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Synthetic efforts targeting soluble species of Co(II) with the low molecular mass physiological ligand citric acid led to the isolation of the first dinuclear complex [Co(2)(C(6)H(5)O(7))(2)(H(2)O)(4)](2-), at pH approximately 5, in the form of its K+ (1) and Na+ (2) salts. Both 1 and 2 were characterized analytically, spectroscopically (FT-IR, UV/visible, EPR), and magnetically. Complex 1 crystallizes in the monoclinic space group P2(1)/n, with a = 10.348(5) A, b = 11.578(6) A, c = 12.138(6) A, beta = 112.62(2) degrees, V = 1342(1) A(3), and Z = 2. Complex 2 crystallizes in the monoclinic space group P2(1)/c, with a = 9.234(4) A, b = 11.913(4) A, c = 11.728(6) A, beta = 99.93(2) degrees, V = 1271(1) A(3), and Z = 2. X-ray crystallography on 1 and 2 reveals the presence of two Co(II) ions, in a dinuclear assembly, octahedrally coordinated by two citrate ligands in a tridentate fashion. The octahedral environment around each Co(II) is complemented by another singly bonded citrate belonging to the adjacent Co(II) unit and two water molecules. Magnetic susceptibility and EPR studies on 1, in the solid state, corroborate the X-ray results, indicating a weak interaction between the two Co(II) ions. Moreover, EPR and UV/visible studies in solution suggest that 1 does not retain its dimeric structure, yielding a mononuclear octahedral Co(II)-citrate species. Detailed speciation studies suggest the presence of a number of species including the mononuclear complex [Co(C(6)H(5)O(7))](-), optimally present around pH approximately 5. In consonance with EPR and UV/visible spectroscopy, [Co(C(6)H(5)O(7))](-) is likely the scaffolding unit on the basis of which the dimer [Co(2)(C(6)H(5)O(7))(2)(H(2)O)(4)](2-) is isolated from aqueous solutions. Collectively, this comprehensive study offers significant structural insight into the Co(II)-citrate speciation and the elucidation of the role of Co(II) in biological fluids.

The preparations, X-ray structures, and detailed physical characterizations are presented for three new tetranuclear Fe(III)/RCO(2)(-)/phen complexes, where phen = 1,10-phenanthroline: [Fe(4)(OHO)(OH)(2)(O(2)CMe)(4)(phen)(4)](ClO(4))(3).4.4MeCN.H(2)O (1.4.4MeCN.H(2)O); [Fe(4)O(2)(O(2)CPh)(7)(phen)(2)](ClO(4)).2MeCN (2.2MeCN); [Fe(4)O(2)(O(2)CPh)(8)(phen)(2)].2H(2)O (3.2H(2)O). Complex 1.4.4MeCN.H(2)O crystallizes in space group P2(1)/n, with a = 18.162(9) A, b = 39.016(19) A, c = 13.054(7) A, beta = 104.29(2) degrees, Z = 4, and V = 8963.7 A(3). Complex 2.2MeCN crystallizes in space group P2(1)/n, with a = 18.532(2) A, b = 35.908(3) A, c = 11.591(1) A, beta = 96.42(1) degrees, Z = 4, and V = 7665(1) A(3). Complex 3.2H(2)O crystallizes in space group I2/a, with a = 18.79(1) A, b = 22.80(1) A, c = 20.74(1) A, beta = 113.21(2) degrees, Z = 4, and V = 8166(1) A(3). The cation of 1 contains the novel [Fe(4)(mu(4)-OHO)(mu-OH)(2)](7+) core. The core structure of 2 and 3 consists of a tetranuclear bis(mu(3)-O) cluster disposed in a "butterfly" arrangement. Magnetic susceptibility data were collected on 1-3 in the 2-300 K range. For the rectangular complex 1, fitting the data to the appropriate theoretical chi(M) vs T expression gave J(1) = -75.4 cm(-1), J(2) = -21.4 cm(-1), and g = 2.0(1), where J(1) and J(2) refer to the Fe(III)O(O(2)CMe)(2)Fe(III) and Fe(III)(OH)Fe(III) pairwise exchange interactions, respectively. The S = 0 ground state of 1 was confirmed by 2 K magnetization data. The data for 2 and 3 reveal a diamagnetic ground state with antiferromagnetic exchange interactions among the four high-spin Fe(III) ions. The exchange coupling constant J(bb) ("body-body" interaction) is indeterminate due to prevailing spin frustration, but the "wing-body" antiferromagnetic interaction (J(wb)) was evaluated to be -77.6 and -65.7 cm(-1) for 2 and 3, respectively, using the appropriate spin Hamiltonian approach. Mössbauer spectra of 1-3 are consistent with high-spin Fe(III) ions. The data indicated asymmetry of the Fe(4) core of 1 at 80 K, which is not detected at room temperature due to thermal motion of the core. The spectra of 2 and 3 analyze as two quadrupole-split doublets which were assigned to the body and wing-tip pairs of metal ions. (1)H NMR spectra are reported for 1-3 with assignment of the main resonances.

Interaction of ZnCl(2) with Hpko (Hpko, di-2-pyridyl-ketonoxime) results in the formation of a uninuclear Zn(Hpko)Cl(2) (1) compound or in a 12-membered tetranuclear metallacrown (OH)(2)[inv12-MC(Zn(II)N(pko))-4]Cl(2) (2) depending on the pH of the mother solution. The addition of H(3)shi (H(3)shi, salicylhydroxamic acid) leads to the formation of the octanuclear 12-membered tetranuclear metallacrown [Zn(2)]([Zn(2)(pko)(4)][12-MC(Zn(II)N(shi))-4](CH(3)OH)(2)) (3). The metallacrown core of 2 is characterized as "inverse" because the zinc atoms, rather than oxygen atoms, are oriented toward the central cavity. Two triply bridging hydroxides are accommodated in the center of the metallacrown ring. The pko(-) ligands form a propeller configuration that imposes absolute stereoisomerism with Lambda and Delta chirality. Each hydroxo oxygen bridges two octahedral zinc atoms and a tetrahedral one. The octanuclear cluster Zn(8)(shi)(4)(pko)(4)(CH(3)OH)(2) contains a 12-membered tetranuclear metallacrown core constructed by four Zn metal atoms and four shi(3-) ligands. So, a part of the cluster can be described as having the formally anionic [12-MC(Zn(II)N(shi))-4](4-) core. Two of the zinc atoms are in octahedral coordination environment while for the other two the geometry is best described as distorted trigonal bipyramidal. The metallacrown core accommodates a binuclear compound with the formula [Zn(2)(pko)(4)]. Two of the ring metal ions create binuclear units with two zinc ions, respectively, with two oxamato oxygens, and two phenolato oxygens, of the four interlinked shi(3-) ligands acting as bridging atoms.

