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Dissertation Jens Hallfeldt Synthese, Kristallstrukturen und magnetische Eigenschaften von komplexen Halogeniden der Lanthanide mit Trimethylpyridinium- und Dimethylpyridiniumkationen dem Fachbereich Chemie der Universität Hannover zur Erlangung des Grades Doktor der Naturwissenschaften – Dr.rer.nat. – genehmigte Dissertation von Dipl.-Chem. Jens Hallfeldt geboren am 21.Juni 1972 in Bückeburg 2003 Jens Hallfeldt Dissertation Das Titelbild zeigt in der oberen Graphik einen Ausschnitt aus der Kristallstruktur von (3,5-Dimethylpyridinium)2[LaCl4(H2O)2]Cl; darunter von links nach rechts: – die beobachtete Elektronendichte in der Ebene durch ein 2,4,6-Trimethylpyridiniummolekül in (2,4,6-Trimethylpyridinium)4[LnCl6]Cl, – die Umgebung von La in (2,6-Dimethylpyridinium)[LaCl4(H2O)2], – Produktkristalle der Reaktion von 2,4,6-Trimethylpyridiniumchlorid mit TbCl3·6H2O, – die Umgebung von Er in (2,4,6-Trimethylpyridinium)3[ErCl5(H2O)]Cl, – die Restelektronendichte um um das freie Wassermolekül in (2,6-Dimethylpyridinium)3[TbCl6] · H2O. Synthese, Kristallstrukturen und magnetische Eigenschaften von komplexen Halogeniden der Lanthanide mit Trimethylpyridinium- und Dimethylpyridiniumkationen dem Fachbereich Chemie der Universität Hannover zur Erlangung des Grades Doktor der Naturwissenschaften – Dr.rer.nat. – genehmigte Dissertation von Dipl.-Chem.Jens Hallfeldt geboren am 21.Juni 1972 in Bückeburg 2003 Referent: Prof.Dr.W.Urland Korreferent: Prof.Dr.P.Behrens Tag der Promotion: 09.02.2004 n ungezählten ühen wächst das chöne pikur VIII IX Danksagung Der praktische Teil der vorliegende Arbeit wurde im Zeitraum vom Juni 2000 bis zum Mai des Jahres 2003 am Institut für Anorganische Chemie der Universität Hannover unter der Leitung von Herrn Prof.Dr.Werner Urland angefertigt. Ihm gilt mein besonderer Dank für die persönliche Betreuung und Unterstützung, die Gewährung weitreichender Freiheiten sowie die vielfältigen Anregungen und Diskussionen. Für die Übernahme des Korreferates danke ich Herrn Prof.Dr.Peter Behrens. Herrn Dr.Rudolf Wartchow gilt mein Dank für das Aufnehmen der Einkristalldatensätze und seine stete Hilfsbereitschaft bei „Problemkristallen“. Herrn Prof.Dr.Josef Breu und Herrn Dominikus Huttner von der Universität Bayreuth gebührt Dank für die Durchführung von Dichtefunktional- und Energieminimierungsrechnungen. Für seine Einführung in die Röntgenstrukturanalyse danke ich Herrn Dr. Helmut Person, dem wie auch Frau Dr. Annette Becker, Herrn Dr. Frank Soetebier, Frau Annemarie Bachthaler und Frau Dagmar Grüne aus dem Arbeitskreis Dank für ihre Unterstützung gilt. Dank, nicht nur für Ihre erfolgreichen Bemühungen um den Betrieb der Röntgenpulverdiffraktometrie, gebührt Herrn Clemens Kühn und Herrn Olaf Oellrich. Den Mitgliedern des Arbeitskreises Behrens gilt mein besonderer Dank für viele schöne Momente bei den gemeinsamen Mittagsrunden und Teestunden und die ausnahmslos hervorragende Zusammenarbeit. Ein Dank für die Übernahme des Lektorats geht an Frau Birthe Musolf und Herrn Alexander Rohde. Nicht zuletzt sei all denen gedankt, die mich mental wie materiell in meiner Studienzeit unterstützt haben. X Kurzzusammenfassung XI Kurzzusammenfassung 