Anomalous Stereochemistry of Pyrazolato-3,5-dicarboxylato-Bridged Dinuclear Chromate(III) Complexes Containing Ethylenediamine-N,N‘-dicarboxylates with Entrapped Unstable Conformations:  X-ray Structure of Na[Cr₂(eddp)(μ-pzdc)]·6H₂O

Abstract

Several new pyrazolato-3,5-dicarboxylato (pzdc) bridged dinuclear chromate(III) complexes containing linear tetradentate O-N-N-O type ligands were synthesized and structurally characterized. Among them, the X-ray structure of the eddp complex Na[Cr2(eddp)(mu-pzdc)].6H2O (eddp = ethylenediamine-N,N'-dipropionate) was determined to have a (sym-cis)-(unsym-cis) geometrical configuration with intramolecular three-center hydrogen bonds, entrapping the unfavored sym-cis configuration for the Cr(eddp) moiety as well as the favored unsym-cis one. As a pair of positional disorders, there were also found to be two conformational isomers with respect to the absolute configurations of the coordinated asymmetric nitrogen atom at the G (in-plane) ring for the unsym-cis moiety. Moreover, chiral pzdc-bridged dinuclear complexes with another type of O-N-N-O ligand, 1,2-cyclohexanediamine-N,N'-diacetate (cdda), were successfully synthesized, isolated, and characterized by column chromatographic behavior, elemental analysis, and chiroptical spectra. There were two diastereomers for Na[(R,R-cdda)Cr(mu-pzdc)Cr(S,S-cdda)] and only one isomer for Na[(R,R-cdda)Cr(mu-pzdc)Cr(R,S-cdda)] and Na[(R,R-cdda)Cr(mu-pzdc)Cr(edda)] (R,R- or S,S- and R,S-cdda = R,R-trans- or S,S-trans- and R,S-cis-1,2-cyclohexanediamine-N,N'-diacetate, and edda = ethylenediamine-N,N'-diacetate). From their circular dichroism (CD) spectra, these complexes could exhibit the delta-delta absolute configuration with ((sym-cis-R,R-cdda)-(unsym-cis-edda or S,S- or R,S-cdda)) geometrical configuration, indicating the abnormal eq-eq (N-Ceq) configuration for the R,R-cdda. The comparison among the CD spectra of the ((cdda)-(cdda)) complexes revealed that two diastereomers of the ((R,R-cdda)-(S,S-cdda)) complex correspond to the conformational isomers resulting from the difference in geometrical orientations of the secondary amine protons on two coordinated asymmetric nitrogen atoms with the opposite absolute configuration in the unsym-cis-S,S-cdda moiety. In a series of the pzdc-bridged Cr(III) complexes the anomalous conformations in two different geometrical configurations could be entrapped probably owing to stereognostic coordination through the intramolecular N-H...O hydrogen bond interaction.

Antiferromagnetic Three-Dimensional Order Induced by Carboxylate Bridges in a Two-Dimensional Network of [Cu3(dcp)2(H2O)4] Trimers

“…A variety of coordination compounds containing transition, lanthanide and alkalineearth metals have been synthesized and reported in the literature. [13][14][15][16][17][18][19][20] The [Cu 3 (dcp) 2 (H 2 O) 4 ] n compound we report here is the first example where all six donors of the dcp 3ligand are observed to coordinate to the metal centers.…”

The building block approach to extended solids: 3,5-pyrazoledicarboxylate coordination compounds of increasing dimensionality

“…A variety of coordination compounds containing transition, lanthanide and alkaline-earth metals has been synthesised and reported in the literature. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] Original interest focused on the catalytic and multi-electron transfer properties of the ligand, 9-12 however recent literature reports the pH-controlled assembly of H 3 dcp coordination frameworks. 7,8,13, 14 Here we describe twelve coordination compounds produced with H 3 dcp where the structures can be understood in terms of the aggregation of simple building blocks.…”

Crystal structure and conformational analysis of s-cis-(acetylacetonato)(ethylenediamine-N,N′-diacetato)-chromium(III)

“…The stereochemisty of octahedral complexes containing quadridentate edda 2− ligand has been described by Legg et al [6], and reiterated by many subsequent authors, notably by Kaizaki et al [44,45]. However, CFF modelling requires (particularly in elucidating statistical thermodynamics) a consideration of all theoretically possible configurations and conformations, which represent local minima on the potential energy surface of [Cr(edda)(acac)].…”