Coordination Chemistry - ACS Publications - American Chemical Society

Downloaded by UNIV OF MINNESOTA on April 16, 2013 | http://pubs.acs.org Publication Date: November 4, 1994 | doi: 10.1021/bk-1994-0565.ch009

"Jannik's Tea Table." From left to right: Flemming Woldbye, Carl Johan Ballhausen, Jannik Bjerrum, Arthur W. Adamson, Edmund Rancke-Madsen, Niels Hofman-Bang, Ingeborg Poulsen, Knud Georg Poulsen, Claus Erik Schiffer, and Christian Klixbull Jérgensen. (Photo courtesy of Fred Basolo.)

In Coordination Chemistry; Kauffman, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

Chapter 9

Jannik Bjerrum's Later Life—Turning Toward Chemical Physics Personal Recollections of a Grateful Student


Christian Κ. Jørgensen Section of Chemistry, University of Geneva, 30 Quai Ansermet, C H 1211 Geneva 4, Switzerland

An interest since 1934 in absorption spectra of copper(II) and nickel(II) complexes as "fingerprint" identification of each species in solution and the awakening awareness of new quantum physical interpretations of excited states (until 1956 by the fragile hypothesis of perturbation by the tiny nonspherical portion of the Madelung potential due to the surrounding electric charges) involved Jannik Bjerrum somewhat remotely during his later years in the (rapidly modifying) frame of "ligand field" theory and the Angular Overlap Model elaborated by Claus Schäffer.After his retirement in 1979, Jannik returned to the old problem of very small formation constants and the relationships between collective properties in physical chemistry and in modern chemical physics. Jannik Bjerrum received a thorough t r a i n i n g (both i n his home laboratory and at the University of Copenhagen) i n c l a s s i c a l chemistry,including q u a l i t a t i v e and quantitative analysis (_1). He developed new synthetic methods and worked on ammonia and ethylenediamine complexes (the favorite ligands (2,3) of Sophus M. J^rgensen) of copper(II) and copper(I) since 1931, followed by the elaboration of the glass-electrode method of studying complexes of Br^nsted bases with ions of metallic elements (4,5) (the two major problems being competing formation of monomeric and/or polymeric hydroxo complexes and the slow or even irreproducible kinetics) such as colored nickel(II) and colorless z i n c ( I I ) , cadmium(II), and nitrogen-bonded complexes. There i s no doubt that Jannik Bjerrum obtained much i n s p i r a t i o n from the k i n e t i c and equilibrium studies of his father Niels Bjerrum (1879-1958), the physical chemist (6) best known for his work on chromium(III) complexes. Jannik obtained a comparable success, studying octahedral cobalt(III) complexes of the and type (later extended to N O but not beyond S.M. Jçirgensen s type Ν 0 prepared v i a [(0 NOJ Co(NH ) ] c r y s t a l s ) . Jannik's great innovation of using activated charcoal as a catalyst for cobalt(III) e q u i l i b r i a also showed i t s i n t r i n s i c l i m i t a t i o n s by inducing 1

3

3

3

3

0097-6156/94/0565-0117$08.00/0 © 1994 American Chemical Society In Coordination Chemistry; Kauffman, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.


