Coordination compounds containing bis-dithiolene-chelated molybdenum(IV) and oxalate: comparison of terminal with bridging oxalate

Two coordination compounds containing tetra- n -butylammonium cations and bis-tfd-chelated molybdenum(IV) [tfd 2− = S 2 C 2 (CF 3 ) 2 2− ] and oxalate (ox 2− , C 2 O 4 2− ) in complex anions are reported, namely bis(tetra- n -butylammonium) bis(1,1,1,4,4,4-hexafluorobut-2-ene-2,3-dithiolato)oxalatomolybdate(IV)–chloroform–oxalic acid (1/1/1), (C 16 H 36 N) 2 [Mo(C 4 F 6 S 2 ) 2 (C 2 O 4 )]·CHCl 3 ·C 2 H 2 O 4 or (N n Bu 4 ) 2 [Mo(tfd) 2 (ox)]·CHCl 3 ·C 2 H 2 O 4 , and bis(tetra- n -butylammonium) μ-oxalato-bis[bis(1,1,1,4,4,4-hexafluorobut-2-ene-2,3-dithiolato)molybdate(IV)], (C 16 H 36 N) 2 [Mo 2 (C 4 F 6 S 2 ) 4 (C 2 O 4 )] or (N n Bu 4 ) 2 [(tfd) 2 Mo(μ-ox)Mo(tfd) 2 ]. They contain a terminal oxalate ligand in the first compound and a bridging oxalate ligand in the second compound. Anion 1 2− is [Mo(tfd) 2 (ox)] 2− and anion 2 2− , formally generated by adding a Mo(tfd) 2 fragment onto 1 2− , is [(tfd) 2 Mo(μ-ox)Mo(tfd) 2 ] 2− . The crystalline material containing 1 2− is (N n Bu 4 ) 2 - 1 ·CHCl 3 ·oxH 2 , while the material containing 2 2− is (N n Bu 4 ) 2 - 2 . Anion 2 2− lies across an inversion centre. The complex anions afford a rare opportunity to compare terminal oxalate with bridging oxalate, coordinated to the same metal fragment, here (tfd) 2 Mo IV . C—O bond-length alternation is observed for the terminal oxalate ligand in 1 2− : the difference between the C—O bond length involving the metal-coordinating O atom and the C—O bond length involving the uncoordinating O atom is 0.044 (12) Å. This bond-length alternation is significant but is smaller than the bond-length alternation observed for oxalic acid in the co-crystallized oxalic acid in (N n Bu 4 ) 2 - 1 ·CHCl 3 ·oxH 2 , where a difference (for C=O versus C—OH) of 0.117 (14) Å was observed. In the bridging oxalate ligand in 2 2− , the C—O bond lengths are equalized, within the error margin of one bond-length determination (0.006 Å). It is concluded that oxalic acid contains a localized π-system in its carboxylic acid groups, that the bridging oxalate ligand in 2 2− contains a delocalized π-system and that the terminal oxalate ligand in 1 2− contains an only partially localized π-system. In (N n Bu 4 ) 2 - 1 ·CHCl 3 ·oxH 2 , the F atoms of two of the –CF 3 groups in 1 2− are disordered over two sets of sites, as are the N and eight of the C atoms of one of the N n Bu 4 cations. In (N n Bu 4 ) 2 - 2 , the whole of the unique N n Bu 4 + cation is disordered over two sets of sites. Also, in (N n Bu 4 ) 2 - 2 , a region of disordered electron density was treated with the SQUEEZE routine in PLATON [Spek (2015). Acta Cryst. C 71 , 9–18].

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.