Vanadium interactions with low molecular mass binders in biological fluids entail the existence of vanadium species with variable chemical and biological properties. In the course of efforts to elucidate the chemistry related to such interactions, we have explored the oxidative chemistry of vanadium(III) with the physiologically relevant tricarboxylic citric acid. Aqueous reactions involving VCl(3) and anhydrous citric acid, at pH approximately 7, resulted in blue solutions. Investigation into the nature of the species arising in those solutions revealed, through UV/visible and EPR spectroscopies, oxidation of vanadium(III) to vanadium(IV). Further addition of H(2)O(2) resulted in the oxidation of vanadium(IV) to vanadium(V), and the isolation of a new vanadium(V)-citrate complex in the form of its potassium salt. Analogous reactions with K(4)[V(2)O(2)(C(6)H(4)O(7))(2)].6H(2)O and H(2)O(2) or V(2)O(5) and citrate at pH approximately 5.5 afforded the same material. Elemental analysis pointed to the molecular formulation K(4)[V(2)O(4)(C(6)H(5)O(7))(2)].5.6H(2)O (1). Complex 1 was further characterized by FT-IR and X-ray crystallography. 1 crystallizes in the triclinic space group P(-)1, with a = 11.093(4) A, b = 9.186(3) A, c = 15.503(5) A, alpha = 78.60(1) degrees, beta = 86.16(1) degrees, gamma = 69.87(1) degrees, V = 1454.0(8) A(3), and Z = 2. The X-ray structure of 1 reveals the presence of a dinuclear vanadium(V)-citrate complex containing a V(V)(2)O(2) core. The citrate ligands are triply deprotonated, and as such they bind to vanadium(V) ions, thus generating a distorted trigonal bipyramidal geometry. Binding occurs through the central alkoxide and carboxylate groups, with the remaining two terminal carboxylates being uncoordinated. One of those carboxylates is protonated and contributes to hydrogen bond formation with the deprotonated terminal carboxylate of an adjacent molecule. Therefore, an extended network of hydrogen-bonded V(V)(2)O(2)-core-containing dimers is created in the lattice of 1. pH-dependent transformations of 1 in aqueous media suggest its involvement in a web of vanadium(V)-citrate dinuclear species, consistent with past solution speciation studies investigating biologically relevant forms of vanadium.

Cobalt is an essential metal ion involved in key biomolecules, regulating processes in human physiology. As a metal ion, Co(II) assumes forms, which are dictated by the nature of organic binders in biological fluids, and the conditions under which metal ion ligand interactions arise. Among the various low molecular mass metal ion binders in biological fluids are amino acids, organic acids, as well as their variably phosphorylated forms. As a representative metal ion binder, the organophosphonate ligand H(2)O(3)P-CH(2)-NH(2)(+)-CH(2)-PO(3)H(-) was employed in aqueous reactions with Co(II), ultimately leading to the isolation of complex [Co(C(2)H(8)O(6)NP(2))(2)(H(2)O)(2)] (1) at pH 2. The complex was characterized analytically, spectroscopically (FTIR, UV-vis, EPR), and magnetically. Compound 1 crystallizes in the monoclinic space group P2(1)/n, with a = 7.361(3) A, b = 8.133(3) A, c = 14.078(5) A, beta = 104.40(1) degrees, V = 816.3(5) A(3), and Z = 2. X-ray crystallography reveals that 1 is a compound with a molecular type of lattice. In it, there exist mononuclear octahedral sites of Co(II) surrounded by oxygens, belonging to terminal phosphonates and bound water molecules. Both ends of the ligand zwitterionic form are involved in binding to adjacent Co(II) ions, thus creating tetranuclear 32-membered rings, with cavities extending in two dimensions and holes in the third dimension throughout the lattice of 1. Similar structural features were observed in other metal organophosphonate lattices of potential catalytic and chemical reactivity. The magnetic and EPR data on 1 support the presence of a high-spin octahedral Co(II) in an oxygen environment, having a ground state with an effective spin S = (1)/(2). The solution UV-vis and EPR data suggest retention of the high-spin octahedral Co(II) ion, consistent with the magnetization measurements on 1. Collectively, the data reflect the existence of a soluble Co(II)-iminodiphosphonate species not unlike those expected in biological fluids containing the specific ligand or ligands similar to that. Both biologically relevant perspectives and a synthetic outlook into Co(II)-organophosphonate materials are discussed.

The synthetic route of partially beta-halogenated via a "metal-assisted" reaction and perhalogenated terbium complexes is described. This protocol allows the facile insertion of the halogens (bromines or chlorides) to the porphyrin peripheral positions. The electronic absorption spectra and the redox potentials of the free porphyrins as well as the terbium complexes are dramatically affected as the number of halogen atoms increase. In fact, two antagonistic effects are responsible for that, the inductive and the distortion effects on the porphyrin ring. They result in a red shift for the Soret band and a stabilization/destabilization of the HOMOs/LUMOs which in turn is manifested by variations on the redox potentials. The novel crystal structure of the Ni(Cl(8)TPP) is discussed in great detail and compared with the previously reported structures of Tb(Cl(8)TPP) (OAc)(DMSO)(2) x 3PhCH(3) x MeOH and H(2)(Br(8)TPP), as well as with other perhalogenated nickel porphyrins available in the literature.

Citrate is abundantly encountered in biological fluids as a natural metal ion chelator. Vanadium participates in biological processes as a catalyst in the active sites of metalloenzymes, as a metabolic regulator, as a mitogenic activator, and as an insulin-mimicking agent. Thus, vanadium chemistry with natural chelators, such as citrate, may have immediate implications on its role in a cellular milieu, and its action as a biological agent. In an effort to comprehend the aqueous chemistry of one of vanadium's oxidation states, namely, V(IV), implicated in its biological activity, reactions of VCl(3) and citric acid were pursued in water and led to V(IV)-citrate complexes, the nature and properties of which depend strongly on the solution pH. Analytical, FT-IR, UV/vis, EPR, and magnetic susceptibility data supported the formulation of X(4)[[VO(H(-1)Cit)](2)] x nH(2)O (H(-1)Cit = C(6)H(4)O(7)(4-); X = K(+), n = 6 (1); X = Na(+), n = 12 (2); X = NH(4)(+), n = 2 (3)) (pH approximately 8) and X(3)[[V(2)O(2)(H(-1)Cit)(Cit)]] x nH(2)O (X = K(+), n = 7 (4)) (pH approximately 5). Complex 2 crystallizes in space group P2(1)/c, a = 11.3335(9) A, b = 15.788(1) A, c = 8.6960(6) A, beta = 104.874(3) degrees, V = 1503.8(2), Z = 2. Complex 3 crystallizes in space group P one macro, a = 9.405(1) A, b = 10.007(1) A, c = 13.983(2) A, alpha = 76.358(4) degrees, beta = 84.056(4) degrees, gamma = 66.102(4) degrees, V = 1169.2(3), Z = 2. Complex 4 crystallizes in space group P2(1)nb, a = 9.679(4) A, b = 19.618(8) A, c = 28.30(1) A, V = 5374.0(4), Z = 8. The X-ray structures of 1-4 are V(2)O(2) dimers, with the citrate displaying varying coordination numbers and modes. 1 exhibits a small ferromagnetic interaction, whereas 4 exhibits an antiferromagnetic interaction between the V(IV) ions. 1 and 4 interconvert with pH, thus rendering the pH a determining factor promoting variable structural, electronic, and magnetic properties in V(IV)-citrate species. The observed aqueous behavior of 1-4 is consistent with past solution speciation studies, and contributes to the understanding of significant aspects of the biologically relevant vanadium(IV)-citrate chemistry.

Two novel 99mTc-(SNS/S) complexes: a mono-ester compound carrying an ethyl ester group on the tridentate ligand, 99mTcO[C(2)H(5)OOCCH(2)N(CH(2)CH(2)S)(2)][SC(6)H(4)CH(3)], 3, and a diester compound, carrying a second ethyl ester group on the monodentate ligand, 99mTcO[C(2)H(5)OOCCH(2)N(CH(2)CH(2)S)(2)][SC(6)H(4)COOC(2)H(5)], 4, were synthesized. The corresponding oxorhenium(V) complexes, 1 and 2 were also synthesized. Enzymatic hydrolysis demonstrated that 3 remains intact after 10 min incubation while 4 is totally converted to an unidentified hydrophilic complex. Tissue distribution data in mice revealed that both complexes, 3 and 4, exhibit significant initial brain uptake (1.42 and 1.01% of injected dose at 5 minutes post injection respectively) and fast blood clearance.

