Jurij V. Brenčič

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.

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.

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].

Synthesis and structural identification of undecaoxotetramethoxotetrapyridinetetra-molybdenum(V) molybdenum(VI) · methanol

Abstract (pyH)2[MoOCl5] reacts with a mixture of methanol, nitromethane and pyridine at room temperature resulting in crystalline Mo5O11(OCH3)4py4 · CH3OH (py = pyridine, C5H5N). X-ray structural analysis identified an asymmetric molecular unit with five molybdenum atoms forming a puckered ring. Molybdenum atoms are connected by oxo and methoxo bridges. The five molybdenum atoms are grouped in two Mo2V pairs with MoMo bonds and one MoVI atom.

Synthesis and structure of a high-nuclearity oxomolybdenum(V) complex, [Mo12O28(OC2H5)4(C6H7N)8]

Abstract (PyH)[MoOBr4(H2O)]·2/3PyHBr (PyH+=pyridinium cation, C5H5NH+) yielded upon the solvothermal reaction with ethanol and 4-methylpyridine (4-MePy, C6H7N) a novel oxoethoxomolybdenum(V) cluster, [Mo12O28(OC2H5)4(4-MePy)8] 1. Molybdenum atoms are grouped into six MoV2 pairs linked by single metal–metal bonds. Three crystallographically independent Mo–Mo distances are 2.5578(14), 2.5981(14) and 2.6489(16) A.

Fluorine containing coordination compounds of Cr(III)

Trans-[Cr(NH3)4F2]I·H2O (A) has monoclinic P2l/m (No. 11) space group witha=5.033 (3),b=16.333 (10),c=5.539 (3) Å and β=98.47 (3)°,Z=2.Cis-[Cr(NH3)4F2]ClO4 (B) has tetragonal space group I4lmd (No. 109) witha=7.417 (1),c=16.610 (2) Å,Z=4. Cr−F and Cr−N bonding distances are 1.894 (3); 2.087 and 2.083 (5) Å for A and 1.887 (6); 2.062 (5) and 2.051 (7) Å for B. Octahedral angles within the cations are close to 90° for both compounds. Cr−N bondtrans to Cr−F bond in thecis compound is shorter. Structures were refined toR2 values of 0.072 (A) and 0.058 (B).Trans-[Cr(NH3)4F2]I·H2O has weak N−H−F hydrogen bonds between the cations. None such interactions were found incis-[Cr(NH3)4F2]ClO4.ZusammenfassungTrans-[Cr(NH3)4F2]I·H2O (A) kristallisiert in der Raumgruppe P2l/m (No. 11) mitZ=2 unda=5,033 (3),b=16,333 (10),c=5,539 (3) Å und β=98,47 (3)°.Cis-[Cr(NH3)4F2]ClO4 (B) kristallisiert in der Raumgruppe I4lmd (No. 109) mitZ=4,a=7,417 (1) undc=16,610 (2) Å. Die Cr−F- und Cr−N-Abstände sind 1,894 (3); 2,087 (6), 2,083 (5) Å für A und 1,887 (6); 2,062 (5), 2,051 (7) Å für B. Die octaedrischen Bindungswinkel innerhalb der Kationen weichen nicht viel von 90° ab. Der Cr−N-Abstand intrans-Position der Cr−F-Bindung ist kürzer. Die Strukturen wurden bis zu GütefaktorenR2 0,072 (A) und 0,058 (B) verfeinert. Bei der Verbindung A wurden schwache N−H ... F-Wasserstoff-Bindungen zwischen verschiedenen Kationen beobachtet, während bei der Verbindung B keine Wasserstoff-Bindungen vorhanden sind.

Preparation and crystal structure of 4-methylpyridinium-[tetrabromobis-(4-methylpyridine) tungstate(III)]

Abstract (pic)2HWBr4pic2 (pic=4-methylpyridine) was prepared as one of the products of WBr4py2 (py=pyridine) reduction at 80°C by 4-methylpyridine. (pic)2HWBr4pic2 has P 2 1 n space group with: a = 8.758(4), b = 14.399(6), c = 27.094(8)A and s = 91.62(2)°. The data were refined to the conventional R factors of 0.076 and 0.088. Structure consists of WBr4pic2− octahedron with the trans position of the 4-methylpyridine rings and the (pic)2H+′ cation, Average WBr and WN bond lengths are 2.58(1) and 2.20(1) A. NN distance within the cation is 2.77(3)A.