Barbara Modec

The solvatothermal synthesis and the crystal structure of polymeric N-methylpyridinium octamolybdate(VI), (Me–NC5H5)4n[Mo8O26]n

Abstract The reaction of (PyH)2[MoOCl5] with pyridine and methanol in the presence of CoCl2·6H2O and H2C2O4·2H2O at 130 °C under solvatothermal conditions afforded (Me–NC5H5)4n[Mo8O26]n 1. The structure consists of infinite molybdenum oxide chains bearing a negative charge and N-methylpyridinium cations. Eight {MoO6} octahedra are arranged in an edge-sharing manner to form compact octamolybdate subunits which are connected through pairs of Mo–O–Mo bridges into extended one-dimensional arrays.

Novel molybdenum(V) squarato complexes based on the dinuclear metal–metal bonded unit: syntheses and structural characterization of dinuclear [Mo2O4(C4O4)(R-Py)4] and tetranuclear [Mo4O8(C4O4)4]4−

Reactions of mononuclear oxohalomolybdates(V) with squaric acid (3,4-dihydroxycyclobut-3-ene-1,2-dione) afforded two types of {Mo2O4}2+ containing species with the squarato ligand engaged in a μ2-1,2-bis(monodentate) binding mode. In the presence of pyridine (Py) or 3,5-lutidine (3,5-Lut) neutral, dinuclear complexes [Mo2O4(C4O4)(Py)4]·2MeOH·0.5Py 1a, [Mo2O4(C4O4)(Py)4]·2Py 1b and [Mo2O4(C4O4)(3,5-Lut)4]·2(3,5-Lut) 1c were obtained. A pair of nitrogen donor ligands and a squarate oxygen occupy the three coordination sites of each metal in the {Mo2O4}2+ unit in 1a, 1b and 1c. The squarate functions as a third, auxiliary bridge between a pair of molybdenum atoms at an average distance of 2.55 A. Using 2,4,6-collidine (Col) afforded (ColMe)4[Mo4O8(C4O4)4]·2MeOH·2Col 2a (ColMe+ = N-methylcollidinium cation, NC9H14+) and (ColH)4(PyEt)[Mo4O8(C4O4)4]Br 2b (ColH+ = protonated 2,4,6-collidine, NC8H12+; PyEt+ = N-ethylpyridinium cation, NC7H10+). The tetranuclear anions of 2a and 2b consist of a rare, cube-like {Mo4O4(μ3-O)4}4+ core with four squarato ligands attached to its periphery. The squarato ligands in the [Mo4O8(C4O4)4]4− anions bridge pairs of molybdenum atoms from neighbouring {Mo2O4}2+ units, spanning an average distance of 3.43 A. The compounds were fully characterized by infrared vibrational spectroscopy, NMR spectroscopy, elemental analyses and X-ray diffraction studies.

From Small {Mo2O4}2+ Aggregates to Infinite Solids

Mononuclear oxohalomolybdates(V) readily generate in the mixtures of alcohols and pyridines through a series of substitution and dimerization reactions, still reactive dinuclear {Mo2O4}2+ fragments which assemble together into larger cluster species. In all, the {Mo2O4}2+ unit with the two molybdenum atoms connected by a single metal-metal bond, appears as a recurrent structural motif, either as a single {Mo2O4}2+ unit in dinuclear compounds or as assemblies of two, three, four or six units through bridging oxygen donor ligands in tetranuclear, hexanuclear, octanuclear and dodecanuclear compounds, respectively. Pyridine, halide, alkoxide and alcohol ligands occupy the peripheral positions of the molybdenum oxide cores. Their structures will be presented in terms of different arrangements and connectivities among the basic dinuclear building blocks. By using a suitable linker, an oxalate adopting a bisbidentate binding mode was shown to serve the purpose, the {Mo2O4}2+ units were connected into infinite chains.

