Anhydrous vs Hydrated f-Element Acetate Polymers Dictated by the Stoichiometry of Protic Acidic/Basic Azole Mixtures

TY - JOUR

T1 - Anhydrous vs Hydrated f-Element Acetate Polymers Dictated by the Stoichiometry of Protic Acidic/Basic Azole Mixtures

AU - Nayak, Amrita

AU - Smetana, Volodymyr

AU - Mudring, Anja Verena

AU - Rogers, Robin D.

N1 - Publisher Copyright: © 2021 The Authors. Published by American Chemical Society.

PY - 2021/4/7

Y1 - 2021/4/7

N2 - Continuing our investigations of ionic liquid (IL) based routes to a library of f-element/soft donor complexes which could be studied crystallographically, we have explored the dissolution of f-element salts in protic imidazole-based ILs containing only soft donors at high temperatures to drive off volatiles, including water and carboxylic or mineral acids. Here we present our results, reacting acidic and basic azoles in 1:3 or 1:1 stoichiometric compositions at elevated temperature, followed by saturation with Nd(OAc)3·xH2O or Ce(OAc)3·xH2O, which led to 13 new metal-acetate polymeric complexes identified by single-crystal X-ray diffraction. We found that the diversity in coordination modes of the simple acetate ligand that interfere with substitution of the softer N donors led to several readily crystallizable complexes forming two distinct groups with respect to f-element interaction with the ionic liquid precursors. When the acidic/basic azole ratio was 1:3, acetate and a neutral basic azole were found to be coordinated to the metal centers but no water, although in one case (2) water was observed in the secondary coordination sphere: [Ce(μ2-OAc)3(C1im)]n (1, C1im = 1-methylimidazole), [Nd(μ2-(OAc)3(C1im)]n·nH2O (2), [Ce(μ2-OAc)3(C2im)]n (3, C2im = 1-ethylimidazole), [Ln(μ2-OAc)3DMF]n (Ln = Nd (4), Ce (5); dimethylformamide (DMF) was substituted for the azole mixture), and [Nd(μ2-OAc)3(C4im)]n (6, C4im = 1-butylimidazole). However, when the stoichiometric ratio was 1:1, water was always observed coordinated to the metal ions with the acidic azole included in the structure as a solvate or cocrystal, despite a higher reaction temperature: [Nd(μ2-OAc)3(OH2)]n·n(1,2,3-Taz) (7, 1,2,3-Taz = 1,2,3-triazole), [Ln(μ2-OAc)3(OH2)]n·n(4,5-DCim) (Ln = Nd (8), Ce (9), 4,5-DCim = 4,5-dicyanoimidazole), [Ln(μ2-OAc)3(OH2)]n·n(3,5-diNH2-1,2,4-Taz) (Ln = Nd (10), Ce (11), 3,5-diNH2-1,2,4-Taz = 3,5-diamino-1,2,4-triazole), [Ce(μ2-OAc)3(OH2)]n·n(3-NH2-1,2,4-Taz) (12, 3-NH2-1,2,4-Taz = 3-amino-1,2,4-triazole), and [Nd(μ2-OAc)3(OH2)]n·n(5-NH2-Tz) (13, 5-NH2-Tz = 5-aminotetrazole). All of the compounds retain the Ln:OAc- ratio of 1:3 and form 1D polymeric chains; however, they exhibit a variety of coordination modes affecting the degree of chain condensation. The isolation of both hydrated and anhydrous products revealed different abilities of the investigated soft N-donors to compete with O-donors finding their place in the coordination sphere of the lanthanide or in the crystal lattice.

AB - Continuing our investigations of ionic liquid (IL) based routes to a library of f-element/soft donor complexes which could be studied crystallographically, we have explored the dissolution of f-element salts in protic imidazole-based ILs containing only soft donors at high temperatures to drive off volatiles, including water and carboxylic or mineral acids. Here we present our results, reacting acidic and basic azoles in 1:3 or 1:1 stoichiometric compositions at elevated temperature, followed by saturation with Nd(OAc)3·xH2O or Ce(OAc)3·xH2O, which led to 13 new metal-acetate polymeric complexes identified by single-crystal X-ray diffraction. We found that the diversity in coordination modes of the simple acetate ligand that interfere with substitution of the softer N donors led to several readily crystallizable complexes forming two distinct groups with respect to f-element interaction with the ionic liquid precursors. When the acidic/basic azole ratio was 1:3, acetate and a neutral basic azole were found to be coordinated to the metal centers but no water, although in one case (2) water was observed in the secondary coordination sphere: [Ce(μ2-OAc)3(C1im)]n (1, C1im = 1-methylimidazole), [Nd(μ2-(OAc)3(C1im)]n·nH2O (2), [Ce(μ2-OAc)3(C2im)]n (3, C2im = 1-ethylimidazole), [Ln(μ2-OAc)3DMF]n (Ln = Nd (4), Ce (5); dimethylformamide (DMF) was substituted for the azole mixture), and [Nd(μ2-OAc)3(C4im)]n (6, C4im = 1-butylimidazole). However, when the stoichiometric ratio was 1:1, water was always observed coordinated to the metal ions with the acidic azole included in the structure as a solvate or cocrystal, despite a higher reaction temperature: [Nd(μ2-OAc)3(OH2)]n·n(1,2,3-Taz) (7, 1,2,3-Taz = 1,2,3-triazole), [Ln(μ2-OAc)3(OH2)]n·n(4,5-DCim) (Ln = Nd (8), Ce (9), 4,5-DCim = 4,5-dicyanoimidazole), [Ln(μ2-OAc)3(OH2)]n·n(3,5-diNH2-1,2,4-Taz) (Ln = Nd (10), Ce (11), 3,5-diNH2-1,2,4-Taz = 3,5-diamino-1,2,4-triazole), [Ce(μ2-OAc)3(OH2)]n·n(3-NH2-1,2,4-Taz) (12, 3-NH2-1,2,4-Taz = 3-amino-1,2,4-triazole), and [Nd(μ2-OAc)3(OH2)]n·n(5-NH2-Tz) (13, 5-NH2-Tz = 5-aminotetrazole). All of the compounds retain the Ln:OAc- ratio of 1:3 and form 1D polymeric chains; however, they exhibit a variety of coordination modes affecting the degree of chain condensation. The isolation of both hydrated and anhydrous products revealed different abilities of the investigated soft N-donors to compete with O-donors finding their place in the coordination sphere of the lanthanide or in the crystal lattice.

UR - http://www.scopus.com/inward/record.url?scp=85103755132&partnerID=8YFLogxK

U2 - 10.1021/acs.cgd.1c00181

DO - 10.1021/acs.cgd.1c00181

M3 - Journal article

AN - SCOPUS:85103755132

SN - 1528-7483

VL - 21

SP - 2516

EP - 2525

JO - Crystal Growth and Design

JF - Crystal Growth and Design

IS - 4

ER -