The density functional theory (DFT) method has been used to study the electronic and molecular structure of mono-, di-, and trinuclear zerovalent nickel complexes containing acetylene and σ-donor ligands. The calculations were carried out for the model compounds (C2H2)2Ni (10) and (C2H2)Ni(PH3)2 (12) with quasi-tetrahedral (10a, 12a) and planar (10b, 12b) conformations as well as for (C2H2)3Ni2 (14) and (C2H2)4Ni3 (23). Rotational preference of complexes 10 and 12 is discussed on the basis of the 18 VE rule, relative energies, and natural bond orbital (NBO) population analyses. Optimized geometries and calculated IR and NMR properties are compared with known experimental data. It is shown how the effective back-bonding into acetylene in-plane π∥* MO(s) accounts for rotational preference of 10 and 12 as well as for the main features of molecular geometry of polynuclear Ni(0) compounds. Binding energies (BEs) of acetylene in 10a and 12b are calculated at the DFT, HF, MP2−MP4, CCSD, and CCSD(T) levels and compared to those of ethylene in (C2H4)2Ni (17), (C2H4)Ni(C2H2) (18), and (C2H4)Ni(PH3)2 (19) as well as to those of CO in Ni(CO) x , x = 4 (20), 3 (21), 2 (22). It turns out that with respect to 10a the bridging acetylene of 14 is bound almost 2 times stronger. Calculated BEs together with energies of association reactions L‘ + NiL2 → NiL2L‘ (L, L‘ = CO, PH3, C2H2) and L + NiL3 → NiL4 (L = CO, PF3, PMe3, PH3, C2H2) as well as of the exchange reaction Ni(CO)4 + 2C2H2 → Ni(C2H2)2 + 4CO are used in the discussion of thermodynamic and kinetic stability of the formally two-coordinated bis(alkyne)Ni compounds.

The solid state supramolecular assembly of prop-2-yn-1-ol and alkynediol transition metal complexes of Pt and Ni has been examined in light of the intermolecular interactions and hydrogen-bonding patterns established by alkyne monoalcohols and diols in the solid state. The analysis has been based on the crystal structure determination of the alcohols 1,1-dimethyl-3-tert-butylprop-2-yn-1-ol (1), tert-butylbis(ethyl)prop-2-yn-1-ol (2), tert-butylcyclohexylprop-2-yn-1-ol (3), and tetramethylalkynediol (4), as well as of the complexes bis(t-butylcyclohexylprop-2-yn-1-ol)M(0) (M = Pt (6a) and Ni (6b) and bis(t-butylcyclopentylprop-2-yn-1-ol)Pt(0) (7), integrated with the data available in the Cambridge Structural Database. It has been shown that the most common hydrogen-bond pattern is that based on a tetramer of −OH groups forming a square, a rhombus, or an open butterfly, irrespective of the molecular complexity. Larger ring systems or chains are established depending on the steric bulk of the substituents on the prop-2-yn-1-ol. Intermolecular and intramolecular hydrogen bond distances have been shown to depend on the type of alcohols, differences having largely a steric origin. The change in the Raman/IR stretching frequency of the C⋮C bond upon coordination of alkynediols to the metal centers has been examined for the nickel compounds and shown to provide a diagnostic tool for recognition of hydrogen-bond formation and typology.

The polyether impression materials tested were significantly more hydrophilic before, during, and after setting than that of VPS impression materials. Regardless of the amount of water in contact with the impression material, the polyether impression materials showed a significantly higher hydrophilicity in the unset stage than the VPS materials. The initial contact angle was not dependent on the thickness of the material. All parameters, including variation of time, volume of water droplet, and thickness of material, resulted in different absolute contact angles, but did not lead to a dramatic change in the ranking of the materials with regard to their hydrophilic behavior.

A variety of tetrasubstituted alkynediols react with (cdt)Ni (cdt = 1.5.9-cyclododecatriene) to give the homoleptic (alkyne)nickel complexes (HOR1R2CC⋮CCR1R2OH)2Ni as yellow crystals that are stable in the solid state at room temperature (R1 = R2 = Et, 1; R1 = Me, R2 = Et, 2; R1 = Me, R2 = Pr, 3; R1 = R2 = −(CH2)5−, 4; R1 = Me, R2 = i-Bu, 5). The 13C-NMR spectra show resonances for the coordinated alkyne carbon nuclei in the 133.5−135.2 ppm region. Only one resonance was found for 1−4 indicating a symmetrical structure. More than one resonance was found for 5 as well as for its platinum analog, compound 8, indicating the presence of different isomeric bis(alkyne)metal complexes. The structure of 1 has been established by single-crystal X-ray diffraction. The central atom is tetrahedrally coordinated to the four carbon atoms of two terminal alkynes. The network of hydrogen bonding between the four OH groups of neighboring molecules, which consists exclusively of intermolecular hydrogen bonds, stabilizes the crystal structure yielding a polymer-like chain. The platinum complex 9 (R1 = R2 = Me) shows similar structural properties. The reaction of (cdt)Ni or (cod)2Pt (cod = 1.5-cyclooctadiene) with the substituted alkynols R3CC⋮CCR1 2OH yields the new bis(alkyne)metal(0) compounds 10 (M = Ni, R = Me, R1 = Me), 11 (M = Pt, R = Me, R1 = Me), and 12 (M = Ni, R = Me, R1 = Et). Single-crystal X-ray structure determinations of 10−12 reveal that the central metal atoms are tetrahedrally coordinated by the four carbon atoms of the alkyne ligands. Two (alkyne)2M units are connected via hydrogen bonds between the four OH groups to form a dimer in the solid state. Complex 10 reacts in solution below −15 °C to yield the trimeric complex (alkyne)4Ni3.

Wasserstoffbrücken bestimmen die Struktur von 1, dem erstem stabile Bis(monoalkin)nickel(0)‐Komplex, im Kristall. Es liegen monomere Stränge aus NiC4‐und O4‐Tetraedern vor, die durch CMe2‐Gruppen getrennt sind. Vermutlich sind auch in Lösung Wasserstoffbrücken für die Stabilität und die Folgereaktionen von 1 wesentlich.magnified image