1. Bei der Umsetzung von LnCl3 ·xH2O (Ln = Ce–Lu, x = 6–7) bzw. LaCl3 mit 2,4,6- Trimethylpyridiniumchlorid bzw. 3,5-Dimethylpyridiniumchlorid bzw. 2,6-Dimethyl- pyridiniumchlorid wurden 22 komplexe Chloride erstmals dargestellt und ihre Kri- stallstrukturen anhand von röntgenographischen Einkristalldaten bestimmt. Es wurden neun neue Strukturtypen gefunden. a) (2,4,6-Trimethylpyridinium)3[LnCl6] (Ln = Nd, Eu, Tb, Tm; Strukturtyp I) b) (2,4,6-Trimethylpyridinium)3[LnCl6] (Ln = Ce, Pr, Sm, Dy, Ho; Strukturtyp II) c) Die Verbindungen (2,4,6-Trimethylpyridinium)3[LnCl6] (Ln = Gd, Er) treten in zwei Modifikationen auf, die jeweils in den Strukturtypen I (a-(2,4,6-Trimethylpy- ridinium)3[LnCl6]) und II (b-(2,4,6-Trimethylpyridinium)3[LnCl6]) kristallisieren. d) (2,4,6-Trimethylpyridinium)4[LaCl6]Cl e) (2,4,6-Trimethylpyridinium)10[LnCl6][LnCl5(H2O)]2Cl3 (Ln = Er, Yb) f) (2,4,6-Trimethylpyridinium)3[LnCl5(H2O)]Cl (Ln = Er, Lu) g) (3,5-Dimethylpyridinium)2[LnCl4(H2O)2]Cl (Ln = La, Pr) h) (3,5-Dimethylpyridinium)3[TbCl6] i) (2,6-Dimethylpyridinium)2[LaCl4(H2O)2] j) (2,6-Dimethylpyridinium)3[LnCl6]·H2O (Ln = Pr, Tb) 2.Zur Abschätzung der thermodynamischen Stabilität der beiden Modifikationen von (2,4,6-Trimethylpyridinium)3[ErCl6] erfolgte eine Berechnung der Gitterenergien. Es ergab sich eine um 31,15 kJ·mol−1 geringere Gitterenergie für b-(2,4,6-Trimethylpyri- dinium)3[ErCl6]. 3. In Equilibrierungsexperimenten konnte die quantitative Umwandlung der a-Modifika- tion in die b-Modifikation von (2,4,6-Trimethylpyridinium)3[ErCl6] unter Anwendung der Röntgenpulverdiffraktometrie dokumentiert werden. Dieses Ergebnis bestätigt das Resultat der Gitterenergieberechnungen. 4. An Pulverproben von (2,4,6-Trimethylpyridinium)10[ErCl6][ErCl5(H2O)]2Cl3 wurden magnetische Messungen durchgeführt. Die Verbindung zeigt paramagnetisches Verhalten. Es konnte eine gute Übereinstim- mung mit den nach dem Angular-Overlap-Modell berechneten Suszeptibilitätswerten erreicht werden. 5. An pulverisierten Proben von (2,4,6-Trimethylpyridinium)3[ErCl6] des Strukturtypes I wurden magnetische Messungen durchgeführt. Die Verbindung erwies sich als paramagnetisch. Auch hier konnte eine gute Überein- stimmung mit den nach dem Angular-Overlap-Modell berechneten Suszeptibilitäts- werten erreicht werden. Stichworte: Komplexe Chloride der Lanthanide, Kristallstrukturen, Magnetismus XII Abstract XIII Abstract 1. By reaction of LnCl3 ·xH2O (Ln = La–Lu, x = 6–7) respectively LaCl3 with 2,4,6-tri- methylpyridinium chloride respectively 3,5-dimethylpyridinium chloride respectively 2,6-dimethylpyridinium chloride 22 complex chlorides have been prepared for the first time. The structures were determined using X-ray diffractometry on single crystals. Nine new structure types were found. a) (2,4,6-Trimethylpyridinium)3[LnCl6] (Ln = Nd, Eu, Tb, Tm; structure type I) b) (2,4,6-Trimethylpyridinium)3[LnCl6] (Ln = Ce, Pr, Sm, Dy, Ho; structure type II) c) The compounds (2,4,6-trimethylpyridinium)3[LnCl6] (Ln = Gd, Er) were both obtained in two polymorphs. They cristallise in structure type I (a-(2,4,6-Trime- thylpyridinium)3[LnCl6]), respectively in structure type II (b-(2,4,6-Trimethylpyri- dinium)3[LnCl6]). d) (2,4,6-Trimethylpyridinium)4[LaCl6]Cl