Ilpo Mutikainen

Distillable Acid–Base Conjugate Ionic Liquids for Cellulose Dissolution and Processing†

Future biorefinery concepts are seriously entertaining the use of ionic liquids (ILs) as a platform media for the processing of woody material as a second-generation biomass feedstock. The main motivation is the demonstrated efficiency of some molten salts in the dissolution of cellulose, a major structural and solvolytically resistant component of lignocellulosic materials. The first report of the use of molten salts for the modification of cellulose came in the form of a patent by Graenacher, where alkyl pyridinium chlorides were used to dissolve cellulose, thus allowing for efficient chemical modification from those media. The melting points of most alkyl pyridinium chloride salts are above 100 8C and, as such, these species do not fall under the common definition of ionic liquids. Nevertheless, the molten compounds solvated cellulose to such a state as to allow for acylation to a high degree. The next generational advance was the discovery by Rogers and co-workers that dialkyl imidazolium based ionic liquids, with melting points below 100 8C, can dissolve cellulose. The most successful of these was 1-butyl-3-methylimidazolium chloride ([bmim]Cl]). This advance was further refined by Ohno et al. into room-temperature ionic liquids capable of dissolving cellulose, such as 1-ethyl-3-methylimidazolium formate ([emim][CO2H]) [3a] or 1-ethyl-3-methylimidazolium dimethylphosphate ([emim][Me2PO4]). [3b] From the structures listed in the claims of the Rogers patent, BASF have also refined this list down to room-temperature ionic liquids, such as 1-ethyl-3-methylimidazolium acetate ([emim][OAc]). It has been reported by BASF, by oral dissemination and unofficial reports, that [emim][OAc] has higher dissolving efficiency for cellulose and has lower toxicity than structures such as [bmim]Cl. However, no detailed studies comparing chlorides with carboxylates or other such structures have been published, although certainly their undeniable high efficiency for dissolution and chemoselectivity has been demonstrated for a number of cellulose modification applications. Despite the high efficiency for the solvation of cellulose, lignin, and even wood in an increasing range of dialkyl imidazolium based ionic liquids, sustainability of prospective processes will depend on the chemical stability of solutes and ionic liquids under process and recycling conditions. There are already some indications that ionic liquids such as [emim][OAc] react chemically with lignocellulosic solutes. This reactivity may lower the recovery of the media upon recycling, although, in the case of the reaction of C2 imidazolium positions with C1 reducing end groups of cellulose, it is possible that this reaction is reversible under aqueous conditions, owing to the lability of the conjugate linkage. A bigger concern is the method of recycling to yield a pure ionic liquid. For most processes, high-purity ionic liquid will be required to maintain efficiency of dissolution and overall sustainability of the process. Decomposition of dialkyl imidazolium based ILs containing basic anions in the presence or absence of solutes proceeds according to three main pathways. From knowledge of the chemical stability of these cations, the pathways are most easily illustrated using a 1,3-diethylimidazolium cation ([eeim]) as countercation (Scheme 1).

The first structural evidence of a polymeric Cu(II) compound with a bridging dicyanamide anion: X-ray structure, spectroscopy and magnetism of catena-[polybis(2-aminopyrimidine)copper(II)bis(μ-dicyanamido)]

Abstract The new Cu(II) coordination compound, catena-[Cu(N(CN)2)2(ampym)2] (in which ampym=2-aminopyrimidine) has been synthesized and investigated by X-ray analysis, ligand field, EPR spectroscopy and magnetic susceptibility. The first compound crystallizes in the monoclinic space group C2/c with a=13.579(6), b=15.453(5), c=7.570(7) A, β=92.03(5)° and refines to an R value of 0.0322. The geometry around the copper(II) atom is axially elongated octahedral with the basal plane formed by the nitrogen of two monodentate coordinating ligands and two (N2) nitrogens of the bridging dicyanamide anions with distances which vary from 1.972(3) to 2.078 A forming an almost perfect square planar geometry. The apical positions are occupied by the other nitrogens (N3) of the bridging dicyanamide anions with a distance of 2.416(3) A. The bridging dicyanamide forms a one-dimensional polymeric chain with the other copper units. The CuCu separation is 7.570 A. Hydrogen bonding (3.1231 A) between the hydrogen atoms of the amino nitrogen and the uncoordinated nitrogen of the ligand forming pairs of ligands stabilizes the lattice, and bridges the chain in 2D-sheets. A Ligand field maximum occurs at 14.3×103 cm−1 and the EPR values, measured as a solid, are g⊥=2.08 and g//=2.29. Magnetic susceptibility of the powdered sample was measured from 4 to 300 K. The inverse susceptibility versus temperature shows that the curve follows the Curie–Weiss law. The μeff versus temperature gives a negligible rise at lower temperature and stays constant at about 1.80–1.84. The characteristic infrared vibrations for the dicyanamide anion are the νs+νas(CN), found as one strong band at 2301 cm−1, and the ν (C  N) , found as two strong bands at 2254 and 2188 cm−1.

