The low molecular weight bacterial products bis(N-methylthioformohydroxamato)copper(II) (fluopsin C) and tris(N-methylthioformohydroxamato)iron(III) (fluopsin F) display broad-spectrum antibiotic activity against both gram-positive and -negative bacteria and fungi. The kinetic lability of these complexes precludes the isolation of cis and trans geometrical coordination isomers in each case. Replacement of these metal ions with ions possessing large crystal field stabilization energies induces kinetic inertness and thereby allows the possibility of isomer separation. In the series of octahedral tris(N-methylthioformohydroxamate)-metal ion substituted complexes, M(th)3 (M = Fe, Co, Cr, Rh), the latter two complexes were sufficiently substitution inert to permit the isolation and characterization of cis and trans geometrical isomers. Geometric isomerism occurs with a half-life of several hours for the chromium(III) complex and several days for the rhodium(III) complex. cis-Rh(th)3 has NMR signais for the coordinated ligand at 3.70 ppm (CH3N) and 7.17 ppm (HC(S)), whereas trans-Rh(th)3 has corresponding signais at 3.51, 3.52 and 3.76 and 7.09, 7.46 and 7.53 ppm, respectively. The cis isomer has a visible absorption maximum at 437 nm (e 490), whereas the trans isomer has the same band at 452 nm (e 725). In the series of square-planar bis(N-methylthioformohydroxamate)-metal ion substituted complexes, M(th)2 (M = Cu, Ni, Pd, Pt), cis and trans isomers were isolated and characterized in the last case. The infrared spectra of the two platinum(II) isomers are virtually superimposable except in the vicinity of 675 and 875 cm-1. In these regions the trans isomer has absorption bands at 686 and 878 cm-1, whereas the cis isomer has absorptions at 649 and 681 cm-1 and 874 and 893 cm-1. The cis isomer has a visible absorption maximum at 429 nm (e 126), whereas the trans isomer has the same absorption at 439 nm (e 116). Geometric isomerism occurs with a half-life of several days. © 1978, American Chemical Society. All rights reserved.
