General: Cis-(tmen)Pd(NO 3 ) 2 [tmen = N,N,N',N'-tetramethylethane-1,2-diamine] 1 , ditopic and tetratopic donors 1,4-di(pyridin-4-yl)benzene (dpb) 2 , 1,2,4,5-tetrakis(1-imidazolyl)benzene (timb) 3 were prepared following the literature procedures. 1,2-di(pyridin-4-yl)ethane (dpe) was purchased from Sigma-Aldrich (USA) and used without further purification. The chemical shifts (δ) in the 1 H NMR spectra are accounted in ppm relative to proton resonance resulting from incomplete deuteration of

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... he solvent D 2 O at 4.79 ppm and spectra were recorded on a Bruker 400 MHz instrument. Electrospray ionization mass spectrometry (ESI-MS) experiments were carried out in Bruker Daltonics (Esquire 300 Plus ESI model) using standard spectroscopic grade solvents acetonitrile and methanol. IR spectra were recorded on a Bruker ALPHA FT-IR spectrometer. TGA analysis of 1 and 2 were performed on a Mettler-Toledo TGA-851 e thermobalance under a stream of nitrogen (flow rate = 50 mL min −1 ) in the temperature range 30−600 C (heating rate = 5 C min −1 ) on alumina crucible of 70 L volume and DSC was performed using a Mettler Toledo instrument at a heating rate of 10 C min −1 under dry N 2 atmosphere. Water adsorption isotherms of the assemblies 1 and 2 are recorded volumetrically Electronic Supplementary Material (ESI) for Chemical Communications This journal is S2 using BELSORP-max apparatus (BEL Japan) after elimination of guest water molecules by evacuation at 120 o C over 12 h. General procedure for the synthesis of aggregates (1 & 2): An aqueous yellow solution of cis- (tmen)Pd(NO 3 ) 2 was added into the solid mixture of 1,2,4,5-tetrakis(1-imidazolyl)benzene (timb) and linear dipyridyl donors (dpe or dpb) and the suspension was allowed to stir at room temperature. After 24 h the colourless solution was filtered, concentrated under reduced pressure and the product (1 or 2) was isolated in pure form after triturating with acetone. Synthesis of 1: The aqueous solution of cis-(tmen)Pd(NO 3 ) 2 (150 mg, 0.433 mmol) was added into the solid mixture of 1,2,4,5-tetraimidazole benzene (timb) (49.4 mg, 0.144 mmol) and 1,2di(pyridin-4-yl)ethane (26.6 mg, 0.144 mmol) to obtain molecular aggregate 1. Isolated yield: 93 %. IR: (cm -1 ) = 3415,