Thermodynamic Studies of Co(II) Complexation with Schiff Base Ligands in Different Nonaqueous Solvents

Öz

This study investigates the synthesis and characterization of two novel Schiff base ligands, L1 and L2, and their complexation behavior with Co(II) ions in non-aqueous media. Ligand L1 was synthesized using o-hydroxyacetophenone and salicylaldehyde with ethylenediamine, while L2 was prepared with 2,3-dihydroxybenzaldehyde and ethylenediamine. Conductometric measurements in ethanol, acetonitrile, and a 1:1 mixture of these solvents at temperatures ranging from 25°C to 40°C determined the stability constants of the Co(II) complexes. Results showed distinct temperature-dependent stability trends: L1 complexes decreased in stability with increasing temperature in all solvents, indicating exothermic reactions, while L2 complexes showed varied behavior, suggesting endothermic reactions in acetonitrile and the mixed solvent. The solvent environment significantly influenced complex stability, with acetonitrile showing the highest stability, followed by the 1:1 solvent mixture and ethanol. L2 exhibited higher stability constants than L1, attributed to additional hydroxyl groups in L2 enhancing Lewis basicity, while the methyl group in L1 caused steric hindrance, reducing stability. Thermodynamic analysis revealed negative ΔG° values (-27.9 to -32.1 kJ/mol) for all reactions, indicating spontaneity. Enthalpy changes (ΔH°) varied, with negative values (-27.6 to -195 kJ/mol) for exothermic and positive values (7.37 and 42.3 kJ/mol) for endothermic reactions. Entropy changes (ΔS°) varied, reflecting differences in molecular organization and solvent-ligand interactions. This study provides insights into factors affecting metal-ligand complexation in non-aqueous environments, with implications for designing coordination compounds for various applications in chemistry

Anahtar Kelimeler

• Conductometry
• Schiff Bases
• Cobalt Complexes
• Stability Constants
• Nonaqueous Solutions
• Thermodynamic Parameters

Farklı Susuz Çözücülerde Schiff Bazı Ligandları ile Co(II) Kompleksleşmesinin Termodinamik Çalışmaları

Öz

Bu çalışma, iki yeni Schiff bazı ligandı (L1 ve L2) ve bunların Co(II) iyonları ile susuz ortamda kompleksleşme davranışını araştırmaktadır. Ligand L1, o-hidroksiasetofenon ve salisaldehitin etilendiamin ile reaksiyonu sonucu, L2 ise 2,3-dihidroksibenzaldehit ve etilendiamin kullanılarak sentezlenmiştir. Co(II) komplekslerinin kararlılık sabitleri, 25°C ile 40°C arasında değişen sıcaklıklarda, etanol, asetonitril ve bu çözücülerin 1:1 karışımında iletkenlik ölçümleriyle belirlenmiştir. Sonuçlar, sıcaklığa bağlı olarak farklı kararlılık eğilimleri göstermiştir: L1 kompleksleri tüm çözücülerde artan sıcaklıkla kararlılığını azaltmış ve ekzotermik reaksiyonlar sergilemiştir, L2 kompleksleri ise asetonitril ve karışık çözücü ortamında endotermik reaksiyonları işaret eden farklı davranışlar göstermiştir. Çözücü ortamının kompleks kararlılığı üzerinde önemli etkileri olduğu görülmüş; en yüksek kararlılık asetonitrilde, ardından 1:1 çözücü karışımı ve etanolde gözlemlenmiştir. L2, daha fazla hidroksil grubunun Lewis bazlığını artırması nedeniyle L1'e kıyasla daha yüksek kararlılık sabitleri sergilemiştir, oysa L1'deki metil grubu, sterik engelleme yaratarak kararlılığı azaltmıştır. Termodinamik analiz, tüm reaksiyonlar için negatif ΔG° değerleri (-27,9 ila -32,1 kJ/mol) ile reaksiyonların kendiliğinden gerçekleştiğini ortaya koymuştur. Enthalpi değişimleri (ΔH°), ekzotermik reaksiyonlar için negatif (-27,6 ila -195 kJ/mol) ve endotermik reaksiyonlar için pozitif (7,37 ve 42,3 kJ/mol) değerler olarak bulunmuştur. Entropi değişimleri (ΔS°) ise moleküler organizasyon ve çözücü-ligand etkileşimlerindeki farklılıklara bağlı olarak değişim göstermiştir. Bu çalışma, susuz ortamda metal-ligand kompleksleşmesini etkileyen faktörlere dair önemli bilgiler sunarak kimya alanındaki çeşitli uygulamalara yönelik koordinasyon bileşiklerinin tasarımına katkıda bulunmaktadır.

Anahtar Kelimeler

• İletkenlik Ölçümü
• Schiff Bazları
• Kobalt Kompleksleri
• Kararlılık Sabitleri
• Susuz Çözücüler
• Termodinamik Parametreler

Kaynakça

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