The simultaneous action of a bidentate aminothiol ligand, LnH, (n = 1: (CH3CH2)2NCH2CH2SH and n = 2: C5H10NCH2CH2SH) and a monodentate thiol ligand, LH (LH: p-methoxythiophenol) on a suitable MO (M = Re, 99gTc) precursor results in the formation of complexes of the general formula [MO(Ln)(L)3] (1, 2 for Re and 5. 6 for 99gTc). In solution these complexes gradually transform to [MO(Ln)(L)2] complexes (3, 4 for Re and 7, 8 for 99gTc). The transformation is much faster for oxotechnetium than for oxorhenium complexes. Complexes 1-4, 7, and 8 have been isolated and fully characterized by elemental analysis and spectroscopic methods. Detailed NMR assignments were made for complexes 3, 4, 7, and 8. X-ray studies have demonstrated that the coordination geometry around rhenium in complex 1 is square pyramidal (tau = 0.06), with four sulfur atoms (one from the L1H ligand and three from three molecules of p-methoxythiophenol) in the basal plane and the oxo group in the apical position. The L1H ligand acts as a monodentate ligand with the nitrogen atom being protonated and hydrogen bonded to the oxo group. The four thiols are deprotonated during complexation resulting in a complex with an overall charge of zero. The coordination geometry around rhenium in complex 4 is trigonally distorted square pyramidal (tau = 0.41), while in the oxotechnetium complex 7 it is square pyramidal (tau = 0.16). In both complexes LnH acts as a bidentate ligand. The NS donor atom set of the bidentate ligand and the two sulfur atoms of the two monodentate thiols define the basal plane, while the oxygen atom occupies the apical position. At the technetium tracer level (99mTc), both types of complexes, [99mTcO(Ln)(L)3] and [99mTcO(Ln)(L)2], are formed as indicated by HPLC. At high ligand concentrations the major complex is [99mTcO(Ln)(L)3], while at low concentrations the predominant complex is [99mTcO(Ln)(L)2]. The complexes [99mTcO(Ln)(L)3] transform to the stable complexes [99mTcO(Ln)(L)2]. This transformation is much faster in the absence of ligands. The complexes [99mTcO(Ln)(L)2] are stable, neutral, and also the predominant product of the reaction when low concentrations of ligands are used, a fact that is very important from the radiopharmaceutical point of view.

The controlled cleavage of coordination polymers consisting of well-defined large units can be employed for the rational synthesis of high nuclearity clusters. This synthetic concept is demonstrated by the conversion (schematically shown) of a three-dimensional Zn II coordination polymer containing repeating hexameric units with a "twin-anchor" arrangement of the metal ions into the corresponding hexanuclear cluster by reaction with a donor solvent., (© 2001 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)

Two oxorhenium and two oxotechnetium [SN(R)S/S] mixed ligand complexes bearing the phenothiazine moiety on the tridentate ligand SN(R)S have been synthesized and characterized. The corresponding complexes at tracer level (99mTc) have also been prepared.

The established biochemical potential of vanadium has spurred considerable research interest in our lab, with specific focus on pertinent synthetic studies of vanadium(III) with a biologically relevant, organic, dicarboxylic acid, malic acid, in aqueous solutions. Simple reactions between VCl3 and malic acid in water, at different pH values, in the presence of H2O2, led to the crystalline dimeric complexes (Cat)4[VO(O2)(C4H3O5)]2*nH2O (Cat = K+, n = 4, 1; Cat = NH4+, n = 3, 2) and K2[VO(O2)(C4H4O5)]2*2H2O (3). All three complexes were characterized by elemental analysis, FT-IR, and UV/visible spectroscopies. Compound 1 crystallizes in the monoclinic space group P2(1)/c, with a = 8.380(5) A, b = 9.252(5) A, c = 13.714(8) A, beta = 93.60(2) degrees, V = 1061(1) A3, and Z = 4. Compound 2 crystallizes in the triclinic space group P1, with a = 9.158(4) A, b = 9.669(4) A, c = 14.185(6) A, alpha = 104.81(1) degrees, beta = 90.31(1) degrees, gamma = 115.643(13) degrees, V = 1085.0(7) A(3), and Z = 2. Compound 3 crystallizes in the monoclinic space group P2(1)/c, with a = 9.123(8) A, b = 9.439(8) A, c = 10.640(9) A, beta = 104.58(3) degrees, V = 887(1) A3, and Z = 2. The X-ray structures showed that, in 1 and 2, the dimers consist of two (V(V)=O)2O2 rhombic units to which two malate ligands are attached. The ligands are triply deprotonated and, as such, they coordinate to vanadium(V), promoting a pentagonal bipyramidal geometry. In 3, the dimeric (V(V)=O)2O2 rhombic unit persists, with the two doubly deprotonated malate ligands coordinated to the vanadium(V) ions. UV/vis and EPR spectroscopic studies on the intermediate blue solutions of the synthesis reactions of 1-3 support the existence of vanadyl-containing dimeric species. These species further react with H2O2 to yield oxidation of V(IV)2O2 to V(V)2O2 and coordination of the peroxide to vanadium(V). From the collective data on 1-3, it appears that pH acts as a decisive factor in dictating the structural features of the isolated complexes. The details of the introduced structural differentiation in the reported complexes, and their potential relevance to vanadium(V) dicarboxylate systems in biological media are dwelled on.

Two series of octahedral oxovanadium(IV) compounds, containing charged or neutral axial ligands, with the tetradentate amidate molecules Hcapca and H2capcah of the general formulae trans-[V(IV)OX(capca)]0/+ (where X = Cl- (1.CH2Cl2), SCN- (2), N3 (3), CH3COO- (4), PhCOO- (5), imidazole (6. CH3NO2), and eta-nBuNH2 (7)) and cis-[V(VI)OX(Hcapcah)]0/+ (where X = Cl- (8.0.5CH2Cl2), SCN (9), N3 (10.2CH3OH), and imidazole (11)), were synthesized and characterized by X-ray crystallography (1.CH3OH,8.CHCl3, 9.2CH3CN, 10.CH3CN and cis-[VO(imidazole)(Hcapcah)+) and continuous-wave electron paramagnetic resonance (cw EPR) spectroscopy. In addition to the synthesis, crystallographic and EPR studies, the optical, infrared and magnetic properties (room temperature) of these compounds are reported. Ab initio calculations were also carried out on compound 8 CHCl3 and revealed that this isomer is more stable than the trans isomer, in good agreement with the experimental data. The cw EPR studies of compounds 1-5, that is, the V(IV)O2+ species containing monoanionic axial ligands, revealed a novel phenomenon of the reduction of their A, components by about 10% relative to the N4 reference compounds ([V(IV)O-(imidazole)4]2+ and [V(IV)O(2,2-bipyridine)2]2+). In marked contrast, such a reduction is not observed in compounds 6. CH3NO2-11, which contain neutral axial ligands. Based on the spin-Hamiltonian formalism a theoretical explanation is put forward according to which the observed reduction of Az is due to a reduction of the electron - nuclear dipolar coupling (P). The present findings bear strong relevance to cw EPR studies of oxovanadium(IV) in vanadoproteins, V(IV)O2+-substituted proteins, and in V(IV)O2+ model compounds, since the hyperfine coupling constant, Az, has been extensively used as a benchmark for identification of equatorial-donor-atom sets in oxovanadium(IV) complexes.

