Crystal and molecular structures of alkali- and alkaline-earth-metal complexes of N,N-dimethylformamide

Abstract

Structures of lithium, sodium, magnesium, and calcium complexes of NJ-dimethylformamide (DMF) have been investigated by X-ray crystallography. Complexes with the formulas LiCl.DMF.1/2H20, NaC104.2DMF, CaC12.2DMF.2H20, and Mg(C104)2.6DMF crystallized in space groups P2]/c, P2/c, Pi, and Ella, respectively, with the following cell dimensions: Li complex, a=13.022 (7) A, b=5.978 (4) A, c=17.028 (10) A, =105.48 (4)O, Z=8; Na complex, a=9.297 (4)A, b=10.203 (3) A, c=13.510 (6) A, /3=110.08 (4)O, Z=4; Ca complex, a=6.293 (4) A, b=6.944 (2) A, c=8.853(5) A, a=110.15 (3)O, /3=105.60 (6)", y=95.34 (5)", Z=1; Mg complex, a=20.686 (11) A, b=10.962 (18) A, c=14.885 (9) A, /3=91.45 (5)O, Z=4. Lithium is tetrahedrally coordinated while the other three cations are octahedrally coordinated; the observed metal-oxygen distances are within the ranges generally found in oxygen donor complexes of these metals. The lithium and sodium complexes are polymeric, with the amide and the anion forming bridging groups between neighboring cations. The carbonyl distances become longer in the complexes accompanied by a proportionate decrease in the length of the central C-N bond of the amide; the N-C bond of the dimethylamino group also shows some changes in the complexes. The cations do not deviate significantly from the lone-pair direction of the amide carbonyl and remain in the amide plane. Infrared spectra of the complexes reflect the observed changes in the amide bond distances.