A new family of spin crossover complexes with a tripod ligand containing three imidazoles: synthesis, characterization, and magnetic properties of [FeIIH3LMe](NO3)2.1.5H2O, [FeIIILMe].3.5H2O, [FeIIH3LMe][FeIILMe]NO3, and [FeIIH3LMe][FeIIILMe](NO3)2 (H3LMe) = Tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine)

A new family of spin crossover complexes, [Fe(II)H(3)L(Me)](NO(3))(2).1.5H(2)O (1), [Fe(III)L(Me)].3.5H(2)O (2), [Fe(II)H(3)L(Me)][Fe(II)L(Me)]NO(3) (3), and [Fe(II)H(3)L(Me)][Fe(III)L(Me)](NO(3))(2) (4), has been synthesized and characterized, where H(3)L(Me) denotes a hexadentate N(6) tripod ligand containing three imidazole groups, tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine. It was found that the spin and oxidation states of the iron complexes with this tripod ligand are tuned by the degree of deprotonation of the imidazole groups and by the 2-methyl imidazole substituent. Magnetic susceptibility and M?ssbauer studies revealed that 1 is an HS-Fe(II) complex, 2 exhibits a spin equilibrium between HS and LS-Fe(III), 3 exhibits a two-step spin transition, where the component [Fe(II)L(Me)](-) with the deprotonated ligand participates in the spin transition process in the higher temperature range and the component [Fe(II)H(3)L(Me)](2+) with the neutral ligand participates in the spin transition process in the lower temperature range, and 4 exhibits spin transition of both the Fe(II) and Fe(III) sites. The crystal structure of 3 consists of homochiral extended 2D puckered sheets, in which the capped tripodlike components [Fe(II)H(3)L(Me)](2+) and [Fe(II)L(Me)](-) are alternately arrayed in an up-and-down mode and are linked by the imidazole-imidazolate hydrogen bonds. Furthermore, the adjacent 2D homochiral sheets are stacked in the crystal lattice yielding a conglomerate as confirmed by the enantiomeric circular dichorism spectra. Compounds 3 and 4 showed the LIESST (light induced excited spin state trapping) and reverse-LIESST effects upon irradiation with green and red light, respectively.     

Superposition of nonorthogonal Slater determinants towards electron correlation problems

We propose variational and nonvariational methods based on the superposition of nonorthogonal Slater determinants. Properties of the reference functions are discussed. In the nonorthogonal configuration interaction method, all the excited configurations of multiple determinants are integrated into a variational space. An efficient way to manipulate matrix elements over determinants of distinct vacuums is presented by introducing similarity transformed operator and bracket transformations. The method enables us to map a matrix multiplication in the nonorthogonal problem to an orthogonal one, and thus maintains a fundamental scaling property along with the amount of data processed in the corresponding orthogonal configuration interaction method. Furthermore, we discuss a coupled-cluster theory employing a vacuum-dependent wave operator, which is entirely size consistent as well as core extensive. These methods are applied to H₂O + nHe(n = 0−2) and a single-bond dissociation of the HF molecule, compared with conventional methods including full and multireference configuration interaction methods. Received: 7 July 1997 / Accepted: 12 September 1997     

Amperometric glucose-sensing electrode based on carbon paste containing poly (ethylene glycol)-modified glucose oxidase and cobalt octaethoxyphthalocyanine

An amperometric enzyme electrode for glucose was prepared by incorporating poly (ethylene glycol)-modified glucose oxidase and cobalt octaethoxyphthalocyanine [CoPc(OEt)₈], a new mediator, into a carbon paste matrix. The polymer-modified enzyme exhibited a higher activity than the native enzyme in the hydrophobic carbon paste medium. CoPc(OEt)₈ could oxidize the enzyme at more negative potentials than unsubstituted cobalt phthalocyanine (CoPc). Further, the CoPc(OEt)₈-mediated enzyme electrode showed a high stability: the electrode response to glucose did not decrease for at least 4 weeks (or for 700 assays), whereas the glucose response from a CoPc-mediated enzyme electrode fell to half of the initial value within 2 weeks (or after 300 assays). CoPc(OEt)₈, a paraffin-oil soluble derivative of CoPc, incorporated in the bulk of carbon paste, diffused towards the electrode surface so as to renew continuously the electrode surface, which resulted in the high stability of the new mediator-based enzyme electrode.     