118

COORDINATION CHEMISTRY

p r e c i p i t a t i o n of black hydroxyoxides that resemble the mineral (known for i t s incorporation of many trace metals) heterogenite. Jannik's concept of the formation curve i s a t o o l for astutely analyzing the c o l l e c t i v e (average) properties of a mixture of a given M ion's complexes i n solution that attains i t s purpose by the choice of highly variant t o t a l M and t o t a l L concentrations. Jannik also used m e t a l l i c electrodes to obtain free [M] v i a Nernst's law, but few elements are " s o f t " enough, although they may work i n amalgams. In 1946 he suggested the p r i n c i p l e of corresponding solutions, which states that (exclusively monomeric) complexes have i d e n t i c a l spectra (per mole) for the same n. Because a monochromatic mercury atomic l i n e at 436 nm was a v a i l a b l e , he studied CuCl^ ,the only constituent absorbing there ( i n an electron transfer band), and he used his (4,5) scheme "upside-down" to deduce the r e l a t i v e amounts of η = 0,1,2,and 3 copper(II) chloro complexes. With modern e l e c t r o n i c recording spectrophotometers, thjs idea i s v e r s a t i l e ; I used_jt to show that K for PdCl^ is 6 M rather than of order 100 M as reported. If the determination of formation constants i s an ultimate goal, the optimal data would be sets of,e.ç[. ,10 or 20 narrow signals from each species i n transparent systems, with i n t e n s i t i e s (above background) proportional to concentrations and also mutually noni n t e r f e r i n g . Raman spectra were the closest to f i t t h i s demand i n 1950-60, but A.W.Langseth (1895-1961) at the University of Copenhagen pointed out that a broad background marred aqueous solutions and that even organic solvents or low-melting s a l t s required exceptional precautions i n order to be s u f f i c i e n t l y limpid. (These d i f f i c u l t i e s have been almost completely removed by modern laser equipment). Hence Jannik turned to absorption spectra i n the v i s i b l e , which he had already studied with p r i m i t i v e spectrophotometers (4) of copper(II) and of n i c k e l ( I I ) aqua-ammonia complexes. Had he been more interested i n the narrow absorption ban^s of t r i v a l e n t lanthanides (2,8^ having electron configurations 4f of praseodymium(III) through 4f of ytterbium(III), he might have turned toward t h e i r complexes (mainly bonded to oxygen atoms i n solvents or in,usually multidentate anions). This approach only gave an intended (9) demonstration of the exchange of methanol with (about 30 times more strongly bound H 0) on 4f neodymium(III), but the spectral changes ( i n p a r t i c u l a r of the exceedingly narrow band moving from 427.3 nm i n water i n d i r e c t i o n of 430 nm) are r e a l l y due more £o Nd(III) i n anhydrous methanol binding chloride, ClNd(CH 0H) , subsequently releasing chloride by addition of smal^ amounts of water, providing mixed complexes (H 0) Nd(CH OH) . Above 20 volume procent (10 molar) water, i t remains a unsettled question whether vanishing y i s accompanied by χ = 9 (as i n several c r y s t a l s ) or, i n part, 8. Hydrochloric acid (10,ll)has to be above 5 M before ClNd(0H ) 2+ can be detected. Related studies (12-14) of cobalt(II) and n i c k e l ( I I ) nitrate and various slowly reacting chromium(III) s a l t s i n ethanol with low water content unexpectedly showed that agreement with the mass-action law ( i n concentration units) i s the exception rather than the r u l e i n such solutions, complicated by the much stronger a f f i n i t y to n i t r a t e , as compared with pure water. Something valuable emerged from t h i s confusion; i t showed that r e l y i n g on "neutral s a l t media" to keep the mass-action law approximately v a l i d (without aberrant variations of " a c t i v i t y c o e f f i c i e n t s " ) i s barely conceivable f o r water concentrations 4

