Investigation of the aggregation of the neodymium complexes of dialkylphosphoric, -oxothiophosphinic, and -dithiophosphinic acids in toluene

Small angle neutron scattering and visible absorption spectroscopy were use d to study the neodymium. complexes of a series of acidic organophosphorus extractants in deuterated toluene at high (greater than or equal to 33% the oretical capacity) metal loading. Organic phases containing 0.10M bis(2-eth ylhexyl)phosphoric acid (HDEHP), bis(2,4,4-trimethylpentyl)oxothiophosphini c acid (HC302), or bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HC301) were used. Under these conditions, the neutron scattering experiments show that HDEHP and HC302 exist as dimeric species in the absence of Nd. Extract ion of Nd disrupts the dimeric structure of the extractants to form dinucle ar complexes with the formula Nd-2(DEHP)(6) or Nd-2(C302)(6). In contrast, 0.10M HC301 is not dimeric in deuterated toluene. At 86% of the theoretical Nd capacity, the extracted complex is also dinuclear with the average form ula Nd-2(C301)(6), but at 46% of the theoretical Nd capacity only the monon uclear complex, Nd(C301)(3), is formed. The Nd hypersensitive transitions i n the visible region of the spectrum provide further support for this inter pretation of the neutron scattering data and the equivalence of the Nd coor dination in highly loaded HDEHP and bis(2,4,4-trimethylpentyl)phosphinic ac id.