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(CH3NH3)3Sb2Cl9 single crystals are grown which appear to be isomorphous with Cs3Sb2Cl9 crystals of β‐modification. They are characterized by the space group Pmcn with the lattice constants: a = 0.7920(5), b = 1.3334(11), and c = 1.966(2) nm. In the crystal one can distinguish the poly‐anionic (Sb2Cl9)3‐ stacks directed along the a‐axis with three crystallographically inequivalent CH3NH 3+ cations. The DSC, dielectric, and PMR studies reveal a structural phase transition at 208 K which is related to a freezing of rotational motion of CH3NH 3+ cations.

Population studies indicate a strong relationship between birth weight (BW) and body size in later life. However, BW as a variable was never accounted for in studies on the relationship between attention-deficit/hyperactivity disorder (ADHD) and overweight. This study aims to assess the relationship between ADHD and overweight with control of birth weight and other confounding factors. Prevalence of overweight was compared in clinical sample of 219 boys with ADHD and 396 boys without ADHD, aged 6–18 years. The following factors were controlled: BW, parents income and education level, place of residence, ADHD type, selected comorbid disorders and stimulant treatment. Overweight and obesity were diagnosed according to the criteria proposed by the International Obesity Task Force. Logistic regression analysis was used to estimate the association between ADHD and the prevalence of overweight and obesity. Boys with ADHD differed significantly from the control group in distribution of low BW (8.2 vs. 3.0 %, χ2 = 8.23, p = 0.02). Low BW was associated with a lower prevalence of overweight than normal and high BW (0 vs. 12.14 %, χ2 = 4.12, p = 0.04). Overweight was observed significantly more often in boys with ADHD (17.3 vs. 8.3 %, χ2 = 11.23, p < 0.001) even after adjustment for BW and other variables (OR = 2.44, 95 % CI 1.38–4.29, p = 0.002) and after controlling for ADHD type, stimulant treatment and selected comorbid disorders. Independently to applied analysis, obesity was not associated with ADHD. Lower birth weight is over twice more often observed in boys with ADHD than in control group. Although this phenomenon may reduce the rate of overweight in the studied group, ADHD remains strongly associated with increased prevalence of overweight.

The dielectric properties of glycinium phosphite (GPI) crystals as a function of temperature and electric field magnitude are investigated. The electric field E is applied perpendicularly to the ferroelectric b-axis in the direction of hydrogen-bonded phosphite chains in the crystal (the c-axis). The shift of the paraelectric–ferroelectric phase transition to lower temperatures proportionally to Ec2 (where Ec is an effective field in the sample) is observed. Strong anomalies in the field dependence of the permittivity in the temperature region are revealed. It is shown that the observed jump-like changes of are caused by the phase transition from the ferro- to paraelectric phase induced by the electric field. Such a transition is connected with the rearrangement of protons on hydrogen bonds and the reversal of the corresponding dipole moments, at which the compensation of their components along the b-axis takes place. The theoretical description of the observed dielectric anomalies, given on the basis of the phenomenological Landau free energy approach, is in good agreement with the experimental data.

A new crystal of 2-aminopyridine phosphate (NC4H4NH2)·H3PO4 has been grown and its x-ray structure and physical properties were studied. At room temperature the crystals are monoclinic, space group C2/c. The flat 2-aminopyridine cations are hydrogen bonded to the anionic [PO4 ] groups. The interesting feature of the crystal structure is the three-dimensional network of hydrogen bonds including, among others, two strong, symmetrical O · · · H, H · · · O interactions with disordered proton locations. Symmetrically related PO4 anions linked through these protons form infinite (PO4)∞ chains along the crystal a-axis. The anomalies in the temperature dependence of the electric permittivity showed that the crystal undergoes ferroelectric phase transition at Tc = 103.5 K. The spontaneous polarization takes place along the crystal a-axis, being parallel to the chains of the hydrogen-bonded PO4. The disordered protons, thermally activated at room temperature, can be frozen at their positions in the ferroelectric phase. The order–disorder continuous type of the transition has been evidenced on the basis of the temperature dependences of electric permittivity and spontaneous polarization measurements.

The dielectric properties of the crystal were investigated under hydrostatic pressure. Pressure effects on its dielectric properties are due to the shift of the paraelectric - ferroelectric transition temperature with pressure. With increasing pressure p, decreases greatly with .

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