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A series of mononuclear CuII complexes, [CuII(4-FBA)2(py)2(H2O)] (1), [CuII(3-FBA)2(py)2(H2O)] (2), and [CuII(3,4-F2BA)2(py)2(H2O)] (3), where 4-FBA = 4-fluorobenzoate, 3-FBA = 3-fluorobenzoate, 3,4-F2BA = 3,4-difluorobenzoate, and py = pyridine, respectively, was synthesized and the complexes crystallographically identified. All the CuII complex crystals share a one-dimensional O–H⋯O hydrogen-bonding chain substructure, although the mutual alignment of fluorinated benzoate (FxBA) ligands exhibits subtle differences among the various compounds, i.e., FxBA ligands align in an antiparallel fashion in crystals 1 and 3, while 3-FBA ligands in crystal 2 are interdigitated with a tilt along the a axis. Reversible phase transitions were found upon heating at 170.7, 171.3, and 267.5 K for crystals 1, 2, and 3, respectively; all crystals showed approximately 3% expansion and shrinkage of the intermolecular O–H⋯O hydrogen bond distances associated with the thermally activated orientational fluctuations of the FxBA ligands in crystals 1 and 3. The increase in dielectric constant with increasing temperature, at 240 K, activated molecular fluctuation in the 3,4-F2BA ligands in crystal 3. Heat capacity measurements indicated that both the expansion and shrinkage of hydrogen bonds, and the molecular fluctuation in 3,4-F2BA ligands, contributed to phase transition, and the latter caused dipole fluctuation, resulting in a dielectric anomaly in crystal 3. [ABSTRACT FROM AUTHOR]

A newly synthesized one-dimensional (1D) hydrogen-bonded (H-bonded) rhodium(II)-η5-semiquinone complex, [Cp*Rh(η5- p-HSQ-Me4)]PF6 ([ 1]PF6; Cp*=1,2,3,4,5-pentamethylcyclopentadienyl; HSQ=semiquinone) exhibits a paraelectric-antiferroelectric second-order phase transition at 237.1 K. Neutron and X-ray crystal structure analyses reveal that the H-bonded proton is disordered over two sites in the room-temperature (RT) phase. The phase transition would arise from this proton disorder together with rotation or libration of the Cp* ring and PF6− ion. The relative permittivity εb′ along the H-bonded chains reaches relatively high values (ca., 130) in the RT phase. The temperature dependence of 13C CP/MAS NMR spectra demonstrates that the proton is dynamically disordered in the RT phase and that the proton exchange has already occurred in the low-temperature (LT) phase. Rate constants for the proton exchange are estimated to be 10−4-10−6 s in the temperature range of 240-270 K. DFT calculations predict that the protonation/deprotonation of [ 1]+ leads to interesting hapticity changes of the semiquinone ligand accompanied by reduction/oxidation by the π-bonded rhodium fragment, producing the stable η6-hydroquinone complex, [Cp*Rh3+(η6- p-H2Q-Me4)]2+ ([ 2]2+), and η4-benzoquinone complex, [Cp*Rh+(η4- p-BQ-Me4)] ([ 3]), respectively. Possible mechanisms leading to the dielectric response are discussed on the basis of the migration of the protonic solitons comprising of [ 2]2+ and [ 3], which would be generated in the H-bonded chain. [ABSTRACT FROM AUTHOR]