Reactions of Al(III) and Ga(III) with citric acid in aqueous solutions, yielded the complexes (NH(4))(5)[M(C(6)H(4)O(7))(2)].2H(2)O (M(III) = Al (1), Ga (2)) at alkaline pH, and the complexes (Cat)(4)[M(C(6)H(5)O(7))(C(6)H(4)O(7))].nH(2)O (M(III) = Al (3), Ga (4), Cat. = NH(4)(+), n = 3; M(III) = Al (5), Ga (6), Cat. = K(+), n = 4) at acidic pH. All compounds were characterized by spectroscopic (FT-IR, (1)H, (13)C, and (27)Al NMR, (13)C-MAS NMR) and X-ray techniques. Complex 1 crystallizes in space group P1, with a = 9.638(5) A, b = 9.715(5) A, c = 7.237(4) A, alpha = 90.96(1) degrees, beta = 105.72(1) degrees, gamma = 119.74(1) degrees, V = 557.1(3) A(3), and Z = 1. Complex 2 crystallizes in space group P1, with a = 9.659(6) A, b = 9.762(7) A, c = 7.258(5) A, alpha = 90.95(2) degrees, beta = 105.86(2) degrees, gamma = 119.28(1) degrees, V = 564.9(7) A(3), and Z = 1. Complex 3 crystallizes in space group I2/a, with a = 19.347(3) A, b = 9.857(1) A, c = 23.412(4) A, beta = 100.549(5) degrees, V = 4389(1) A(3), and Z = 8. Complex 4 crystallizes in space group I2/a, with a = 19.275(1) A, b = 9.9697(6) A, c = 23.476(1) A, beta = 100.694(2) degrees, V = 4432.8(5) A(3), and Z = 8. Complex 5 crystallizes in space group P1, with a = 7.316(1) A, b = 9.454(2) A, c = 9.569(2) A, alpha = 64.218(4) degrees, beta = 69.872(3) degrees, gamma = 69.985(4) degrees, V = 544.9(2) A(3), and Z = 1. Complex 6 crystallizes in space group P1, with a = 7.3242(2) A, b = 9.4363(5) A, c = 9.6435(5) A, alpha = 63.751(2) degrees, beta = 70.091(2) degrees, gamma = 69.941(2) degrees, V = 547.22(4) A(3), and Z = 1. The crystal structures of 1-6 reveal mononuclear octahedral complexes of Al(III) (or Ga(III)) bound to two citrates. Solution NMR, on both 4- and 5- species, reveals rapid intramolecular exchange of the bound and unbound terminal carboxylates. Upon dissolution in water, the complexes, through a complicated reaction cascade, transform to oligonuclear 1:1 species that, in agreement with previous studies, represent the thermodynamically stable state in solution. The data provide, for the first time, structural details of low MW, mononuclear complexes of Al(III) (or Ga(III)) with citrate that are dictated, among other factors, by pH. The properties of 1-6 may provide clues relevant to their biological association with humans.

The "3 + 1" ligand system [SN(R)S/S combination] was applied in order to synthesize neutral mixed-ligand oxotechnetium complexes of the general formula 99mTcO[SN(R)S]/[S] as potential 5-HT1A receptor imaging agents. The complexes are carrying the 1-(2-methoxyphenyl)piperazine moiety, a fragment of the true 5-HT1A antagonist WAY 100635, either on the monodentate ligand [S] or on the tridentate ligand [SN(R)S]. The complexes MO[EtN(CH2CH2S)2] [o-MeOC6H4N(CH2CH2)2NCH2CH2S] (3), MO[o- MeOC6H4N(CH2CH2)2N(CH2)3N(CH2CH2S)2][PhS] (6) and MO[o-MeOC6H4N(CH2CH2)2N(CH2)3N(CH2CH2S)2] [PhCH2CH2S] (9), where M = 99mTc, were prepared at tracer level using 99mTc glucoheptonate as precursor. For structural characterization, the analogous oxorhenium (M = Re, 1, 4 and 7, respectively) and oxotechnetium (M = 99gTc, 2, 5 and 8, respectively) complexes were prepared by ligand exchange reactions. All products were characterized by elemental analysis and spectroscopic methods. Complexes 1, 4 and 7 were further characterized by crystallographic analysis. For 1, the coordination geometry about rhenium can be described as trigonally distorted square pyramidal (tau = 0.36), while for 4 and 7, as distorted trigonal bipyramidal (tau = 0.66 and tau = 0.61, respectively). The coordination sphere about oxorhenium in all complexes is defined by the SNS donor atom set of the tridentate ligand and the sulfur atom of the monodentate coligand. The structure of the 99mTc complexes 3, 6 and 9 was established by comparative HPLC using authentic oxorhenium and oxotechnetium samples. The binding affinity of oxorhenium compounds for the 5-HT1A receptor subtype was determined in rat brain hippocampal preparations (IC50 = 6-31 nM). Preliminary tissue distribution data in healthy mice revealed the ability of all three 99mTc complexes to cross the intact blood-brain barrier (0.49-1.15% ID at 1 min p.i.). In addition, complexes 6 and 9 showed significant brain retention. These promising results have demonstrated that the SNS/S mixed-ligand system can be used in the development of 99mTc complexes as potential 5-HT1A receptor imaging agents.

The copper complexes with the phenoxyalkanoic acids MCPA, 2,4-D, 2,4,5-T and 2,4-DP in the presence of a nitrogen donor heterocyclic ligand, phen or bipyam, were prepared and characterized. Interaction of Cu(II) with phenoxyalkanoic acids and bipyam leads to dinuclear or uninuclear neutral complexes while in the presence of phen uninuclear neutral or cationic forms have been isolated. The crystal structure of bis(1,10-phenanthroline)(2-methyl-4-chloro-phenoxyacetato)copper(ll) chloride-methanol(1/1)-water(1/0.6), 1 has been determined and refined by least-squares methods using three-dimensional MoK, data. 1 crystallizes in space group P1, in a cell of dimensions a = 14.577(6)A, b = 1 1.665(5) A, c = 12.249(6) A, alpha = 98.38( 1)degrees, beta = 112.18( 1) degrees, gamma = 104.56(1 ) degrees, V= 1,798( 1) A3 and Z= 2. The cyclic voltammograms of uninuclear cationic complexes in dmf exhibit an extra cathodic wave due to the chloride ion. The available evidence supports an increasing antimicrobial effeciency for the cationic complexes.

The synthesis and characterization of a series of mixed-ligand oxorhenium(V) complexes containing the o-diphenylphosphinophenolato ligand (HL) and model peptide fragments acting as the tridentate coligand are reported. Thus, by reacting equimolar amounts of tiopronin, Gly-Gly, Gly-L-Phe, or glutathione (GSH) peptides on the [(n-C4H9)4N][ReOCl3(L)] precursor in refluxing MeCN/MeOH or aqueous MeCN/MeOH mixtures, the following complexes were obtained: ReO([SC(CH3)CONCH2COO][L])[(n-C4H9)4N], 1, ReO([H2NCH2CONCH2COO][L]), 2, ReO)[H2NCH2CONCH(CH2C6H5)COO][L]), 3, and ReO([SCH2CH(NHCOCH2CH2CHNH2COOH)CONCH2COO][L])Na, 4. The compounds are closed-shell 18-electron oxorhenium species adopting a distorted octahedral geometry, as demonstrated by classical spectroscopical methods including multinuclear NMR. X-ray diffraction analyses for 1 and 2 are also reported. By comparative stability studies of complexes 1-3 against excess GSH it was shown that complex 3 containing the bulky C6H5CH2 substituent adjacent to the coordinated carboxylate group of Phe is the most stable complex.

