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Molybdenum(VI) complexes of different nuclearity, mononuclear, [MoO2(L1 or 2) (MeOH)]MeOH (1MeOH and 2MeOH), [MoO2(L1 or 2)(D)] [D = pyridine, (1a and 2a), 3-methylpyridine, (1b and 2b) and 4-methylpyridine, (1c and 2c)], binuclear [{; ; ; ; MoO2(L1 or 2)}; ; ; ; 2(D)] (D = 4, 4'-bipyridine (1d, 1d' and 2d), and polynuclear complexes [MoO2(L1 or 2)]n (3 and 4) were synthesized by solution based reactions of enaminones (H2L1 = 3-(2-hydroxy-4- methylphenylamino)-1-phenylbut-2-en-1-one ; H2L2 = 3-(2- hydroxy-5-methylphenylamino)-1-phenylbut-2-en- 1-one) with the dioxobis(acetylacetonato)molybdenum( VI) complex, [MoO2(acac)2]. Reactions of the mononuclear complexes 1MeOH and 2MeOH with pyridine and its derivatives resulted in corresponding mononuclear [MoO2(L1 or 2)(D)] or binuclear [{; ; ; ; MoO2(L1 or 2)}; ; ; ; 2(D)] complexes. In case of [{; ; ; ; MoO2(L1)}; ; ; ; 2(4, 4-bpy)] two polymorphic forms are obtained (1d and 1d'). The cross-linked transformations of [MoO2(L1 or 2)(D)] complexes in solution or when exposed to vapors of N-heterocyclic bases have been explored. Crystal and molecular structures of ten complexes (1MeOH, 2MeOH, 1a–d, 1d' , 2b–d) were determined by the single-crystal X-ray diffraction analysis. Enaminone ligands and their molybdenum complexes were characterized by elemental and TG analysis, IR and NMR spectroscopy and screened for their in vitro cytotoxic and antibacterial activities. None of the tested compounds showed cytotoxic ability against THP-1 and HepG2 cell lines. Compounds 1MeOH, 1b, 2MeOH, 2a and 3, exhibited weak antibacterial activity on Moraxella catarrhalis strain while other complexes did not show antibacterial properties towards Staphylococcus aureus, Enterococcus faecalis and Escherichia coli bacteria.

Mononuclear oxomolybdenum(V) complexes with thiosemicarbazonato ligands as condensation products of aldehydes (salicylaldehyde, 2-hydroxynaphthaldehyde) with thiosemicarbazides (H2NNHC:SNHR; R = H, CH3, C6H5) were prepared. The [MoOCl2HL] complexes (HL = thiosemicarbazonato ligand) were characterized by chemical analysis, IR spectroscopy, thermogravimetry and two of them, [MoOCl2{C6H4(O)CH:NNHC:SNHC6H5}] and [MoOCl2{C10H6(O)CH:NNHC:SNHC6H5}] · CH3CN, by single-crystal X-ray structural analysis. In both complexes the MoO3+ core is coordinated by a monobasic tridentate ONS thiosemicarbazonato ligand and two chloro ligands. The coordination around the molybdenum atom is a distorted octahedron. NH4[MoOCl4(CH3CN)] and unstable (C5H5NH)2[MoOCl5] · CH2Cl2 were isolated from the acetonitrile solution of (NH4)2[MoOCl5] and from the acetonitrile and dichloromethane (1:1) solution of (C5H5NH)2[MoOCl5], respectively. Isolation and structural characterization of NH4[MoOCl4(CH3CN)] from the acetonitrile solution suggests the [MoOCl4(CH3CN)]− anion to be the reaction intermediate in the synthesis of molybdenum(V) thiosemicarbazonato complexes. (C5H5NH)2[MoOCl5] · CH2Cl2 is a rare example of a structurally characterized simple oxohalomolybdate(V) with a six-coordinate octahedral [MoOCl5]2− anion.

Polynuclear [MoO2{;SalTSC-4-Me};]n (I), [MoO2{; VanTSC-4-Me};]n (II) and mononuclear [MoO2{;SalTSC-4-Me};(CH3OH)] (1a), [MoO2{; VanTSC-4-Me};(CH3OH)] (2a) and [MoO2{;VanTSC-4-Me};(H2O)] × CH3CN (2b) complexes have been prepared by the reaction of the [MoO2(acac)2] (acetylacetonate ligand, acac , C5H7O2 ) with 1 (salicylaldehyde 4-methylthiosemicarbazone ligand, C6H4(OH)CH:NNC(SH)NHCH3H2SalTSC-4-Me) or 2 (3-methoxy-salicylaldehyde 4-methylthiosemicarbazone, CH3OC6H3(OH)- CH:NNC(SH)NHCH3, H2VanTSC-4-Me) in acetonitrile or in dry methanol. All complexes have been characterized by means of chemical analyses, thermogravimetric analyses, IR spectroscopy and some of them by 1H, 13C NMR spectroscopy and X-ray crystallography. In all mononuclear complexes molybdenum atom is coordinated by two terminal oxo-oxygen atoms, by ONS atoms from the ligand molecule and by an oxygen atom from methanol (in 1a and 2a) or water (in 2b) molecules. Ligands 1 and 2 have been characterized by means of 1H, 13C NMR spectroscopy and X-ray crystallography. Molecules of both ligands are found to be in the thioketo tautomeric form.