3

2

2

3

n

+

2

x

3


9. J0RGENSEN

119

Jannik Bjerrum's Later Life

below 10 volume percent. I t was shown (9,10,12.) that these anomalies are not e s s e n t i a l l y due to lower d i e l e c t r i c constants of the bulk solvent; the r e l a t i v e binding of water compared to n i t r a t e or chloride anions i s "chemical" i n o r i g i n . Jannik Bjerrum and I (having d i f f e r e n t , but complementary,distinct motivations) sought a convincing explanation for absorption bands (i.e.,colors) of complexes containing a p a r t i a l l y f i l l e d 3d-,4d-, or 5d-shell (the corresponding 4 f problem can be reduced (2) to the d i s t r i b u t i o n of J - l e v e l s of an i s o l a t e d Ln ion, each of t h e i r (2J+1) states d i f f e r i n g very s l i g h t l y i n energy because of the l i g a t i n g atoms marginally perturbing (15-19) the spherical symmetry). In 1952 the p r e v a i l i n g r a t i o n a l i z a t i o n of chemical bonding i n d complexes was (rather unconvincingly) based on hybridization theory (20-23) incorporating the Lewis paradigm (from 1916) of electron-pair bonds. One afternoon i n late f a l l 1952 Jannik's student C a r l Johan Ballhausen and I encountered a paper (24) by the late F r i e d r i c h U s e and by Hermann Hartmann,who ascribedl^he purple color of conceptually simple 3d systems, such as Ti(0H ) , to the energy difference between high-lying (4 states) and tne ground state (6 almost coincident states) due to the (very small) nonspherical deviation U(x,y,z) from the (huge) s p h e r i c a l part U ( r ) of ^ h e ^ a d g l u n g ^ o t e n t i a l (having the titanium nucleus at (0,0,0) and r = χ + y + ζ ). However much such an " e l e c t r o s t a t i c c r y s t a l f i e l d " got described i n 10 or 20 books (the most i n s t r u c t i v e perhaps being the one (25) by the late John S. G r i f f i t h ) , t h i s description collapsed at the Solvay meeting on Chemistry at Brussels (May 1956) and had a c t u a l l y reduced i t s e l f ad absurdam by Hermann Hartmann and Hans Ludwig Schlâfer's paper (26) i n 1954 showing that the " c r y s t a l f i e l d parameter" (only one f o r a regular octahedral d-group MX with s i x ^dentical M-X distance^ R) i s the same (within a factor of 1.1) f o r 3d chromium(III) and 3d vanadium(III) complexes of oxide, hydroxide, oxalate, malonate, and aqua ligands (usually s l i g h t l y smaller f o r anion ligands than f o r H 0) and invariably larger (27) f o r ammonia. A further d i f f i c u l t y was that noncubic perturbations i n MX^L, trans- and cis-MX^I^, quadratic MX , and l i n e a r XMX should have been much more prominent and dependent on R i n contrast to R f o r MX^ with a l l nuclei on Cartesian axes. During conversations Jannik emphasized (and cautiously elaborated by textbook arguments)that formation constants Κ are related (28) to to RT(ln Κ ), replacing one or several aqua ligands with the n'th instance o? the ligand considered. A c t u a l l y , i n h i s thesis (4) h e discussed the f a r larger free energy decrease of a gaseous ion M when immersed i n water and binding Ν aqua ligands (including quite s i g n i f i c a n t "second-sphere" s t a b i l i z a t i o n ) . This was transgressing the very powerful taboo i n pre-1950 p h y s i c a l chemistry that numerical differences of free energy f o r t r a n s f e r r i n g a set of species from one phase (e.£., a vacuum, or very low pressure of helium) to another (e.£., a solvent) are dogmatically devoid of meaning, unless the set of species i s e l e c t r i c a l l y neutral (as are Al and three-. CI but not any single ion). This i n i t i a t e d a réévaluation of the Debye-Hiickel concept of single-ion a c t i v i t i e s as a function of concentration and almost resulted i n the abandonment of the Arrhenius paradigm by a few c r i t i c a l readers. Niels Bjerrum's l a s t paper (29)discussed single-ion a c t i v i t i e s , a t y p i c a l Danish scruple. q


+

2

Q

2

4

z +


120


A major reason f o r the clash of c l a s s i c a l p h y s i c a l chemistry with the concepts of chemical physics was the series l i m i t s i n the 1895 Rydberg formula (30) providing precise i o n i z a t i o n energies I [.i.e., the energy.difference between the ground state of M and the ground state of M ] f o r many monatomic gaseous ions and atoms (n = 1). Admittedly,the huge I are differences of energy rather than of free energy, but i t i s also true that the separation between concepts (of major concern to p h y s i c a l chemistry) such as enthalpy and free energy usually are several orders of magnitude smaller than I . As Planck stated concerning adversaries of new paradigms, the persons finding i t sacrilegious to define the chemical i o n i z a t i o n energy f o r the


reaction

î H

2

(g) + H 0 2

(aq) = H 0 3

+

(aq) + e" (g)

