Cadmium and mercury acetates have been reacted with pyrazole (Hpz) and 3,5-dimethylpyrazole (Hdmpz), affording distinct mixed-ligand species, selectively prepared upon slightly modifying the reaction ...conditions. Two polymorphs of {Cd(mu-ac)2(Hpz)2}n, as well as the {Cd(mu-ac)2(Hdmpz)2}n species (Hac = acetic acid), were obtained by solution chemistry, while the two-dimensional {Cd3(mu3-ac)4(mu-pz)2(Hpz)2}n and {Cd(mu-ac)(mu-pz)}n polymers were prepared upon controlled thermal treatment of one of the {Cd(mu-ac)2(Hpz)2}n forms. Two mercury derivatives, {Hg3(mu-ac)3(mu-pz)3}n and {Hg(ac)(mu-dmpz)}n, were also prepared, the latter containing one-dimensional chains of Hg(II) ions bridged by C-mercuriated Hdmpz ligands. All their crystal structures (but one) were determined by powder diffraction methods using conventional X-ray laboratory equipment, supported by 13C CPMAS NMR measurements. The latter method helped in assigning a C-metalated nature to an amorphous material of Hg(ac)(pz) formula, obtained by employing EtOH as a solvent. A few other Hdmpz-containing cadmium acetates were also prepared, but their polyphasic nature, evidenced by diffraction methods, hampered their complete structural characterization.
Diaquacobalt(II) n‐dodecane‐α,ω‐dioate (2) has been synthesized by metathesis of the corresponding potassium soap 1 and has been fully characterized by chemical and spectroscopic analysis. The ...crystal structure of 2 has been established by X‐ray powder diffraction techniques combined with electron diffraction experiments. It crystallizes in a monoclinic cell P21/a; a = 9.6558(8), b = 7.4793(6), c = 19.8936(2) Å, β = 95.648(9)°, V = 1429.7(3) Å3; Z = 2 and consists of stacked layers of cobalt(II) ions connected by carboxylato bridges, thus forming chains that extend along the a axis. These layers are separated by alkyl chains arranged quasi‐perpendicularly to the polar sheets. Structure analysis reveals a rare anti‐anti conformation of the Co−OCO−Co fragments, which is thought to be responsible for the weak antiferromagnetism of the CoII chains. The exchange coupling constant between the magnetic centres has been estimated as J = −2.08 K.
The double stranded Cu(II)2-metallacyclic complex of formula Cu2(mbpb)2.2H2O (1) and the triple stranded Ni(II)2-metallacyclic complexes of formula Ni2(Hmbpb)3PF6.21H2O (2), ...Co(H2O)6Ni2(mbpb)3)THF.10H2O (3) and {Ag2(H2O)Ni2(mbpb)3}.11H2O (4) (where H2mbpb is the bisbidentate dinucleating bridging ligand 1,3-bis(pyridine-2-carboxamide) benzene) have been synthesised and characterised by single-crystal X-ray diffraction. Within the dinuclear molecules, metal ions are bridged by either fully or semideprotonated bisbidentate ligands, which are coordinated through the pyridine and amidato nitrogen donor atoms. In complex 4 the triple stranded dinuclear Ni2 units are connected to the Ag+ cations through O-amidato bridges and Ag-pi(benzene) interactions to afford a 1D bimetallic chain. Cu2 (1) and Ni2 (2-4) complexes exhibit ferromagnetic coupling between the metal ions through the bridging ligand with J(Cu-Cu) = 21.1 cm(-1) and J(Ni-Ni) in the range of 2.9-3.6 cm(-1), respectively. Amongst copper(II) dinuclear complexes bearing m-phenylenediamidato bridges, complex 1 exhibits the stronger ferromagnetic exchange coupling reported so far. DFT calculations firstly confirm that the spin polarisation mechanism is responsible for the ferromagnetic coupling, and secondly allows us to predict stronger ferromagnetic couplings in Cu(II)(2) complexes with larger tetrahedral distortions of the CuN4 coordination environment.
Continuing our work on the structural and magnetic aspects of the one-dimensional (1-D) coordination polymers of the M(pmdc)(H(2)O)(2) x H(2)O kind (M = Fe, Co, Ni, Cu, Zn; pmdc = ...pyrimidine-4,6-dicarboxylate), we have combined ab initio X-ray powder diffraction methods with in situ thermodiffractometry and thermal analyses to characterize the selective and reversible transformation of the M(pmdc)(H(2)O)(2) x H(2)O compounds (M = Fe, Co, Ni, Cu) into the bis-hydrated M(pmdc)(H(2)O)(2) counterparts by moderate heating, which is followed by an irreversible transformation into two-dimensional (2-D) anhydrous species. The structural features of the transient bis-hydrated species and of the completely dehydrated one are described for M = Cu. Remarkably, the first dehydration process does not alter the 1-D nature of the M(pmdc)(H(2)O)(2) chains; on the contrary, the second dehydration gives rise to the loss of the axially coordinated water molecules with a concomitant condensation of the 1-D chains into 2-D layers through ancillary carboxylate bridging groups. The magnetic properties of the anhydrous M(pmdc) species (M = Co, Ni, Cu) have been investigated, showing that these phases behave as 1-D antiferromagnets with interchain interactions. Notably, in the case of the Ni(pmdc) system, a weak ferromagnetic ordering, arising from a spin canting phenomenon with a blocking temperature of 13 K, is observed.
