STRUKTUR SOLVASI DAN SIFAT DINAMIKA ION Cu+ DAN Cu2+ DALAM PELARUT AMONIA CAIR DAN LARUTAN AMONIA: SIMULASI DINAMIKA MOLEKUL AB INITIO QUANTUM MECHANICAL CHARGE FIELD (QMCF)

WAHYU DITA SAPUTRI, Prof. Dr.rer.nat. Karna Wijaya, M.Eng. ; Prof. Dr.rer.nat. Harno Dwi Pranowo, M.Si.

2019 | Disertasi | DOKTOR KIMIA

Struktur solvasi dan sifat dinamika ion Cu+ dan Cu2+ dalam amonia cair pada 235,15 K, dan larutan amonia 18,6% pada 298,15 K telah diinvestigasi menggunakan simulasi dinamika molekul QMCF (DM QMCF). Simulasi ini juga dilakukan untuk mengetahui perbandingan sifat dinamik antara amonia cair model fleksibel dan rigid terutama pada kulit solvasi kedua. Preferensial solvasi ion Cu+ dan Cu2+ terhadap ligan NH3 atau H2O diidentifikasi pada sistem larutan amonia 18,6%. Metode simulasi DM QMCF memiliki dua daerah simulasi, yaitu daerah mekanika kuantum (MK) dan mekanika molekul (MM). Daerah MK diperpanjang dan dibagi menjadi daerah inti (core) dan daerah layer. Metode perhitungan pada tingkat Hartree-Fock (HF) digunakan pada daerah MK, dengan himpunan basis LANL2DZ-ECP untuk ion Cu2+ dan Cu+, dan himpunan basis DZP-Dunning untuk ligan NH3 dan H2O. Sistem ion Cu2+ dalam amonia cair dan larutan amonia 18,6% membentuk kompleks oktahedral [Cu(NH3)6]2+ yang stabil tanpa ada perpindahan ligan NH3 di kulit solvasi pertama selama proses simulasi berlangsung. Jarak Cu2+-NH3 pada pelarut amonia cair model fleksibel, model rigid, dan larutan amonia 18,6% masing-masing sebesar 2,17 Angstrom; 2,19 Angstrom; 2,19 Angstrom. Pada sistem ion Cu+ dalam amonia cair membentuk kompleks berkoordinasi 3 (95,7%) dan 4 (4,3%). Jarak Cu+-NH3 pada pelarut amonia model fleksibel dan rigid, masing-masing sebesar 2,23 Angstrom dan 2,24 Angstrom. Pada larutan amonia 18,6% terbentuk kompleks dengan bilangan koordinasi 3 (5,2%); 4 (83,3%); 5 (10,8%); 6 (0,7%), dan terjadi perpindahan ligan NH3 dan H2O di kulit solvasi pertama. Jarak Cu+-NH3 pada larutan amonia 18,6% sebesar 2,23 Angstrom. Pada ketiga sistem ion Cu+ ini, kompleks yang paling stabil adalah [Cu(NH3)4]+ tetrahedral terdistorsi, meskipun terdapat perpindahan ligan di kulit solvasi pertama. Secara garis besar sifat dinamika solvasi ion Cu+ lebih tinggi dibandingkan Cu2+, dan analisis NBO menunjukkan bahwa kekuatan interaksi elektrostatik Cu2+-NH3 lebih tinggi dibandingkan Cu+-NH3. Pada sistem pelarut amonia cair, sifat dinamika ligan NH3 model fleksibel lebih tinggi dibandingkan model rigid terutama pada kulit solvasi kedua. Preferensial solvasi ion Cu2+ dan Cu+ terhadap ligan NH3 lebih tinggi dibandingkan H2O pada larutan amonia 18,6%.

Solvation structures and dynamical properties of Cu2+ and Cu+ in liquid ammonia at 235.15 K and 18.6% aqueous ammonia at 298.15 K have been investigated via quantum mechanical charge field molecular dynamics (QMCF MD) simulation. This simulation is also carried out to compare the dynamical properties of flexible and rigid ammonia models was also carried out, especially in the second solvation shell. The preferential solvation of Cu+ and Cu2+ ions to NH3 or H2O ligands was identified in the 18.6% aqueous ammonia solutions. The QMCF MD simulation method has two simulation regions, namely quantum mechanics (QM) and molecular mechanics (MM). The QM region is extended and divided into core and layer areas. The QM region is treated via ab initio Hartree-Fock (HF), using LANL2DZ-ECP basis set for Cu2+ and Cu+, and DZP-Dunning for NH3 and H2O ligands. Cu2+ ion in liquid ammonia and 18.6% aqueous ammonia solution formed a stable octahedral complex [Cu(NH3)6]2+ with the absence of first shell ligand exchange during simulation time. The distance of Cu2+-NH3 in flexible, rigid ammonia, and 18.6% aqueous ammonia solutions were 2.17 Angstrom; 2.19 Angstrom ; 2.19 Angstrom, respectively. Cu+ in liquid ammonia formed complexes coordinating 3 (95.7%) and 4 (4.3%). The distances of Cu+-NH3 in flexible and rigid ammonia were respective 2.23 Angstrom and 2.24 Angstrom. In the 18.6% aqueous ammonia solution, complexes with the coordination number of 3 (5.2%); 4 (83.3%); 5 (10.8%); 6 (0.7%) were formed, with NH3 and H2O ligand exchange in the first solvation shell. The distance of Cu+-NH3 in 18.6% aqueous ammonia solution was 2.23 Angstrom. All of these Cu+ ion solvation systems indicated the most stable complex was [Cu(NH3)4]+ distorted tetrahedral, even though there was a ligand displacement on the first solvation shell. In general simulation, the dynamical properties of Cu+ ion was higher than Cu2+, and NBO analysis also showed that electrostatic interaction of Cu2+-NH3 was higher than Cu+-NH3. In liquid ammonia solution, the dynamical properties of flexible ammonia model was higher than the rigid model, particularly in the second solvation shell. The preferential Cu+ and Cu2+ ions to NH3 ligand was higher than H2O in 18.6% aqueous ammonia solutions.

Kata Kunci : simulasi, DM QMCF, struktur, dinamika, solvasi, Cu+, Cu2+, amonia cair, larutan amonia / simulation, QMCF MD, structural, dynamical, solvation, Cu+, Cu2+, liquid ammonia, aqueous ammonia