Donor/acceptor organotriiron(II) hydrazone chromophores: structural, spectroscopic and electrochemical properties

New conjugated trinuclear organoiron(II) complexes in which a trans-1,2-ferrocenyl-ferrocenylene ethene fragment (electron-donors) is attached to an electron-deficient cationic mixed sandwich via a hydrazone bridge have been prepared. These complexes have therefore the basic architectural and electronic properties necessary to exhibit second-order non-linear optical behaviour.