A new series of mixed-ligand oxorhenium complexes 4-9, with ligands 1-3 (L1H2) containing the SNN donor set and monodentate thiols as coligands (L2H), is reported. All complexes were synthesized using ReOCl3(PPh3)2 as precursor. They were isolated as crystalline products and characterized by elemental analysis and IR and NMR spectroscopy. The ligands 1 and 2 (general formula RCH2CH2NHCH2CH2SH, where R = N(C2H5)2 in 1 and pyrrolidin-1-yl in 2) act as tridentate SNN chelates to the ReO3+ core, leaving one open coordination site cis to the oxo group. The fourth coordination site is occupied by a monodentate aromatic thiol which acts as a coligand. Thus, three new "3 + 1" [SNN][S] oxorhenium complexes 4-6 (general formula ReO[RCH2CH2NCH2CH2S][SX], where R = N(C2H5)2 and X = phenyl in 4, R = N(C2H5)2 and X = p-methylphenyl in 5, and R = pyrrolidinlyl and X = p-methylphenyl in 6) were prepared in high yield. Complex 4 adopts an almost perfect square pyramidal geometry (tau = 0.07), while 6 forms a distorted square pyramidal geometry (tau = 0.24). In both complexes 4 and 6, the basal plane is formed by the SNN donor set of the tridentate ligand and the S of the monodentate thiol. On the other hand, the ligand 3, [(CH3)2CH]2NCH2CH2NHCH2CH2SH, acts as a bidentate ligand, probably due to steric hindrance, and it coordinates to the ReO3+ core through the SN atoms, leaving two open coordination sites cis to the oxo group. These two vacant positions are occupied by two molecules of the monodentate thiol coligand, producing a novel type of "2 + 1 + 1" [SN][S][S] oxorhenium mixed-ligand complexes 7-9 (general formula ReO[[(CH3)2CH]2NCH2CH2NHCH2CH2S][SX][SX], where X = phenyl in 7, p-methylphenyl in 8, and benzyl in 9). The coordination sphere about rhenium in 7 and 8 consists of the SN donor set of ligand 3, two sulfurs of the two monodentate thiols, and the doubly bonded oxygen atom in a trigonally distorted square pyramidal geometry (tau = 0.44 and 0.45 for 7 and 8, respectively). Detailed NMR assignments were determined for complexes 5 and 8.

The first two mononuclear manganese citrate complexes, (NH4)4[MnII(C6H5O7)2] (1) and (NH4)5[MnIII(C6H4O7)2].2H2O (2) were synthesized in aqueous solutions near physiological pH values. They were isolated in their pure crystalline forms and characterized by elemental analyses and spectroscopic techniques, including UV/visible, electron paramagnetic resonance, Fourier transformed infrared, and magnetic susceptibility measurements. Compound 1 crystallizes in the monoclinic space group P2(1)/c, with a = 8.777(1) A, b = 13.656(3) A, c = 9.162(2) A, beta = 113.62(2) degrees, V = 1006.2(6) A3, and Z = 2. Compound 2 crystallizes in the triclinic space group P1, with a = 9.606(3) A, b = 9.914(3) A, c = 7.247(3) A, alpha = 91.05(1) degrees, beta = 105.60(1) degrees, gamma = 119.16(1) degrees, V = 571.3(3) A3, and Z = 1. The X-ray crystal structures of 1 and 2 revealed that, in both cases, the manganese ion is six-coordinate and is bound by two citrate ligands in a distorted octahedral fashion. In the case of complex 1, the citrate ion binds to Mn2+ as a triply deprotonated ligand, retaining the central carbon hydroxyl hydrogen, whereas, in the case of compound 2, the citrate ligand coordinates to Mn3+ as a fully deprotonated entity. Compound 2 contains water molecules of crystallization in the unit cell which, through extensive hydrogen-bonding interactions, bestow considerable stability upon the Mn(3+)-citrate assembly. There are significant contributions to the stabilities of the assembled lattices in 1 and 2 arising from the ammonium counterions neutralizing the high anionic charges of the complexes. The EPR spectra attest to the presence of paramagnetic Mn2+ and Mn3+ species in the solid state. Corroborative evidence is obtained from the magnetic susceptibility measurements in the range 5-300 K. Complexes 1 and 2 present clear cases of mononuclear manganese citrate species relevant to manganese speciation in biological media and potentially related to the beneficial as well as toxic effects of manganese on humans.

Citric acid represents a class of carboxylic acids present in biological fluids and playing key roles in biochemical processes in bacteria and humans. Its ability to promote diverse coordination chemistries in aqueous media, in the presence of metal ions known to act as trace elements in human metabolism, earmarks its involvement in a number of physiological functions. Cobalt is known to be a central element of metabolically important biomolecules, such as B12, and therefore its biospeciation in biological fluids constitutes a theme worthy of chemical and biological perusal. In an effort to unravel the aqueous chemistry of cobalt in the presence of a physiologically relevant ligand, citrate, the first aqueous, soluble, mononuclear complex has been synthesized and isolated from reaction mixtures containing Co(II) and citrate in a 1:2 molar ratio at pH approximately 8. The crystalline compound (NH4)4[Co(C6H5O7)2] (1) has been characterized spectroscopically (UV/vis, EPR) and crystallographically. Its X-ray structure consists of a distorted octahedral anion with two citrate ligands fulfilling the coordination requirements of the Co(II) ion. The magnetic susceptibility measurements of 1 in the range from 6 to 295 K are consistent with a high-spin complex containing Co(II) with a ground state S=3/2. Corroborating this result is the EPR spectrum of 1, which shows a signal consistent with the presence of a Co(II) system. The spectroscopic and structural properties of the complex signify its potential biological relevance and participation in speciation patterns arising under conditions consistent with those employed for its synthesis and isolation.

Novel vanadium(III) and oxovanadium(IV) compounds with the diamidate ligand 1,2-bis(2-pyridinecarboxamide)benzene (H2bpb) were synthesized and structurally characterized. H2bpb is capable of binding to vanadium in either its anionic (dianionic-monoanionic) or its neutral form, resulting in complexes of various geometries and stoichiometries. The dianionic form (bpb2-), in NHEt3(trans-[VCl2(bpb)]) (1) and [VO(bpb)(H2O)]05dmso036CH3OH013H2O (6x05dmsox036CH3OHx013H2O), acts as a planar tetradentate bis[N-amidate-N-pyridine] equatorial ligand. The monoanionic form (Hbpb-) behaves as an (Npy,Oam) or (Npy,Nam) chelator in [V(Hbpb)3]2CHCl3 (22CHCl3) as well as a mu 2-bridging-eta 4-(Npy,Oam-Npy,Nam) in [VOCl(Hbpb)](2)x2CH3NO2 (3x2CH3NO2), while the neutral H2bpb behaves as a mu 2-bridging-eta 4-bis(Npy,Oam) in [VOCl(H2bpb)](2)x104CH3OHx123thfx074H2O (4x104CH3OH123thf074H2O). Compound 4x104CH3OHx123thfx074H2O crystallizes in the triclinic system P1, with (at 25 degrees C) a = 9140(2) A, b = 11058(2) A, c = 14175(2) A, alpha = 99013(5) degrees, beta = 104728(7) degrees, gamma = 102992(7) degrees, V = 13149(4) A3, Z = 1, while compound 605dmso036CH3OH013H2O crystallizes in the monoclinic space group P2(1)/n with (at 25 degrees C) a = 11054(5) A, b = 11407(5) A, c = 16964(7) A, beta = 932(1) degrees, V = 2136(2) A3, Z = 4. Variable temperature magnetic susceptibility studies of the dimeric compounds 3x2CH3NO2 and 4x104CH3OH show g values for the V(IV) centers that are slightly smaller than 20 (as expected for d1 ions) and indicate small antiferromagnetic coupling between the two vanadium(IV) centers. Ab initio calculations were also carried out, providing results concerning the effect of the relative strength and the deformation energy involved in the eta 2-(Npy,Nam) and eta 2-(Npy,Oam) bonding modes in the ligation of Hbpb- to vanadium.