Polymeric metal diazolates typically appear as insoluble and intractable powders, the structure of which could only be retrieved by the extensive use of ab-initio X-ray powder diffraction (XRPD) ...methods from conventional laboratory data. A number of selected examples from the metal pyrazolate, imidazolate, pyrimidin-2-olate and pyrimidin-4-olate classes are presented, highlighting the specific crystallochemical properties, material functionality and methodological aspects of the structure determination process. Linear and helical one-dimensional polymers, layered systems and three-dimensional networks are described, with particular emphasis on polymorphism and on the thermal, optical, magnetic and sorption properties. A brief outline of the method, as it has been tailored in our laboratories during the last decade, is also offered.
The reaction between Rh(mu-OH)(COD)(2) (COD = 1,5-cyclooctadiene) and 73% HF in THF gives Rh(3)(mu(3)-OH)(2)(COD)(3)(HF(2)) (1). Its crystal structure, determined by ab initio X-ray powder ...diffraction methods (from conventional laboratory data), contains complex trimetallic cations linked together in 1D chains by a mu(3)-OH...F-H-F...HO-mu(3) sequence of strong hydrogen bonds. The complex Rh(mu-F)(COE)(2)(2) (COE = cyclooctene; 2), prepared by reacting Rh(mu-OH)(COE)(2)(2) with NEt(3).3HF (3:2), has been characterized. Complex 1 reacts with PR(3) (1:3) to give RhF(COD)(PR(3)) R = Ph (3), C(6)H(4)OMe-4 (4), (i)Pr (5), Cy (6) that can be prepared directly by reacting Rh(mu-OH)(COD)(2) with 73% HF and PR(3) (1:2:2). The reactions of 1 with PPh(3) or Et(3)P have been studied by NMR spectroscopy at different molar ratios. Complexes RhF(PEt(3))(3) (7), RhF(COD)(PEt(3)) (8), and RhF(PPh(3))(3) (9) have been detected. The complex Rh(F)(NBD)(iPr(3)P) (NBD = norbornadiene; 10) was prepared by the sequential treatment of Rh(mu-OMe)(NBD)(2) with 1 equiv of NEt(3).3HF and (i)Pr(3)P. The first isolated bifluoride rhodium(I) complexes Rh(FHF)(COD)(PR(3)) R = Ph (11), (i)Pr (12), Cy (13), obtained by reacting fluoro complexes 3, 5, and 6 with NEt(3).3HF (3:1), have been characterized. The crystal structures of 3 and 11 have been determined.
The two ion pairs (4,7‐Me2indenyl)2ZrMe+MeB(C6F5)3− (1 b) and (indenyl)2ZrMe+ MeB(C6F5)3− (2 b) have been generated in situ by reaction of stoichiometric B(C6F5)3 with the corresponding dimethyl ...zirconocenes. It has been shown that molecular mechanics computations, guided by experimental 1H/1H NOE correlations, can provide information on the conformers present in solution. The dynamics of the ion pairs has also been investigated, showing the occurrence of both the processes previously characterized for this class of compounds, namely the B(C6F5)3 migration between the two methyl groups and dissociation–recombination of the whole MeB(C6F5)3− anion, the latter process being much faster than the first one (about three order of magnitude). Moreover, it has been shown that in certain conditions intermolecular processes can occur, which mimic the above‐mentioned dissociative exchanges. In particular, the presence of species containing loosely bound MeB(C6F5)3− anion fastens the exchange of this anion, while the presence of free B(C6F5)3 accelerates its exchange between the two methyl sites.
Molecular mechanics computations, guided by experimental NOE correlations, can provide information on the solution conformers, even for a system with a flat potential energy surface, such as that constituted by the ion pairs originating from the reaction of B(C6F5)3 with bisindenyl dimethyl zircononium complexes (see figure). Moreover, it has been shown that under certain conditions intermolecular processes can take place, which mimic the well established dissociative borane or methylborate exchanges.
Local attractions characterize the interanionic O−H⋅⋅⋅O hydrogen bonds in crystalline potassium hydrogenoxalate. This is the conclusion of theoretical and experimental studies on the electron density ...distribution. This contradicts a recent claim that such interactions are electrostatically repulsive. The picture shows the Laplacian function of the electron density in the region of the hydrogen bond.
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