The first oxalate-bridged one-dimensional polymer containing MoV2 dimers with single metal–metal bonds. Syntheses and structures of (MeNC5H5)2n[Mo2O4(C2O4)Cl2]n and (3-MePyH)2n[Mo2O4(C2O4)Cl2]n

Hydrothermal reactions of mononuclear oxochloromolybdate(V) with oxalic acid in alcohol (methanol or 2-propanol) and pyridines (pyridine or 3-methylpyridine) media have afforded two polymeric compounds of molybdenum(V): N-methylpyridinum catena-μ-oxalato-O1,O2:O1′,O2′-(dichloro-di-μ-oxo-dioxodimolybdate(V)), (MeNC5H5)2n[Mo2O4(C2O4)Cl2]n1 and 3-methylpyridinium catena-μ-oxalato-O1,O2:O1′,O2′-(dichloro-di-μ-oxo-dioxodimolybdate(V)), (3-MePyH)2n[Mo2O4(C2O4)Cl2]n2. The compounds were fully characterized by X-ray structural analysis, infrared and NMR spectroscopy. The essentially isostructural anionic chains in 1and 2 are built of alternating pairs of {Mo2O4}2+ containing edge-sharing octahedra and planar oxalates giving a Mo ∶ oxalate ratio of 2. The bisbidentate oxalate acts as a bridge between two dinuclear subunits. The formation of a N-methylpyridinium cation from methanol and pyridine in the presence of molybdenum(V) and oxalic acid has not been documented before.

Complexation of Molybdenum(V) with Glycolic Acid : An Unusual Orientation of Glycolato Ligand in {Mo2O4}2+ Complexes

(PyH)5[Mo(V)OCl4(H2O)]3Cl2 and (PyH)n[Mo(V)OBr4]n reacted with glycolic acid (H2glyc) or its half-neutralized ion (Hglyc(-)) to afford a series of novel glycolato complexes based on the {Mo(V)2O4}2+ structural core: (PyH)3[Mo2O4Cl4(Hglyc)]. (1)/ 2CH 3CN (1), (PyH) 3[Mo 2O 4Br 4(Hglyc)].Pr(i)OH(2), (PyH)2[Mo2O4(glyc) 2Py 2] (3), (PyH) 4[Mo 4O 8Cl 4(glyc) 2].2EtOH (4), and [Mo 4O 8(glyc) 2Py 4] (5) (Py = pyridine, C 5H 5N; PyH(+) = pyridinium cation, C 5H 5NH (+) and glyc (2-) = a doubly ionized glycolate, (-)OCH 2COO (-)). The compounds were fully characterized by X-ray crystallography and infrared spectroscopy. The Hglyc (-) ion binds to the {Mo 2O 4} (2+) core through a carboxylate end in a bidentate bridging manner, whereas the glyc (2-) ion adopts a chelating bidentate coordination through a deprotonated hydroxyl group and a monodentate carboxylate. The orientations of glyc (2-) ions in 3- 5 are such that the alkoxyl oxygen atoms occupy the sites opposite the multiply bonded oxides. {(C6H5) 4P}[Mo(VI)O 2(glyc)(Hglyc)] ( 6), an oxidized complex, features a reversed orientation of the glyc(2-) ion. The theoretical DFT calculations on the [Mo(V)2O4(glyc) 2Py 2](2-) and [Mo(VI)O2(glyc)2](2-) ions confirm that binding of glycolate with the alkoxyl oxygen to the site opposite the MoO bond is energetically more favorable in {Mo(V)2O4}(2+) species, whereas a reversed orientation of the ligand is preferred in Mo(VI) complexes. An explanation based on the orbital analysis is put forward.

Proficiency of the electron-deficient 1,3,5-triazine ring to generate anion–π and lone pair–π interactions

Two new 1,3,5-triazine-based ligands, namely 2-chloro-4,6-bis-N-[2-methylsulfanyl-N-(pyridin-2-ylmethyl)aniline]-1,3,5-triazine (cspat) and 2,4,6-tris-N-[N-2-(methylsulfanyl)-N-(pyridin-2-ylmethyl)ethanamine]-1,3,5-triazine (spet), have been purposely designed to favour anion–π and/or lone pair–π interactions in their coordination compounds. Three copper coordination compounds from these ligands, i.e. [Cu(cspat)Br2] (1), [Cu(cspat)(NO3)2] (2) and [Cu(Hspet)(NO3)2](NO3)·0.5H2O (3), have been obtained and their single-crystal X-ray structures have been determined. As expected, the solid-state structures of the three CuII compounds are composed of supramolecular networks of anion–π and/or lone pair–π non-covalent bonds.