Predicting Cellulose Solvating Capabilities of Acid-Base Conjugate Ionic Liquids

Different acid-base conjugates were made by combining a range of bases and superbases with acetic and propionic acid. Only the combinations that contained superbases were capable of dissolving cellulose. Proton affinities were calculated for the bases. A range, within which cellulose dissolution occurred, when combined with acetic or propionic acid, was defined for further use. This was above a proton affinity value of about 240 kcal mol(-1) at the MP2/6-311+G(d,p)//MP2/ 6-311+G(d,p) ab initio level. Understanding dissolution allowed us to determine that cation acidity contributed considerably to the ability of ionic liquids to dissolve cellulose and not just the basicity of the anion. By XRD analyses of suitable crystals, hydrogen bonding interactions between anion and cation were found to be the dominant interactions in the crystalline state. From determination of viscosities of these conjugates over a temperature range, certain structures were found to have as low a viscosity as 1-ethyl-3-methylimidazolium acetate, which was reflected in their high rate of cellulose dissolution but not necessarily the quantitative solubility of cellulose in those ionic liquids. 1,5-Diazabicyclo[4.3.0]non-5-enium propionate, which is one of the best structures for cellulose dissolution, was then distilled using laboratory equipment to demonstrate its recyclability.

Mixed-Lanthanoid Metal–Organic Framework for Ratiometric Cryogenic Temperature Sensing

A ratiometric thermometer based on a mixed-metal Ln(III) metal-organic framework is reported that has good sensitivity in a wide temperature range from 4 to 290 K and a quantum yield of 22% at room temperature. The sensing mechanism in the europium-doped compound Tb0.95Eu0.05HL (H4L = 5-hydroxy-1,2,4-benzenetricarboxylic acid) is based not only on phonon-assisted energy transfer from Tb(III) to Eu(III) centers, but also on phonon-assisted energy migration between neighboring Tb(III) ions. It shows good performance in a wide temperature range, especially in the range 4-50 K, reaching a sensitivity up to 31% K(-1) at 4 K.

Mononuclear Manganese(III) Complexes as Building Blocks for the Design of Trinuclear Manganese Clusters: Study of the Ligand Influence on the Magnetic Properties of the [Mn3(μ3-O)]7+Core

The synthesis, crystal structure, and magnetic properties of three new manganese(III) clusters are reported, [Mn 3(mu 3-O)(phpzH) 3(MeOH) 3(OAc)] (1), [Mn 3(mu 3-O)(phpzMe) 3(MeOH) 3(OAc)].1.5MeOH (2), and [Mn 3(mu 3-O)(phpzH) 3(MeOH) 4(N 3)].MeOH (3) (H 2phpzH = 3(5)-(2-hydroxyphenyl)-pyrazole and H 2phpzMe = 3(5)-(2-hydroxyphenyl)-5(3)-methylpyrazole). Complexes 1- 3 consist of a triangle of manganese(III) ions with an oxido-center bridge and three ligands, phpzR (2-) (R = H, Me) that form a plane with the metal ions. All the complexes contain the same core with the general formula [Mn 3(mu 3-O)(phpzR) 3] (+). Methanol molecules and additional bridging ligands, that is, acetate (complexes 1 and 2) and azide (complex 3), are at the terminal positions. Temperature dependent magnetic susceptibility studies indicate the presence of predominant antiferromagnetic intramolecular interactions between manganese(III) ions in 1 and 3, while both antiferromagnetic and ferromagnetic intramolecular interactions are operative in 2.

