A novel luminescent platinum(II)-diimine complex, Na 2 [Pt(CN) 2 (dcbpy)]·nH 2 O (H 2 dcbpy = 4,4Ј-dicarboxy-2,2Ј-bipyridine, n = 2 or 5) was synthesized and investigated by using X-ray diffraction measurements and spectroscopy. Complex Na 2 [Pt(CN) 2 (dcbpy)]·2H 2 O was first obtained as a red amorphous solid (1A) that exhibits bright luminescence at 623 nm. After recrystallization, two crystalline forms, the dihydrate form, 1C, and the pentahydrate form, Na 2 [Pt(CN) 2 -(dcbpy)]·5H 2 O (2), were obtained and analyzed by the single-crystal X-ray diffraction method. Upon exposure of the amorphous form 1A to hydrophilic vapours such as those of

Reactions of a Pt(II)-diimine-based metalloligand Na 2 [Pt(CN) 2 (4,4'-dcbpy)] (4,4'-H 2 dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) with alkaline-earth metal salts Mg (NO 3 exhibit any chromic behaviour. Combination analysis of powder X-ray diffraction, thermogravimetry, and IR spectroscopy suggests that the dimensionality of the coordination network contributes considerably to both the structural flexibility and luminescence properties; that is, the low-dimensional flexible coordination network formed in MPt-4 complexes with smaller alkaline-earth metal ions enables a structural rearrangement induced by thermal and mechanical stimuli and vapour adsorption, resulting in 25 the observed multichromic behaviour.

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The cover picture shows the amorphous–crystalline transformation of the newly synthesized platinum(II)–diimine complex Na2[Pt(CN)2(dcbpy)]·2H2O induced by exposure to several hydrophilic solvent vapours. The transformation is accompanied by siginificant colour and luminescence changes. Details are discussed in the article by M. Kato et al. on p. 2465 ff.