A set of enantiomerically pure cyclic multinuclear complexes with the formula cis‐a2PdLnn+ a2=(R,R)‐1,2‐diaminocyclohexane (R,R‐dach), (S,S)‐1,2‐diaminocyclohexane (S,S‐dach); n=4, 6; ...LH=2‐hydroxypyrimidine (2‐Hpymo), 4,6‐dimethyl‐2‐hydroxypyrimidine (2‐Hdmpymo) and 4‐hydroxypyrimidine (4‐Hpymo) were obtained by reaction of cis‐a2Pd(H2O)22+ and LH in aqueous media. The polynuclear complexes were studied by 1H NMR spectroscopy and X‐ray crystallography. These studies revealed that the N1,N3‐bridging mode exhibited by the pyrimidine moieties is ideally suited for formation of inorganic analogues of calixarenes (metallacalixarenes) in a self‐assembly process. The most stable species are the tetranuclear metallacalix4arenes, which are obtained in all cases. Hexanuclear species, namely, a2Pd(2‐dmpymo)66+, were also isolated and fully characterised. 1H NMR experiments show conversion of a2Pd(2‐dmpymo)66+ to a2Pd(2‐dmpymo)44+ on heating. Analogously to organic calixarenes, these systems are also capable of incorporating hard metal ions at the oxo surface. Additionally, investigations on the receptor properties of these metallacalixarenes towards mononucleotides showed that enantioselective recognition processes occur in aqueous media.
Enantiomerically pure metallacalixarenes with general formula cis‐a2PdLnn+ (a2=(R,R)‐ or (S,S)‐1,2‐diaminocyclohexane) were obtained from cis‐a2Pd(H2O)22+ and hydroxypyrimidines LH in aqueous media. The most stable species are the tetranuclear metallacalix4arenes (n=4), which were obtained in all cases. Metallacalix6arenes were also isolated for LH=4,6‐dimethyl‐2‐hydroxypyrimidine and were shown to undergo conversion to the corresponding metallacalix4arenes on heating (see scheme).
The oxonate dianion has been coupled to divalent transition metal ions, allowing the isolation of coordination polymers of formula M(Hoxonato)
n
·
xnH
2O (M
=
Mn, Co, Ni, Zn), Zn(Hoxonato)(bpy)
0.5
n
...·
nH
2O and Ni(Hoxonato)(bpy)
n
·6
nH
2O. The latter, after thermal activation, is capable to selectively adsorb carbon dioxide over methane.
Display omitted
► Isolation and characterization of oxonate-containing coordination polymers. ► Retrieval of key structural features and responses to temperature by XRPD. ► Selective capture of the greenhouse gas CO
2 over CH
4.
Four novel coordination compounds of formula M(Hoxonato)
n
·
xnH
2O (
1
M
⊂
x
H
2O
; H
3oxonic: 4,6-dihydroxy-1,3,5-triazine-2-carboxylic acid; M
=
Mn, Co, Zn,
x
=
3; M
=
Ni,
x
=
4) were prepared and characterized. The isomorphous Mn(II), Co(II) and Zn(II) derivatives contain densely packed 1D helical chains. To increase the dimensionality of these systems, the M(Hoxonato)
n
secondary building unit was coupled to rod-like
N,
N′-spacers, allowing the isolation of Zn(Hoxonato)(bpy)
0.5
n
·
nH
2O (
2
Z
n
⊂
H
2O
; bpy: 4,4′-bipyridine) and Ni(Hoxonato)(bpy)
n
·6
nH
2O (
3
Ni
⊂
6H
2O
). The M(Hoxonato)
n
chains are pillared by the bpy spacers within 2D corrugated layers in the former, into 2D rectangular grid layers in the latter. The thermal behavior of all the species was investigated by coupling simultaneous thermal analysis and thermodiffractometry. Static gas adsorption measurements with N
2 (77
K) and CO
2 (273
K) revealed that activated
3
Ni
⊂
6H
2O
possesses permanent porosity. Dynamic gas separation studies towards CH
4:CO
2 mixtures (0.73:0.27 v/v, 273
K) proved that this system is able to selectively capture CO
2 up to 0.16
mmol per gram of material.
Three polycrystalline metal organic frameworks containing the polytopic deprotonated 1,4-bis(5-tetrazolyl)benzene ligand have been prepared and fully characterised by analytical, magnetic, ...spectroscopic, gas adsorption and powder diffraction methods.
The recently proposed high-yield synthesis of the 1,4-bis(5-tetrazolyl)benzene ligand (H
2btb) allowed the preparation of three new metal organic frameworks, namely Ag
2(btb),
1, Cu
2(btb),
2, and Cu
2(OH)
2(btb),
3. These polycrystalline materials were fully characterised by spectroscopic, gas adsorption, thermal and diffraction methods, the latter revealing rather dense frameworks for
1 and
3. Despite many different synthetic approaches,
2 invariably gave a poorly resolved, but highly reproducible, powder diffraction trace, hampering a complete structural characterisation. Magnetic measurements performed on
3 showed that it behaves as an antiferromagnetic material, the r.t. magnetic moment per Cu atom being only 1.24μ
B. The reactivity of
1 was proved in excess of triphenylphosphine (PPh
3), allowing the isolation of the dinuclear species
4, (PPh
3)
3Ag
2(btb). An additional species
5, formulated as (PPh
3)Ag
2(btb), could be selectively isolated on varying the reaction conditions; at variance, pyrazine, in solution or in molten form, did not react with
1.