By employing an N,N′-ditopic spacer 2-aminopyrazine (ampyz), two-dimensional (2D) (1) and three-dimensional (3D) (2) azido-bridged cobalt(II) coordination networks with the identical formula [Co(N3)2(ampyz)]n have been synthesized and characterized structurally and magnetically. Compound 1 was prepared by the layer diffusion method in ambient temperature and crystallized in the high symmetric space group Immm. The 2D square-grid structure of 1 contains the perfect symmetric linear of alternating double end-on (EO) and double end-to-end (EE) azido-bridged CoII chains which are linked together by an ampyz spacer in trans-arrangement. The intralayer π-π stacking interactions among ampyz spacers additionally stabilize this layer. The adjacent 2D layers are assembled by the intermolecular hydrogen bonding between the NH2 of the ampyz and the EE azido ligands building a 3D structure. Compound 2 was prepared by a hydrothermal technique and shows a 3D framework containing a zigzag chain of similarly alternating double EO and double EE azido-bridged CoII center. In contrast, this chain is linked by two ampyz spacers in cis-fashion giving rise to a 3D structure. The magnetic investigation of 1 shows the coexistence of a big spin canting angle and metamagnetism having magnetic ordering at 10 K, whereas the magnetic behavior of 2 simply exhibits spin-canted antiferromagnetism below TN of 16 K. [ABSTRACT FROM AUTHOR]

Three new supramolecular metal-coordination architectures [M(H2O)4(ampyz)2][M(H2O)6](SO4)2(H2O)2(M = Co (1), Fe (2), and mixed Co/Fe (3); ampyz = 2-aminopyrazine) and a Cd(ii) coordination polymer [Cd(ampyz)(H2O)2(SO4)]n(H2O)n(4) were synthesized by layered diffusion and structurally characterized. Compounds 1–3are isomorphous. Monomeric complex units [M(H2O)4(ampyz)2]2+are assembled by intermolecular hydrogen bonding and π–π stacking viaampyz moieties to build 2D sheets. These layers are linked by intermolecular hydrogen bonding viaampyz ligand, [M(H2O)6]2+unit, sulfate anion and lattice and coordinated water molecules to stabilize 3D supramolecular structure. Compound 4shows a 2D coordination network where the sulfato connector and the bridging ampyz link Cd(ii) ions. Lattice water molecules are filled in between the layers viathe hydrogen bonds stabilizing 3D supramolecular network of 4. Interestingly, compounds 1–3exhibit water-induced reversible crystal-to-amorphous transformations with chromotropism and compound 4also shows water-induced reversible structural phase transformation confirmed by spectroscopic techniques, elemental analyses, TGA, and XRPD. These results demonstrate the significant role between coordination bridges and weaker intermolecular interactions for the structural conversion even though 1–3lack coordination bridges for the maintenance of their structures, however, the weak intermolecular interactions, especially hydrogen bonding, play a key role to the recovery of the crystalline phase. [ABSTRACT FROM AUTHOR]

Abstract: The reactions of 2-hydroxyphenylethanone oxime (Me-H2salox) and (2-hydroxy-phenyl)-phenyl-methanone oxime (Ph-H2salox) with Mn(ClO4)2·6H2O in MeOH afford trinuclear manganese complexes of [Mn3O(Me-salox)3(MeOH)3(ClO4)]·MeOH (1·MeOH) and [Mn3O(Ph-salox)3(MeOH)3(ClO4)]·2MeOH (2·2MeOH), respectively. X-ray analysis shows that both complexes contain a manganese triangle core, [MnIII 3O]7+. The structural distortion from the twisting of the oxime ligands dominates the ferromagnetic interactions within the three Mn ions in both compounds and results in an S = 6 ground state. The frequency dependence of out-of-phase signals in the alternating current (AC) magnetic susceptibility measurements and the temperature-dependent and sweep-rate-dependent hysteresis loops are indicative of single-molecule magnet behavior. Moreover, both complexes show step-wise magnetization, indicating the occurrence of quantum tunneling of magnetization (QTM). Interestingly, a tail to tail arrangement in the crystal packing of complex 1·MeOH results in strong intermolecular H-bonding interactions and leads to the exchange-bias effect from the antiferromagnetic interaction between the adjacent Mn3 molecules. In contract, QTM steps of complex 2·2MeOH show an absence of the exchange-bias effect due to a weak intermolecular interaction from a head to tail arrangement. [Copyright &y& Elsevier]