The copper complexes with the commercial auxin herbicides MCPA, 2,4-D, and 2,4,5-T in the presence of a nitrogen donor heterocyclic ligand, phen or bipyam, were prepared and characterized. The available evidence supports a dimeric structure for the 2,4-D complex in the presence of bipyam while phen leads to monomeric forms. The EPR spectrum of Cu2(2,4-D)4(bipyam)2 at 4 K in the solid state exhibits an axial signal which corresponds to almost isolated S = 1/2 magnetic ions. Magnetic data for the dimer show a weak antiferromagnetic interaction between the two metal ions with J = -08 cm-1. The crystal structures of tetrakis[(2,4-dichlorophenoxy)acetato]bis(2,2'-bipyridylamine)dicopper(II), 1, bis(1,10-phenanthroline)[(2,4,5-trichlorophenoxy)acetato]copper(II) chloride, 2, and aqua(1,10-phenanthroline)bis[((2-methyl-4-chlorophenoxyacetato]copper(II), 3, were determined and refined by least-squares methods using three-dimensional MoK alpha data. 1 crystallizes in space group P1, in a cell of dimensions a = 10813(1) A, b = 12138(1) A, c = 11909(1) A, alpha = 86448(3) degrees, beta = 80127(3) degrees, and gamma = 63982(3) degrees, and V = 13837(2) A3, with Z = 1 2 crystallizes in space group I2/a, in a cell of dimensions a = 29958(9) A, b = 11342(3) A, c = 21196(7) A, beta = 10794(1) degrees, and V = 68522(4) A3, with Z = 8 3 crystallizes in space group P1, in a cell of dimensions a = 87419(8) A, b = 12512(1) A, c = 14598(1) A, alpha = 110737(1) degrees, beta = 95742(2) degrees, gamma = 103286(2) degrees, V = 14241(2) A3, with Z = 2.

A mixed-valence Mn(III)-Mn(II)-Mn(III) trinuclear complex of stoichiometry MnIIIMnIIMnIII(Hsaladhp)2(Sal)4.2CH3CN (1), where H3saladhp is a tridentate Schiff-base ligand, has been structurally characterized with X-ray crystallography. The Mn(III)Mn(II)Mn(III) angles are strictly 180 degrees as required by crystallographic inversion symmetry. The complex is valence-trapped with two terminal Mn(III) ions in a distorted square pyramidal geometry. The Mn(III)...Mn(II) separation is 3.495 A. The trinuclear complex shows small antiferromagnetic exchange J coupling. The magnetic parameters obtained from the fitting procedure in the temperature range 10-300 K are J1 = -5.7 cm-1, g = 2.02, zJ = -0.19 cm-1, and R = 0.004. The EPR spectrum was obtained at 4 K in CHCl3 and in tetrahydrofuran glasses. The low-field EPR signal is a superposition of two signals, one centered around g = 3.6 and the other, for which hyperfine structure is observed, centered around g = 4.1 indicating an S = 3/2 state. In addition, there is a 19-line signal at g = 2.0. The multiline signal compares well with that observed for the S2 or S0* states of the oxygen-evolving complex. 1H NMR data reveal that the trinuclear compound keeps its integrity into the CHCl3 solution. Crystal data for complex 1: [C54H52N4O18Mn3], M = 1209.82, triclinic, space group P1, a = 10.367(6) A, b = 11.369(6) A, c = 13.967(8) A; alpha = 112.56(1) degree, beta = 93.42(2) degrees, gamma = 115.43(1) degree, Z = 1.

The use of the substituted benzotriazole ligand btaOH (1-hydroxybenzotriazole) in copper(II) chemistry has yielded a structurally and magnetically very interesting complex. The [Cu2(O2CMe)4(H2O)2]/btaOH.H2O/aqueous NH3 (1:4:4, 1:3:3, 1:2:2) reaction system in MeOH gives dark brown-green [Cu(btaO)2(MeOH)]n (4) in approximately 80% yield. 4 crystallizes in the tetragonal space group P4(3)2(1)2 with (at 25 degrees C) a = 9.915(1) A, b = 9.915(1) A, c = 14.715(2) A, and Z = 4. The structure consists of a 3D, diamond-like copper(II) lattice. The CuII atom has a square pyramidal geometry with four btaO- ligands at the basal plane. The btaO- ion functions as a bidentate bridging ligand, with N(3) and the deprotonated oxygen being the ligating atoms. Dc and ac magnetic susceptibility measurements, together with low-field (10 G) and high-field (up to 5000 G) magnetization data, are consistent with ferromagnetic interactions on the scale of the crystal lattice with two critical temperatures: 6.4 and 4.4 K. The former critical temperature could correspond to a transition from a paramagnetic to a ferromagnetic state; the latter one, to a transition from a ferromagnetically ordered state to its 3D ordering. The magnetic data, along with the field dependence of the magnetization and the EPR data, are also in line with a soft magnet. Moreover, the EPR studies performed on 4 reveal unique features reported for the first time in the field of molecular magnetism.

A series of octahedral six-coordinate oxorhenium(V) mixed ligand complexes containing the common [ReO(L)]2+ fragment (L = o-OC6H4P(C6H5)2] have been synthesized and characterized. Hence, it was shown that the [ReO(L)]2+ moiety can accommodate a variety of tridentate ligands containing a central amine group amenable to deprotonation and different combinations of lateral groups, such as ethylamine, substituted ethylamine, ethylthiol, and ethylthioether arms. In particular, by reaction of equimolar amounts of the pertinent HLn ligands with the [(n-C4H9)4N][ReOCl3(L)] precursor in refluxing acetonitrile/methanol or dichloromethane/methanol mixtures, the following series of [ReO(Ln)(L)]+/0 oxorhenium(V) complexes has been generated: ReO[[N(CH2CH2NH2)2][o-OC6H4P(C6H5)2]]Cl (1); ReO[[C2H5)2NCH2CH2NCH2CH2S][o-OC6H4P5)2]] (2); ReO[[(CH2)4NCH2CH2NCH2CH2S][o-OC6H4P(C6H4P(C6H5)2]] (3); and ReO[[C2H5SCH2CH2NCH2CH2S][o-OC6H4P(C6H5)2]] (4). The complexes are closed-shell 18-electron oxorhenium species, which adopt octahedral geometries both in solution and in the solid state, as established by conventional physicochemical techniques including multinuclear NMR and single-crystal X-ray diffraction analyses.