slowly l e f t the arena. One day i n 1957 Jannik forgot that on p. 79 of his thesis (4) the hydration energy of a gaseous proton i s close to 10.5 eV. A review by Rosseinsky (31) estimated the value as 11.2 eV, and slowly, t h i s concept became less objectionable (28,30,32), and a IUPAC report (33) gave a constant (4.42 V compared to 4.5 V by Rosseinsky) that one should add to a standard oxidation g o t e n t i a l Ε i n aqueous solution (4.6 V i n CH CN) to obtain l = (E + 4.42) eV, easy to compare with I of gaseous ions (or, f o r that matter, with photoelectron 1^ values of gaseous molecules ). f removal of two electrons, e.£., T1(I)-»T1(III) are twice t h i s expression and f o r aqua ions 2(+1.25 + 4.42) = 11.34 eV, because Ε f o r thallium(I) aqua ions i s +1.25 V r e l a t i v e to the standard hydrogen electrode. In Copenhagen an early interest i n " c r y s t a l f i e l d " theory centered around the s t a b i l i z a t i o n of p a r t l y f i l l e d shells d i n octahedral complexes. Jannik,being f u l l y aware of the dependence of observed constants on (perhaps minute) differences of energy, wrote a short (34) note and presented a paper (35) i n Amsterdam comparing 3d-group M(II) values with a l i n e a r interpolation between Ca(II) and Zn(II) and r a t i o n a l i z i n g t h e i r v a r i a t i o n by the one-electron energy difference ( E ~ E ) = ^ between the antibonding (x -y ) and (3z - r ) o r b i t a l s (at i d e n t i c a l energy i n regular octahedral MX^) and o r b i t a l s (xy), (xz), and (yz) at a d e f i n i t e lower energy. As l a t e r elaborated (36,37) the agreement i s p l a u s i b l e , but a controversy with R.J.P.Williams arose concerning the usually much higher Κ values of copper(II) complexes compared (38,39) to n i c k e l ( I I ) and zinc(II) (with a few near (35) exceptions f o r the ligands ethylenediaminetetraacetate and 1,10phenanthroline). According to Williams, the covalent bonding i s much more pronounced i n the rather oxidizing Cu(II), but t h i s comparison i s unfortunately muddled by the consequence of the Jahn-Teller e f f e c t that (χ -y ) contains one strongly antibonding^lijctron i n quadratic or distorted octahedral complexes, but the (3z - r ) o r b i t a l two weakly antibonding electrons. This l i n e of thought counts the number (a) of antibonding electrons (16,40) representing a s t a b i l i z a t i o n , under equal circumstances proportional to (2q-5a) i n MX^. The idea remains viable as a r a t i o n a l i z a t i o n of differences, when comparing with q= 0, 5 (high-spin S= 5/2), and 10. I t may be added that the e l e c t r o s t a t i c version of " c r y s t a l f i e l d " s t a b i l i z a t i o n (34,35) was based on a paper (41) published i n 1952 by two s o l i d - s t a t e p h y s i c i s t s at the P h i l i p s laboratory i n Eindhoven. However, these authors were more interested i n d i f f e r e n t i a l changes of ionic r a d i i (being somewhat shorter f o r d electron densities not being s p h e r i c a l l y symmetric, i n contrast to 3

