Tomoaki Sugaya

Pre‐Melting Structure Transformation of Water Clusters in Nanoporous Molecular Crystals

Inorganic porous compounds such as mesoporous silica, zeolite, and silica gel can confine many water molecules within their hydrophilic pores. These water molecules form multi-dimensional water molecule clusters (WMCs). These clusters are thought to play an important role in enzymes and biological membranes. 2] In differential scanning calorimetry (DSC) analyses of these compounds, such nanopore-confined WMCs often show a solid–liquid phase transition, which results from a macroscopic cooperative interaction between the confined water molecules. Furthermore, the exothermic freezing peaks of WMC in the nanopores of SBA-15 and MCM-41 are separated into a few low-intensity and broadened sub-peaks. Meanwhile, the characteristic broadening of the endothermic melting peaks is attributed to pre-melting of ice near the pore walls and dependent on the pore-size distribution of the nanopores. The appearance of such sub-peaks and an unusual peak shape is not observed at the water–ice transition for bulk water. The appearance of sub-peaks is believed to result from water layers in the partially filled nanopores. The layers exist under different thermodynamic conditions as compared to boundary water at the interface between the pore wall and the WMC. 7] Herein, we report the appearance of two different broadened endothermic and exothermic sub-peak populations in DSC scans of nanotube-like WMCs. These “water nanotubes” (WNTs) are one-dimensional (1-D) channels of WMCs that exist in nanoporous H-bonding metal-coordination crystals of {[Co(H2bim)3](TMA)·20H2O}n (1; where H2bim stands for 2,2’-biimidazole and TMA stands for trimesate, see Scheme 1). Apart from a large peak at 245 K corresponding to a typical first-order phase transition from frozen ice nanotubes (INTs) to molten WNTs, in the ascending DSC curve of crystals of 1 (Figure 1), a small broadened peak can be observed at low temperature, which corresponds to a pre-melting phenomenon, usually occurring at the surface, and which results from the transition of the completely frozen WMC conformation to the INT conformation with partially moving water molecules. By solving the X-ray crystal structure of the molecular WMC at 104 K below the pre-melting transition, we show that this premelting endothermic peak results from the motion of water molecules involved in a structural transition. We previously reported the construction of a 2D H-bonded metal-coordination polymer by self-organization of tris-2,2’-biimidazole cobalt(III) ([Co(H2bim)3] 3 ) and TMA . Biimidazole metal complexes can not only form complementary intermolecular H-bonds of the dual N H···N type by mutual deprotonation, but also intermolecular H-bonds of the dual N H···O type through bonding with either of the two O atoms of a carboxyl group. The difference in acidity between the imidazolate NH group and the carboxylate COO gives rise to a strong ionic interaction, which is reinforced by two H-bonds of the electrostatic N H···O type. As such, 1D nanoporous channels of 1 form by the alternate stacking of Dand Lhexagonal sheets in a (6,3)-net. Two Dand L-chiral sheets of 1 assemble through alternating H-bonds between Dor L-[Co(H2bim)3] 3 + and TMA , as shown in Figures 1S and 2S (Supporting Information). A tube-like WNT arrangement is formed from the twenty water molecules in the periodic unit, which are stabilized by the nanopore. From X-ray crystal analysis at 296 K, despite the fact that the WNT is in the molten state, it can be observed that the electron densities of the oxygen Scheme 1. [Co(H2bim)3] 3 + and TMA .

Molecular cable-like 1-D iodic spiral chains covered with triple helices stabilized in guest-included chiral porous framework

The supramolecular crystal {[Pr(DMFA)](3)[Ni(II)(Hbim)(3)](2)I}(n) with intricate chiral networks of [Ni(II)(Hbim)(3)](-) molecules is reported. It includes a cationic architecture as a guest, constructed from chiral nanotubes that penetrate I(-) chains with spiral channels wrapped by triple helices. The I(-) chains have AC conductivity in crystals like a molecular cable.

Self-Organization of

Anionic tris (biimidazolate) nickelate (II) ([Ni(Hbim)3]−), which is a hydrogen-bonding (H-bonding) molecular building block, undergoes self-organization into honeycomb-sheet superstructures connected by complementary intermolecular H-bonds. The crystal obtained from the stacking of these sheets is assembled into channel frameworks, approximately 2 nm wide, that clathrate two cationic K

Observation of the First Spin-Crossover in an Iron(II) Complex with an S6 Coordination Environment: tris[bis(N,N-diethylamino)carbeniumdithiocarboxylato]iron(II)hexafluorophosphate

For the first time, the spin-crossover (SCO) phenomenon has been observed in an FeII -S6 system in a tris(chelate)-type iron(II) complex with a zwitterionic sulfur donor bidentate, bis(N,N-diethylamino)carbeniumdithiocarboxylate (EtL), [FeII (EtL)3 ](PF6 )2 (1), as synthesized by the reaction of a precursor complex [FeII (CH3 CN)6 ](PF6 )2 with EtL. In the solid state, the high-spin (HS) d6 state at ambient temperature and the low-spin (LS) d6 state at temperatures lower than approximately 240 K were evidenced by magnetic measurements with SQUID and Mössbauer spectra in the temperature range 4-290 K. X-ray analyses of the crystals at various temperatures disclosed that the distorted trigonal prismatic coordination environments essentially do not change; however, contraction of Fe-S distances by approximately 10 % (0.22 Å), ordering of alkyl groups in EtL and PF6 - counteranions, and formation of significant intermolecular S⋅⋅⋅S interactions between adjacent molecules (average distances of 3.59 Å) take place during the transition from the HS to the LS state. A large decrease in the volume of the formula unit (78.1 Å3 ) might be responsible for the large activation barrier, thereby resulting in a slow phase transition upon cooling.

Crystal structure of [5-bromo-2-(pyridin-2-yl-κN)phenyl-κC1](pentane-2,4-dionato-κ2O,O′)platinum(II)

In the title complex, [Pt(C11H7BrN)(C5H7O2)], two crystallographically non-equivalent dimers stacked by π–π interactions are arranged antiparallel to each other.

Water nanotubes clathrating solvent molecules stabilized by molecular 1-D nanoporous crystals

A one-dimensional (1-D) water nanotube-like cluster (WNT) clathrating a tetrahydrofuran (THF-hydrate) is constructed from new 4461074 polyhedral units of 30 water molecules and including three THFs into the unit in the center like a clathrate hydrate, which was stabilized into a molecular nanoporous crystal.

2-{[2,2-Bis(diethyl­amino)­ethan-2-ylium­thio­yl]sulfan­yl}-1,1-bis­(diethyl­amino)­ethyl­ium bis­(perchlorate)

The title salt, C20H42N4S2 2+·2ClO4 −, was obtained from the reaction of bis(diethylamino)carbeniumdithiocarboxylate, (Et2N)2C2S2, with Fe(ClO4)2·6H2O in CH2Cl2. The title compound, in which one of the S atoms of (Et2N)2C2S2 is bound to a 1,1-bis(diethylamino)ethane moiety, has two carbenium C atoms, and the charge compensation is provided by two perchlorate anions. The N2C—CS2 bond length is 1.512 (4) Å, corresponding to a C—C single bond, and the dihedral angle between N2C– and –CS2 planes [72.0 (2)°] is smaller than that of (Et2N)2C2S2 [82.0 (1)°]. The crystal structure features C—H⋯S hydrogen bonds.