The synthesis, spectroscopic characterization, and electrochemical study of eleven heteroleptic and their corresponding homoleptic lanthanide sandwiches are reported. Studies in solution have been carried out in solvents of different basicity, in order to elucidate the equilibrium between the protonated and deprotonated form of these complexes. The investigated compounds are represented by the formulas Ln(III)H(oep)(tpp) and [Ln(III)(oep)(tpp)](-) corresponding to the protonated and deprotonated forms, respectively (in the case of heteroleptic), and the formulas Ln(III)H(tpp)(2) and [Ln(III)(tpp)(2)](-) (in the case of the homoleptic porphyrin double-deckers), where Ln Nd,., Lu (except Pm), oep = 2,3,7,8,12,13,17,18-octaethylporphyrinate, and tpp = 5,10,15,20-tetraphenylporphyrinate). Various spectroscopic methods are used for the physicochemical characterization of the title complexes. The electronic spectra of the complexes above present different features in CH(2)Cl(2) and in DMF. In the latter solvent they reveal features similar to those of the analogous actinide(IV) porphyrin double-decker. The electrochemical studies carried out in CH(2)Cl(2) and THF demonstrate clearly that the redox behavior of the double-deckers, heteroleptic or homoleptic, is strongly dependent on the proton on the porphyrinic core. In CH(2)Cl(2), four reversible oxidation processes and two quasi-reversible waves are observed for the protonated species in both homo- and heteroleptic double-deckers. In contrast, two oxidations and two reductions are observed in THF for the homoleptic derivatives, while the corresponding heteroleptic ones undergo three oxidations and one reduction process. The structure of the new heteroleptic double-decker Gd(III)H(oep)(tpp) was determined by X-ray diffraction at 298 and 21 K. Both structures are compared with the first analogous structure of Sm(III)H(oep)(tpp). According to the spectroscopic and structural data reported for the heteroleptic protonated derivatives, the oep macrocycle is the favored binding site of the proton in solutions as well as in the solid state.

A vertex-sharing double square pyramid of cobalt(II) ions (see picture) is present in the nonanuclear complex 1, obtained by treating cobalt acetate with 0.5 equivalents of (py 2 )CO. The corresponding 1:1 reaction gave 2, which has a central core with a cubane structure. py=pyridine., (© 1999 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)

A series of vanadium(III) and oxovanadium(IV/V) compounds with the ligands, N-(2-nitrophenyl)pyridine-2-carboxamide (Hpycan), N-(phenyl)pyridine-2-carboxamide (Hpheca), and N-(2-pyridyl)acetamide (Hpyra), containing the amide functionality, was prepared and characterized both in solution and in solid state. All vanadium compounds contain a vanadium-amide oxygen bond. Crystal data for [VOCl(2)(OC(2)H(5))(Hpheca)] (4) are monoclinic; P2(1)/a; a = 12.668(5) Å, b = 8.084(3) Å, c = 17.222(6) Å, alpha = 108.148(12) degrees; Z = 4. In addition to the synthesis and crystallographic studies, the optical, infrared, and magnetic properties of these compounds are reported. Electron paramagnetic resonance [of oxovanadium(IV) species] and (1)H, (13)C{(1)H}, and (51)V nuclear magnetic resonance [of oxovanadium(V) compounds] properties are reported as well.

Complexes of Zn(II), Cd(II) and Pt(II) metal ions with the anti-inflammatory drugs, 1-methyl-5-(p-toluoyl)-1H-pyrrole-2-acetic acid (Tolmetin), alpha-methyl-4-(2-methylpropyl)benzeneacetic acid (Ibuprofen), 6-methoxy-alpha-methylnaphthalene-2-acetic acid (Naproxen) and 1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-acetic acid (indomethacin) have been synthesized and characterized. In the structurally characterized Cd(naproxen)2 complex the anti-inflammatory drugs acts as bidentate chelate ligand coordinatively bound to metal ions through the deprotonated carboxylate group. Crystal data for 1: [C32H26O8Cd], orthorhombic, space group P22(1)2(1), a = 5.693(2) (A), b = 8.760(3) (A), c = 30.74(1) (A), V = 1533(1) A3, Z = 2. Antibacterial and growth inhibitory activity is higher than that of the parent ligands or the platinum(II) diamine compounds.

The preparation, characterization and antitumour properties of the complex [Cu(O2CMe)2L2] (1), where L = 1-methyl-4,5-diphenylimidazole, are described. The crystal structure of 1 (triclinic, space group P1, a = 6.743(1), b = 8.006(1), c = 15.898(1) A, alpha = 102.87(1), beta = 101.10(1), gamma = 76.76(1) degree, Z = 1) has been determined (R = 0.0254, Rw = 0.0275). In the centrosymmetric complex the copper ion is in an essentially square planar environment consisting of two pyridine-type imidazole nitrogen atoms and an oxygen atom from each acetate ligand; the second oxygen atoms of the carboxylate functionalities are involved in weak interactions with the metal completing the coordination to a very distorted tetragonal bipyramid. Complex 1 has been also characterized by elemental analyses, thermal methods, variable-temperature magnetic susceptibility and spectroscopic (IR and far-IR, FT-Raman, UV/VIS, EPR) techniques. The effect of the complex on the in vitro DNA strand breakage was examined. It was found that 1 causes degradation on the linearized pKS DNA, ds and ss DNA. High concentrations of this Cu(II) complex cause scissions on the relaxed and the supercoiled DNA. Furthermore, the in vivo cytogenic effect of 1 was examined on human lymphocyte cells. This study presents indications that 1 could have some relevance in the treatment of tumour cell lines. An orbital interpretation of the interaction of 1 with the DNA bases is proposed.

Regio- and site-selective Diels-Alder reactions of o-quinone monooxime 1 are reported. The electron rich dienophiles 2, 4, 6, 8, and 10 react with the exocyclic diene system of monooxime 1 leading to the coumarin derivatives 3, 5, 7, 9, 11, and 12. The electron deficient dienophiles 13a,b and 18 react with the quinoid and the pyrone diene systems of compound 1 affording the cycloadducts 14a,b, 17a,b, and 19.

The simultaneous action of the tridentate ligand (C(2)H(5))(2)NCH(2)CH(2)N(CH(2)CH(2)SH)(2) and the monodentate coligand HSC(6)H(4)OCH(3) on a suitable ReO(3+) precursor results in a mixture of syn- and anti-oxorhenium complexes, ReO[(C(2)H(5))(2)NCH(2)CH(2)N(CH(2)CH(2)S)(2)] [SC(6)H(4)OCH(3)], in a ratio of 25/1. The complexes are prepared by a ligand exchange reaction using ReO(eg)(2) (eg = ethylene glycol), ReOCl(3)(PPh(3))(2), or Re(V)-citrate as precursor. Both complexes have been characterized by elemental analysis, FT-IR, UV-vis, X-ray crystallography, and NMR spectroscopy. The syn isomer C(17)H(29)N(2)O(2)S(3)Re crystallizes in the monoclinic space group P2(1)/n, a = 14.109(4) Å, b = 7.518(2) Å, c = 20.900(5) Å, beta = 103.07(1) degrees, V = 2159.4(9) Å(3), Z = 4. The anti isomer C(17)H(29)N(2)O(2)S(3)Re crystallizes in P2(1)/n, a = 9.3850(7) Å, b = 27.979(2) Å, c = 8.3648(6) Å, beta = 99.86(1) degrees, V = 2163.9(3) Å(3), Z = 4. Complete NMR studies show that the orientation of the N substituent chain with respect to the Re=O core greatly influences the observed chemical shifts. Complexes were also prepared at the tracer ((186)Re) level by using (186)Re-citrate as precursor. Corroboration of the structure at tracer level was achieved by comparative HPLC studies.

