Supramolecular Synthon Frustration Leads to Crystal Structures with <i>Z</i>′ > 1

A systematic study into frustration in compounds participating in more than one supramolecular synthon or simultaneously belonging to other categories such as hydrates, co-crystals or crystallizing in a chiral space groups has been undertaken using the Cambridge Structural Database (CSD). The study shows that the combination of more than one directional synthon or the combination of directional synthons with other particular categories of molecule results in markedly increased percentages of structures with Z′ > 1. The majority of combinations show percentages higher than the CSD average of 8.8% and some cases have Z′ > 1 percentages in excess of 60% such as the combination of a carboxylic acid dimer and a molecule in a chiral space group (64.7%). Individual cases have been highlighted and outliers have been discussed and resolved

Acyl Polysilanes: New Acyl Anion Equivalents for Additions to Electron-Deficient Alkenes

Silenes, generated through thermolysis of acylpolysilanes, add to α,β-unsaturated esters to form cyclobutanes and silylsubstituted cyclopropanes in moderate yields. Upon Si−C bond oxidation the cyclopropanes are converted directly to 1,4-dicarbonyl compounds, thus demonstrating the formal acyl anion chemistry of acyl polysilanes

Acyl Polysilanes: New Acyl Anion Equivalents for Additions to Electron-Deficient Alkenes

Silenes, generated through thermolysis of acylpolysilanes, add to α,β-unsaturated esters to form cyclobutanes and silylsubstituted cyclopropanes in moderate yields. Upon Si−C bond oxidation the cyclopropanes are converted directly to 1,4-dicarbonyl compounds, thus demonstrating the formal acyl anion chemistry of acyl polysilanes

Structural Characterization of a Photoinduced Molecular Switch

The crystal structures in both irradiated and nonirradiated states of a photoinduced molecular switch based on the spin-crossover phenomenon are presented. From the structural point of view, the light-induced metastable high-spin state of the spin-crossover complex [Fe(phen)2(NCS)2] (phen = 1,10-phenanthroline) shows significant differences with the low-spin state but also with the thermally induced high-spin state

Cooperative Hydrogen-Bonding Effects in a Water Square: A Single-Crystal Neutron and Partial Atomic Charges and Hardness Analysis Study

Four isomorphous complexes of formula [M(L)4(H2O)2]SO4·2H2O (M = Co, 1a; Ni, 1b; Cu, 1c; Zn, 1d) have been isolated and characterized by single-crystal X-ray diffraction and neutron diffraction using the quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin as well as by thermogravimetric analysis. The structures contain a discrete, strongly hydrogen-bonded water tetramer which causes a significant distortion of the metal coordination sphere in each case. Partial atomic charges and hardness analysis (PACHA) calculations reveal that the shortest hydrogen bonds are not the strongest in this constrained, cyclic solid-state structure and show that the distortion at the metal center is caused by the drive to maintain the integrity of the water tetramer. The system undergoes a disorder−order transition on slow cooling that provides insight into the nature of communication between water squares

Cooperative Hydrogen-Bonding Effects in a Water Square: A Single-Crystal Neutron and Partial Atomic Charges and Hardness Analysis Study

Four isomorphous complexes of formula [M(L)4(H2O)2]SO4·2H2O (M = Co, 1a; Ni, 1b; Cu, 1c; Zn, 1d) have been isolated and characterized by single-crystal X-ray diffraction and neutron diffraction using the quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin as well as by thermogravimetric analysis. The structures contain a discrete, strongly hydrogen-bonded water tetramer which causes a significant distortion of the metal coordination sphere in each case. Partial atomic charges and hardness analysis (PACHA) calculations reveal that the shortest hydrogen bonds are not the strongest in this constrained, cyclic solid-state structure and show that the distortion at the metal center is caused by the drive to maintain the integrity of the water tetramer. The system undergoes a disorder−order transition on slow cooling that provides insight into the nature of communication between water squares

Structural, Magnetic, and Photomagnetic Studies of a Mononuclear Iron(II) Derivative Exhibiting an Exceptionally Abrupt Spin Transition. Light-Induced Thermal Hysteresis Phenomenon

