STRUCTURAL EVALUATION AND SOLUTION INTEGRITY OF ALKALI-METAL SALT COMPLEXES OF THE MANGANESE 12-METALLACROWN-4 (12-MC-4) STRUCTURAL TYPE

The preparation of a variety of salt complexes of [12-MC(Mn(III)N(shi) )-4] (1) provides the structural basis for the first quantitative inve stigation of the cation and anion selectivity of metallacrowns. The pr eparation, X-ray crystal structures, and solution integrities of cryst alline salts (LiCl2)[12-MC(Mn(III)N(shi))-4](-) ([(LiCl2). 1](-)), (Li (trifluoroacetate))]12-MC(Mn(III)N(shi))-4] ([(LiTFA). 1]), (Li)[12-MC (Mn(III)N(shi))-4](+) ([(Li). 1](+)), (NaBr)(2)[12-MC(Mn(III)N(shi))-4 ] ([(NaBr)(2) . 1]), and (KBr)(2)[12-MC(Mn(III)N(shi))-4] ([(KBr)(2) . 1]) of the metallacrown [12-MC(Mn(III)N(shi))-4] (1) are described. E ach salt complex of the metallacrown forms from a generic one-step, hi gh-yield synthesis giving 1:1 metal:metallacrown adducts with lithium and 2:1 metal:metallacrown complexes with sodium and potassium ions. O n the basis of synthetic preference, the trend for the cation affinity is Li+ > Na+ > K+ and that for anion affinity is Cl- > Br- > TFA(-) > F- approximate to I-3(-). The 12-metallacrown-4, structural parameter s compare favorably with those of 12-crown-4, an organic crown ether, as well as with those of the topologically similar alkali metal comple xes of porphyrin and phthalocyanine dianions, solidifying the structur al analogy between metallacrowns and crown ethers. The solution integr ities of the alkali metal halide salts of [12-MC(Mn(III)N(shi))-4] wer e confirmed by using paramagnetically shifted H-1 NMR, FAB-MS, ESI-MS, and UV-vis spectroscopies. Analysis of the H-1 NMR spectra and ESI-MS of the complexes proves that both the halide ions and the cations rem ain bound to the metallacrown upon dissolution. Investigations of meta llacrown ligand exchange rates demonstrate that the metallacrowns are inert to ligand exchange in DMF and acetonitrile. This broad series of salt complexes of a single metallacrown allows for comparison of the structural features influencing the stability and specificity of joint cation/anion binding in this relatively new molecular class. X-ray pa rameters: (LiCl2)[12-MCh(Mn(III)N(shi))-4](-) ([(LiCl2). 1](-)), tricl inic space group, P (1) over bar, a 12.516(2) Angstrom, b = 13.780(2) Angstrom, c = 19.943(3) Angstrom, alpha = 85.20(1)degrees, beta = 84.5 7(1)degrees, gamma = 72.18(1)degrees, V = 5059(2) Angstrom(3), Z = 2, R = 0.0773, R(w) = 0.0887; (Li(trifluoroacetate))[12-MC(Mn(III)N(shi)) -4] ([(LiTFA). 1), (monoclinic space group, Cc, a = 20.261(6) Angstrom , b = 19.577(5) Angstrom, c = 16.134(5) Angstrom, beta = 99.81(2)degre es, Z = 4, refined on \F\(2), wR(2) = 0.271; (Li)[12-MC(Mn(III)N(shi)) -4](+) ([(Li). 1](+)), (monoclinic space group, P2(1)/n, a = 14.814(4) Angstrom, b = 14.909(3) Angstrom, c = 32.26(1) Angstrom, beta = 102.4 2(2)degrees, Z = 4, refined on \F\(2), wR(2) = 0.0684; (NaBr)(2)[12-MC (Mn(III)N(shi))-4] ([(NaBr)(2) . 1]), monoclinic space group, P2(1)/n, a = 14.131(4) Angstrom, b = 13.845(3) Angstrom, c = 16.539(4) Angstro m, beta = 96.17(2)degrees, Z = 2, R = 0.0416, R(w) = 0.0419; (KBr)(2)[ 12-MC(Mn(III)N(shi))-4] ([(KBr)2 . 1), monoclinic space group, P2(1)/n , a = 11.654(3) Angstrom, b = 17.392(5) Iq, c = 16.786(5) Angstrom, be ta = 98.40(2)degrees, Z = 2, R = 0.0649, R(w) = 0.0850.