Mononuclear molybdenum(VI) [MoO2L2] (1a, 1b, 2a, 2b) and dinuclear molybdenum(V) [Mo2O4(L-1b)(2)(CH3OH)(2)] (3b) complexes have been prepared by the reaction of [MoO2(acac)(2)] or [Mo2O3(acac)(4)] (acac = acetylacetonate ion), respectively, with the appropriate beta'-hydroxy-beta-enaminones (HL). Also, two isomeric enaminones (HL1a and HL1b) have been prepared by the reaction of ethyl 2-hydroxy-4-(4-hydroxy-6-methyl-2H-pyran-2-on-3-yl)-4-oxo-2-butenoate (ehmpb) and o-anisidine. All the prepared molybdenum(VI) complexes are built up of mononuclear molecules with cis-MoO22+ cores, while the dinuclear molybdenum(V) complex contains a Mo2O42+ core. In all complexes ligand L is coordinated in a didentate fashion to molybdenum through two oxygen atoms and not through the nitrogen atom. One neutral solvent molecule CH3OH in the molybdenum(V) complex, acting as a monodentate ligand, completes the octahedral coordination of each Mo atom. All compounds have been characterized by means of chemical analyses, IR and one- and two-dimensional NMR spectroscopy. The molecular and crystal structures of the molybdenum(VI) (1a), molybdenum(V) (3b) complexes and of ligand HL1b have been determined by a single crystal X-ray diffraction method. (C) 2004 Elsevier Ltd. All rights reserved.

The acetato complexes of molybdenum(VI), (V) and (IV): [MoO2(OCOCH3)2] (1), Na2[Mo2O4(OCOCH3)6]·NaOCOCH3·CH3COOH (2), K[MoO2(OCOCH3)3]·CH3COOH (3), [Mo2O3(OCOCH3)4] (4), [Mo3O2(OCOCH3)6(H2O)(OH)2]·16H2O (5) and [Mo3O2(OCOCH3)6(H2O)3]Cl2·14H2O (6) have been prepared and characterized by chemical analyses, ESR and IR spectroscopy. The crystal structures of 2 and 3 have been determined by single-crystal X-ray crystallography. Both complexes contain octahedrally coordinated molybdenum atoms with bonds formed to two terminal oxo-oxygen atoms and four oxygen atoms from the acetate ligands. In 2 two acetate ligands are monodentately bonded to each molybdenum atom while the third one together with its centrosymmetrical pair acts as a bridging ligand between two molybdenum atoms. In 3 two acetate ligands are monodentately and one bidentately bonded to molybdenum. In both structures the acetic acid molecules are not involved in bonding to molybdenum but act as bridges over both (in 2) or only one oxygen atom (in 3) connecting centrosymmetrically related sodium and potassium ions, respectively.

The novel hexanuclear oxoclusters of the general formula R[Mo 6 O 12 (OCH 3 ) 4 (acac) 3 ] ( 1 – 7 ), where R=CH 3 NH 3 ( 1 ), C 5 H 5 NH ( 2 ), (CH 3 ) 2 CHNH 3 ( 3 ), (CH 3 ) 3 CNH 3 ( 4 ), C 5 H 11 NH ( 5 ), (C 2 H 5 ) 3 NH ( 6 ), and C 6 H 5 NC 11 H 13 O 2 ( 7 ) have been obtained by the reactions of the binuclear oxomolybdenum(V) complex [Mo 2 O 3 (acac) 4 ] (acac=acetylacetonate ion) with a variety of alkyl or aryl amines or corresponding alkyl or aryl ammonium chlorides in methanol. The formation of 3,5-diacyl-2,6-dimethyl-1-pheny-l-pyridinium cation in 7 is explained by the cyclization via Hantzsch condensation of acetylacetone, formaldehyde and aniline. The molecular structures of complexes 5 , 6 and 7 have been determined by a single-crystal X-ray diffraction study. In all salts the anion is of hexanuclear nature in which molybdenum atoms are bridged by oxo-oxygen and methoxo-oxygen atoms. Six Mo-octahedra are fused through edges, thus allowing the formation of localized metalmetal bonds between three pairs of molybdenum atoms.

The [Mo_2O_2S_2(OSCC_6H_5)_2] (1) has been prepared either by the reaction of [Mo_2O-3(C_5H_7O_2)_4] or of [Mo_4Cl_2O_6(O_2CCH_3)_6]ˇ(CH_3CO)_2O with thiobenzoic acid. The product was then used to prepare two complexes of the general formula [Mo_2O_2S_2(OSCC_6H_5)_2L_2] (where L = pyridine (2) or gama-picoline (3)). All complexes were characterized by elemental analyses, IR spectra and magnetic measurements. The structures of (2) and (3) were proved by X-ray structure analysis. Both complexes are dinuclear containing Mo_2O_2S_2 core with two Mo atoms linked by a Mo-Mo single bond. The Mo atoms are octahedrally coordinated by oxo-oxygen, two bridging sulfido-sulfurs, one pyridine (or gama-picoline)-nitrogen and thiobenzoato-sulfur and thiobenzoato-oxygen atoms.