Square planar coordination, high

Sc2 anions. Highly asymmetric opposite Se4-Se3/Se4-Se5 distances of 242.5(4)/298.9(4) pm are observed in the square-planar coordination sphere of the central Se4 atom. 

The Ni(II) complexes l-3g with hexaaza and pentaaza macrocyclic ligands as well as the Ni(II) cyclam complex display a low-spin square-planar and high-spin octahedral complex interconversion in aqueous solution (7, 12-14). However, complexes l-3a favor formation of the high-spin form upon addition of acid, which is in contrast to the cyclam complex. The protonation of tertiary nitrogen atoms at the bridgehead position facilitates the axial coordination of anion or water because of hydrogen-bonding between them 12, 14a). 

Hence the elongation of the anion octahedron is such that the cation is in square-planar coordination while the anion is surrounded by a deformed tetrahedron of four cations (Fig. 51). This distortion of the crystal structure from NiS(h) to PtS exactly corresponds to the transition from high-spin ds pyrite NiSa to diamagnetic PdSa by elongation of the anion octahedra. 

Finally trifluorides are found among the group 11 elements. AgFs contains highly elongated AgFe octahedra which are connected to a 3D framework. It is one of the few metallic fluorides known so far. An forms a stable molecular trihalides with each of the halides, AU2X6, with square-planar coordinated An atoms. ... 

Platinum is found in compounds having a smaller range of oxidation states than is the case for many of the earlier elements in the periodic table. The differences between it and Pd are somewhat more marked than for analogous pairs of earlier elements. The coordination numbers see Coordination Numbers Geometries) tend to be lower than for earlier elements a CN of six is rarely exceeded and a CN of four is common. Many important concepts in coordination chemistry, such as square-planar coordination and the trans effect, were first discovered in Pt complexes. The high electronegativity of the element is reflected in a poor 7t-basic character, which helps account for the lack of a binary carbonyl. 

High-temperature superconductors are based on copper, which has NQR-active nuclei, and NQR spectra can be obtained on these superconductors while they are in the superconducting state, which excludes magnetic fields. For the classic superconductor YBa2Cu306.9, two Cu NQR signals can be obtained. The square-planar-coordinated Cu(l) gives an NQR signal at 22.05 MHz, for which = 38.9 MHz... 

The only other example of square-planar coordination around tin(II) atom, Sn N( Pr2PSe)2 2 (127), was reported in 2005. It seems that this coordination mode is possible only when the tin atom is coordinated to soft, highly polarizable donor atoms. °... 

Two molecules of acetonitrile were found to be enclosed within the unit ceU of 14d, whereas 14c contains one acetonitrile per unit cell. An increased Pl-Pd-P2 angle of 88.54(4)° in 14d compared to 86.98(7)° in 14c or 85.82(7)° in DPPE-PdCl2 14 a (solvated with one molecule of dichloromethane) was observed, which reflects the steric demand of the isopropyl moieties. [(DPPE)PdCl2] shows approximately a square-planar arrangement of the two P and two Cl atoms around the Pd center. In contrast, in 14b-d the square-planar coordination is highly distorted. 

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