No abstract

No abstract

No abstract

a low-symmetry environment such as that of the protein blue sites, it is known from model studies31,67 that an increase in the size of the fused chelate rings can lead to a significant distortion of the metal geometry. Thus, it is expected that ligand homologues of pyt-N,S-im containing longer carbon chains between the donor atoms will give rise to copper(II) complexes that progressively approach the spectral behavior of the blue sites. The synthesis of such ligand systems is currently under way in this laboratory. Finally, while the attention is usually focused only on the spectral properties of copper(II) model systems, it is important to give parallel development to the characterization of the corresponding copper(I) systems, even though they generally exhibit poor spectral properties. We have shown in this and in previous studies50,51c that careful examination of the solution behavior of copper(I) complexes can give useful information about the groups involved in metal binding.Acknowledgment This work was supported by a grant from the Italian MPI. I thank the Italian CNR for instrumentation facilities, M. Bonfá for recording the NMR spectra, P. Russo for recording the MS spectra, and C. Pessina for assistance in the synthesis of 1 -phenyl-3-formyl-2( 1 //)-pyridinethione. Registry No. I, 61856-49-3; III, 91002-69-6; [IV] [C104] ( = Cu(I)), 91002-60-7; [IV][C104]2 (M = Cu(II)), 91002-62-9; [I-V][C104]2 (M = Zn(II)), 91002-64-1; [V][C104], 91002-66-3; [VI] [C104]2, 91002-68-5; 4-|[(2-aminoethyl)thio]methyl]-5-methylimidazole, 38585-67-0.

The compounds K,M11xM1111-xF3 ( x = 0.4-0.6; M" = Mn, Ni; MI1' = V, Cr) were prepared and studied. The tetragonal tungsten bronze structure formed for M" = Mn and M"' = V, Cr, and the modified pyrochlore structure formed for MI1 = Ni and M111 = V, Cr, except for &.soNio.soCro.MF3, which formed the tetragonal bronze structure. From their magnetic behavior, we conclude that all of the tetragonal bronze compounds are ionically ordered and belong to space group P4gc (Ck). Magnetic ordering in these compounds occurs in two steps. Linear trimers (MI1)) and (MI1')' form first, giving rise to a quasi-paramagnetic region, followed at lower temperatures by long-range magnetic ordering. The 180' M2t-F-M3t magnetic interactions appear to be ferromagnetic. Samples of compositions Na, 2s&.2sM"o,soM"'o,50F3 and Nao,soM~~o,50M~~~o,~oF3 were also prepared and studied.KxMn.rV1-xF3, &.6ONi0.6Ocr0.40F3, and Na0.25&.25M~.50Cr0,50F3The crystal structure of layered, tetragonal VO(H2As04)2 (a = 9.1305 (1) A, c = 8.1318 (2) A) has been refined in space group M/mcm from laboratory X-ray powder diffraction data by the Rietveld method, giving RW4= 10.1% and RF = 5.5%. Disorder of the vanadium atoms over two sites results from infinite .V=O-.V=O-chains orienting In the fc-directions at random, due to the flexibility of the arsenate groups that link neighboring chains. The two modes of ordering the vanadyl chains to give structures with P4/ncc and 14cm symmetry, both of which have been reported, are also discussed. The structure of the lithium derivative Li4VO(As04)2 (a = 9.0293 (2) A, c = 9.0053 (4) A), obtained by ion exchange, has P4/ncc symmetry due to partial ordering between vanadyl chains and has been refined to Rwp = 13.8% and RF = 9.3%. The lithium ions occupy irregular five-coordinate sites between vanadyl arsenate layers. The different behavior of the VO(H2X04)2 compounds (X = P, As) toward ionic exchange reactions is discussed in the light of these results.