Crystal and solution structures of calcium complexes relevant to problematic waste disposal: calcium gluconate and calcium isosaccharinate

Abstract

The single-crystal structures of calcium d-gluconate and calcium -d-isosaccharinate have been determined using X-ray diffraction at 100 K. Surprisingly, given its significance in industrial and medical applications, the structure of calcium d-gluconate has not previously been reported. Unexpectedly, the gluconate crystal structure comprises coordination polymers. Unusually, the calcium coordination number is nine. Adjacent metal centres are linked by three -oxo bridges, with a metal-metal separation of 3.7312 (2) Å . One of the gluconate ligands contradicts a suggestion from 1974 that a straight chain conformation is associated with an intramolecular hydrogen bond. This ligand binds to three adjacent metal centres. The use of synchrotron radiation provided an improved crystal structure with respect to that previously reported for the isosaccharinate complex, allowing the location of the hydroxy hydrogen sites to be elucidated. In contrast to the gluconate structure, there are no -oxo bridges in the isosaccharinate coordination polymer and the isosaccharinate bridging coordination is such that the distance between adjacent metal centres, each of which is eight-coordinate, is 6.7573 (4) Å . Complementing the crystal structure determinations, modelling studies of the geometries and coordination modes for the aqueous [CaGluc] + and [CaIsa] + complexes are presented and discussed. research papers Acta Cryst. (2018). B74, 598-609 V. Bugris et al. Calcium complexes relevant to problematic waste disposal 599

Single crystal growth of water-soluble metal complexes with the help of the nano-crystallization method

“…A 7 keV threshold was applied for the hybrid pixel Pilatus detector 34 in order to minimize the X-ray fluorescence caused by the cobalt complex being irradiated with copper radiation. 35 The cobalt center in 1a was assigned without any doubt to be a Co(II), because the Co-N bond length in 1a is 2.1259 (16) Å. This value is perfectly in line with the range of Co(II)-N bond lengths between 2.117(8) and 2.141(7) Å in [Co(II)(bpy) 3 ]Cl 2 .…”

“…Purity: >95% ( 1 H-NMR). TLC: R f = 0.52 (MeOH/CH 2 Cl 2 3 : 17 16;H,4.81;N,11.47. Found: C,48.74;H,4.67;N,11.93.…”

“…Bugris et al described the calcium(II) complexes of two similar polyhydroxy carboxylates, gluconate and isosaccharinate. 16 These two structures display very different shortest metal to metal distances of 3.7312(2) Å and 5.734(1) Å respectively, because in the first case a µ-oxo bridge formed by the carboxylate was present but not in the latter.…”

Magnesium(II) d-Gluconate Complexes Relevant to Radioactive Waste Disposals: Metal-Ion-Induced Ligand Deprotonation or Ligand-Promoted Metal-Ion Hydrolysis?

“…(It is worth mentioning that a complex hydrogen-bonding network is present in MgGluc + and MgGlucOH 0 , respectively. Such intramolecular interactions were found in the NaGluc and CaGluc 2 0 solid complexes as well. , ) More importantly, strong hydrogen bonding is seen between O1A and O1W as well as O3 and O3W, as for MgGluc + .…”

“…Such intramolecular interactions were found in the NaGluc and CaGluc 2 0 solid complexes as well. 74,75 ) More importantly, strong hydrogen bonding is seen between O1A and O1W as well as O3 and O3W, as for MgGluc + .…”