ALKALI METAL-RESPONSIVE GEOMETRIC AND SPECTRAL CHANGES IN A COBALT(II) COMPLEX OF A CONSTRAINED DICARBOXYLATE - A CARBOXYLATE SHIFT-MEDIATED METALLOCHROMOIONOPHORE

A mononuclear Co(II) complex of the convergent dicarboxylate ligand xy lenediamine bis-(Kemp's triacid imide) (XDK) and neocuproine (neo, 2,9 -dimethyl-1,10-phenanthroline) has be en prepared both by demetallatio n of a dinuclear precursor with neocuproine and by direct synthesis. T he X-ray structure of this complex, [Co(XDK)(neo)]. 3CH(3)OH (1 . 3CH( 3)OH) (monoclinic P2(1)/c, a = 13.352(2), b = 16.026(3), c = 23.145(7) Angstrom, beta = 96.64(2)degrees, V = 4919(2) Angstrom(3), Z = 4, T = 173 K) shows the cobalt ion to be in a highly distorted trigonal bipy ramidal environment, with asymmetrical binding by the carboxylates of XDK. Complex 1 reacts readily with alkali metal salts to afford hetero dimetallic complexes, such as [KCo(XDK)(neo)(PF6)] (2) and [Rb2Co2(XDK )(2)-(neo)(2)(H2O)(BPh(4))(2)] (3). The X-ray structures of 2 . 2CH(3) CN: and 3 . 2CHCl(3) reveal that XDK undergoes a carboxylate shift upo n formation of the alkali metal adducts, resulting in a highly unusual distorted trigonal pyramidal geometry at the cobalt ion (2 . 2CH(3)CN : monoclinic P2(1)/c, a = 14.261(2), b = 14.275(2), c = 26.113(4) Angs trom, beta = 100.95(1)degrees, V = 5219(1) Angstrom(3), Z = 4, T = 188 K. 3 . 2CHCl(3): triclinic, P ($) over bar 1, a = 12.130(2), b = 16.4 09(3), c = 17.315(3) Angstrom, alpha = 100.09(2), beta = 103.83(1), ga mma = 96.35(2)degrees, V = 3252(1) Angstrom(3), Z = 1, T = 213 K). The alkali metal ions bind to the carboxylate and amide carbonyl oxygen a toms as well as to the PF6- or BPh(4)(-) anion. The alteration in Co(I I) geometry upon binding of the alkali metal ions to 1 is reflected by significant changes in its visible spectrum. These changes permit the reactions to be monitored spectroscopically, from which their 1:1 sto ichiometries were clearly evident.