Oxidative addition of halogens to 1,3- and 1,5-(Ph2PN)2(SN)2: x-ray crystal structure of 1,5-(Ph2PN)2(NSBr)2 and a comparison of the crystal structures of the 12-membered ring 1,3,7,9-(Ph2PN)4(SN)2 and the corresponding dication (Ph2PN)4(SN)22+