Ferromagnetic trinuclear carbonato-bridged and tetranuclear hydroxo-bridged Cu(II) compounds with 4,4′-dimethyl-2,2′-bipyridine as ligand. X-ray structure, spectroscopy and magnetism

Abstract A controlled synthesis, characterisation and single-crystal X-ray analysis of two novel copper(II) compounds with the ligand 4,4′-dimethyl-2,2′-bipyridine (abbreviated dmbipy) is described. In a CO2 atmosphere, with sodium hydroxide added, the carbonato-bridged triangular trinuclear compound [Cu3(dmbipy)6(μ3-CO3)](BF4)4(C2H5OH)(H2O) (1) is obtained. Compound 1 crystallises in the monoclinic space group P21/n with a=16.169(6), b=23.351(11), c=21.312(7) A, β=91.26(3), Z=4. The three copper ions are connected via the oxygen atoms from the symmetrically bridging carbonato group, resulting in a triangular array of copper atoms. Each copper has a distorted square-pyramidal environment with a basal plane formed by three nitrogen atoms of the two chelating bipyridine groups and the oxygen atom of the bridging carbonato group (Cu–N/O distances about 2.0 A). The apical position at each copper is occupied by the fourth nitrogen atom of the bipyridines with distances varying from 2.100(11) to 2.146(11) A. In all other experimental conditions the tetranuclear hydroxo-bridged compound [Cu4(dmbipy)4(μ3-OH)2(μ-OH)2(H2O)2](BF4)4(H2O)4 (2) is obtained. Compound 2 crystallises in the monoclinic space group P21/c with a=13.274(8), b=21.685(7), c=11.266(7) A, β=107.71(4), Z=2. The structure consists of two bis(hydroxo)-bridged dinuclear planar units which are connected with long Cu–O bonds to form a tetranuclear unit. Each Cu ion has a similar square-pyramidal coordination geometry: the equatorial plane of each Cu ion consists of two nitrogen atoms of the dmbipy ligand (Cu–N distances 1.945–2.003 A), and two bridging hydroxo oxygen atoms (Cu–O distances 1.945–1.973 A). The apical position of Cu1 is occupied by an oxygen atom of a water molecule with a distance of 2.262 A. The second copper atom, Cu2, has the apical position occupied by an oxygen atom of a bridging hydroxo group at a distance of 2.349 A; this bond is responsible for the formation of the tetranuclear unity. Compound 1 exhibits a ferromagnetic interaction between the copper ions with a J=29.3 cm−1 and a very weak ferromagnetic intercluster interaction with zj′=2.4 cm−1. Compound 2 also exhibits a ferromagnetic interaction between the copper ions with a J=31.1 cm−1 and an overall magnetic interaction between the two dimeric units J′=8.76 cm−1

Synthesis, spectroscopic characterization, X-ray crystal structure and magnetic properties of oxalato-bridged copper(II) dinuclear complexes with di-2-pyridylamine

The syntheses and characterization of a series of dinuclear μ-oxalato copper(II) complexes of the general type [(NN) 1 or 2 Cu(C 2 O 4 )Cu(NN) 1 or 2 ] 2+ , where NN=didentate dpyam (di-2-pyridylamine) ligand, are described. The crystal structures of three representative complexes have been determined. The dinuclear-oxalate bridged compounds [Cu(dpyam) 4 (C 2 O 4 )](ClO 4 ) 2 (H 2 O) 3 (1) and [Cu 2 (dpyam) 4 (C 2 O 4 )](BF 4 ) 2 (H 2 O) 3 (2) crystallize in the non-centrosymmetric triclinic space group P which are isomorphous and isostructural. The compound [Cu 2 (dpyam) 2 (C 2 O 4 )(NO 3 ) 2 ((CH 3 ) 2 SO) 2 ] (3) crystallizes in the centrosymmetric monoclinic space group P with all Cu-oxalate contacts in the equatorial plane. All three complexes contain six-coordinate copper centres bridged by planar bis-didentate oxalate groups from the equatorial position of one chromophore to the equatorial position of the other one. Both chromophores in 1 and 2 exhibit the compressed octahedral Cu(II) geometry, while 3 displays an elongated octahedral Cu(II) environment. The IR, ligand field and EPR measurements are in agreement with the structures found. The magnetic susceptibility measurements, measured from 5 to 280 K, revealed a very weak ferromagnetic interaction between the Cu(II) atoms for compound 1 and 2 , with a singlet–triplet energy gap ( J ) of 2.42 and 3.38 cm −1 , for compounds 1 and 2 , respectively. Compound 3 has a strong antiferromagnetic interaction with a J of −305.1 cm −1 , in agreement with coplanarity of the magnetic orbitals.

