George - B. Kouffman California Stote University, Fresno Fresno, California 93710
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Heinrich ley (1872-1938) and His Concept of Inner Complex Salts
According to Diehl ( I ) , "the idea of the ring structure in ethylenediamine complexes runs subconsciously through the early papers of Werner without being definitely expressed." In his very first paper on the coordination theory (1893), Werner (2) discussed the structures of the violet (cis) and green (trans) forms of [Co(NHzCHzCHzNHz)zX2]X, discovered by his scientific adversary Sophus Mads JBrgensen (3, 4). In his treatment of what is regarded as the classic case of geometric isomerism among coordination compounds, Werner recognized that the ethylenediamine molecule occupied two coordination positions. In 1899, Werner and Vilmos (5) described the compound [Co(NHzCHzCHzNHz)zCzO~]Cl,in which, in addition to the ethylenediamine molecule, the oxalate anion was regarded as what Morgan (6) later called a chelate group. In 1901, Werner (7) prepared the nonelectrolyte bis(2,4-pentanedionato)platinum(II), an inner complex of platinum with the enolate anion of acetylacetone
in which he postulated a structure involving chelate rings. This compound has been widely regarded in the literature (8-10) as both the first inner complex and the first acetylacetonate complex to he discovered, hut as early as 1887, A. Comhes, the discoverer of acetylacetone ( l l ) , had prepared acetylacetonates of aluminum, copper, magnesium, iron, and lead (12). Furthermore, in 1899 Urhain and Dehierne had prepared chromium(II1) acetylacetonate (13). Definitions
in which each bidentate ligand is bonded to the central metal ion by both a primary valency and a secondary valency, forming a cyclic structure. Ley gave no explanation for the term "inner," but Mellor (9) assumes that it referred to Werner's inner (nonionizahle) coordination sphere as opposed to the outer (ionizable) coordination sphere. Thus an inner complex salt is a coordination compound with all ligands in the inner sphere, i.e., it is a nonelectrolyte, and the term "salt" is actually a misnomer (15). Liehhafsky (16) interprets Ley's term as follows: "inner connotes ring formation; complex, the presence of a second (coordinating) valence; and salt, the presence of a primary bond involving a negative group (in this case, NHzCHZCOO-) derived from an acid." Ley apparently intended the term inner complex to he restricted to nonelectrolytes. This restriction has been accepted hy Diehl (1) and many others but questioned hy Liehhafsky (16) and West (17). Neutral species are formed whenever the coordination number and charge of the metal ion equal the sum of the donor groups and charges, respectively, of the combining chelate groups. The commonest inner complexes are formed from bidentate ligands with one replaceable hydrogen atom and metals, the coordination numbers of which are twice their ionic charge (8). Functional groups coordinating to the metal through primary valencies (with displacement of hydrogen) include -COOH, -OH, -SOaH, -NOH, -NHz, and N R H . Those coordinating through secondary valencies (without displacement of hydrogen) include -NHz, >NH, -N
