Crystal-to-crystal polymerisation of monosubstituted [PW11O39Cu(H2O)]5- Keggin-type anions.

The reaction between neutral bis(picolinate)copper(II) complexes and copper(II)-monosubstituted Keggin-type phosphotungstate anions formed in situ leads to the formation of the hybrid [C(NH2)3]10[{PW11O39Cu(H2O)}2{Cu(pic)2}]·10H2O compound (1, pic = picolinate) in the presence of structure-directing guanidinium cations. Single-crystal X-ray diffraction studies demonstrate that 1 contains dimeric {PW11O39Cu(H2O)}2{Cu(pic)2} molecular species constituted by two Keggin-type anions linked by one {Cu(pic)2} octahedral complex through axial coordination to their terminal oxygen atoms. The extensive hydrogen-bonding network established by guanidium cations and Keggin clusters plays a key role in retaining the crystallinity of the system throughout dehydration to allow a single-crystal-to-single-crystal (SCSC) transformation into the anhydrous [C(NH2)3]10[{PW11O39Cu}2{Cu(pic)2}] (2a) at 170 °C. Structural modifications involve the re-orientation, shifting in ca. 1.5 Å and condensation of all the {PW11O39Cu} units to result in {PW11O39Cu}n chains in an unprecedented solid-state polymerisation. This phase transition also implies the cleavage of Cu-O bonds induced by the rotation and translation of Keggin-type anions, in such a way that hybrid dimeric units in 1 are dismantled and {Cu(pic)2} complexes become square planar. The irreversibility of the phase transition has been confirmed by combined thermal and diffractometric analyses, which evidence that the anhydrous phase adsorbs only one water molecule per cluster to become the [C(NH2)3]10[{PW11O39Cu}2{Cu(pic)2}]·2H2O (2h) hydrated derivative without any significant alteration in its cell parameters, nor in its crystalline structure. Phase transformations have been monitored by electron paramagnetic resonance spectroscopy.

Rearrangement of a Krebs-type polyoxometalate upon coordination of N,O-bis(bidentate) ligands.

Selective coordination of 2,3-pyzdc to the Krebs-type [{Ni(H2O)3}2(WO2)2(SbW9O33)2](10-) anion promotes a skeletal rearrangement that results in the [(2,3-pyzdc)2{NaNi2(H2O)4Sb2W20O70}2](22-) (Ni4) hybrid dimer showing a novel dinickel containing a 20-tungsto-2-antimonate(III) framework stabilized by N,O-bis(bidentate) bridging ligands. The solution stability and magnetism of Ni4 is discussed.

Functionalization of Krebs-type polyoxometalates with N,O-chelating ligands: a systematic study.

The first organic derivatives of 3d-metal-disubstituted Krebs-type polyoxometalates have been synthesized under mild bench conditions via straightforward replacement of labile aqua ligands with N,O-chelating planar anions on either preformed or in situ-generated precursors. Nine hybrid clusters containing carboxylate derivatives of five- or six-membered aromatic N-heterocycles as antenna ligands have been obtained as pure crystalline phases and characterized by elemental and thermal analyses, infrared spectroscopy, and single-crystal X-ray diffraction. They all show the general formula [{M(II)L(H2O)}2(WO2)2(B-ß-XW9O33)2](n-) and can be classified as follows: 1-SbM, where L = 1H-imidazole-4-carboxylate (imc), X = Sb(III), n = 12, and M(II) = Mn, Co, Ni, Zn; 1-TeM, where L = imc, X = Te(IV), n = 10, and M(II) = Mn, Co; 2-SbNi, where L = 1H-pyrazole-3-carboxylate (pzc), X = Sb(III), n = 12, and M(II) = Ni; and 3-SbM, where L = pyrazine-2-carboxylate (pyzc), X =Sb(III), n = 12, and M(II) = Co, Zn. The 3d-metal-disubstituted tungstotellurate(IV) skeleton of compounds 1-TeM is unprecedented in polyoxometalate chemistry. The stability of these hybrid Krebs-type species in aqueous solution has been confirmed by (1)H NMR spectroscopy performed on the diamagnetic 1-SbZn and 3-SbZn derivatives. Our systematic study of the reactivity of disubtituted Krebs-type polyoxotungstates toward diazole-, pyridine-, and diazinecarboxylates demonstrates that organic derivatization is strongly dependent on the nature of the ligand, as follows: imc displays a "universal ligand" character, as functionalization takes place regardless of the external 3d metal and heteroatom; pzc and pyzc show selectivity toward specific 3d metals; pyridazine-3-carboxylate and pyrimidine-4-carboxylate promote partial decomposition of specific precursors, leading to [M(II)L2(H2O)2] complexes; and picolinate is inert under all conditions tested.

trans-Di-aqua-bis-(pyridazine-3-carboxyl-ato-κ(2) N (2),O)copper(II).

In the title compound, [Cu(C5H3N2O2)2(H2O)2], the Cu(II) ion, located on an inversion center, exhibits an octa-hedral coordination geometry. The equatorial plane is defined by two trans-related N,O-bidentate pyridazine-3-carboxyl-ate ligands and the axial positions are occupied by two water mol-ecules. In the crystal, mol-ecules are connected by O-H⋯O hydrogen bonds between the water mol-ecules and the noncoordinating carboxyl-ate O atoms, forming layers parallel to the bc plane. The layers are stacked along the a axis by further O-H⋯O hydrogen bonds between the water mol-ecules and the coordinating carboxyl-ate O atoms. Weak C-H⋯O hydrogen bonds are also observed between the pyridazine rings and the water mol-ecules and between the pyridazine rings and the non-coordinating carboxyl-ate O atoms.

Diaqua-bis-(1H-imidazole-4-carboxyl-ato-κ(2)N(3),O)cobalt(II).

The title compound, [Co(C(4)H(3)N(2)O(2))(2)(H(2)O)(2)], contains a Co(II) cation on a twofold rotation axis, exhibiting a distorted octa-hedral coordination geometry. The equatorial plane is formed by two N,O-bidentate 1H-imidazole-4-carboxyl-ate ligands and the axial positions are occupied by water mol-ecules. The crystal packing consists of a three-dimensional network stabilized by O-H⋯O and N-H⋯O hydrogen bonds, together with weak π-π inter-actions [centroid-centroid distance = 3.577 (2) Å] between the imidazole rings.

Tetra-kis(µ(2)-ferrocene-carboxyl-ato-κO:O')bis-[(methanol-κO)copper(II)] methanol disolvate.

The complex mol-ecule of the title compound, [Cu(2)Fe(4)(C(5)H(5))(4)(C(6)H(4)O(2))(4)(CH(3)OH)(2)]·2CH(3)OH, lies about an inversion centre and contains two centrosymetrically related Cu(II) atoms bridged by four O:O'-bidentante ferrocene-carboxyl-ate anions, leading to a dimeric tetra-bridged unit with a paddle-wheel geometry. The Cu(II) atom has a distorted square-pyramidal coordination environment with four O atoms from four ferrocene-carboxyl-ate ligands in basal positions and an O atom from a methanol mol-ecule in an apical position. One of the two crystallographically independent ferrocenyl groups has a staggered conformation, while the other is eclipsed. The mol-ecules are connected into a chain along the b axis by O-H⋯O hydrogen bonds involving coordinated and uncoordinated methanol mol-ecules and the O atom from a ferrocene-carboxyl-ate unit.