The new spin-crossover compound Fe(PM-BiA)2(NCS)2 with PM-BiA = N-(2-pyridylmethylene)aminobiphenyl has been synthesized. The temperature dependence of χMT (χM = molar magnetic susceptibility and T = temperature) has revealed an exceptionally abrupt transition between low-spin (LS) (S = 0) and high-spin (HS) (S = 2) states with a well-reproducible hysteresis loop of 5 K (T1/2↓ = 168 K and T1/2↑ = 173 K). The crystal structure has been determined both at 298 K in the HS state and at 140 K in the LS state. The spin transition takes place without change of crystallographic space group (Pccn with Z = 4). The determination of the intermolecular contacts in the LS and HS forms has revealed a two-dimensional structural character. The enthalpy and entropy variations, ΔH and ΔS, associated with the spin transition have been deduced from heat capacity measurements. ΔS (= 58 J K-1 mol-1) is larger than for other spin transition bis(thiocyanato) iron(II) derivatives. At 10 K the well-known LIESST (light-induced excited spin state trapping) effect has been observed within the SQUID cavity, by irradiating a single crystal or a powder sample with a Kr+ laser coupled to an optical fiber. The magnetic behavior recorded under light irradiation in the warming and cooling modes has revealed a light-induced thermal hysteresis (LITH) effect with 35 T1/2 < 77 K. The HS → LS relaxation after LIESST has been found to deviate from first-order kinetics. The kinetics has been investigated between 10 and 78 K. A thermally activated relaxation behavior at elevated temperatures and a nearly temperature independent tunneling mechanism at low temperatures have been observed. The slow rate of tunneling from the metastable HS state toward the ground LS state may be explained by the unusually large change in Fe−N bond lengths between these two states

Cooperative Hydrogen-Bonding Effects in a Water Square: A Single-Crystal Neutron and Partial Atomic Charges and Hardness Analysis Study

Four isomorphous complexes of formula [M(L)4(H2O)2]SO4·2H2O (M = Co, 1a; Ni, 1b; Cu, 1c; Zn, 1d) have been isolated and characterized by single-crystal X-ray diffraction and neutron diffraction using the quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin as well as by thermogravimetric analysis. The structures contain a discrete, strongly hydrogen-bonded water tetramer which causes a significant distortion of the metal coordination sphere in each case. Partial atomic charges and hardness analysis (PACHA) calculations reveal that the shortest hydrogen bonds are not the strongest in this constrained, cyclic solid-state structure and show that the distortion at the metal center is caused by the drive to maintain the integrity of the water tetramer. The system undergoes a disorder−order transition on slow cooling that provides insight into the nature of communication between water squares

Cooperative Hydrogen-Bonding Effects in a Water Square: A Single-Crystal Neutron and Partial Atomic Charges and Hardness Analysis Study

Four isomorphous complexes of formula [M(L)4(H2O)2]SO4·2H2O (M = Co, 1a; Ni, 1b; Cu, 1c; Zn, 1d) have been isolated and characterized by single-crystal X-ray diffraction and neutron diffraction using the quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin as well as by thermogravimetric analysis. The structures contain a discrete, strongly hydrogen-bonded water tetramer which causes a significant distortion of the metal coordination sphere in each case. Partial atomic charges and hardness analysis (PACHA) calculations reveal that the shortest hydrogen bonds are not the strongest in this constrained, cyclic solid-state structure and show that the distortion at the metal center is caused by the drive to maintain the integrity of the water tetramer. The system undergoes a disorder−order transition on slow cooling that provides insight into the nature of communication between water squares

Cooperative Hydrogen-Bonding Effects in a Water Square: A Single-Crystal Neutron and Partial Atomic Charges and Hardness Analysis Study

Four isomorphous complexes of formula [M(L)4(H2O)2]SO4·2H2O (M = Co, 1a; Ni, 1b; Cu, 1c; Zn, 1d) have been isolated and characterized by single-crystal X-ray diffraction and neutron diffraction using the quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin as well as by thermogravimetric analysis. The structures contain a discrete, strongly hydrogen-bonded water tetramer which causes a significant distortion of the metal coordination sphere in each case. Partial atomic charges and hardness analysis (PACHA) calculations reveal that the shortest hydrogen bonds are not the strongest in this constrained, cyclic solid-state structure and show that the distortion at the metal center is caused by the drive to maintain the integrity of the water tetramer. The system undergoes a disorder−order transition on slow cooling that provides insight into the nature of communication between water squares