67. The k(H) of the hydride-transfer step for both reactions were calculated on the basis of the k(obs) and K. The corresponding deuterium kinetic isotope effects (e.g., KIE(OD)(H) = k(H)(i-PrOH)/k(H)(i-PrOD) and KIE(beta-D6)(H) = k(obs)(i-PrOH)/k(obs)((CD3)2CHOH)), as well as the activation parameters, were derived. For the reaction of PhXn(+) (62 degrees C) and MA(+) (67 degrees C), primary KIE(alpha-D)(H) (4.4 and 2.1, respectively) as well as secondary KIE(OD)(H) (1.07 and 1.18) and KIE(beta-D6)(H) (1.1 and 1.5) were observed. The observed EIE and KIE(OD)(H) were explained in terms of the fractionation factors for deuterium between OH and OH(+)(OH(delta+)) sites. The observed inverse kinetic solvent isotope effect for the reaction of PhXn(+) (k(obs)(i-PrOH)/k(obs)(i-PrOD) = 0.39) is consistent with the intermolecular hydride-transfer mechanism. The dramatic reduction of the reaction rate for MA(+), when the water or i-PrOH cosolvent was replaced by AN, suggests that the hydride-transfer T.S. is stabilized by H-bonding between O of the solvent OH and the substrate alcohol OH(delta+). This result suggests an H-bonding stabilization effect on the T.S. of the alcohol dehydrogenase reactions.     

Effects of

Effects of cetyltrimethylammonium bromide (CTABr) micelles on second-order rate constants (k(n)(obs)) for nucleophilic reactions of amines (piperidine and n-butylamine) with ionized phenyl salicylate (PS(-)) reveal a nonlinear decrease with the increase in [D(n)] (where [D(n)] = [CTABr](T) - cmc) at a constant [NaBr] and 35 degrees C. The observed data, at a constant [NaBr], fit reasonably well to a pseudophase model of micelles, and such a data fit gives kinetic parameters such as CTABr micellar binding canstant (K(S)) of PS(-). The effect of [NaBr] upon K(S) is explained with the empirical relationship K(S) = K(S)(0)/(1 + psi[NaBr]), where psi is an empirical parameter.     

One-dimensional octacyanomolybdate-based Cu(II)--Mo(V) bimetallic assembly with a novel rope-ladder chain structure

A new type of one-dimensional cyanide-bridged Cu(II)--Mo(V) bimetallic assembly, [Cu(cyclam)](3)[Mo(CN)(8)](2)x5H(2)O (cyclam = 1,4,8,11-tetraazacyclotetradecane), was prepared by self-assembling Mo(CN)(8)(3)(-) and Cu(cyclam)(2+) ions in a 2:3 stoichiometric ratio. The overall molecular view is delineated as a novel rope-ladder chain structure. It displays a dominant ferromagnetic behavior within a pentanuclear Cu(3)Mo(2) unit (J(p) = 3.88 cm(-)(1)). Interunit ferromagnetic interactions (J(c) = -0.03 cm(-)(1)) through a longer magnetic pathway of Cu--Mo and weak antiferromagnetic couplings (zJ' = -0.46 cm(-)(1)) resulting from interchain interactions are obtained.