Structural isomerism among octanuclear oxomolybdenum(V) coordination compounds with pyridines. Two isomers of [Mo8O16(OCH3)8(RPy)4]

Abstract The condensation of dinuclear {Mo2O4}2+ leads, under conditions of the solvothermal synthesis, to two distinct architectures: (i) the cluster species of [Mo8O16(OCH3)8Py4]·2CH3OH (Py=pyridine, C5H5N) (1·2CH3OH) whose four building blocks, {Mo2O4}2+ units, are linked through doubly or triply bridging oxo and methoxo groups into a compact array; and (ii) [Mo8O16(OCH3)8(4-MePy)4] (4-MePy=4-methylpyridine, C6H7N) (2) which displays an open, bent cyclic structure made of four building blocks linked to each other by pairs of methoxo bridges. The MoMo distances within dinuclear units, 2.5638(12) and 2.6012(13) A in 1, and 2.5661(3) A in 2, are characteristic for single metal–metal bonds. All metal atoms of 1 are in a distorted octahedral coordination; each octahedron shares several edges (two, three or four) with its neighbors. Compound 2 displays two types of coordination polyhedra, square pyramids and octahedra (four of each) that are connected through common edges. Each polyhedron shares two edges with the adjacent polyhedra.

EDA Complexes of N-halosaccharins with N- and O-donor ligands

A series of EDA complexes of N-iodosaccharin (NISac) and N-bromosaccharin (NBSac) with nitrogen and oxygen electron-pair donors, NISac·H2O, NISac·THF, NISac·Py, NISac2·Pyz and NBSac2·Pyz, was prepared and examined by X-ray diffraction and NMR. The complexes are relatively stable, crystalline compounds with the ligand bound to the halogen atom in a nearly linear arrangement N–halogen–ligand. The halogen–ligand distances are inversely proportional to the donor ability of the ligand. The interactions between ligand and halogen are stronger for iodine than bromine. The X-ray structure analysis has shown that for some compounds the N–X bond in the halosaccharin moiety is not coplanar with the isothiazole ring, and the quantum-chemical calculations demonstrate a high flexibility of the corresponding angle. Complexes were modelled also by DFT calculations using B3LYP and MPW1K functionals. A better fit of the computed geometry was obtained by the geometry optimization in a polar solvent continuum than in vacuum.

Octanuclear oxomolybdenum(V) clusters with pyridine or alkyl-substituted pyridines: crystal structures of [Mo8O16(OCH3)8L4] (L=3-methylpyridine, 3,5-lutidine)

Abstract Simple synthetic routes for the preparation of octanuclear oxomolybdenum(V) clusters with stoichiometry [Mo8O16(OCH3)8L4] (L=4-methylpyridine (4-MePy) (a), 4-ethylpyridine (4-EtPy) (b), 4-tert-butylpyridine (4-ButPy) (c), pyridine (Py) (d), 3-methylpyridine (3-MePy) (e), 3,5-lutidine (3,5-Lut) (f)) are described. Crystal structures of e and f were investigated by X-ray diffraction. The puckered ring structure made up of eight molybdenum atoms linked together by pairs of methoxy groups and pairs of oxo groups was recognized in both. The solubility of the compounds in pyridines was employed for the substitution of coordinated pyridine for a different pyridine. The octanuclear clusters have been found to react in pyridines at elevated temperatures to oxomolybdenum(V,VI) clusters with the formula [Mo10O26L8].

P-stereogenic phospholanes or phosphorinanes from o-biarylylphosphines: two bridges not too far.

The discovery of a concise regiodivergent asymmetric route to nonclassical P-stereogenic 5- or 6-membered benzophosphacycles, under conditions-dependent radical (oxidative addition) versus anionic (S(N)Ar) benzannulation, is reported.