Complexes with Carbazones, Thiocarbazones, and Formazans
Spectrophotometric studies on acetate-buffered solutions (pH 4.8) of Mn2+ ions and ligand 1, 2, or 3 at 25°C and ionic strength I=0.1(NaClO4) reveal the formation of the Mn(HL)+ complexes in each case which show the following absorption maxima λmax (in nm
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CompLexes with Carbazones, Thiocarbazones, and Formazans
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CompLexes with Carbazones, Thiocarbazones, and Formazans
32.1
Complex~s
with 1, 5-Diphenylcarbazone or Derivatives
R---NH-NH-R-N=N-@-R/
ligand
0 (= H2L)
R
R'
formuLa
1
H
H
C13H12N40
2
N0 2
H
C13HllNs03
3
H
N02
C13HllNs03
Complexes in Solution. Spectrophotometric studies on acetate-buffe red soLutions (pH 4.8) of Mn 2+ ions and ligand 1, 2, or 3 at 25°C and ionic strength 1= 0.1 (NaCL04) reveaL the formation of the Mn(HL)+ compLexes in each case which show the foLlowing absorption maxima Amax (in nm), the moLar extinction coetticients Log E (in L· moL-l. cm- 1), and the stability constants Log K, determined spectrophotometricaLly: Ligand
compLex
Amax
Log
Mn(C13HllN40)+
531
2.76
E
log K*l
2
Mn(C13Hl0Ns03)+
595
3.23
4.12 3.61
3
Mn(C13HlONs03t
572
3.18
3.50
*l K is not defined in [1]; presumably, K = [Mn(HL)+]/[Mn 2+][HL -]. The spectra and stability constants of the complexes [1] and the polarographic behavior of the complex with ligand 1 [9] suggest a structure with a five-membered chelate ring formed by coordination of one azo nitrogen atom and the oxygen atom of the deprotonated enoLic hydroxy group. The solutions of the compLexes which are not very stable obey Beer's law up to concentrations of 0.075 mmoliL [1]. Mnll(C13HllN40)2 was prepared by adding a sodium acetate-butte red aqueous solution of an Mn ll salt dropwise to an ethanoLic solution of 1,5-diphenylcarbazone (4%). After standing for 24 h at room temperature, the dark brown complex had precipitated. It was washed with distiLled water and a little ethanol (to remove excess Ligand). The IR spectrum recorded from Vaseline muLIs shows strong absorption bands (wave numbers in cm- 1) which were assigned as folIows: 3400 to 3200 cm- 1 (br) to v(OH); -1550 cm- 1 (free Ligand 1662 cm- 1) to v(N=N); -1500 cm- 1 to v(C=N). (IR bands are only given for aseries of divalent metal complexes.) Bands of the free Ligand at 1662 and 1650 cm- 1 which were assigned to v(C=O) or v(NH) vibrations, respectively, have vanished on complexation. The IR data indicate enoLization of the Ligand and its coordination by one N atom of both the azo and the hydrazide group to form a six-membered chelate ring. The complex units are connected by hydrogen bonds with the enoLic hydroxy group as the proton donor [2]. Extraction-spectrophotometric studies on aqueous solutions containing an Mn ll salt and solutions of 1, 5-diphenylcarbazone in toluene at pH 7.45 (acetate butter 0.2 M) [3, 4] or -8 [5] at 20 to 22°C under nitrogen confirm the formation of the Mn(C13HllN40h complex. The complex shows absorption maxima at 285 nm with log E = 4.40 [4] and at 495 nm [4,5] with log E = 4.38 [4] or 4.43 [5]. The partition coefficient [4] and extraction constants were evaluated [4,5]. The Mn(C13HllN40h complex is stable for only 1 to 2 min [7]. It is readily oxidized under the experimental conditions [4]. The Mn(C13HllN40h complex can be utiLized for the spectrophotometric determination of Mn in b
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