c h e m

o

r

q

1

2

q


9. J0RGENSEN


ά ,high-spin d°, and d ) . In a l l of these cases, the slopes between reference closed-shells Ca(II) and Zn(II) or Sc(III) and Ga(III) are not r e a d i l y amenable to a general hypothesis (39,42), and today, "ligand f i e l d " e f f e c t s seem to be a minor,superposed contribution. With time the l a t t e r quantities descended to a status similar to solvent and substituent inductive pK changes of acids. Being more impressed by extensive calculations and applied mathematics than I, i n 1956-1960 Jannik established a modus vivendi with the nonspherical e l e c t r o s t a t i c paradigm as the conceptual picture of d-group energy l e v e l s . Then, a constructive a l t e r n a t i v e was slowly established by Claus E Schâffer (16,40,43) as the angular overlap (A.O.M.) model of one-electron energy differences between the f i v e dl i k e o r b i t a l s (derived from ideas behind the extended Huckel treatment) An important argument_was_the v e r i f i e d comparison (40) of the i f - a n t i bonding e f f e c t (OH ,F ,C1 ,Br ,1 ) and the f T -bonding e f f e c t i n CN , pyridine, 2,2 -bipyridine, ( l i k e l y to be larger (44) f o r CO) with the ^-antibonding e f f e c t of ammonia ("one-lone-pair-ligands" being c a l l e d L) i n chromium(III) ML^, ML^X, and trans- and c i s - M L ^ (40,45). In addition to the one-electron energy parameters, a f a i r l y complicated system of i n t e r e l e c t r o n i c repulsion (Slater-Condon-Shortley parameters) introduced i n 1954 by Tanabe and Sugano (46) and elaborated by Claus E.Schâffer (27,47,48)agreed with expectations of the (not overwhelming) extent of covalent bonding induced from the nephelauxetic series of central atoms ( i n a d e f i n i t e oxidation state) and of ligands. The most appealing r a t i o n a l i z a t i o n of the nephelauxetic (cloudexpanding e f f e c t (49) i s a superposition of the moderate expansion of the 3d (or 4d or 5d) radialfunction (due to the corresponding c e n t r a l f i e l d adapting to an e f f i c i e n t M charge below the integer ζ indicated by the oxidation state) and the more "chemical" e f f e c t of d e r e a l i z a t i o n of the antibonding molecular o r b i t a l s acquiring nodes between the M and X nuclei (or even between (27) two adjacent X n u c l e i \ The work i n Copenhagen begun i n 1953 i s a prime example of the inductive approach to selected areas of t h e o r e t i c a l chemistry, unlike the more fashionable deductive method inherited from physics v i a ancient geometry, Descartes, Newton, Maxwell, E i n s t e i n , and Dirac. This does not imply that applied group theory (for which I am g r a t e f u l for the f r u i t f u l collaboration with Claus Schâffer since 1956) was not a major component i n answering the question "why are d^ complexes so frequently colored ?".Hbwever,if>comparing atomic spectra, the c l o s e l y related question of. 4f^ energy l e v e l s , and positions, band shapes, and i n t e n s i t i e s of d systems i n solution and (frequently s y n c r y s t a l l i z e d as i n ruby) i n s o l i d s (45) i s not ( i n practice) a systematic derivation from the n o n r e l a t i v i s t i c Schrôdinger equation (30), any more than one can argue that the weather forecast or the results of roulette i n a gambling casino a r e , s t r i c t l y speaking, Newtonian mechanics. Chemistry Department A of the Technical University of Denmark (T.U.) occupied the major part of the Farimagsgade wing of the L i e b i g style laboratory building ( c o l l o q u i a l l y c a l l e d "S^lvtorvet" [ S i l v e r Market] after the adjacent plaza) u n t i l the T.U. part moved to Lundtofte i n a f i e l d 17 km north of Copenhagen. In 1962 Jannik moved (with h i s smaller s t a f f appointed by the u n i v e r s i t y ) to the new buildings f o r chemistry, nonnuclear physics, and mathematics i n the five-pronged Ε-shaped "H.C.0rsted I n s t i t u t e " at Universitetsparken 5. During the time when I studied and worked at the "S^lvtorvet" building (1950-1958) the organization was rather unique and s l i g h t l y unreal and υ

