STRUCTURAL CHARACTERIZATION OF ENCAPSULATION REACTIONS BASED ON THE TRIS(ETHANE-1,2-DIAMINE)COBALT(III) ION

On the basis of structural comparisons involving intermediates and side products of encapsulation reactions as well as several cage complexes, the efficiency of the base-catalysed reaction between formaldehyde, nitromethane and [Co(en)3]3+ (en = ethane-1,2-diamine) to give [Co((NO2)2sar)]3+ appears to be explicable in terms of the 'interlocking' of constituent parts without appreciable concomitant bond length or bond angle distortions. Thus, the structures of the podand ligand complexes LAMBDA-[Co(NO2sen)] Cl3.2H2O [orthorhombic, space group P 2(1)2(1)2(1), a 18.755(6), b 11.598(4), c 9.164(3) angstrom; R 0.038 for N(o) 1735 'observed' reflections] and DELTA,LAMBDA-[Co(N(t)-Me,NO2sen)]Cl3.4H2O [monoclinic, P2(1)/n, a 18.613(5), b 9.301(3), c 13.779(4) angstrom, beta 107.10(2)-degrees; R 0.051 for N(o) 2644] show very close configurational and conformational similarities to those of the cage complexes DELTA,LAMBDA-[Co(NO2azasar)] Cl3.3H2O [monoclinic, P 2(1)/c, a 9.339(3), b 15.479(9), c 17.360(7) angstrom, beta 114.15(3)-degrees; R 0.048 for N(o) 2612], DELTA,LAMBDA-[Co((NO2)2sar)] Cl3.2H2O [triclinic, P1BAR, a 13.592(3), b 10.024(3), c 9.772(3) angstrom, alpha 62.89(2), beta 82.96(3), gamma 85.15(2)-degrees; R 0.045 for N(o) 5646] and DELTA,LAMBDA-[Co((OH)2sar)] Cl3.3H2O [monoclinic, P2(1)/c, a 15.97(1), b 8.758(4), c 16.760(4) angstrom, beta 98.72(4)-degrees; R 0.052 for N(o) 2400], as well as to published structures of [Co(en)3]3+, [CO(tame)2]3+ [tame = 1,1,1-tris-(aminomethyl)ethane = ethylidynetris(methanamine)] and other cage complexes. Some of these similarities may be associated with common hydrogen-bonding patterns in the solids resulting from anion 'chelation' by adjacent NH moieties in the metal ion coordination spheres. Necessary caution in relating structural and electronic properties is implied by the structure determination for DELTA,LAMBDA-[Co(Cl,ClCH2absar)](NO3)3 [monoclinic, P2(1)/c, a 14.750(6), b 9.264(3), c 17.959(7) angstrom, beta 95.80(3)-degrees; R 0.061 for N(o) 1431], one of the products of molecular rearrangement following nitrosation of [Co((NH2)2sar)]3+. Despite marked electronic spectral and electrochemical differences with its parent complex, [Co(Cl,ClCH2absar)] (NO3)3 contains cobalt(III) in a coordination environment which remains similar to those in more symmetrical cage complexes.