Contribution of 155Gd Mössbauer data to the study of the magnetic interaction in heterodinuclear 3d-Gd (3d = Cu, Ni) coordination complexes.

The valence shell of the gadolinium element corresponds to 4f7 5d1 6s2, so that the trivalent GdIII ion possesses free 5d and 6s orbitals. It has been previously shown by CASSCF methods that the 5d orbitals, along with the 6s Gd orbitals, which are expected to be unoccupied, present a slight spin density and that the magnetic behaviour of CuII-GdIII complexes can only be reproduced if the 5d Gd orbitals are taken into account in the active space. 155Gd Mössbauer isomer shifts of 3d-Gd complexes, L1CuGd(NO3)3, L1NiGd(NO3)3·acetone, L2Cu(acetone)Gd(NO3)3, L2Ni(H2O)2Gd(NO3)3 where L1 and L2 are hexadentate Schiff base ligand, are almost unchanged (0.62-0.64 mm s-1 relative to 155Eu/SmPd3 source) though the values are slightly smaller than a typical ionic compound GdF3 (0.67 mm s-1). The very similar isomer shift values of the 3d-Gd complexes indicate that there is no change in the small electron density of the 6s orbital and that the spin delocalization or spin polarization concerns the 5d Gd orbitals, in agreement with the crystal structure and Mössbauer spectrum of the Gd complex of nitrogen-coordinating tridentate ligand PrnTBP, [Gd(PrnTBP)3](OTf)3. Thus the observed 155Gd Mössbauer isomer shifts of 3d-Gd complexes give an experimental proof for the participation of 5d Gd orbitals to the magnetic interaction in these 3d-Gd complexes.

Synthesis, structures and reactions of cyclometallated gold complexes containing (2-diphenylarsino-n-methyl)phenyl (n = 5, 6).

Reaction of (C6H3-2-AsPh2-n-Me)Li (n = 5 or 6) with [AuBr(AsPh3)] at -78 degrees C gives the corresponding cyclometallated gold(I) complexes [Au2[(mu-C6H3-n-Me)AsPh2]2] [n = 5, (1); n = 6, (9)]. 1 undergoes oxidative addition with halogens and with dibenzoyl peroxide to give digold(II) complexes [Au2X2[(mu-C6H3-5-Me)AsPh2]2] [X = Cl (2a), Br (2b), I (2c) and O2CPh (3)] containing a metal-metal bond between the 5d9 metal centres. Reaction of 2a with AgO2CMe or of 3 with C6F5Li gives the corresponding digold(II) complexes in which X = O2CMe (4) and C6F5 (6), respectively. The Au-Au distances increase in the order 4 < 2a < 2b < 2c < 6, following the covalent binding tendency of the axial ligand. Like the analogous phosphine complexes, 2a-2c and 6 in solution rearrange to form C-C coupled digold(I) complexes [Au2X2[mu-2,2-Ph2As(5,5-Me2C6H3C6H3)AsPh2]] [X = Cl (5a), X = Br (5b), X = I (5c) and C6F5 (7)] in which the gold atoms are linearly coordinated by As and X. In contrast, the products of oxidative additions to 9 depend markedly on the halogens. Reaction of 9 with chlorine gives the gold(I)-gold(III) complex, [ClAu[mu-2-Ph2As(C6H3-6-Me)]AuCl[(6-MeC6H3)-2-AsPh2]-kappa2As,C] (10), which contains a four-membered chelate ring, Ph2As(C6H3-6-Me), in the coordination sphere of the gold(III) atom. When 10 is heated, the ring is cleaved, the product being the digold(I) complex [ClAu[mu-2-Ph2As(C6H3-6-Me)]Au[AsPh2(2-Cl-3-Me-C6H3)]] (11). Reaction of 9 with bromine at 50 degrees C gives a monobromo digold(I) complex (12), which is similar to 11 except that the 2-position of the substituted aromatic ring bears hydrogen instead halogen. Reaction of 9 with iodine gives a mixture of a free tertiary arsine, (2-I-3-MeC6H3)AsPh2 (13), a digold diiodo compound (14) analogous to 11, and a gold(I)-gold(III) zwitterionic complex [I2Au(III)[(mu-C6H3-2-AsPh2-6-Me)]2Au(I)] (15) in which the bridging units are arranged head-to-head between the metal atoms. The structures of 2a-2c and 4-15 have been determined by single-crystal X-ray diffraction analysis. The different behaviour of 1 and 9 toward halogens mirrors that of their phosphine analogues; the 6-methyl substituent blocks C-C coupling of the aryl residues in the initially formed oxidative addition product. In the case of 9, the greater lability of the Au-As bond in the initial oxidative addition product may account for the more complex behaviour of this system compared with that of its phosphine analogue.

Biferrocene-M(mnt)2 charge-transfer complexes (M = Ni, Co; mnt = maleonitriledithiolate). structure, valence states, and magnetic properties.

