¹H NMR RESEARCH İNTO DİAMAGNETİC 1,2,4,1^‘,2^‘,4^‘-HEXAMETHYLFERROCENE, PARAMAGNETİC HEXAFLUOROPHOSPHATE OF 1,2,4,1^‘,2^‘,4^‘-HEXAMETHYLFERRİCİNİUM AND ELECTRON EXCHANGE BETWEEN THEM