def bonds2str(bonds):
    """
    Convert list of bonds into TopoCIF string.
    """
    bs = []
    for b in bonds:
        bs.append(" ".join(
            [f"{x:<5}" for x in b[:3]] + [f"{1:>3}"] + \
            ["{:>2} {:>2} {:>2}".format(*b[3])] + [f"{1:>3}"] + \
            ["{:>2} {:>2} {:>2}".format(*b[4])] + [f"{'V':>2}{1:>2}"]
        ))
    
    return "\n".join(bs)