Alkoxo-bridged dinuclear copper(II) compounds with 2-amino-picolines as ligands: Synthesis, spectroscopy, magnetism and X-ray crystal structures

Abstract The synthesis, spectroscopic, magnetic and structural characterisation of four new alkoxo-bridged dinuclear copper(II) compounds are described. All four compounds have the general formula [Cu(μ-OR−)(L)2]2(A−)2, in which μ-OR=CH3O− or CH3CH2O−, L=2-amino-3-picoline (abbreviated as 3pic) and 2-amino-5-picoline (abbreviated as 5pic) and A=NO3− or ClO4−. The title compounds all consist of dinuclear units with bridging methoxo groups for [Cu(3pic)2(CH3O)2(NO3)2](CH3OH)2 (1), [Cu(3pic)2(CH3O)2(ClO4)2](CH3OH)2 (2), Cu(5pic)2(CH3O)2(ClO4)2 (3) and a bridging ethoxo group for Cu(5pic)2(C2H5O)2(ClO4)2 (4) with two picoline ligands linked to each copper via the pyridine N atom, providing a square planar CuN2O2 unit. The nitrate anions in compound (1) are bridging at semi-coordination distance (Cu–ONO3 2.735–2.793 A), the perchlorate anions in compounds (2) and (3) are at semi-coordination distance (Cu–OClO4 2.701–3.042 A); on the other hand the perchlorate anion in compound (4) has only one semi-coordination bond (Cu–OClO4 2.826 A). The Cu–Cu distances within the dinuclear units are 2.9957(12), 2.9872(15), 2.996(5), and 3.0123(18) A for compounds (1), (2), (3) and (4), respectively, with Cu–O–Cu angles of 102.3(8), 101.33(13), 103.8(5), and 103.38(16)° for compounds (1), (2), (3) and (4), respectively. The structures are stabilized by intramolecular H-bonds between the amino hydrogens and Omethoxo and/or Oanion atoms (shortest contacts N–H⋯Omethoxo 3.108 A; N–H⋯Oanion 2.914 A). The magnetic susceptibility measurements of the alkoxo-bridged compounds display a diamagnetic behaviour below room temperature with an estimated exchange parameter 2J of

Synthesis and characterisation of cyclopentadienyl complexes of barium: precursors for atomic layer deposition of BaTiO3.

Cyclopentadienyl complexes Ba(C5Me5)2(THF)2 (1), Ba(C5Me5)2(A) (A = THF, dien, trien, diglyme, triglyme) (2-5), Ba(Pr(i)3C5H2)2(THF)2 (6), Ba(Bu(t)3C5H2)2(THF) (7), Ba(Me2NC2H4C5Me4)2 (8) and Ba(EtOC2H4C5Me4)2 (9) were prepared and characterised with TGA/SDTA, NMR and MS. Crystal structures of 2, 4, 5, 7, 8 and 9 are presented. All complexes prepared sublime under reduced pressure and complexes 1, 6 and 7 showed volatility also under atmospheric pressure. Complexes 1, 6 and 7 lose the coordinated THF when evaporated while complexes 2-5 are sublimable as complete molecules under reduced pressure. Complexes with bulky cyclopentadienyl ligands (6 and 7) are the most thermally stable and volatile among the prepared barocenes. X-ray structure determinations reveal that all the complexes studied are monomeric. Complexes 1, 7 and 8 were successfully tested in BaTiO3 thin film depositions by atomic layer deposition (ALD).

Synthesis, magnetism and X-ray structures of [Cu(2-aminopyrimidine)2(μ-OH)(CF3SO3)]2(2-aminopyrimidine)2, a new hydroxo-bridged dinuclear Cu(II) compound generating extremely small antiferromagnetism

The synthesis, optical and magnetic properties and X-ray crystal structure of [Cu(2-aminopyrimidine)2(OH)(CF3SO3)]2(2aminopyrimidine)2, a new dinuclear hydroxo-bridged copper(II) compound with a CuOCu angle of 97.96° and a very small antiferromagnetic interaction for which the singlet–triplet exchange parameter J, is described. The magnetic exchange coupling is almost negligible and, depending on the actual sample, varies from − 1.8 to − 7.2 cm − 1 .