e) (2,4,6-Trimethylpyridinium)10[LnCl6][LnCl5(H2O)]2Cl3 (Ln = Er, Yb) f) (2,4,6-Trimethylpyridinium)3[LnCl5(H2O)]Cl (Ln = Er, Lu) g) (3,5-Dimethylpyridinium)2[LnCl4(H2O)2]Cl (Ln = La, Pr) h) (3,5-Dimethylpyridinium)3[TbCl6] i) (2,6-Dimethylpyridinium)2[LaCl4(H2O)2] j) (2,6-Dimethylpyridinium)3[LnCl6]·H2O (Ln = Pr, Tb) 2. The relative thermodynamic stabilities of the two polymorphs of (2,4,6-trimethylpyri- dinium)3[ErCl6] were predicted by lattice energy calculations. The results of the calculations show a lower lattice energy of the b-(2,4,6-trimethylpy- −1 ridinium)3[ErCl6] by 31.15 kJ·mol . 3. The complete transformation of the a-polymorph into the b-polymorph of (2,4,6- trimethylpyridinium)3[ErCl6] could be proved in equilibration experiments using X-ray powder diffractometry. This result is in line with the lattice energy calculations. 4. Magnetic susceptibility measurements on crushed crystals of the complex chloride (2,4,6-trimethylpyridinium)10[ErCl6][ErCl5(H2O)]2Cl3 were performed. The compound shows paramagnetic behavior. The magnetic data were interpretatated using ligand field calculations applying the angular overlap model where a good agree- ment of the observed calculated susceptibilities is observed. 5. On powder samples of (2,4,6-trimethylpyridinium)3[ErCl6] (type I) magnetic suscepti- bility measurements were performed. The compound shows paramagnetic behavior and a good agreement of the observed susceptibilities with calculated susceptibilities applying the angular overlap model. Keywords: complex chlorides of the lanthanides, crystal structures, magnetism XIV Inhaltsverzeichnis XV Inhaltsverzeichnis Kapitel 1 Einleitung . 1 Kapitel 2 Methoden der Röntgenstrukturanalyse . .5 2.1 Grundlagen der Röntgenbeugung . 5 2.2 Röntgenpulverdiffraktometrie . 6 2.3 Einkristalldiffraktometrie . 6 2.3.1 Imaging-Plate-Diffraction-System (IPDS) . 6 2.4 Rechenverfahren zur Kristallstrukturanalyse . 6 2.4.1 Direkte Methoden . 8 2.4.2 Korrekturen . 8 2.4.3 Gütefaktoren der Strukturbestimmung . 11 2.4.4 Verfeinerung der Wasserstoffatome . 12 2.5 Rechenprogramme . 14 Kapitel 3 Magnetische Eigenschaften . .15 3.1 Grundbegriffe . 15 3.2 Magnetische Eigenschaften der Materie . 16 3.3 Interpretation der magnetischen Suszeptibilitätsmessungen . 19 3.3.1 Einleitung . 19 3.3.2 Das Angular-Overlap-Modell (AOM) . 22 3.3.3 Rechenprogramme . 23 XVI Inhaltsverzeichnis Kapitel 4 Das SQUID-Magnetometer . 25 4.1 Gerätebeschreibung . 25 4.2 Meßtechnik . 25 4.2.1 Probenvorbereitung und Funktionsprinzip der Signalaufnahme . 25 4.2.2 Funktionsweise des SQUID-Sensors . 27 4.2.2.1 Makroskopische Quanteninterferenz . 27 Kapitel 5 Berechnung der Gitterenergie . 31 5.1 Vorbemerkungen . 31 5.2 Berechnung der Gitterenergiewerte . 32 5.2.1 Dichtefunktionaltheorie . 32 5.2.2 Energieminimierungsrechnungen nach der „Rigid Body“-Näherung . 32 Kapitel 6 Synthese der komplexen Chloride . 35 6.1 Edukte . 35 6.2 Darstellung der komplexen Chloride . 36 6.2.1 Darstellung der Verbindungen mit 2,4,6-Trimethylpyridiniumionen . 36 6.2.2 Darstellung der Verbindungen mit 3,5-Dimethylpyridiniumionen . 37 6.2.3 Darstellung der Verbindungen mit 2,6-Dimethylpyridiniumionen . 37 6.3
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