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⁻

Abstract

Reactions of mononuclear oxohalomolybdates() with squaric acid (3,4-dihydroxycyclobut-3-ene-1,2-dione) afforded two types of {Mo 2 O 4 } 2ϩ containing species with the squarato ligand engaged in a µ 2 -1,2-bis(monodentate) binding mode. In the presence of pyridine (Py) or 3,5-lutidine (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 {Mo 2 O 4 } 2ϩ 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 Å. Using 2,4,6-collidine (Col) afforded (ColMe) 4 [Mo 4 O 8 (C 4 O 4 ) 4 ]ؒ2MeOHؒ2Col 2a (ColMe ϩ = N-methylcollidinium cation, NC 9 H 14 ϩ ) and (ColH) 4 (PyEt)[Mo 4 O 8 (C 4 O 4 ) 4 ]Br 2b (ColH ϩ = protonated 2,4,6-collidine, NC 8 H 12 ϩ ; PyEt ϩ = N-ethylpyridinium cation, NC 7 H 10 ϩ ). The tetranuclear anions of 2a and 2b consist of a rare, cube-like {Mo 4 O 4 (µ 3 -O) 4 } 4ϩ core with four squarato ligands attached to its periphery. The squarato ligands in the [Mo 4 O 8 (C 4 O 4 ) 4 ] 4Ϫ anions bridge pairs of molybdenum atoms from neighbouring {Mo 2 O 4 } 2ϩ units, spanning an average distance of 3.43 Å. The compounds were fully characterized by infrared vibrational spectroscopy, NMR spectroscopy, elemental analyses and X-ray diffraction studies.

Novel hydrogenmaleato molybdenum(V) complexes based on a dinuclear metal–metal bonded unit: syntheses and structural characterization of (PyH)3[Mo2O4Cl4(OOCCH CHCOOH)] and (PyH)3[Mo2O4Br4(OOCCH CHCOOH)] · CH3CN

“…If multidentate ligands coordinate first, two different situations can be distinguished: (i) the ligand occupies the available coordination sites of the {Mo 2 O 4 } 2þ core in the ''terminal'' mode [6], or (ii) the ligand exploits its bridging capacity and coordinates to two or more dinuclear cores, yielding either polymeric materials [7] or discrete entities [8]. When the self-assembly precedes, the ligands occupy the peripheral positions of the clusters thus obtained, either in a ''terminal'' [9] or in a bridging mode connecting the neighbouring cores into polymeric materials [10]. A series of the oxalato complexes illustrates some of the above- 4 ] 4À with the squarate engaged in a l 2 -1,2-bis(monodentate) binding mode in both [9].…”

“…When the self-assembly precedes, the ligands occupy the peripheral positions of the clusters thus obtained, either in a ''terminal'' [9] or in a bridging mode connecting the neighbouring cores into polymeric materials [10]. A series of the oxalato complexes illustrates some of the above- 4 ] 4À with the squarate engaged in a l 2 -1,2-bis(monodentate) binding mode in both [9]. A distinctive feature can be recognized between the two ligands: the oxalate realizes several binding modes in coordination to the {Mo 2 O 4 } 2þ core, while the squarate only one.…”

The solid state structure of pyridinium hydrogen squarate

“…The reaction vessel was allowed to cool slowly to room temperature. The vessel contained an orange solution and two solid phases: orange crystals of [Mo 2 O 4 (Py) 4 (Sq)]·2Py and colourless crystals of (PyH)(HSq) [11].…”

“…Recent research on the acid and its anions has been focused on their applications as active pharmaceutical ingredients [4][5][6], or fluorescent biomarkers with large second-and third-order nonlinear optical responses [7,8]. Their application in crystal engineering has also been reported [9,10] [11]. In the latter case, the metal ions bridged by the squarate belong to two different {Mo V 2 O 4 } 2+ cores.…”

Dinuclear cobalt and manganese squarate complexes with bidentate N-donor ligand: syntheses, crystal structures, spectroscopic, thermal and voltammetric studies

“…It is also observed that the squarate anion, with Cu(II) and Ni(II), acts as a tetramonodentate ligand and forms polynuclear compounds [17]. The chelating and bis-chelating coordination modes are only possible in complexes with larger metal ions, such as alkaline and rareearth cations [18][19][20]. In all the cases reported so far, metal-squarate complexes have been found to be interesting in terms of the structural relationships between their respective solid-state architectures [21].…”