Two mixed-valence Mn(III)Mn(II) complexes and a homo-valence Mn(II) trinuclear manganese complex of stoichiometry Mn(III)Mn(II)Mn(III)(5-Cl-Hsaladhp)(2)(AcO)(4)(MeOH)(2).4CH(3)OH (1a), Mn(III)Mn(II)Mn(III) (Hsaladhp)(2)(AcO)(2)(5-Cl-Sal)(2)(thf)(2) (3a) and Mn(II)Mn(II)Mn(II) (AcO)(6)(pybim)(2) (1b) where H(3)saladhp is a tridentate Schiff base ligand and pybim a neutral bidentate donor ligand, have been structurally characterized by using X-ray crystallography. The structurally characterized mixed-valence complexes have strictly 180 degrees Mn(III)-Mn(II)-Mn(III) angles as required by crystallographic inversion symmetry. The complexes are valence trapped with two terminal Mn(III) ions showing Jahn-Teller distortion along the acetate or salicylate-Mn(III)-X axis. The Mn.Mn separation is 3.511 Å and 3.507 Å respectively. The mixed-valence complexes have S = (3)/(2) ground state and the homovalence complex S = (5)/(2), with small antiferromagnetic exchange J couplings, -5.6 and -1.8 cm(-1), respectively, while the powder ESR spectra at 4 K show a broad low field signal with g approximately 4.3 for Mn(III)Mn(II)Mn(III) and a broad temperature-dependent signal at g = 2 for Mn(II)Mn(II)Mn(II). Crystal data for 1a: [C(36)H(60)O(20)N(2)Cl(2)Mn(3)], triclinic, space group P&onemacr;, a = 9.272(7) Å, b = 11.046(8) Å, c = 12.635(9) Å, alpha = 76.78(2) degrees, beta = 81.84(2) degrees, gamma = 85.90(2) degrees, Z = 1. Crystal data for 3a: [C(48)H(56)O(18)N(2)Cl(2)Mn(3)], monoclinic, space group P2(1)/n, a = 8.776(3) Å, b = 22.182(7) Å, c = 13.575(4) Å, beta = 94.44(1) degrees, Z = 2. Crystal data for 1b: [C(36)H(36)O(12)N(6)Mn(3)], triclinic, space group P&onemacr;, a = 13.345(6) Å, b = 8.514(4) Å, c = 9.494(4) Å, alpha = 75.48(1) degrees, beta = 75.83(1) degrees, gamma = 76.42(1) degrees, Z = 1.

A new approach to the "3 + 1" mixed ligand oxotechnetium complexes of the general formula TcOL1L2, with ligands (L1H(2)) containing the SNN donor set and various monodentate thiols as coligands (L2H) is reported. The ligands L1H(2) (1-3, general formula R(1)CH(2)CH(2)NHCH(2)C(R(2))(2)SH where R(1) = N(CH(3))(2) and R(2) = H in 1, R(1) = pyrrolidin-1-yl and R(2) = H in 2, and R(1) = piperidin-1-yl and R(2) = CH(3) in 3) act as tridentate SNN chelates to the TcO(3+) core, leaving open one coordination site cis to the oxo group. In the presence of a monodentate thiol (L2H) and using (99)Tc(V)-gluconate as precursor, the vacancy is filled by the thiol which acts as the coligand. With this approach four neutral oxotechnetium complexes (4-7, general formula TcO[R(1)CH(2)CH(2)NCH(2)C(R(2))(2)S][SR] where RSH = p-methoxybenzenethiol, or p-methylbenzenethiol or benzyl mercaptan) were prepared in high yield by reacting L1H(2) and L2H with Tc(V)-gluconate in a ratio 1:1:1. The complexes were characterized by elemental analysis and spectroscopic methods. Complete assignments of (1)H and (13)C NMR resonances were made for all complexes. X-ray crystallographic studies of 5 (R(1) = pyrrolidin-1-yl, R(2) = H, RSH = p-methylbenzenethiol) and 7 (R(1) = piperidin-1-yl, R(2) = CH(3), RSH = benzyl mercaptan) showed that the complexes crystallize in the monoclinic space group P2(1)/n (a = 10.223(1) Å, b = 9.283(1) Å, c = 18.337(2) Å, beta = 97.262(2) degrees, V = 1726.3(4) Å(3), Z = 4; a = 11.876(2) Å, b = 10.470(2) Å, c = 17.098(3) Å, beta = 105.990(4) degrees, V = 2043.8(6) Å(3), Z = 4, for 5 and 7, respectively). Complexes5 and 7 have distorted square pyramidal coordination geometry with the oxo ligand in the axial position. The steric requirements of the oxo group cause the Tc atom to be displaced 0.68 Å out of the mean equatorial plane of the NNSS donor atoms in both complexes.

A series of 22 mixed-ligand complexes of the general formula TcOL(1)L(2), where L(1)H(2) are N-substituted bis(2-mercaptoethyl)amine ligands, [SN(R)S], and L(2)H are monodentate thiols as coligand, is reported. The complexes were prepared by the ligand exchange method using Tc-gluconate as precursor and equimolar quantities of the two ligands. In all cases the syn stereoisomer was formed in high yield and isolated as a crystalline product. In four cases HPLC analysis demonstrated the presence of the anti stereoisomer in the reaction mixture. Although the yield was less than 1%, one anti isomer, 4a, was successfully isolated as brown crystals. The isolated complexes were characterized by spectroscopic methods and elemental analysis. The formation of the two diastereomers, syn and anti, was expected due to the configuration of the nitrogen substituent (R) with respect to the central TcO core. The X-ray crystallography showed that the coordination geometry of the syn isomers 9, 11, and 18 is trigonal bipyramidal while for the anti isomer 4a it is distorted square pyramidal. This is the first documentation of syn/anti isomerism in N-substituted TcO[SN(R)S][S] mixed-ligand complexes.

In developing 99mTc complexes as potential brain-imaging agents, we investigated the coordination chemistry of ligands containing sulfur and nitrogen donor atoms with the general formula R-CH2CH2N(CH2CH2SH)2 (R = C2H5S, (C2H5)2N). These ligands act as tridentate SNS chelates to the TcO3+ core, leaving open one coordination site cis to the oxo group. In reactions with the highly reactive [99TcOCl4]- precursor, this vacancy was occupied by a chlorine atom. When the ligands reacted in the presence of 4-methoxythiophenol, using 99Tc(V)-gluconate as precursor, the vacancy was filled with 4-methoxythiophenol, which acted as coligand. Thus neutral mixed ligand complexes of the general formula [TcO((SCH2CH2)2NCH2CH2R)X], where X = Cl or 4-methoxythiophenol, were synthesized. The complexes were characterized by UV-vis, IR, 1H NMR, crystallographic, and elemental analyses. The crystal structures of 3a (R = C2H5S, X = Cl) and 4b (R = (C2H5)2N, X = 4-methoxythiophenol) demonstrated that the coordination geometry is trigonal bipyramidal with the N1 and Cl or S3 occupying the apical positions and the basal plane defined by the S1 and S2 of the tridentate ligand and the oxo group. The complexes 4a(99mTc) (R = C2H5S, X = 4-methoxythiophenol) and 4b(99mTc) were prepared using 99mTc-glucoheptonate as precursor and were purified by HPLC. Biodistribution in mice showed high initial brain uptake (3.68% and 3.56% dose/organ for 4a(99mTc) and 4b(99m-Tc), respectively). Complex 4b(99mTc) displayed significantly higher brain/blood values and prolonged retention in brain as well. The results suggest that structural modifications based on configurations 4a,b may provide novel 99mTc brain-imaging agents with improved biological characteristics.