Stereochemistry of racemic hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-dienenickel(II) thiocyanate, C₁₆H₃₂N₄Ni(SCN)₂ · H₂O

Abstract

The diamagnetictrans-diene thiocyanate salt of the macrocyclic hexamethyl-1,4,8,11-tetraazacyclotetradecadienenickel(II) complex crystallizes in the triclinic system with unit cell dimensions:a = 7·334(4),b = 8·808(6),c = 21·04(2) Å; α = 63·7(0·9), β = 103·8(1·4), γ = 110·2(1·3) °; space groupP¯1;Z = 2. The positions of all 62 atoms of the formula unit C₁₆H₃₂N₄Ni(SCN)₂.H₂O have been determined and refined by least-squares methods toR= 0·071 for 3536 X-ray diffractometric reflections. The optical activity of the two amine groups yields a racemic isomer. The only local symmetry element of the macrocyclic complex is the twofold rotation axis with the N-H bonds oriented on the same side of the approximate ligand plane. Both the C(CH₃)₂ and the imine groups are in atrans-configuration in the ring. The space group ensures that the crystal is a racemate, containing equal numbers of both enantiomers. One of the (SCN)⁻ groups is at a distance Ni-S 3·28 Å, the other one is 4·65 Å. No rotational disorder of the CH₃ groups has been observed. The three C-H bonds of the CH₃ groups are in approximately antiprismatic orientations with respect to the three σ-bonds in the case of bonding to a C(sp³) atom. The average of the C(sp³)-C(sp²) bond lengths is 1·53 Å, and the mean value for the C(sp³)-C(sp²) bonds is 1·50 Å, with 3σ = 0·03 to 0·04 Å. The distances N(sp²)-C(sp³) 1·47 Å and 1·48 Å are significantly longer than the bond lengths N(sp²)=C(sp²) of 1·28 and 1·30 Å.