Viktor Gutmann

The acceptor number — A quantitative empirical parameter for the electrophilic properties of solvents

The electrophilic properties of 34 solvents have been characterized by the Acceptor Number (AN) which has been derived from31P-n.m.r. measurements of triethylphosphine oxide dissolved in the respective solvents. Relationships are found between the acceptor numbers and theZ-values,ET-values andY-values, as well as the free energies of solvation of anions and the redox potentials of the hexacyanoferrate(III)—hexacyanoferrrate(II) system in different solvents. The new parameter provides—together with the donor number—a useful guide in choosing the most appropriate solvent for a given reaction.

Structural and electronic responses of coordination compounds to changes in the molecule and molecular environment

A. Introduction B. The first bond length variation rule and the “pile up” and “spill over” effects C. The second bond length variation rule D. Variations in bond angles (i) Bond angle variation in trimethylchlorostannane (ii) Bond angle variation in tetranuclear Cu(II) complexes E. Effects at the terminal positions F. Solvent and substituent effects on iron-phenanthroline complexes ....... G. Spin transition systems H. Solvatochromism of coordination compounds (i) Bis-cyano-bis-phenanthroline-iron complexes (ii) Mixed-ligand copper and nickel complexes (iii) Solvent effects on hexathiocyanatochromate(Il1) I. Molecular system organization: chemical functionality (i) System organization in ironphenanthroline complexes (ii) Molecular system organization of haemoglobin (iii) Conclusion Acknowledgement References 159 160 163 I64 I65 168 169 169 171 172 172 173 176 177 179 180 181 I81 I81

Spin-crossover complexes in solution. III. Substituent- and solvent effects on the spin-equilibrium of 4-substituted iron(II)-2,6-bis-(benzimidazol-2′-yl)-pyridine systems

SummaryTransition metal complexes of the composition [Fe(4-X-bzimpy)2](ClO4)2 [bzimpy = 2,6-bis-(benzimidazol-2′-yl)pyridine and X=H, OH, Cl] show thermally accessible spin-crossover behaviour in solution that depends on both the ligand and the solvent.1H-NMR spectroscopy and UV-visible spectroscopy measurements suggest that ligand substituent effects, solvent donor-acceptor properties and hydrogen-bonding may be employed to “fine-tune” the ligand field strength and hence to affect the spin-crossover behaviour. The ligand substitution changes in solution are reflected by the magnetic data (X=H:μexp=2.50 μB; X=OH:μexp=4.20 μB and X=Cl:μexp=4.30 μB at 294 K in MeOH), and by the shift of metal-to-ligandcharge-transfer band (X=H, λ=557 nm; X=OH, λ=520 nm; X=Cl, λ=500 nm). [Fe(bzimpy)2](ClO4)2 exhibits a pronounced spin-crossover equilibrium (1A1 →5T2) in solution (Ksc=0.26 at 293 K; μexp=1.30 → 3.40 μB for 213 → 328 K in MeOH). A small variation of magnetic moments of [Fe(4-OH-bzimpy)2](ClO4)2 (μexp=3.77 → 4.73 μB at 220 → 332 K) might indicate either the existence of (temperature dependent) hydrogen bonding between the ligand and solvent molecules or a temperature dependent variation in the population of the5Eg sublevel. The presence of strong donor solvents (DN ⩾ 30) shifts the spin-state of the complexes.ZusammenfassungÜbergangsmetallkomplexverbindungen der Form [Fe(4-X-bzimpy)2](ClO4)2 [bzimpy = 2,6-bis-(benzimidazol-2′-yl)-pyridin und X = H, OH, Cl] zeigen thermisch anregbare Spinübergänge in Lösung, welche sowohl vom Liganden als auch vom Lösungsmittel beinflußt werden.1H-NMR- und UV-Vis-spektroskopische Messungen zeigen, daß Substituenteneffekte, Donor- und Acceptor-Eigenschaften der Lösungsmittel und Wasserstoffbrückenbindungen herangezogen werden können, um die Ligandenfeldstärke und damit das Spinübergangsverhalten zu verändern. Substituentenvariation führt zu änderungen der magnetischen Momente in Lösung (X = H:μexp = 2.50 μB; X = OH:μexp = 4.20 μB; X = Cl:μexp = 4.30 μB bei 294 K in MeOH) und zu einer Verschiebung dercharge-transfer — Bande (X = H, λ = 557 nm; X = OH, λ = 520 nm; X = Cl, λ = 500 nm). [Fe(bzimpy)2](ClO4)2 zeigt ein thermisch stark verschiebbares Spin-Gleichgewicht (1A1 →5T2) in Lösung (Ksc = 0.26 bei 293 K; μexp = 1.30 → 3.40 μB für 213 → 328 K in MeOH). Die relativ geringe Veränderung des magnetischen Moments von [Fe(4-OH-bzimpy)2](ClO4)2 (μexp = 3.77 → 4.73 μB bei 220 → 332 K) deutet auf die Existenz (temperaturabhängiger) Wasserstoffbrückenbindungen zwischen Liganden und Lösungmittelmolekülen oder auf eine temperaturabhängige Änderung der Besetzung der5Eg-Zustände. Die Anwesenheit von starken Donor-Lösungsmitteln (DN ⩾ 30) beeinflußt den Spinübergang.

Polarographisches Halbwellenpotential und Solvatation von Metallionen

ZusammenfassungDie polarographischen Halbwellenpotentiale der Perchlorate von Tl(I), Rb(I), K(I), Na(I), Ba(II), Zn(II), Cd(II), Mn(II), Co(II), Ni(II) sowie von Bisbiphenylchrom(I)jodid wurden in Dimethylsulfoxid, Dimethylformamid, Trimethylphosphat und Nitromethan gemessen. Die gemeinsame Diskussion mit den schon bekannten Werten der Halbwellenpotentiale dieser Ionen in Äthylensulfit, 1,2-Propandiolcarbonat, Acetonitril und Wasser führt zum Ergebnis, daß die Lage des Halbwellenpotentials eines Ions, bezogen auf dasjenige von Bisbiphenylchrom(I) mit steigender Donorzahl des Lösungsmittels zu negativeren Werten verschoben wird. Die Kurven imE1/2 vs.

Spectroscopic and thermodynamic studies on solvatochromic nickel(II) complexes

DZ_{SbCl_5 }

Spin-transition behaviour of transition metal complexes with 2,6-bis-(benzimidazol-2′-yl)-pyridine induced by deprotonation of the complex

-Diagramm nehmen bei vorwiegend elektrostatischer Solvatation einen anderen Verlauf, als bei stärker kovalentem Bindungscharakter der Solvatbindungen.AbstractThe polarographic half-wave potentials are reported for the perchlorates of Tl(I), Rb(I), K(I), Na(I), Ba(II), Zn(II), Cd(II), Mn(II), Co(II), Ni(II) as well as for bisbiphenylchromium(I) iodide in dimethyl sulphoxide, dimethylformamide, trimethyl phosphate and nitrobenzene. For the discussion the half-wave potentials of these ions in ethylene sulphite, 1.2-propanediol carbonate, acetonitrile and water are included. It is shown that the value for the half-wave potential of an ion referred to that of bisbiphenylchromium(I) iodide is shifted to more negative potentials, by increasing donor number of the solvent. The curves in theE1/2 vs.

Spin-crossover complexes in solution, I. Substitutional lability of [Fe(bzimpy)2](ClO4)2

DN_{SbCl_5 }