± u

#


121

1

q



122


s u r r e a l i s t i c . About a dozen people, including Jannik much of the time, spent one to several hours drinking tea every afternoon (I f e e l that any reference to a painting by Leonardo da V i n c i would be rather t a s t e l e s s , but the scene resembled i t ) and t a l k i n g about chemistry, some mathematics, and very l i t t l e internal p o l i t i c s (Jannik, the highest-ranking representative of the Danish King, was present,taking his ulcer medication). They were the "inner group" (with a small minority of r e a l T.U. people) trying i t s best to manage the unwieldy output of students, f i r s t and second year stud.polyt. (chemical engineering) about a hundred each year, including 1.4 university stud.mag.(aspirants to become tea drinkers). At any time, our laboratory might burn or blow up, but never have a student r e v o l t ( i t was before 1968). The closest analogy i s a dozen Oxford college fellows t r y i n g to form a c i v i l i z i n g Langmuir-Blodgett f i l m on the affluent natives of Zanzibar (destined to do more managing than chemical research and reading). Jannik's pedagogic influence was not only the t a c i t (not alluding to me) example of how to behave when p r a c t i c i n g the most f a s c i n a t i n g of a l l professions. He had a great influence by a l l o t i n g the f i n a l tasks before obtaining the medieval degree of magister scientiarum (meaning that one i s a f u l l - f l e d g e d u n i v e r s i t y teacher). I was a s i n g u l a r i t y inside a tiny minority of tea drinkers (_1). I knew every comma i n the Royal Resolution about how to become a candidatus magisterii ( i t saved from 43 afternoons of organic lab synthesis). This species (and with chemistry as major subject, only marginally less scarce than unicorns) i s expected to become a Gymnasium (secondary school) teacher i n h i s s p e c i a l i t y after having then passed a month of p r a c t i c a l pedagogics (which I never dared to t r y ) . For the f i r s t three years, such students studied nearly equal amounts of mathematics, astronomy, and chemistry (disregarding t h e i r s p e c i a l i z a t i o n , except f o r p r a c t i c a l laboratory work some afternoons). I l i t e r a l l y shopped around (as the university advised) several days i n August 1950, looking at: t h e o r e t i c a l physics; atomic spectra (with my o l d f r i e n d , Professor Ebbe Rasmussen); astrophysics; and f i n a l l y inorganic (etc.) chemistry. A r r i v i n g at t h i s scenario of King Arthur and h i s Round Table (even Arthur Adamson from Los Angeles arrived l a t e r and learned h i s languages nos. 21 to 29 i n Copenhagen), I stayed. In May 1951, I presented a seminar, "Differences and Some S i m i l a r i t i e s between Lanthanides and Transthorium Elements" (that the Royal Resolution tolerated during any year but scheduled f o r me i n 1954). A few perspicacious colleagues r e a l i z e d that there would be minor problems one day. Apparently Jannik was s a t i s f i e d with a r a t i o n a l i z a t i o n of the dgroup colors now developing, but the arguments by Racah (50) about 4 f were adapted by Claus Schâffer to d configurations both f o r spherical and octahedral symmetry. It should be remembered(51,52) that a pure configuration d or f has many admirable properties ( l i k e a polyhedron with many d i f f e r e n t faces) but that the Schrôdinger manyelectron solutions normally contain several percent (30) of each of a few d i f f e r e n t configurations possessing squared amplitudes mixed with the preponderant (49) electron configuration (evaluated by HartreeFock technique) determining the J-values of the lower-lying energy l e v e l s . Very diplomatically Jannik c a l l e d a l l r a t i o n a l i z a t i o n s of observed excited states "ligand f i e l d " theory, disregarding the fact q