Abstract
The novel coordination polymers Cu(Hoxonic)(H
2
O)
n
(
1
) and Cu(Hoxonic)(bpy)
0.5
n
⋅
1.5
n
H
2
O (
2⊂H
2
O
) (H
3
oxonic: 4,6‐dihydroxy‐1,3,5‐triazine‐2‐carboxylic acid; bpy: ...4,4′‐bipyridine) have been isolated and structurally characterised by ab initio X‐ray powder diffraction. The dense phase
1
contains 1D zig‐zag chains in which Hoxonic dianions bridge square‐pyramidal copper(II) ions, apically coordinated by water molecules. On the contrary,
2⊂H
2
O
, prepared by solution and solventless methods, is based on 2D layers of octahedral copper(II) ions bridged by Hoxonic ligands, further pillared by bpy spacers. The resulting pro‐porous 3D network possesses small hydrated cavities. The reactivity, thermal, magnetic and adsorptive properties of these materials have been investigated. Notably, the adsorption studies on
2
show that this material possesses unusual adsorption behaviour. Indeed, guest uptake is facilitated by increasing the thermal energy of both the guest and the framework. Thus, neither N
2
at 77 K nor CO
2
at 195 K are incorporated, and CH
4
is only minimally adsorbed at 273 K and high pressures (0.5 mmol g
−1
at 2500 kPa). By contrast, CO
2
is readily incorporated at 273 K (up to 2.5 mmol g
−1
at 2500 kPa). The selectivity of
2
towards CO
2
over CH
4
has been investigated by means of variable‐temperature zero coverage adsorption experiments and measurement of breakthrough curves of CO
2
/CH
4
mixtures. The results show the highly selective incorporation of CO
2
in
2
, which can be rationalised on the basis of the framework flexibility and polar nature of its voids.
Reaction of copper(II) salts with 4-hydroxypyrimidine (4-Hpymo) in water:ammonia solutions leads to formation of the mononuclear Cu(4-pymo)
2(NH
3)
2(H
2O)
2 species (
1) and a 3D open framework ...polymer, Cu(4-pymo)
2
·
nH
2O
∞ (
2), which possesses wide channels and voids that can reversibly accommodate guest molecules with no relevant structural change.
Reaction of Cu
2+ salts with 4-hydroxypyrimidine (4-Hpymo) in water:ammonia (9:1) solutions at room temperature leads to formation of either Cu(4-pymo)
2(NH
3)
2(H
2O)
2 (
1) or Cu(4-pymo)
2
·
nH
2O
∞ (
2), depending on which crystal nucleation process occurs. Selective formation of
2 is possible by using non-coordinating Et
3N as a base. X-ray diffraction analyses have been performed in both cases showing that
1 is a mononuclear compound in which the heterocyclic ligands monodentately coordinate the copper ions through the N1 nitrogen atom.
2 is a 3D sodalite type open framework, in which each 4-pymo ligand bridges two copper ions through both nitrogen atoms in the
N,
N
′-exobidentate mode. Heating
1 at 110 °C in air generates an amorphous phase (
2a), which shows the same chemical analysis and spectroscopic properties as dehydrated
2. Crystalline Cu(4-pymo)
2
·
nH
2O
∞ (
2), possesses interesting physico-chemical properties related to its porous nature. Indeed, this material reversibly absorbs N
2 and water vapour with minimal structural changes.
Abstract
The novel porous {M(F‐pymo)
2
}
n
⋅
2.5
n
H
2
O coordination networks (M=Co, Zn; F‐pymo=5‐fluoropyrimidin‐2‐olate), possessing sodalitic topology, have been synthesised and structurally ...characterised by means of powder diffraction methods. Thermodiffractometry demonstrated their plasticity: when heated up to 363 K, they reversibly transform into three‐dimensional dehydrated {M(F‐pymo)
2
}
n
species, with significantly different lattice parameters. Further heating induces irreversible polymorphic transformations into layered phases, in which the original MN
4
coordination sphere changes into an MN
3
O one. A mixed‐metal phase, {Co
x
Zn
1−
x
(F‐pymo)
2
}
n
⋅
2.5
n
H
2
O, was also prepared, showing that zinc is preferentially inserted, when starting from a Co/Zn reagent ratio of 1:1. The solid–gas adsorption properties of the anhydrous 3D frameworks have been explored towards N
2
, H
2
(77 K) and CH
4
, CO
2
(273 K). These results show that these materials permit the diffusion of CO
2
molecules only. Remarkably, the CO
2
adsorption process for the {Co(F‐pymo)
2
}
n
network proceeds in two steps: the first step takes place at low pressures (<600 kPa) and the second one above a threshold pressure of 600 kPa. By contrast, the {Zn(F‐pymo)
2
}
n
network only permits CO
2
diffusion by applying pressures above 900 kPa. This type of behaviour is typical of porous networks with gated channels. The high CO
2
selectivity of these systems over the rest of the essayed probe gases is explained in terms of flexibility and polarity of the porous network. Finally, the magnetic studies on the Co
II
systems reveal that the as synthesised {Co(F‐pymo)
2
}
n
⋅
2.5
n
H
2
O material behaves as an antiferromagnet with a
T
N
of about 29 K. At variance, the {Co(F‐pymo)
2
}
n
layered phase shows an unusually weak ferromagnetic ordering below 17 K, arising from a spin‐canting phenomenon.
The Re2(micro-trz-kappaN1:kappaN2)2(micro-OH)(CO)6- (trz = 1,2,4-triazolate) organometallic anion reacts with Ag+ to afford a 2D organometallic/coordination network, ...AgRe2(micro3-trz-kappaN1:kappaN2:kappaN4)2(micro3-OH)(CO)6n x 4nCH3OH, which shows dynamic structural changes triggered by solid-liquid guest exchange processes.
PDF
