SPECTROSCOPIC STUDIES OF Mx[Pt(CN)4] · yH2O *

Square planar [Pt(CN),]’complexes tend to crystallize in columnar structures. The distances between the molecular units along the columnar axis are short, compared with the separations from column to column. This structure type is expected to exhibit some interesting physical properties. One compound (K2[Pt(CN)4]Bro,3 3.2H2O(KCP Xo,3)) of the relatively large series of the tetracyanoplatinates has become famous mainly because of its extremely anisotropic conductivity.’-’ However, most members of the tetracyanoplatinates are nonconducting compounds. This might be the reason why these have not attracted as many scientific investigations. TABLE 1 shows a list of the tetracyanoplatinates (MCP) which crystallize in columnar structures. The Pt-Pt-distances R in the direction of the column can be varied according to the choice of the cations M and/or the crystal water content y from R = 3.67 6; to 3.09 6;. This allows the “adjustment” of the intermolecular interaction in the direction of the chains over a large range. This adjustment by the chemical substitution method, however, is discontinuous. Application of high pressure, on the other hand, permits “tuning” the in-chain interaction to any intermediate value. Consequently, the spectroscopic properties can be tuned continuously, as well. The purpose of the present paper is, first, to summarize recent results found by spectroscopic investigations with polarized light under ambient conditions, a t high pressure, and at low temperature. A correlation between the transition energies and structural properties is pointed out. Mainly R-dependent trends are discussed, and the results of an electronic band structure calculation are presented. In the second part of the paper the influence of the immediate surrounding on the [Pt(CN),]’columns is discussed. For this purpose, rare earth cations (e.g. M = Sm’+) with energy levels near the excited column states are used as “probe” ions. Energy transfer from the tetracyanoplatinate columns (donors) to Sm3+ (acceptor) is observed. Thus, a new system for energy-transfer investigations is presented that exhibits interesting aspects because of the tuneability of the donor states.

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