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We acknowledge support from the University of St Andrews, the China Scholarship Council (studentship to YYG) and Leverhulme Trust (RPG-2018-065). Four new hybrid lead(II) halide perovskites, γ-(FA)2PbBr4, (FA)1.5(AA)0.5PbBr4, (PY)(GA)PbBr4 and (PY)(TZ)PbBr4 ((FA)=formamidinium, (AA)=acetamidinium, (PY)=pyrazolium, (GA)=guanidinium and (TZ)=1,2,3-triazolium), adopt (110)-oriented layered perovskite structures. While (PY) is found to template the formation of ‘conventional’ (110)-oriented structure types (i. e. containing staggered [PbBr4]∞ layers), (FA) is shown to facilitate formation of much less common variants based 3 : 1 ordering of the interlayer species or 3×2 step-like corrugation of the perovskite-like layers themselves. Postprint

The solid-state supramolecular structure of 6-methylisocytosine dihydrogen monophosphate adduct ½2-NH2-6-CH3-C4H2N2O2� þ 2 � H2PO � 4 , has been determined by single-crystal X-ray diffraction at room temperature. In this paper a revised model, based on single proton transfer from one molecule of phosphoric acid to the pyridine N atoms opposite to the methyl substituent of the two aminooxo tautomers of 6methylisocytosine, has been used for the crystal structure analysis of the ionic complex. 6-Methylisocytosine molecules form hemiprotonated centrosymmetric pairs by complementary WC triple hydrogen bonds. Dihydrogen phosphate anions act as bridges between charged WC dimers to generate ribbons via four cation-to-anion N–H ��� O hydrogen bonds. Ribbons are then interconnected to form a threedimensional network by means of a further series of O–H ��� O anion-to-cation hydrogen bonds.