Implementation of the CCSD(T)-F12 method using cusp conditions

The explicitly-correlated coupled-cluster singles and doubles with perturbative triples method (CCSD(T)-F12) is implemented using the cusp conditions. Numerical tests for a set of 16 molecules have shown agreement of correlation energies within 1 mE(h) between the cusp-condition and fully-optimized CCSD(T)-F12 methods. Benchmark calculations on 13 chemical reactions with the cusp-condition CCSD(T)-F12 method reproduce experimental enthalpies within 2 kJ mol(-1). It is also shown that regular unitary-invariant ansatz cannot exactly satisfy singlet and triplet cusp conditions in open-shell situations. We present an extended ansatz which can handle both conditions exactly.     

Comparative study on solvation free energy expressions in reference interaction site model integral equation theory

The performance of the recently proposed partial wave (PW) free energy functional is compared with those of two previous expressions, Gaussian fluctuation (GF) and hypernetted chain (HNC), within the reference interaction site model framework. The applications to the calculations of ambient and supercritical water, solvation free energies of organic molecules, and partition coefficients clearly show that the PW and GF free energy expressions provide more reliable results than the HNC functional, indicating rather associative situations of geometry in ordinary liquids of medium-sized molecules.     

Interrelationship between superprotonic conductivity and strain in CsHXO4

In order to clarify the mechanism of superprotonic conductivity (SPC) for the hydrogen-bonded compound CsHXO₄ (X=S, Se), we have investigated the elastic properties of CsHXO₄ with various transition temperatures (T_c), at which CsHXO₄ exhibits a structural phase transition from a low-temperature monoclinic phase with low protonic conductivity (phase II) to a high-temperature SPC phase (phase I). It was found that, in CsHS_xSe_1 − xO₄ (x=0–1), the transition temperature T_c decreases in proportion to the square of spontaneous strain b in the a_II–b_II plane of phase II. This result indicates that the spontaneous strain in the a_II–b_II plane plays an important role in the appearance of SPC in CsHXO₄. Moreover, thermodynamic analyses suggest that proton migration in phase I is induced by the release of the strain energy. From these results, it is deduced that the phase transition temperature in CsHXO₄ is determined by the competition between the kinetic energy of proton and the released-strain energy.     

Comparative Investigation on the Concentration-Dependences of the Half-Band Widths of Infrared Absorption and Raman Bands

It is demonstrated that the fashions of the concentration-dependences of half-band widths are markedly different between the corresponding bands in i.r. absorption and Raman spectra when the i.r. absorption intensities of the bands are extremely large. On the other hand, when the i.r. intensities are not so great, the similar behaviour is observed for the changes in the half-band widths. In this study, these phenomena have been discussed in terms of the vibrational relaxation of resonance type and the local field effect.     

Synthesis and properties of 2-azidodeoxyadenosine and its incorporation into oligodeoxynucleotides

2-Azidodeoxyadenosine (7) was conveniently synthesized from deoxyguanosine (2) by use of a combined reagent of TMSN₃–BuONO. The structure of the tautomer of the azido derivative was determined by ¹H NMR. Reaction of 7 with iPr₂NP(OEt)₂ gave an intermediate 10 of the Staudinger reaction. Incorporation of 7 into a DNA 13mer resulted in a significant decrease of the T_m value of the DNA duplex upon hybridization with the complementary strand. The thermal stability was discussed based on the hydrogen bond energy and electrostatic repulsion.     

The Sensitization Effect in the Laser-Induced Infrared Fluorescence Spectroscopy by Addition of SF6. II

The sensitization effect in the IR-F spectroscopy by addition of SF₆ was investigated in case of acetone as a sample. We kept the partial pressure of acetone constant, varied that of SF₆, and investigated the variations of the degree of sensitization. The experimental data shows that the degree of sensitization increases steeply and is saturated as the partial pressure of SF₆ becomes higher. The results were examined in terms of the kinetics of the intra-and intermolecular energy transfer involved in the emission of infrared radiation in question.     

Explicitly correlated wave functions: summary and perspective

We summarize explicitly correlated electronic structure theory in perspective of future work in the field. Earlier stages of approaches with different Ansätze in physics and chemistry are described. We then discuss recent advances focusing on explicitly correlated wave functions using cusp conditions. Removal of Coulomb singularities in terms of the rational generator is brought out from the viewpoint of many-body perturbation theory. On the basis of decomposition schemes for many-electron integrals in R12 and F12 methods, we further discuss the possibility of increasing the accuracy of molecular numerical integration and massively parallel calculations of explicitly correlated methods.