Naslov
Disappearing and concomitant polymorphism of nickel(II) complexes with 6-hydroxypicolinic acid. Structural and DFT studies

Autori
Kukovec, Boris-Marko ; Vaz, Pedro D. ; Calhorda, Maria Jose ; Popović, Zora

Izvornik
Crystal growth & design (1528-7483) 10 (2010), 8; 3685-3693

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
polymorphism; nickel(II) complexes; 6-hydroxypicolinic acid; crystal structure; DFT

Sažetak
The recrystallization of the complex [Ni(6-OHpic)2(H2O)2] (1) from the mixture of pyridine and acetone led to the formation of three different polymorphs of [Ni(6-OHpic)2(py)2]. The stable monoclinic polymorph 3 was obtained by evaporation of the solution, while the slow diffusion of acetone into the pyridine solution of 1 yielded the orthorhombic polymorph 2. Further attempts to prepare 2 again were unsuccessful (disappearing polymorph). The new pseudopolymorph [Ni(6-OHpic)2(py)2] • py (4) was obtained under the same conditions as 3, but again not reproducibly (concomitant and a disappearing polymorph). Trans-[Ni(6-OHpic)2(py)2] formed one intramolecular O–H...O hydrogen bond and one intermolecular one to afford dimers (3) and infinite zigzag chains (2). When two intramolecular O–H...O hydrogen bonds were present, the dimers were hold by π–π stacking (4). DFT calculations showed trans-[Ni(6-OHpic)2(py)2] to be the most stable isomer. The hydrogen bonded dimers are the most stable motif, followed by π–π stacked dimers (9.6 kcal mol–1) and zigzag chains (24.7 kcal mol–1). The trans isomer of the [Ni(6-OHpic)2(py)2] monomer observed in all polymorphs is the most stable isomer of that complex. Thermogravimetric studies showed the initial loss of two coordinated water molecules in 1 and pyridine in 3 in similar temperature ranges.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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