Copper difluoride, structure

Copper (continued) cynates, 17 322, 323 diaminodithioether complexes, 17 185 diazene complexes, 27 232 difluoride, structure, 27 85, 86, 87, 88 dinuclear sites, 40 362-367 diphosphine complexes of, 14 235-239 electron-density distributions of complexes, 27 34, 41... 

Fig. 1. The puckered layers of [MF4J units in the structures of (a) silver and (b) copper difluorides. Single circles show atoms in one puckered layer and dashed circles those in the adjacent layer below. Those atoms from the adjacent layer above, which complete the distorted octahedral coordination, are shown hatched. (In silver difluoride they are directly above the dashed circles.)...

The change in symmetry from copper to silver is related to rather subtle structural differences. If only the four short M—F bonds are considered, then both structures consist of puckered layers formed by joining the square, [MF4] units through corners. These puckered layers lie directly over one another, related by a translation in copper difluoride, but are displaced alternately, related by a glide plane, in silver difluoride (27), (see Fig. 1). In both structures, the fluorine atoms are arranged in considerably distorted hexagonal close-packed arrays, the distortion being more marked for silver. 

Transition metal difluorides are known mainly for first transition series elements, with palladium and silver difluorides from the second series, and no examples from the third. All these compounds have either the rutile structure, or, for chromium, copper, and silver, a distorted variant, which can be correlated with a Jahn-Teller distortion of the octahedral coordination of the ions. This rutile structure type is associated with smaller cations and, for comparison, although zinc difluoride has the same rutile structure, cadmium and mercury difluorides have the cubic fluorite structure with eight coordination of the cations (12). 

A structural study of dibromo(l,4,8,ll-tetraazacyclo-tetradecane)copper(II) and diaqua(l,4,8,ll-tetraaza-cyclotetradecane)copper(II) difluoride four hydrate complexes in crystal and in aqueous solution by X-ray absorption near edge structure measurements and DV-Xa calculations... 

In the present study, we synthesized dibromo(l,4,8,ll-tetraazacyclotetradecane)copper(II) ([CuBr2(cyclam)]) and diaqua(l,4,8,ll-tetraazacyclotetradecane)copper(II) difluoride four hydrate ([Cu(cyclam)-(H20)2]F2 4H20) complexes and performed single crystal structure analysis and X-ray absorption near-edge structure (XANES) measurements in crystals and in aqueous solution. Furthermore, DV-Xa molecular orbital calculations have been made for models based on these results, and the structures and electronic states of the [Cu(cyclam)] complexes in crystals and in aqueous solution are discussed, in particular, on the axial coordination to Cu(II). 

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