Charge-transfer salts of branched-alkyl biferrocenes, (1',1' ''-R2-1,1' '-biferrocene)[Ni(mnt)2] (1a, R = isopropyl; 2a, R = dineopentyl) and (1',1' ''-R2-1,1' '-biferrocene)2[Co(mnt)2]2 (1b, R = isopropyl; 2b, R = dineopentyl), were prepared. Their valence states were investigated using X-ray crystallography and Mössbauer spectroscopy. Complexes 1a and 1b show segregated-stack crystal structures that contain columns of acceptors, whereas structures of 2a and 2b, which contain bulky donors, are rather discrete. All of the complexes contain mixed-valent biferrocenium monocations. A two-step valence transition was found in complex 1a. The crystal contains two crystallographically independent cations: one undergoes valence localization below room temperature; the other undergoes valence localization below ca. 130 K. The former transition is derived from asymmetry of the crystal environment around the cation, whereas the latter one is caused by symmetry lowering coupled with a spin-Peierls transition (T(C) = 133.2 K) associated with the dimerization of the acceptors. This compound was found to exhibit a dielectric response based on valence tautomerization. Other complexes (1b, 2a, and 2b) show a valence-trapped state. In all complexes, charge localization was found to occur through local electrostatic interactions between the donor's cationic moiety and the acceptor's electronegative moieties.

Formation of the intermediate-spin iron(III) porphyrin complexes with (dxz, dyz)3(dxy)1(dz2)1 electron configuration.

On the basis of the difference in meso-13C chemical shifts, we have concluded that the intermediate-spin iron(III) complexes with highly ruffled and highly saddled porphyrins have different electron configurations. While the latter has a conventional (dxy)2(dxz, dyz)2(dz2)1, the former adopts a novel (dxz, dyz)3(dxy)1(dz2)1.

Molecular structures of five-coordinated halide ligated iron(III) porphyrin, porphycene, and corrphycene complexes.

Molecular structures of 12 porphyrin analogues, Fe(III)(EtioP)X(1(a)-1(d)), Fe(III)(EtioCn)X(2(a)-2(d)), and Fe(III)(Etio-Pc)X(3(a)-3(d)), where X = F (a), Cl (b), Br (c), and I (d), are determined on the basis of X-ray crystallography. Combined analyses using Mössbauer, (1)H NMR, and EPR spectroscopy as well as SQUID magnetometry have revealed that 3(d) exhibits a quite pure S = 3/2 spin state with a small amount of an S = 5/2 spin admixture. In contrast, all the other complexes show the S = 5/2 spin state with a small amount of the S = 3/2 spin admixture. The structural and spectroscopic data indicate a strong correlation between the spin states of the complexes and the core geometries such as Fe-N bond lengths, cavity areas, and DeltaFe values.

Highly saddle shaped (porphyrinato)iron(III) iodide with a pure intermediate spin state.

Combined analyses using NMR, EPR and Mössbauer spectroscopy as well as SQUID magnetometry have revealed that highly saddle shaped Fe(OETPP)I adopts an essentially pure intermediate spin state in spite of the coordination of an iodide ligand.

Saddle-Shaped Six-Coordinate Iron(III) Porphyrin Complexes Showing a Novel Spin Crossover between S=1/2 and S=3/2 Spin States.

The field strength of the axial ligands determines the spin state of saddled iron(III) porphyrin complexes. Strong axial ligands (L), such as imidazole and 4-dimethylaminopyridine, lead to the formation of complexes with a pure S=1/2 state, while weak ligands, such as THF, give complexes with a pure S=3/2 state. Intermediate strength ligands, such as pyridine and 4-cyanopyridine, give complexes that show a novel spin crossover between the S=1/2 and S=3/2 states.

Sulfur-Bridged Sandwich Cubane-Type Molybdenum-Antimony Cluster. Synthesis, X-ray Structure, and (121)Sb Mössbauer Spectra of [(H(2)O)(9)Mo(3)S(4)SbS(4)Mo(3)(H(2)O)(9)](CH(3)C(6)H(4)SO(3))(8).24H(2)O.

A sulfur-bridged sandwich cubane-type molybdenum-antimony cluster [(H(2)O)(9)Mo(3)S(4)SbS(4)Mo(3)(H(2)O)(9)](8+) (2) has been synthesized through the reaction of incomplete cubane-type molybdenum cluster [Mo(3)S(4)(H(2)O)(9)](4+) (1) with antimony metal, and has been isolated as 2(pts)(8).24H(2)O (2.pts) (Hpts = p-toluenesulfonic acid), whose structure has been characterized by X-ray crystallography. Crystal data of 2.pts: triclinic, space group P&onemacr;, a = 14.468(3) Å, b = 18.531(5) Å, c = 13.713(6) Å, alpha = 105.26(2) degrees, beta = 119.71(1) degrees, gamma = 72.48(3) degrees, V = 3016(1) Å(3), Z = 1, D(calcd) = 1.696 g cm(-)(3), D(obsd) = 1.72 g cm(-)(3), R (R(w)) = 4.7 (7.5) for 6593 reflections (I > 2.0sigma(I)). The Mo-Sb distances (3.68[2]) Å) are much longer than the Mo-Mo (2.717[7] Å) distances. Peak positions and epsilon values (lambda(max), nm (epsilon, M(-)(1) cm(-)(1))) of the electronic spectrum of 2.pts in 2 M HCl are 384 (13 220), 625 (10 440), and 700 (10 080). The (121)Sb Mössbauer parameters (delta = -2.64 mm s(-)(1), e(2)qQ = 18.1 mm s(-)(1), eta = 0.29), and the binding energies (eV) and full widths at half-maximum (in parentheses, eV) obtained from XPS spectrum (Sb(3d3/2), 540.3(2.3); Mo(3d3/2), 233.2(2.1); Mo(3d5/2), 230.2(1.9); (C(1s) = 285.0)) of 2.pts indicate that the oxidation number of antimony is III, and the mean oxidation number of molybdenum is +3.5.