Synthesis and characterization of the three geometrical isomers of difluoro(1,3-propanediamine-N,N'-diacetato)chromate(III). Crystal structure of trans-Li[CrF2(1,3-pdda)].2H2O

Syntheses and Characterization of (Diamine-N,N‘-dicarboxylato)chromate(III) Dinuclear Complexes Bridged by Pyrazole-3,5-dicarboxylate: X-ray Structures of Na[Cr2(edda)2(μ-pzdc)]·5H2O and Na[Cr2(trdda)2(μ-pzdc)]·3H2O

“…This NMR pattern suggests the existence of unsym- cis configuration(s) in complex 1 . On the other hand, since the Cr(III)−trdda complex favors the unsym- cis configuration, , complex 2 is predicted to take the (unsym- cis )−(unsym- cis ) configuration.…”

“…For example, in the case of octahedral cis -[M(O−N−N−O)X 2 ] type complexes with linear tetradentate ethylenediamine- N , N‘ -diacetate- (edda-) type ligands, there are 12 possible geometrical isomers and their enantiomers, which result from pairwise combinations of geometrical isomers (sym- cis and unsym- cis in Figure ) as shown in Figure . In such dinuclear complexes, the isomer distribution depends not only on the intramolecular interactions but also on the different stability of geometrical configurations in mononuclear complexes, where the stable geometrical configuration of edda Cr(III) complexes with all five-membered chelates is the sym- cis isomer − and trimethylenediamine- N , N‘ -diacetate (trdda) or ethylenediamine- N , N‘ -dipropionate(eddp) with six-membered chelate rings prefers the unsym- cis one. − Therefore, the pzdc-bridged dinuclear complexes will be a suitable candidate to reveal the role of noncovalent interaction recognizing the geometrical configuration when forming dinuclear complexes.

1 Pyrazole-3,5-dicarboxylic acid.

2 Two possible isomers of cis -[Cr(edda)X 2 ] type complex: sym- cis (left); unsym- cis (right).

3 Twelve possible isomers of the [Cr 2 (O-N-N-O) 2 (μ-pzdc)] - type dinuclear complex: (sym- cis )-(sym- cis ) ( A , B ); (sym- cis )-(unsym- cis ) ( C−F ); (unsym- cis )-(unsym- cis ) ( G−L ).

…”

Alkali metal cation complexation and solvent interactions by robust chromium(III) fluoride complexes

“…Interaction of fluoride complexes with protic solvents leading to solvatochromism is well established and has been investigated especially by Kaizaki and co-workers [10][11][12][13]. However, spectral consequences of more general second sphere interactions have not been reported for fluoride complexes and the possibility of spectroscopic cation sensing by fluoride complexes has not been investigated.…”

Deuteron nuclear magnetic resonance study of chromium [Cr(edda)(X)2]n complexes (X2 = two monodentates or a bidentate; edda = ethylenediamine-N,N'-diacetato) and complete assignment of the deuteron NMR spectrum of (1,2-propylenediamine-N,N,N',N'-tetraacetato)chromate [Cr(1,2-pdta-.alpha.-d8]-

“…Although the trans isomer is not expected to form, it could also give rise to two resonances and make differentiation between a sym-cis and a trans isomer difficult, as was the case for the isomers of [CrF2( 1,3-pdda)]". 4 The use of a bidentate ligand to complete the coordination sphere of an edda/pdda complex can simplify the problem since formation of the trans isomer is precluded.…”

“…In an earlier study, the stereochemistry of Cr(III) complexes of 1,3-propanediamine-A, A-diacetate (1,3pdda)8 was elucidated, and the three possible geometric isomers of [CrF2(l,3-pdda)]-(Figure 1) were characterized by 2H NMR and an X-ray crystallographic study. 4 For the analogous linear quadridentate ligand edda, with one less carbon in the diamine backbone, ring strain apparently prevents the formation of the trans isomer, and only the sym-cis and unsym-cis (Figure 1) isomers have been reported for Co(III) and Cr(III) complexes of edda.9 For Cr(III), only one unsym-cis isomer has been reported along with the predominant and more stable sym-cis isomer. 10 The close similarity between the ligand field spectra of the two isomers precludes definitive characterization by electronic absorption spectroscopy.…”