q

q

q



9. JQRGENSEN

123


that one should then add a year (1955; 1959;1965; 1971; 1986) etc.(?) as when speaking about a developing airplane type. As the actresses i n the "salon" said to Louis XIV i n the movie •Versailles" by Sacha Guitry, "We were the Golden Age", the tea drinkers are not overstepping t h e i r q u a l i f i c a t i o n s by saying something s i m i l a r . I have reached the conclusion that I remained an inorganic chemist due to a meeting i n September 1950 with my h i e r a r c h i c a l superior, Lene Rasmussen (Magister 1953; Lecturer at the Ife University, Ibadan,in Nigeria,1964 and l a t e r back at Aarhus University) i n the q u a l i t a t i v e analysis course (this would correspond to General Chemistry i n United States because there were 55 elements to separate) during both f i r s t year semesters. I was l a t e r appointed sub-instructor there, and f o r a few years Amanuensis I I . Jannik required Lene to write a short book on unusual oxidation states (for the Magister degree), and she and I decided what was "unusual". We both recognized many p r o l i f e r a t i n g mistakes i n l i t e r a t u r e but also the adamant concept that facts are stubborn (as one l i v i n g i n St.Petersburg once wrote). Since my period of photoelectron spectra of inorganic s o l i d s (1970-1979), which I spent r e s h u f f l i n g and wrinkling quantum chemistry quite a b i t , I now r e a l i z e that I have recycled (or regressed) to the role of a part-time atomic spectroscopist as well as astrophysicist because I was i n v i t e d to write reviews f o r Comments on Inorganic Chemistry (30), edited by Fred Basolo, and f o r Comments on Astrophysics (53), edited by V i r g i n i a Trimble. In 1992, at the XXIX.ICCC i n Lausanne where I received a free sample (909 pages) of Inorganica Chimica Acta, I suddenly f e l t as i f I had stumbled over the e x i t from the Elverh^j ("The Fairy H i l l " ) where I had l i v e d as a chemist f o r 40 years. — But what an experience \ When Jannik r e t i r e d i n 1979, he returned to h i s e a r l i e r passions in the laboratory. Just as Lene and I had determined the largest formation constants of any ammonia or ethylenediamine complexes (54), of palladium(II), Jannik determined the smallest constants: iron(III) 3

η ) +

2

n ) +

i n FeCl " and various FeCl (OH.) * ~ ( 5 5 ) , CuCl (OH ) < " (56); + 2+ n ^ x NiCl(0H_) (57), octahedral CiCriOHOr , Cl Cr(0H )„ ,and probably n

1

x

c

Ζ

Cl Cr(OH ) 3

Ζ

D 2

D +

3

n

o

Ζ

Ζ 4

i n 12.5 M L i C l (58); B r N i ( O H ) w i t h 2

5

Κ

= 0.005 M

χ

and not f a r (60) from Κ ~0.003, Κ ^0.00035, and Κ ~ 4 · 1 θ " 3

3

n

5

(59).

for

+

+

Br C r ( 0 H ) / ~ ) . Jannik (61)reviewed octahedral (H 0) Co(NCS) and η z b-n — z D (H 0) Co(NCS) as well as tetrahedral Co(NCS) and (H 0)Co(NCS) ~ ana compared them with n i c k e l ( I I ) thiocyanates i n various solvents. These results are important f o r the spectra of inner-sphere complexes with a number of aqua and anionic ligands, whereas I submit r e s p e c t f u l l y that the arguments about d e f i n i t e a c t i v i t y c o e f f i c i e n t s (62) are rather c i r c u l a r . Jannik's l a s t publications may i l l u s t r a t e the pragmatic fact that spectra i n the v i s i b l e region are much more uniquely c h a r a c t e r i s t i c f o r the f i r s t coordination sphere, as Niels Bjerrum t o l d Werner i n 1909 f o r cases l i k e [ClCr(0H )^] as compared to ion-pairs. Disregarding undoubted " s a l t e f f e c t s " (Î2,63) t h i s i s a major d i s t i n c t i o n between chemical physics and physical chemistry. n

o

4

c

2

2


124


Acknowledgment s


I am grateful to my early student comrade Claus E . S c h â f f e r , for most valuable advice, constructive c r i t i c i s m , and continued discussions about applied group theory. I am also grateful to Professor Fred Basolo for his f r i e n d l y con versations, since he f i r s t v i s i t e d Jannik and Copenhagen and for favoring inductive discussions of s i g n i f i c a n t d e t a i l s of absorption spectra of complexes rather than r e l y i n g on ephemeral fashion i n computer chemistry. I f i n a l l y wish to thank Professor George B. Kauffman for his kind i n v i t a t i o n to p a r t i c i p a t e i n the Denver symposium and for his c a r e f u l and extended e f f o r t to e d i t and ameliorate my papers.

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9. JQRGENSEN 32. 33. 34. 35.


36. 37. 38. 39. 40. 41. 42. 43. 44. 4.5. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63.


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RECEIVED March 28, 1994


Coordination Chemistry - ACS Publications - American Chemical Society

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